Fundamental Food Microbiology, Third Edition - Fuad Fathir

48 FUNDAMENTAL FOOD MICROBIOLOGY
different types of molds, such as Alternaria, Fusarium, and Aspergillus. Vegetables
can have enteric pathogens, especially if animal and human wastes and polluted
water are used for fertilization and irrigation. They include Lis. monocytogenes,
Salmonella, Shigella, Campylobacter, Clo. botulinum, and Clo. perfringens. They
can also have pathogenic protozoa and parasites. If the vegetables are damaged, then
plant pathogens (e.g., Erwinia) can also predominate. Many of the microorganisms
can cause different types of spoilage (different types of rot) of raw products. Pathogens
can grow in plant products and cause foodborne diseases (e.g., listeriosis or
botulism). Lactic acid bacteria have important roles in the natural fermentation of
vegetables (e.g., sauerkraut). Different methods used to process vegetables and
vegetable products greatly reduce the microbial population.
Fruits, because of their high carbohydrate content and low pH, favor the growth
of different types of molds, yeasts, and lactic acid bacteria. Microorganisms generally
come from air, soil, insects, and harvesting equipment. In general, microbial populations
are 10 3–6 /g. Improperly harvested and processed fruits can have pathogens
that survive, grow, and cause foodborne disease. Molds, yeasts, and bacteria can
cause different types of spoilage. Natural flora, especially yeasts in fruits, can be
important in alcohol fermentation.
Microorganisms enter nuts from soil (peanuts) and air (tree nuts). During processing,
air, equipment, and water can also be the sources. Nuts are protected by
shells, but damage on the shell can facilitate microbial contamination. Raw nuts and
nutmeats can have 10 3–4 microorganisms/g, with Bacillus and Clostridium spores,
Leuconostoc, Pseudomonas, and Micrococcus predominating. Because of a low A w,
bacteria do not grow in the products. However, when used as ingredients, they can
cause microbiological problems in the products. Molds can grow in nuts and nutmeats
and produce mycotoxins (from toxin-producing strains such as aflatoxins by
Aspergillus flavus).
VII. CEREAL, STARCHES, AND GUMS
Cereal includes grains, flour, meals, breakfast cereals, pasta, baked products, dry
mixes, and frozen and refrigerated products of cereal grains (also beans and lentils).
Starches include flours of cereals (e.g., corn, rice), tapioca (from plant), potatoes,
and other tubers. Gums are used as stabilizers, gelling agents, and film, and are
obtained from plants, seaweeds, and microorganisms (e.g., tragacanth, pectin, xanthan,
agar, and carrageenan) and as modified compounds (e.g., carboxymethyl cellulose).
They are rich in amylose and amylopectin, but can also have simple sugars
(e.g., in grains) and protein (e.g., in lentils). Microbial sources are mainly the soil,
air, insects, birds, and equipment. 1,2
Unprocessed products (grains) may contain high bacterial levels (aerobic plate
count @10 4 /g, coliform @10 2 /g, yeasts and molds @10 3 /g). They may also contain
mycotoxins produced by toxicogenic molds. Processed products may also contain
a wide variety of yeasts, molds, and bacteria. Flours and starches may have higher
microbial counts, similar to those of grains, whereas processed products (such as
breakfast cereals and pasta) may contain aerobic plate count of 10 2–3 /g, coliform of