Preservation of Juices

Preservation of Juices

Preservation of Juices: Fruit juices, RTS and nectars are preserved by pasteurization or by using chemical preservatives. Squashes, crushes, syrups and cordials are preserved by adding chemical preservative like potassium metabisulphite or sodium benzoate.

1. Pasteurization: Preservation of fruit juices by application of heat is the most common method. Pasteurization is a process in which juice is heated to 1000C or slightly below for a sufficient time to inactivate/kill the micro-organisms, which cause spoilage. Usually the fruit juices are pasteurized between 75 and 880C with times ranging from 30 sec to 30 min depending on the type of heating system, the nature of the juice and the size of the container. Pasteurization can be performed either by heating at low temperature for a long time (LTLT) or heating at high temperature for short time (HTST). Commonly followed methods are:


a. Holding pasteurization:
In this method, the prepared juice is filled into glass bottles with a proper head space and the bottles are sealed airtight. After sealing the bottles are pasteurized. However, this method is not followed for commercial scale products.


b. Pasteurization by overflow method:
In this method, the juice is heated to a temperature about 2.5oC higher than the pasteurization temperature and filled into the hot sterilized bottles up to the brim. Care should be taken to maintain the temperature during filling and sealing operation. The sealed bottles are processed in boiling water for specified period. After processing the bottles are cooled. On cooling, the juice contracts to leave a small headspace in the bottle which does not contain any air. The method is commercially followed in preservation of all types of juices in the food industry.


c. Flash Pasteurization:
In this process, the juice is heated only for short time at a temperature about -5.5oC than the pasteurization temperature, filled into the containers and sealed air tight under cover of a steam to sterilize the seal and then cooled. This process is also known as HTST (High temperature and short time) method and the juice is heated vary rapidly. Flash pasteurization helps to minimize the loss of flavour, better retention of vitamins, keep juice uniformly cloudy and minimize the cooked taste of the juice.


2. Aseptic processing and packaging of fruit juices: Aseptic processing and packaging is defined as the process in which a commercially sterile product is packed into pre-sterilized container in a sterile environment. The system make use of high temperature short time (HTST) sterilization in the temperature range of 90-110oC for acid products (pH<4.6) and ultra high temperature (UHT) sterilization 121oC and above for low acid foods (pH>4.6). The commercial aseptic sterilization process takes place in a continuous, closed system. Aseptic processing may produce products with better retention of nutrients and excellent sensory quality. Apple, mango, litchi, pineapple drinks etc. in tetra pack are processed commercially using aseptic processing and packaging system.


3. Preservation with chemical: Fruit juices, pulps, squash, cordial, syrup, RTS drinks etc, are preserved with chemical preservatives. Fruit juice and pulps in bulk are preserved with chemical preservatives. Two chemical preservatives most commonly used in preservation of fruit and vegetable products are
(i) Benzoic acid (benzoates)
(ii) Sulphur dioxide (Sulphites).

i) Benzoic acid: Benzoic acid is the effective agent but sparingly soluble in water, thus its sodium salt, which is water soluble, is generally used. Benzoic acid is more effective against yeast as compared to moulds. However, it does not stop lactic acid and acetic acid fermentation. The quantity of sodium benzoate required depends on the nature of the juice, its acidity and type of microbial infection. The limit of benzoic acid to be added in various products as per FPO (Fruit Products Order) is given in Table 8.2.


ii) Sulphur dioxide: Potassium meta-bi-sulphite (K2O2SO2 or K2S2O2) is commonly used as a source of sulphur dioxide. On addition to fruit juice or beverage it reacts with acid of the juice and form potassium salt and sulphur dioxide, which is liberated and form sulphurous acid with the water of the juice. Sulphur dioxide is more effective against mould spores and bacteria than yeast and also inhibits enzymes etc. It acts as antioxidant and bleaching agent thus help in the retention of ascorbic acid, carotene and other oxidisable compounds. It also retards non-enzymatic browning or discoloration of the product. Its effectiveness depends on the acidity, pH, temperature and other substances present in the fruit juice.

