Candida krusei is the major contaminant of ultrafiltration and reverse osmosis membranes used for cranberry juice production

Ultrafiltration (UF) and reverse osmosis (RO) are commonly used for the clarification and concentration of fruit juices. However, one of the main limitations of filtration membranes is biofouling, which reduces membrane efficiency and can contaminate the filtered product and lead to spoilage. In this study, the microbial fouling layers of UF and RO membranes from a Canadian cranberry juice processing plant were characterized. Unlike the microbiota found in cranberry juice, which is dominated by Bacillus sp. and other bacteria, both UF and RO membranes were mainly colonized by several strains of the yeast Candida krusei. A variation in bacterial and yeasts count was observed between tubular UF and spiral-wound RO membranes, and the analysis of the spatial distribution highlighted the homogeneity of the contamination across each membrane. Surprisingly, RO membranes had a higher level of contamination when compared to UF membranes. Furthermore, six strains of C. krusei were further characterized through multilocus sequence typing analysis, five of which exhibited unique allelic profiles and two of which were found to contain a new TRP1 allele.