Processing of Horticultural Crops (1+2)

Introduction

Introduction
The preservation by using common salt, spices and vinegar is a common method for preparation of pickles, sauce and chutneys. Salt is mostly used as preservative in pickles in combination with acid. Minimum concentration of salt to act as preservative is about 12%. It inhibits enzymatic browning/discoloration by acting as an anti-oxidant. It exerts its preservative action by:

• Causing high osmotic pressure and thus suppress the microbial cells.
• Dehydrating food by tying up the moisture thus making it unavailable for the growth of microorganisms.
• Salt in the food affects the solubility of oxygen and thus growth of aerobic microorganisms is inhibited
• Chlorine in sodium chloride being good oxidizing agent is toxic to microorganisms
• Salt increases the permeability of the cell wall and thus cause changes in the permeability. Only the haloduric microorganisms can tolerate these effects while others are unable to survive.
• Similarly addition of acid to the food lowers the pH of the food which inhibits the growth of spoilage causing microorganisms.
• Addition of spices and edible oil in these products besides improving flavour and taste also help in preservation.

Thus preservation by using salt, spices and acid is one of the most ancient and effective methods of food preservation. Vegetable sauce, continental sauce, tomato sauce, mixed fruit chutney, mango pickle, lime/lemon pickle, mixed vegetable pickle etc are common products made in this category.

PICKLES: The preservation of fruit and vegetables in salt and vinegar is called pickling. Pickles may prepare without fermentation or with partial or complete fermentation. Spices, edible oil, sugar/jaggery etc are added to improve taste and palatability of the product. Thus, pickles are good appetizer and help in digestion by stimulating the flow of gastric juices. The nutritive value of pickle varies with the kind of raw material used and method of preparation such as with or without fermentation. Manufacturing of pickle has developed as an industry in the country. Mango pickle, cauliflower, turnip, carrot (mixed vegetable), anola, lime/lemon pickle etc. are the commercial products available in the market.

Pickling process: Pickling is the process of fermentation by lactic acid forming bacteria, present on the surface of commodities. Lactic acid bacteria (active at 30^oC) convert fermentable sugar in the food to lactic acid and volatile acids. The acid and brine acts upon vegetable tissues to produce characteristic taste and aroma of pickle. The salt and lactic acid formed preserve the pickle by preventing the growth of putrefactive bacteria provided oxygen is excluded. Fermented cucumber and olive pickles are quite common. Pickle is prepared by using either of following processes followed by finishing and packing:

• Curing or fermentation with dry salting
• Fermentation in brine
• Salting without fermentation

A). Dry salting
The dry salt added to the prepared vegetables, extracts the juice from the vegetables and forms the brine. The brine is then fermented by lactic acid forming bacteria which serves the purpose of pickling. The method is known as dry salting.

Procedure for dry salting

1. Vegetables are washed, sliced and placed in barrel in layers to which salt is sprinkled followed by placing another vegetable layer and sprinkled with salt. Generally, 3 kg dry salt is used for each 100 kg of prepared vegetable. The salt is added in layers till the barrel is ¾ full. The vegetables are covered with a cloth and wooden board along with a weight to press the vegetable. Brine is formed in 24 hours.
2. The barrel is placed in warm and dry place to allow the fermentation to proceed within short period. Once brine is formed, fermentation and bubbles of CO₂ begin to rise from the liquid. The fermentation temperature is 27-32⁰ C and completes in 8-10 days.
3. When the gas bubbles cease to form, the fermentation is considered as complete. This may be confirmed by taping the barrel gently. The pickle is then pressured and packed by excluding the air.
4. If air is not removed from the pickle, pickle scum (a type of mould yeast) appears on the surface, which destroys the lactic acid formed by fermentation and spoils the pickle.

