Fundamental Food Microbiology, Third Edition - Fuad Fathir

36 FUNDAMENTAL FOOD MICROBIOLOGY
Natural microflora exist in ecological balance with their hosts, and their types and
levels vary greatly with the type of plants and animals as well as their geographical
locations and environmental conditions. Besides natural microorganisms, a food can
be contaminated with different types of microorganisms coming from outside sources
such as air, soil, sewage, water, feeds, humans, food ingredients, equipment, packages,
and insects. Microbial types and their levels from these sources getting into
foods vary widely and depend on the degree of sanitation used during the handling
of foods.
An understanding of the sources of microorganisms in food is important to
develop methods to control access of some microorganisms in the food, develop
processing methods to kill them in food, and determine the microbiological quality
of food, as well as set up microbiological standards and specifications of foods and
food ingredients. The predominant types that can get into food from each of these
sources and methods to reduce the levels of microorganisms are briefly discussed here.
II. PREDOMINANT MICROORGANISMS IN DIFFERENT SOURCES
A. Plants (Fruits and Vegetables)
The inside tissue of foods from plant sources are essentially sterile, except for a few
porous vegetables (e.g., radishes and onions) and leafy vegetables (e.g., cabbage and
Brussels sprouts). 1–5 Some plants produce natural antimicrobial metabolites that can
limit the presence of microorganisms. Fruits and vegetables harbor microorganisms
on the surface; their type and level vary with soil condition, type of fertilizers and
water used, and air quality. Molds, yeasts, lactic acid bacteria, and bacteria from
genera Pseudomonas, Alcaligenes, Micrococcus, Erwinia, Bacillus, Clostridium, and
Enterobacter can be expected from this source. Pathogens, especially of enteric
types, can be present if the soil is contaminated with untreated sewage. Diseases of
the plants, damage of the surface (before, during, and after harvest), long delay
between harvesting and washing, and unfavorable storage and transport conditions
after harvesting and before processing can greatly increase microbial numbers as
well as predominant types. Improper storage conditions following processing can
also increase their numbers.
Proper methods used during growing (such as use of treated sewage or other
types of fertilizers), damage reduction during harvesting, quick washing with goodquality
water to remove soil and dirt, and storage at low temperature before and
after processing can be used to reduce microbial load in foods of plant origin.
B. Animals, Birds, Fish, and Shellfish
Food animals and birds normally carry many types of indigenous microorganisms
in the digestive, respiratory, and urinogenital tracts, the teat canal in the udder, as
well as in the skin, hooves, hair, and feathers. Their numbers, depending on the
specific organ, can be very high (large intestinal contents can have as high as 10 10
bacteria/g). Many, as carriers, can harbor pathogens such as Salmonella serovars,