Effects of Orange Juice Fortification with Thiols on <i>p</i>-Vinylguaiacol Formation, Ascorbic-Acid Degradation, Browning, and Acceptance during Pasteurization and Storage under Moderate Conditions

Abstract

Pasteurization of orange juice produced sub-taste-threshold levels of p-vinylguaiacol (PVG) and induced ascorbic-acid degradation but had almost no effect on browning. Fortification with glutathione, l-cysteine, or N-acetyl-l-cysteine at concentrations below 4.0 mM had no effect on PVG formation and browning but inhibited ascorbic-acid degradation during pasteurization and improved juice acceptance. Storing the orange juice for 12 weeks at 25 °C resulted in a PVG content that reached its taste threshold; fortification with the above concentrations of thiols reduced PVG formation and browning. Storage at 35 °C resulted in a PVG level about 10-fold above its taste threshold, 25% degradation of ascorbic acid, and significant browning. Fortification with thiols at concentrations below 4 mM reduced PVG formation, ascorbic-acid degradation, and browning. Sensory evaluation tests indicated increased hedonic scores due to thiol fortification during pasteurization and storage (though not statistically significant for the latter), and aroma-similarity tests performed on juice stored at 35 °C indicated that fortification with 1.0 mM glutathione results in an aroma similar to that of the control juice stored at 4 °C. Keywords: Orange juice; glutathione; l-cysteine; N-acetyl-l-cysteine; p-vinylguaiacol (PVG); ascorbic acid; browning; acceptance