445
Chapter 32
Control by Physical Removal
introduction
Microorganisms can be physically removed from solid and liquid foods by several methods. In
general, these methods can partially remove microorganisms from food, and by doing so, they
reduce the microbial level and help other antimicrobial steps that follow to become more effective.
They are generally used with raw foods before further processing.
Physical Methods
Centrifugation
Centrifugation is used in some liquid foods, such as milk, fruit juices, and syrups, to remove suspended undesirable particles (dust, leucocytes, and food particles). The process consists of exposing the food in thin layers to a high centrifugal force. The heavier particles move outward and
are separated from the lighter liquid mass. Although this is not intended to remove microorganisms, spores, large bacterial rods, bacterial clumps and chains, yeasts, and molds can be removed
because of their heavier mass. Under high force, as much as 90% of the microbial population can
be removed. Following centrifugation, a food will have fewer thermoduric microorganisms (bacterial spores) that otherwise would have survived mild heat treatment (e.g., milk pasteurization) and
increased microbial load in the pasteurized product.
Filtration
Filtration 1,2 is used in some liquid foods, such as soft drinks, fruit juices, beer, wine, and water,
to remove undesirable solids and microorganisms and to give a sparkling clear appearance. As
heating is avoided or given only at minimum levels, the natural flavors of the products and heatsensitive nutrients (e.g., vitamin C in citrus juices) are retained to give the products natural characteristics. The filtration process can also be used as a step in the production of concentrated
juice with better flavor and higher levels of vitamins. Many types of filtration systems are available. In many filtration processes, coarse filters are used initially to remove large particles; this is
Chapter 32
Control by Physical Removal
introduction
Microorganisms can be physically removed from solid and liquid foods by several methods. In
general, these methods can partially remove microorganisms from food, and by doing so, they
reduce the microbial level and help other antimicrobial steps that follow to become more effective.
They are generally used with raw foods before further processing.
Physical Methods
Centrifugation
Centrifugation is used in some liquid foods, such as milk, fruit juices, and syrups, to remove suspended undesirable particles (dust, leucocytes, and food particles). The process consists of exposing the food in thin layers to a high centrifugal force. The heavier particles move outward and
are separated from the lighter liquid mass. Although this is not intended to remove microorganisms, spores, large bacterial rods, bacterial clumps and chains, yeasts, and molds can be removed
because of their heavier mass. Under high force, as much as 90% of the microbial population can
be removed. Following centrifugation, a food will have fewer thermoduric microorganisms (bacterial spores) that otherwise would have survived mild heat treatment (e.g., milk pasteurization) and
increased microbial load in the pasteurized product.
Filtration
Filtration 1,2 is used in some liquid foods, such as soft drinks, fruit juices, beer, wine, and water,
to remove undesirable solids and microorganisms and to give a sparkling clear appearance. As
heating is avoided or given only at minimum levels, the natural flavors of the products and heatsensitive nutrients (e.g., vitamin C in citrus juices) are retained to give the products natural characteristics. The filtration process can also be used as a step in the production of concentrated
juice with better flavor and higher levels of vitamins. Many types of filtration systems are available. In many filtration processes, coarse filters are used initially to remove large particles; this is