Total Oxalate-Soluble Pectin Concentration in Asian Pear (Pyrus serotina Rehd) Fruit in Relation to Ripening, Storage and Internal Browning Disorder

Oxalate Soluble Pectin (OSP) is related to fruit firmness with respect to the chelation of calcium ions with carboxyl groups of adjacent polyuronide chains. This study was carried out to explore the effect of time of fruit harvest, foliar spray with CaCl۲ during growing season on OSP, Polygalacturonase Activity (PGA), fruit firmness and the effects on fruit shelf life, quality and Internal Browning (IB) disorder. Fruit samples were collected from Asian pear (Pyrus serotina Rehd.) trees ‘KS’۹ and ‘KS’۱۳ on European pear (Pyrus communis L.) seedling rootstocks. Fruits were picked on the ۱st and ۱۵th August, ۲۰۰۶ and stored at ۱ºC and ۸۰-۸۵% relative humidity (RH). Five stages of extraction were performed on fruit samples including one pre-harvest, one at the time of harvest, and three following fruit harvest. Results indicated that OSP increased slightly during fruit ripening as well as during storage. In both the studied cultivars, the level of OSP in fruit harvested fifteen days after Optimum Time for Harvest (OTH) was higher than that harvested at OTH. The level of OSP in fruit softened after harvest significantly increased starting from the time of harvest. The relationship between flesh firmness, IB and OSP concentration showed the highest correlations in the both of the studied cultivars among PGA. In conclusion, flesh firmness and IB were correlated with the extent of OSP concentration. In addition, fruit, sprayed with CaCl۲ and harvested early, contained less OSP, PGA and IB following long-term storage.

Keywords:

Firmness , Polygalacturonase activity , Softening , Soluble solid concentration , storage , Titratable acids