• An important food preservation system combines salting to selectively control microorganisms and fermentation to stabilize the treated food materials.
• Pickling is one of the oldest, and most successful, methods of food preservation known to humans
• The process when applied to vegetables is called pickling.
• When applied to meat it is called curing.
Pickling remains a major form of preservation in many countries because it:
(1) yields desirable organoleptic qualities;
(2) provides a means for extending the processing season of fruits and vegetables;Factors involved in vegetal fermentation
(3) requires relatively little mechanical energy input.
Salt
• exerts a growth repressing action on certain microorganisms by limiting available water and dehydrating protoplasm, causing plasmolysis.
• 26.5 % sodium chloride at room temperature corresponds to saturation concentration.
• Salometer degree( a scale used in pickling industry)
• 0 % NaCl —– 0 degree
• 2.65 % NaCl—10 degree
• 26.5 % NaCl—100 degree (No free water available for microbial growth
Salt for pickling
• Every common salt is suitable as long as it is pure.
• Impurities or additives can cause problems.
• Salt with chemicals to reduce caking should not be used as they make the brine cloudy.
• Salt with lime impurities can reduce the acidity of the final product and reduce the shelf life of the product.
• Salt with iron impurities can result in the blackening of the vegetables.
• Magnesium impurities impart a bitter taste.
• Carbonates can result in pickles with a soft texture.
Salt concentration
• Lactic acid bacteria tolerate high salt concentrations.
• The salt tolerance gives them an advantage over other less tolerant species and allows the lactic acid microorganisms to begin metabolism, which produces acid, which further inhibits the growth of non-desirable organisms.
• Leuconostoc is noted for its high salt tolerance and for this reason, initiates the majority of lactic acid fermentations.
Important microorganisms in plants:
I- Pseudomonas, Bacillus, Chromobacterium, Enterobacter,
• Less research on fermented vegetables compared to other fermented foods because cheap,
• produced at small scale by traditional methods
• very little public health problems occured.
Lactic acid fermentations
Lactic acid fermentations are carried out under three basic types of condition:
I-dry salted II-brined III-non-salted.
I- Dry salted fermented vegetables
• the vegetable is treated with dry salt.(3%)
• The salt extracts the juice from the vegetable and creates the brine.
• vegetable washed in potable cold water and drained.
• placed in a layer of 2.5cm depth in container (a barrel or keg).
• Salt is sprinkled over the vegetables.( repeated until the container is three quarters full.)
• A cloth is placed and a weight added to compress the vegetables and assist the formation of a brine in 24 hours , fermentation starts and bubbles of carbon dioxide begin to appear.
• Fermentation takes between one and four weeks =f( temp)
• Fermentation is complete: no more bubbles, then pickle can be packaged in a mixtures of vinegar and spices or oil and spices
SAUERKROUT FERMENTATION
• It is a perfect example of microbial succession.
• Shredding cabbage: ( sugar 2.4-6.4 %, if it is too high product will be too acidic) ( In Turkish style cabbage is divided into four rather than slicing)
• Washing : to reduce chromogens ( bacteria which produce undesired color) and to wash out contaminating yeast and mold.
• Salting : Optimum salt concentration is 2.5 %, ıt should be evenly distributed. Higher levels of salt ( 3.5 % ) will support the growth of pediococcus, low levels ( 1 % ) will support groth of Leuconostoc mesentroides.
• Pressing: To make it anaerobic
Microbial Succession
• First enterobacter ( gas producer) and erwinia ( produces cellulases and pectinases ) will grow.
• Later L. mesentroides will grow ( it is desired at this stage). It produces lactic acid ( 0.7 % ) PH drops and this will suppress growth of gram(-) bacteria.It also produces mannitol ( bitter taste) which can only be utilised by L. Plantarum. By this way it supports growth of L. plantarum.
• Finally L. Plantarum grows to produce more acid ( 2 %) and using mannitol reduces bitterness.
• Further growth of L. pentoaceticus may increase acid to 2.5 %
• Opt. Temp. is around 21ºC.
• A variation of just a few degrees alters the activity of the microbial process and affects the quality of the final product.
• temperature control is one of the most important factors in the sauerkraut process.
• A temperature of 18º to 22º C is most desirable for initiating fermentation since this is the optimum temperature range for the growth and metabolism of L. mesenteroides.
• Temperatures above 22ºC favour the growth of Lactobacillus species.
Sauerkrout defects
– High temperature fermentation suppresses growth of Leuconostoc( which produces desired flavor compounds)
– too long fermentation may favor the growth of gas forming L. Brevis.
– Soft krout: may be due to faulty fermentation, exposure to air and excessive pressing.
– dark brown or black krout: air exposure, uneven salting ( salt burn) or high temperature.
– pink krout: caused by red asporagenous yeast growth
– slimmy or ropy krout: caused by encapsulated varieties of L. Plantarum ( edible but not salable)
II- Brine salted fermented vegetables
• Brine (salt solution) is used for vegetables which inherently contain less moisture.
• The strong brine solution draws sugar and water out of the vegetable, which decreases the salt concentration.
