Inhibition by Thiol Compounds of Off-Flavor Formation in Stored Orange Juice. 2. Effect of l-Cysteine and N-Acetyl-l-cysteine on p-Vinylguaiacol Formation

The formation of p-vinylguaiacol (PVG), a major off-flavor in citrus products, was reduced by 30–80% in model solutions of orange juice (MOJ) and in single-strength orange juice (SSOJ) fortified by l-cysteine and stored at 45 °C. The fortification by 2.5 mM N-acetyl-l-cysteine was also effective in reducing PVG content. Experiments with MOJ samples indicated that, concomitant with the inhibition of PVG formation due to the fortification by l-cysteine, vanillin production and ferulic acid degradation were accelerated. It is concluded that although off-flavors in citrus products such as PVG and 2,5-dimethyl-4-hydroxy-3(2H)-furanone are formed by different routes, their production may be reduced by a common approach, namely application of minor amounts of naturally occurring thiol compounds such as l-cysteine.