Identification of Potential Bioactive Peptides in Sheep Milk Kefir through Peptidomic Analysis at Different Fermentation Times

Abstract

Sheep farming is an important socioeconomic activity in most Mediterranean countries, particularly Spain, where it contributes added value to rural areas. Sheep milk is used in Spain mainly for making cheese, but it can be used also for making other dairy products, such as the lactic-alcoholic fermentation product known as kefir. Dairy products have health benefits because, among other reasons, they contain molecules with biological activity. In this work, we performed a proteomics strategy to identify the peptidome, i.e., the set of peptides contained in sheep milk kefir fermented for four different periods of time, aiming to understand changes in the pattern of digestion of milk proteins, as well as to identify potential bioactive peptides. In total, we identified 1942 peptides coming from 11 different proteins, and found that the unique peptides differed qualitatively among samples and their numbers increased along the fermentation time. These changes were supported by the increase in ethanol, lactic acid, and D-galactose concentrations, as well as proteolytic activity, as the fermentation progressed. By searching in databases, we found that 78 of the identified peptides, all belonging to caseins, had potential biological activity. Of these, 62 were not previously found in any milk kefir from other animal species. This is the first peptidomic study of sheep milk kefir comprising time-course comparison.

Investigation of Acid Tolerance Mechanism of Acetobacter pasteurianus under Different Concentrations of Substrate Acetic Acid Based on 4D Label-Free Proteomic Analysis

“…The mass error tolerance for secondary fragment ions was also set to 20 ppm. The false discovery rate (FDR) for protein identification and peptide-spectrum match (PSM) identification were set to 1% [24]. The identified proteins need to contain at least one unique peptide segment.…”

Comparison of Milk Kefirs Obtained from Cow’s, Ewe’s and Goat’s Milk: Antioxidant Role of Microbial-Derived Exopolysaccharides

“…While milk naturally contains peptides with biological activities, the microbial proteolytic activity during milk kefir (MK) fermentation significantly enhances the peptide content. These peptides may exert a number of beneficial effects, including antimicrobial, antioxidant, angiotensin-converting enzyme (ACE)-inhibitory, immunomodulatory, and antithrombotic effects [ 2 , 3 , 4 , 5 , 6 ]. Due to the high protein content of dairy products, the role of microbial enzymes in the release of free amino acids and peptides potentially responsible for antioxidant activity has been extensively studied.…”