Isolation, purification, characterization, and analysis of the antioxidant activity of antioxidant peptides from walnut milk fermented with Lactobacillus paracasei SMN-LBK

Microbial fermentation is an important method to obtain antioxidant peptides. In this study, Lactobacillus paracasei SMN-LBK was used to ferment biprotein (walnut milk) to enhance the antioxidant capacity of the active peptide. The optimal fermentation process of 5% inoculum, 1:7 plant protein ratio, 37 °C and 12 h resulted in 77.63% ± 0.36% DPPH scavenging, 93.31% ± 0.25% ABTS scavenging and 79.37% ± 0.02% metal ion chelating capacity. The hydrolysis products were classified into three molecular weight classes using an ultrafiltration membrane system. DPAP-3 with a molecular weight of less than 3 kDa had the highest antioxidant activity. DPAP-3 was further separated into three subclasses using gel filtration chromatography. These subclasses were characterized using nano-liquid chromatography-tandem mass spectrometry (NanoLC-MS/MS) and screened by searching https://biochemia.uwm.edu. Four antioxidant peptides were identified using a combination of hydrophobic amino acids, positive ion-charge interactions, and numerical values. Two of these peptides were from animals and one from plants. Their amino acid sequences are as follows PCRGVLLR, IHIPLPRWV, QSKVLPVPQK, and KVLPVPQKA, with molecular docking binding energies of −7.8, −8.3, −7.4, and −7.7 kcal/mol, respectively. The results suggest that fermentation of plant-animal proteins with Lactobacillus paracasei can produce antioxidant peptides that can be used as functional ingredients in food products. This has the potential to conserve animal protein resources.