446 ◾ Fundamental Food Microbiology
followed by ultrafiltration. Ultrafiltration methods, depending on pore size of the filter materials
(0.45–0.7 mm), are effective in removing yeasts, molds, and most bacterial cells and spores from
liquid products.
Filtration of air is also used in some food-processing operations, such as spray drying of milk,
to remove dust from the air used for drying. The process also removes some microorganisms with
dust from the air, and this reduces the microbial loads in food.
Trimming
Fruits and vegetables showing damage (with a greater chance of microbial contamination) and
spoilage are generally trimmed. 3–5 In this manner, areas heavily contaminated with microorganisms are removed. Trimming the outside leaves in cabbage used for sauerkraut production also
helps reduce microorganisms coming from soil. Trimming is also practiced for the same reason
to remove visible mold growth from hard cheeses, fermented sausages, bread, and some low-pH
products. However, if a mold strain is a mycotoxin producer, trimming does not ensure removal
of toxins from the remaining food. Trimming is also used regularly to remove fecal stain marks,
unusual growths, and abscesses or small, infected areas from carcasses of food animals and birds.
Although this method helps remove highly contaminated areas, it does not ensure complete
removal of the causative microorganisms. Thus, a beef carcass can have an area contaminated with
feces along with enteric pathogens. Merely removing the visibly tainted area by trimming does not
help remove pathogens from the surrounding areas that do not show the taint. This is an important concern in the production of safer foods.
Washing
Washing equipment and work areas has been discussed under cleaning and sanitation in Chapter
31. Here, only washing foods is discussed. 6–8 Fruits and vegetables are washed regularly to reduce
temperature (which helps reduce the metabolic rate of produce and microbial growth) and remove
soil. Washing also helps remove the soil-laden microorganisms from food, especially from raw
fruits and vegetables. It is also used for shell eggs to remove fecal materials and dirt. During
the processing of chicken and turkey, the carcasses are exposed to water several times. During
defeathering, they are exposed to hot water; following evisceration, they are given spray washings; and finally they are exposed to cold water in a chilling tank. Although these treatments are
expected to reduce microbial load, they can spread contamination of undesirable microorganisms,
particularly enteric pathogens. Thus, higher percentages of chicken have been demonstrated to be
contaminated with salmonellae when coming out of the chill tank than before entering the tank.
This aspect is discussed in Chapter 36. Carcasses of food animals, such as beef, pork, and lamb, are
washed to remove hair, soil particles, and microorganisms. Instead of hand-washing, automated
machine-washing at a high pressure is currently used to effectively remove undesirable materials
and microorganisms from the carcass. In addition to high pressure, the effectiveness of hot water,
steam, ozonated water, and water containing chlorine, acetic acid, propionic acid, lactic acid,
tripolyphosphates, or bacteriocins (nisin and pediocin) of lactic acid bacteria has been studied for
removing microorganisms, particularly enteric pathogens, such as Salmonella spp., Campylobacter
jejuni, Escherichia coli O157:H7, and Listeria monocytogenes, separately or in combination. The
results were not consistent. Some of these agents also have a bactericidal property. However, studies show that all the agents can reduce bacterial contamination to a certain level from the carcass surfaces, and a combination of two or more components may be better. 3,4 The European
followed by ultrafiltration. Ultrafiltration methods, depending on pore size of the filter materials
(0.45–0.7 mm), are effective in removing yeasts, molds, and most bacterial cells and spores from
liquid products.
Filtration of air is also used in some food-processing operations, such as spray drying of milk,
to remove dust from the air used for drying. The process also removes some microorganisms with
dust from the air, and this reduces the microbial loads in food.
Trimming
Fruits and vegetables showing damage (with a greater chance of microbial contamination) and
spoilage are generally trimmed. 3–5 In this manner, areas heavily contaminated with microorganisms are removed. Trimming the outside leaves in cabbage used for sauerkraut production also
helps reduce microorganisms coming from soil. Trimming is also practiced for the same reason
to remove visible mold growth from hard cheeses, fermented sausages, bread, and some low-pH
products. However, if a mold strain is a mycotoxin producer, trimming does not ensure removal
of toxins from the remaining food. Trimming is also used regularly to remove fecal stain marks,
unusual growths, and abscesses or small, infected areas from carcasses of food animals and birds.
Although this method helps remove highly contaminated areas, it does not ensure complete
removal of the causative microorganisms. Thus, a beef carcass can have an area contaminated with
feces along with enteric pathogens. Merely removing the visibly tainted area by trimming does not
help remove pathogens from the surrounding areas that do not show the taint. This is an important concern in the production of safer foods.
Washing
Washing equipment and work areas has been discussed under cleaning and sanitation in Chapter
31. Here, only washing foods is discussed. 6–8 Fruits and vegetables are washed regularly to reduce
temperature (which helps reduce the metabolic rate of produce and microbial growth) and remove
soil. Washing also helps remove the soil-laden microorganisms from food, especially from raw
fruits and vegetables. It is also used for shell eggs to remove fecal materials and dirt. During
the processing of chicken and turkey, the carcasses are exposed to water several times. During
defeathering, they are exposed to hot water; following evisceration, they are given spray washings; and finally they are exposed to cold water in a chilling tank. Although these treatments are
expected to reduce microbial load, they can spread contamination of undesirable microorganisms,
particularly enteric pathogens. Thus, higher percentages of chicken have been demonstrated to be
contaminated with salmonellae when coming out of the chill tank than before entering the tank.
This aspect is discussed in Chapter 36. Carcasses of food animals, such as beef, pork, and lamb, are
washed to remove hair, soil particles, and microorganisms. Instead of hand-washing, automated
machine-washing at a high pressure is currently used to effectively remove undesirable materials
and microorganisms from the carcass. In addition to high pressure, the effectiveness of hot water,
steam, ozonated water, and water containing chlorine, acetic acid, propionic acid, lactic acid,
tripolyphosphates, or bacteriocins (nisin and pediocin) of lactic acid bacteria has been studied for
removing microorganisms, particularly enteric pathogens, such as Salmonella spp., Campylobacter
jejuni, Escherichia coli O157:H7, and Listeria monocytogenes, separately or in combination. The
results were not consistent. Some of these agents also have a bactericidal property. However, studies show that all the agents can reduce bacterial contamination to a certain level from the carcass surfaces, and a combination of two or more components may be better. 3,4 The European