| Summary: | 碩士 === 國立臺灣海洋大學 === 食品科學系 === 94 === Abstract
This study investigated the antioxidative activity in the hydrolysates of egg albumin protein (EAP), whey protein concentrate (WPC), soy protein isolate (SPI) and Tilapia muscle protein (TMP) by using the crude extract of tilapia viscera as the enzyme source. Protein substrates were hydrolyzed at 50℃ for 12 hours at different pH values (4.0, 7.0 and 9.0).The lyophilized hydrolysates were then measure for the scavenging effect on α,α-diphenyl-β-picrylhydrazyl (DPPH) radical, reducing power, inhibition on linoleic acid peroxidation, Fe2+-chelating effect, and scavenging effect on superoxide anion radical. On the whole, the WPC (at pH 7.0) and SPI (at pH 4.0) hydrolysates exhibited higher antioxidative activities, but the TMP (at pH 4.0) hydrolysate had the highest reducing power than other hydrolysates. The WPC (at pH 7.0) and SPI (at pH 9.0) were chosen to evaluate the effect by hydrolsis temperature (40℃ and 50℃) and time (0~24 hours). The results showed that the hydrolysis carried out at 40℃ for 12 hours was a better condition.
Accordingly, the lyophilized hydrolysates of WPC (at pH 7.0) and SPI (at pH 4.0), which were hydrolyzed at 40℃ for 12 hours, together with their low-molecule-weight fractions (LMW), which were treated with 80% ethanol to precipitate proteins were prepared and measured for antioxidative activity at different concentrations. The reducing power, Fe2+-chelating effect, and DPPH radical and superoxide anion scavenging effects in the WPC hydrolysate were higher than that in WPC-LMW. On the contrary, the inhibition on linoleic acid peroxidation were stronger in the latter. The SPI hydrolysate had higher inhibition on linoleic acid peroxidation, Fe2+-chelating effect, and DPPH radical and superoxide anion scavenging effects, but SPI-LMW was higher in reducing power. Among the four lyophilized powders , SPI hydrolysate was the highest in the inhibition on linoleic acic peroxidation (IC50 = 0.055 mg/mL), Fe2+-chelating effect (IC50 = 18.68 mg/mL), and scavenging effect on superoxide anion radical (IC50 = 0.10 mg/mL). On the contrary, the WPC hydrolysate was the highest in reducing power (IC50 = 2.12 mg/mL) and scavenging effect on DPPH radical (IC50 = 0.89 mg/mL). Regarding the measurement on scavenging DPPH radical, here was found that the IC50 values determined by HPLC method decreased by 36.4~58.9% as compared with that by photometric method.
The inhibitory activity against angiotensin I-converting enzyme (ACE) by the lyophilized hydrolysates of WPC (at pH 7.0) and SPI (at pH 4.0) after hydrolyzing at 40℃ for 0~24 hours. The data showed that the inhibitory activity on ACE increased with hydrolysis time. The 24-hour hydrolysates (IC50 = 0.71~0.96 mg/mL) exhibited lower ACE inhibitory activity than their low-molecule-weight fractions (IC50 = 0.24~0.35 mg/mL ).
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