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 CaCl2 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’9 and ‘KS’13 on European pear (Pyrus
communis L.) seedling rootstocks. Fruits were picked on the 1st and 15th August, 2006 and
stored at 1ºC and 80-85% 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 CaCl2 and harvested early, contained less
OSP, PGA and IB following long-term storage.