Fundamental Food Microbiology, Third Edition - Fuad Fathir

226 FUNDAMENTAL FOOD MICROBIOLOGY
which may be a major reason for food fermentation being so popular among early
civilizations located in high-temperature zones. The knowledge of safety and stability
of fermented foods has been transferred through the centuries and helped us understand
their scientific basis.
It is now known that the food-grade bacteria associated with food fermentation
can produce several types of metabolites that have antimicrobial properties, some
of which are listed in Table 16.1. 1 There could be many more that are currently not
identified. At present, there is an increased interest in the use of these antimicrobials
in nonfermented foods to increase their stability and safety. Some of them, such as
lactate and acetate (vinegar), have been used in many foods for a long time, whereas
the others have generated much interest as potential food biopreservatives in place
of some currently used nonfood preservatives such as nitrite, sulfite, parabens,
diacetate, and ethylformate. Their effectiveness as food biopreservatives is discussed
in this chapter. In addition, currently some yeasts have been found to inhibit the
growth of molds in fruits and vegetables. This aspect is also briefly discussed.
II. VIABLE CELLS OF LACTIC ACID BACTERIA AS PRESERVATIVES
The process involves the addition of viable cells of mesophilic Lactococcus lactis,
some Lactobacillus species, and Pediococcus species in high numbers to control
spoilage and pathogenic bacteria during the refrigerated storage of a food at or below
5�C. 2 In the presence of mesophilic lactic acid bacteria, the growth of psychrotrophic
spoilage and pathogenic bacteria is reported to be controlled. Growth of some of
these spoilage and pathogenic bacteria at slightly higher temperatures (@10 to 12�C)
is also reduced. Studies were conducted by adding lactic acid bacteria to fresh meat,
seafood, liquid egg, and some processed meat products, such as bacon, against
Clostridium botulinum, Salmonella serovars, and Staphylococcus aureus. In refrigerated
raw milk, meat, egg, and seafood, cells of Lactobacillus, Lactococcus, and
Leuconostoc species were added to control the growth of psychrotrophic spoilage
bacteria such as Pseudomonas spp. In some studies, growth of the psychrotrophs
was inhibited by 90% or more during 4 to 10 d of refrigerated storage. Addition of
cells of lactic acid bacteria in refrigerated raw milk also increased the yield of cheese
and extended the shelf life of cottage cheese.
The inhibitory property can be because of the release of intracellular antimicrobial
compounds, such as organic acids, bacteriocins, and hydrogen peroxide, from
Table 16.1 Antimicrobial Compounds of Food-Grade Bacteria
Metabolites Effectiveness
Organic acids: lactic, acetic, propionic Against bacteria and fungi
Aldehydes, ketones, and alcohols:
acetaldehyde, diacetyl, ethanol
Against bacteria
Hydrogen peroxide Against bacteria, fungi, and phages
Reuterine Against bacteria and fungi
Bacteriocins Against Gram-positive bacteria, normally