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Chapter 8
Microbial Metabolism
of Food Components
introduction
Bacterial growth in food occurs though the metabolism of food components or nutrients mainly
in the cytoplasm and cytoplasmic membrane (also in periplasmic space in Gram-negative bacteria) of cells. 1 The complete process involves the transport of nutrients from the environment
(for macromolecules after their enzymatic breakdown) inside the cell through the cell wall and
cell membrane, the breakdown of nutrients to generate energy and active building blocks, the
synthesis of cell components from the building blocks (mainly macromolecules and structural
and functional components), and the release of unusable end products into the environment.
In addition, the recycling of cellular materials, cell differentiation, the repair of injured structures, and adaptation to environmental stresses are also mediated through metabolic processes.
Some of these aspects are important in food microbiology and are briefly discussed in several
sections in this book: sporulation in Chapter 9, sublethal injury and repair and stress adaptation in Chapter 10, and nutrient transport in Chapter 12. Several energy-generation and
energy-degradation processes that are important in food microbiology are briefly discussed
here (and also in Chapter 12).
Respiration and Fermentation During Growth
During growth in a food, microorganisms synthesize energy and cellular materials. A large portion of the energy is used to synthesize cellular components. This is achieved through linking
the energy-producing reactions with the reactions involved in the synthesis of cell materials. The
energy-generating reactions are of the nature of oxidation, and in microorganisms, they are organized in sequences (metabolic pathways) for gradual liberation of energy from an organic substrate
(in a reduced state). The energy is then either used directly in an endergonic reaction or stored
for release during a later reaction. The energy can be stored by forming energy-rich intermediates
Chapter 8
Microbial Metabolism
of Food Components
introduction
Bacterial growth in food occurs though the metabolism of food components or nutrients mainly
in the cytoplasm and cytoplasmic membrane (also in periplasmic space in Gram-negative bacteria) of cells. 1 The complete process involves the transport of nutrients from the environment
(for macromolecules after their enzymatic breakdown) inside the cell through the cell wall and
cell membrane, the breakdown of nutrients to generate energy and active building blocks, the
synthesis of cell components from the building blocks (mainly macromolecules and structural
and functional components), and the release of unusable end products into the environment.
In addition, the recycling of cellular materials, cell differentiation, the repair of injured structures, and adaptation to environmental stresses are also mediated through metabolic processes.
Some of these aspects are important in food microbiology and are briefly discussed in several
sections in this book: sporulation in Chapter 9, sublethal injury and repair and stress adaptation in Chapter 10, and nutrient transport in Chapter 12. Several energy-generation and
energy-degradation processes that are important in food microbiology are briefly discussed
here (and also in Chapter 12).
Respiration and Fermentation During Growth
During growth in a food, microorganisms synthesize energy and cellular materials. A large portion of the energy is used to synthesize cellular components. This is achieved through linking
the energy-producing reactions with the reactions involved in the synthesis of cell materials. The
energy-generating reactions are of the nature of oxidation, and in microorganisms, they are organized in sequences (metabolic pathways) for gradual liberation of energy from an organic substrate
(in a reduced state). The energy is then either used directly in an endergonic reaction or stored
for release during a later reaction. The energy can be stored by forming energy-rich intermediates