232 ◾ Fundamental Food Microbiology
Microbial Proteins and Food Additives
Single-Cell Proteins (SCPs) 3
Molds, yeasts, bacteria, and algae are rich in proteins, and the digestibility of these proteins ranges
from 65% to 96%. Proteins from yeasts, in general, have high digestibility as well as biological
value. In commercial production, yeasts are preferred. Some of the species used are from genera
Candida, Saccharomyces, and Torulopsis. Some bacterial species have been used, especially from
genus Methylophilus.
The use of microbial proteins as food has several advantages over animal proteins. There may
not be enough animal proteins to feed the growing human population in the future, especially in
many developing countries. Also, microbial proteins can be produced under laboratory settings.
Thus, land shortage and environmental calamities (such as drought or flood) can be overcome.
They can be produced on many agricultural and industrial wastes. This will help alleviate waste
disposal problems and also reduce the cost of production. Microbial proteins can be a good source
of B vitamins, carotene, and carbohydrates.
There are some disadvantages of using microbial proteins as human food. They are poor in
some essential amino acids, such as methionine. However, this can be corrected by supplementing
microbial proteins with the needed essential amino acids. The other problem is that proteins from
microbial sources can have high-nucleic acid content (RNA and DNA; 6%–8%), which, in the
human body, is metabolized to uric acid. A high serum-acid level can lead to kidney stone formation and gout. However, through genetic manipulations, the nucleic acid content in microbial
proteins has been reduced.
Even though, at present, the use of microbial proteins as a protein source in human food is
limited, they are being used as a protein source in animal feed. An increase of microbial proteins
will automatically reduce the use of grains (such as corn and wheat) as animal feed, which then
can be used as human food. 3
Amino Acids
Proteins of most cereal grains are deficient in one or more of the essential amino acids, particularly
methionine, lysine, and tryptophan. To improve the biological values, cereals are supplemented with
essential amino acids. Supplementing vegetable proteins with essential amino acids has been suggested to improve the protein quality for people who either do not consume animal proteins (people
on vegetarian diets) or do not have enough animal proteins (such as in some developing countries,
especially important for children). To meet this demand, as well as for use as nutrient supplements,
large amounts of several essential acids are being produced. At present, because of economic reasons, they are mostly produced from the hydrolysis of animal proteins followed by purification.
In recent years, bacterial strains have been isolated, some of which are lactic acid bacteria that produce and excrete large amounts of lysine in the environment. Isolating high-producing strains of other
amino acids and developing strains by genetic and metabolic engineering that will produce these
amino acids in large amounts can be important for economical production of essential amino acids.
Nutraceuticals and Vitamins
Many vitamins are added to foods and also used regularly by many as supplements. Thus, there is
a large market for vitamins, especially some B vitamins and vitamins C, D, and E. Some of these
Microbial Proteins and Food Additives
Single-Cell Proteins (SCPs) 3
Molds, yeasts, bacteria, and algae are rich in proteins, and the digestibility of these proteins ranges
from 65% to 96%. Proteins from yeasts, in general, have high digestibility as well as biological
value. In commercial production, yeasts are preferred. Some of the species used are from genera
Candida, Saccharomyces, and Torulopsis. Some bacterial species have been used, especially from
genus Methylophilus.
The use of microbial proteins as food has several advantages over animal proteins. There may
not be enough animal proteins to feed the growing human population in the future, especially in
many developing countries. Also, microbial proteins can be produced under laboratory settings.
Thus, land shortage and environmental calamities (such as drought or flood) can be overcome.
They can be produced on many agricultural and industrial wastes. This will help alleviate waste
disposal problems and also reduce the cost of production. Microbial proteins can be a good source
of B vitamins, carotene, and carbohydrates.
There are some disadvantages of using microbial proteins as human food. They are poor in
some essential amino acids, such as methionine. However, this can be corrected by supplementing
microbial proteins with the needed essential amino acids. The other problem is that proteins from
microbial sources can have high-nucleic acid content (RNA and DNA; 6%–8%), which, in the
human body, is metabolized to uric acid. A high serum-acid level can lead to kidney stone formation and gout. However, through genetic manipulations, the nucleic acid content in microbial
proteins has been reduced.
Even though, at present, the use of microbial proteins as a protein source in human food is
limited, they are being used as a protein source in animal feed. An increase of microbial proteins
will automatically reduce the use of grains (such as corn and wheat) as animal feed, which then
can be used as human food. 3
Amino Acids
Proteins of most cereal grains are deficient in one or more of the essential amino acids, particularly
methionine, lysine, and tryptophan. To improve the biological values, cereals are supplemented with
essential amino acids. Supplementing vegetable proteins with essential amino acids has been suggested to improve the protein quality for people who either do not consume animal proteins (people
on vegetarian diets) or do not have enough animal proteins (such as in some developing countries,
especially important for children). To meet this demand, as well as for use as nutrient supplements,
large amounts of several essential acids are being produced. At present, because of economic reasons, they are mostly produced from the hydrolysis of animal proteins followed by purification.
In recent years, bacterial strains have been isolated, some of which are lactic acid bacteria that produce and excrete large amounts of lysine in the environment. Isolating high-producing strains of other
amino acids and developing strains by genetic and metabolic engineering that will produce these
amino acids in large amounts can be important for economical production of essential amino acids.
Nutraceuticals and Vitamins
Many vitamins are added to foods and also used regularly by many as supplements. Thus, there is
a large market for vitamins, especially some B vitamins and vitamins C, D, and E. Some of these