Differential expression of genes and enzymes involved in cell wall degradation during ripening of strawberry cultivars

MARTÍNEZ, G; ROSLI, H; VILLARREAL, N; BUSTAMANTE, C; DOTTO, M; CIVELLO, P

Talca

Congreso; Congreso Internacional Post Harvest Fruit: the path to success.; 2004

Universidad de Talca

Strawberry is a soft fruit that shows an important reduction during ripening. Fruit softening has been correlated with solubilization and depolimerization of cell wall constituents. Heat treatments have been shown to be effective to delay softening in many products. In strawberries, hot air treatments have been used to maintain fruit firmness during postharvest. In this work, it was evaluated the effect of heat treatments on cell wall composition and activities of different softening associated enzymes (PME, PG, EGase, beta-gal and beta-xyl) in the internal and external zones of the strawberry fruit receptacle. Strawberries (75 % red color) were heat-treated at 45 ºC during 3 h in an air oven. After treatment the fruit were stored at 20 ºC for 2 d. The internal and external zones of heat- treated fruit remained firmer than controls after 1 d of storage at 20 ºC. After 2 d of storage the difference was still observed in the external zone. Heat treatments reduced EGase and beta-xyl activity in both zones and maintained higher levels of hemicelluloses than control fruit. PG and beta-gal activity were also inhibited by the treatment. Heat treated fruit maintained higher levels of HCl soluble pectins and had lower levels of water-soluble pectins than control fruit. PME was increased by the treatments and heat-treated fruit presented higher EDTA soluble pectins that control fruit. Results show that firmness, enzymatic activity and cell wall composition are different in the external and internal zone of strawberry fruit. Furthermore, heat treatments modify cell wall degradation by differentially affecting pectins and hemicellulose solubilization.