In Vitro Digestibility
(IVPD)
The vitro digestibility of samples by thermal treatment conditions was
determined using the method of Hao et al [22] and Di et al.
[21]. The vitro gastric and intestinal digestion were simulated by
the pepsin and trypsin, respectively. The digestive base fluid
(simulated intestinal fluid (SIF) and simulated gastric fluid (SGF)) was
prepared according to Hao et al. before the experiment [22]. The
experimental steps were as follows: the sample solution (1g
100mL-1) and an equal amount of SGF solution and
pepsin (2000 U mL-1) were mixed, then the pH of
mixture solution was adjusted to 2.0 with 1 M HCl. Thereafter, the
mixture was incubated in Shaking Water Bath with 150 rpm at 37 ºC. The
digestive solution was collected at different time including 0, 1, 5,
10, 30, 60 and 120 min. The gastric digestion was terminated by boiling
water bath immediately for 10 min. The digestion solution was
centrifugated at 4700 × g for 15 min at 8 °C. Then, the bicinchoninic
acid (BCA) method was used to determine the protein content in
supernatant [21]. The vitro digestibility rate of walnut meal flour
was expressed according to the following equation.
\(\text{IVPD}\left(\%\right)=\frac{PC_{0}-PC_{t}}{PC_{0}}\times 100\)(6)
Where PC0 was the initial protein content;
PCt was the protein content after simulated in vitro
digestion.
SIF solution and sample solution digested by pepsin was mixed in a ratio
of 1:1 (v/v) and the trypsin solution with the activity of 1000 U
mL-1 was added at the same time. The pH of mixture
solution was adjusted to 7.0 with 1 M NaOH. Then, the mixture was
incubated and oscillated in a water bath at 37 ºC for 0, 1, 5, 10, 30,
60 and 120 min. Finally, the intestinal digestion was ended in ice bath
for 30 min. After centrifugation, the protein content of supernatant was
measured as above described. All data was done in triplicate.