School Science Lessons
Topic 19b Cooking, fabrics, hardware, beauty, household chemicals
2009-09-18
Please send comments to: J.Elfick@uq.edu.au
Table of contents
19.3.0 Cooking
19.3.5 Microwave cooking
19.4.1 Checklist of household chemicals
19.4.2 Kitchen hints
19.4.2.1 Stain removal
19.5.0 Fabrics in the home
19.5.1 Natural and synthetic fabrics
19.6.0 Hardware, laundry, painting, cleaning, preserving
19.7.0 Beauty and skin care products
19.8.0 Common measures
19.3.0 Cooking
19.3.1 Taste, smell, flavour
19.3.2 Anatomy and physiology of meat
19.3.3 Boiling, test the cooking water of boiled vegetables
19.3.3a Tests for iron in cooking water
19.3.3.1 Mashed potato, pommes purée
19.3.4 Baking and retention of nutrients
19.3.4.1 Tests for dextrins in toast
19.3.4.2 Browning reactions of fruits and vegetables
19.3.4.2.1 Tests for lemon juice effect on apple browning
19.3.4.3 Non-enzymatic browning, caramelization
19.3.4.4 Non-enzymatic browning, the Maillard reaction
19.3.4.5 Roasting meat
1. Observe roasting meat
2. Toughness and flavour of cooked meat
3. Cooked collagen turn into gelatine
4. The browning reaction is affected by temperature
19.3.4.6 Meat treatments, marinades, salting meat, marbled beef
19.3.5 Microwave cooking
19.3.5.1 Microwave radiation
19.3.5.2 Microwave cooking
19.3.5.3 Microwave containers
19.3.5.4 Superheating in a microwave oven
19.5.0 Fabrics in the home
19.5.1 Natural and synthetic fabrics
19.5.2 Dyes
19.5.3 Dyes with a mordant
19.5.4 Natural dyes
19.5.5 Washing clothes with washing soda
19.5.6 Permanent crease solution, hair straightening, permanent wave
19.5.1 Natural and synthetic fabrics
19.5.1.1 Test silk
19.5.1.2 Test wool
19.5.1.3 Test cotton
19.5.1.4 Test rayon
19.5.1.5  Test linen, string, and leather
19.5.1.6 Test to distinguish wool from cotton
19.5.1.7 Burning tests for fibres
19.5.1.8 Test nylon
19.6.0 Hardware, laundry, painting, cleaning, preserving
19.6.1 Paints, fire-retardant, anti-fouling, fluorescent, phosphorescent
19.6.2 Bases in the kitchen and laundry, washing powders, di-sodium tetraborate (III)-10-water (borax)
19.6.3 Metals in the kitchen, aluminium, iron, zinc, chromium
19.6.4 Bath cleaning, borax
19.6.5 Prepare preserving agents for cut flowers
19.6.6 Prepare household soap
19.6.7 Prepare camphor oil
19.7.0 Beauty and skin care products
19.7.1 Perfumes and smells
19.7.2 Lipstick
19.7.3 Hair products
19.7.4 Sunscreens and sun-protective clothing
9.226 Teeth and toothpaste
19.8.0 Common measures
3.5.1 Spoon volume
3.5.2 British liquid measures, imperial measures (fl. oz. = imperial fluid ounce)
3.5.3 American liquid measures, US measures
3.5.4 Miscellaneous measures
3.14.0 Oven temperatures
19.4.1 Checklist of household chemicals
Abrasives Silicon carbide
Acetic acid, vinegar, dissolves grease, mild disinfectant, cleaning toilets
19.2.10 Egg white, albumen, and egg yolk
Alcohol, ethanol, ethyl alcohol
Acetone, nail polish remover (not in recent formulations)
Adhesives
Algaecides, in swimming pools
Alum
Aluminium
Ammonia, cloudy ammonia
Ammonium carbonate, smelling salts
Ammonium chloride, soldering flux
Ammonium nitrate, garden fertilizer
Ammonium sulfate, garden fertilizer
Anti-freeze
Aspirin
Baking powder
Baking soda
Bakelite
Bean curd
Bitumen, asphalt (pitch, "tar" on roads)
Bleach, domestic bleach, sodium hypochlorite
Borax
Boric acid, boracic acid eye medicine
Calcium carbonate, egg shell, marble, geological chalk
Calcium hydroxide, whitewash
Calcium hypochlorite, bleaching powder
Calcium oxide, garden lime, soil conditioner and fertilizer
Calcium sulfate, school chalk, blackboard chalk
Candle paraffin wax, polish
Carbon charcoal, graphite is the "lead" in a lead pencil
Carbon dioxide, soda water, aerated waters, cleans carpet stains
Carbon tetrachloride, dry cleaning fluid
Cement, calcium + aluminium silicates, Portland cement
Chlorine bleach
Chlorine gas, swimming pool chlorine
Chromium
Citric acid, lemon juice
Clay
Copper
Copper (II) sulfate, Bordeaux mixture garden fungicide is copper (II) sulfate and calcium hydroxide
Corrosion
Cream of tartar
Creosote
Cyanoacrylate glue, "Supaglue", " Astrabond"
Detergent
Dry cell torch battery
Dyes
Effervescent fruit salts
Emulsion, face cream
Fat
Food additives
Fire, extinguisher chemicals
Flour
Formic acid, ant poison
Gas-Pak
Gelatine
Glass
Graphite, soft lead pencil
Glucose
Gluten, wheat starch
Hydrogen peroxide
Hydrochloric acid, muriatic acid, cleans bricks and masonry
Ice
Ink
Iodine, tincture of iodine antiseptic for cuts in the skin and mouth gargles
Iron, nails, tie wire, steel wool
Kerosine, kerosene, paraffin oil
Lead, fishing sinker, roofing material
Lemon juice, citric acid, deodorizes, mild bleach, cleaner
Lime, garden lime
Linseed oil
Magnesium hydroxide, milk of magnesia medicine
Magnesium sulfate, Epsom salts medicine and garden fertilizer
Methylated spirit
Milk
Olive oil
Petrol, gasoline, motor oil, grease
Petroleum jelly, petrolatum, "Vaseline"
Paraffin
Polymers
Potassium permanganate, Condy's crystals, disinfectant
Putty
Polyvinyl acetate, "white glue", e.g. "Aquadhere"
Rust
Red lead paint
Silicon carbide
Silicone sealant, "Bathtub Caulk" "Silicone Sealer" for fish tanks
Sodium silicate, water-glass egg preserver
Silica, quartz, quartz sand
Soap
Sodium bicarbonate, bicarbonate of soda, water softener, cleaner, mild disinfectant, absorbs odours
Sodium carbonate, washing soda, dissolves grease, disinfectant, softens water, cleans stains, absorbs odours
Sodium chloride, common salt
Sodium metabisulfite, home brewing sterilizer
Sodium hydroxide, caustic soda, dissolves grease in drains
Solder
Starch
Sucrose, sugar
Sulfur
Talc, talcum powder, geological talc, tailor's chalk, magnesium silicate
Tin
Tungsten carbide electric lamp filaments
Turpentine, turps, used for thinning oil-based paint
Urea
Water
Yeast
Zinc
19.4.2 Kitchen hints
Avoid hot foods in refrigerator that produce steam which forms frost.
Clean burnt food in aluminium pan with salt and vinegar or ammonia solution
Clean chrome plated taps, with kerosene.
Clean coffer stains on pottery with bleach or salt and water or washing soda solution
Clean copper with salt and lemon.
Clean fur from kettle with by soaking in lemon juice or vinegar.
Clean garbage tines with bleach solution.
Clean laminated surfaces with methylated spirit.
Clean oily pans with oil and salt crystals.
Clean refrigerator with bicarbonate of soda solution, not detergent, then rinse with lemon juice because refrigerator frost layer absorbs smells.
Clean scuff marks on the floor with an ink rubber. remove stubborn marks with turpentine and steel wool.
Clean silver plate with borax and soap solution.
Clean silver ware tarnished by eggs by putting in aluminium pan and washing soda or dip silver ware in water eggs boiled in.
Clean stainless steel with steel wool and lemon juice.
Clean stains on marble with lemon juice or vinegar.
Clean toaster with brush to not damage element.
Clean tops of stoves with ammonia solution.
Clean utensils containing flour or eggs and milk glasses in cold water because hot water cooks the food onto the utensil.
Clean vacuum flasks with bicarbonate of soda.
Clean wooden chopping boards by rinsing in bleach solution to get rid of garlic smell.
Use a smear of glycerine in ice cubes trays sticking to avoid sticking to freezer shelf.
