TMT-labeled quantitative proteomic analysis to identify proteins associated with the stability of peanut milk.

BACKGROUND: Peanut milk benefits human health mainly due to its high protein content and suitable amino acid composition. To reveal the molecular mechanism affecting the quality of peanut milk, tandem mass tag (TMT)-labeled proteomic analysis was applied to identify the proteome variation between two peanut cultivars that produced peanut milk with the best and worst stability. RESULTS: A total of 478 differentially abundant proteins (fold change >1.2 or <0.83, P < 0.05) were identified. Most of these proteins were located in the cytoplasm and chloroplasts. Correlation analysis showed that RNA recognition motif (RRM) domain-containing protein (17.1 kDa) had a negative relationship with the sedimentation rate of peanut milk and that 22.0 kDa class IV heat shock protein was negatively correlated with the creaming index (P < 0.05). Bioinformatic analysis showed that the molecular function of RRM domain-containing protein (17.1 kDa) was associated with RNA binding and nucleotide binding, and 22.0 kDa class IV heat shock protein was involved in the pathway of protein processing in the endoplasmic reticulum. CONCLUSION: Overall, the differentially abundant proteins in the biological metabolic pathway might offer some potential markers to guide future peanut breeding, especially for the production of peanut milk. © 2021 Society of Chemical Industry.

Novel ACE Inhibitory Peptides Derived from Simulated Gastrointestinal Digestion in Vitro of Sesame (Sesamum indicum L.) Protein and Molecular Docking Study.

The aim of this study was to isolate and identify angiotensin I-converting enzyme (ACE) inhibitory peptides from sesame protein through simulated gastrointestinal digestion in vitro, and to explore the underlying mechanisms by molecular docking. The sesame protein was enzymatically hydrolyzed by pepsin, trypsin, and α-chymotrypsin. The degree of hydrolysis (DH) and peptide yield increased with the increase of digest time. Moreover, ACE inhibitory activity was enhanced after digestion. The sesame protein digestive solution (SPDS) was purified by ultrafiltration through different molecular weight cut-off (MWCO) membranes and SPDS-VII (< 3 kDa) had the strongest ACE inhibition. SPDS-VII was further purified by NGC Quest™ 10 Plus Chromatography System and finally 11 peptides were identified by Nano UHPLC-ESI-MS/MS (nano ultra-high performance liquid chromatography-electrospray ionization mass spectrometry/mass spectrometry) from peak 4. The peptide GHIITVAR from 11S globulin displayed the strongest ACE inhibitory activity (IC50 = 3.60 ± 0.10 µM). Furthermore, the docking analysis revealed that the ACE inhibition of GHIITVAR was mainly attributed to forming very strong hydrogen bonds with the active sites of ACE. These results identify sesame protein as a rich source of ACE inhibitory peptides and further indicate that GHIITVAR has the potential for development of new functional foods.

Dual-enzyme hydrolysis for preparation of ACE-inhibitory peptides from sesame seed protein: Optimization, separation, and identification.

To prepare and identify ACE-inhibitory peptides originated from sesame seed protein, peptides with strong ACE-inhibitory activities were obtained via the optimization of protease and hydrolysis conditions, and these peptides were purified and identified by membrane separation, gel filtration, and liquid chromatography-mass spectrometry. Results showed that the dual-enzyme comprised alcalase and trypsin with the enzyme activity ratio of 3:7 was suitable to produce ACE-inhibitory peptides. The highest ACE-inhibitory activity of 98.10 ± 0.26% was obtained at the following parameters, pH 8.35, E/S ratio of 6,145 U/g, and hydrolysis time of 4.4 hr. ISGAQPSLR and VVISAPSK ranked the first and second ACE-inhibitory activity among 15 identified ACE-inhibitory peptides. Both peptides influenced ACE via binding with the S1 pocket, S2 pocket, and Zn2+ ion. ISGAQPSLR even impacted the S1' pocket. ISGAQPSLR and VVISAPSK acted as a competitive and noncompetitive inhibitor, respectively. ACE-inhibitory peptides derivated from sesame seed protein have potential applications in functional food. PRACTICAL APPLICATIONS: Although sesame seed protein is proven as the precursor of ACE-inhibitory peptide, preparing ACE-inhibitory peptide from sesame seed protein is still suffering from insufficient information on hydrolysis condition and the peptide sequence. Therefore, the performance of the typical protease on preparing ACE-inhibitory peptide from sesame seed protein has been evaluated, the effect of the amino acid composition of sesame seed protein and cleavage specificity of protease on the generation of ACE-inhibitory peptide has been investigated, hydrolysis conditions have been optimized, the peptide sequence has been identified to illuminate the effect of sesame seed protein fraction on the formation of ACE-inhibitory peptide and discuss the structural characteristics. ACE-inhibitory peptides originating from sesame seed protein could apply in functional food. It is promising for dual-enzyme hydrolysis to utilize in preparation of high-value bioactive peptides.

