150 Modern Food Microbiology
to ethanol that results from malting is then carried out by yeasts. The use of koji in the fermentation
of soybean products is another example of the way in which alcoholic and lactic acid fermentations
may be carried out on products that have low levels of sugars but high levels of starches and proteins.
Whereas the saccharifying enzymes of barley malt arise from germinating barley, the enzymes of koji
are produced by Aspergillus oryzae growing on soaked or steamed rice or other cereals (the commercial
product takadiastase is prepared by growing A. oryzae on wheat bran). The koji hydrolysates may be
fermented by lactic acid bacteria and yeasts, as is the case for soy sauce, or the koji enzymes may act
directly on soybeans in the production of products such as Japanese miso.
Defined and Characterized
The word fermentation has had many shades of meaning in the past. According to one dictionary
definition, it is “a process of chemical change with effervescence . . . a state of agitation or unrest . . . any
of various transformations of organic substances.” The word came into use before Pasteur’s studies on
wines. Prescott and Dunn
56 and Doelle
12 have discussed the history of the concept of fermentation,
and the former authors note that in the broad sense in which the term is commonly used, it is “a process
in which chemical changes are brought about in an organic substrate through the action of enzymes
elaborated by microorganisms.” It is in this broad context that the term is used in this chapter. In the
brewing industry, a top fermentation refers to the use of a yeast strain that carries out its activity at the
upper parts of a large vat, such as in the production of ale; a bottom fermentation requires the use of
a yeast strain that will act in lower parts of the vat, such as in the production of lager beer.
Biochemically, fermentation is the metabolic process in which carbohydrates and related compounds
are partially oxidized with the release of energy in the absence of any external electron acceptors.
The final electron acceptors are organic compounds produced directly from the breakdown of the
carbohydrates. Consequently, incomplete oxidation of the parent compound occurs, and only a small
amount of energy is released during the process. The products of fermentation consist of some organic
compounds that are more reduced than others.
The Lactic Acid Bacteria
This group is composed of 13 genera of Gram-positive bacteria at this time:
Carnobacterium Oenococcus
Enterococcus
Pediococcus
Lactococcus
Paralactobacillus
Lactobacillus
Streptococcus
Lactosphaera
Tetragenococcus
Leuconostoc
Vagococcus
Weissella
With the enterococci and lactococci having been removed from the genus Streptococcus, the member
of this genus of most importance in foods is S. salivarius subsp. thermophilus. S. diacetilactis has
been reclassified as a citrate-utilizing strain of Lactococcus lactis subsp. lactis.
Related to the lactic acid bacteria but not considered to fit the group are genera such as Aerococcus,
Microbacterium, and Propionibacterium, among others. The last genus has been reduced by the transfer
to ethanol that results from malting is then carried out by yeasts. The use of koji in the fermentation
of soybean products is another example of the way in which alcoholic and lactic acid fermentations
may be carried out on products that have low levels of sugars but high levels of starches and proteins.
Whereas the saccharifying enzymes of barley malt arise from germinating barley, the enzymes of koji
are produced by Aspergillus oryzae growing on soaked or steamed rice or other cereals (the commercial
product takadiastase is prepared by growing A. oryzae on wheat bran). The koji hydrolysates may be
fermented by lactic acid bacteria and yeasts, as is the case for soy sauce, or the koji enzymes may act
directly on soybeans in the production of products such as Japanese miso.
Defined and Characterized
The word fermentation has had many shades of meaning in the past. According to one dictionary
definition, it is “a process of chemical change with effervescence . . . a state of agitation or unrest . . . any
of various transformations of organic substances.” The word came into use before Pasteur’s studies on
wines. Prescott and Dunn
56 and Doelle
12 have discussed the history of the concept of fermentation,
and the former authors note that in the broad sense in which the term is commonly used, it is “a process
in which chemical changes are brought about in an organic substrate through the action of enzymes
elaborated by microorganisms.” It is in this broad context that the term is used in this chapter. In the
brewing industry, a top fermentation refers to the use of a yeast strain that carries out its activity at the
upper parts of a large vat, such as in the production of ale; a bottom fermentation requires the use of
a yeast strain that will act in lower parts of the vat, such as in the production of lager beer.
Biochemically, fermentation is the metabolic process in which carbohydrates and related compounds
are partially oxidized with the release of energy in the absence of any external electron acceptors.
The final electron acceptors are organic compounds produced directly from the breakdown of the
carbohydrates. Consequently, incomplete oxidation of the parent compound occurs, and only a small
amount of energy is released during the process. The products of fermentation consist of some organic
compounds that are more reduced than others.
The Lactic Acid Bacteria
This group is composed of 13 genera of Gram-positive bacteria at this time:
Carnobacterium Oenococcus
Enterococcus
Pediococcus
Lactococcus
Paralactobacillus
Lactobacillus
Streptococcus
Lactosphaera
Tetragenococcus
Leuconostoc
Vagococcus
Weissella
With the enterococci and lactococci having been removed from the genus Streptococcus, the member
of this genus of most importance in foods is S. salivarius subsp. thermophilus. S. diacetilactis has
been reclassified as a citrate-utilizing strain of Lactococcus lactis subsp. lactis.
Related to the lactic acid bacteria but not considered to fit the group are genera such as Aerococcus,
Microbacterium, and Propionibacterium, among others. The last genus has been reduced by the transfer