234 ◾ Fundamental Food Microbiology
Monascus sp. 9 (fungus), astaxanthin (pink-red) from Xanthophyllomyces dendrorhous (yeast), arpink
red from Penicillium oxalicum (fungus), riboflavin from Ashbya gossypii (fungus), β-carotene from
Blakeslea trispora (fungus). The pink-red color pigment astaxanthin gives the red color to salmon,
trout, lobster, and crabs. Another red pigment, produced by Monascus sp., has been used for a long
time in the Orient to make red rice wine. Because pigment production may involve multistep reactions, recombinant DNA techniques to produce some fruit colors by microorganisms may not be
economical. However, they can be produced by the plant cell culture technique.
Exopolysaccharides (EPS)
Different polysaccharides are used in food systems as stabilizers and texturizers. Although many
of them are of plant origin, some are obtained from microbial sources. 10,11 Strains of many lactic acid bacteria, such as Streptococcus thermophilus, Lab. rhamnosus, Lab. helveticus, Lab. casei,
and Lac. lactis, produce many different types of exopolysaccharides (EPS) that contain units of
glucose, galactose, rhamnose, mannose, and other carbohydrates. Many of these strains are currently being used to produce fermented dairy products with better consistency and texture (in
yogurt and buttermilk), to hold moisture in low fat–high moisture cheeses (in mozzarella cheese).
Some examples of EPS produced by microorganisms include xanthan, gellan, alginate, cellulose,
dextran, curdlan, succinoglycan, levan, galactopol, fucopol, etc. 12 Dextran, an EPS produced
by Leuconostoc mesenteroides while growing in sucrose, is used as a stabilizer in ice cream and
confectioneries. Xanthan gum, produced by Xanthomonas campestris, is also used as a stabilizer.
Introducing lactose-hydrolyzing genes in Xanthomonas species can enable it to grow in whey to
produce the stabilizer economically.
Organic Acids
Production of lactic (by lactic acid bacteria), propionic (by propionic acid bacteria), and acetic (by
acetic acid bacteria) acids and their different uses in foods are discussed in Chapters 12, 17, and 41.
Several other organic acids and their salts are used in foods to improve taste (flavor and texture)
and retain quality. Production of ascorbic acid by yeasts and its use as a vitamin supplement have
also been discussed. Ascorbic acid is also used in some foods as a reducing agent to maintain color
(to prevent color loss by oxidation). It also has an antibacterial action. Citric acid is used in many
foods to improve taste and texture (in beverages) and stabilize color (in fruits). It also has some
antibacterial property. Citric acid is produced by the mold Aspergillus niger.
Preservatives
Bacterial cells of lactic acid bacteria, several organic acids produced by them, and their bacteriocins can be used to control spoilage and pathogenic bacteria in foods. This aspect is discussed in
Chapter 17.
Microbial enzymes in Food Processing
Many enzymes are used in the processing of food as food additives. 13 About 80% of the total
enzymes produced, on a dollar basis, is used by the food industries. Use of specific enzymes instead
of microorganisms has several advantages. A specific substrate can be converted into a specific
Monascus sp. 9 (fungus), astaxanthin (pink-red) from Xanthophyllomyces dendrorhous (yeast), arpink
red from Penicillium oxalicum (fungus), riboflavin from Ashbya gossypii (fungus), β-carotene from
Blakeslea trispora (fungus). The pink-red color pigment astaxanthin gives the red color to salmon,
trout, lobster, and crabs. Another red pigment, produced by Monascus sp., has been used for a long
time in the Orient to make red rice wine. Because pigment production may involve multistep reactions, recombinant DNA techniques to produce some fruit colors by microorganisms may not be
economical. However, they can be produced by the plant cell culture technique.
Exopolysaccharides (EPS)
Different polysaccharides are used in food systems as stabilizers and texturizers. Although many
of them are of plant origin, some are obtained from microbial sources. 10,11 Strains of many lactic acid bacteria, such as Streptococcus thermophilus, Lab. rhamnosus, Lab. helveticus, Lab. casei,
and Lac. lactis, produce many different types of exopolysaccharides (EPS) that contain units of
glucose, galactose, rhamnose, mannose, and other carbohydrates. Many of these strains are currently being used to produce fermented dairy products with better consistency and texture (in
yogurt and buttermilk), to hold moisture in low fat–high moisture cheeses (in mozzarella cheese).
Some examples of EPS produced by microorganisms include xanthan, gellan, alginate, cellulose,
dextran, curdlan, succinoglycan, levan, galactopol, fucopol, etc. 12 Dextran, an EPS produced
by Leuconostoc mesenteroides while growing in sucrose, is used as a stabilizer in ice cream and
confectioneries. Xanthan gum, produced by Xanthomonas campestris, is also used as a stabilizer.
Introducing lactose-hydrolyzing genes in Xanthomonas species can enable it to grow in whey to
produce the stabilizer economically.
Organic Acids
Production of lactic (by lactic acid bacteria), propionic (by propionic acid bacteria), and acetic (by
acetic acid bacteria) acids and their different uses in foods are discussed in Chapters 12, 17, and 41.
Several other organic acids and their salts are used in foods to improve taste (flavor and texture)
and retain quality. Production of ascorbic acid by yeasts and its use as a vitamin supplement have
also been discussed. Ascorbic acid is also used in some foods as a reducing agent to maintain color
(to prevent color loss by oxidation). It also has an antibacterial action. Citric acid is used in many
foods to improve taste and texture (in beverages) and stabilize color (in fruits). It also has some
antibacterial property. Citric acid is produced by the mold Aspergillus niger.
Preservatives
Bacterial cells of lactic acid bacteria, several organic acids produced by them, and their bacteriocins can be used to control spoilage and pathogenic bacteria in foods. This aspect is discussed in
Chapter 17.
Microbial enzymes in Food Processing
Many enzymes are used in the processing of food as food additives. 13 About 80% of the total
enzymes produced, on a dollar basis, is used by the food industries. Use of specific enzymes instead
of microorganisms has several advantages. A specific substrate can be converted into a specific