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 Fruit Pickling
      It is a food preservation that has been long used to slow down the rottenness of vegetables and fruits and to prolong the shelf life of products for several months without using a refrigerator; as a result, it requires low investment, simple machinery, and low technology. The pickling process came to exist as a result of demand to keep food out of its season for use or consumption during journey, especially by sea. Apart from extending the shelf life, pickling also yields desirable flavor and taste. Presently, pickled mangoes, pickled santol, pickled otaheite goose-berry, pickled garcina, etc. are popular among Thai consumers.

      Types of Pickled Fruits

      Microorganisms in Pickling

      Chemical Changes in the Pickling Process

      Pickling Process

 

Types of Pickled Fruits

1. Processed Pickles. It takes several weeks to complete the pickling process while the crispness and unique flavor and taste of pickles remain. The concentration of brine solution used for pickling will be less than 12%, mostly around 4-8% or ° - 1 cup of salt per 1 gallon of water. The brine solution concentration at this level is high enough to inhibit the growth of organisms and suitable for growth of the organisms producing lactic acid. The brine solution should be kept at 21 ° C; and fruits must be submerged in salt solution throughout the whole period of pickling process. If there is fungi on the surface of pickling solution, it must be immediately got rid of because fungi will decompose lactic acid and build the environment in which the organisms causing damage can grow. However, the most proper concentration of salt solution depends on type of fruits to be pickled. This type of pickling needs organisms which use oxygen for growing so as to change sucrose in fruits to lactic acid.

2. Unfermented Pickles. It is used for pickling fruits with high content in acid, such as lime, mango, otaheite goose-berry, etc., by using salt with high concentration at 20-25%. The purpose of this method of pickling is to preserve fruits in brine solution or as a step to eliminate bitter taste in dried fruit products e.g. myrobalan or preserved fruits.

 

 Microorganisms in Pickling
    

The pickling process needs bacteria in the Lactobacteriaceae family to change sucrose in fruits to lactic acid. There are five genera in this family which are:

  1. Streptococcus 
  2. Pediococcus  
  3. Diplococcus 
  4. Leuconostoc 
  5. Lactobacillus

 

These bacteria are positive gram and cannot build spore. They, therefore, need vitamin B complex and amino acid for growing, but cannot grow in the environment with the presence of acetic acid concentrated higher than 3-6%. The bacteria in these groups can quickly activate the pickling process by adding the increasing amount of carbon dioxide in the system. These bacteria are divided into two groups. They are given below.

  1. Homofermentative This group uses 85-95% of sugar in producing only lactic acid. The remaining will be used for generating energy and volatile compound. Streptocooccus faecalis, Pediococcus cerevisiae are examples of this group of bacteria.
  2. Heterofermentative This group uses 50% of sugar in producing lactic acid. Another 25% is utilized to create acetic acid and ethanol. The remaining percentage of sugar will be used for producing carbon dioxide. Leuconostoc mesenteroides, Leuconostoc fermenti are examples of this group of bacteria.

    Fermented foods have acid to control the growth of microorganisms because each type of microorganisms requires different amount of acid for growing. So, the final products will contain just the bacteria that can survive in high acid. The increasingly high acid condition will later destroy itself; as a result, yeast and fungi that tolerate acid will further grow. Fungi is able to utilize acid while yeast will produce an alkali substance. As a consequence, the acidity will gradually reduce to the level that the bacteria can further function.

 Chemical Changes in the Pickling Process
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     The reaction occurred during the pickling process will yield acceptable texture, appearance, flavor and taste of fermented foods. Such a reaction may happen as a result of the performance of microorganisms which will use enzymes in their cells to decompose nutrients e.g. carbohydrate, protein, and fat, leading to compounds that give good flavor/taste and new phenomenon to foods. The following are examples of chemical changes of foods caused by microorganisms in the pickling process.

Sucrose + Streptococcus spp. Lactic acid (yogurt, fermented fruit)
Sucrose + Saccharomyces spp. (yeast) Alcohol + gas (wine)
Alcohol + oxygen + Acetobacter spp. Acetic acid + water (vinegar)

    Factors affecting the fermentation are pH balance, quantity of oxygen, temperature, quantity of salt, and starting agent. When these factors are in the proper environment, the microorganisms can fully grow and produce the sufficient amount of enzymes for activating the chemical reaction . As a consequence, the pickling can speedily carry on until the fermented foods reach the quality accepted by the consumers.

