School Science Lessons
2017-02-01 SP LI
Please send comments to: J.Elfick@uq.edu.au
19 Food, household items and products, beauty
an skin care, cooking
Table of contents
19.7.0 Beauty and skin care products
19.4.4 Food additives
19.2.0 Food composition
19.3.6 Food preservation
19.1.0 Household chemicals
19.5.0 Household fabrics
19.9.0 Household hints, kitchen
126.96.36.199 Ethylene absorption by oxidation with
19.2.0 Food composition
17.0 Coconut oil
188.8.131.52 Colloids in food
19.2.11 Composition of edible oils
184.108.40.206a Electrophoresis, food dyes, marking
3.98 Elements in food
3.90 Fats in food
220.127.116.11 Fish oils
18.104.22.168 Ice cream
22.214.171.124 Make jelly with fresh pineapple
and tinned pineapple
4.3.0 Margarine label
19.1.0 Household chemicals
19.1.5 Acid-base indicators in the
19.1.0 Household chemicals, chemicals in the home
126.96.36.199 Acidulated water
9.141 Benedict's test
19.1.17 Cooking fats
188.8.131.52 Emulsifying (surface active)
9.142 Fehling's test
19.1.6 Food acids, acids in foods
19.9.0 Household hints
184.108.40.206 Leavening agents
220.127.116.11 Polyhydric alcohols
12.3.1 Taste of acids, solid acids
in the home
10.2.3 Triple scale wine hydrometer
18.104.22.168 Wheat and flour
19.1.20 Dipsticks to test the vitamin
C, ascorbic acid, content of food
19.1.9 Prepare baking powder
19.1.7 Prepare carbon dioxide, sodium
hydrogen carbonate with sour milk, vinegar
19.6.7 Prepare camphor oil
19.6.6 Prepare soap, household soap
19.6.5 Prepare preserving agents
for cut flowers
22.214.171.124 Prepare self-leavened flour,
19.1.4 Prepare vinegar from wine
4.2.6 Prepare vinegar with Acetobacter
19.1.3 Solid acids, add sodium carbonate
19.1.2 Solid acids, pH
19.1.1 Solid acids, solubility
126.96.36.199 Use flour to clean brass
188.8.131.52 Use flour to make glue
184.108.40.206 Use flour to make papier-mâché
220.127.116.11 Use flour to make play
19.1.16 Table salt and rock salt
19.3.01 Water content of food
18.104.22.168 Water retention agents
22.214.171.124 Tests for glucose, urine
9.141 Tests for reducing sugars, Benedict's
126.96.36.199 Tests for borax / turmeric adulteration
1.0 Clinitest, Tests for glucose
2.0 Clinistix, Tests for glucose
3.0 Diastix, Tests for glucose
4.0 Glucose tolerance, Tests for glucose
5.0 Glucose ferricyanide, Tests for glucose
6.0 Nelson-Somogyi tests, Tests for glucose
7.0 Glucose oxidase, Tests for glucose
8.0 Glycosylated haemoglobin, Tests for glucose
188.8.131.52.1 Tests for ketones
184.108.40.206 Tests for nitrates / nitrites with
220.127.116.11 Tests for sulfites
18.104.22.168 Tests for tartaric acid
22.214.171.124 Tests for urine
126.96.36.199 Tests, Multiple reagent strips
3.98 Elements in food
See diagram 3.2.98: Find nitrogen in foods
1. Collect small pieces of different foods together, such as cheese,
bread, flour, sugar, leaves, maize.
Heat a piece of each, about the size of a rice grain, on a tin lid or
metal bottle top.
Hold the lid with tongs.
Black carbon is always left on the lid.
2. Heat small amounts of food with copper oxide
in a small test-tube. Copper oxide releases oxygen to the food.
Test the gas in the test-tube with lime water by withdrawing a little
gas in a teat pipette and bubbling the gas through the lime water.
The lime water turns milky indicating the presence of carbon dioxide.
Also, water is condensed on the cooler parts of the tube.
3. Put a small amount of crushed food in a test-tube
and add three times that volume of soda lime.
Mix the substances thoroughly then heat the test-tube. Use your hand
to fan gases from the mouth of the test-tube towards you to
smell ammonia at the mouth of the tube.
Test the gases with wet blue and red litmus paper.
The red litmus paper turns blue.
If the food gives off ammonia gas, the nitrogen in the ammonia must
have come from the food.
4. Mix separately cane sugar, vegetable oil and
egg white with soda lime, then heat the mixtures.
Note any smell of ammonia at the mouth of the test-tube containing the
The nitrogen in the ammonia came from the protein in the egg white.
5. Heat a mixture of 0.5 cm of sucrose and 1.0 cm of concentrated sulfuric
acid gently for 2 seconds and then leave to stand.
Note the vigorous reaction and the colour change from white sugar to
C12H22O11 + (H2SO4
catalyst) --> 12C + 11H2O
19.1.0 Household chemicals,
chemicals in the home
Acids are used give tartness to foods, or to alter the acidity of the
medium, i.e. to lower the pH in canned products, to prevent the
crystallization of jams and jellies.
Bases are used as ingredients of baking powders used in pastry production,
and in powders for effervescent beverages.
Improving agents includes chemical compounds that enhance the quality
criteria of foods, e.g. flavour and
consistency, and substances used for polishing and glazing confectionery
188.8.131.52 Sequestrants, sequestering
agents, either removes an ion or makes it ineffective by forming a complex
with it, e.g. a chelate
An example is the sequestration of Ca2+ ions in water softening.
A sequestrant binds with metal ions to prevent them from catalysing
chemical reactions that spoil preserved food.
Metals such as copper, iron and nickel get into food from processing
machinery or because of chemical reactions with the container.
The sequestrant citric acid acts as a synergist (increases the effect)
Sequestrants are used in shortenings, mayonnaise, lard, margarine, cheese.
