Ultraviolet-C resistance of selected spoilage yeasts in orange juice.

This study determined the ultraviolet-C (UV-C) dose necessary to reduce 90% population (DUV-C) of 17 spoilage yeasts and their composited inoculum in orange juice (pH 3.71, 11.60 °Brix, 0.55% citric acid, 2.46% w/v insoluble solids). Growth parameters of all test yeasts were first established to standardize the growth stage of the cells prior to harvesting and eventual UV-C challenge studies. Approximately 4-5 log CFU/ml cells in the mid-stationary growth phase (30.3 t0 39.9 h, 25 °C) were suspended in 4 ml turbulent flowing juice and subjected to UV-C irradiation at an incident surface irradiance of 3.64-4.97 mW/cm2. The inactivation rates of each yeast and their composited inoculum were determined using 2 methods namely, the linear regression and Baranyi and Roberts (1994) model-fitting. Results showed that the yeasts exhibited either log-linear or biphasic inactivation behavior with downward concavity or inactivation lag. Regardless of the method of determination, Cryptococcus albidus (LJY1) exhibited the significantly greatest (p < 0.05) UV-C resistance with DUV-C values of 1924.31 and 2174.63 mJ/cm2. On the other hand, Candida parapsilosis was determined to be least resistant with a DUV-C values of 245.83 and 357.88 mJ/cm2. Majority of the DUV-C values determined from the model-fitting were greater than those calculated from linear regression. However, only those determined for the composited inoculum were significantly different. The results of this study address knowledge gaps pertinent to the UV-C resistance of less studied spoilage yeast, and help in better understanding the utility of this non-thermal food processing technology.