Pre-treatment with Weak Basic and Detergent Solutions Improves the Enzymatic Peeling Process of Persimmon Fruit

Abstract

In the enzymatic peeling process of persimmon fruit, heat treatment prior to enzyme treatment is indispensable, as heat inactivation of polygalacturonase inhibiting protein (PGIP) greatly enhances the enzymatic degradation of pericarp tissue, and heat treatment produces cracks on the pericarp surface of certain cultivars. These cracks act as channels that introduce enzyme solution into the pericarp tissue. Since the frequency of crack formation affects the quality of peeled fruit, a combination of PGIP heat inactivation and mechanical perforation using metal needles, instead of heat-induced crack formation, has been proposed to improve the enzymatic peeling process of persimmon fruit. However, this process requires specially designed machinery to achieve uniform perforation. In the course of investigating the chemical components of the cuticle membrane of persimmon fruit, we found that the cuticle loses its stretching strength with the removal of wax, one of the main components of the cuticle membrane. Raw fruit treated with chloroform/methanol (1 : 1, v/v) to weaken the cuticle membrane before heat-treatment, showed increases in surface cracks and improved enzymatic peeling efficiency. A practical process applicable to food processing was achieved using a combination of chemical treatment in a detergent solution, for wax extraction, and heat treatment in a weak alkali solution, producing results similar to treatment with perforation. Using this new process, the entire enzymatic peeling process of persimmon fruit can be performed in solutions without mechanical perforation.