184.108.40.206 Emulsifying (surface
active) agents, "food soaps" (E433-444) are used to stabilize emulsions
of oil and water components
220.127.116.11 Polyhydric alcohols
are used as a humectant to keep from drying.
They may also be sweet, e.g. sugarless chewing gum may contain mannitol
(E421) sorbitol (E420) and glycerol (E422, and have the
same calorific value as cane sugar, 16.5 kj / g.
18.104.22.168 Water retention
agents, e.g. polyphosphates (E450-452) are used in processing poultry,
fish and mammalian meats to
bind water and minimize "drip".
Phosphates are also used in soft drinks.
However, excessive intake of phosphates from processed food may harm
bone growth in children.
22.214.171.124 Acidulated water
is water that has been made slightly acidic by the addition of an acid
substance such as lemon juice or
vinegar (about one teaspoon to half a litre of water).
Peeled fruit and vegetables such as apples, pears, celeriac, globe artichokes
and salsify are immersed in acidulated water to prevent
them from discolouring.
It can also be used for cooking.
Cauliflower will be snowy white if boiled in acidulated water.
19.1.1 Solid acids, solubility
| Citric acid, C6H8O7
| Tartaric acid, C4H6O6
| Boric acid, H3BO3|
Shake different solid acids in separate test-tubes half filled with
Which of the acids are the most soluble and the least soluble in water?
19.1.2 Solid acids, pH
Divide the solution in one test-tube into three portions in three different
Test the first solution with litmus paper.
Add drops of methyl orange solution to the second solution.
Add drops of phenolphthalein solution to the third solution.
19.1.3 Solid acids, add sodium
See diagram: 9.154: Lime water test for carbon
Add a little solid sodium carbonate to a sample of each acid solution.
Note what happens in each case.
Pass gases from the reaction through lime water.
Shake the test-tube so that the gas mixes with the lime water.
The milky precipitate shows that carbon dioxide forms when acids react
with sodium carbonate.
19.1.4 Prepare vinegar from
is Gram stain negative, has ellipsoidal to rod-shaped cells occurring
singly, in pairs, or short chains to form
colonies that are beige to brown, round to wavy.
Its grows the substrates glucose, ethanol, organic acids, and glycerol.
It is an obligate aerobe so it requires oxygen.
It is often found on spoiled and unspoiled fruit and can be isolated
It is a spoilage organism converting ethanol to acetic acid.
It is sensitive to very low pH but can grow at wine pH and survive low
Its optimum temperature is 20-25oC.
It can withstand ethanol levels as high as 15%.
Acetic acid bacteria derive their energy from the oxidation of ethanol
to acetic acid during respiration.
C2H5OH + O2 --> CH3COOH
Live vinegar, or vinegar culture, contains the
acetobacter bacteria, which converts alcohol to acetic acid and produces
(mothery, mother-of-vinegar) a gelatinous slime of yeast and acetic
acid bacteria that eventually forms on the surface of the wine vinegar
This smooth, leathery, greyish film becomes quite thick and heavy.
It should not be disturbed.
It often becomes heavy enough to fall and is succeeded by another formation.
If the "mother" falls, remove and discard it.
An acid test will indicate when all of the alcohol is converted to vinegar.
Wine making suppliers sell acid test kits and acetobacter as "mother"
or vinegar culture.
Some of the vinegar can be withdrawn and pasteurized for use while the
remaining unpasteurized vinegar containing the living bacteria
may be used as a culture to start another batch.
So a piece of the "mother" is not necessary to start a new batch of
Some people add diluted wine to the culture every 4 to 8 weeks, depending
on the temperature and when most of the alcohol is
converted to vinegar as determined by an acid test.
Adding more alcohol to the culture keeps it alive, prevents spoilage
and increases the quality of vinegar.
Acetic acid (ethanoic acid) is a weak acid, only
about 1% dissociates in water, pH of 2-3, so it can be used for cooking,
foods, salad dressings, with cooked fish, a cleaning aid and treating
stings from marine animals.
CH3COOH (aq) <--> CH3COO- (aq)
+ H+ (aq)
Pasteurizing kills vinegar bacteria and prevents
the formation of the "mother", which could lead to spoilage.
Pasteurized vinegar keeps indefinitely if tightly capped and stored
in a dark place at room temperature but above high temperature
cause a loss of acidity, flavour and aroma.
If unpasteurized vinegar is exposed to oxygen without alcohol present,
bacteria can convert the vinegar to carbon dioxide and water.
When first made, vinegar has a strong, sharp taste
but it becomes mellow with age when esters form as in wine.
If undisturbed, suspended solids fall to leave clear and bright vinegar
that can be siphoned off into sanitized bottles with plastic caps.
Avoid stored vinegar contact with metal or air.
The quality of vinegar improves for up to two years and then gradually
In Japan, the polished rice vinegar komesu and
the unpolished rice vinegar kurosu are traditional seasonings that are made
saccharification of rice, alcohol fermentation, and oxidation of ethanol
to acetic acid.
An alcoholic liquid with vinegar, called moromi, is fermented in covered
containers to prevent bacterial contamination.
A crepe pellicle of acetic acid bacteria, Acetobacter genera,
covers the moromi surface and the fermentation is allowed to continue for
about a month.
See also 4.2.6: Prepare vinegar with Acetobacter aceti
1. To prepare vinegar from wine, use 10-11% alcohol wine, although dilute
the alcohol to 5.0 to 7% alcohol.
containing less than 10% alcohol is subject to spoilage.
The alcohol concentration should not inhibit the activity of the bacteria
that transform the wine.
The vinegar process may not get started with over 12.5% alcohol or if
the wine was treated with sulfur.
Wine should contain no excess sugar because it increases the chance
of spoilage and the formation of a slime-like substance in the
The wine does not have to be clear before it is combined with the vinegar
culture because vinegar clears as it ages.
