Abstract
Three bulk samples of two different cultivars of kiwifruit, green (Actinidia deliciosa L.) and golden (Actinidia chinensis L.) were bought ripe, ready to eat from a local market. The aim of the study was to determine the oxalate composition of each of the three fractions of kiwifruit, namely skin, pulp and seeds. The pulp consisted of 90.4% of the edible portion of the two cultivars while the skin and seeds made up a mean of 8.0% and 1.6% respectively. Total oxalate was extracted with 2.0 M HCL at 21 °C for 15 min and soluble oxalates extracted at 21 °C in water for 15 min from each fraction. The total and soluble oxalate compositions of each fraction were determined using ion exchange HPLC chromatography. The pulp of golden kiwifruit contained lower amounts of total oxalates (15.7 vs. 19.3 mg/100 g FW) and higher amounts of soluble oxalates (8.5 vs. 7.6 mg/100 g FW) when compared to the green cultivar. The skin of the green cultivar contained lower levels of insoluble oxalates (36.9 vs. 43.6 mg/100 g FW), while the seeds of the green cultivar contained higher levels of insoluble oxalates 106.7 vs. 84.7 mg/100 g FW.
Highlights
Kiwifruit is currently one of New Zealand’s largest horticultural export crops with 380,000 tonnes being harvested in 2009 and 361,066 tones being exported to over 55 countries in the same year [1].Kiwifruit has become a significant fruit in the New Zealand domestic market
The amounts of total oxalates in golden kiwifruit reported in the literature varies from 7.8 to 45 mg/100 g fresh weight (FW), while the values for green kiwifruit ranged from 12.7 to 84.3 mg/100 g FW [2,4,5,6]
The distribution of the skin and pulp of each cultivar were similar, except that the green kiwifruit cultivar contained a higher proportion of seeds compared to golden kiwifruit of similar size and weight (Table 1)
Summary
Kiwifruit is currently one of New Zealand’s largest horticultural export crops with 380,000 tonnes being harvested in 2009 and 361,066 tones being exported to over 55 countries in the same year [1]. Kiwifruit has become a significant fruit in the New Zealand domestic market. Studies have shown that green kiwifruit contained moderate amounts of total oxalate which is largely found as calcium oxalate in raphide crystals. These crystals of insoluble oxalate are responsible for the irritant factor or “catch” which is used to describe an irritation of the mucous membranes of the mouth [2]. The amounts of total oxalates in golden kiwifruit reported in the literature varies from 7.8 to 45 mg/100 g fresh weight (FW), while the values for green kiwifruit ranged from 12.7 to 84.3 mg/100 g FW [2,4,5,6]
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