This study aimed to determine the oxidation by hydroxyl free radicals of the myosin head (S1) and tail (Rod) from porcine myofibrillar protein (MP) hydrolyzed by trypsin and to investigate the effect of clove extract on protein oxidation sites. To this end, unoxidized MP, oxidized MP and oxidized MP bound to clove extract were analyzed by one-dimensional electrophoresis, two-dimensional electrophoresis and mass spectrometry (MS). The results of one-dimensional electrophoresis showed that clove extract had a better protective effect on the S1 site. The small fragments generated by the decomposition of Rod and S1 were cross-linked to actin mainly through disulfide bonds. The results of two-dimensional electrophoresis and MS confirmed that subunits or fragments of major MP components such as myosin or actin were produced after MP oxidation, and the addition of clove extract effectively controlled the generation of these fragments, confirming the inhibitory effect of clove extract on protein oxidation at the molecular level. The MS identification of the peptides showed that the main amino acid sites modified by MP oxidation induced by hydroxyl radicals were methionine and cysteine. This study shows that the addition of clove extract in meat processing and storage can improve the functional properties of meat products.

In this study, black soybean protein was enzymatically hydrolyzed to prepare xanthine oxidase (XOD) inhibitory peptide. Based on XOD inhibitory activity and degree of hydrolysis (DH), various proteases were screened, and the hydrolysis parameters were optimized. Furthermore, the protein hydrolysate was fractionated by membrane separation into several fractions. The molecular mass ranges of the resulting fractions were determined based on XOD inhibitory activity, and their amino acid composition, molecular mass distribution, peptide sequences, activity and stability were analyzed. The results showed that the optimum enzymatic hydrolysis conditions were as follows: alkaline protease dosage of 1.5%, hydrolysis time of 4 h, temperature of 50 ℃, pH 9.0, and substrate concentration of 3%. Under the optimized conditions, the XOD inhibition rate and DH of the protein hydrolysate were 73.61% and 21.29%, respectively. The XOD inhibitory activity of F3, obtained from ultrafiltration of the hydrolysate, was the highest (with a half-maximal inhibitory concentration (IC₅₀) of 8.76 mg/mL), with the molecular mass ≤ 1500 Da. In F3, hydrophobic and basic amino acids accounted for 56.66% and 20.16% of the total amino acids, respectively. This fraction had good stability under high-temperature treatment, simulated gastric and trypsin digestion. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) identified 18 peptides in F3, with an average molecular mass of approximately 500–1400 Da. In these peptides, hydrophobic amino acids at the N-terminus and C-terminus accounted for 44.86% and 33.14%, respectively, and basic amino acids accounted for 33.57% and 39.29% of the total amino acid residues, respectively. The results of this study provide a theoretical basis for the high value utilization of black bean protein.

To enrich the flavor and nutritional efficacy of soymilk powder, this study investigated the effects of adding different ratios of pea peptides on the quality, nutrition and flavor of soymilk powder. The reconstitutability of soymilk powder was examined based on solubility and caking rate, and its in vitro bioactive functions were evaluated in terms of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and cholesterol scavenging capacity. The changes in the structural properties and flavor quality of soymilk powder caused by addition of pea peptides were explored by Fourier transform infrared (FTIR) spectroscopy, nanoparticle size analyzer, confocal laser scanning microscopy (CLSM), and headspace solid phase microextraction (HS-SPME)-gas chromatography-mass spectrometry (GC-MS). The results showed that the addition of 30%pea peptides to soymilk powder increased the protein content by 13.05% and solubility by 11.23%, decreased the caking rate by 4.20%, enhanced the DPPH radical and cholesterol scavenging capacity by 19.84% and 21.25%, respectively, and significantly improved the reconstitutability in hot water at 70 ℃. The structural analysis results revealed that pea peptide addition altered the secondary structure of proteins, reduced the average particle size, and resulted in more uniform particle size distribution in reconstituted soymilk, thereby improving the solubility of soymilk powder. Additionally, pea peptide addition changed the concentrations of the key flavor components geranylacetone, myristic acid, 3-methylthiopropanal, 2-methylpyrazine and 2,5-dimethylpyrazine in reconstituted soymilk, while decreasing the concentrations of off-flavor substances, such as hexanal, trans-2-nonenal, nonanal, n-hexanol, 1-octen-3-ol and naphthalene.