Vinegar is a mixture of at least 5% acetic acid, if it is sold, with
water and flavouring and colouring chemicals depending on the method
of production, e.g. balsamic vinegar, apple vinegar, brown vinegar and
2. The simplest method to prepare vinegar is to
leave an open, 3/4 filled bottle of wine in a dark place, at 24-29oC,
for 6-8 weeks.
Cover with netting to allow access to air but to keep away vinegar flies.
3. Use 2 measures of dry wine, (11 to 12% alcohol),
1 measure of water, (boiled 15 minutes and allowed to cool), 1 measure
vinegar culture with active bacteria.
Some wines contain sulfites or preservatives that could kill the vinegar
4. For a steady supply of vinegar, use a 5 litre
wide mouth glass or stainless steel container, (not plastic), whose capacity
is at least a
gallon and pour one litre of wine and 200 mL of vinegar into it.
Remove the cover for a half hour every day.
In a couple of weeks the madre (mother), a viscous starter, will have
settled to the bottom of the jug, while the vinegar above it will be
ready for use.
Add more wine as you remove vinegar to keep the level in the jug constant.
19.1.5 Acid-base indicators
in the home
| 5.6.1 pH and acid-base indicators,
acidity and alkalinity, ionization of water
| 5.6.2 Test common solutions with
| Baking soda, sodium hydrogen
Use grape juice or red cabbage juice for acid-base indicators.
Note the sour tastes of fruit and vinegar and the taste of baking soda.
Grape juice turns red in acid lemonade and blue in alkaline dishwater.
Use flower pigments as pH indicators.
19.1.6 Food acids, acids in
Acetic acid, ethanoic
Benzoic acid, in cranberries,
prunes and plums
Butyric acid, in decomposition
of butter, rancid butter
Caffeotannic acid, no such compound,
in tannin from coffee berries, mainly chlorogenic acid, C16H18O9,
an antioxidant ester
Citric acid, C6H8O7,
in citrus fruits, lemon, orange
Lactic acid, in milk digestion
Malic acid, C4H60O5, HO2CCH2CHOHCO2H,
DL-malic acid, green apple sour taste
Oxalic acid, C2H2O4.2H2O,
ethanedioic acid, in tea, cocoa, pepper, rhubarb
Tannic acid in tea
Tartaric acid in grapes,
pineapples, potatoes, carrots
126.96.36.199 Leavening agents
Leavening is foaming in batters and dough to make the final product
lighter and softer to eat.
1. Mechanical leavening agents includes whisking cream or egg whites
to make air foams for sponge cakes, batters and meringues.
Also, beating white sugar with butter, creaming, is used to make cookies.
2. Chemical leavening agents are usually baking
powder (a mixture), and baking soda (sodium bicarbonate, sodium hydrogen
carbonate) that react with acidic ingredients to form carbon dioxide
bubbles in the mixture.
Acidic ingredients may include buttermilk, chocolate, cream of tartar
(potassium bitartrate), fruit preserves, lemon juice, molasses,
monocalcium phosphate, sodium aluminium phosphate, sodium aluminium
sulfate, sour milk, vinegar, yoghurt.
Cream of tartar is the most common ingredient in baking powder mixtures.
However, "double acting" baking powder may use monocalcium phosphate
and sodium aluminium sulfate to slow the release of carbon
The best combination of a leavening agent with an acidic ingredient
cannot be decided in the chemistry laboratory because different
combinations affect speed of carbon dioxide release, flavour development,
surface browning, texture, moisture content and palatability.
So the best combination must be decided by cooks and people who pay
for and consume the end products.
3. Biological leavening agents include generation
of carbon dioxide by yeast fermentation for production of fermented food.
Bakers' yeast Saccharomyces cerevisiae from the brewing industry
is used to make bread and cakes.
Baking yeast is in two forms, compressed yeast cake and active dry yeast.
The "brewer's yeast" sold in health food stores for nutritional purposes
is not an active yeast so is not a leavening agent.
Lactobacillus bacteria, (over 120 species), is used to make cheese,
chote, cider, kimchi, pickles, sauerkraut, silage, sourdough bread,
Natural yeasts and strains of lactobacillus, both from the air, vary
in their characteristics in different places so local products, e.g. beer
and baked products, may have their own eating characteristics and taste.
19.1.7 Prepare carbon dioxide,
sodium bicarbonate with vinegar
Baking soda, sodium hydrogen
Add vinegar, or acid buttermilk or sour unpasteurized milk or or fruit juice
to sodium bicarbonate, (sodium hydrogen carbonate).
The reaction forms carbon dioxide.
188.8.131.52 Wheat and flour
Wheat, (Triticum aestivum)
1. Bread and noodle wheat
Bread and noodle wheat are the dominant types of wheat planted throughout
They fall into classifications that have different receivable standards.
From APH, (Australian Prime Hard), with high quality requirements through
to FEED, which has limited quality requirements.
Queensland conditions are conducive to the production of high quality
grain and the breeding and development of new varieties reflects
Flour milled from Australian Prime Hard wheat is used to produce high-protein,
Chinese-style, yellow, alkaline noodles and Japanese
Ramen noodles of superior brightness, colour and eating quality.
Australian Prime Hard flour is also suitable for the production of high-protein,
high-volume breads and wanton dumpling skins.
Australian Prime Hard can be blended with lower-protein wheat to produce
flours suitable for a wide range of baked products.
2. Durum wheat, (Triticum durum)
Durum wheat is used in the production of pasta products, where the main
requirement is grain of high protein, preferably more than
13% and a minimum of 11.5 %.
Grain appearance is also important because downgrading can occur due
to black point, weather damage and mottling.
Acceptable levels of black points are as follows: ADR1 3%, ADR2 5% and
3. Soft wheat
Soft wheat represents two distinct types.
