Relation of Highly Polymerized Procyanidin to the Potential Browning Susceptibility in Pear Fruits

Abstract

The European pears, 'Bartlett' (Ba), 'Aurora' (Au), 'Conference' (Co), and 'La France' (LF) were less susceptible to browning than were 'General Leclerc' (GL), 'Grand Champion' (GC), 'Beurré Hardy' (BH), and 'Joséphine de Malines' (JM). The acetone extracts (AE) of Ba, Au, Co and LF had less phenolics than did GL, BH, GC and JM. The ratio of the phenolics in AE to total phenolics was also bigger in the latter 4 cultivars. The amount of monomeric and/or oligomeric flavan-3-ols (procyanidin) in methanol extracts (ME) was larger than that in the AE of Ba, Au, Co and LF, whereas the amount of procyanidin in the AE was similar to or higher than that in the ME of GL, BH, GC and JM. The relative degree of polymerization (RDP) of procyanidin assessed by the butanol-HCI method and the vanillin-sulfuric acid method showed that RDP of procyanidin in Ba and Au was low, RDP in LF, GL, BH, GC and JM was high in both ME and AE. Polyphenoloxidase (PPO) activity of 8 cultivars varied, the highest activity occurred in LF and the lowest in GC. Highly polymerized procyanidin in AE did not react with PPO directly in a test solution, whereas browning of the mixture occurred in the presence of PPO and chlorogenic acid. The resulting brown color was darker than it was in the mixture of chlorogenic acid and PPO only, indicating that highly polymerized procyanidin plays an important role in tissue browning and its level is strongly related to the potential browning in pear fruits.