Effect of processing on the antioxidant activity and other quality parameters of Muscadine grape juice

Muscadine grapes are native to southeastern parts of the United States. They are widely processed into juices and wines. They contain high amounts of polyphenols that are generally known to have high levels of antioxidant activity, offering potential health benefits. Since the juice is always consumed after processing, the effect of processing on the antioxidant activity and other quality parameters needs to be determined.;Unpasteurized Muscadine grape juice was obtained from Paulk vineyards in Georgia. Juice was thermally pasteurized at 85 °C for 53 s. To obtain microbiologically safe conditions for High Pressure Processing (HPP) of juice, microbial equivalence between thermal processing and HPP was established using Saccharomyces cerevisiae strain. For HPP, the juice was vacuum packed in pouches and processed at pressures ranging from 275 - 425 MPa for 5 - 15 min. Total phenolics in juice samples were measured using Folin - Ciocalteu method. The antioxidant activity was determined using chemical antioxidant assay - Oxygen Radical Absorbance Capacity (ORAC) and biological antioxidant assay - Cellular Antioxidant Activity (CAA) assay. "Difference from Control" sensory test was performed to find the overall difference in the sensory quality of unpasteurized and processed juice samples. The effect storage time and temperature on total phenolics, ORAC value, color and ellagic acid content was determined for the processed juice samples.;Results showed no significant change in total phenolics and ORAC value, after processing. Cellular antioxidant activity increased significantly in high pressure processed sample as compared to thermally processed sample. No overall difference was perceived during sensory evaluation between any of the samples. During storage, total phenolics and ORAC value decreased with time, but the choice of process had no impact on these parameters. Browning index (BI) calculated from measured color indicators, was different for thermally processed and high pressure processed samples, but both samples showed an increase in the BI with time. Ellagic acid content was found to be higher in high pressure processed storage samples compared to unpasteurized and thermally processed samples. Thus, HPP did not offer any special benefit over traditional thermal processing for Muscadine grape juice.