Ability of thermophilic lactobacilli to hydrolyze food animal and vegetable proteins

Abstract

The cell envelope-associated proteinase (CEP) of lactobacilli has a key role for bacterial nutrition and contributes to the development of the organoleptic properties of fermented milk and vegetable products; moreover, it can release bioactive health-beneficial peptides from milk proteins and diminish allergic reactions. The aim of this study was to compare the ability of industrially relevant species of thermophilic lactobacilli strains to hydrolyze proteins from animal (caseins and β-lactoglobulin) and vegetable (soybean and wheat) sources. In addition, the influence of the peptide content in the growth medium on the CEP activity was evaluated. Lactobacillus delbrueckii subsp. lactis (CRL 581 and 654), L. delbrueckii subsp. bulgaricus (CRL 454 and 656), L. acidophilus (CRL636 and 1063) and L. helveticus (CRL 1062 and 1177) were grown in a chemically defined medium supplemented or not with casitone (1%). Protein hydrolysis was evaluated by SDS-PAGE and RP-HPLC. Proteinase production was inhibited by the presence of casitone in different extent and was Lactobacillus species-dependent; the L. delbrueckii subsp. lactis species was the most affected (97-99% inhibition) while L. acidophilus the least influenced one (33-50% inhibition). All strains hydrolyzed mainly β-casein while the degradation of α-casein was strain-dependent. Contrariwise, -Casein was poorly degraded by the studied strains. L. delbrueckii subsp. bulgaricus CRL 656, L. acidophilus CRL 636 and L. helveticus CRL 1062 were able to hydrolyze the major milk allergenic protein β-lactoglobulin while L. delbrueckii subsp. lactis strains, L. delbrueckii subsp. bulgaricus CRL 656 and L. helveticus CRL 1177 degraded the gliadin cereal protein in a higher extent. Respect to soy proteins, the L. acidophilus and L. helveticus strains showed the lowest proteolytic ability. This study deepens into the understanding of the proteolytic diversity of lactic acid bacteria for exploiting this complex system in the manufacture of novel functional foods. The rational selection of proper strains when formulating hydrolyzed food products of different origin (dairy or vegetable) is of utmost importance since proteinases specificities are strain-dependent.