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 p roducts, was reduced by 30-80% in model solutions of orange juice (MOJ ) and in single-strength orange juice (SSOJ) fortified by L-cysteine a nd stored at 45-degrees-C. The fortification by 2.5 mM N-acetyl-L-Cyst eine was also effective in reducing PVG content. Experiments with MOJ samples indicated that, concomitant with the inhibition of PVG formati on due to the fortification by L-cysteine, vanillin production and fer ulic 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.