ศูนย์นวัตกรรมเทคโนโลยีหลังการเก็บเกี่ยว

Effect of selected browning inhibitors on phenolic metabolism in stem tissue of harvested lettuce.

Tomas-Barberan, F. A.; Gil, M. I.; Castaner, M.; Artes, F.; Saltveit, M. E.;

Journal of Agricultural and Food Chemistry Year: 1997 Vol: 45 Issue: 3 Pages: 583-589 Ref: 22 ref.

1997

บทคัดย่อ

Wound-induced changes in phenolic metabolism cause stem browning (butt discoloration) in harvested lettuce. Stem tissue near the harvesting cut exhibited increased phenylalanine ammonia lyase (PAL) activity and accumulation of caffeic acid derivatives during storage of iceberg lettuces at 2.5 deg C for 1 week. These o-diphenols are oxidized by the enzyme polyphenol oxidase [catechol oxidase] (PPO) to produce brown pigments. This browning reaction can readily be followed by measuring Hunter a* values. Browning of stem disks excised from near the harvesting cut and stored at 5 deg for 7 days was studied. Browning was reduced by washing stem disks with solutions of 0.3 M calcium chloride, 1.0 mM 2,4-D, or 0.5 M acetic acid. These browning inhibitors appeared to act in different ways. Calcium chloride decreased PAL activity to 60% of the control, but did not substantially affect the accumulation of phenolic compounds. The mechanism of calcium action could be to decrease PPO activity or to preserve m

embrane structure. PAL activity was inhibited 60% by 2,4-D, and the biosynthesis of phenolic compounds was strongly inhibited but not suppressed. Acetic acid completely inhibited PAL activity and the production of wound-induced phenolics. PAL was irreversibly inhibited by acetic acid, and this may explain its role as a browning inhibitor.