Slide 1

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