Studies on the Peel Puffing of the Satsuma Mandarin

III. The Conversion of Pectic Substances and Calcium Distribution within the Peel

Abstract

1. Satsuma mandarin fruits were examined from July to December for 3 pectic fractions obtained from the albedo and flavedo of the peel. The maximum values of the 3 pectic substances were obtained in late July or early August with subsequent gradual decrease toward harvest. The content of ammonium oxalate soluble pectic substances (ASP) remained lower than that of the other pectic substances throughout the growth period.
2. The amount of hydrochloric acid soluble pectic substances (HSP) as percentage of the total pectic substances (TP) was highest at the beginning of the growth in both albedo and flavedo, followed by ASP and then by water soluble pectic substances (WSP). The ratio of WSP to HSP, however, was reversed and such trend continued toward harvest because a rapid increase in the WSP fraction occurred immediately after the beginning of the growth. The percentage of ASP remained nearly constant throughout the growth period.
3. TP, WSP and ASP contents in the albedo were higher in the non-puffy than in the puffy fruit. HSP contents, however, were slightly lower in the former than in the latter. The calcium content of the flavedo was increased up to 1.05 per cent in late July with a subsequent decrease approaching to 0.5 per cent in early December. Although the same tendency was observed on the time course change of calcium content in both albedo and flavedo, the change was more slow-going in the former than in the latter.
4. At harvest time the variation of calcium content among cell wall fractions of the peel was greatest in lignin, followed by oxalic acid soluble pectins. In both non-puffy and puffy fruits, the calcium content was lowest in the cellulose fraction of albedo. Generally, the cell wall of the peel of non-puffy contained more calcium than that of puffy fruit peel except hemicellulose and cellulose fractions of albedo.