Determination of Soluble and Insoluble Oxalate Contents in Kiwifruit (Actinidia deliciosa) and Related Species

Abstract

Change of oxalate contents in green-fleshed 'Hayward' and 'Bruno' and in yellow-fleshed 'Golden King' and 'Yellow Queen' kiwifruit, and related species were analyzed during their development and storage. Calcium oxalate crystals in kiwifruit are observed in the form of raphide showing long and needle-shape in the green-fleshed cultivars but short in the yellow-fleshed ones ; the raphide crystals in A. arguta and A. rufa were likewise short. The oxalate contents, which was determined by enzymatic analysis, attained maximum in fruit sampled in July during their early development period. The level gradually decreased with the increase in size until harvest in late October ; it continued to decrease during cold storage. The oxalate content decreased slightly faster in the yellow-fleshed fruits than it did in the green-fleshed ones. The oxalate content in A. arguta was lower than that in A. deliciosa, whereas that in A. rufa was slightly higher.