The Effect of Yeast Kluyveromyces marxianus as a Probiotic on the Microbiological and Sensorial Properties of Set Yoghurt during Refrigerated Storage

Background & objectives: Probiotic dairy products as a functional food have a positive effect on the health of consumers that have been confirmed by scientific evidence. Yoghurt is considered as one of the most popular dairy foods in Iran, which the incorporation of the probiotics into the yoghurt matrix can improve their microbiological and sensory properties and subsequently will play a vital role in promoting the health of the community. The aim of this study was to investigate the effect of yeast Kluyveromyces marxianus on the microbial and sensorial properties of probiotic yoghurt during refrigerated storage. Methods: In this in vitro study, the yeast Kluyveromyces marxianus PTCC=5189 was used to produce probiotic yoghurt and Aspergillus parasiticus PTCC=5018 (IR 63) and Penicillium chrysogenum PTCC=5074 were used as known pathogens and the main spoilage agents in yoghurt. Changes in the number of probiotic yeasts and spoilage species as well as the sensory acceptability of the samples during 28 days of storage at 4°C were evaluated and compared with the control samples. Results: The population of both species, involved in yoghurt spoilage, during refrigeration were significantly reduced by the presence of Kluyveromyces marxianus (p<0.01). After 28 days of storage, the number of Kluyveromyces marxianus was at the recommended level of the International Dairy Federation with a 7.35 log CFU/g. The sensory evaluation results demonstrated that the control yoghurt samples were more acceptable. Conclusion: Kluyveromyces marxianus has a significant effect on improving microbiological properties and can be used in the formulation and production of probiotic yoghurt with high storage capability and optimal sensory acceptability.