 Pickling Process
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   The pickling process will differ depending on the raw material used for pickling. Generally, the steps of pickling process are as follows:

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Details of Each Step

  1. Fruits used for pickling should be firm, fresh, clean, free of bruises and fungi, and right size. They also should not be waxed because the pickling solution cannot penetrate the wax; as a result, the pickled fruits will not be crisp. If necessary, fruits should be cut into pieces before pickling. For highest quality, fermentation should start within 24 hours after fruits have been harvested and stored in a cold room or in a cold place with good ventilation. Fruits that are suitable for pickling should be under ripe so the texture of fruits is firm and crisp.
  2. For the selecting process, fruits that are rotten, broken or too soft should be taken out. Then, select the proper size.
  3. Cleaning is done to eliminate soils on the surface of fruits. These soils are the source of bacteria causing undesirable texture.
  4. After being cleaned, some fruits need to be cut into a desirable form before fermentation takes place. In case of wanting pickled fruits to be unusually crisp, the fruits must be wet before soaking in a lime-water solution (1/4-1/2 cup of food-grade lime/1 gallon of water) overnight. After that the fruits are washed and soaked in clean water for one hour. Repeat the rinsing and soaking steps twice more to remove excess lime absorbed by fruits. Failure to remove lime adequately may increase the risk of botulism.
  5. Fruits can be pickled in a large stoneware crocks, large glass jar or food-grade sterilized plastic containers. Do not use aluminum, copper, brass, galvanized or iron containers for pickling fruits because these materials can react with acid or sodium, yielding undesirable color of the finished products. Generally speaking, a one-gallon container is needed for each 5 pounds of fresh fruits. So, it should not be over packed because the pickling solution will over flow during sterilization. The stain of the pickling solution will stay on the rim of a jar, resulting in the jar not being closed tightly. If the jar is loosely packed, then, the air is still in the jar.
  6. Pour pickling solution in the bottle. The ingredients of pickling solution are as follows:
    1. Salt: It should not be iodized salt because iodine will inhibit bacteria to work on the fermenting process.
    2. Sugar: It may be sugar made from sugar cane or beet root. It should be white sugar, giving a product a lighter color. If it is brown sugar, the color of the product will be darker and its smell and taste stronger. Honey can be used as a sweetener, but should be ? of sugar.

    3. Spices: Use fresh whole spices for the best quality and flavor in pickles by tying whole spices loosely in a clean white cloth or cheesecloth bag and then remove the bag from the product before packing the jars. Powered spices may cause the product to darken and become cloudy.
    4. Water: Use clean water without the presence of any compound, particularly iron because it gives the product a dark color.
    5. Alum: It is used to firm fermented fruits. For good result, use 1/8 tea spoon of alum/a 8-quart sized jar.
    6. Others such as citric acid, preservative like sodium benzoate.
    7.      Pickling solution should be clear without any sediment and boiled at the approximate temperature of 76-82.2 ? C. Let it warm before pouring it over fruits 1-2 inches high. Stir inside the jar with a plastic spatula to expel air. Clean the rim of the jar with clean cloth. Then, tightly close the jar with a cork cap or lid.

  7. The products are stored. Fermentation will gradually go on throughout the storing period. The proper length of fermenting depends on type of fruit, including the demand of consumers' taste.
  8. After being fully pickled, the products must be pasteurized to stop the pickling process and destroy bacteria that may spoil the products since the products contain high acid. In doing so, jars must be place in a canner half filled with warm water(48-60 ? C). Add hot water to a level of 1 inch above jars. Then heat the water to 82-85 ? C and start timer. Process for 30 minutes and then immediately remove jars from canner at the end of processing time.

     Heating pickled fruits before packing is called hot pack. Another method, raw pack, is giving heat to pickled fruits after packing. The processing time is given below.

Recommended Processing Time
Style of Pack
Jar Size
Processing Time
Hot pack
Pints
10
Quarts
15
Raw pack
Pints
20

Pickling Process    please click here.....

   
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Thailand Institute of Scientific and Technological Research (TISTR)
Food Technology Department
35 Technopolis, Klong 5, Klong Luang, Pathumthani 10120 Thailland
Tel.: (662) 577-9000, 577-9155-6
Fax : (662) 577-9009, 577-9128

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