Use cold water after cooking to prevent perish of pressure cooker rubber seal.
Use covers for food and drink in refrigerator to avoid dehydration.
Use cut lemon over ant trails and deter ants with mixture of borax and sugar.
Use hot water to free stuck screw top lid.
Use hot water to melt the congealed grease in blocked sink then use caustic soda to dissolve the grease or use plumbers suction cup.
Use ice water inside and hot water outside to free glasses stuck together.
Use jar of soapy water to store used steel wool and prevent from rusting.
Use mixture of vinegar and kerosene for floor polish.
Use mixture of vinegar and Condy's crystals to neutralize bad smells.
Use oil to stop chopping boards, wooden bowls, and cricket bats from splitting.
Use refrigerator to store candles to stop excessive drips.
Use tea solution from teapot to remove fishy smells.
19.4.2.1 Stain removal
1. Stain removal depends on solubility and chemical reactions. Clean stains immediately to prevent further chemical bonding to the material. Scrape off excess solid and soak up excess liquid. Try the treatment first on an inconspicuous part of the material. Work inward from the edge to prevent outward diffusion and spreading of the stain. Do not rub. Allow material to dry before consecutive treatments.
2. Salt heated in the oven and rubbed into serge or gabardine will remove stains and grease spots.
3. Table of stains and treatments 1. to 12.
beer 1.
 chocolate 1. 2.
 fruit juice 9. 2.
 ink, fountain pen 9. 1. 6.
 paint, oil- base 3. 2. 1.
beetroot 1.
 cocoa 1. 2. 10.
furniture polish 2.
 lipstick 1. 2.
rust 1. 2. 11
bleach 1.
 coffee / tea 1. 2. 10.
grass 4. mildew (fungus) 1. 5.
 shoe polish 1. 2.
blood 10. 6.
 cooking oils 1. 2.
 gravy / sauce 1. 9.
 milk 1. 2. 9.
soft drinks 1. 5. 9.
burn or scorch 5.
 crayon/ marker 2.
 grease 2. 1.
 nail polish 2. 8.
 tar 1. 2. 3.
candle wax 3.
 egg 1.
 ice cream 1.
 salad oil / dressing 1. 2.
 wine, red 6. 9. 12.
chewing gum 7. faeces / urine / vomit 1.
 ink, ball point 1. 4.
 paint, emulsion 1. 2. 10.
wine, white 1.
Treatments
1. Mixture of wool detergent with one teaspoon of clear vinegar in one litre of warm water.
2. Organic solvent, e.g. dry cleaning fluid, mineral turps, light petroleum. Be careful! Ensure good ventilation and keep away from flame! Remove stains caused by fatty substances, e.g. chocolate, butter, or grease with commercial dry cleaning solvents, e.g. tetrachloroethylene, CCl2=CCl2. Dry cleaning refers to cleaning textiles with organic solvents rather than water, e.g. chlorinated hydrocarbons such as chlorinated ethylene are used
3. Mixture of mineral turps with dry cleaning fluid Be careful! Ensure good ventilation and keep away from flame!
4. methylated spirit. Be careful! Ensure good ventilation and keep away from flame!
5. Hydrogen peroxide, 20 vols. Dilute one part to 10 with cold water. Do not use on dark or patterned material. Much stain removal is carried out by oxidation using oxidizing bleaches, e.g. hydrogen peroxide, sodium perborate, sodium hypochlorite. Do not use bleach on wool because it attacks the chemical linkages that hold the wool together.
6. Dye stripper diluted one part to 50 with cold water. Do not use on dark or patterned material.
7. Use a freezing agent to solidify the gum, and then scrape it off.
8. Acetone
9. Clean, warm water. Do not use hot water.
10. Cold water only.
11. Weak acidic solution, e.g. vinegar or lemon juice diluted with cold water. Lemon juice is used to stop fish smells and refrigerator smells, remove kettle "fur", and clean copper and stainless steel kitchen ware. The juice is acidic, and the stain or smell may be acid-soluble. Lemon juice contains ascorbic acid, vitamin C, an active reducing agent, i.e. electron donor, that can reduce molecular oxygen. If the stain is reduced by ascorbic acid to a substance that is not coloured, the lemon juice bleaches the stain. The skin of lemons contains oils, e.g. lemon oil. The stain may be soluble in the oil. Most stains are because of organic chemicals that more soluble in the organic compounds in lemon juice then in water. Lemon juice may convert the stains into substances that are more soluble in water or the lemon juice.
12. Absorbent powder, e.g. salt or talc. Sprinkle on spillage, leave overnight, then vacuum off. Use large amounts of salt on a fresh red wine stain on a table cloth before the red dye becomes attached to the cloth.
19.5.1 Natural and synthetic fabrics
List the natural and synthetic fabrics found in the home.
19.5.1.1 Test silk
Heat a small piece of real silk in a dry test-tube, and hold at the mouth of the test-tube a moist piece of red litmus paper. The litmus paper turns blue, caused by ammonia. Animal fibres, e.g. silk, contain nitrogen compounds. When heated they form ammonia.
19.5.1.2 Test wool
Heat a small piece of wool in a dry test-tube, and hold at the mouth of the test-tube a moist piece of red litmus paper. The litmus paper turns blue, caused by ammonia. Animal fibres, e.g. wool, contain nitrogen compounds. When heated they form ammonia.
19.5.1.3 Test cotton
Heat a small piece of cotton in a dry test-tube, and hold at the mouth of the test-tube a moist piece of blue litmus paper. The litmus paper turns red, caused by ammonia. Cotton is of plant origin so does not contain nitrogen compounds and does not produce ammonia. You can make a piece of litmus paper blue by pouring a few drops of limewater on it and washing it in water.
19.5.1.4 Test rayon
Heat a small piece of rayon in a dry test-tube, and hold at the mouth of the test-tube a moist piece of blue litmus paper. The litmus paper turns red, caused by ammonia. Rayon is of plant origin so does not contain nitrogen, so does not form ammonia. Rayon forms acid vapours when heated.
19.5.1.5  Test linen, string, and leather
Decide which is of animal origin and which is of vegetable origin. Leather is of animal origin, does not contain nitrogen compounds, so does not form ammonia.
19.5.1.6 Test to distinguish wool from cotton
Place a finger width of sodium hydroxide solution in a test-tube and add a strand of wool. Heat the solution. Describe what you see. Repeat the experiment with cotton and see if the same thing happens. The wool dissolves, the cotton does not dissolve. Cotton is of plant or vegetable origin, does not contain nitrogen compounds, so does not form ammonia. Cotton forms acid vapours when heated.
19.5.1.7 Burning tests for fibres
Holding each of the materials - wool, silk cotton, rayon - in the test-tube holder over a tin lid or dish, try burning each with the spirit burner flame. Note how easily or otherwise they burn, whether they leave much ash or char, and whether any easily recognized smell is formed. Wool burns slowly, appearing to melt together. It chars, and gives a smell of singed hair. Silk bums readily, with an yellow-orange flame. A black bead of ash is formed and a smell of burning hair. Cotton and rayon bum easily, leaving only grey ash.
19.5.1.8 Test nylon
Note how nylon behaves when heated in the test-tube. It first melts to a brown liquid, and ammonia is evolved. It does not burn easily. Nylon is a synthetic (man-made) fibre that gives ammonia when heated. However, the way it melts distinguishes it from animal fibres.
19.5.2 Dyes
Boil the fabric for five minutes in 10% hydrochloric acid. Mix 1 g congo red or methylene blue powder, 4 g sodium hydrogen carbonate, 1 g sodium sulfate, 100 mL deionized water. Slowly add the mixture to water while stirring. Boil the fabric for 4 to 5 minutes and then rinse it in cold water and leave to dry.
19.5.3 Dyes with a mordant
If you cannot dye a fabric directly, use a mordant that combines with the dye and forms an insoluble "lake" in the fibres. A lake is a pigment formed by interaction of a dye and a "base" to metallic salts, oxides and hydroxides. Mordants are hydroxides of aluminium, chromium and iron.
Heat white cotton fabric for 10 minutes in a dilute solution of ammonium sulfate. Then put it in dilute ammonia solution for 5 minutes. Rinse the fabric in clean water and hang it up to dry. Study the effect of the mordant by boiling the mordanted and unmordanted pieces of cotton in methylene blue solution for 5 minutes. Rinse and dry. Compare the colour of the fabrics.