  • The SO2 should not be used in naturally colored juices like phalsa, Jamun, pomegranate and strawberry juices, on account of its bleaching action.
  • It should also not be used in those juices, which are to be packed into tin containers, because it may act on the tin of the containers causing pinholes, forms hydrogen sulphide and black compounds.
  • The potassium meta-bi-sulphite should be first dissolved in a small quantity of water and then added to the juice to be preserved. The limit of SO2 to be added in different processed products according to Food Safety and Standards Regulation 2011 and FPO specification is given in Table. 8.2

Table 8.2: Limits for permitted preservatives in fruit juice and beverages as per Fruit Products Order.

Fruit juice/beverages

Preservative

Part per million (ppm)

1.Fruit pulp or juice for conversions into jams and other products

a. Cherries

b. Strawberries & Raspberries

c. Other fruits

2. Fruit juice concentrate

3. Squashes, crushes, fruit syrup, sharbats, cordials,

 fruit juice and barley water.

4. Sweetened ready to serve Beverages

SO2

SO2

SO2

SO2

SO2

Or

Benzoic acid

SO2

or

Benzoic acid

3,000

2,000

1,000

1,500

350

600

70

120



4. Preservation by sugar: Fruit juice containing 66% sugar generally does not ferment. Fruit syrup or sharbats with high total solids (65% and above) have a very low water activity hence micro-organism do not grow. The sugar acts as a preservative by osmosis and does not support the growth of micro-organism. However, the growth of mould and yeast can occur on the surface of jams or jellies which need to be protected by using airtight packing or covering the product with molten paraffin wax.

5. Preservation by freezing: The properly frozen juice retains its freshness, colour, taste and aroma for a long time. De-aerated juice is transferred into containers, which are hermetically sealed and frozen. Freezing does not sterilize fruit juices, it merely reduces the temperature to the point where micro-organisms do not multiply and chemical changes take place very slowly. The more rapidly a juice is frozen, the smaller the ice crystal formed and the less the amount of colloidal matter coagulates. When the juice is frozen to -18oC, practically all of the juice will be solid except for a little thick syrup in the centre of the containers. This method is particularly useful in the case of juices whose flavour is adversely affected by heating.


6. Preservation by drying: Micro-organisms need water for their growth and multiplication and as the water is removed, they are unable to grow. Fruit juices can be preserved in the form of powder by different methods viz., spray drying, drum drying, freeze-drying, foam-mat drying etc. Fruit juice powders are highly hygroscopic and require special care in packing. It should be packed in free flowing powder form in hermetically sealed containers with in package desiccant to prolong the shelf-life of the product. Lemon juice powder can also be prepared by using foam mat drying process.


7. Preservation by carbonation: Carbonation is a process of mixing carbon dioxide under pressure with water, juice or beverages so that the product when served; gives off gas in fine bubbles and has the characteristics taste. Carbonated beverages are generally bottled with carbon dioxide content ranging from 1 to 8 g/litre. Though this concentration is much lower than that required (14.6 g/litre) for complete inhibition of microbial growth, yet it is significant in supplementing the lethal effect of acidity on pathogenic bacteria. Carbonation also helps in removal of air which creates anaerobic condition and reduces the oxidation of ascorbic acid. Since moulds and yeasts require oxygen for their growth and as such become inactive in the presence of carbon dioxide. Thus the absence of air and presence of carbon dioxide in fruit beverages help to prevent the growth of moulds and yeast. The keeping quality of carbonated beverages is enhanced by adding about 50ppm sodium benzoate. Carbon dioxide in beverages is measured in terms of gas volume. The gas volume is defined as the amount of gas in millilitres that a given volume of water will absorb at atmospheric pressure i.e. 760 mm of Hg at 15.50C temperature. Generally 1.3-4.0 gas volume CO2 is used for carbonation of fruit juice. Lime, lemon, grape, apple juice can be carbonated by using carbonation process.


8. Preservation by filtration: In this method, the clarified fruit juices (particularly apple and grapes) are passed through special filters, which are capable of retaining yeasts and bacteria. Various types of germ proof filters are used for this purpose and the method is used for soft drinks, fruit juices and wines.



