The quality of fresh-cut lettuce is diminished by wound-induced browning. Increased demand for minimally processed lettuce and tighter restriction on chemical treatment demands improved un- derstanding of enzymatic browning, as well as simple and natural treatments to control it (Martin-Diana et al. 2005). Accumulated
Fig. 7. The effect of different treatments on color changes during storage detected by colorimeter. (A) L* (from 0 black to 100 white); (B) a* (from ea* green to þa* red); (C) b* (from eb* blue to þb* yellow). C: untreated, CD: treated with 0.5 g/L trans-cinna- maldehyde for 30 min, E: treated with 200 mL/L ethanol water solution for 2 min; HS: treated in 50 C water for 90 s; SA: treated with 1 g/L salicylic acid for 1 min. All treatments were applied immediately after cutting. Data presented are the means of six replicates. Different letters indicate significant differences among mean values (P < 0.05; t-test).
Fig. 8. Photographs showing the antibrowning effects of different treatments on let- tuce stem discs on day 7 (A) and day 14 (B). C: untreated control; CD: treated with
0.5 g/L trans-cinnamaldehyde for 30 min; E: treated with 200 mL/L ethanol for 2 min; HS: treated in 50 C water for 90 s; SA treated with 1 g/L salicylic acid for 1 min. All treatments were applied immediately after cutting.
evidence indicates that browning in fresh-cut lettuce is caused by the increased PAL activity and accumulation of phenolic com- pounds stimulated by tissue damage. Treatment of lettuce stem discs with 200 mL/L ethanol significantly retarded browning. Ethanol treatment drastically repressed the expression of PAL mRNA, inhibited PAL activity, and increased the ratio of CO2/O2.
Therefore ethanol treatment was able to inhibit phenolic meta-
bolism which is critical for tissue browning. Moreover, ethanol treatment was more effective than other antibrowning methods, such as cinnamaldehyde, heatshock and salicylic acid, for main- taining quality of lettuce stem discs. In short, ethanol was demonstrated to be effective for the dual functions of inhibiting browning and microbial growth during 14 days of storage and therefore has great potential for use as a commercial treatment for fresh-cut lettuce.