Differences in levels of pectic substances and firmness in fruit from six sweet cherry genotypes

The composition of sweet cherry fruit cell-walls relative to firmness was investigated for six cultivars and selections based on previous firmness data and harvest date at Summerland, B.C. Among the cultivars and selections, 'Merpet' had the lowest fruit firmness (early ripening), followed by 13S-27-17, 'Celeste', 13S-34-50, 'Lapins', and 'Sweetheart' (late ripening). In general, the firmer fruit cultivars and selections had a greater concentration of alcohol insoluble residues (AIR) (mg / g fruit) and more total AIR per fruit. Softer fruit genotypes had a greater amount of polymers weakly associated with the cell wall (e.g., the water soluble fraction). However, softer fruits had less of the highly esterified and tightly bound pectins (e.g., Na₂CO₃ soluble fraction). Total amount of hemicellulosic neutral sugars and uronic acids were not related to fruit firmness. Xyloglucan in hemicellulose fractions appeared to be less in softer fruits but the relationship was not consistent across all cultivars and selections.