Ong, Law - Hygrothermal Properties of FVFs
Table 2.2. Water activity (aw) and the microorganisms in foods (Beauchat, 1981)
aw Microorganisms Product examples
0.95 Pseudomonas, Escherichia, Proteus,
Shigells, Klebsiella, Bacillus, Clostridium
perfringens
Fresh fruit, vegetable, meat and
fish
0.91 Salmonella, Vibrio parahaemolyticus, C.
botulinum, Serratia, Lactobacillus,
Pediococcus
Cheese, ham, fruit juice concen-
trates
0.87 Most yeasts Fermented sausage, sponge cakes,
dry cheese, margarine
0.80 Most molds Fruit juice concentrates, con-
densed milk, syrup, flour, rice
0.75 Halophilic bacteria Jam, marmalade, glace fruits,
marzipan, marshmallows
0.65 Xerophilic molds Rolled oats with 10% moisture,
jelly, molasses, nuts, dried fruits
0.60 Osmophilic yeasts Dried fruits with 15-20% mois-
ture, toffees, caramels, honey
0.50 No microbial proliferation Pasta with 12% moisture, spices
with 10% moisture
0.40 No microbial proliferation Whole egg powder with 5% mois-
ture
0.30 No microbial proliferation Cookies, crackers and bread
crusts with 3-5% moisture
0.20 No microbial proliferation Whole milk powder with 2-3%
moisture, dried vegetables with
5% moisture, corn flakes with 5%
moisture
Table 2.3. Water activity threshold for enzymatic reaction in selected foods and sub-
strates (Drapron, 1985)
Food /substrate Enzyme Temperature
(°C)
Water activity thresh-
old
Grain Phytases 23 0.90
Wheat germ Glycoside-
hydrolases
20 0.20
Rye flour Amylases 30 0.75
Macaroni Phospholipases 25 - 30 0.45
Wheat flour Proteases 35 0.96