Influence of Cell Wall Calcium Content in FruitFirmness during the Ripening of Plums (Prunus domestica L.)

Abstract

‘Raínha Claudia Verde’ is a regional variety of Prunus domestica L. well adapted to a specific region in South of Portugal. In order to understand the different postharvest behavior of this variety produced in different orchards, cell wall polysaccharides and cell wall calcium fruit content were studied during ripening in two consecutive years. During harvest period pectic fractions soluble in water, carbonate and KOH were prepared from alcohol-insoluble residue (AIR) of plums. Galacturonic and neutral sugars contents were measured during fruit ripening and fruit firmness was also evaluated. The calcium fruit level was determined in the AIR during harvest season as well as in dry matter. Fruit firmness was significantly higher in second year and it was probably related with calcium fruit content and pectic polysaccharides. Also between orchards there was a significant difference in calcium fruit content, and this might influence the overall fruit texture during postharvest. During fruit ripening water soluble pectic polysaccharides does not change significantly, which was in accordance with the small decrease in tissue firmness. The occurrence in the supernatant of the cellulosic residue of highly branched polysaccharides might be the consequence of matrix material associated with microfibrilar phase. During ripening, it was not evident the depolymerization of hemicellulosic fraction. The loss of fruit firmness is a consequence of many cellular events which are influenced by external factors. The knowledge of calcium content in the cell wall and the pectic polysaccharides could be of great importance to local farmers to predict fruit texture.