| Summary: | 博士 === 國立嘉義大學 === 食品科學系研究所 === 102 === Okara was heated (70℃, 20 min), defatted with hexane, alkaline-treated (2N NaOH) and precipitated at isoelectric point to obtain okara protein isolate (OPI). OPI was further hydrolyzed with proteases either by single enzyme (including Alcalasem, Protamex, Flavourzyme and Papain) or by two-stage hydrolysis consisting of Protamex and Flavourzyme. In the first stage of the two-stage hydrolysis, Protamex was used with the hydrolysis conditions of 5% substrate concentration, E/S=1%, 50℃, pH 7.0 and 120 min; and the hydrolytic product was denoted as P120. In the second stage, Flavourzyme was used with the hydrolysis conditions of E/S=0.5%, 50℃, pH 7.0 and 60 min; and the hydrolytic product was denoted as P120+F60. The results showed that two-stage hydrolysis could achieve the degree of hydrolysis (DH) of OPI to 22.3% with less bitter taste.
P120+F60 was consecutively separated into four fractions (denoted as Ret 1 , Per 2, Per 3and Per 4) by ultrafiltration membranes with molecular-weight cut-off (MWCO) of 10kDa, 3kDa and 1kDa.The four fractions as well as OPI, P120 and P120+F60 were tested for their hydroxyl and ABTS free radical scavenging activities. The scavenging activities for both free radicals were more than 49% when the concentration of P120+F60 was 10 mg/mL. However, the scavenging activities for both free radicals were 85% when Per 3 and Per 4 were used at the level of 10 mg/mL, which was comparable to BHA and ascorbic acid at the level of 1.0 mg/mL.
The inhibitory activities of angiotensin-I converting enzyme (ACE) of the above okara protein products were also tested. The IC50 values for OPI, P120+F60 and Per 4 were 39.1, 0.56 and 0.09 mg/mL, respectively. The inhibitory activity of Per 4 was about one fourth of the antihypertension drug Enalapril. The amino acid composition analysis revealed that the content of hydrOPIHobic amino acid was 40.08%, and the high level of prolein and leucine might partly explain the antioxidant and anti-AGE activities.
The ability of OPI and hydrolysate fractions for catalyzing lipolysis in differentiated 3T3-L1 adipocytes was tested. Relative lipid accumulation (RLA) was decreased by 37% and the glycerol release was increased by 108.3% when P120+F60 at the level of 400 ppm and Per 4 at the level of 100 ppm were used. Disintegration of fat drops was observed when adipocytes were stained with Oil-Red O.
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