Changes and Variations in the Pectic Constitution of Ripening Peaches as Related to Product Firmness

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Abstract
SUMMARY: Samples of 6 commercial varieties of peaches–5 freestone (Ranger, Triogem, Sun‐high, Elberta, and Afterglow), and 1 clingstone (Ambergem)–were examined at 4 stages of postharvest ripeness. Fresh fruit samples were tested for firmness and analyzed for pectin‐esterase activity and for three pectin fractions (water‐soluble, Versene‐soluble, and Versene‐insoluble). Shear press readings were taken on the corresponding canned samples as well as subjective firmness ratings for each variety at each stage of ripeness.In Ambergem, the proportions of the three pectin fractions remained relatively constant in fruits held 4 days at 25°C. In freestone peaches, the proportion of water‐soluble pectin increased rapidly at the expense of the other two fractions. There were significant statistical differences between the freestone varieties in the proportions of Versene‐soluble pectin retained with advancing ripeness. The differences in pectin constitution were related to the firmness of the fresh and canned products. Pectin‐esterase activity was markedly lower for Elberta than for the other freestone varieties. The level of pectinesterase activity was not in itself related to firmness retention but may be involved indirectly in demethylation for cationic‐binding.

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