Development, validation, and application of a fast, simple, and robust SPE-based LC-MS/MS method for quantification of angiotensin I-converting enzyme inhibiting tripeptides Val-Pro-Pro, Ile-Pro-Pro, and Leu-Pro-Pro in yoghurt and other fermented dairy products

Exploring structural features of sleep-enhancing peptides derived from casein hydrolysates by chemometrics and random forest methodology

Milk casein is regarded as source to release potential sleep-enhancing peptides. Although various casein hydrolysates exhibited sleep-enhancing activity, the underlying reason remains unclear. This study firstly revealed the structural features of potential sleep-enhancing peptides from casein hydrolysates analyzed through peptidomics and multivariate analysis. Additionally, a random forest model and a potential Tyr-based peptide library were established, and then those peptides were quantified to facilitate rapidly-screening. Our findings indicated that YP-, YI/L, and YQ-type peptides with 4-10 amino acids contributed more to higher sleep-enhancing activity of casein hydrolysates, due to their crucial structural features and abundant numbers. Furthermore, three novel strong sleep-enhancing peptides, YQKFPQY, YPFPGPIPN, and YIPIQY were screened, and their activities were validated in vivo. Molecular docking results elucidated the importance of the YP/I/L/Q- structure at the N-terminus of casein peptides in forming crucial hydrogen bond and π-alkyl interactions with His-102 and Asn-60, respectively in the GABAA receptor for activation.

Release of Leu-Pro-Pro from corn gluten meal by fermentation with a Lactobacillus helveticus strain

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitory peptides are potential alternatives to the synthetic ACE inhibitory drugs, but the in vivo antihypertensive effects of most of them have not been confirmed. The tripeptide Leu-Pro-Pro (LPP) is one of the few peptides that have been proved clinically effective in reducing the blood pressure of hypertensive patients and casein is currently its major source. LPP is contained in multiple fractions of zein, and corn gluten meal (CGM) is hence a potential new source of LPP. For this purpose, CGM was fermented with a Lactobacillus helveticus strain and the medium composition was optimized; the decoloration of the resultant hydrolysate was investigated as well.

RESULTS

LPP could be successfully released from CGM by fermentation with the strain Lactobacillus helveticus CICC 22536. The highest LPP content and protein recovery of 561 mg kg^-1 and 14.92% occurred in the medium containing 20 g L^-1 glucose, 15 g L^-1 beef extract, 60 g L^-1 CGM, 10 g L^-1 CaCO₃ , 0.5 g L^-1 NaCl, and inoculation amount 6%. The supplementation of Flavourzyme® further improved the two parameters to 662 mg kg^-1 and 36.94%, respectively. The permeate of the hydrolysate after ultrafiltration through a 5 kDa membrane could be effectively decolored by the macroporous resin XAD-16 without notable protein loss, and its LPP content was further boosted to 743 mg kg^-1 .

CONCLUSION

CGM is a potential new source of LPP and its ultrafiltered and decolored hydrolysate could be used to develop new antihypertensive functional foods. © 2021 Society of Chemical Industry.