Study of the effect of thermal pasteurization and high hydrostatic pressure in the viability of Zygosaccharomyces rouxii population in concentrated grape juices

ROJO M.C.; CRISTIANI M.; SZERMAN, N.; LERENA M.C.; VARGAS A.S.; MERCADO L. A.; COMBINA M.

Bariloche

Simposio; 34th International Specialized Simposium on Yeast (34 ISSY).; 2018

CONICET

The process of juice concentration involves the elimination of water until a concentration of sugars and osmotic pressure capable of inhibiting the microbial development is reached. However, these products are not free of microbiological spoilage problems, being Zygosaccharomyces rouxii the most frequent spoilage microorganism. Many efforts have been done in the industry to avoid yeast spoilage using a non-chemical approach, where pasteurization and high hydrostatic pressure (HHP) could be suitable technologies. The aim of this work was to find the conditions of thermal pasteurization and HHP necessary to reach the inactivation of Z. rouxii and the extension of the shelf-life of concentrated grape juice. Different Z. rouxii were inoculated in concentrated grape juice at 107 CFU/g. The samples were submitted to pasteurization using different temperature (70, 75, 80 and 85 ºC) and times (5, 10, 20, 30, 45, 60, 75 and 85 seconds); and to HHP using different pressures (300, 400, 500 and 600 MPa) and times (2, 3 and 5 minutes). Pasteurization at 70 ºC was not lethal for Z. rouxii in any of the times evaluated, while a reduction of 7 logarithms was obtained at 75 and 80ºC for 90 seconds, and at 85ºC for 5 seconds. The application of HHP at 300 MPa was not lethal for Z. rouxii in none of the evaluated conditions. A significant reduction in viable populations of Z. rouxii was observed at 400 MPa, although a slowly recovery of the cells was observed, resulting in spoilage after 14 days of storage at 28 °C. Treatments with pressures over 500 MPa resulted in a significant reduction in the population and an extension of the shelf life of the stored product was observed. Our studies suggest that both technologies; HHP and pasteurization; could be applied to increase the microbial stability of concentrated grape juices.