Food Ingredients and Enzymes of Microbial Origin ◾ 233
are obtained from plant sources, several are synthesized, and a few are produced by microorganisms. 4 Vitamin C is now produced by yeast by using cheese whey. Microorganisms have also been
a source of vitamin D. Many are capable of producing B vitamins.
The possibility of using gene-cloning techniques to improve production of vitamins by microorganisms may not now be very practical or economical. Vitamins are produced through multienzyme systems, and it may not be possible to clone the necessary genes. In recent years, through
metabolic engineering, strains of lactic acid bacteria have been developed that when used in dairy
fermentation produce high amounts of folate and some cyanocobalamin (B 12 ) in the fermented
products, thereby increasing the nutritional value of the products. In addition, strains of lactic
acid bacteria have been developed that produce low-calorie sweeteners, such as mannitol, sorbitol,
and tagatose. 3
Flavor Compounds and Flavor Enhancers
Flavor compounds and enhancers include those that are associated directly with the desirable aroma and taste of foods and indirectly with the strengthening of some flavors. 5–7 Many
microorganisms produce different types of flavor compounds, such as diacetyl (butter flavor
by Leuconostoc), acetaldehyde (yogurt flavor by Lactobacillus acidophilus), some nitrogenous and
sulfur-containing compounds (sharp cheese flavor by Lactococcus lactis), propionic acid (nutty
flavor by dairy Propionibacterium), pyrazines (roasted nutty flavors by strains of Bacillus subtilis
and Lac. lactis), and terpenes (fruity or flowery flavors by some yeasts and molds). Some natural
flavors from plant sources are very costly because only limited amounts are available and the
extraction process is very elaborate. By employing biotechnology, they can be produced economically by suitable microorganisms. Natural vanilla flavor (now obtained from plants), if produced
by microorganisms, may cut the cost to only a 10th or less. Natural fruit flavors are extracted
from fruits. Not only is it costly, but also large amounts of fruits are wasted. The possible production of many of these flavors by microorganisms through recombinant DNA technology is being
studied.
Several flavor enhancers are now used to strengthen the basic flavors of foods. Monosodium
glutamate (MSG, enhances meat flavor) is produced by several bacterial species, such as
Corynebacterium glutamicum and Micrococcus glutamicus. Also, 5ʹ nucleotides, such as inosine
monophosphate and guanosine monophosphate, give an illusion of greater viscosity and mouthfeel in foods such as soups. They can be produced from Bac. subtilis.
Several small peptides, such as lysylglycine, have strong salty tastes. They can be produced
by recombinant DNA technology by microorganisms and used to replace NaCl. Sweet peptides,
such as monellin and thaumatin from plant sources, can also be produced by microorganisms
through gene cloning. At present, the dipeptide sweetener aspartame is produced synthetically,
but a method to produce it by microorganisms has been developed. By metabolic engineering,
strains of lactic acid bacteria have been developed that can produce large quantities of diacetyl (for
the aroma of butter), acetaldehyde (for the aroma of yogurt), α-ketoglutarate (to produce cheese
flavor), and other compounds. 3
Colors
Many bacteria, yeasts, and molds produce different color pigments. The possibility of using some
of them, especially from those that are currently consumed by humans, is being studied. 8 Some
of the common fermentative food-grade pigments include yellow, red, and orange pigments from
are obtained from plant sources, several are synthesized, and a few are produced by microorganisms. 4 Vitamin C is now produced by yeast by using cheese whey. Microorganisms have also been
a source of vitamin D. Many are capable of producing B vitamins.
The possibility of using gene-cloning techniques to improve production of vitamins by microorganisms may not now be very practical or economical. Vitamins are produced through multienzyme systems, and it may not be possible to clone the necessary genes. In recent years, through
metabolic engineering, strains of lactic acid bacteria have been developed that when used in dairy
fermentation produce high amounts of folate and some cyanocobalamin (B 12 ) in the fermented
products, thereby increasing the nutritional value of the products. In addition, strains of lactic
acid bacteria have been developed that produce low-calorie sweeteners, such as mannitol, sorbitol,
and tagatose. 3
Flavor Compounds and Flavor Enhancers
Flavor compounds and enhancers include those that are associated directly with the desirable aroma and taste of foods and indirectly with the strengthening of some flavors. 5–7 Many
microorganisms produce different types of flavor compounds, such as diacetyl (butter flavor
by Leuconostoc), acetaldehyde (yogurt flavor by Lactobacillus acidophilus), some nitrogenous and
sulfur-containing compounds (sharp cheese flavor by Lactococcus lactis), propionic acid (nutty
flavor by dairy Propionibacterium), pyrazines (roasted nutty flavors by strains of Bacillus subtilis
and Lac. lactis), and terpenes (fruity or flowery flavors by some yeasts and molds). Some natural
flavors from plant sources are very costly because only limited amounts are available and the
extraction process is very elaborate. By employing biotechnology, they can be produced economically by suitable microorganisms. Natural vanilla flavor (now obtained from plants), if produced
by microorganisms, may cut the cost to only a 10th or less. Natural fruit flavors are extracted
from fruits. Not only is it costly, but also large amounts of fruits are wasted. The possible production of many of these flavors by microorganisms through recombinant DNA technology is being
studied.
Several flavor enhancers are now used to strengthen the basic flavors of foods. Monosodium
glutamate (MSG, enhances meat flavor) is produced by several bacterial species, such as
Corynebacterium glutamicum and Micrococcus glutamicus. Also, 5ʹ nucleotides, such as inosine
monophosphate and guanosine monophosphate, give an illusion of greater viscosity and mouthfeel in foods such as soups. They can be produced from Bac. subtilis.
Several small peptides, such as lysylglycine, have strong salty tastes. They can be produced
by recombinant DNA technology by microorganisms and used to replace NaCl. Sweet peptides,
such as monellin and thaumatin from plant sources, can also be produced by microorganisms
through gene cloning. At present, the dipeptide sweetener aspartame is produced synthetically,
but a method to produce it by microorganisms has been developed. By metabolic engineering,
strains of lactic acid bacteria have been developed that can produce large quantities of diacetyl (for
the aroma of butter), acetaldehyde (for the aroma of yogurt), α-ketoglutarate (to produce cheese
flavor), and other compounds. 3
Colors
Many bacteria, yeasts, and molds produce different color pigments. The possibility of using some
of them, especially from those that are currently consumed by humans, is being studied. 8 Some
of the common fermentative food-grade pigments include yellow, red, and orange pigments from