Enzymatic Preparation and Structure-activity Relationship of Sesaminol.

As a valuable natural antioxidant, sesaminol can be used in food and medicine industries, but it is trace in sesame seeds and oil, and it is feasible to prepare sesaminol from sesaminol triglucoside (STG) which is abundant in defatted sesame cake. Therefore, in order to establish an effective enzymatic preparation method and elucidate the antioxidant structure-activity relationship of sesaminol, a suitable glycosidase for preparing sesaminol from STG were screened, enzymatic hydrolysis was optimized by single-factor test and response surface methodology, and finally, the structure-activity relationship of sesaminol was illustrated by comparative molecular field analysis (CoMFA). These results suggested that ß-galactosidase was the optimal glycosidase for enzymatic hydrolysis of STG to prepare sesaminol. Under the optimal conditions of a reaction temperature of 50°C, reaction time of 4.0 h, pH of 5.5, substrate concentration of 1.0 mg/mL, and enzyme dosage of 20 mg/mL, the conversion rate of sesaminol was 98.88±0.67%. Sesaminol displayed excellent antioxidant ability in 2,2-diphenyl-1-picrylhydrazyl (DPPH, IC50 = 0.0011 mg/mL), 2,2'-azinobis-(3-ethyl-benzothiazoline-6-sulfonate) (ABTS, IC50 = 0.0021 mg/mL) radical scavenging activities and Ferric reducing antioxidant power (FRAP, 103.2998 mol/g) compared to other sesaminol derivatives. According to －log (IC50 of DPPH) and －log (IC50 of ABTS), CoMFA models were successfully established based on Q2 >0.5 (QDPPH 2 = 0.558, QABTS 2 = 0.534). The active site of sesaminol tended to be located on the hydroxyl group of the benzene ring (R1 position). A positive correlation between the bulky and positively charged groups at the 1H, 3H-furo [3, 4-c] furan group, the small, negatively charged groups at the R1 position and the antioxidant activity of sesaminol. This study provides an effective method to prepare sesaminol, reveals the structure-activity relationship of sesaminol and provides theoretical basis to design the novel compound.

Extraction, identification and structure-activity relationship of antioxidant peptides from sesame (Sesamum indicum L.) protein hydrolysate.

To elucidate the sequence, origin and structure-activity relationship of antioxidant peptides from sesame protein, sesame protein was hydrolysed by a dual-enzyme system comprised alcalase and trypsin, then this hydrolysate was fractionated by ultrafiltration and preparative HPLC. Subsequently, peptides in the high antioxidant activity fraction were identified by nano liquid chromatography-electrospray ionization-tandem mass spectrometry (Nano-LC-ESI-MS/MS), finally the structure-activity relationship of antioxidant peptide with the strongest activity in the sesame peptides was illustrated by comparative molecular field analysis (CoMFA). The results showed that seven novel antioxidant peptides were discovered, their sequences were as follows, RDRHQKIG, TDRHQKLR, MNDRVNQGE, RENIDKPSRA, SYPTECRMR, GGVPRSGEQEQQ and AGEQGFEYVTFR. The SYPTECRMR was the hydrolysate of 2S albumin, the others derived from 11S globulin. The SYPTECRMR whose IC50 Values of DPPH and ABTS were 0.105 mg/mL and 0.004 mg/mL respectively exhibited the highest antioxidant activity among the seven sesame peptides. The active site of SYPTECRMR tended to locate on Cys6 and Met8. A positive correlation between Cys6, Met8, the bulky C-terminal amino acid residue (Arg9), the negative charged group around sulphur-containing amino acids and the antioxidant activity of SYPTECRMR was observed from the CoMFA model. The results presented herein suggested that sesame protein hydrolysates have potential applications in functional food due to their high antioxidant activity, the CoMFA model could provide insight into the structure-activity relationship of antioxidant peptide, which is useful to screen, identify and design the novel antioxidant peptide.