Polyphasic identification of a <i>Zygosaccharomyces rouxii</i> isolated from grape juice concentrate and its control using thermal processing

Abstract

<abstract> <p>A yeast, isolated from grape juice concentrate by a grape juice processing company in central Washington, was subjected to thermal processing in 52° Brix grape juice concentrate, commercial grape juice, and Yeast-Mold (YM) medium to determine <italic>D</italic>-values and <italic>z</italic>-values in the search for an effective means of control. At 50 ℃ in grape juice concentrate the <italic>D</italic>-value was 33.44 minutes, dropping rapidly as the temperature increased to 52.5 ℃, 55 ℃, 57.5 ℃, and 60 ℃. From this data, a <italic>z</italic>-value was determined to be 4.38 ℃. Grape juice and YM broth were similarly tested. Commercial grape juice at 45 ℃, 47 ℃, and 50 ℃ showed <italic>D</italic>-values of 9.80, 7.68, and 1.42, respectively, resulting in a <italic>z</italic>-value of 5.69 ℃. The isolate heat treated in YM broth at 40 ℃, 45 ℃, 46 ℃, 47.5 ℃, and 50 ℃ showed no effect at 40 ℃ but at higher temperatures, with a <italic>D</italic>-value of 2.28 at 45 ℃, 1.61 at 46 ℃, 1.05 at 47.5 ℃, and with a <italic>z</italic>-value of 7.46 ℃. This data suggests that an increase in the concentration of sugars in the environment has a protective effect on the yeast against elevated temperatures. Even so, pasteurization at 90 ℃ for thirty seconds appears to be an effective means of control for the yeast investigated. A yeast with the identical colony and cell morphology was isolated from 52° Brix grape juice concentrate from the same grape juice processing company. Both isolates were subjected to 28S DNA sequencing and FAME analysis for identification and determined to be <italic>Zygosaccharomyces rouxii</italic>, a known problem yeast in the grape juice and wine-making industry, to this point unknown in the central Washington region.</p> </abstract>