The Soft Biscuit type (9 to 105% protein), is suitable for the biscuit
industry, and the Soft Noodle type (9 to 11.5% protein), is suitable
for the manufacture of cakes, pastry and white salted noodles.
Soft Biscuit types are best grown using irrigation and suitable crop
management to achieve target protein levels.
Capped domestic market volumes exist so growers should seek pre-plant
4. Feed wheat
Feed wheat is generally high yielding varieties that have quality limitations
for use in flour and noodle production.
5. Forage wheat
Forage wheat is commonly the winter type and have the major advantage
of adaptability to a wide range of sowing times.
The winter habit delays maturity in early sowing, thus extending the
period of vegetative growth.
Maturity varies once vernalization requirements have been met.
In Australia, winter wheat ise usually sown in late March or early April.
Effects of grain defects on end-product quality
1. Black point
Excessive levels may result in "specky" semolina or discoloured bran,
wheat germ and divide flours (pastry flour).
The end products are often visually unattractive, especially with durum
products, e.g. pasta.
2. Sprouting (low falling number)
The finished product is affected by high levels of alpha amylase in
the flour, which causes "key holing" in bread, fragile noodles,
discoloured biscuits and cakes.
Sprouting has a small impact on pasta except at FN (falling numbers)
< 200 seconds.
3. Frost damage
Frost damage can cause low failing number, reduced flour yield, increased
grain hardness and very poor baking performance for bread,
biscuits and breakfast cereals.
4. Excessive screenings
Excessive screenings causes reduced grain and flour yield, (so loss
of profitability), but has little effect on end product quality, other than
excluding excess screenings caused by frost and heat stress damage.
Samples tested with high screenings have poor baking quality.
This may be attributed to heat stress damage during grain filling, which
was also believed to be responsible for the high screenings.
4. Low density
Reduced grain and flour yield (loss of profitability), has little effect
on end-product quality, excluding low density due to frost and
heat stress damage.
5. Heat damage
For heat damage due to drying at temperatures above 600oC,
the flour produced from this grain is of poor baking quality and baked
products are often unsaleable. requirements have been met.
In Australia, winter wheat is usually sown in late March or early April.
184.108.40.206 Prepare self-leavened
flour, "self-raising flour"
sulfate, (potassium alum)
Plain flour and self-raising flour
Baking soda, sodium hydrogen
"Plain flour" is "wheat flour" made from the endosperm "kernels" of
wheat grains by grinding and sifting.
"Self-raising flour" contains plain flour and baking soda, sodium hydrogen
In the kitchen, to test whether flour is plain flour or self-raising
flour, place a little on your tongue.
If you feel a tingle, this indicates that the flour is self-raising
Use self-leavened flour to make steamed bread.
Mix the flour with water without addition of any baking soda.
Knead the dough and let it stand for 10 to 15 minutes.
This kind of flour is made by blending a small quantity of chemical
sponging agent, also called baking powder, with ordinary flour.
The sponging agent contains 20 to 40% of sodium hydrogen carbonate,
and 35 to 50% of acidic substances such as sodium dihydrogen
phosphate, potassium hydrogen tartrate and aluminium potassium sulfate
(potassium alum, Al2(SO4)3.K2(SO4).24H2O)
agents, e.g. starch and aliphatic acids.
Sodium hydrogen carbonate reacts with acidic substances to produce carbon
dioxide, while the acidic substances decompose the
carbonate to lower the basicity of finished products.
The filling agents are used to prevent the flour from moisture absorption,
agglomeration and loss of effects.
They can also regulate the forming rate of gas or make the bubbles be
When water is added to self-leavened flour, the hydrolysis of sodium
hydrogen carbonate shows basicity, while hydrolysis of sodium
dihydrogen phosphate shows acidity.
The reaction results in release of carbon dioxide.
The heat decomposes sodium hydrogen carbonate to make spongy steamed
220.127.116.11 Use flour to make
Add five drops food colouring to two cups water.
Then add two cups flour, one cup salt, one teaspoon cream of tartar,
and two tablespoons vegetable oil.
Cook and stir over medium heat for three minutes (or until the mixture
Turn onto board or cookie sheet and kneed to proper consistency.
Store in an air tight container.
18.104.22.168 Use flour to make
Mix flour and water to a pancake batter consistency for use on paper,
light-weight fabric, and cardboard.
22.214.171.124 Use flour to make
Mix one cup flour with two thirds cup water in a medium size bowl to
a thick glue consistency.
To thicken, add more flour. Cut newspaper strips approximately one to
two inches in width.
Dip each strip into the paste, gently pull it between your fingers to
remove excess paste, and apply it to any object (an empty bottle,
carton, or canister).
Repeat until surface you want to cover (clay, cartons, bottles, or any
disposable container makes a good base).
Continue until the base is completely covered. Let dry, then decorate
with poster paint.
After the paint dries, coat with shellac.
126.96.36.199 Use flour to clean
brass and copper.
Mix equal parts flour and salt, and add one teaspoon white vinegar to
make a paste.
Spread a thick layer on the brass and let dry.
Rinse and wipe off paste.
19.1.9 Prepare baking powder
Baking powder is a chemical leavening agent and sponging agent.
To prepare 10 g of baking powder, weigh 3 g of sodium hydrogen carbonate,
2 g of starch and 0.7 g of calcium phosphate.
Mix them with 5.3 g of sodium dihydrogen phosphate in a small beaker.
Weigh flour and the prepared sponging agent in the ratio of 50 to 1,
and mix them thoroughly to make 20 g of self-leavened flour.
Add 15 mL water to the prepared self-leavened flour and knead the dough.
Lay aside the dough for 5-10 minutes (leaven dough) and then make the
dough into spongy, delicious steamed bread by steaming for
19.1.16 Table salt and rock
1. Common salt is sodium chloride crystals.
Common salt, rock salt, comes from the naturally occurring mineral of
sodium chloride called halite.
