Adherence to Stainless Steel of Yeast Strains Isolated from Apple Juice Processing Plants

LOZANO, JORGE E.; TARIFA, MARÍA CLARA; BRUGNONI, LORENA INÉS

Hangzhou

Congreso; BIT´s 2nd Annual World Congress of Food Science and Applications in Food Technology 2013; 2013

Argentina is the largest clarified concentrated apple juice producer and exporter country in the southern hemisphere. The use of ultrafiltration (UF) for clarification greatly simplifies the process operation and improves product quality. A major operational problem in UF processes is caused by fouling, which results in flux decline and/or increase in pressure drop during filtration. Biofilms are considered the most serious problem in food industry, where the initial microbial cell deposition is a critical early stage event in the overall process. Yeast represents one of the most common contaminants during apple juice processing. The objective of this work was to study the initial attachment on stainless steel of wild yeast strains isolated from UF membranes used for clarify apple juice. Organisms were 11 yeast strains from the genus Candida, Kluyveromyes, Rhodotorula and Pichia isolated from PVDF (polyvinylidene fluoride) membranes. The surface was AISI 304 stainless steel coupons (15x25x1 mm). Yeast suspensions were made in 12 °Brix apple juice by adjusting the optical density (OD) at 550 nm to 0.125 (107 cells ml-1). To determine number of adherent viable yeast cells coupons were stained with fluorescein diacetate (FDA) and examined under an Olympus BX 51 epifluorescence microscope. All yeast adhered (360 to 4740 cells/cm2) to stainless steel, although differences were observed according to species and strains. Within the first 60 min. peaks of adhesion were reached with cells clusters covering in some cases the entire length of the surface. A positive correlation between biofilms formation and cell surface hydrophobicity was found, characteristics suggested as one of the key factors in biofilm formation. Despite the substantial effort in understanding the fundamentals of membrane fouling, knowledge about biofouling is necessary in order to implement strategies that limit or slow down this process.