Thermal Resistance of Microorganisms and Polyphenol Oxidase as Related to Solar Pasteurization of Concord Grape Juice 1.

Pasteurization conditions for grape juice were examined and the concept of pasteurizing grape juice utilizing solar energy was explored in this study. The z-values of four selected micro-organisms in grape juice were approximately 5-8 C, whereas polyphenol oxidase in fresh grapes had a z-value of 8.0 C at pH 3 .4. Using a 0.5 m2 solar collector test module constructed for this study, 2.5 h were required to heat the grape juice from 10 to 85 C. The solar pasteurized juice and commercially pasteurized juice were different in flavor and color but not in pH, titratable acidity or soluble solids.