Transcript Microorganisms and fermented food products

Specific
fermented
food
products
• Vegetable
products
• Fermented
sausage
• Cereal
products
Alcoholic
beverages
• Beer
• Distilled spirits
• Wine
Single cell
protein
Some Asian
Fermented
Food
Products
•
•
•
•
Soy sauce
Miso
Tempeh
Fish sauces
 VEGETABLE PRODUCTS
 Nearly all vegetable material are fermentable by lactic acid bacteria. They
contain sugars and are nutritionally adequate for the growth of lactic acid
bacteria.
 Environmental factors important in the fermentation of vegerables are:
 The establishment of anaerobic conditions.
 The use of a suitable salt concentration to withdraw liquid and nutrients
from the product.
 Maintenance of a temperature suitable to fermentation, and
 The presence of suitable lactic acid bacteria.
 Sauerkraunt is essentially acid cabbage. Cabbages are trimmed to remove
green, broken, or dirty leaves, washed, and then cut into shreds of about
1mm wide.
 The shredded cabbage is then packed into tanks or vats to which 2.25% salt
is added and then thoroughly mixed.
 The tank is then covered with a plastic sheet large enough to extend over the
edge of the tank.
 Failure to keep the cabbage submerged during fermentation may permit
the growth of yeasts and moulds on the surface giving rise to undesirable
flavours which diffuse throughout the entire mass of Sauerkraunt and
producing softening and darkening of the product.
 A satisfactory salt concentration favours the growth of the various lactic
acid bacteria in their natural sequence and yields a kraunt with a proper
salt-acid balance.
 Leuconostoc mesenteroides initiates the fermentation which is subsequently
continued by the more acid tolerant species Lactobacillus brevis, L.
plantarum and Pediococcus cereviseae. Temperatures between 25-30oC seem
to be optimal for prduct quality and a completed fermentation in 2-3 weeks.
 In the preparation of cucumber pickles immature cucumbers are
washed, placed in barrels or tanks and brined.
 Sometomes 1% glucose may be added to help the fermentation if the
cucumbers are low in sugar. The brine added may range from 8% NaCl
to 10.5% NaCl.
 Salt is added at weekly intervals to eventually bring the final
concentration of salt to 16%. The fermentation is essentially lactic and
takes 6-9 weeks depending upon salt addition and temperatures.
 Eventually, the more acid and salt tolerant Lactobacillus plantarum
takes over and predominates to the completion of the fermentation
(total titratable acidity 0.6-0.8%).
 Other
pickled vegetables include turnips, radishes, chard,
cauliflower, brussel sprouts, lettuce, tomatoes, peas and green beans.
In all cases initial salting is used which is then followed by a lactic
acid fermentation initiated by Leuconostoc mesenteroides and
completed by other lactic acid bacteria such as Lactobacillus brevis
and L. plantarum.
 In processing, they are first treated with and kept submerged in a 1.25-2% lye
(sodium hydroxide) solution at about 15-21oC until the lye has penetrated one
half to three quarters into the pit.
 They are then washed several times with water to remove the lye.
 After washing, the olives are put into a barrel and covered with a salt brine, the
concentration of which varies with the kind of olive (10-15% brine solution
giving final concentration of 6-9% upon stabilization; 5-6.25% brine solution
giving 2.5-4% upon stabilization).
 Lactic acid fermentation of the barreled olives begins and may take between 6 and 10
months depending upon temperature. The fermentation has been divided into several
stages:
 The first stage lasting 7 to 14 days during which the brine becomes stabilized,
foods for microorganisms are ;eached from the olives and potential spoilange
organisms such as Pseudomonas, Bacillus and yeasts grow until the growth of
Leuconostoc mesenteroides has begun
 An intermediate stage lasting 2 to 3 weeks during which Leuconostoc
mesenteroidesI becomes predominant in growth and acid production and
Lactobacillus plantarum and L. brevis begin to grow and produce acid, and
 The final stage whete the lactobacilli, in particular L. plantarum, predominates. An
average temperature of around 20 to 25oC favours a rapid fermentation yielding a
final acidity of around 0.7-1.0% as lactic, pH 4.0-3.8. the fermented olives are
finally sorted, graded and packed into glass jars under vacuum with brine (7%
 Sausage define as a food prepared from chopped and seasoned meats.
 Basically, meats such as pork and beef are taken and carefully chopped
(comminuted).
