Fundamental Food Microbiology, Third Edition - Fuad Fathir

266 FUNDAMENTAL FOOD MICROBIOLOGY
the generation time of Lactococcus spp. becomes longer. However, Bacillus sp.,
because of its aciduric nature, can then start multiplication, metabolize proteins, and
increase the pH (say 5.8). In the high pH, the Pseudomonas spp. present initially
can then grow by metabolizing NPN and proteinaceous compounds and increase the
pH further by producing basic metabolites (amines, NH 3). This way, the predominant
spoilage microorganisms and the metabolites associated with spoilage (e.g., nature
of spoilage) of a food can change if a food is stored for a fairly long time. 3
VI. CONCLUSION
Growth of microorganisms in food to a high level causes detectable changes in the
quality of food, which is generally termed as spoilage. Spoilage characteristics differ
with the differences in microbial type and the food component being metabolized.
Different aspects of food spoilage are discussed in this chapter. In Chapter 19,
spoilage of specific food groups, the predominant microorganisms involved, and the
nature of spoilage are discussed.
REFERENCES
1. Gill, C.O., The control of microbial spoilage in fresh meat, in Advances in Meat
Research: Meat and Poultry Microbiology, Vol. 2, Pearson, A.M. and Dutson, T.R.,
Eds., AVI Publishing, Westport, CN, 1986, p. 49.
2. Kraft, A.A., Health hazard vs. food spoilage, in Psychrotrophic Bacteria in Foods,
CRC Press, Boca Raton, FL, 1992, p. 113.
3. Sinell, H.J., Interacting factors affecting mixed populations, in Microbial Ecology of
Foods, Vol. 1, Silliker, J.H., Ed., Academic Press, New York, 1980, p. 215.
4. Ray, B., Foods and microorganisms of concern, in Food Biopreservatives of Microbial
Origin, Ray, B. and Daeschel, M.A., Eds., CRC Press, Boca Raton, FL, 1992, p. 25.
QUESTIONS
1. Describe when a food is considered spoiled by microorganisms. You put a packet
of lunchmeat in the refrigerator 2 to 3 weeks back and forgot about it. When you
opened it, you thought it had a slightly sour odor. You asked your friends to smell
it, but they said it smelled fine. What could be the reasons for this difference?
2. You opened a 2-l bottle of soft drink and kept it in the refrigerator and forgot
about it. After 2 weeks, you found some molds growing on the surface of the
liquid. Describe the sequence of events that resulted in this spoilage.
3. Discuss the significance of microbial types and numbers in food spoilage.
4. A food is usually spoiled by limited (usually one or two) types of microorganisms
among the many types initially present. Describe how this predominance is established.
5. At present, psychrotrophic bacteria seem to be the most important spoilage bacteria.
Suggest the possible reasons.