220 Chapter 11
Table 11.1. The lower a w range of development of microorganisms
Bacteria Yeasts Molds a w
E. coli 0.99
Str. fecalis 0.98
Vib. metschnikovii 0.97
Pse. fl uorescens 0.97
Clo. botulinum 0.97
Campylobacter ssp. 0.97
Shighella 0.97
Yersinia enterocolitica 0.97
Clo. perfringens 0.96
Bac. cereus 0.96
Bac. subtilis 0.95
Sal. newport 0.95
Ent. aerogenes 0.94
Microbacterium 0.94
Vib. parahaemolyticus 0.94
Lac. viridescens Schizosaccharomyces Rhisopus 0.93
Mucor 0.93
Rodotorula 0.92
Mic. roseus Pichia 0.91
Anaer. Staphylococcus 0.91
Lactobacillus Saccharomyces 0.90
Pediococcus Hansenula 0.90
Candida Asp. niger 0.88
Debaryomyces 0.88
Torulopsis Cladosporium 0.87
Staphylococcus aureus Torulaspora Paecilomyces 0.86
Listeria monocyt. 0.83
Penicillium 0.80
Asp. ochraceus 0.80
Halophilic bacteria 0.75
Asp. glaucus 0.72
Chrysosporium fastidum 0.70
Zygosaccharomyces rouxii Monascus bisporus 0.60The a w of the material has to be decreased
to a certain level in order to inhibit the growth
of contaminating microorganisms. During
drying, this decrease will be achieved by
lowering the moisture content. It is necessary
to know the relation between the moisture
content and a w. This relation is rather com-
plicated and changes from material to mate-
rial. Two groups of components are able to
diminish the a w value:- the water soluble compounds
- materials able to swell in water (In meat,
structural proteins are such components.)
In meat products, the fi rst group is impor-
tant, and in meat meal, it is the second one.