Diversity of Yeast Microbiota in Spoiled Iranian Doogh and Effects of Kluyveromyces marxianus on its Protein Profiles

Abstract Background and Objective: Microbial contamination can cause undesirable changes in food products. In addition to consumer’s health, these changes can challenge the product market. Doogh as one of the traditional dairy may be contaminated by a wide range of microbiota. Awareness of the contaminant types can be an accurate strategy to eliminate contaminations. Regarding importance of food safety as well as industry demand, the present study was an attempt to better understanding of the yeast microbiota diversity in spoiled Doogh. Also the effect of predominant yeast metabolites on proteins and peptides profiling of Doogh were investigated. Results demonstrated purposeful industrial strategies to secure quality parameters and boost the shelf life of Doogh. Material and Methods: Swollen packages of pasteurized Doogh samples were collected from a local dairy plant within one year. Identification was carried out using morphological, biochemical and molecular techniques. Then, protein and peptide profiles of the inoculated Doogh samples with high proteolytic activities of the isolated yeasts were compared with control using SDS-PAGE and MALDI-TOF-MS techniques. Results and Conclusion: Totally, 13 isolates belonged to two genera of Kluyveromyces and Candida were isolated and identified. Based on 18S rRNA gene sequencing, eight isolates were identified as Kluyveromyces marxianus; four isolates were matched with Kluyveromyces lactis and one isolate was identified as Candida kefyr. Furthermore, o-phthaldialdehyde assay showed that Kluyveromyces marxianus contain the highest proteolytic activity, compared to other identified isolates. Results showed that the activity of Kluyveromyces marxianus linked the protein profiles to β-lactoglubolin and α-lactalbumin isoforms and several peptides with molecular weight less than 10 kDa. Small changes in organoleptic properties can directly affect the product marketing and jeopardizes survival of the industries. By increasing necessary measures on the critical points in the production lines, adoption of right strategies to decrease or eliminate contaminants and hence improve the quality of the products is possible.