Different pasteurization temperatures to reduce osmophilic population of yeasts in concentrated grape juices

ROJO M.C.; STURM M.E.; LERENA M.C.; TORRES A.; MERCADO L.; COMBINA M.

Mendoza

Congreso; 37° Congreso Mundial de la Vid y el Vino; 2014

Organizacion Internacional de la Vid y el Vino (OIV)

The concentraded grape juice is a commodity and is used as a feedstock of certain foods, sweetener and pharmaceutical industry. Previous studies in our laboratory showed that Zygosaccharomyces rouxii is the main yeast responsible for the spoilage of concentrated grape juice in Argentina. The aim of this study was to apply different treatments of pasteurization to reduce the population of Z. rouxii. Concentrated grape juice at 68 °Brix and pH 3.2, was inoculated with 1.106 cells per milliliter from a strain of Z. rouxii (MC8) previously selected for its high heat resistance. Pasteurization treatments were: temperature (70, 72.5, 75, 80 and 85 ºC) and time (5, 10, 20, 30, 45, 60, 75, 90 seconds). To study the survival of the cells, the samples were plated on WL medium (Oxoid) and incubated at 28 °C for 3 days. Using data obtained survival curves (log CFU/mL)/time were performed. For survival curves fitting was used Simplified Double Weibull model, which showed two different populations, one more sensitive populations and other more resistant. These results showed that lower temperatures at 72.5 °C was nonlethal to populations Z. rouxii in concentrated grape juice. Temperatures above 75 °C may be applied to pasteurize the product, obtaining a 7 log reduction after 90 seconds for temperatures of 75 °C and 80 °C and after 30 seconds for temperatures above 85 °C. Whereas the industry sets an arbitrary value of 12 decimal reductions to consider industrial sterility and according to the results, suggest a program of 75-80 °C for 180 seconds, or 85 °C for 60 seconds thereby ensuring the microbiological quality and safety of the product.