A Simplified Method for the Determination of Total Oxalate-Soluble Pectin Content in Japanese Pear

The oxalate-soluble pectin is related to fruit firmness with respect to the chelation of calcium ions with carboxyl groups of adjacent polyuronide chains. However, the accurate total oxalate-soluble pectin content is not easily attainable. Using the Japanese pear fruits (Pyrus serotina Rehder var. culta‘Housui’) as our model, we proposed a simple method to define extraction time of total oxalate-soluble pectin in fruit without repetition based on half-extraction time which is the time when oxalate-soluble pectin was extracted up to 50%. There were two stages of extraction: primary- and secondary-extraction stages. The different picking dates did not affect the extraction rates and the unaccomplished ratios in the primary stage in which half-extraction time embedded but did affect in the secondary stage (P<0.01). The extraction time of total oxalate-soluble pectin could also be estimated. The method recommended that the extraction should be done until half-extraction time was reached and the total oxalate-soluble pectin could be estimated by multiplying the pectin content at half-extraction time by two. We also postulate that the method may prove useful for other fruit and vegetables as well. Half-extraction time of Japanese pear was 2.1 h.