Physicochemical properties of whole-bean soymilk and the effect of simulated gastrointestinal digestion on its antioxidant activity

• Main Authors: Hsin-Yu Kuo, 郭心羽
• Other Authors: An-I Yeh
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/41289066495907475158

博士 === 國立臺灣大學 === 食品科技研究所 === 102 === Soymilk, made from soybean (Glycine max), is a traditional beverage in Asian countries such as China, Japan, Korea and Taiwan. In traditional soymilk processing, okara (soy pulp), rich in protein, oil, especially, in dietary fiber and some isoflavone, is filtered and hugely generated. Though part of okara is used as animal feed, it is mostly considered as waste and has caused lots of disposal problems. On the other hand, it had been proved that media mill can effectively reduce particle size of cellulose and starch to nano/submicron scale. In order to reduce the amount of okara as well as increase utilization of soybean, in this study, we performed media milling and high speed blending for whole-bean soymilk production, which were compared with soymilk produced by filtered process. By utilizing media milling, it did not have to remove okara from soymilk, and lead to a product with higher dietary fiber content (2.43 g/100 g soymilk) compared to those of filtering (0.48 g/100 g soymilk) and blending (2.26 g/100 g soymilk). Media-milled soymilk had similar particle size distribution, pH, morphology, appearance but significantly higher solid recovery (98.40 ± 0.46%), viscosity (160.59 ± 4.26 cp), stability than those of filtered one (75.67 ± 0.74%, 4.22 ± 0.02 cp, respectively) with the same amount of raw material consumed. In contrast with mean particle size of blended soymilk (volume-mean diameter (DV) 348 ± 227 μm, number-mean diameter (DN) 2.84 ± 1.79 μm), that of media-milled one (DV 26.6 ± 14.6 μm, DN 0.099 ± 0.095 μm) decreased significantly. Besides, total polyphenol (34.21 ± 2.55 mg GAE/100 g soymilk) and isoflavones (47.35 ± 0.33 mg/100 g soymilk) of media-milled soymilk were significantly higher than those of filtered (28.21 ± 0.40 mg GAE/100 g soymilk, 31.25 ± 0.07 mg/100 g soymilk) and blended (28.54 ± 2.62 mg GAE/100 g soymilk, 42.51 ± 1.05 g/100 mg soymilk) ones. What’s more, media milling might induce the transformation of isoflavones from conjugated glucoside to bioactive aglycone. By using DPPH, ABTS radical scavenging activity and oxygen radical absorbance capacity (ORAC) assay, the antioxidant activities of media-milled soymilk were better than those of filtered and blended ones. As to the sensory evaluation, the hedonic scores of filtered soymilk were significantly higher than that of media-milled one. The hedonic scores of media-milled soymilk can be elevated by appropriate dilution. After conducting the simulated gastrointestinal digestion, though total isoflavones content of soymilk decreaed, total polyphenol, isoflavone aglycone and chemical antioxidant activities (ABTS radical scavenging activity and ORAC) significantly increased. Additionally, media-milled soymilk gastrointestinal digesta possessed significantly higher total polyphenol, isoflavones content, chemical and cellular antioxidant activity (CAA) related to filtered and blended ones. It revealed that media-milled soymilk owned not only prior physicochemical properties but also higher contents of bioactive compounds and better antioxidant activity after simulated gastrointestinal digestion, therefore, can be ingested as bio-functional beverage.