2009_Book_FoodChemistry

766 16 Legumes
Fig. 16.6. Soybean processing
16.3.1.2.2 Soy Milk
Soybeans are swollen and ground in the presence
of a 10-fold excess of water. Heating the suspension
close to its boiling point for 15–20 min
pasteurizes the suspension and inactivates lipoxygenase
enzyme and proteinase inhibitors. A soy
milk preparation enriched with calcium and vitamins
is of importance in infant nutrition as a replacement
for cow’s milk, which close to 7% of
infants in the USA are unable to tolerate.
16.3.1.2.3 Tofu
When calcium sulfate (3 g salt/kg milk) is added
to soy milk at 65 ◦ C, a gel (called soy “curd”)
slowly precipitates. The curd is separated from
excess fluid by gentle squeezing in a special
wooden filter box. A washing procedure then
follows. The water content of the product is about
88%. Tofu contains 55% protein and 28% fat dry
weight. In China and some other Asian countries,
tofu is the largest source of food protein. It is
consumed fresh or dried, or fried in fat and
seasoned with soy sauce.
16.3.1.2.4 Soy Sauce (Shoyu)
Defatted soy meal is used as a starting material
in the production of this seasoning sauce
(Fig. 16.7). The meal is moistened, then mixed
with roasted and crushed wheat and heated in
an autoclave for 45 min. The mix ratio in Japan
is fixed at 1:1, while in China it varies up to
4:1. Increasing the amount of soy decreases
the quality of the endproduct. The mix, with
a water content of 26%, is then inoculated
with Aspergillus oryzae and Aspergillus soyae.
Initial incubation is at 30 ◦ C for 24 h and then
at 40 ◦ C for an additional 48 h. This fermentation
starter, called “koji”, is then salted to
18% by addition of 22.6% NaCl solution.
Inoculation with Lactobacillus delbrueckii
and with Hansenula yeast species results in
lactic acid fermentation, which proceeds under
gentle aeration in order to prevent the growth