It is often found as cubic crystals and associated with gypsum in Triassic
Sea salt is extracted from evaporated sea water.
Table salt may be made from rock salt or naturally evaporated sea salt
and contain iodine (iodized salt) anti-caking agents,
e.g. anti-caking agent (554) and potassium iodate.
Kosher salt is a coarse salt with large crystals used for drawing blood
Pickling salt is a fine grained salt used for pickling and it contains
no additives, e.g. anti-caking agents.
Grey sea salt, "Sel gris", is unprocessed, and has minerals from the
Indian black salt, kala namak, has a brown black in colour and a smoky,
Rock salt is a grey colour, contains minerals and impurities, and is
used in ice cream machines and for melting ice and snow on the roads
using brine and sea sand.
2. Table salt may be "iodized" by the addition of
potassium iodide or potassium iodate.
About 0.01% potassium iodide in table salt is added as a nutrient for
the thyroid hormone thyroxine for those on an iodine deficient diet,
which leads to goitre.
However, the iodide will oxidize in air to iodine that is lost through
Thiosulfate was formerly used as a stabilizer but now it is normally
Because alkaline conditions prevent oxidation, bases such as sodium
bicarbonate or phosphates may also be added.
Potassium iodate may be used to avoid these problems.
3. Atmospheric moisture may cause the cubic crystals
of sodium chloride to stick together and the salt does not flow.
This problem can be solved by using about 0.5% drying agents, e.g. carbonates
(E501-4) and sodium aluminium silicate (E554).
Another method is to change the shape (habit) of the cubic salt crystals
to a form that does not provide large flat surfaces to pack
Salt normally crystallizes as cubes because the octahedral faces of
the crystal consisting of either all Na+ or all Cl-
grow faster than the
cubic faces with alternating Na+ and Cl-.
If an impurity is absorbed onto the surface of the fast growing octahedral
faces, e.g. urea, the reverse happens, and octahedral crystals
form instead of cubes.
So more than 13 ppm potassium ferrocyanide K4Fe(CN)6.3H2O)
(E536) is added to table salt.
This compound is quite safe, however, to avoid using the word "cyanide"
on labels, the compound may be referred to as "yellow
prussiate of potash" or the IUPAC name "hexacyanoferrate".
4. Sprinkling salt on water causes the surface to contract momentarily
towards the crystals, while with pepper, the opposite tends to
4.1 Examine the label on a contained of table salt and note the contents
in addition to sodium chloride.
4.2 Prepare a freezing mixture and measure its temperature.
A mixture of ice and sodium chloride, freezing mixture, has temperature
The salt lowers the melting point of ice.
The salted ice is still at 0oC but above its new melting
point so it melts.
19.1.17 Cooking fats
Shortening is solid, white fat made from hydrogenated vegetable oil.
Solid fats derived from coconuts are quite saturated.
Lard is the rendered fat from pig abdomen.
Deep frying requires fats / oils with heat tolerant properties, e.g.
corn oil and peanut oils, but not butter, margarine, lard and olive oil.
19.1.20 Dipsticks to test
the vitamin C, ascorbic acid, content of food
1. Use dipsticks to measure vitamin C content in fruit juices.
You may fin more than in the original fruit because the processor adds
the minimum to replace any vitamin naturally present that has
not survived processing and storage.
2. Test the effect of boiling vitamin C in water.
3. Test the effect of cooking at different pH values by adding sodium
carbonate of soda.
4. Test the effect of boiling in the absence of oxygen.
If blend vegetables and measure vitamin C content before and after,
you will find a large increase because the boiling extracts the
soluble vitamin from the food.
5. Test your urine and establish how much you excrete after taking a
dose (1 -2 g) over a period of one day?
Measure the volume of urine and the concentration of vitamin C.
Plot the amount of the original vitamin remaining, and the rate of excretion
during the day.
188.8.131.52 Tests for glucose,
A pre-mixed synthetic urine called "Quick Fix" may be available.
Prepare artificial urine samples
Sample 1. Dissolve 1g serum albumin, 3g sodium chloride and 5g urea
in 1 litre of water.
Sample 2. Dissolve 1g serum albumin, 3g sodium chloride and 1g glucose
in 1 litre of water.
Test the artificial urine samples for colour, odour, turbidity (clear
or cloudy) PH (universal indicator) protein (more cloudy in hot water)
The tests for reducing sugars gives no values for fructose, galactose,
or the non-reducing disaccharides, sucrose and lactose, but maltose
The tests are used measure the hydrolysis of sucrose to glucose (invertase
or H+) the formation of glucose in germinating seeds, for
glucose in urine and indirectly blood glucose.
The commonly used Benedict's test measures total reducing substance
and does not accurately measure the amount of glucose present
in the blood because of the presence of non-glucose reducing substances,
e.g. glutathione, uric acid, ascorbic acid, and creatinine.
1.0 Clinitest tablet, a form of
Benedict's test for glucose
Add 10 drops of water to five drops of urine and add one Clinitest tablet.
The solution effervesces then boils without heating with a Bunsen burner
because the Clinitest tablet contains sodium hydroxide and
citric acid besides Benedict's reagent.
If the solution turns blue the test is negative.
If the solution turns green to orange or an orange flash, the test is
This oxidation method to measure blood glucose is based on the reducing
properties of glucose.
Glucose will reduce cupric salts to cuprous salts it a hot alkaline
solution and the quantity of cuprous salts produced is proportional to
the glucose concentration.
Oxidation methods to measure blood sugar give results higher than other
methods because they also measure reduction of some
2.0 Clinistix strip, test for
Test for glucose, test for (+) glucose in urine, indicator substance
"Clinistix" strip is impregnated with the enzymes glucose oxidase and
peroxidase, and a chromogen system, the indicator substance
The o-toluidine is oxidized to a blue-green substance, (Schiff base),
with varying shades of colour, which is then compared with the
standard chart provided in the kit to report the approximate level of
glucose present in the urine.
