ศูนย์นวัตกรรมเทคโนโลยีหลังการเก็บเกี่ยว

Phenolic metabolism and ethanolic fermentation of intact and cut lettuce exposed to CO2-enriched atmospheres.

Mateos, M.; Ke, D.; Cantwell, M.; Kader, A. A.;

Postharvest Biology and Technology Year: 1993 Vol: 3 Issue: 3 Pages: 225-233 Ref: 25 ref.

1993

บทคัดย่อ

Intact heads and cut leaf tissue of crisphead lettuce (cultivars Salinas and Vanguard) were kept in air or air + 5%, 10% or 20% CO2 for 10 or 20 days at 2.5 deg C and then transferred to air at 20 deg for 12 h to study CO2 effects on phenolic metabolism and fermentation products. Exposure of cut midribs to 5, 10 or 20% CO2 increased extractable activity of phenylalanine ammonia-lyase (PAL) when assayed at its optimum pH (8.5). The effect increased with increased CO2 concentration. However, exposure to 20% CO2 reduced cytoplasmic pH, hence PAL activity in vivo was lower than the activity recorded at pH 8.5. Total phenolic content of cut midribs was reduced under 20% CO2-enriched atmosphere probably due to this decrease in PAL activity. The phenolic content rapidly increased after the tissue was transferred from 20% CO2 at 2.5 deg to air at 20 deg when cytoplasmic pH returned to its normal value and PAL activity was restored. Such effects of CO2 on PAL and phenolic compounds were of lower magnitud

e in intact heads, probably due to their lower sensitivity to phenolic metabolism. For intact heads, only the 20% CO2 treatment for 20 days significantly increased extractable PAL activity. Off-flavour developed in the intact heads exposed to 20% CO2, which was associated with increased concentrations of ethanol and acetaldehyde. When exposed to 20% CO2, levels of ethanol and acetalydehyde in cut midribs were only about half of those in intact heads.