ALPHA-AMYLASE AND STARCH DEGRADATION IN KIWIFRUIT

Alpha-amylase activities and activity gel profiles were measured in ki wifruit Actinidia deliciosa var. deliciosa ([A. Chev.], C. F. Liang an d Ferguson cv. Hayward) during fruit development and postharvest ripen ing. As fruit developed, alpha-amylase activity increased on a per fru it basis, mirroring the increase in starch content in the fruit. Alpha -amylase activity increased approximately 2-fold between 134 days afte r anthesis (DAA), (when fruit starch content is at its maximum before beginning to decline) and harvest. During postharvest ripening with an d without ethylene treatment at 20 degrees C, or during postharvest st orage at 0 degrees C, enzyme activity remained similar to harvest valu es until fruit were ripe and most of the starch converted to sugars. A t this point activity decreased 4-5-fold. Several amylolytic bands as well as starch phosphorylase and debranching enzyme were visible in st arch activity gels. Starch phosphorylase was lower in ripe fruit, as w as the intensity of two amylolytic bands. None of the other amylolytic bands or the debranching enzyme changed in response to fruit developm ent or ripening. The same results occurred if gels were incubated at p H 6.1 or pH 8.0. These results are discussed in relation to the initia tion of net starch degradation at the commencement of fruit ripening.