19.5.4 Natural dyes
See appendix: Alum | See appendix: Cream of tartar
Colour: Plant material
Brown: Used ground coffee
Green: Azalea leaf
Purple: Red cabbage leaf
Yellow: Onion skin, marigold (Calendula officinalis) flowers
Heat plant material in water without boiling until dye appears. To make a mordant, dissolve 3 g potash alum [Al2(SO4)3.K2(SO4).24H2O] [also shown as KAl(SO4)2.12H2O] in 100 mL hot water, dissolve 1 g cream of tartar in 100 mL hot water and then put these solutions into an old pot or saucepan. Soak a woollen garment in the warmed mordant solution overnight. Replace the mordant with the dye. Put the woollen garment in the dye and observe the colour change in the wool. Rinse the dyed garment with water and dry slowly.
19.5.5 Washing clothes with washing soda
When washing clothes you need to disperse clay particles and keep them in solution to be thrown away when the washing water is discarded and clothes are rinsed. So washing soda, Na2CO3.10H2O, is added so the highly exchangeable sodium ions displace calcium ions. Detergents use polyphosphates or zeolite to make calcium inactive in the system.
19.5.6 Permanent crease solution, hair straightening, permanent wave
See 16.3.6.0.1: Fibrous proteins and globular proteins | See appendix: Sodium metabisulfite
Hair waving to hair straightening depends on chemical treatment of the disulfide bond in the protein cysteine. The disulfide bonds that give proteins their macroscopic structure can be split at room temperature and slightly alkaline pH by the action of sulfides or mercaptans A reducing agent converts the (-S-S-) bonds to (-SH) groups. The hair is combed to straighten and to wave it. An oxidizing agent restores the (-S-S-) bonds to create straight hair or a "permanent wave". Hairdressing salons use thioglycollic acid in a pH buffer and a cuticle softener to make the internal structure of the hair floppy. This reaction produces the smell of rotten eggs from hairdressing salons! After combing and setting the wet hair, the hairdresser neutralizes the thioglycollic acid with hydrogen peroxide so that new disulfide bonds form to keep the hair in the new shape.
1. Make a 3% sodium metabisulfite solution and add a few drops of detergent. Make a crease with two samples of woollen material. Sponge the solution along the crease in one sample, then press the crease with a steam iron for 30 seconds. On the other sample, press the crease with a steam iron for 30 seconds. Immerse both samples in warm water. Compare the creases. The protein polymer in the treated wool has a "permanent " crease.
Repeat the experiment with human hair to achieve a "permanent wave".
19.6.1 Paints, fire-retardant, anti-fouling, fluorescent, phosphorescent
1. Fire retardant paints contain substances that decompose on heating to give gases that do not support combustion, e.g. phosphates, tungstates, borates and carbonates. Some of these substances fuse on heating to give a glass-like layer on the surface. Other substances are not flammable, e.g. silicones, chlorinated resins, mineral powders. Although water based plants may be non-flammable before use, they may become flammable when painted on a surface and dried.
2. Anti-fouling paints used in marine construction may contain inorganic poisons, e.g. Cu and Hg salts, or organic molecules, e.g. entachlorophenol or organo-tin groups in the polymer. The later decompose to non-toxic inorganic tin on release into the sea water.
3. Fluorescent paints absorb ultraviolet radiation and re-emit it as visible light when irradiated. They contain zinc and cadmium sulfides, and organic dyes.
4. Phosphorescent paints are irradiated with ultraviolet light and continue to glow in the dark after the irradiation has stopped. Phosphors may include ZnS (green, yellow, orange) CuS and SrS (bluish) to other salts to change colour.
19.6.2 Bases in the kitchen and laundry, washing powders, di-sodium tetraborate (III)-10-water (borax)
See 12.10.3: Hydrolysis of sodium carbonate | See appendix: Sodium carbonate decahydrate, washing soda | See appendix: Sodium tetraborate, borax
Alkaline solutions are used for cleaning greasy dishes and for laundry, e.g. washing soda. Washing powders usually contain di-sodium tetraborate (III)-10-water (borax) and sodium carbonate and are alkaline in solution. Baking soda has a basic reaction and can neutralize the acids in fruit or in bee stings.
19.6.3 Metals in the kitchen, aluminium, iron, zinc, chromium
Aluminium and iron are affected by acids in the kitchen. Reactions of steam with zinc on galvanized iron. Cleaning of zinc and aluminium with alkalis. Possibility of aluminium in place of iron in foods by displacement.
19.6.4 Bath cleaning, borax
1. Mix equal parts of common salt, borax and kerosene into a paste. Rub on a dirty bath to remove dirt and grease. Finish rubbing with a soapy cloth and a dry cloth.
19.6.5 Prepare preserving agents for cut flowers
The bacteria in water will rot the cuts on stems of cut flowers, causing the block of capillaries, a decline in water absorbability and the deficiency in biogenic nutrition, and finally withering up the flowers. Water with a certain amount of a preservative agent added can prolong the life of cut flowers. Preservative agents usually contain the following:
1. Nutritious substances: Sucrose and oxime are usually used. Both serve as source of energy and bring stomas to shut up to weaken transpiration.
2. Bactericide: Silver nitrate, copper (II) sulfate or sodium hypochlorite can be used.
3. Ethylene inhibitor: Silver nitrate or silver thiosulfate is commonly used.
4. Acidified water: The pH value is kept to 3 to 4.
1. Use a small quantity of alcohol and water to dissolve 0.1 g of oxime in a large beaker and then pour more water in to dilute the solution to 500 mL (the mass percentage of oxime is about 0.02%). Add a few drops of dilute sulfuric acid to adjust the pH value of the solution to pH 5 to pH 6. While stirring, dissolve 0.025 g of silver nitrate (the mass percentage is about 0.005%) and 10 g of sucrose. After mixing this prepared preservative solution, use it for cut flowers.
2. Test quality of the preserving agent for cut flowers. Pour 500 mL of tap water into another large beaker. Put the same number of cut flowers as those in the above experiment in the water. Under the same conditions make a comparison, every three days, about the number of flowers and the water absorbing quantity. Pour 500 mL of tap water into another large beaker. Put the same number of cut flowers in the water. Under the same conditions make a comparison, every three days, between the two cases about the number of flowers and the water absorbing quantity.
3. Some people claim that the best preservative for cut flowers is a solution of 11/2 teaspoons of sucrose in 200 mL of water. Other people recommend a very dilute solution of household bleach.
4. Dissolve small amounts of ammonium chloride, potassium nitrate, and sodium carbonate or camphor in water. These substances are supposed to keep flowers from losing their turgidity by stimulating cells and preventing growth of bacteria. Wilted flowers may revive if the cut stems are placed in a dilute solution of camphor.
19.6.6 Prepare household soap
See 12.12.0: Soaps and synthetic detergents (syndets)
1. Add to a tin can half full with water, 2.27 kg dripping (animal fat) free from salt, 0.45 kg resin. Boil for 30 minutes then add 1 tablespoon borax or kerosene and 0.45 kg caustic soda. When bubbling stops (from adding the caustic soda) boil for two hours. Leave in tin for two days then cut into slabs with a tight wire. BE CAREFUL Add caustic soda gradually to avoid boiling over!
19.6.7 Prepare camphor oil
1. Crush camphor cake. Add salad oil, 5 mL eucalyptus oil, and a few drops of turps. Put ingredients in small bottle. Put bottle in saucepan containing water. Slowly bring water to boil. Use camphor oil when cool.
19.7.1 Perfumes and smells
Perfumes (fragrances) are essential oils usually concentrated in the petals of flowers that may be extracted by liquid fat, ethanol steam distillation and vacuum distillation for more sensitive oils and supercritical solvents, e.g. carbon dioxide. The underarm smell is a mixture of many "notes" (types of smells) mainly isovaleric acid, 5-andost-16-en-3-one and 5-andost-16-en-3-ol also 4-ethyloctanoic acid, the goat smell. The banana scent is isoamyl acetate. Oil of cloves is eugenol. Synthetic musk galaxolide. Mercaptan is a smelly sulfur compound put in odourless natural gas to give it a warning smell. The human male scent is androstenone. The smell of acetone in the breath is a symptom of diabetes. Eau de Cologne 4711 contains lemon, orange, bergamot, and rosemary essences. Garlic odour is formed by enzymes when garlic cells are cut or crushed. Anti-perspirants are based on aluminium salts that form aluminium hydroxide gel in sweat pores blocking the pore.
Fragrances used in women's toileteries include amber, caramel, citrus (orange essence) (green mandarin) (bergamot from orange peel), freezia, fuchsia, gardenia, honeysuckle, jasmine, lily of the valley, lily, magnolia, musk (white musk), osmanthus, peony, praline, prickly pear, rose, sandlewood, strawberry (wild strawberry), vanilla, violet petals, wood (white wood).
