Effect of thermal, high hydrostatic pressure, and ultraviolet-C processing on the microbial inactivation, vitamins, chlorophyll, antioxidants, enzyme activity, and color of wheatgrass juice

The comparative study determined the fate of vitamin C, chlorophyll, antioxidants, enzymes (polyphenol oxidase [PPO], peroxidase [POD]) and effect on color of wheatgrass juice processed by thermal, high hydrostatic pressure (HHP), or ultraviolet-C light (254 nm; UV-C) to inactivate Escherichia coli P36, Listeria innocua ATCC 51742, and Salmonella Typhimurium WG49. A thermal treatment at 75 degrees C for 15 s, HHP at 500 MPa for 60 s, and UV-C fluence of 69.2 mJ cm(-2) was required to achieve the target 5 log CFU reduction of the test bacteria. Thermal treatment resulted in a significant (p < 0.05) loss of enzyme activities (75.3% POD and 40.0% PPO), total phenolic content (TPC; 36.0%), vitamin C (27.4%), chlorophyll (12.4%), and negatively impacted the juice color. UV-C treatment significantly (p < 0.05) decreased the TPC of the juice and resulted in a 20.0% decrease in PPO activity. In comparison, HHP significantly (p < 0.05) increased the chlorophyll content by 9.0% with negligible impact on the nutritive content, and PPO and POD levels. HHP would be preferentially selected over UV-C and thermal treatment for wheatgrass juice based on changes induced by processing.