3.9. Pectin methylesterase activity (PME)
EFF and Ca(NO3)2 treatment significantly influenced the PME
activity during storage (Fig. 5). PME activity peaked between 7d
and 14 d of storage in control fruit and thereafter showed a sharp
and abrupt decline in parallel with the loss in fruit quality. EFF
(0.015% v/v hexanal) treated fruit showed a gradual increase in
PME activity which peaked at 28 d of storage, and then declined.
Calcium nitrate treated fruit a similar pattern of increase with the
peak temporally appearing earlier at 14 d. PME removes the methyl
group of galacturonic acid polymers of pectin. De-esterification of
pectin chain by PME may make the chain more susceptible to
polygalacturonase mediated degradation (Carpita and Gibeaut,
1993) facilitating a rapid loss of cell wall structure. Thus, PME
activity appears to show a significant influence in determining the
postharvest shelf life and quality in guava. EFF treatment of tomato
fruit has been shown to downregulate the transcript levels of PME
(Tiwari and Paliyath, 2011). A decrease in PME transcripts after EFF
treatment along with a decline in polygalacturonase transcripts,
may lead to a decrease in breakdown of pectin and leading to
enhanced firmness during the course of storage.