protein, health functional ingredie

protein, health functional ingredients, and fermented food (Bra’s,
Bernardino, Lopes, & Menezes, 2005; Kim, Choi, & Joo, 1992; Kim
et al., 2008; Uhm & Yoon, 2011). The powder form of soybean or
soybean powder is widely used for its convenience and efficacy
as well as the economic value of low import tax rate compared
to the whole soybean. In addition, the powder form of soybean
can be easily applied to extract oil and protein as well as to mix
with other food ingredients to produce processed food, such as
whole soybean curd and modern soya paste. Generally, soybean
contains about 20% of lipid and 40% of protein. Due to such high
content of lipid, soybean becomes easily oxidised when it is processed
to the powder form. The pulverization process breaks the
cell structure of soybean and the lipid placed in the dried soybean
is exposed to the air and light (Chun, Kim, Mok, Lee, & Kwon, 2003,
chap. 10). In the soybean powder, the reaction of oil with oxygen in
the air is critical and not desirable because the reaction will
adversely affect the flavour in the final product made of soybean
powder. It might be an important to characterise the effect of
temperature and the oxygen level in the pulverizer on the oxidation
of soybean during powdering process.
The degree of rancidity is evaluated by measuring the level of
compounds formed by lipid oxidation. Methods for assessing
secondary oxidation products of lipid are thiobarbituric acid(TBA)
test, oil stability index(OSI) method, fluorescence assay
(Fereidoon, 2005, chap. 8). Among these methods, TBA test is
the most widely used method to detect the oxidation of lipids
in food area due to its simplicity and accuracy, although its detail
mechanism upon each species is rather uncertain. Among these
methods, TBA test is the most widely used method to detect
the oxidation of lipids in foods due to its simplicity and accuracy,
although its detail mechanism upon each species is rather uncertain.
To overcome the weakness of TBA test, several modifications
on TBA test were reported (Asakawa & Matsushita, 1979;
Draper et al., 1993; Hu & Zhong, 2010). The red pigment
produced after reacting thiobarbituric acid (TBA) directly with
oxidised foods or their distillates has been identified to be a condensation
product of one molecule of malondialdehyde (MDA)
with two molecules of TBA. As MDA is believed to be derived
from some decomposition product of the oxidised unsaturated
fatty acids, spectrophotometric measurement of the TBA–MDA
complex gives what is thought to be a quantitative measure of
fat oxidation. Most of chemical methods require a process to extract
the oil from the food to evaluate the oxidation of lipids. But
TBA test can directly detect the lipid oxidation from the powder
without extracting the oil. Such direct measurement provides
time efficiency and high accuracy.