FILLING and PROCESSING: Bottles are thoroughly washed with hot water and filled leaving 1.5-2.5 cm headspace. The bottles meant for heat processing are sealed by using crown corks whole those preserved by using chemical preservative can be sealed by using PP (pilfer proof) caps.

B). Method for preparation of fermented fruit beverages
Fruit juices which have undergone alcoholic fermentations by yeasts, contains varying amounts of alcohol are called fermented fruit beverages. These beverages include wine, champagne, cider, port, sherry, musket, perry, orange wine, berry wine etc.

1. Wine:
Wine may be defined as a fermented beverage prepared from grapes after alcoholic fermentation. When other fruits are used for preparation of wine then these are called by prefixing the name of fruits for example plum wine, peach wine etc. Wines are of two kinds viz. dry and sweet.

  • Dry wines contain practically very little or no sugar, whereas sweet wines contain some sugar and taste sweet. The alcohol content of these wines ranges from 7 to 20 percent.
  • The wines are also categorized on the basis of alcohol contents as Light, medium or strong wines
  • ‘Light wine’ contains alcohol contents of 7 to 9 percent.
  • ‘Medium wine’ with alcohol 9 to 16 percent and,
  • ‘Strong wine’ with alcohol of 16 to 20 percent.
  • Generally wine with more than 12% alcohol are fortified with fruit brandy (alcohol) prepared by distilling grape wine.
  • Still wines are without any carbon-dioxide.
  • Sparkling wines contain carbon-dioxide.

Method for preparation of wine

Fruits suitable for wine making: Wine can be prepared from the apple, custard apple, pear, plum, jamun, muskmelon, coconut toddy, pomegranate, banana, guava, ber, strawberry, peach, kiwi fruit, raspberry, cherry, pineapple, date, apricot, litchi and mixed fruits (Table 8.3). Wine may be red or white depending on the grapes used. The red coloured grapes are crushed and fermented to give red wine, whereas white wine is prepared from fermentation of white grape juice.

Preparation of fruits for fermentation

Beauty Seedless, Arka Shyam, Concord etc. cultivars of grapes are generally used for wine making. In case of white grapes, the juice is taken whereas, in case of coloured grapes, crushed grapes without any stems (must) are taken for fermentation. Fruits are crushed to extract the juice or in pulpy fruits, the fruit pulp is used. The sugar content is maintained between 22-24 percent and an acidity of 0.6 to 0.8 percent should be maintained. In low sugar fruits, the cane sugar is added to raise the TSS to 22 percent. Sulphur dioxide is also added to the must at the rate of 50-70 ppm to check the growth of wild yeasts and bacteria, which are undesirable.

Table 8.3: Different types of wines.

Type

Characterization

Champagne

It is made chiefly in France with certain varieties of grapes. Champagne is a sparkling clear wine and also made in several other countries. Generally the fermentation is allowed to proceed to completion in bottles. These bottles are specially made to withstand high pressure of gas produced during fermentation.

Port

This is fortified sweet red wine originally in Portugal, but now produced in other countries.

Muscat

It is prepared from Muscat variety of grapes in Australia, California, Italy and Spain

Tokay

It is famous fortified wine of Hungary

Sherry

Sherry is a Spanish wine, which is matured by placing the filled barrel in sunlight having a temperature of 54 to 60oC for 3 to 4 months

Perry

The wine prepared from pears is called as Perry. It can be prepared from the culled fruits and fruit trimmings of the canneries.

Orange wine

Sweetened orange juice is fermented to produce orange wine. The method of preparation is similar to that of grape wine. Orange peel oil should be minimum in the juice, otherwise its presence stop the fermentation completely.

Berry wine

The wine made from fruits like strawberry, blackberry and elderberry is known as berry wine.

Feni

Feni is a wine made from fermentation of cashew apple, in some places like Goa.

Nira

Nira is prepared from the juice of the palm tree



Last modified: Wednesday, 7 March 2012, 5:13 AM