This study, for the first time, investigated the total protein changes and protease activity pattern of three cultivars of kiwifruit including Abbott, Allison and Hayward, cultivated in the north of Iran, during 6 months of fruit development from July to December 2008. During the last month of sampling, fruits were stored in ambient temperature. According to the result of fruit extracts, pattern of changes in total protein concentration showed three significant steps: low concentration of protein during the early stages of fruit development until middle of July for Allison and Hayward and early August for Abbott, increasing protein concentration until middle of October for Allison and Hayward and late October for Abbott, and steady state level of protein concentration until harvesting time. During storage time of fruits, all three cultivars showed increasing level of total protein concentration. Among the cultivars, Hayward and Allison showed the lowest and highest total protein concentration, respectively. Protease activity showed increasing pattern in all of the investigated cultivars significantly until harvesting time. During postharvest time, Hayward did not show any significant change in protease activity but, the other two cultivars had increasing pattern from 10 to 20th of storage and then decreased significantly. Among the cultivars, Abbott showed the lowest and Allison the highest level of total protease activity at harvesting and postharvesting time. SDS-PAGE, ion-exchange chromatography and zymogram native-PAGE of fruits extraction showed that dominant protein and protease activity in these cultivars during fruit development and ripening process is related to actinidin.

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