Changes in rind firmness and cell wall polysaccharides during citrus fruit development and maturation

Changes in rind firmness and cell wall polysaccharide composition were measured in fruit with a) a soft rind,('Satsuma' mandarin, Citrus unshiu Marc., cv, Aoshima), and b) a firm rind (hassaku, C, hassaku Hort, ex Tanaka), from August to January of the following year, Rind firmness was similar in both species in August, but hassaku had significantly firmer rind than did mandarin from September to January. Both flavedo and albedo tissues were extracted, and the extracts were hydrolyzed and fractionated to yield four fractions: (hot water, EDTA, hemicellulose, and cellulose). In flavedo tissue, sugar concentration was highest in the cellulose fraction, and lowest in the hemicellulose fraction. The concentration in all fractions decreased as the fruit developed and matured. Although the sugar concentration in the cellulose and EDTA fractions of both species was similar in August, it was significantly higher in both fractions in hassaku than in mandarin in January. The sugar concentration of each fraction from albedo tissue was in the order: cellulose > hemicellulose > hot water > EDTA, The range of variation in cell wall sugars in albedo tissue was smaller than that in flavedo tissue. Chemical name used: ethylenediaminetetraacetic acid (EDTA).