Vitamin C content in the fruit of various cultivars of kiwifruit and other Actinidia species was estimated by determination of L-ascorbic acid and L-dehydroascorbic acid using ion-pair reversed-phase high-performance liquid chromatography. Fruit of A. deliciosa cv. Hayward, the most common commercially available cultivar, contained 65.5 mg/100 g fresh weight (FW) vitamin C. Vitamin C content in A. deliciosa fruit varied from 29 mg/100 g FW to 80 mg/100 g FW. In most cultivars of A. chinensis, vitamin C content in fruit was higher than that of Hayward. In particular, vitamin C content in cv. Sanuki Gold fruit reached more than 3-fold that of Hayward on a weight for weight basis. In A. argutafruit, there was wide variation in vitamin C content, with concentrations ranging from 37 to 185 mg/100 g FW. In cv. Gassan, Issai, and Mitsuko, vitamin C content of the fruit was much higher than that of Hayward. In A. arguta fruit, the ratio of L-ascorbic acid to total ascorbic acid tended to be higher than that of other species.

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Soluble sugars, sugar alcohol, and organic acid contents in Actinidia fruits at the eating-ripe stage were determined in various genotypes using high-performance liquid chromatography: five A. deliciosa, seven A. chinensis, two A. rufa, eight A. arguta, and three interspecific hybrids. The main soluble sugars in A. deliciosa and A. rufa fruits were glucose and fructose, although sucrose was present in smaller amounts. In contrast, sucrose was the predominant sugar in A. arguta fruits, followed by fructose and glucose. Most Actinidia fruits tested here contained myo-inositol as a sugar alcohol component. In particular, myo-inositol contents in A. arguta fruits were 0.575-0.982 g/100 g fresh weight, which is the highest level among all foods. Regarding the organic acid component, citric and quinic acids predominated over malic acid in all Actinidia fruits tested. Compared to A. deliciosa and A. chinensis, the proportion of quinic acid was higher in A. rufa and lower in A. arguta.Keywords: Actinidia spp., kiwifruit, sugar, organic acid, myo-inositol *To whom correspondence should be addressed. E-mail: nishi@komajo.ac.jp IntroductionThe kiwifruit industry has made remarkable progress since the fruit was introduced to the world market from New Zealand in the 1950s (Ferguson, 2004). The export of fresh kiwifruit from New Zealand led to rapid expansion of kiwifruit plantings (Ferguson and Huang, 2007), and the fruit is now grown in many countries, especially in Italy, China, France, Greece, and Japan in the northern hemisphere, and in New Zealand and Chile in the southern hemisphere. Consequently, kiwifruit has become a commonly consumed fruit that is easily obtainable year-round in many countries.Although the genus Actinidia is composed of 76 species and about 125 taxa (Ferguson and Huang, 2007), until recently, the kiwifruit market has been dominated by a single cultivar, Actinidia deliciosa 'Hayward.' Its fruit possess several beneficial attributes such as excellent flavor, green flesh color, high vitamin C content, and exceptionally long storage life. In 2000, the yellow-fleshed fruit of a novel cultivar, A. chinensis "Hort16A", which was developed in New Zealand, made its entry into the world market. In addition, some novel cultivars of kiwifruit and the related Actinidia crops have recently been introduced into the world market on a small scale; others are anticipated in the near future (Ferguson and Huang, 2007;Nishiyama, 2007). These Actinidia fruits have a wide diversity in size, shape, hairiness, flesh color, and flavor. Differences are also apparent in their vitamin C contents (Ferguson and MacRae, 1992;Nishiyama et al., 2004), carotenoids such as lutein and β-carotene (McGhie and Ainge, 2002;Montefiori et al., 2005;Nishiyama et al., 2005), and a cysteine protease actinidin (Nishiyama and Oota, 2002;Nishiyama, 2007).The fruit flavor can be affected by amounts of several constituents including sugars, organic and amino acids, and volatile aromatic compounds. In particular, the flavor of the fruit flesh is hig...