19.7.2 Lipsticks
Lipstick contains an oil-based wax, antioxidant, preservative, perfume, and colour. The body is made of castor oil and carnuba wax or beeswax. Lipstick must be thixotropic, i.e. stiff in the tube and stays in the tube when the lipstick is put down on a table but liquid under pressure. The original red colour of lipstick, carmine, came the crushed bodies of the cochineal insect, Coccus cacti.
19.7.3 Hair products
In hair, the hydrogen bonds within individual helices of keratin, and disulfide bridges between adjacent helices, give strength and elasticity. Water can disrupt the hydrogen bonds, making the hair limp. When the hair dries, new hydrogen bonding gives hair the shape of the curler. Permanent wave solutions give new disulfide bridges between the helices. Hair contains keratin protein chains in a protein matrix. A single hair may support 80 g. Hairstyles depend on the frictional forces between hairs which can be altered with setting and styling lotions. Wet hair carries 1/3 its weight in water. This increases the friction between straight hairs that combined with the surface tension that drags hairs together makes combing wet straight hair a difficult task. However, with very curly hair, as seen in Papua New Guinea and Africa, water relaxes the hair structure and reduced friction between hairs, so the hair can be straightened. Sulfides at slightly alkaline pH can split disulfide bonds between keratin molecules. The solution is buffered with thioglycollic acid then neutralizes with hydrogen peroxide so that the sets again with hydrogen sulfide given off. The latter accounts for the strange smell coming from women's hairdressing salons where "permanent waves" are produced. Women's hair has a growing phase 6 years and reaches 70 -80 cm. Men's hair has a growing phase 4 years and reaches. 40-50 cm. The black colour of hair is caused by melanin pigment but redheaded people also have an iron based pigment. Hydrogen peroxide bleaches melanin in hair and softens the hair cortex thus weakening it. Old men sometime produce baby hair, called lanugo. A change in humidity twists hair that can be used in novelty "weather houses" to predict changes in the weather.
permanent wave poly (vinyl) pyrrolidine polymers.
Nappy rash caused by bacteria, Bacillus ammoniagenes, from the colon and ammonia from the urinary area.
CO(NH2)2 + 2H2O --> CO3(NH4)2 --> 2NH3 + H2O + CO2
19.7.4 Sunscreens and sun-protective clothing
1. Overexposure to ultraviolet A (UVA) and ultraviolet B (UVB) can cause immediate and long-term skin damage, e.g. sunburn, rashes, tissue damage to premature wrinkling and skin cancer. Many changes with ageing are the result of damage by too much sun. A skin tan occurs when the skin produces additional pigment to protect itself against sunburn from ultraviolet rays. Try to minimize your exposure to the sun between 10 a.m. and 3 p.m. to wear a hat and tightly-woven clothing that covers the body, and use maximum protection sunscreens.
2. Sun-protective clothing fabrics have a tight weave and a dark colour. The garment should have a label listing its Ultraviolet Protection Factor (UPF) value. The higher the UPF, the more the protection from UV rays, e.g. UPF rating of 20 only allows 1 / 20th of the sun's UV radiation to pass through it. For children apply sunscreens with a minimum SPF of 15 about 30 minutes before they go outdoors. Infants should not be in the sun. Sunscreens may irritate baby skin and the developing eyes of a baby are vulnerable to sunlight.
3. The best sunscreens block both UVB (UV radiation with wavelength between 315 and 280 nm) which can cause sunburn, and UVA (UV radiation with wavelength between 380 to 315 nm) which damages the skin without causing sunburn. The peak sensitivity of the skin is the 290 to 320 nm range that causes sunburn and skin cancer. Sunscreen inhibits the production of Vitamin D so 15 minutes per day of direct exposure to the sun is needed. Too much sunbathing is one of the major causes of skin cancer across the world. An immediate but short lasting sun tan occurs the hormone alpha-melanocyte stimulating hormone is made when the body is exposed to sunlight and is responsible for the development of the pigment melanin when pale unoxidized melanin granules near the skin surface are changed by ultraviolet light to the dark brown oxidized form. A lasting sun tan occurs when the amino acid tyrosine produces extra melanin.
4. The higher the sun protection factor, SPF, the more protection a sunscreen offers against UVB, the ultraviolet radiation that causes sunburn. A sunscreen with SPF 10 blocks 90.0% of UVB, SPF 20 blocks 95.0% of UVB, SPF 30 blocks 96.7% of UVB and SPF 60 blocks 98.3% of UVB. The SPF indicates how long you can stay in the sun without the skin reddening about 6 hours after exposure. The exposure needed to produce reddening is called the minimum erythemal dose, MED. SPF = exposed time for MED in protected skin / exposed time for MED for unprotected skin. So if you burn in 10 minutes without sunscreen and you apply an SPF 15 sunscreen, you should be protected from sunburn for 10 X 15 = 150 minutes. However, protection depends on the skin type of the user, amount applied, frequency of reapplication, activities, e.g. swimming, time of day, season, and the percentage of UV reflected to scattered by the environment, e.g. snow to sand. Swimming and perspiration may reduce the SPF value. No sunscreen product screens out all UVA rays. Sunscreens with the same SPF numbers may have different ingredients to different combinations of the same ingredients. Test a new sunscreen first to avoid any allergic reaction. Apply 30 minutes before you go outside and reapply after swimming to activity that causes perspiration. However, invisible damage and skin ageing can be caused by ultraviolet type A, which does not cause reddening pain. Normal sunscreen does not block UVA as effectively as UVB. UVA may cause DNA damage to cells deep within the skin and increasing the risk of malignant melanomas. Claims of "all day protection" should be ignored because an SPF over 30 does not provide significantly better protection.
5. Most sunscreens containing either an organic chemical compound that absorbs ultraviolet light, e.g. oxybenzone, or an opaque material that reflects light, e.g. zinc oxide. The principal ingredients are usually aromatic molecules conjugated with carbonyl groups that absorbs high energy ultraviolet rays. Most ingredients, but not undergo significant chemical change, so they retain the UV-absorbing potency without significant photodegradation. Allowable active ingredients in sunblocks include: p-Aminobenzoic acid (PABA) Avobenzone, Cinoxate, Dioxybenzone, Homosalate, Menthyl anthranilate, Octocrylene, Octyl methoxycinnamate, Octinoxate, Octyl salicylate, Oxybenzone, Padimate O, Phenylbenzimidazole sulfonic acid, Sulisobenzone, Titanium dioxide, Trolamine salicylate, Zinc oxide, Tinosorb (applied to clothing) Mexoryl (not USA).
19.3.0 Cooking
16.3.6.0.1 Fibrous proteins and globular proteins, collagen
1. The four basic methods of cooking are as follows:
1.1 Wet heating: boiling, steaming, pasteurization 100oC to 120oC
1.2 Dry heating: baking, roasting, up to 250oC
1.3 Hot oil frying, up to 300oC
1.4 Microwave cooking, up to 120oC.
2. Cooking breaks down long molecules to smaller molecules that are more easily digested. Cooking may also release flavours and destroy unwanted flavours. Cooking may also raise temperature so that enzyme reactions can occur. If meat is cooked too fast on a high flame the outside becomes scorched and covered with carbon that acts as a thermal insulator so that the meat takes longer to cook thoroughly. So slow cooking results in more thorough cooking.
2.1 Braising is done after browning the food in some fat then half immersing in liquid in sealed pot and cooked slowly.
2.2. Broiling is the same as grilling in England but in USA it means grilling food under direct heat source as in an electric oven.
2.3. Caramelizing is browning of sugars in solution when heated above 150°C. The sugars breakdown to many compounds, including sugars, and carbon. Onions are commonly caramelized.
2.4. Frying is putting food into a bath of hot fat or oil. It involves sealing and browning. If the temperature does not exceed 180°C, the fat or oil used should not break up or decompose. The food should be dry or dipped into flour, bread crumbs or batter. Potato is commonly deep fried. If a fire occurs, drop in baking soda and cover the pan with a lid. At temperature 300oC, the wet potato chips sizzle, dry out and go brown on the outside.
2.5. Poaching is cooking by simmering in water. Unlike boiling, the water temperature is kept below boiling point. Eggs are commonly poached.
2.6. Roasting is cooking food with dry heat and can be done in an oven or over an open fire. Meat and poultry are commonly roasted. Fish and vegetables can also be roasted.
