Foods and Bacteria
The most common usage for bacteria in food preparation is with dairy fermentations.
Yogurt and cheeses have been made for centuries using bacteria. The ancients may not
have known exactly what kind of bacteria that was needed or if what was needed was,
indeed, bacteria. All they knew was that the previous batch was required to make a new
one. Many people lack the ability to break down and absorb lactose, the sugar molecule
in milk. As a result, it enters the gut, producing acid and gas, causing pain and diarrhea.
Fermented milk products metabolize lactose into lactic acid, which is more tolerable for
many people. The most common fermented milk product is yogurt. The lactobacilli used
in the making of many yogurts, however, may not be the same type as found within the
common flora of humans as there are many different strains (see Probiotics). The
following are some of the bacteria used in the diary industry:
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Acidophilus milk is made with Lactobacillus acidophilus.
Butter is made from pasteurized cream, to which a lactic acid starter has been
added. The starter contains, for example, Streptococcus cremoris or S. lactis, but
requires Lactobacillus diacetylactis to give it its characteristic flavor and odor.
Cheese is often made with Streptococcus and Lactobacillus bacteria.
Fermentation lowers the pH, thus helping in the initial coagulation of the milk
protein, as well as giving characteristic flavors. In such Swiss cheeses as
Emmentaler and Gruyere, the typical flavor is the result of the use of
Propionibacterium. Cheese can be classified within two groups -- ripened and
unripened. Unripened cheeses consist of cottage cheese, cream cheese, and
Mozzarella, for example. These are soft cheeses and are made by the lactic acid
fermentation of milk. Many different bacteria are used to produce the various
cheeses, but Lactococcus lactis and Leuconostoc cremoris are used most often.
Soft cheeses can take one to five months to ripen; hard cheeses, three months to a
year or more; and very hard cheeses, like Parmesan, can take twelve to eighteen
months. The blue veins found in cheeses, like Stilton and Roquefort, are caused
by growth Penicillium roqueforti, which is deliberately added now to cheese.
Originally, it was found as a natural contaminant of the areas where it was made.
The holes in Swiss cheese are the result of Propionibacterium shermanii. The
surfaces of Camembert and Brie are innoculated with Penicillium camembertii,
which then develops in a skin on the surface. Limburger is soaked in brine to
encourage the growth of Brevibacterium linens (it should come as no surprise that
this is the same bacteria isolated from smelly feet!)
Kefir includes many different microbes, including yeasts, lactobacilli, lactococci,
and leuconostocs. Depending on geographical locations, the precise types of
microbes will vary.
Yogurt usually requires the addition of Lactobacillus bulgaricus, Lactococcus
thermophilus, and/or Streptococcus thermophilus to the milk.
Bacteria are not only used for fermentaion in the dairy industry, but for use in other such
food production as in the processing of coffee and cocoa, the manufacturing of food
additives, and other such processes such as the making of xanthan gum and vinegar.
Bacteria, and most viruses do not tolerate acids. This is the reason that vinegar retards the
growth of most bacteria. The following is a list of other foods where bacteria and other
microbes are necessary for the making of certain foodstuffs.
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Glutamic acid requires Corynebacterium glutamicum for its formation. Biotin is
a cofactor essential for lipid synthesis in bacteria. By growing C. glutamicum on
limited amounts of biotin, it causes the bacterial membrane to leak sufficient
quantities of glutamic acid.
Lysine -- The bacterium, Brevibacterium flavum is used in the industrial
biosynthesis of lysine. Mutants no longer susceptible to feedback inhibition have
been isolated to be used industrially to increase the yield of amino acids.
Baker's yeast (Saccharomyces cerevisiae) provides a variety of enzymes that
enable carbohydrates to be broken down producing sufficient carbon dioxide to
give bread its characteristic texture.
Beers, etc. -- Traditionally, the natural yeasts on grape skins determine the quality
of wine produced. These natural yeasts, especially Saccharomyces cerevisiae
(beer in Spanish is "cervesa") and Saccharomyces ellipsoideus, ferment the grapes
to make wine. It used to be a risky business leaving it up to nature to decide the
quality. Now winemaking has become a regulated science with the use of these
yeasts. Beers, lagers, and ales generally rely on the yeast Saccharomyces
cerevisiae, although lager yeasts will probably always be known as Saccaromyces
carlsbergensis.
Sauerkraut-making requires the bacteria Leuconostoc mesenteroides and
Lactobacillus brevis to ferment sugars that provide a variety of such organic
products as lactic acid, acetic acid, ethanol, and mannitol. These bacteria are
known as 'heterofermentative' bacteria. Later a 'homofermentative' bacteria,
Lactobacillus plantarum takes over, producing only lactic acid. Later,
Enterococcus faecalis and Pediococcus cerevisiae assume the fermentation
process if the salt brine is not what it sould be.
Sourdough bread requires the help of a yeast, Saccharomyces exiguus, along
with lactobacilli, to provide its characteristic texture and flavor.
Dill pickles are simply fermented cucumbers. Streptococci starts the process of
fermentation, but as the pH level falls, leuconostoc and pediococcus species, as
well as Lactobacillus plantarum continue the process.
Olives are edible only after fermentation with Lactobacillus plantarum and
Lactobacillus mesenteroides.
Coffee and chocolate require Erwinia dissolvens, leuconostoc, and lactobacillus
species plus the yeasts of the genus Saccharomyces to remove the tough outer
coats. The microbes do not affect the taste of coffee but are necessary to confer
the characteristic taste to cocoa and chocolate. The bacteria S. napoli and S.
eastbourne often use chocolate as a vector. It is thought that the chocolate
provides protection for the bacterium as it passes through the acidic environment
of the stomach. This was observed when higher incidents of illness were reported
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in children.
Soy sauce is made from a mixture of soy beans and rice fermented by a variety of
bacteria and fungi. These include Lactobacillus delbrueckii, Aspergillus oryzae,
Aspergillus soyae, and Saccharomyces rouxii.
Meat products, like salami and bologna sausages, require some fermentation
with Pediuococcus cerevisiae, Lactobacillus plantarum and some members of the
genus Bacillus. Country cured hams use fungi of the genus Aspergillus and the
genus Penicillium in their fermentation process. Izushi (sushi), a Japanese
delicacy made from a mixture of fish, rice, and other vegetables is produced by
fermentation with lactobacilli.