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 °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 (2.5 mM 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 °C produced aroma that was most similar to that of the control juice kept at 4 °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.