Effect of ultrahigh temperature treatment on qualities of watermelon juice.

The watermelon juice was pasteurized by the ultrahigh temperature (UHT) treatment, and the qualities of the pasteurized juice were compared to screen the optimal UHT. The UHT of 120 and 135°C inactivated the microbial colonies and maintained the original color of the watermelon juice. The temperature of 120 and 135°C was also maintained the phenolic content by reducing the polyphenoloxidase activity. Moreover, the C9 aldehydes, especially the (,)-2,6-nonadienal, presented the main aroma of the watermelon juice. The C9 aldehydes were formed as the results of the heat reduction and enzymatic metabolism. The temperature of 120 and 135°C reduced the alcohol dehydrogenase activity and well maintained the C9 aldehyde content of the watermelon juice. Hence, the temperature of 120°C of the UHT treatment was the optimal temperature for the production of the watermelon juice.