Antioxidative ability of cell wall components in fruits against ascorbic acid oxidation.
Motomura Y., Yoshida Y.
Author Affiliation: Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, 036-8561, Japan.
: 669-676
Abstract : Ascorbic acid (AsA) oxidizes rapidly in an aqueous solution and/or in the presence of copper ions. The antioxidative ability of water- and hot water-soluble cell wall components, extracted from 18 cultivars of fruit flesh (i.e. apple (Malus pumila), black currant (Ribes nigrum), gooseberry (Ribes grossularia [R. uva-crispa]), pear (Pyrus communis), red currant (Ribes vulgare [R. rubrum]), Japanese apricot (Prunus mume), melon (Cucumis melo), loquat (Eriobotrya japonica), strawberry (Fragaria ananassa), peach (Prunus persica), pawpaw (Carica papaya), orange (Citrus iyo), banana (Musa sapientum [M. paradisiaca]), pineapple (Ananas comosus), nectarine (Prunus persica), mango (Mangifera indica), grape (Vitis labrusca × V. vinifera) and kiwifruit [Actinidia deliciosa]) against AsA oxidation was examined. UV absorbance of an aqueous solution of AsA decreased remarkably with time and had nearly disappeared after 12 h. When the fraction extracted with water from alcohol-insoluble residue of fruit flesh was added to an AsA solution, the decrease in UV absorption slowed compared with the control. Among 18 cultivars, the fractions from the flesh of melon, loquat and strawberry demonstrated remarkable effect in maintaining UV absorbance (higher antioxidant activity), while those of grape, mango and kiwifruit showed lower activity. Among the fractions extracted with water, hot water and HCl successively, water- and hot water-soluble fractions showed antioxidant activity, while less activity was found in the HCl-soluble fraction. In apple and pear fruits, the activity varied with cultivar, and increased with maturity, and by storage in apple. Using fractionation by gel permeation chromatography, water- and hot water-soluble fractions from apple flesh were separated into four subfractions, and antioxidant activity of each subfraction was evaluated. The highest activity was found in the subfraction which included lower molecular-weight substances. In an AsA solution with added CuSO4, UV absorbance decreased quickly and had nearly disappeared within 15 minutes. In a mixture of hot water fraction, CuSO4 and AsA, UV absorbance decreased slightly at a slower rate compared with the solution without the hot water fraction. In an AsA solution with pectin from apples, the decrease in UV absorbance was noticeably inhibited. Pectins with a low rate of esterification displayed a relatively higher level of activity than those with a high rate of esterification. These results suggest that comparatively low molecular and low esterified pectic compounds could possess antioxidative ability.