Fruit Juices and Their Preservation
Fruit juices have an important place, being rich in essential minerals, vitamins and other nutritive factors, they are quite popular. The nutritive value of fruit juices is far greater than that of synthetic products which are at present being bottled and sold in large quantities throughout the year. If real fruit juices could be substituted for these synthetic preparations, it would be a boon to the consumer as well as to the fruit grower. There is, therefore, great scope in the country for the production of fruit juices and allied products.
With the rapid progress in fruit farming during the last two decades, fresh juices are increasingly sold by vendors in large cities and towns. The demand for fresh juices is on the increase, but these cannot be had easily during off-season of their fruits. Therefore, fruit juices have to be preserved in a form in which they can be made available to the public during off-season.
Till about 20 years ago, only grapes and apple juices were produced, and these juices were used almost exclusively for medicinal purposes. These were generally recommended by doctors for infants and invalids. Now-a-days, however, due to common use of fruit-juices as breakfast foods etc, a large variety of them is produced on a big scale from fruits such as orange, pineapple, grape, apple, pomegranate, lemon, mango, banana, peach and plum etc. They are now becoming more popular than the carbonated beverages from apples and grapes.
In India, the pure fruit juice industry is still in its infancy. Preparation of these juices is limited to small scale. Production of best quality fruit juice requires costly equipment. Recently, few units have taken up fruit juice production on a large scale without compromising with their nutritional properties.
Fruit juices, especially orange, apple and grape juices, are concentrated using modern equipment so that there should not be any loss in their nutritional value and flavour. Sometimes, the required flavour is added back to the concentrates to get full fruit taste and flavour on dilution for serving. These concentrates are used as basis for soft drinks, medicinal preparations, baby foods, tonic foods etc. The frozen orange juice concentrate (four to one) is an excellent example in this case. Concentration is effected by freezing or by application of heat employing high vacuum etc. Fruit juice and concentrates are further converted into free-flowing fruit juice powders by puff drying. Sometimes, sealed in flavours are blended with the powders so as to get natural fruit juices on reconstitution for serving as beverages etc.
Preservation of Fruit Juices
Freshly extracted juices are highly attractive in appearance and possess good taste and aroma, but deteriorate rapidly, if kept for some time. This is due to:
(a) Fermentation (by mould yeast & bacteria).
(b) Enzymes present in juice affect colour and flavour (e.g. apple juice turns brown after some time due to oxidative enzyme).
(c) Chemicals present in juice may inter-react to spoil taste and aroma.
(d) Juices on exposure to air, turn bitter due to some reaction.
(e) Metal used for extraction or storing may spoil taste and flavour.
To retain the natural taste and aroma of the juice, it is necessary to preserve it soon after extraction by these methods:
Pasteurisation :- Preservation of fruit juices by heat is the most popular method. Here juice is heated at high temperature, say 80-100°, for a short time to kill bacteria followed by cooling and packing in boiled containers and sealing.
Preservation with Chemicals :- Preservation with the help of chemicals keeps the juice free from spoilage for a longer period of time. These chemicals are sodium benzoate, potassium meta-bisulphite (used as a source of sulphur dioxide), citric acid, acetic acid and ascorbic acid ete. But their uses should be within the limit (for 1000 g juice, 4-5 g chemical is used).
Preservation with Sugar :- Fruit juices containing 66 per cent or more of sugar do not ordinarily ferment. Sugar absorbs most of the available water; consequently, water is not available for the growth of bacteria. It is very difficult to induce fermentation in highly concentrated sugar solutions. Sugar syrups containing 66 per cent sugar (sp. gr. 1.330) have so little moisture available for micro-organisms to grow. Thus sugar acts as a preservative by osmosis and not as a true poison for bacteria. Citric acid is also added to sugar solution because it prevents crystallisation of sugar and converts it into invert sugar (glucose + fructose).
Preservation by Freezing :- The best way of preserving pure fruit juices is by freezing. The properly frozen juice retains its freshness, colour and aroma for a long time. This method is especially useful in the case of juices whose flavour is adversely affected by heating.
Preservation by Drying :- It is done in the same way as milk drying.
Preservation by Carbonation & Filtration :- Moulds and yeasts require oxygen for their growth. As they are aerobic, they become inactive in the presence of carbon dioxide. Although carbonated beverages contain sugar much below 66 per cent, the absence of air and presence of carbon dioxide in them help to prevent the growth of mould and yeast.
Pure fruit juices like orange juice, apple juice, pineapple juice etc. which are highly prized as nutritive foods, are packed in large quantities in many countries. Apple juice is generally bottled, while other juices are canned.
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