Inactivation of candida inconspicua in the turnip juice by heat and sonication

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Turnip juice which is mainly produced in Çukurova region is widely consumed in Turkey as a fermented beverage. Degradation of lactic acid by film forming yeasts and consequently decreasing acidity and increasing pH is one of the most important factors in turnip juice spoilage. Due to the spoilage, an undesirable taste forms and spoilage microorganisms which are not active at low pH turnip juice are stimulated and cause further spoilages. Heat treatment seems to be a solution for inactivation of these microorganisms, however pasteurization causes an undesirable taste. Even though it is forbidden, preventing the development of yeasts by using antimicrobials has been widely used in the production of turnip juice. In this study, application of sonication as an alternative method has been tested for inactivation of spoilage yeasts in turnip juice. For this reason, Candida inconspicua isolated and identified from turnip juice at the film forming stage of the spoilage. The pH of turnip juice inoculated with this isolate, increased from 3.46 ± 0.01 to 7.30 ± 0.03 in 9 days. At the next step, the inhibitory effect of sonication and mild heat treatment (45-50ºC) on Candida inconspicua has been observed in pasteurized turnip juice sample inoculated with this isolate. While the D values of isolated Candida inconspicua were found 147 and 4.7 min. at 45-50ºC, respectively, by application of sonication at 50ºC the D value reduced to 0.576 min. In this study, the time ranges required for 12 D inactivation at 45 and 50ºC were 210-509 and 6.96-7.08 min., respectively. Based on these findings, we conclude that a combination of sonication and 50ºC heat treatment can be used for inactivation of the yeasts cause spoilage in turnip juice.