• Document: INTRODUCTION. Such chemical substances which are added to food materials to prevent their spoilage are known as chemical preservatives.
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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 sulfite or potassium bisulfite 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 sulfur dioxide and potassium carbonate. The sulfur 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 of sugar. iii. For different concentration of KHSO3. EXPERIMENT AIM: To study the effect of potassium bisulphite as a food preservative under various conditions (temperature, concentration and time). APPARATUS: Beaker, pestle and mortar, glass bottles, balance and peeler. CHEMICALS: Fresh fruits, potassium bisulphite and sugar. THEORY: Food materials undergo changes due to time, temperature and enzymatic action. So these become unfit for use. These changes can be checked by adding small amounts of potassium bisulphite. The effectiveness of potassium bisulphite as preservative depends upon its concentration under different conditions. PROCEDURE: Wash the fresh fruit and peel off their outer skin. Grind it in a pestle and mortar to a paste. Mix with sugar and colouring materials. The material so formed is called fruit jam. This can be used to study the effect of concentration, temperature and time. Effect of concentration of sugar: Take three bottles labelled as A, B and C. Put 100g of fruit jam in each bottle. Now, add 5g, 10g and 15g of sugar to bottle A, B and C. Mix the contents thoroughly and close the bottle. Keep these bottles to stand for a week. Note the changes taking place in jam daily. Bottle number A B C Weight of jam taken 100 gm 100 gm 100 gm Weight of sugar added 5 gm 10 gm 15 gm Weight of KHSO3 0.5 gm 0.5 gm 0.5 gm Observation (Days) Colour Dark orange Dark orange Dark orange Odour Pleasant smell Pleasant smell Pleasant smell Day 1 Fungus Fungus not Fungus not Fungus not formed formed formed Colour Dark orange Orange Light Orange Odour Pleasant smell Pleasant smell Pleasant smell Day 2 Fungus Fungus not Fungus not Fungus not formed formed formed Colour Dark orange Orange Light Orange Odour Pleasant smell Pungent smell Pungent smell Day 3 Fungus Fungus not White Fungus White Fungus formed formed formed is more than B Colour Orange Light Orange Light Orange Day 4 Odour Pungent Smell Pungent Smell Pungent Smell Fungus White Fungus White fungus Fungus turned is formed has increased greenish in colour Bottle number A B C Weight of jam taken 100 gm 100 gm 100 gm Weight of sugar added 5 gm 10 gm 15 gm Weight of KHSO3 0.5 gm 0.5 gm 0.5 gm Observation (Days) Colour Dark orange Light Orange Yellow Colour

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