Preserving food for long time was a necessity of mankind since time immemorial. The availability of certain food items was limited to a particular season. Man’s desire to use them throughout the year motivated him to invent certain methods by which food items could be stored for a longer duration without a significant change in taste.
Food items can be categorized into perishable and non-perishable food items. Perishable items are those which get spoilt soon and are more prone to the attack of micro-organisms. Examples of some such items are vegetables, fruits, meat, eggs, milk etc. These items have a very short shelf life. On the other hand non-perishable foods are those which take a long duration to get spoilt like rice, wheat, oils, dried pulses etc.
The aim of using preservatives is to convert these perishable food items to non-perishable ones or extend the shelf-life. Food gets spoilt due to the attack of micro-organisms like bacteria, fungi, yeast etc. They bring some undesirable chemical changes in the food. Food preservatives inhibit these chemical changes through various ways.
Food preservatives are of two types: natural and artificial; and both try to maintain the quality, edibility and nutritive value of the foods.
Classification of Natural Food Preservatives
Depending on their mode of action, food preservatives are broadly classified into three kinds.
• Antimicrobial preservatives which inhibit the growth of the microorganisms
• Antioxidant preservatives which inhibit the oxidation of food ingredients like fats, lipids etc
• Preservatives which target the enzymes within the food stuffs and hence prevent the natural activities like ripening of food or post harvest ageing of food stuffs.
Some of the natural food preservatives include substances like salt, sugar, rosemary extract, essential oils, vinegar etc. Out of these, substances like salt, sugar and oils are used in our day-to-day life. Ongoing research is targeted towards the search of some new natural food preservatives. Let us discuss about a few preservatives in detail.
Salt: Salt has been used to preserve food items like meat and fish since ages. At very high concentrations of salt the cells of the micro-organisms loose water and dehydrate by the process of osmosis. It inhibits the growth of bacteria, yeasts and molds by the process of osmosis. Salting of meat preserves it for years. During pickling, raw mangoes, tomatoes etc are treated with considerably large amounts of salt. Even some vegetables like cabbage cauliflower and cucumber can be preserved by pickling them with salting.
Sugar: Sugar is a carbohydrate and the mechanism by which it stores food is same as that of salt. This substance also dehydrates the microorganisms by the process of osmosis. There are two ways in which the food stuffs can be stored in sugar.
1. Thick concentrated sugar syrup can be prepared and the food substances can be immersed in it.
2. The food items can be cooked in sugar until sugar reaches the point of crystallization. A higher concentration of sugar sweetens the food and either inhibits the growth of microorganisms or kills them by the process of osmosis. Sugar is generally used to preserve fruits like apple, peach, pear, plum etc in the form of jams and jellies.
Vinegar: This acidic solution is prepared by the fermentation of sugar and water solution. The process of fermentation is carried beyond the alcohol stage. Vinegar contains acetic acid which kills the bacteria due to its acidity or lower pH. Vinegar is used to preserve meats and vegetables during pickling. Even during the process of canning vinegar is used to increase the shelf life of the food items.
Rosemary Extract: This is prepared by the distillation of rosemary leaves and is known for its pleasant aroma and flavor. This substance has been used as a preservative since ages because of its antioxidant properties. It prevents the oxidation of food stuffs thus retaining the flavor and color of the food. The natural compounds present in the Rosemary extract like phenolic diterpenes, rosmarinic acid, carnosol are responsible for its antioxidant properties.
Some Traditional Practices of Food Preservation
With the advancement in technology, man has conquered many difficult situations. In olden days, means of transport were not that efficient and moreover crops and vegetables grown in a particular area were very much dependent on the seasonal conditions in that area. These conditions encouraged people at that time to adapt certain practices which helped them to preserve food throughout the year. Some of these traditional practices are as follows –
• Indian plums commonly known as ber in Hindi and regu pandu in Telugu is a seasonal fruit which is generally seen in the market between Jan – march. A dish called regu adaa helps to preserve it for the whole year. To prepare this, seeds are removed and the fruits are beaten into a semi-solid paste. After adding salt, the paste is made into small biscuits and then sun dried.
• Cluster beans commonly known as Guar-ki-phalli in Hindi and goru chikkudu in Telugu is a nutritious vegetable. In order to preserve it we have to cut them into medium size pieces and soak them in buttermilk along with salt. This has to be soaked for a span of 24 hours and then sundried. These sundried pieces can be fried in oil and eaten along with rice.
• Coccinia cordifolia commonly known as kundru in Hindi and dondakayi in Telugu can be cut into pieces. After applying salt to these pieces, they can be sun-dried and later these pieces can be stored for a long duration. Whenever required they can be fried and taken along with rice.
• Brinjal commonly known as baingan in Hindi and vankai in Telugu is very commonly used vegetable across India. Even this vegetable can be cut into pieces and dried in sun after applying salt. Before cooking the dried pieces have to be soaked for half an hour and then can be used to prepare a tasty curry along with tamarind water and jaggery.
• Mango – Good raw mangoes are available only in the summer season. They can be preserved in different forms of pickles. Apart from that small mango pieces can be sundried after application of salt. These mango pieces can be added to dhal through out the year.
It is true that nowadays we get all the food stuffs throughout the year with a variation in price. Fruits are no longer seasonal and they are ripened with the help of chemicals like ethylene. A few months back around November 2010 there was a heavy increase in the market price of all the vegetables. This crisis situation stayed for a span of three months but it affected many people. If we can adopt these traditional practices in our day to day life we can be ready to face any sort of odd situations. Not only this, we can prevent the wastage of huge quantities of food items also.