• It is crucial that the salt concentration does not fall below 12o salometer. (add extra salt periodically to the brine)
• The microbial populations of the fermenting vegetables = f ( the concen. of salt, temp. of the brine, the availability of fermentable materials and the numbers and types of micro-organisms present at the start of fermentation.
• Rate of the fermentation = f (concentration of salt, temperature.)
• Most vegetables can be fermented at 12.5o to 20o salometer salt( sauerkrout microbial succession)
• About 40o salometer, the sequence is skewed towards the development of a homofermentation, dominated by Lactobacillus plantarum.
• About 60o salometer, the lactic fermentation ceases to function and if any acid is detected during brine storage it is acetic acid, presumably produced by acid-forming yeasts which are still active at this concentration of salt
• Brining vegetables in salt, and the resultant lactic acid fermentation, is an ancient form of preservation.
Two new methods of pickling cucumbers, which represent the largest volume of a single vegetable preserved by pickling, have been developed during the 1900s. Both methods use lower salt concentrations and result in a milder product.
I- pasteurization and direct acidification, was developed and began commercial production in the 1940s.
II- refrigeration and direct addition of acid and preservative, was introduced in the 1960s.
Relative quantities of cucumbers preserved by the 3 pickling methods in 1984
were:
brine fermentation, 43%; pasteurization, 43%; refrigeration, 14%.
A-Pasteurized Pickles
• Vegetables which are fresh or only partially fermented may be preserved by the addition of vinegar or acetic acid and subsequent pasteurization.
• Vinegar alone is not sufficient to insure product safety, and so requires an additional form of preservation such as heat or refrigeration.
• The steps involved in producing pasteurized or ‘fresh-pack’ pickles are the following:
• slice, cube, or dice product;
• place in clean container;
• mix water, salt, vinegar, sugar, spices and bring to boil;
• add hot brine to container;
• seal and pasteurize.
Two possible pasteurization methods include:
(1) heating such that the center of the jar or can reaches 75 °C, and holding for 15 min, followed by a prompt cooling to 35 °C or below,
(2) heating at 70 °C for 10 min, followed by prompt cooling
• The pasteurization process essentially destroys spoilage microorganisms and prohibits fermentation from occurring.
• Both acid-forming bacteria, which are active in brine fermentation, and yeasts, which cause gas production, are destroyed by pasteurization.
• The pasteurization process inhibits polygalacturonase, the enzyme responsible for pickle softening.
• Enzyme activity may also be controlled through use of appropriate salt concentrations.
• Calcium chloride, and KAl(SO4) is often added to brine to aid in firming cucumber pickles
• Pasteurized pickled products have steadily gained in popularity, and have a very different flavor and texture to that of fermented pickled products.
B-Refrigerated Pickles
Represent the latest development in pickling technology, are produced by direct acidification and addition of sodium benzoate or another preservative.
• In these nonfermented pickles, the preservative takes the place of pasteurization in preventing spoilage of the product.
• essentially the same as that used for pasteurized pickles, but instead of pasteurizing, the sealed containers are refrigerated.
• It is essential that this type of pickle is kept refrigerated throughout the production process and during subsequent consumption.
C-Fermented Pickles
• There are three general methods which may be used for cucumber fermentation;
(1) salt stock; (2) genuine dill; and (3) overnight dill.
(1)Salt stock
• involves fermentation in 5–8% ( salt conc. increased 1%/week up to 16 % salt) until all fermentable sugars have been converted to acids and other products. ( can be stored for several years)
• Desalting to an acceptable organoleptic level (2–2.5% salt) is carried out by leaching in water.( quick leaching in warm,43-54 C, water, 10-14 hrs)
• Salt stock pickles make up the largest percentage of fermented pickle products.
• The controlled fermentation of pickles has been a goal of the industry for years.
• In particular, most processors now acidify and purge tanks after brine is added.
• Acidification inhibits the growth of acid-sensitive Gram-positive and Gram-negative bacteria and, therefore, favors the growth of lactic acid bacteria.
• Purging decreases the incidence of bloating, which results from carbon dioxide production by both the fermenting microorganisms and the cucumber itself.
BLOAETER DAMAGE ( HOLLOW CUCUMBER)
Bloater damage occurs due to high level of gas production during fermentation.
Reasons: large cucumbers (with thick skin) higher fermentation temperatures ( which supports growth of gas producing bacteria such as coliforms, heterofermentative lactic bacteria and yeast ).
Preventing: Inoculating with L. Plantarum purging out produced CO2 with nitrogen gas definately using small size cucumbers will
(2)Genuine dill pickle
• fermented in 4–5% salt, to which dill weed, garlic, and other spices have been added.
• 3–6 weeks for fermentation to reach completion,
• where the lactic acid content is 1.0–2.5% and the salt content is 3–3.5%.
• not require desalting, ( sold with the filtered fermentation liquor. )
• It should be thightly closed, can be kept 12 months, otherwise film yeast will grow and utilize lactic acid( addition of 0.1 % potassium sorbate is helpful to reduce this risk).
