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 The scientific basis for pickling and the defects of pickles

The scientific basis for pickling and the defects of pickles



Pickling is classified under one of the methods of preserving vegetables and fruit 

  the pickling process has undergone scientific foundations after the discovery of microbiology 
and the study of lactic acid fermentation  

Pickles are considered appetizing foods in addition to their economic importance by preserving agricultural raw materials when the prices are cheap while maintaining high quality 
 of taste and flavor And color
 
The preservation process is done by raising the percentage of table salt and lactic acid in the product with the addition of a percentage of vinegar, which does not provide the appropriate environment for the growth of unwanted bacteria  ,  
and attention must be paid not to expose the surface of the brine solution to the air and the surface of the pickles is covered with a layer of oil or a layer of green plants such as grape leaves Or dill

There are many types of pickles such as sauerkraut and pickled red onions, pickled beets


:Definition of pickle

They are vegetable pieces from the roots, leaves, or stems treated with brine، with or without addition of organic acids, as lactic acid is formed in the middle in addition to by-products that are the products of lactic fermentation of carbohydrates , and under anaerobic conditions and by lactic bacteria.


:Definition of lactic fermentation 

It is the simplest type of fermentation in which hex sugar is broken down into two lactic acid molecules by lactic acid bacteria such as Lactobacillus plantatarum, ، Lactobacillus previs

According to the following equation:
by anaerobic conditions and by lactic acid bacteria
C6H12O6 2CH3CHOCHCOOH
Lactic acid bacteria prevent the growth of unwanted microorganisms and produce flavoring substances that result from the accumulation of organic acids and thus vegetables acquire the characteristics specific  to each type

Types of lactic fermentation according to the bacteria that do it and the resulting products

 Homo fermentative: performed by  lactic acid
 bacteria such as Lactobacillus plantarum , Pediococcus serevisiae
It only produces lactic acid, which gives an unpleasant flavor

Hetero-fermentative lactic fermentation
performed by mixed or heterogeneous lacti acid bacteria, including Lactobacillus brevis , Leuconostoc masenteroides
It produces lactic acid and other by-products such as vinegar, alcohol and carbon dioxide , The smaller the amount of by-products produced, the more successful the fermentation process

:Practical note

  1. The speed of fermentation depends on the percentage of sugar present in vegetables and fruits of monosaccharides and disaccharides, as more sugar increases the speed of growth, and thus speeds up the process of pickling 
  2. And depends on the percentage of added salt, the presence of sodium chloride salt in a ratio of 8-10% is the ideal percentage for pickling
  3. The required temperature is in the range of 20-25 ° C or even 30 ° C If the temperature drops below the minimum level, fermentation slows and the temperature rises above the upper limit, which speeds up the process, but produces unwanted products

:Conditions for successful pickling

1- We choose healthy fruits with ideal ripeness because the fruits of late ripeness are characterized by the thickness of the outer skin and will retain carbon dioxide gas, which leads to the phenomenon of pickle floating

2- We use water that is soft and not hard because the hard one contains sodium and magnesium bicarbonate, and this raises the alkalinity of the product and leads to turbidity with the pickling solution.

3- Pickling utensils should be white plastic materials or non-colored glass or stainless steel containers coated with a layer of enamel (varnish)

4- Complete coverage of fruits with brine to ensure anaerobic conditions for the action of lactic acid bacteria

Example

:Sauerkraut manufacturing stage


A- We choose healthy and ripe cabbage heads and leave them for two days to wilt and facilitate the cutting process

B- We cut the leaves homogeneously and then wash them with water

C-Weigh the slices and weigh the necessary amount of salt, where we put the salt at a rate of 2.5% of the weight of the slices, mix them together and put them in the containers for pickling with the addition of water and place a weight on the surface

D- We must enssure that the temperature is not less than 20 ° C, so that slow fermentation does not occur and does not rise above 30 ° C, so that unwanted fermentation occurs،
cover the slices completely with saline to prevent the growth of fungi and membranous yeasts


Pickle defects

shriveling
Withering and shrinkage of pickles due to a high 
concentration of salt or sugar

hollow pickles
Because of the thickening of the peel of the fruits, which works to trap gases inside them, or the use of fruits that are late in maturity, or the use of a large amount of salt

slippery pickles
The viscous pickle due to exposing the packages to the air and thus working on the growth of the membrane yeasts on the surface and the formation of the white film, this yeast works to oxidize the lactic acid, which creates conditions for the growth of unwanted bacteria that consume the fermentation products and make unwanted changes to the product

soft pickles
Soft pickle due to the growth of some types of fungi that secrete enzymes that consume pectin substances in the fruits, leading to their softness. This defect can be avoided by adding calcium chloride salt at a rate o
f 0.3-0.5 g per 
liter of solution. 

black pickles
The blackening of the pickle, due to the salt's containment of iron salts, forms iron tannin, which gives the pickle its black color Or the formation of hydrogen sulfur gas, which combines with iron and gives iron sulfur and that also turns the pickle black In addition to the existence of a reason, which is the growth of bacillusnigri ficans, forming a black pigment that dissolves with water in an alkaline mix. 

Blanching
Due to exposure to strong light when packing in transparent glass containers 

  • The appropriate salt concentration for the growth of lactic acid bacteria should be 8-10% (the concentration is higher than 16% is used for preservation because at this concentration the growth of the desired and unwanted bacteria stops), add sugar in a small amount, add lactic acid at the beginning of the fermentation process because it allows the growth of lactic acid bacteria and inhibiting the activity of unwanted microorganisms

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