Methods to remove air /expel air from the pickle:

1. 1. By making air seal on the surface of brine by pouring 0.6 cm thick layer of edible oil (rapeseed oil/mustard oil or cotton seed oil) on the top of it. The oil being lighter than brine floats on the surface and prevents the access of air in to the pickle.
2. 2. After dry salting and fermentation, the barrel is filled with the prepared vegetables to its maximum capacity and covered with a lid. A 1.25 cm hole is bored in the lid (cover). The barrel is filled up to the brim with the brine so that very little air is left inside. It is allowed to stand for 48 hours till all gas bubbles ceases to rise. When the bubbling stops the vent hole is closed tightly and barrel kept in a cool dry place.
3. 3. The barrel is kept undisturbed. The molten paraffin wax is poured over the surface of the brine. It imparts air tight-seal. The paraffin wax can be easily separated from the brine and the wax can be remelted and reused.

B). Fermentation in Brine (Brining)
Immersing vegetable or unripe fruits like mangoes in salt-solution of known concentration for a certain length of time is called brining. Brining is generally used for pickling of cucumber, olives, raw mangoes and similar other vegetables, which do not contain sufficient juice to form brine with dry salt.

Brine preparation: Brine is prepared by dissolving common salt in water and filtered through a muslin cloth. The amount of brine required to cover the vegetable is approximately equal to about half the volume of the material to be fermented (for each barrel of 100 litres, about 50 litres of brine is required). Brine with 8 -10 % strength is considered optimum for the growth of salt tolerant lactic acid bacteria.
Thus vegetables are placed in 10 % brine to allow lactic acid fermentation to take place and then the proportion of salt is increased gradually, so that when pickle is ready, salt concentration would have reached 15 % level. The brine strength can also be maintained by adding dry salt. Brining takes about 4-5 weeks.

C). Salting without fermentation
In this method, vegetables raw mango slices are packed with a large quantity of salt to inhibit fermentation. Generally, 25 kg salt is mixed with 100 kg of prepared vegetable. The cured vegetables are drained and excess salt is removed by soaking in cold or warm water. After removal of salt, the vegetables are stored in plain vinegar 10% (100 grain) strength. This treatment reduces the tendency of the vegetable to shrivel when packed in sweetened and spiced vinegar and also helps in absorption of vinegar by the vegetable tissues.

Packing: After curing, the vegetables become semi translucent in appearance with their colour changing from green to dark olive green or yellowish green. During this process the raw flavour of the vegetables is lost and the texture becomes firm and crisp. For good keeping quality they are packed by using salt, vinegar and lactic acid in sufficient quantities which act as preservative either singly or in combination.

1. Salt: The concentration of 15-20% salt is used for pickling. Mould and lactic acid forming bacteria do not grow at this concentration. The fermentation of vegetables is inhibited when they are covered with strong brine or packed with fairly large quantity of salt. This method of preserving is applicable to those fruit and vegetables which contain very little sugar because sufficient lactic acid cannot be formed by fermentation to act as preservative.

2. Vinegar: Vinegar acts as preservative in vinegar pickles by lowering down the pH of final product. The final concentration of acid as acetic acid in the finished pickle shall not be less than 2%. However, vegetables are placed in strong vinegar of 10 % acidity to avoid dilution of the vinegar by the water liberated from the tissues. This treatment helps to expel the gases present in the intracellular spaces of vegetative tissues and prevents subsequent dilution of the vinegar in the pickle. Spiced vinegar can be prepared by soaking the ground spices in vinegar, boiling the spices in the vinegar or by adding essential oil of spices and added to the prepared pickle.

3. Lactic Acid: Though bacteria do not grow in acidic media, yet lactic acid bacteria are capable of growing in acidic media and can also produce acid through their action on the substrate. They can also grow in high salt concentration of 8-10%. This principle is used in pickling as growth of undesirable organism is inhibited by adding salt and allowing the lactic fermentation to proceed.
The pickled vegetables (onion, garlic, green chilies, olives etc) are then packed in to the glass jars without damaging the shape and appearance of the pieces and covered with fresh vinegar to fill up the spaces between the pieces. The closed jars are then stored in a cool dry place for some time to allow thorough absorption of vinegar before sending them to the market. Brined vegetables and raw mango slices are also used for preparing different types of pickles by using combinations of spices, salt and vinegar.