BIOFILM FORMATION UNDER LAMINAR FLOW CONDITIONS OF YEAST ISOLATED FROM AN APPLE JUICE PROCESSING PLANT

The attachment of microorganisms to a surface is a critical step of biofilm fouling in food processing equipment. The goal of this research was to determine the potential of four yeast strains isolated from an apple juice processing plant, to initiate biofilm formation on stainless steel surfaces (SSS) both under static and laminar flow conditions. The isolated yeasts were Kluyveromyces marxianus, Candida krusei, Zygosaccharomyces sp. and Rhodotorula mucilaginosa. Micro-colonies, indicating the starting of biofilm formation, were observed after 16 h. Cell numbers per SSS significantly changed with yeast strain and time. Results seem to indicate that adhesion and colonization of the studied yeast under laminar flow conditions differed from that observed under static conditions. Particularly, when adhesion of K. marxianus, C. krusei and R. mucilaginosa was reduced one log cycle, Zygosaccharomyces sp. increased 0.5 log units as compared with the assays made under static conditions. PRACTICAL APPLICATIONS The persistence of microorganisms in biofilms is a serious hygienic problem in the food industry. Moreover, the microbial attachment greatly reduces the heat transfer and operating efficiency of the processing equipment. For example, biofilm formation greatly reduces the permeability of filtration membranes. We observed that the yeast strains more frequently isolated from concentrated apple juice processing plants present a rapid capacity of adhesion to stainless steel (the most commonly used surface in food processing plants), after a short time of contact, both under static or laminar flow conditions. The fruit juice industry should be alert to the fast colonization rate of yeast on the surfaces involved in the production processes.