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Chapter 12
Biochemistry of Some
Beneficial traits
introduction
Beneficial microorganisms metabolize some of the components present in starting materials (i.e.,
food, such as milk or meat) to produce energy and cellular materials and to multiply. In this process, they produce some end products that are no longer necessary for the cells, and therefore, these
byproducts are excreted into the environment. Some of these byproducts impart unique characteristics (mostly texture and flavor) to the remaining components of the starting materials. These are
bioprocessed or fermented products and are considered desirable by consumers. Some of the byproducts of fermentation can also be purified and used as food additives. The production of several of
these byproducts by some desirable microorganisms is discussed in this chapter (see also Chapter 8).
Before describing the metabolic pathways used by these microbes, it will be helpful to review
the components of foods (substrates) used in fermentation. Before the substrates are metabolized
inside microbial cells, they have to be transported from the outside environment. It will be beneficial to recognize, in brief, the cellular components involved in the transport of these substrates.
The important substrates available in the starting materials of fermentation include several
carbohydrates, proteinaceous and nonprotein nitrogenous (NPN) compounds, and lipids. The
important fermentable carbohydrates in foods are starch, glycogen (in meat), lactose (in dairy
products), sucrose, maltose (from breakdown of starch), glucose, fructose, and pentoses (from
plant sources). The proteinaceous and NPN components include mainly large proteins (both
structural and functional), peptides of different sizes, and amino acids. Lipids can include triglycerides, phospholipids, fatty acids, and sterols. Microorganisms differ greatly in their ability to
transport these components from the outside and metabolize them inside the cells.
Mechanisms of transport of nutrients
Nutrient molecules have to pass through the cell barriers: the cell wall and the cell membrane.
However, in most Gram-positive lactic acid bacteria, the main barrier is the cytoplasmic membrane.
Chapter 12
Biochemistry of Some
Beneficial traits
introduction
Beneficial microorganisms metabolize some of the components present in starting materials (i.e.,
food, such as milk or meat) to produce energy and cellular materials and to multiply. In this process, they produce some end products that are no longer necessary for the cells, and therefore, these
byproducts are excreted into the environment. Some of these byproducts impart unique characteristics (mostly texture and flavor) to the remaining components of the starting materials. These are
bioprocessed or fermented products and are considered desirable by consumers. Some of the byproducts of fermentation can also be purified and used as food additives. The production of several of
these byproducts by some desirable microorganisms is discussed in this chapter (see also Chapter 8).
Before describing the metabolic pathways used by these microbes, it will be helpful to review
the components of foods (substrates) used in fermentation. Before the substrates are metabolized
inside microbial cells, they have to be transported from the outside environment. It will be beneficial to recognize, in brief, the cellular components involved in the transport of these substrates.
The important substrates available in the starting materials of fermentation include several
carbohydrates, proteinaceous and nonprotein nitrogenous (NPN) compounds, and lipids. The
important fermentable carbohydrates in foods are starch, glycogen (in meat), lactose (in dairy
products), sucrose, maltose (from breakdown of starch), glucose, fructose, and pentoses (from
plant sources). The proteinaceous and NPN components include mainly large proteins (both
structural and functional), peptides of different sizes, and amino acids. Lipids can include triglycerides, phospholipids, fatty acids, and sterols. Microorganisms differ greatly in their ability to
transport these components from the outside and metabolize them inside the cells.
Mechanisms of transport of nutrients
Nutrient molecules have to pass through the cell barriers: the cell wall and the cell membrane.
However, in most Gram-positive lactic acid bacteria, the main barrier is the cytoplasmic membrane.