Transcript microorganism and fermented food product

* The biochemistry of
fermentation
* Microorganisms Involved In
Food Fermentations
* Chemical aspects of food
fermentations
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Lactic acid bacteria
Propionic acid bacteria
Acetic acid bacteria
Yeasts
Fungi
o Fermentation as the result of an anaerobic type of metabolism.
The most commonly used
microorganisms is glucose.
energy
substrate
among
o In the presence of oxygen many microorganisms metabolitze
glucose producing water, carrbondioxide and large amounts of
energy (ATP) which is used for growth activities.
o Such end product metabolites often include large amounts of
lactic acid, acetid acid and ethanol as well as minor amounts of
other volatile organic acids, alcohols and their esters.
o Fermented food are the result of the activity of a few species of
microorganisma among the thousands of known species of
bacteria, yeasts and moulds.
o Of the food fermenting organisms the lactic acid producing
bacteria, acetic acid producing bacteria and some alcohol
producing yeasts are most important.
o Certain mould species also play a very important role in some
fermented foods.
o The lactic acid produced lowers the pH value of the growth
environtment and has a sour taste. It is also inhibitory to the
growth of many other microbial species.
o Within this group two sub-divisioins are rcogniized, the
homofermentative
organism.
organism
and
the
heterofermentative
o Homofermentative species essentially produce only lactic acid
from their sugar metabolism whereas the heterofermentative
species produce carbondioxide and minor amounts of other
volatile acids, alcohols and esters in addition to lactic acid.
o Some important species in this group include :
o Streptococcus thermophilus, Streptococcus lactis and St. Cremoris. These
are Gram positive coccus shapped bacteria which occur in chains and
all are of great economic importance in the dairy industry.
o Pediococcus cereviseae. These are Gram positive cocci, typically
occuring in pairs or tetrads. Although this species in noted for beer
and wine spoilange, it plays an important role in meat and vegetable
fermentations.
o Leuconostoc mesenteroides, leuconostoc dextranicum. These are Gram
positive cocci occuring in pairs or short chains. However, they are very
important species in initiating fermentation of vegetables and are also
found in fruit juices, wines, and other foods.
o Lactobacillus lactis, L. acidophilus, L. bulgaricus, L. plantarum, L.
delbrueckii. These organism are Gram positive rod shaped bacteria
frequently forming pairs and chains of cells. They are very important in
milk and vegetable fermentations.
o Species belonging to this groups are found in the genus are
Propionibacterium and are Gram positive rod shaped organism.
o They are of significance in food fermentations since they are
capable of fermenting carbohydrates and even lactic acid with
the production of propionic and acetic acid and carbondioxide.
o They are important in Swiss cheese fermentation.
o There are Gram negative rod shaped bacteria found in the genus
Acetobacter for example Acetobacter aceti.
o Their metabolism is essentially aerobic (unlike the species
above) but their main concern with food fermentation is the
ability to oxidize alcohol and other carbohydrate substances to
acetic acid.
o They are used in vinegar manufacture.
o Yeasts carry out classical alcoholic fermentations where the
main product of their metabolism is ethanol.
o Saccharomyces
cereviseae is the most important species
involved in the production of alcoholic beverages such as beers
and wines and is also used for dough fermentation in bread
manufacture.
o Certain moulds are used in the preparation of several of cheese
and in the fermentation of many Asian foods such as soy sauce
and tempeh.
o Species
belonging to the genera Aspergillus,
Penicillium are most important in the activities.
Rhizopus,
o Foods, in general, furnish a satisfactory medium for the growth
of a variety of microorganisms.
o Fermentations are enzyme-induced chemical alterations in the
food; the enzymes involved may be produced
microorganisms or they may be indigenous to the food.
by
o The character of fermented foods will be determined by the
nature and quality of the food itself, the changes that occur as a
result of the action of its inherent enzymes, the alterations that
occur as a result of microbial fermentation, and the interactions
that occur between the products of these activities and
constituents of the foods.
o Fermentatios by desirable organisms impart flavour, bouquet
and texture to the fermented foods. In many lactic acid
fermentations, the high acidity, low pH and low redox potential
attained are responsible for inhibition of other organisms and of
undesirable chemical changes
o Pure culture fermentations rarely occur naturally.
o The broad spectrum of nutrients supplied by foods support the
growth of yeasts and many species of lactic acid bacteria so that
mixed fermentation normally occur.
o Food sugars provide the energy for the microbial metabolic
processes, but proteins lipids, vitamins, nucleic acids and minerals
are essential for the synthesis of cell constituents.
o In addition of food carbohydrate alterations during fermentation,
food proteins, fats and nucleic acids may also be degraded with
consequent effects upon food flavour, and texture.
o Many of the chemical alterations which do occur in fermented
foods cannot be attributed entirely to the action of
microorganism and it is believed that food indigenous enzymes
are also responsible. Generally, such activity is associated with
curing, ripening, and aging rather can actual fermentation.