2.7. Sautéing and deglazing is briefly cooking food in a shallow pan for quick sealing and browning of small pieces of food. However, The Concise Larousse Gastronomique defines "Saute" as to cook meat, fish, or vegetables in fat until brown, using a frying pan (skillet) a saute pan or even a heavy saucepan and "Deglaze" as to heat wine, stock or other liquid together with the cooking juices and sediment left in the pan after roasting or sautéing to make a sauce or gravy.
3. Woks are used mainly in Chinese cooking where all the food is first chopped and peanut oil or other oils are added to swirl around to coat the bottom of the wok. When the oil starts to smoke, add the chopped food. The salt in cooking water increases the osmotic pressure of the water and stops the food losing desirable flavour molecules by diffusion. Food cooked in salt water is no more salty than food cooked in unsalted water, unless you drink the liquid in which the food was cooked.
4. Cooking time is proportional to the square of the smallest radius of the food rather than its weight.
4.1 Taste raw and cooked to note the difference in flavour of different foods raw, cooked without salt, and cooked with salt, rice or wheat flour, banana, peanut, bean curd, onion, beef, fish.
4.2. Try to eat raw potato, raw rice and raw meat! Cooking breaks down inedible and indigestible large molecules and fibres to smaller structures that can be eaten and digested. Similarly cooking destroys some bad flavours, poisons, bacteria and other organisms that may be harmful if eaten in raw food.
19.3.1 Taste, smell, flavour
See 9.246: Sense of taste | See 19.4.4.25: Sweeteners, food additives | See 19.4.4.18: Food acids, food additive
Tastes, smells and flavours are usually due to many chemical components. For example a recentg study of the favour of the orange cultivar Kozan in Turkey found 34 components of flavour, including seven esters, two aldehydes, five alcohols, five terpenes, twelve terpenols, and three ketones. The major flavour components were linalool, limonene, β-phellandrene, terpinene-4-ol and ethyl 3-hydroxy hexanoate.
Taste
The four basic tastes are sweet, sour, bitter and salt, also "umami", the savoury taste.
Sweet: Different sugars have different sweetness.
Sour: Acids always taste sour
Bitter: Most alkaloids taste bitter, e.g. purgative aloes (Aloe sp.) wormwood (Artemisia absinthium) used in the illegal (in some countries) alcoholic drink absinthe, lupulin in hops (Humulus lupulus) used in making bitter beer, amygdalin in bitter almonds (Prunus amygdalus) colocynth in the bitter apple (Colocynthis sp.) quinine in bark of Cinchona sp. and used in tonic water, caffeine in Coffea sp. and used in coffee.
Salt: Most sodium salts and most chlorides taste salty.
Umami: The the taste of monosodium glutamate used in Asian cooking and Parmesan cheese. The "trigeminal sense" allows us to "taste" chillies and onions.
Smell
The sense of smell depends on small molecules that can be carried in the air, e.g. from ripening fruit and flowers but also air from the back of the mouth carry molecules from the food being chewed up to the olfactory epithelium of the nasal cavities, the "after taste". Cooked food tastes differently from uncooked food, e.g. uncooked meat is relatively tasteless. People who lack the sense of smell are called anosmic. People who lack the sense of taste are called ageusic.
Flavour
The flavour is the quality perceived by the sense of taste assisted by the sense of smell.
1. Test blindfolded students for their ability to identify food with some students with nose clips or holding their noses:
1.1 Bland and tasty foods, e.g. potato crisps,
1.2 Whole foods and pureed foods.
1.3 Raw and cooked vegetables. Be careful if using raw onions or chillies. Some students may be allergic to them.
1.4 Tomato and monosodium glutamate
1.5 Table salt and sugar.
2.1 Note the difference between olive oil and a similar oil, e.g. safflower oil. Then try to identify the oils when blind-folded and the nose pinched.
19.3.2 Anatomy and physiology of meat
Meat consists of muscle fibres, connective tissues and fats. The muscle fibres largely consist of two proteins, myosin and actin. extended along the fibres and can move past one another, to cause a similar contraction. Meat is muscles attached to bones by tendons. Muscles contain long protein fibres actin and myosin. These fibres slide along each other when stimulated by nerve impulses, which make the muscle shorter and fatter. If muscles are used for short, fast bursts of energy, then glucose from the blood provides the fuel. If the muscles have to give long sustained activity, then fat provides the energy and in this case another protein, called myoglobin, is needed to help oxidize the fat and provide the energy.
Myoglobin is a single chain protein of 153 amino acids, containing a haeme that is the main oxygen carrying pigment of muscle tissues. Myoglobin is bright red, so muscles that work a lot are red while those that are used for less regular, sudden movements are pale or even white.
Fibrous tissues that surround the muscles and connect them to the tendons and bones are made from collagen. The more collagen in the meat, the tougher it is. There are three main types of connective tissue: collagen, reticulin and elastin. Collagen is the most abundant and the most important for the cook to appreciate. Collagen is a complex molecule made up from three strands that are twisted together rather like a rope. Collagen derives its stiffness and strength from the arrangement of these intertwined helices. However, if collagen is heated to temperatures above about 60oC, the three strands can separate and the material loses its strength. Once denatured into single strands, collagen becomes a very soft material, and is given a different name, gelatine. You already know that gelatine is a soft, tender, material, since it is used as the basis of all jellies. The collagen is mostly found around bundles of muscle fibres and helps to hold them together. The muscles are then joined to the bones with yet more sinews (yet more "connective tissue") which cooks recognize as tough "gristly" material. These sinews are made from the proteins reticulin and elastin; reticulin and elastin can only be denatured and softened by heating for very long times at temperatures above 90oC.
Muscles consist of bundles of long cells called muscle fibres or myofibrils. Resting myofibrils contain two types of proteins actin and myosin arranged side by side. The muscle contracts when the actin and myosin proteins slide together. like the finger from each hand to form the protein actomysin the presence of calcium ions Ca2+ powered by the energy carrying molecule ATP (adenosine triphosphate).
After an animal is slaughtered, blood circulation stops, and muscles exhaust their oxygen supply. Muscle can no longer use oxygen to generate ATP and turn to anaerobic glycolysis, a process that breaks down sugar without oxygen, to generate ATP from glycogen, a sugar stored in muscle. The breakdown of glycogen produces enough energy to contract the muscles, and also produces lactic acid. With no blood flow to carry the lactic acid away, the acid builds up in the muscle tissue. If the acid content is too high, the meat loses its water binding ability and becomes pale and watery. If the acid is too low, the meat will be tough and dry. As glycogen supplies are depleted, ATP regeneration stops, and the actin and myosin remain closed in a permanent contraction of actomysin called rigor mortis.
Freezing the carcass too soon after death keeps the proteins all bunched together, resulting in very tough meat. Individual protein molecules in raw meat are wound in coils, which are formed and held together by bonds. When meat is heated, the bonds break and the protein molecule unwinds. Heat also shrinks the muscle fibres both in diameter and in length as water is squeezed out and the protein molecules recombine, or coagulate. Because the natural structure of the protein changes, this process of breaking, unwinding, and coagulating is called denaturing. The protein of meat congeals when heated. If it is further heated after it has congealed, its combination is broken and it becomes a compound called melanoidin with a chemical amino carbonyl reaction to oxygen in air and others.
Most animal muscle is roughly 75% water, 20% protein, and 5% fat, carbohydrates, and assorted proteins.
Observe the arrangement of bone muscle, tendons and connective tissue is a piece of meat selected for roasting. Mature beef should have areas of muscle separated by fat, an arrangement called marbling.
19.3.3 Boiling, test the cooking water of boiled vegetables
See 7.5.0.1: Elevation of boiling point, ebullioscopic constant, kB
Meat cooked in hot water has no roasted flavours because the temperature does not rise above 100oC. Vegetables with large surface / mass ratios (e.g. spinach) are especially sensitive to loss of vitamins. Vitamin C is a most unstable nutrient in neutral and alkaline conditions, and in the presence of oxygen; folic acid may be even more unstable; and thiamine, riboflavin, carotene and niacin are sensitive under certain conditions. Nutrient losses increase if large amounts of cooking water are used. Cooking for longer times also results in a greater loss of nutrients.
Test cooking water of boiled vegetables
1. Boil green vegetables in water, e.g. spinach brussels sprouts, spring greens. Removed the cooked vegetables and filter the cooled cooking water. Observe the green colour of the cooking water because of beta carotene, vitamin A precursor. Test the cooking water for vitamin C with a Vitamin C dipstick.
