Proteolytic Activity of Different Lactic Acid Bacteria Species Cultivated on Media with Plant Proteins

The aim of the present study was to evaluate the ability of different lactic acid bacteria strains to degrade plant proteins from various sources. The species included were Lactobacillus delbrueckii ssp. bulgaricus, Lactobacillus helveticus, Lacticaseibacillus casei and Lactiplantibacillus plantarum, cultivat¬ed in plant protein-enriched media, containing pea-, soy-, rice- or hemp protein. Sterile 10% reconstituted skimmed milk (RSM) was used as a reference growth medium and for the initial selection of high- and low-proteolysis-capable strains. The quantification assay was the o-phthalaldehyde spectrophotometric method. Initially, L. delbr. ssp. bulgaricus strains and L. helveticus strains were cultured for 16 hours at 37°C and 42°C in RSM, while L. casei and L. plantarum strains were tested after 16- and 24-hour cultivation at 32°C and 37°C in RSM. In a strain-dependent manner, L. delbrueckii ssp. bulgaricus and L. helveticus cultures showed strong proteolysis in milk (up to 10.5 mM) and milk proteolysis by L. casei was low (less than 2 mM). For L. delbrueckii ssp. bulgaricus and L. helveticus cultures, the accumulation of products of proteolysis in plant protein-containing media was lower than RSM demonstrating the best results with pea protein. Furthermore, proteolysis by L. casei strains in plant protein media exceeded that in RSM by up to 5 mM. The combination of milk and pea protein resulted in a dramatic increase of proteolysis (up to 24 mM) by L. delbrueckii ssp. bulgaricus, L. helveticus and L. casei, which are of interest for the application of mixed plant-milk substrates.