INHIBITION BY THIOL COMPOUNDS OF OFF-FLAVOR FORMATION IN STORED ORANGE JUICE .1. EFFECT OF L-CYSTEINE AND N-ACETYL-L-CYSTEINE ON 2,5-DIMETHYL-4-HYDROXY-3(2H)-FURANONE FORMATION

Orange juice stored at 45-degrees-C for 7 and 14 days resulted in increased browning and increased concentration of sugar degradation products such as 5-(hydroxymethyl)furfural (HMF) and 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF). Addition of L-cysteine (2.5-12.3 mM) significantly reduced browning and HMF and DMHF formation in the 14-day-stored orange juice in a dose-related manner. Ascorbic acid retention increased with increasing L-cysteine concentrations. Low levels (2.5mM and below) of L-cysteine and N-acetyl-L-cysteine reduced browning and DMHF formation, but only L-cysteine reduced ascorbic acid degradation. Sensory similarity analyses indicated that orange juice fortified with 0.5 mM L-cysteine during 14 days of storage at 45-degrees-C produced aroma that was most similar to that of the control juice kept at 4-degrees-C compared to other treatments. The addition of N-acetyl-L-cysteine produced juices with aroma that was located in an inferior position in the similarity diagram when compared to that of juices fortified by L-cysteine.