Fundamental Food Microbiology, Third Edition - Fuad Fathir

98 FUNDAMENTAL FOOD MICROBIOLOGY
process is reversible, i.e., a spore does not have to germinate after activation if the
environment is not suitable. 1,2
D. Germination
Several structural and functional events occur during germination. Once the germination
process starts, the dormant stage is irreversibly terminated. Structural changes
involve hydration of core, excretion of Ca 2+ and DPN, and loss of resistance and
refractile property. Functional changes include initiation of metabolic activity, activation
of specific proteases and cortex-lytic enzymes, and release of cortex-lytic
products. Generally, germination is a metabolically degradative process.
Germination can be initiated (triggered) by low pH, high temperature, high
pressure, lysozyme, nutrients (amino acids, carbohydrates), calcium-DPN, and other
factors. The process can be inhibited by D-alanine, ethanol, EDTA, NaCl (high
concentrations), NO 2, and sorbate. 1,2
E. Outgrowth
Outgrowth constitutes the biosynthetic and repair processes between the periods
following germination of a spore and before the growth of a vegetative cell. The
events during this phase include swelling of the spore due to hydration and nutrient
uptake; repair and synthesis of RNA, proteins, and materials for membrane and cell
wall; dissolution of coats; cell elongation; and DNA replication. The factors that
can enhance the process include favorable nutrients, pH, and temperature. With the
termination of the outgrowth stage, vegetative cells emerge from spores and enter
the vegetative cell cycle of growth by binary fission. 1,2,4
The sporulation process, as discussed previously, involves irreversible cellular
differentiation processes in an unfavorable environment and is regulated and
expressed by a large number of genes. The functions of many genes have been
studied with mutants of Bacillus subtilis (spo mutants) that block formation of
different components during the sporulation process. Expression of these functional
genes is regulated by the genes coding for specific sigma factors (d). In a favorable
environment, germination and outgrowth are also mediated through other genes that
enable an endospore to enter in the cell division cycle. 1
V. IMPORTANCE OF SPORES IN FOOD
Spore formation, especially by molds and some bacterial species, enables them to
survive for a long time and provides a basis for the continuation of the species. It
also provides a means of their easy dissemination by dust and air in the environment. 1
In this manner, foods can be contaminated by their spores rather easily from various
sources. In a suitable food environment, spores germinate, grow, and produce undesirable
(or desirable) effects. Mold and yeast spores are relatively sensitive to heat,
and their growth can also be prevented by storing foods in the absence of air.