Changes in Antioxidant Activity of Alcalase-Hydrolyzed Soybean Hydrolysate under Simulated Gastrointestinal Digestion and Transepithelial Transport

Peptides from Alcalase-hydrolyzed soybean protein hydrolysate(SPH)may hold the potential as natural antioxidants.In addition,the effect of human gastrointestinal(GI)tract on peptide bioavailability needs to be explored.In this study,the impact of simulated GI digestion and transepithelial transport on various antioxidant properties of SPH were investigated.SPH displayed DPPH radical scavenging(IC50=4.22 mg/m L),ABTS·+radical scavenging(IC50=2.93 mg/m L),reducing power and metal ion-chelating activities(IC50=0.67 mg/m L).Furthermore,SPH significantly(P<0.05)inhibited the generation of intracellular reactive oxygen species(ROS)in Caco-2 cells.After simulated GI digestion,the antioxidant properties of SPH were enhanced,except for a decrease in ABTS·+radical scavenging activity.After transepithelial transport,the permeates maintained partial antioxidant activity and the LC-MS/MS data further identified the absorbed soybean peptides.These results suggest that SPH contains the antioxidant peptides that are potentially bioavailable and can be regarded as a promising source of functional food ingredients.

Antioxidant Activity and Protective Effects of Alcalase-Hydrolyzed Soybean Hydrolysate in Human Intestinal Epithelial Caco-2 Cells

Soybeans are known as a promising source of bioactive peptides.However,knowledge on the antioxidant behaviors of soybean protein hydrolysate(SPH)in the human intestinal epithelium is limited.In this study,SPH was prepared with Alcalase and subsequently ultrafiltered into four peptide fractions as SPH-I(<3 kDa),SPH-II(3~5 k Da),SPH-III(5~10 k Da)and SPH-IV(>10 kDa).The antioxidant properties of SPH and membrane fractions were investigated using different chemical assays and their protective effects against oxidative stress were evaluated using H2 O2-stressed human intestinal Caco-2 cells.Results showed that SPH-I exhibited the strongest 2,2-diphenyl-1-picrylhydrazyl(DPPH)radical scavenging activity(IC50=2.56 mg/m L)and reducing capacity while SPH-III had the best metal ion-chelating activity(IC50=0.29 mg/m L).Both SPH and the peptide fractions dose-dependently suppressed intracellular reactive oxygen species(ROS)accumulation induced by H2O2 in Caco-2 cells,but the strongest inhibitory effect was observed for SPH-I.Amino acid(AA)results revealed that SPH-I was rich in hydrophobic and antioxidant AAs,which could contribute to its stronger antioxidant properties.Additionally,SPH-I protected Caco-2 cells from H2O2-induced oxidative stress via inhibiting lipid peroxidation and stimulating antioxidant enzyme activities.These results suggest that SPH-I and constitutive peptides can be beneficial ingredients with antioxidant properties and protective effects against ROS-mediated intestinal injury.

Possible Mechanism Associated with Herbicidal Activity of Soybean Meal Hydrolysate (SMH)

Soybean meal hydrolyzate （SMH） has been proposed for use as a natural preemergence herbicide.However,the mechanism by which SMH exerts its herbicidal activity remains unclear.In this paper,the herbicidal activities of SMH against perennial ryegrass （Lolium perenne L.） under non-sterile and sterile conditions were evaluated and the relationship between the molecular weight of the ultrafiltration （UF） fractions of SMH and their herbicidal activities were investigated.Besides,the ammonia content changes of the media of SMH treatments 7 d after incubation were also analyzed.The results showed that SMH inhibited the radicle growth of germinating L.perenne seeds in a dose-dependent manner under non-sterile condition.However,SMH in the concentrations investigated increased the radicle length and shoot length by 14-17% and 11-15% respectively under sterile condition.The ammonia contents in the SMH media at all treatments increased greatly from less than 0.01 mg L-1 to up to 11.86-41.37 mg L-1 after 7 d incubation under non-sterile condition.However,ammonia content did not change under sterile condition,proposing that the herbicidal activity might be caused by the free ammonia released from SMH by microbial activity.There was no difference on the perennial ryegrass radicle inhibition among the UF fractions of SMH on an equivalent N basis.It could be concluded that SMH exerted its herbicidal activity through the free ammonia released under non-sterile condition instead of by specific peptide（s） in SMH.

Calcium-binding ability of soy protein hydrolysates

This present study investigated the ability of various soy protein hydrolysates (SPHs) in binding calcium. It was demonstrated that the amount of Ca-bound depended greatly on the SPHs obtained using different proteases, which included: neutrase, flavourzyme, protease M and pepsin. The maximum level of Ca-bound (66.9 mg/g) occurred when protease M was used to hydrolyze soy protein. Peptide fragments exhibiting high Ca-binding capacity had molecular weights of either 14.4 or 8–9 kDa. The level of Ca-bound increased linearly with the increment of carboxyl content in SPHs, and further deamidation on SPHs from protease M improved Ca-binding of the hydrolysate.

Separation and Identification of Glutamine Peptides from Defatted Soybean Meal by Enzymatic Hydrolysis

Glutamine peptides were obtained from defatted soybean meal by enzymatic hydrolysis using a combination of Protamex~? and trypsinase. The results showed that the extent of hydrolysis and the concentration of Gln peptides in the hydrolysate were 22.02%and 6.05 mmol/L, respectively. The hydrolysates were fractionated by size-exclusion chromatography on a Sephadex G-15 into five major fractions(GelF1–GelF5). The peptide(GelF1) fraction with the highest glutamine peptide content(51.8%) was further evaluated to determine its molecular weight distribution. Most(92.37%) peptides were less than 1 000 Da. Glutamic acid and glutamine were the most abundant amino acids, accounting for up to 12.98% of the total amino acid content. In addition, the total amino acid content in GelF1 was higher than that in GelF2 and GelF3.