Ripening and microstructure of apricot (Prunus armeniaca L.)

Colour, texture, pectin autolysis, membrane permeability and microstructure (SEM, TEM), beta-galactosidase and polygalacturonase were studied in apricots (cv. Magyar kajszi) harvested in mature green, straw yellow, bright orange and deep orange stages. The L* increased from mature green to straw yellow then decreased from straw yellow to deep orange state. The a* values increased with ripening. The bright and deep orange apricots were significantly softer than the mature green and straw yellow ones and the membrane permeability increased with ripening. The presence of beta-galactosidase enzyme was proved by immunoblotting analysis using monoclonal anti-beta-galactosidase clone GAL-13 (Sigma) in all ripening stages. The enzyme activity was very low in mature green stage and increased significantly (P> 95%) with increasing ripeness and during storage. The PG activity was very low in the mature green apricot. A significant (P> 95%) increase was observed in the straw yellow apricot and in the riper fruits. The mature green apricot showed a regular, the straw yellow and bright orange samples showed a moderately regular tissue structure, while the tissue of the deep orange apricot collapsed (SEM). The cell wall and the middle lamella of the green apricot (TEM) were intact. Generally, there were intact cytoplasm membranes with some damaged parts. In the straw yellow apricot, the cell wall started to loosen, the middle lamella lost pectic polysaccharides. The structure of the cytoplasm was not recognisable, the tonoplast and the cytoplasm membrane were injured. The cell wall of the bright orange apricot was similar to that of the straw yellow ones. The middle lamella dissolved and hairy, fibrillar structure of cell wall was found in the deep orange samples.