 Salts, spices and curing agents are added, either before or after chopping or
grinding.
 Typical additives might include sodium nitrate, sodium nitrite (to maintain meat
colour) salt, glucose, sucrose, pepper, garlic, all spice, nutmeg, mustard and
corriander.
 The mixture is well mixed, blended, stuffed into a casing, an then removed to a
smokehouse. During smoking the temperature of the product is maintained at 2832oC for 12-16 hours during which time a lactic acid fermentation develops within
the sausage.
 This is favoured further by raising the temperature tp 37-40oC for a further 4 to 8
hours, the sausage is removed and allowed to dry and cool at room temperature.
 The product is then aged at temperatures between 10 and 15oC.
 The added sugars fermented by bacteria that produce the fermentation products
contributing to a tangy flavour. Also the reduction of pH as a result of this fermentation
has a preservative effect. Salt is added primarily as a flavouring agent but it also
improves the texture of the sausage and has a mild preservatitive effect. The various
spices added impart flavour which is enhanced by the smoking operation. Smoking also
aids in the development of colour and retards fat oxidation.
 Pediococcus cereviseae and Lactobacillus plantarum seem to predominate in the
fermentation possibly because of the warmer fermentation temperatures used.
 To avoid the uncertainties of natural fermentation and thus variation in product quality,
many sausage manufactures today add starter cultures of Pediococcus cereviseae and
Lactobacillus plantarum.
 Breads
• The organism which is primarily concerned in bread production is baker’s
yeast Saccharomyces cereviseae.
• The dough consists of a mixture of flour, water, salt, yeasts and various other
additives. Sometimes sugar is added.
• The temperature at which the fermentation is allowed to proceed is very
important. Optimum temperature is around 25 to 30oC. The pH of the freshly
mixed dough is around 60 but as a result of fermentation this drops to a value
of pH 4.5.
 Production of baker's yeast
• The medium which is used for industrial yeast production is either sugar
beet molasses (supplemented with the Vitamin, biotin), or sugar cane
molasses, diluted to contain about 10% sugar. Ammonium and phosphorus
salts are added,as well as magnesium sulphate, to supply the other nutrients
required for yeast growth.
• The baking properties of this type of yeast is maintained for sore months on
storage at room temperature.
 Beer
o Beer and other similar beverages are made from barely and water
and flavoured with the female flower of the hop plant.
o Depending upon the type of beer produced fermentation may last 4
to 8 days.
o Saccharomyces cerevisiae is a "top" yeast and during fermentation it
is carried to the fermenting beer on bubbles of carbon dioxide
thereby producing a yeasty head. It is used for the brewing of
traditional ale type beers.
o Saccharomyces
carlsbergensis now called Sacch. uvarum, is a
"bottom" yeast and settles to the bottom of the fermenting beer. It is
used for the brewing of traditional lager type beers. Lager beers are
usually fermented around 5 to 10oC while ale type beers are often
fermented between 10 to 20oC.
 Distilled Spirits
o Spirits or distilled liquors are those produced by
distillation of an alcohol- ically fermented product.
o Whiskeys are distilled from a fermented grain mash
for example, rye whisky is distilled from a fermented
rye mash; scotch whisky is distilled from a fermented
barley mash and bourbon from a corn mash.
o Rum is a distillate from alcoholically fermented sugar
cane juice, syrup or molasses. For these products
special strains of Saccharomyces cerevisiae are used
which give high yields of alcohol. Brandy is the
distilate from, grape wine.
 Wine
o Wine results from the alcoholic fermentation by yeasts of the
sugars, glucose and fructose contained in grapes and other fruits.
Wine yeasts can grow well in the highly acid conditions (pH 3 to 4)
in grape juice and can resist 10% or more alcohol, and resist the
sulphur dioxide which is added to suppress spoilage bacteria.
o In the production of red wines, grapes are harvested and crushed
to expel the sugary juice. Potassium or sodium metabisulphite is
added to the crused grapes, which is called the must' to give
approximately 100 ppm sulphurdioxide to inhibit the growth of
spoilage bacteria and wild yeasts.
o Commonly, a special strain of Saccharomyces
cerevisiae is
inoculated into the must to ensure that the desired fermentation
occurs. Fermentaion temperature is generally around 20 to 25oC
and fermentation lasts for several weeks.
o Alcohol content rises to about 10 to 15% and helps to extract the
red pigments from the grape skins giving colour to the wine. White
wines are made in a similar way to the above the temperature of
fermentation is generally maintained at temperatures between 10
and 15oC.
