Bioactive Compounds Produced by the Accompanying Microflora in Bulgarian Yoghurt

Abstract

Bulgarian yoghurt is associated with health benefits and longevity of consumers. The specific microflora producing bioactive metabolites is responsible for this effect. The present study examines the biodiversity in four homemade yoghurts from regions containing endemic microflora. Metagenome sequencing indicated Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus were predominant in all samples. In addition, yoghurts contained accompanying lactic acid bacteria (LAB) including Lacticaseibacillus paracasei, Lb. helveticus, Limosilactobacillus fermentum, Lb. rhamnosus, Lactococcus lactis, Pediococcus acidilactici, Leuconostoc mesenteroides, and Leuc. pseudomesenteroides. A negligible amount of pollutant strains was found. Twenty-four LAB strains were isolated from the yoghurts and identified. Lb. delbrueckii subsp. bulgaricus strains were genotyped by randomly amplified polymorphic DNA–PCR (RAPD), multi-locus sequence typing (MLST), and pulse field gel electrophoresis (PFGE), which demonstrated their uniqueness and non-commercial origin. To estimate the bioactive metabolites produced by the accompanying microflora, yoghurts fermented by single LAB strains were analyzed using liquid chromatography and mass spectrometry (LC-MS). The fermented samples contained large amounts of free essential amino acids (arginine, citrulline, tryptophan, lysine, and histidine), the neuroprotector indole-3-propionic acid (IPA), and significant quantities of the cyclic antimicrobial peptides cyclo(phenylalanyl-prolyl) and cyclo(leucyloprolyl). The disclosure of these special qualities draws attention to the accompanying microflora as a source of potential probiotic strains that can fortify the yoghurts’ content with bioactive compounds.

Microbiological and Metagenomic Characterization of a Retail Delicatessen Galotyri-Like Fresh Acid-Curd Cheese Product

“…We previously analyzed this type of natural yogurt starter and confirmed it to contain typical strains of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus [24], in agreement with relevant studies by others on the microbiology of yogurt and yogurt starters [20,23]. The basic yogurt curd was fresh and nondrained.…”

“…In most Greek rural areas, excess ewe's/goat's milks, mainly in the summer, are preserved by making yogurt at home, which is strained and often mixed with trimmed white brined cheeses to consume as an appetizer. In addition to naturally fermented yogurt, fresh acid-curd cheeses and white brine cheeses produced in Greece, Bulgaria, and other Balkan or East Mediterranean countries since antiquity have been associated with beneficial effects on human health, attributed to the probiotic properties of their indigenous LAB [6,19,20]. Therefore, it is important to characterize the microbiota of Greek yogurt or of traditional Greek acid-curd cheese products prepared with yogurt in order to detect novel LAB strains with high biotechnological or probiotic potential for the development of novel functional foods.…”

Traditional Bulgarian Dairy Products: Ethnic Foods with Health Benefits

“…bulgaricus and S. thermophilus. Their proto-cooperation was comprehensively reviewed in several studies [10,[39][40][41]. Briefly, L. bulgaricus, which is a bacterial species with high proteolytic activity, releases free amino acids that favour the growth of S. thermophilus.…”

“…The high proteolytic activity of LAB leads to increased levels of free amino acids (FAA) in dairy products. As part of the accompanying microflora of yoghurt, L. fermentum, L. paracasei, and P. acidilactici release high amounts of lysine and tryptophan, while L. helveticus accumulates L-arginine and its precursor L-citrulline in homemade Bulgarian yoghurts [41]. The last two amino acids are used in the treatment of cardiovascular diseases, irritable bowel syndrome, endothelial dysfunction, hypertension, heart failure, atherosclerosis, and ischemia-reperfusion injury [64].…”

“…Both peptides were produced by S. thermophilus and LAB of the accompanying microflora (L. fermentum, Leuc. mesenteroides, and P. acidilactici) [41].…”