Preliminary evaluation of probiotic potential of yeasts isolated from bovine milk and curd of Sri Lanka

Abstract

There has been mounting interest in the health benefits associated with live microorganisms commonly known as probiotics. Many probiotic bacterial species have been identified. However, the potential of yeasts as a source of probiotics has not been well explored. The present study was carried out to screen and identify potential probiotic yeasts from selected dairy sources available in Sri Lanka. Yeasts from raw bovine milk and curd were isolated, purified, selected and phenotypically characterized by performing morphological, physiological and biochemical tests. Isolates were assessed for their ability to survive under simulated gastro-intestinal conditions to explore their probiotic potential. Approximately, 190 colonies similar to yeast were isolated and 45 isolates of the division Ascomycota were selected and coded for convenience (SLDY_001-SLDY_045). Most promising probiotic isolates (20) were genotypically identified to be species of Pichia (55%), Candida (30%), and Kluyveromyces (15%) of the family: Saccharomycetaceae. Considering a threshold of >95% similarity to the type strain, eight different yeast species were identified. Isolates (SLDY_005, SLDY_006 and SLDY_039) of Kluyveromyces marxianus species showed the highest probiotic potential from the pool. The strain confirmation and in-vitro/invivo safety assessment of these isolates will further verify their suitability as probiotic starter cultures to be used in local food and pharmaceutical industries.

Invited review: Characterization of new probiotics from dairy and nondairy products—Insights into acid tolerance, bile metabolism and tolerance, and adhesion capability

“…Generally, most of the strains retained their viability at low pH, with the exception of K2-6, M4-5, M4-6, and M8-1 (Şanlidere Aloğlu et al, 2016). Rajawardana et al (2019) reported that yeast strains could grow and survive for up to 5 h at a range of pH values (YPD broth adjusted to pH 1.5, 3.0, and 9). Those authors found that the viability of several strains of yeast decreased at pH 1.5 and increased at pH 9 over 5 h. Their results suggested that the yeast strains survive in the extreme acidic and alkaline conditions encountered in the stomach and intestines.…”

“…In addition, the commercial strain and P. kudriavzevii exhibited similar results regarding tolerance to gastric juice. Rajawardana et al (2019) tested the tolerance of yeast to simulated gastric enzymes (YPD broth, pepsin, and pancreatin separately, with 2 pH levels: 2 and 8). They found that, at pH 8, the isolates showed steady growth and survival in gastric and pancreatic juices, whereas at pH 2, the isolates exhibited a slow growth.…”