IDENTIFICATION OF CONTAMINATION SOURCES OF ZYGOSACCHAROMYCES ROUXII DURING THE PRODUCTION OF CONCENTRATE GRAPE JUICES

ROJO, M.C.; CUELLO, R.; GONZALEZ, M; PONSONE M.L.; MERCADO L.; COMBINA, M.; GUEVARA, F.; MARTINEZ, C.

Bento Goncalves

Congreso; 39th World Congress of Vine and Wine; 2016

OIV

Mendoza and San Juan are the most important producer of grape juice concentrates in Argentina, being responsible for 100% of the total production. Zygosaccharomyces rouxii is the main spoilage yeast of grape juice concentrates. The major economic losses caused by organism spoilage gives the identification of the contamination source a high priority; only when the nature of the spoilage is understood a decision can be made on cleaning procedures and product recall. The aim of this study was to identify the source of contamination of this species during grape juice concentration. A total of 63 samples were taken along the production chain at the three processing plants chosen for this study. Twenty nine of the samples corresponded to grape juice and 34 to surface/equipment. The sampling points were determined "in situ" and depended on the production scale and concentration process in each plant. Osmotolerant and osmophilic isolates were identified and Z. rouxii isolates were molecularly typified by RAPD PCR. Equipment surfaces that harbored the highest number of osmophilic yeasts in the three processing plants were stainless still tanks, pumps and connectors, hoses and filling pipes, floors and wash water. Unexpectedly, most yeast species isolated from these surfaces were not identified as Z. rouxii. All these species displayed osmotolerant characteristics and were previously described in fresh concentrates and/or pasteurized fruit juices. Z. rouxii was only isolated from two surfaces with remains of grape juice. Unlike the findings in the equipment surfaces of the processing plants, grape juice concentrate samples obtained during different processing stages showed a clear predominance of Z. rouxii species. The presence of this species was associated with juices that had been concentrated to some degree. Overall, limited polymorphism (3 molecular patterns) was observed in Z. rouxii isolates from each processing plant. Each of the three processing plants exhibited a dominant molecular pattern for Z. rouxii isolates, and the main molecular pattern was different for each of the processing plants. Based on our overall results, presence of Z. rouxii in the final stages of grape juice processing can be explained by recontamination with this species once the grape juice was pre-concentrated or concentrated through contact with improper sanitized surfaces. This surfaces ?difficult to clean? surfaces could be a reservoir of this spoilage yeast.