Maturity evaluation of kiwifruit determined on the basis of starch and pectin contents and related enzyme activities.

Abstract

Since it is difficult to judge maturity of kiwifruit by appearance, growers measure the soluble solids (S.S.) content using a refractometer. In order to find a suitable harvest index other than S.S. and firmness, starch content, total pectin (TP) and water soluble pectin (WSP) contents, β-amylase and polygalacturonase (PG) activities of kiwifruit were investigated. The S.S. content, measured with a refractometer, and firmness of kiwifruit stored at room temperature (20°C), with or without ethylene treatment were compared. Kiwifruit treated with ethylene after harvest showed more uniform firmness and S.S. content than those without ethylene treatment. β-Amylase and PG activities, TP and WSP contents could not be used as alternative harvest and shipment indices for kiwifruit owing to fluctuation in their values. The use of S.S. content as a maturity index appeared to be applicable in 'Hayward' but not in the early-ripening cv. Koryoku. If 'Koryoku' were to be harvested based on the optimum S.S. content, the fruit would have to be shipped within 2 days after ethylene treatment to maintain suitable firmness. In 'Koryoku', the period of highest starch content is a better maturity index than S.S. content. Harvesting at the suitable period would ensure longer storage and maintenance of firmness and sweetness.