CHANGES IN PECTIC POLYSACCHARIDES OF CELL-WALL PREPARATION FROM CHINESE QUINCE FRUIT DURING HEAT TREATMENT

ABSTRACT To identify suitable conditions for converting pectin covalently (and ionically) attached in the cell wall of Chinese quince (Pseudocydonia sinensis) fruit into water extractable pectins, the cell-wall preparation (alcohol-insoluble solids [AIS]) was boiled for up to 4 h in the presence or absence of citric acid (1–4%, w/v). During the heat treatment, the Na2CO3-soluble and chelator (trans-1,2-cyclohexanediaminetetraacetic acid)-soluble pectin decreased and the water-soluble pectin increased dramatically. The presence of citric acid accelerated this change, and at higher concentrations, the reaction progressed faster. However, smaller increases in water-soluble pectin and a remarkable decrease in hemicellulose were observed when the AIS was boiled with 4% citric acid. High-performance size-exclusion chromatography analysis revealed that the average molecular weight of polysaccharides in each pectic fraction shifted to lower values during the heat treatment. The best conditions for heat treatment conversion of protopectin to water-soluble pectin seemed to be under conditions of 1% (w/v) citric acid for 4 h, or 2% (w/v) citric acid for 2 h. PRACTICAL APPLICATIONS Chinese quince (Pseudocydonia sinensis) is a medicinal fruit traditionally used in folk medicines and medicinal foods. They are often subjected to heating for a certain time to decompose the cell wall and to obtain a decoction that is rich in medicinal ingredients including pectin. Pectin is a dietary fiber that has many pharmacological properties. The study of the pectin degradation during boiling could reveal the best condition to obtain a decoction containing high amounts of water-soluble pectin. The optimized condition may be usable when producing a medicinal food from Chinese quince fruit.