Formation of Free Amino Acids and Bioactive Peptides During the Ripening of Bulgarian White Brined Cheeses.

Bioactive peptides and free amino acids obtained from Bulgarian goat, sheep and cow white brined cheeses, produced with same starter culture, during ripening were evaluated. The concentration of total free amino acids was increasing in all tested cheeses in the first 30 days of ripening. In the next 30 days in sheep cheeses, the concentration increased as recorded for most of the amino acids. Amino acids with highest levels detected throughout the whole ripening period in goat, sheep and cow cheese types were leucine, phenylalanine, arginine, valine and lysine. MALDI-TOF analysis of evaluated cheeses resulted in detection of production of bioactive peptide derivates from milk proteins: 51 peptides in cow, 31 peptides in sheep and 22 peptides in goat cheeses. Peptide αs1-CN (f35-40) was found only in cow cheese. In cow cheese, higher intensity was detected for αs1-CN (f1-9) and ß-CN (f194-203 and f203-219) peptides. In goat cheese was recorded αs1-CN peptides, and there was a tendency to increase the peptides released from ß-CN, with the highest intensity of fragments αs1-CN (f1-9 and f24-30) and ß-CN (f194-209 and f203-219). In sheep cheese, the recorded primarily peptides were αs1-CN and peptides released from ß-CN. Different bioactive peptides, derivate from casein, were detected as follows: 6 peptides were ACE inhibitory peptides, 3 peptides were αS1-casokinins, 1 peptide was caseinophopeptide, 1 peptide was immunopeptide. Twelve bioactive peptides were recorded to be derivates from ß-casein: 1 peptide was ACE peptide, 4 peptides were caseino-phosphopeptides, 1 peptide was immunopeptide, 1 peptide ß-casokinin, 1 antibacterial peptide and 4 multifunctional peptides. Of peptides released by proteolysis of αS2-CN was found 1 bioactive peptide with antimicrobial activity. On our best knowledge, this paper contributes new data about free amino acids and bioactive peptides in the connection between type of milk and period for cheese ripening in the Bulgarian goat, sheep and cow white brined cheeses.

Proteolytic and antimicrobial activity of lactic acid bacteria grown in goat milk.

We examined 62 strains and 21 trade starter cultures from the collection of LB Bulgaricum PLC for proteolytic and antimicrobial activity of lactic acid bacteria (LAB) grown in goat milk. The aim of this study was to investigate the fermentation of caseins, α-lactalbumin and ß-lactoglobulin by LAB, using the o-phthaldialdehyde (OPA) spectrophotometric assay and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The proteolysis targeted mainly caseins, especially ß-casein. Whey proteins were proteolyzed, essentially ß-lactoglobulin. The proteolytic activity of Lactococcus lactis l598, Streptococcus thermophilus t3D1, Dt1, Lactobacillus lactis 1043 and L. delbrueckii subsp. bulgaricus b38, b122 and b24 was notably high. The proteolysis process gave rise to medium-sized peptide populations. Most of the examined strains showed antimicrobial activity against some food pathogens, such as Escherichia coli, Staphylococcus aureus, Salmonella cholere enteridis, Listeria monocytogenes, Listeria innocua and Enterobacter aerogenes. The most active producers of antimicrobial-active peptides were strains of L. delbrueckii subsp. bulgaricus and S. thermophilus, which are of practical importance. The starter cultures containing the examined species showed high proteolytic and antimicrobial activity in skimmed goat milk. The greatest antimicrobial activity of the cultures was detected against E. aerogenes. The obtained results demonstrated the significant proteolytic potential of the examined strains in goat milk and their potential for application in the production of dairy products from goat's milk. The present results could be considered as the first data on the proteolytic capacity of strains and starter cultures in goat milk for the purposes of trade interest of LB Bulgaricum PLC.