2. Put some unpeeled new potatoes into boiling water for different lengths of time. Remove them and cut them open. Observe the growth with time of a translucent ring from the outside. Inside the ring the potato still has an opaque white texture. The width of the ring is the distance that has reached a temperature of 60oC.
3. Put dry peas in a measuring cylinder and measure the volume of water needed to fill the cylinder to the 100 mL mark. Put the peas in boiling water for 15 minutes boiling. Put the boiled dry peas in the measuring cylinder and measure the volume of water needed to fill the cylinder to the 100 mL mark. Calculate the percentage change in the volume of the peas.
4. Use a microscope to observe the characteristic shape of starch grains, e.g. potato, rice, wheat, maize. Boil the starch grains until the cells burst and the starch forms a gelatinous mass leaving empty cell wall envelopes "ghosts". This gelating action occurs at different temperatures: barley 51oC to 61oC, tapioca 52oC to 64oC, pea 57oC to 70oC, potato 58oC to 66oC, wheat 50oC to 64oC, maize (corn) 62oC to 70oC, rice 68oC to 70oC.
5. Show the effect of the salivary enzyme amylase on raw and boiled starch measured using dipsticks specific for glucose.
6. Show that vitamins and minerals may be lost in the water vegetables are boiled in, e.g. spinach, Brussels sprout. Note the colouring of beta carotene, vitamin A precursor in the water used for boiling.
7. Drop small pieces of raw and cooked liver into test-tubes containing 10 vols (3%) hydrogen peroxide and compare the rate of effervescence because of the enzyme peroxidase catalase. Fresh pineapple contains a powerful proteolytic enzyme called bromelase, but in tinned pineapple it is inactivated. So a pineapple garnish for ham, gammon, should be made of fresh pineapple. Fresh pineapple interferes with setting gelatine and whipped egg whites because the enzyme is active.
19.3.3a Tests for iron in cooking water
1. Use a mixture of 1% potassium ferrocyanide and 1% hydrochloric acid to make potassium ferrocyanide. A deep blue precipitate shows iron. Boil water for a long time in a clean iron pot. The cooled water may test positive for iron and this iron may be an important source of iron in some countries.
2. Tests for iron in the water vegetables were boiled in. Add to a sample of the cooking water 1% potassium ferrocyanide and 1% hydrochloric acid, mixed just before use. A deep blue precipitate indicates iron. In some cultures the iron in the diet may come from the use of iron pots.
19.3.3.1 Mashed potato, pommes purée
Two types of potato are as follows: 1. the floury type with cells that separate and that breakdown easily when cooked, e.g. "King Edward" and 2. the waxy type with cells that are firmly held together when cooked, e.g. "Charlotte". Most new potatoes are waxy type. Floury types make a mashed potato that is light, fluffy, and thick. Waxy types make mashed potato that is thick, smooth and silky textured. Floury types contain more starch granules per cell than waxy types and are more dense. The cells contain starch granules. The cell walls are a network of cellulose held together by hemi-cellulose. During cooking, the hemi-cellulose breaks down, the cell walls get weaker, the cells start to separate and break open. The starch granules absorb water and expand. Many granules are also released from the cells of the floury types. Prevent potatoes from absorbing water during cooking, which makes the mashed potato wet, by either cooking them in their skins or first peel then steam them. Also, you can cook them at a temperature below the boiling point, leave to cool, then cook again before they are mashed. The first cooking activates enzymes which allow the pectin to react with calcium to make a glue to hold the cells together during the second cooking. Mash potatoes so that the cells are opened without breaking the released starch granules to form an unpleasant sticky jelly.
Use iodine solution to examine slices of floury type and waxy type potatoes. Also, examine the starch grains before and after cooking.
19.3.4 Baking and retention of nutrients
Retention of nutrients may be low, e.g. vitamin C retention in baked apple 40%, thiamine retention in potatoes 41%. Baking powders destroy thiamine that needs slightly acid conditions to keep stable during baking. Bread loses little nutritional value during baking but toasting causes loss of protein and vitamins, depending on how much drying out and browning. The heating, rolling and flaking processes to manufacture breakfast cereals do not affect protein content, but explosion puffing, e.g. puffed wheat, puffed rice, reduces the nutritive value. However, you usually eat these foods with milk.
19.3.4.1 Tests for dextrins in toast
Heated starch breaks into shorter length polymers called dextrins. Prepare an iodine solution with 1 g iodine, 2 g potassium iodide 100 mL of water. Starch gives a blue black colour. Dextrins give a brown red colour. Very small dextrins give no colour.
Prepare toast with a thin slice and a thick slice of bread. Grind the toast to fine crumbs. Shake the crumbs with water and filter with a Buchner funnel. Add ammonium sulfate to precipitate starch and leave dextrins in solution. Tests for dextrins with iodine solution. The thin slice produces more dextrins than the thick slice.
19.3.4.2 Browning reactions of fruits and vegetables
Phenolase browning occurs at the cut surface of light-coloured fruits and vegetables, e.g. apples, bananas, potatoes, where phenols oxidize to orthoquines which then polymerize to form melanin brown pigment. The phenolases, the enzymes that catalyze the phenols oxidation, contain copper. Phenolase are active in the pH 5 to 7 range and can become inactivated below pH 3. Phenolase browning is an enzymatic-catalytic reaction. Other browning reactions of food are non-enzymatic reactions, e.g. Maillard reaction, caramelization, and ascorbic acid oxidation. When tissues are damaged, polyphenolic substances from the vacuoles of the plant cells contact the oxidase called phenolase (phenol oxidase enzyme) in the cytoplasm of plant cells and in the presence of oxygen produce substances that protect the plant and favour wound healing. However, these substances produce a brown coloration.
Browning can be prevented by the following processes:
1. Immersion in water or dilute salt solution or coating with syrup so that the substrate has no contact with oxygen. Concentrated sugar solution also depresses enzyme activity. Also, storage in carbon dioxide or nitrogen prevents the browning reaction.
2. Boiling or steaming to inactivate the protein enzymes that are denatured by heat. Browning does not occur in cooked fruits and vegetables.
3. Adding acid to lower the pH, e.g. lemon juice or cream of tartar (potassium hydrogen tartrate, KHC4H4O7). Ascorbic acid may also act as an antioxidant to reduce quinones.
4. Lower the temperature to depress enzyme activity. However, some fruits become brown even when frozen, e.g. banana skin.
5. Use sulfur dioxide or sulphites, e.g. sodium sulfite, sodium metabisulfite, that react with quinones formed from phenolic compounds to block further reactions. A sulfur dioxide concentration of 10 ppm. (10 mg per litre) inhibits phenolase. Sulfites are used in the processing of dried fruits, red wine, red and white grape juice. However, sulfites may cause medical problems to people who have sulfite sensitivity.
6. Dehydration makes phenolase inactive, even in bananas.
Browning may be a useful process as when plums become prunes, grapes become raisins and green tea leaves become black tea.
7. Lemon juice contains two components that can block the browning reaction:
7.1 Organic acids, mainly citric acid, with pH < 2, that lower the pH of the apple tissure below the best pH for the action of oxidases.
7.2 The biological antioxidant vitamin C that is oxidised to colourless substances.
Test the effects of anti-browning compounds by using cut slices of celeriac or celery.
19.3.4.2.1 Tests for lemon juice effect on apple browning
1. Put a slice of fresh apple on a sheet of wax paper. Examine the exposed moist surface with a magnifying glass.
2. Every minute, take another look at the apple and note any change in appearance. After 5 minutes, remove the skin of the apple and describe the appearance of this newly exposed fruit surface.
3. Use two new slices of apple. Place them side-by-side on a fresh sheet of wax paper. Soak the end of a cotton swab in lemon juice. Use this swab to paint the exposed surface of one of the apple slices. Every minute, re-examine the apple slices. Describe any changes and note whether both slices change at the same rate.
4. Repeat the experiment with two new slices of apple. Crush a vitamin C table and grind it to a powder. Rub the powder on one of the apple slices. Note any changes in the cut surfaces of the apple slices.
19.3.4.3 Non-enzymatic browning, caramelization
Non-enzymatic browning is a chemical process that produces a brown colour in foods without the activity of enzymes. Caramelization is the oxidation of sugar, a process used extensively in cooking to release volatile chemicals producing the characteristic caramel flavour and brown colour. The complicated chemical processes that are not fully understood include sucrose inversion to fructose and glucose, condensation to result in the formation of carbon, isomerization of aldoses to ketoses, dehydration, fragmentation reactions and unsaturated polymer formation, production of melanins. Caramelization temperatures of different sugars include the following: fructose 110oC, galactose 160oC, glucose 160oC, maltose 180oC, sucrose 160oC. The brown colour may be due to fructose dianhydride and carbon particles. Caramel is used as a flavouring and food colouring E150 in candy and Coca Cola and other foods.