Compared to Benedict's test, which detects the total sugar present in
urine, the strip test detects semi-quantitatively the amount of
glucose present in urine.
Dip the reagent area of the "Clinistix" strip in fresh urine for two
Gently tap the edge of the strip against the side of the urine container
to remove excess urine.
Compare the test area closely with a colour chart exactly 30 seconds
after dipping the strip in the urine.
Hold the strip close to the colour chart and match carefully.
3.0 Diastix strip
"Diastix" strip has an area impregnated with the above enzymes together
with potassium iodide and a blue background dye.
The oxygen liberated in the final reaction binds with the dye to produce
a series of colour changes 30 seconds after wetting the strip
4.0 Glucose tolerance test
After fasting, blood glucose is measured then the patient drinks 50
g of glucose dissolved in 100 mL of water.
Samples of urine are collected periodically, e.g. every half hour for
Fasting blood glucose is about 80 to 120 mg / 100 mL and after two hours
blood glucose should be < 120 mg / 100 mL.
If blood glucose exceeds 150 mg / mL (and fasting blood glucose was
> 120 mg / 100 mL) the diagnosis is diabetes mellitus.
Glucose does not pass into the urine unless blood glucose is up to 180
mg / 100 mL, the renal threshold.
5.0 Glucose ferricyanide test
Glucose reduces yellow ferricyanide to colourless ferrocyanide in a
hot alkaline solution.
The decrease of yellow colour is proportional to the glucose concentration.
6.0 Nelson-Somogyi test
See: Water quality, Colorimeters,
"Scientrific", (commercial website)
The reducing sugars when heated with alkaline copper tartrate reduce
the copper from the cupric to cuprous state and thus cuprous
oxide is formed.
When cuprous oxide is treated with arsenomolybdic acid, the reduction
of molybdic acid to molybdenum blue takes place.
The blue colour developed is compared with a set of standards in a colorimeter
at 620 nm.
Non-glucose reducing substances can be removed to produce a protein-free
filtrate by use of acids to precipitate proteins from the
sample thus removing interference with colour reactions, turbidity and
foaming, e.g. the zinc sulfate-barium hydroxide method of
Nelson-Somogyi is said to give the closest value of "true glucose".
7.0 Glucose oxidase
Enzyme methods for measurement of blood glucose are quite specific for
glucose only, e.g. the enzymes glucose oxidase and hexokinase.
Glucose oxidase catalyses the oxidation of glucose to gluconic acid
and hydrogen peroxide
glucose + O2 --> gluconic acid + H2O2
Hexokinase catalyses the phosphorylation of glucose in the presence
Glucose-6-phosphate forms and is converted to 6-phosphogluconate by
a second enzyme, glucose-6-phosphate dehydrogenase.
Then the NADPH can be measured.
glucose + ATP --> G-6-P + ADP
G-6-P + NADP --> 6-phosphogluconate + NADPH + H+
8.0 Glycosylated haemoglobin
If blood glucose level is high for some time, haemoglobin becomes glycosylated,
i.e. the glucose molecule binds covalently to the last
valine group of the β chain and stays there for the about 120 days the
life of the red blood cell.
Measurement of blood glucose level is only a measure of the patient
blood glucose level at the time of sampling but measurement of
glycosylated haemoglobin shows the blood glucose level for the preceding
184.108.40.206.1 Tests for
See 16.5.01: Ethyl acetoacetonate
1. Add drops of 10% ferric chloride to 5 mL of urine.
Ferric phosphate forms but dissolves in excess ferric chloride.
The solution turns brown-red if acetoacetic acid is present.
2. Rotheras's test, Acetest, Ketostix uses nitroprusside to detect acetone
acetoacetic acid, and beta-hydroxybutyric acid (BHB, not
an acetone) by colour change from pink to purple in acetoacetate.
Ketostix detects acetoacetate, but not BHB nor acetone.
Sodium nitroprusside dihydrate, Sodium nitroferricyanide, Na2[Fe(CN)5NO].2H2O
220.127.116.11 Multiple reagent
It is a firm plastic strip to which are affixed several separate reagent
Sugar, serum albumin, urobilinogen and bilirubin are the four biochemical
substances tested in a random urine sample.
Although the heat and acetic acid test detects the presence of proteins
such as albumin, only a semi-quantitative test will be really useful.
It makes use of the same principle as described above for the strip.
The final colour ranging from green to brown.
It is based on the coupling of bilirubin with diazotized dichloronaniline
in a strongly acid medium.
The colour ranges through various shades of tan.
It is based on Rothera's reaction principle and on the development of
colours, ranging from buff pink for a negative reading
to purple when acetoacetate reacts with nitroprusside.
It also detects acetone but not beta-hydroxybutyrate.
Specific gravity (relative
In the presence of an indicator the polyelectrolytes present in urine
give colours ranging from
deep blue-green in urine of low ionic concentration through green to
yellow green in urine of increasing ionic concentration.
This test is based on the double indicator principle that gives a broad
range of colours covering the entire urinary pH range.
Colours range from orange through yellow and green to blue.
The test area of the reagent strip is impregnated with an indicator,
tetrabromophenol blue, buffered to pH 3.0.
At this pH it is yellow in the absence of protein.
Protein forms a complex with the dye turning the colour of the dye to
green or bluish green.
The colour is compared with the colour chart provided, which indicates
the approximate protein concentration.
It is based on the protein error of the pH indicator.
At a constant pH, the presence of protein leads to the development of
any green colour.
Colours range from yellow for "negative" through yellow green and green
to green blue for "positive" reactions.
