Characterisation of the cell walls of loquat (Eriobotrya japonica L.) fruit tissues

Loquat fruit (Eriobotrya japonica L. cv. Algor) was dissected to give the following tissue zones: epidermis or epicarp, flesh or mesocarp, integument (a thin layer surrounding the seed cotyledons), seed testa, kernel and hairy receptacle. The alcohol insoluble residues (AIRs) from all these tissues were proved to be free of starch, except loquat kernel which on a fresh weight basis contained about 34% of starch. AIRs were analysed for moisture, ashes, protein, lignin and the component sugars were released by two hydrolytic procedures which helped to distinguish the sugars from non-cellulosic polysaccharides and cellulose. Their major component polysaccharides were inferred to be pectic polysaccharides since all AIRs were very rich in sugars such as uronic acids, arabinose and galactose. Pectic polysaccharides contributed up to 70% of total cell wall polysaccharides in the edible flesh of the loquat fruit. Important differences in the degree of branching, degree of esterification and in the amounts of Ca and Mg associated with pectic polysaccharides were detected among pectic polymers depending on the loquat tissue zone. These compositional and structural differences may be related to the role that these pectic polymers play within the tissues which form the loquat fruit.