The melting point of sucrose is 186oC. The solubility of sucrose is 2.59 g sucrose per g water at 50oC.
Be careful! "Toffee" burns are very painful and dangerous. Wear a full face mask and gloves. Sputtering of hot sugar may occur.
1. Add two measures of sugar to one measure of water. Stir and heat in a Pyrex beaker or non-stick deep pot until all the sugar is dissolved. Keep heating and adding more sugar until no more can dissolve. Remove the heat when the solution has a straw colour. Do not allow boiling to occur. You can check the temperature of the solution with a special "candy thermometer". Pour the hot solution into paper cups and immediately clean the Pyrex beaker or saucepan. Leave to cool. The glassy solid may be eaten or used in movie sets for imitation glass bottles and windows so that actors are not hurt when hit with a "bottle" of when they jump through a "glass window". After removing the heat, and while the solution is still hot, add whipped cream and butter to make the French desert "creme brulee" ("burnt custard").
2. Put granulated sugar or glucose in a shallow porcelain-lined evaporating dish or metal pan with a volume of ten times the volume of sugar used. Heat the sugar over an electric stove until it froths up suddenly then immediately turn off the stove or remove the dish or pan from the stove. Add water to bring the dark brown viscid mass to the consistency of a heavy syrup. The product will be insoluble in water if more than 15% of the original weight of the sugar is lost. If the caramel dissolved in water is cloudy, carbonization has occurred so some of the sugar has been reduced to carbon.
19.3.4.4 Non-enzymatic browning, the Maillard reaction
The Maillard reaction (Louis Maillard 1912) refers to the chemical reactions between 1. the aldehydes and ketones from reducing sugars and 2. proteins or amino acid. The reactive carbonyl group of the sugar interacts with the amino group of the amino acid. The type of amino acid decides the many flavour compounds produced and these compounds may then breakdown to form more new flavour compounds. The Maillard reactions produce caramel candies made from milk and sugar, the browning of bread in toast, malting of barley to give the colour of beer, chocolate, coffee, maple syrup, lightly roasted peanuts, colour of condensed milk. The carbonyl group of the sugar reacts with the amino group of the amino acid, producing water and N-substituted glycosylamine that undergoes Amadori rearrangement to form ketosamines that react further to produce various short chain products, brown nitrogenous polymers and melanoidin. Melanoidin is light brown and has the good smell of grilled meat. However, melanoidin is easy to volatize, so its smell disappears if it is heated for a long period of time with low heat. his is why cooks grill meat for a short period of time over a high flame. Over 200oC carbonization occurs and the protein component causes a bad smell. Pentose sugars react more than hexoses, which react more than disaccharides. Different amino acids produce different amounts of browning.
1. Make toast from white bread and brown bread or wholemeal bread
Put equal thickness slices of white bread and brown bread or wholemeal bread in each side of a toaster. Turn on the toaster and note the time taken for each slic to start to burn. The brown bread or wholemeal bread slice burns faster than the white bread slice because the white bread contains less sugar and protein for the Maillard reaction. If the white bread slice is really white it may reflect more radiation from the toaster than darker slices.
2. Make caramel confectionery
Boil together sugar and milk or butter until the solution turns brown. You can check the temperature of the solution with a special "candy thermometer". To make toffee heat the solution to 160oC. Add baking soda and vinegar to make honeycomb toffee. Leave to cool.
19.3.4.5 Roasting meat
When muscle fibres are heated above about 40oC the proteins start to denature. In muscle proteins, which are extended along the muscle fibres, this change of shape involves the proteins coiling up. This coiling process inevitably causes some contraction of the muscle. Muscles contract during cooking so pieces of meat contract along the direction of the muscle fibres. When the protein molecules are denatured, the muscles contract so the meat becomes harder. The meat will be tough. The cooking time should be long enough to degrade the connective tissue present in the meat, without toughening the muscle proteins.
The toughening occurs in two stages. The first stage is caused by the muscle proteins that are extended along the muscle fibres contracting into coils as they denature. The pieces of meat should be getting thinner during this stage as the fibres contract. The second stage is the coagulation of the now denatured muscle proteins into lumpy, knotty masses. There should be a much greater degree of toughening in this stage, but no noticeable changes in the shape of the pieces of meat. Meat is roasted to 1. to make it tender to eat 2. to give it a roasted flavour 3. to kill any harmful bacteria 4. to create an acceptable warm temperature for eating when fats are still liquid
Low temperature roasting
Most cooks first brown the meat at a high temperature to seal in the meat juices during cooking before letting it cook through at a lower temperature. However, cooking at less than 70oC. can produce tender meat before the meat is browned on the outside. Slow cooking for a long time at a low temperature causes collagen in the meat to breakdown into gelatine and the meat fibres to shrink and release the meat juice to form a gravy. The fibres separate easily and are tasty. The high temperature surface searing of the meat following the slow cook creates lots of aroma molecules when the ribose and the amino acids released from the meat react together and these add to the rich flavour. This final heating also kills off any bacteria that may have survived the slow cooking.
1. Observe roasting meat
The meat consists mainly of three materials: water, proteins and fat. When a strong source of heat is applied to the surface of the meat, the protein coagulates and aggregates to form crust, possibly the result of the Maillard reaction as in the formation of crust on bread. The presence of heat and water, will make the collagen (the proteins present in meat) degrades to form a gelatine. This the reason why the meat is removed and this brown crust appears at surface. However, if the meat is warmed too long, the evaporation of the water associated to the coagulation of the other proteins in the surface, will have for inverse effect to dry and harden the meat. It is necessary here all the art and the experience (experiment) of the cook to find the equivalence completed between these two opposite phenomena.
The chemistry of the browning of meat is still the subject of disagreement and further research. Some chemists say that the Maillard reaction occurs when the denatured proteins on the surface of the meat recombine with the sugars present. The combination creates the "meaty" flavour and changes the colour, the browning reaction. When meat is cooked, the outside reaches a higher temperature than the inside, triggering the Maillard reaction and creating the strongest flavours on the surface. As many as six hundred components have been identified in the aroma of beef. However, if the Maillard reaction is strictly the reaction between an amino and and a reducing sugar, there are not many reducing sugars in meat so the browning of meat may be due more to the breakdown of tetrapyrrole rings in myoglobin, the muscle protein.
During roasting, different changes occur at different temperatures:
40oC Red muscle proteins denature, meat is still red
55oC to 60oC Red muscle proteins coil and shrink. Water bound to protein starts to flow. The myosin molecules start to shrink and squeeze out fluid from the muscle cells. Shrinking fibres makes the meat firmer.
60oC to 65oC Produces "rare meat" that is pink and juicy. Muscle proteins start coagulating. Collagen begins to denature and breakdown to form gelatine which dissolves in water.
65oC to 70oC Produces grey protein. Water bound to protein stops flowing. Kills bacteria on the surface of the meat. These bacteria may be harmless even if they cause meat to spoil. The food poisoning bacteria Salmonella and Escherichia coli (E. coli) are killed above 68oC. However, minced meat may have surface bacteria mixed throughout the meat so all the meat should reach that temperature.
80oC This produces "well done" meat that is brown grey and dry tough meat.
90oC Collagen turns into gelatine.
100oC to120oC Roast and fried flavours and brown colours form as proteins and carbohydrates breakdown into smaller sugar molecules and aldehydes and react with amino acids sulfur gives agreeable aromas so cooks add garlic or onions because of their high sulfur content. The meat smell is because of the molecule bis-2-methyl-3-furyl-disulfide. Similar reactions gives the colour and flavour to bread crust, toast, biscuits and caramel toffee. All these reactions are called the Maillard reaction, browning reaction, and they occur at above 140oC. Caramelization of sugars occurs at about 150oC.
Above 200oC carcinogenic molecules may form in barbecued meat.
2. Toughness and flavour of cooked meat
Cut a slice of meat 10 equal size pieces. Start cooking the pieces every 2 minutes in a frying pan or under a grill
until all the pieces are being cooked then turn all the pieces every minute. After the last piece has been cooking for 3 minutes turn off the heat. Note the colour of each piece. Test the pieces for toughness and flavour by 1. chewing 2. cutting with a blunt knife. Pieces cooked for up to 8 minutes are probably tender but pieces cooked for longer are increasingly tougher. Note an increasing of flavour with cooking time.