 Species of bacteria, yeasts, fungi and algae have all been considered as potential sources of
food protein, called single-cell protein, since all these organisms are unicellular.
 Saccharomyces cerevisiae, Candida utilis and Kluyveromyces fraqilis are three yeast species
which have been most studied as source of single cell protein.
 In single-cell protein production the object is to produce cell mass so that aerobic growth on
substrates is encouraged by intensive aeration of the growing culture. Some substrates used for
yeast single-cell protein production include:
 Molasses and sugar wates (Saccharomyces cereviseae)
 Paper industry and wood pulp wasres (Candida utilis and Saccharomyces cereviseae)
 Cellulosic, wood and starch hydrolysates (Candida utilis)
 Hydrocarbons (Candida utilis), and
 Whey wates from the dairy industry (Kluyveromyces fragilis ferments lactose in whey)
 Despite the obvious economic advantages of using microorganisms
as foods several objections have arisen which have prevented and
delayed their wide spread use as a source of food for humans.
 Microorganisms, in general, have high nucleic acid content which on
continual consumption by humans gives rise to metabolic disorders
such as gout. Nucleic acids, therefore, have to be removed or
extracted from the microbial protein and this adds an extra
processing operation.
 Animal and human feeding trials with microbial proteins have
suggested possible toxicological problems which require further
research..
 SOY SAUCE
o One of the universal of oriental fermented foods is soy sauce
which is a brown, salty, tangy sauce used frequently as a
flavouring agent.
o For the manufacture of soy sauce a mash consisting of boiled
soybeans (or defatted, chemically hydrolyed soybeans),
roasted and crushed wheat, and steamed wheat bran is
inoculated with the koji and spread in trays. This is incubated
at about 300C for 3 days after which it is soaked with 24%
sodium chloride brine. The brined mash is held for about 3
months to a year, depending upon temperature, after which it
is filtered to yield the raw soy sauce and a residue which is
used for animal feed. The sauce is heated to 80 to 850C,
filtered, and bottled. The finished sauce is high in soluble
proteins, peptides and amino acids and has a dark brown
colour a pleasing aroma.
 During soy sauce fermentation the proteinases, amylases and other
enzymes produced aspergilus oryzae in the koji act upon the mash.
There are three stages in the fermentation of the mash:
 lactic acid fermentation by lactic acid bacteria (Lactobacillus
delbrueckii) from the koji, followed by more acid production by
pediococcus soyae
 alcoholic fermentation by yeasts such as Saccharomyces rouxii.and
 completion of fermentation and aging. The acid conditions
developed by the lactic acid bacteria acidify the mash and reduce
bacterial spoilage risks.
 MISO
o Miso is essentially a fermented blend of rice, soybeans,
sometimes barley, andsalt. It is used as a soup and also as a
flavouring substance for other foods.
o A two stage fermentation is used: the first, an aerobic fermentation
is carried out by strains of Aspergillus oryzae; the second, an
anaerobic fermentation is carried out by the yeast Saccharomyces
rouxii.
 TEMPEH
o Tempeh is a very important source of protein in the Indonesian
diet and is essentially a fermented soybean product.
o Dry soybeans are washed, soaked overnight at about 25oC, and in
the morning the seedcoats are removed and the soaking water is
discarded. The beans are then boiled for about thirty minutes.
o After cooling they are then inoculated with spores of the mould
Rhizopous oligosporus or Rhizopus oryzae, placed in shallow trays
and incubated about 30oC for 20 to 24 hr. bay this time the beans
are completely covered and bound together by the white mycellia
of the mould. The product is now ready for consumption.
 FISH SAUCES
 A variety of fish sauces are prepared in Asian countries.
 Basically, small fish or shrimps are cleaned, washed, mixed with
salt (1 kg salt to 10 kg fish) and packed tightly into containers.
 After several months of storage a clear amber liquid usually forms
which is separated from undegraded residue and used as a sauce.
The sauce is rich in proteins and salt.
 During storage the fish tissue is enzymatically hydrolysed by
enzymes native to the food andenzymes produced by developing
microorganisms. It is believed that strains of lactic acid bacteria
such as Leuconostoc mesenteroides, Pediococcus cerevisiae and
Lactobacillus plantarum do developed. Some yeast species are also
thought to develop in the fermentations.