Effect of heat treatments on cell wall degradation and softening in stawberry fruit

VICENTE ARIEL; COSTA LORENZA; MARTINEZ GUSTAVO; CHAVES ALICIA; CIVELLO PEDRO

Talca, Chile

Simposio; Post Harvest Fruit: the path to success; 2004

Strawberry is a soft fruit that shows an important reduction of firmness 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 producís. In strawberries, hot air treatments have been used to maintain fruit firmness during postharvest. In this work, it was evaluated the effect ofheat treatments on cell wall composition and activities of different softening associated enzymes (PME, PG, EGase, P-gal and P-xyl) in the internal and external zones of the strawberry fruit receptacle. Strawberries (75 % red color) were heat-treated at 45°C during 3 h in an air oven. After treatment the fruit were stored at 20°C for 2 d. The internal and externa! zones of heat-treated fruit remained fírmer than controls after 1 d of storage at 20 °C. After 2 d of storage the difference was still observed in the external zone. Heat treatments reduced EGase and P-xyl activity in both zones and maintained higher levéis of hemicelluloses than control fruit. PG and P-gal activity were aiso inhibited by the treatment. Heat treated fruit maintained higher levéis of HC1 soluble pectins and had lower levéis of water-soluble pectins than control fruit. PME was increased by the treatments and heat-treated fruit presented higher EDTA soluble pectins than 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.