3. Cooked collagen turn into gelatine
Use meat with lots of connective tissue and still connected to the bones with tendons, e.g. shin beef, oxtail. Cut the meat and tendons into small pieces, and cover with water, heat to boiling and leave to simmer. Do not allow all the water to evaporate! After each 30 minutes remove 50 mL of the water and place in a container in a refrigerator. After each removal of water replace with 50 mL of boiling water. Water removed after about 2 hours simmering thickens on cooling until water removed after 3 hours forms jelly as it cools. Collagen in meat and tendons heated to above 60oC changes from its triple stranded helical form into a single stranded form called gelatine. Gelatine is soluble in water so its concentration increases as more collagen denatures during simmering. When cold, high concentrations of gelatine molecules aggregate together in a loose gel or jelly.
4. The browning reaction is affected by temperature
Cook 8 pieces of meat at different temperatures. Heat the oven until the temperature is steady at 100oC. Put in a piece of meat for the time listed below. Raise the temperature of the oven and cook the next piece of meat. Note the colour, and the occurrence of the cooked meat smells and tastes, and the burnt meat smells and tastes. Cook each piece for half the cooking time for each side. 100oC Cooking time 12 minutes; 120oC Cooking time 9.5 minutes, 140oC Cooking time 8 minutes, 160oC Cooking time 7 minutes, 180oC Cooking time 6 minutes, 200oC Cooking time 5.5 minutes, 220oC Cooking time 5 minutes, 240oC Cooking time 4 minutes
19.3.4.6 Meat treatments, marinades, salting meat, marbled beef
1. Marinades are made of acid, oil, and herbs. The acid is to denature the proteins and open the meat structure for flavour to enter. Marinades work best on meats that are not too dense or where the meat is cut into pieces.
2. Salting meat, brining, adds moisture to the meat through osmosis because the meat's cell fluids are less concentrated than the salt water. Water leaves the muscle cells and salt flows in to dissolve fibre proteins and concentrate the cell fluids so water is attracted back into the meat. So salting meat adds both salt and water to the meat muscle. Not all the water is squeezed out by cooking because of the added water.
3. Many flavour or aroma molecules cannot dissolve in water but can dissolve in fat. Muscles that are used often consume the stored fat, and so the meat from these muscles has little fat. Older the animals have fat energy reserves in their muscles. Meat with white streaks of fat is called marbled and gives beef with the best flavour. Ageing allows enzymes in the muscle cells to breakdown the overlapping proteins, which makes the meat tender.
19.3.5.1 Microwave radiation
See 27.01: Electromagnetic spectrum
1. Microwaves are a form of high frequency radio waves similar to the waves used by AM and FM radio. Microwaves enter from the outside of food losing about half their energy every 3 cm. Microwaves are reflected by metals so the walls of the microwave oven are made of stainless steel or epoxy coated stainless steel. so that the microwaves can bounce around the inside and not escape into the kitchen. The holes in the steel door are too small to let the microwaves pass through. Microwaves are transmitted by paper, glass and some plastics which do not absorb microwave energy and do not become hot. Microwaves are absorbed by food containing moisture.
2. The microwave region of the electromagnetic spectrum is from frequency 300 MHz, wavelength 1 m, to 300 000 MHz, wavelength 1 mm. In Australia, microwave ovens operate at 2450 MHz, (Class B / Group 2, ISM equipment Standard CISPR11), wavelength 12 cm. In other places the wavelength may be 12.24 cm. This is a lower frequency and lower energy than ionizing radiation. Microwave radiation is generated in an electronic tube called a magnetron. For safety reasons, when the microwave door is opened,. switches must cut the power. The power flux density of microwave radiation should not exceed 50 W / M2 at any point 5 cm or more from the external surface of the oven. The inside of a microwave oven is coated with metal that acts like a Faraday cage and reflects the microwaves like a mirror.
19.3.5.2 Microwave cooking
Microwave cooking occurs because water is a strong absorber of microwaves so the water in food boils and turns to steam. In a normal oven, the range of black body radiation is generated but only some longer sections of this radiation are absorbed by the food. The radiation penetrates the surface of the food for about one wavelength for infrared heat radiation < 1 / 10 mm. Only the outside of the food is directly affected and the inside of the food is heated by conduction. The 12 cm wavelength microwaves penetrate deeper into the food. Avoid exploding food, e.g. eggs, tomatoes, apples, by cutting into them before microwave cooking. Also avoid food with spikes because electrical arcing may occur between the spikes to cause charring of the food. Elevate the cooking pan in the microwave oven to allow more bounce of microwaves up from the floor of the microwave oven and get more even cooking.
19.3.5.3 Microwave containers
Microwave cooking containers should not absorb the radiation so they should be made from material with low polarity, i.e. low dielectric constant and low dissipation factor at 2450 MHz. The material should be stable at high temperature and have good resistance to oil vapour. e.g. polystyrene and certain glass. Never use metal containers or plates decorated with metal leaf  in microwave ovens because microwave cannot pass through metal and are reflected to damage the magnetron. Remove meal foil packaging and twisted ties or tags. Do not use dishes with metallic rims, cups with glued-on handles, delicate glassware, cut glass vases, jars with metal lids. However, you can use metal foil to protect food that might overcook in some areas. Do not cook in plastic food storage bags because they may melt. However, "GLAD WRAP" may be used to cover dishes but do not remove it immediately after cooking. Do not use brown paper bags or newspaper because they contain metallic impurities that may cause blue spark arcing and damage the oven. Do not put mercury thermometers in the microwave oven. Do not put a wet cat in the microwave oven. Use containers labelled "microwave oven safe". Use shallow round dishes because microwaves penetrate only 2 to 3 cm into most food. Food in the corners or dishes with corners will receive more energy and probably overcook. Arrange food containers in a ring at outside of the rotating turntable. Sometimes it pays to put the container containing thin food on top of another container on the turntable to get more bounce of microwaves through the food. Remember that if food is not cooked through, e.g. poultry, then bacteria may remain unharmed inside.
19.3.5.4 Superheating in a microwave oven
When tap water is heated on a stove top, the maximum superheating is 100.75oC. However, in a microwave oven, superheating temperatures of 105oC to 110oC can occur. The microwave oven heats the water directly and the container indirectly, the opposite of what happens when heating a container of water on a stove. In the microwave oven the water is not heated near the beaker surface where nucleation is most likely to occur. Evaporation occurs only at the water surface and is not fast enough to cool the bulk water. There is much less superheating in plastic cups because water does not wet plastic and many more nucleation sites are available for boiling. It is dangerous to put a cup of still water in the microwave oven because when you try to remove the cup nucleation may occur and the water boils, forms bubbles and steam, and may scold your hand. To avoid the delayed eruptive boiling of liquids after cooking, leave to stand for at least 20 seconds before removing food or liquids from the microwave oven.
1. Test a container for potential microwave oven use. Fill a one cup glass measure with water and put it in the microwave oven alongside the container to be tested, e.g. a ceramic dish. Heat for on high for 60 seconds. If the container is microwave oven safe, it will remain cool but the water should be hot. However, you cannot use this test on plastic containers that must be labelled microwave "oven safe".
2. Cook a potato for 2 minutes then cut it open to see the translucent areas finger-like regions extending from the outside where the potato has been heated above 60oC. This show that microwave ovens do not provide a uniform density of microwave energy. So "hot spots" and "cold" spots may exist in microwave ovens unlike the conventional oven. This phenomenon is the reason cooks suggest leaving food cooked by microwaves to "stand" for some time after cooking to allow the temperature to equalize in the food.
3. Compare popcorn cooked in the microwave with popcorn cooked on the conventional stove. Use the same number of corn (maize) grains and later count the number of unpopped grains. Carefully open popcorn bags away from your face!
4. Do not put sealed tins or glass jars in a microwave oven, e.g. babies bottles fitted with a screw cap. Remove food from tin cans. If boiling liquids in a microwave oven use a wide moth container. Eggs cooked in the microwave may explode. Egg yolk contains fat so tends to cook more quickly than egg white. Even out of the shell, eggs may explode in the microwave because rapid heating causes a build-up of steam, so before cooking puncture egg yolks and whites. Also, puncture skins of potatoes, apples, sausages and oysters to allow steam to escape. Food with a high fat content, e.g. sausage roils, may catch fire if overcooked.
5. To observe the effect of the wavelength of microwaves take out the turntable and put a one cup glass measure with water and a long stick of uncooked spaghetti. Heat at high for one minute. The spaghetti will have an uncooked area every 12 cm.