Ehrlich's benzaldehyde reaction is a test for urobilinogen in the urine,
by dissolving 2 g of
dimethyl-p-aminobenzaldehyde in 100 mL of 5% hydrochloric acid and adding
this reagent to urine.
A red colour in the cold indicates the presence of an excessive amount
18.104.22.168 Tests for nitrates
/ nitrites with dipsticks
Sensitivity for nitrate = 10-500 mg / L.
Sensitivity for nitrite = 1 -50 mg / L.
Interference from nitrite removed by adding aminosulfonic acid so separate
nitrite strip not needed.
1. The tests for oxides of nitrogen in air.
Sensitivity 1 mL of NO2 / m3 of air.
2. The tests for nitrite in saliva, average 7 mg / L, except after foods
with high nitrate level, e.g. celery, beets, where you obtain
elevated levels for 24 hours.
3. The tests for nitrate / nitrite in fermented raw meat, e.g. salami,
legal limit 500 mg / kg, nitrate, Cured meat (corned beef) legal limit
125 mg / kg, nitrite, Canned ham, legal limit 50 mg / kg, nitrite.
4. The tests for nitrite in vegetable, e.g. Conventional carrots 40-100
mg / kg, Organically grown carrots 200-400 mg / kg,
Fresh spinach 5 mg / kg, if refrigerated for two weeks 300 mg / kg.
5. The tests for denitrification in waterlogged soils, soil + nitrate
+ glucose ---> N2O, Sensitivity: nitrate 10-500 mg / L nitrite
1-50 mg / L
Nitrates and nitrites (E249-253) occur naturally in many vegetables.
Additional nitrite can be derived from nitrate by bacterial activity
in the gut.
22.214.171.124 Tests for tartaric
Grape juice and wine (added acetic acid ensures total tartrate is measured)
Less than 1 g / L indicates very poor quality.
Sensitivity: 0.5-10 g / L
126.96.36.199 Tests for borax
/ turmeric adulteration of food
Borax or boric acid adulteration
Detect borax or boric acid adulteration in chopped and squeezed meat
by adding concentrated hydrochloric acid, then dip turmeric
paper into the filtered solution.
The turmeric paper turns bright cherry-red colour,
Add a drop of ammonia solution to the coloured turmeric paper, which
turns dark green to black to show the presence of boric acid
in the meat.
Add borax to solution to solutions of food, e.g. ground rhubarb root
or mustard made from Sinapsis alba, to detect adulteration with
turmeric to improve the colour of the product.
The addition of borax causes a deep brown colour to detect the adulteration.
188.8.131.52 Tests for urine
Reagent dipsticks ("Dip-stix") can be used to test for the following
chemicals in a fresh urine sample: blood, protein, glucose, ketones,
nitrite, N-acetyl-B-glucosaminidase, bilirubin, robilinogen.
184.108.40.206 Tests for water
pH, free chlorine and total chlorine, chlorine / chloramine, ammonia
(NH3 / NH4+) nitrite and nitrate, oxygen.
220.127.116.11 Tests for sulfites
1. Tests for air pollution
Sensitivity: 5 mL (13 Mg) of SO2 / m3 air
2. Tests for sulfite preservatives
Legal limits: Fruit juices 115 mg / L, concentrated 600 mg / kg, Gelatine
1000 mg / kg, Dehydrated carrots 1000 mg / kg,
Cheese 300 mg / kg, Sausages 500 mg / kg, Wine 300 mg / kg, Sensitivity:
10-500 mg / L.
18.104.22.168 Colloids in foods
Most foods and their components of lipids, proteins and carbohydrates
are colloidal, e.g. milk consists of fat particles dispersed in
Margarine is an emulsion of water, flavours, colours, and vitamins in
a semi-solid fat, mayonnaise is oil, vinegar and egg yolk.
Blood, enzymes, muscle tissue, bone skin and hair all involve colloids.
Lotions, creams and ointments are mostly emulsions of oils dispersed
in water or vice versa.
Emulsions are one form of colloids.
Other examples of colloids are paints, rubbers, oils, pigments, plastics,
gels, starches, air pollution and clouds.
food dyes, marking pen ink
See diagram 22.214.171.124a: Electrophoresis
Electrophoresis is the movement of colloidal particles in a fluid caused
by an electric field.
Gel electrophoresis is used to sort molecules based on their size and
An electric field is applied to make molecules move through an agar
gel to make negatively charged molecules move towards the
positive terminal and positively charged molecules move towards the
Larger molecules move slower than smaller molecules leaving the different
sized molecules as bands the gel.
1. Cut the sides of a 10 cm × 5 cm flat bottom plastic container down
to 3 cm height, e.g. a margarine container.
Fold a piece of aluminium foil over one short end of the container to
cover both the outside end and extend to the bottom of the
Do the same at the other end of the container.
2. Make a comb from a piece of flat thick plastic,
e.g. the lid of an ice cream container for a thin comb or a styrofoam
meat tray for a
The comb must fits neatly into the width of the plastic container.
It has two lips that hang over the sides of the plastic container tub
to keep the comb in place.
However, the teeth of the comb should not touch the bottom of the plastic
Cut 6 teeth in the comb.
Each tooth should be 5 mm wide and 15 mm long.
3. Prepare a 0.1% bicarbonate buffer by dissolving
0.2 g of sodium bicarbonate in 200 mL of water.
Mix 1g of agar in 100 mL of the 0.1% bicarbonate buffer and heat to
boiling in a microwave oven.
Heat for 30 seconds then 10 second pulses until it boils.
Leave to cool to hand temperature.
4. Make 1 cm diameter spots of vegetable food dyes,
e.g. cochineal or ink from coloured marker pens on filter paper.
5. Prepare a 1% agar gel solution by dissolving
1f of agar in 100 mL in bicarbonate buffer solution.
Fill the plastic container with agar gel to a depth of 1 cm.
