Integration of gallic acid (GA) and its derivative epigallocatechin gallate (EGCG; 20, 120, and 240 μmol/g, protein basis) into whey protein isolate (WPI) at room temperature and pH 3.0 and pH 7.0 was investigated. At pH 7.0, both phenolics caused significant structural changes and EGCG induced greater digestibility of WPI. Total sulfhydryl in WPI decreased from 28.6 to 7.6 μmol/g and surface hydrophobicity declined by nearly 50% with 240 μmol/g EGCG at pH 7.0. Similar but less appreciable changes were produced by GA and at pH 3.0. Isothermal titration and fluorescence quenching tests showed moderately weak binding of WPI with GA but strong binding with EGCG at pH 7.0. Both phenolics at high concentrations lowered the thermal transition temperature of β-lactoglobulin by 0.5 °C to 1.4 °C and promoted its digestion. The phenolics also displayed a remarkable synergism with peptides in the WPI digest exerting radical scavenging activity.

After oil bodies (OBs) were extracted from ungerminated soybean by pH 6.8 extraction, it was found that 24 and 18 kDa oleosins were hydrolyzed in the extracted OBs, which contained many OB extrinsic proteins (i.e., lipoxygenase, β-conglycinin, γ-conglycinin, β-amylase, glycinin, Gly m Bd 30K (Bd 30K), and P34 probable thiol protease (P34)) as well as OB intrinsic proteins. In this study, some properties (specificity, optimal pH and temperature) of the proteases of 24 and 18 kDa oleosins and the oleosin hydrolysis in soybean germination were examined, and the high relationship between Bd 30K/P34 and the proteases was also discussed. The results showed (1) the proteases were OB extrinsic proteins, which had high specificity to hydrolyze 24 and 18 kDa oleosins, and cleaved the specific peptide bonds to form limited hydrolyzed products; (2) 24 and 18 kDa oleosins were not hydrolyzed in the absence of Bd 30K and P34 (or some Tricine-SDS-PAGE undetectable proteins); (3) the protease of 24 kDa oleosin had strong resistance to alkaline pH while that of 18 kDa oleosin had weak resistance to alkaline pH, and Bd 30K and P34, resolved into two spots on two-dimensional electrophoresis gel, also showed the same trend; (4) 16 kDa oleosin as well as 24 and 18 kDa oleosins were hydrolyzed in soybean germination, and Bd 30K and P34 were always contained in the extracted OBs from germinated soybean even when all oleosins were hydrolyzed; (5) the optimal temperature and pH of the proteases were respectively determined as in the ranges of 35-50 °C and pH 6.0-6.5, while 60 °C or pH 11.0 could denature them.

Soybean oil bodies (OBs), naturally pre-emulsified soybean oil, have been examined by many researchers owing to their great potential utilizations in food, cosmetics, pharmaceutical, and other applications requiring stable oil-in-water emulsions. This study was the first time to confirm that lectin, Gly m Bd 28K (Bd 28K, one soybean allergenic protein), Kunitz trypsin inhibitor (KTI), and Bowman-Birk inhibitor (BBI) were not contained in the extracted soybean OBs even by neutral pH aqueous extraction. It was clarified that the well-known Gly m Bd 30K (Bd 30K), another soybean allergenic protein, was strongly bound to soybean OBs through a disulfide bond with 24 kDa oleosin. One steroleosin isoform (41 kDa) and two caleosin isoforms (27 kDa, 29 kDa), the integral bioactive proteins, were confirmed for the first time in soybean OBs, and a considerable amount of calcium, necessary for the biological activities of caleosin, was strongly bound to OBs. Unexpectedly, it was found that 24 kDa and 18 kDa oleosins could be hydrolyzed by an unknown soybean endoprotease in the extracted soybean OBs, which might give some hints for improving the enzyme-assisted aqueous extraction processing of soybean free oil.

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Oil bodies (OBs) from soybean and other plant seeds are greatly examined owing to their potential utilizations in food ingredients. The determination of its macronutrients and micronutrients would be very meaningful for its efficient utilization in the future.

Preheated (80 °C for 9 min) whey protein isolate (HWPI) was reacted with 20, 120, and 240 μmol/g (protein basis) gallic acid (GA) or epigallocatechin gallate (EGCG) at neutral pH and 25 °C. Isothermal titration calorimetry and fluorometry showed a similar trend that GA binding to HWPI was moderate but weaker than EGCG binding. However, the shift of maximal fluorescence emission wavelength in opposite directions in response to GA (blue) and EGCG (red) suggests discrepant binding patterns. Electrophoresis results showed that EGCG induced formation of HWPI complexes while GA only had a marginal effect. Both free and phenolic-bound HWPI exhibited mild antiradical activity. However, when subjected to in vitro digestion, synergistic radical-scavenging activity was produced between the phenolics and peptides with the highest synergism being observed on 120 μmol/g phenolics.

α-Galactosidase (α-GAL) dietary supplement is used to alleviate flatulence discomfort caused by raffinose family oligosaccharides (RFOs), but reported efficacy varies among consumers. This study investigated the hypothesis that factors such as stomach acid, gastrointestinal (GI) enzymes (pepsin and pancreatin), and food proteins could affect the activity of α-GAL against RFOs. Strong acidic conditions (pH < 2.0) and GI proteases were found detrimental to α-GAL whereas soy protein could protect α-GAL. In soymilk samples with 1 and 5 mg/mL protein, α-GAL retained 60 and 100% of activity (P < 0.05) throughout the entire digestion (pepsin+pancreatin, 3 h) at pH 2.5 whereas α-GAL was completely inactivated within 1 h of pepsin digestion in water. Isolated soy protein was more protective of α-GAL than soymilk protein. The results were corroborated by SDS-PAGE and the release of galactose as evidenced with the thin layer chromatography.