Objective
The objective of this project is to investigate
the effectiveness of potassium bisulphite as
a food preservative. This study will examine
its preservative properties under various
conditions.
INTRODUCTION
Growth of microorganisms in a food material
can be inhibited by adding certain chemical
substances. However the chemical
substances should not be harmful to the
human beings.
Such chemical substances which are
added to food materials to prevent
their spoilage are known as chemical
preservatives.
In our country, two chemical preservatives
which are permitted for use are:
1. Benzoic acid (or sodium benzoate)
2. Sulphur dioxide (or potassium bisulphite)
Benzoic acid or its sodium salt, sodium
benzoate is commonly used for the
preservation of food materials. For the
preservation of fruits, fruit juices, squashes
and jams sodium benzoate is used as
preservative because it is soluble in water
and hence easily mixes with the food
product.
Potassium hydrogen sulphite or
potassium bisulphite is a chemical
compound with the chemical formula
KHSO3. It is used during the production of
alcoholic beverages as a sterilising agent.
It is made by the reaction of sulphur dioxide
and potassium carbonate. The sulphur
dioxide is passed through a solution of the
potassium carbonate until no more carbon
dioxide is given off. The solution is
concentrated and then allowed to crystallize
Potassium bisulphite is used for the
preservation of colourless food materials
such as fruit juices, squashes, apples and
raw mango chutney. This is not used for
preserving coloured food materials because
Sulphur dioxide produced from this chemical
is a bleaching powder.
Potassium bisulphite on reaction with acid of
the juice liberates Sulphur dioxide which is
very effective in killing the harmful micro-
organisms present in food and thus prevents
it from getting spoiled.
The advantage of this method is that no
harmful chemical is left in the food.
The aim of this project is to study the effect
of potassium bisulphite as food
preservative.
i. At different temperatures.
ii. At different concentrations and
iii. For different intervals of time.
Material required
Apparatus
Beaker
Conical Flasks (100 ml)
Glass Bottle
Glass Rod
Balance Scale
Knife
Pestle and Mortar
Peeler
Chemical
Sugar
Potassium Bisulphite
Fresh Fruits
Theory
Food materials undergo natural changes due
to temperature, time and enzymatic action
and become unfit for consumption. These
changes may be checked by adding small
amounts of potassium bisulphite. The
effectiveness of KHSO3 as preservative
depends upon its concentration under
different conditions which may be
determined experimentally.
Procedure:
Take fresh fruits, wash them thoroughly
with water and peel off their outer cover.
Grind it to a paste in the mortar with a
pestle.
Mix with sugar and colouring matter.
The material so obtained is fruit jam. It
may be used to study the effect of
concentration of sugar and KHSO3,
temperature and time.
(A)Effect of concentration of
Sugar:-
Take three wide mouthed reagent
bottles labelled as I II III.
Put 100 gm of fruit jam in each bottle.
Add 5.0 gm, 10.0 gm and 15.0 gm of
sugar to bottle No. I, II and III
respectively.
Add 0.5 gm of KHSO3 to each bottle
Mix contents thoroughly with a stirring
rod.
Close the bottle and allow them to stand
for one week or 10 days at room
temperature.
Observe the changes taking plae in Jam
every day
Records:
(B) Effect of concentration of
KHSO3 :-
1. Take bottles labelled as I, II, III.
2. Put 100 gm of Jam in each bottle.
3. Add 5.0 gm of sugar to each bottle.
4. Add 1.0 gm, 2.0 gm and 3.0 gm of KHSO3
to bottle No. I, II and III respectively.
5. Mix the contents thoroughly with a glass
rod.
6. Keep all the bottles at room temperature
for about 10 days and observe the changes
everyday.
Records:
Result: the increase in concentration
of KHS03 increases more time of
prevention.
(C) Effect of temperature:-
1. Take 100 gm of Jam in three bottles
labelled as I, II and
2. Add 10.0 gm of sugar and 1.0 gm of
KHSO3 to each bottle.
3. Mix the contents thoroughly with a
stirring rod.
4. Keep bottle No. I in the refrigerator at 0
deg * C , bottle No. II at room temperature
(25 deg * C) and bottle No. III in a
thermostat at 50 deg * C Observe the
changes taking place in the jam for 10 days.
RECORD:
Result: the increase in temperature
causes fast fermentation of jam.
(D) Effect of time:-
1. Take three bottles and label them as
I, II and III.
2. To each bottle add 25 g of Jam and 1
g of potassium bisulphite.
3. Keep bottle I for 7 days, bottle II for
14 days and bottle III for 21 days at
room temperature.
4. Note the changes taking place in
each bottle and record the
observations.
Result: with increase of days the
quantity of the jam deteriorates.
Conclusion
Food containing more amount of sugar is
not favourable to keep for a long time
Potassium bisulphite is a good preservative.
Uses
There are a number of uses for potassium
bisulphite as a food preservative. The
Manitoba Agriculture, Food and Rural
Initiatives reports this product works to
prevent the growth of mold, yeast and
bacteria in foods. It is also an additive for
homemade wine. Potassium bisulphate is
found in some cold drinks and fruit juice
concentrates. Sulphites are common
preservatives in smoked or processed meats
and dried fruits. In spray form, it may help
prevent foods from discolouring or
browning.
Availability
Potassium bisulphite is primarily a
commercial product. You might find this
chemical compound at meat processing
plants. Manufacturers of juice drinks and
concentrate will use potassium bisulphite to
increase the shelf life of their products. The
preservative is also available for home use.
Allergies
Sulphites such as potassium bisulphite can
trigger an attack for those with asthma.
Potassium bisulphite may cause lung
irritation.
Bibliography
The necessary information for the project is
collected from the references stated below:
http://en.wikipedia.org/wiki/Potassium
bisulfate
http://www.thetrustedtrolley.com.au
http://www.livestrong.com/article/
308673-potassium-bisulphate-as-a-food-
preservative/