Insert the comb so that the top of the agar solution is just below the
top of the teeth of the comb.
Fix the comb 2 cm from one end of the plastic container.
Leave the gel to set undisturbed for 15 minutes.
When the gel is set, carefully remove the comb.
6. Cut out 3 mm × 4 mm rectangular pieces of the
colour spots and insert them into the wells formed from the teeth of the
Pour 100 mL of bicarbonate buffer solution into the plastic contained
to completely cover the gel.
Some colour from the paper rectangles may diffuse into the buffer solution
but this will not affect the colours diffusing through the gel.
7. Connect the gel to five 9 volt batteries connected
in series with wire leads and alligator clips.
Connect the end of the tank with the samples to the negative terminal
of the battery.
If fewer batteries are used the samples will take longer to run and
may diffuse into the gel.
Leave the circuit connected for 45 minutes until separation of samples
126.96.36.199 Ice cream
Ice cream is a foam preserved by freezing.
Under a microscope you can see solid globules of milk fat, air cells,
ice crystals, solution of concentrated sugars, salts and suspended
The ice crystals were formed by water freezing out of the solution to
a point where the lowering of the freezing point caused by the
concentration of the remaining solutes in the water corresponds to the
Manufacturers can expand the ice cream with air to double its volume.
Expanded ice cream feels fluffier and has a warmer taste.
Ice cream containing less milk fat has bigger ice crystals, coarser
texture and colder taste but the addition of emulsifiers and stabilizers
can mask these low fat properties but prepare the ice cream sticky.
If not stored at a low enough temperature, partial thawing causes the
smaller crystals to melt and later refreezing to larger crystals.
Ice cream on the tongue crystallizing out the lactose, milk sugar, which
stays on the tongue after the ice has melted leaving a sweet taste.
3. In some countries ice cream has the following composition:
1. > 10% milk fat by legal definition (10% to 16% fat),
2. 9% to 12% non-fat milk solids (caseins, whey proteins and lactose
3. 12% to 16% sweeteners, e.g. sucrose and glucose-based corn syrup
4. 0.2% to 0.5% added stabilizers and emulsifiers,
5. 55% to 64% water from milk.
4. The sugars, including the lactose from the milk
components, contribute to a depressed freezing point so that the ice cream
unfrozen water so that at typical serving temperatures, -15oC
to -18oC it is not too hard to scoop.
The colligative property of freezing point depression of a solution
is greater with lower the molecular weight molecules so the
monosaccharides fructose and glucose produce a softer ice cream than
the disaccharide sucrose.
Polysaccharides stabilizers add viscosity to the unfrozen portion of
the water so that it cannot migrate within the product to produce a
coarse and icy ice cream that is less firmer to the chew.
The smaller ice crystals are less detectable to the tongue.
Stabilizers prevent icy tasting.
5. Refrozen ice cream, that has not been stirred,
becomes a mixture if ice crystals and dehydrated ingredients.
So it is harsh on the tongue and may be susceptible to infection by
Use a coffee tin with a plastic lid.
Half fill the coffee tin with 250 mL of double cream, 250 mL of whole
milk, 2 teaspoons of vanilla extract.
Firmly attach the plastic lid and use adhesive tape to attach the lid
Put the coffee tin in a plastic bucket with a tight lid.
Add 10 cm of ice cubes to the space around the coffee tin then 200 g
of rock salt to the same level as its height.
Then almost fill the bucket with ice cubes and attach the bucket lid
and use adhesive tape to attach the lid more tightly.
Turn the bucket on its side and roughly roll it forwards and backwards
for 10 minutes.
Open the bucket and coffee tin and observe the layer of frozen ice cream
lining the inside of the coffee tin.
Friction between ice cubes in the rolling bucket causes some ice to
melt but not refreeze because the salt has lowered the freezing point.
The super-chilled water so formed cools the walls of the coffee tin.
The ice cream mixture starts to freeze but does not form big crystals
because of the motion of the bucket.
The stirring from the rolling motion incorporates air and to prevents
large ice crystals from forming to produce a smoothly textured,
semi-solid foam that is malleable and can be scooped.
The salt water is cooled by the ice, and the action of the salt on the
ice causes it to partially melt, absorb latent heat and bringing the
mixture below the freezing point of pure water.
The immersed container can also make better thermal contact with the
salty water and ice mixture than it could with ice alone.
188.8.131.52 Make jelly with
fresh pineapple and tinned pineapple
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.
184.108.40.206 Ethylene absorption
by oxidation with sodium permanganate
Some commercial products use zeolite particles coated with sodium permanganate
to absorb ethylene and so prolong the storage life
of fruit and vegetables in a refrigerator, e.g. "Blue Apple"
The chemical reaction is as follows:
3CH2CH2 + 2NaMnO4 + H2O
--> 2MnO2 + 3CH3CHO + 2NaOH
3CH3CHO + 2NaMnO4 + H2O --> 3CH3COOH
+ 2MnO2 + 2NaOH
3CH3COOH + 8NaMnO4 --> 6CO2 + 8MnO2
+ 8NaOH + 2H2O
Combining equations 1-3 generates:
3CH2CH2 + 12NaMnO4 --> 12MnO2
+ 12NaOH + 6CO2
Even if the reaction does not go all the way through to the carbon dioxide-producing
step, many of the intermediate products formed
either become irreversibly bound to the media or act as reactants themselves.
Such is the case of the sodium hydroxide (NaOH) formed in equation 1
The NaOH will react with the acetic acid formed in equation 2 to produce
the sodium acetate salt (NaCOOCH3) through a simple
acid-base neutralization reaction.
This is shown below.
CH3COOH + NaOH --> NaCOCH3 + H2O
Combining equations 1, 2, and 5 generates:
3CH2CH2 + 4NaMnO4 --> 3NaCOOCH3
+ 4MnO2 + NaOH + H2O