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247 Crop Post-Harvest: Science and Technology , First Edition. Edited by Debbie Rees, Graham Farrell and John Orchard. © 2012 Blackwell Publishing Ltd. Published 2012 by Blackwell Publishing Ltd. 12 Kiwifruit, Guava, Passion Fruit and Lychee Graham Farrell The account presented here concentrates on recent findings and new initiatives in the post-harvest aspects of four commodities with important roles in an expanding market for exotic fruits and vegetables. General, comprehensive volumes on the post-harvest behaviour and handling of these fruits, inter alia, are given by Nagy and Shaw 1980, Morton 1987, Mitra 1997, Wills et al. 1998, Thompson 2003 and Gross et al. 2002. Warrington and Weston 1990 provide an in-depth study of all aspects of kiwifruit from a New Zealand perspective. KIWIFRUIT The genus Actinidia comprises about 50 species of kiwifruit, mostly from temperate forests in south-western China. The main commercial variety is Hayward Actinidia deliciosa A. Chev. C. F. Liang A.R. Ferg., preferred for its good storage characteristics over other varieties, but A. chinensis Planch. and the hardy kiwifruit A. arguta Sieb. Zucc. Planch. ex Miq. are also cultivated com- mercially. Kiwifruit has been an economic success mainly because of its good keeping qualities over long periods at 0°C Hewett et al. 1999. Mature fruits are broadly oval, green-brown in colour and densely covered with fine hairs. The pulp is bright green with a mass of small black seeds. Kiwifruit plants are vines with the fruits borne on long pedicels Cheah Irving 1997. Production Italy is the main producer of kiwifruit, followed by New Zealand and Chile Rushing 2002. California is the major producer in the United States, accounting for 95 of all kiwifruit produced nationally. Chinese production is forecast to increase rapidly, reaching about 0.5 million tons MT and accounting for half of world output by the end of 2006 Huang et al. 2004. Table 12.1 shows some production figures by region. Harvesting Kiwifruit are nonclimacteric and are among the few fruits that retain large amounts of starch at maturity. Hydrolysis of starch continues after harvest even at low temperatures and is complete a few weeks later, when the starch is converted to soluble sugars mainly glucose and fructose, with some sucrose. At the limit of carbohydrate accumulation kiwifruit will have reached the best quality for consumption and so delays in harvest will not further improve the flavour Strik 2000. In the past, maturity was based on arbitrary harvest dates, fruit colour or firmness but these characters are not good guides to maturity. However, firmness is used in the United States, with a minimum force of 6.4 kg, using a penetrometer with an 8 mm tip, considered appropriate, together with a minimum soluble solids content SSC of 6.5 Crisosto et al. 1999. Penetrometer readings should be taken on fruit at 37–39°C Crisosto 1997. In New Zealand, measurement of firmness using a noncontact laser air-puff method has been described by McGlone and Jordon 2000. Positive correlations between SSC and fruit maturity and eating quality have been established, and so refractometer 248 Crop Post-Harvest: Science and Technology measurements of SSC are the favoured method for assessing harvest maturity. In New Zealand the minimum level of SSC for export fruit is 6.2 measured in a sample of ten fruit. If two fruits from the sample have SSC less than 5.8, then the orchard is not up to export quality standard Rushing 2002. However, work in California suggested that some vineyards could produce kiwifruit of high taste quality 12 ripe soluble solids concentration, as measured by consumer acceptance tests, before they reach 6.5 SSC assessed when fruit are still hanging on the vines Crisosto Crisosto 2001. Higher SSC levels, up to 15, have been suggested for long-term storage Mitchell et al. 1991, and in the United States a value of 14 is recommended for table ripeness Crisosto et al. 2002; Rushing 2002. A rapid increase in soluble solids and softening are notable characteristics of kiwifruit maturity Cheah Irving 1997. Jordan et al. 2000 used post-harvest density as an indicator of SSC and dry matter content, whereas Osborne and Jordan 1996 and Osborne et al. 1999 recommended near- infrared NIR spectroscopy as an alternative low-cost, nondestructive method for estimating SSC and grading kiwifruit. Advances in NIR methods suggest that use of the technique at harvest could identify less mature kiwifruit leading to a reduction in post-harvest rots Clark et al. 2004. Electrical impedance spectroscopy has been used to detect ripening in nectarine, persimmon and tomato though this method revealed no impedance change as kiwifruit ripened. It was speculated that immobility of electrolytes within the cell wall of ripening kiwifruit was responsible for the effect Bauchot et al. 2000. Once maturity has been reached all kiwifruit in the vineyard can be collected at the same time since there are no visible features to enable pickers to separate mature from immature fruit Crisosto Kader 1999. However, larger fruit can be picked first and the smaller fruits allowed to increase in size and then picked at a later date Mainland 1998. Picking is usually done by hand, with the fruits snapped off the pedicel at the abscission layer during dry periods to limit storage rots. Pickers should wear soft cotton gloves to prevent damage to the skin of the fruit. Fruits should be unshrivelled and free from sun scald, scars, growth cracks, insect injury, internal damage or bruising and decay Crisosto et al. 2002; Rushing 2002. Avoiding mechanical damage during harvesting and transport to pack houses is important to prevent the release of ethylene that may soften adjacent fruit. Grading Criteria for grading are subjective and largely rely on superficial appearance Rushing 2002. In the United States, grades include US Fancy, US No. 1 and US No. 2 USDA 1986. Assigning fruit according to size is difficult because of variability in length and diameter, and so size designations are based on the number of kiwifruits that can be placed in a tray. In the United States, size criteria defined by the Californian Kiwifruit Administration Committee are usually used. These vary from year to year; with recent tray equivalency size designations ranging from 21 22 fruits in an 8 lb sample, fairly uniform size variation equals 0.5 in 2 to 45 55 fruits in an 8 lb sample, fairly uniform size variation equals 0.25 in 2 . Tolerances also apply, relating to the weight of the sample and the number of fruits that do not fall within the diameter range KAC 2004. Cooling Historically, kiwifruits were cooled to 0°C as soon as possible after harvest to prolong shelf life using forced air cooling; hydro-cooling was not advised because the hairs on the fruit surface retained moisture that hastened the development of rots. However, current advice suggests that fruits should be maintained under ambient conditions for several days since all types of cooling predispose fruits to stem-end rots, as reported by Lallu 1997 and Lallu et al. 1997 in New Zealand and Cheah and Irving 1997 in the United States. Furthermore, in Chile, curing for up to 72 h did not lead to softening during cold storage Retamales et al . 1997. Chill sensitivity may result at temperatures near 0°C, with pitting, scalding or ring shaped, granular or water soaked lesions in the outer pericarp at the stylar end Lallu 1997. Freezing damage may occur in the field before harvest; if late in the season the shoulders are affected when cells in that area collapse leading to a pinch- ing of the fruit at the stem end. Freezing in store causes translucency and yellowing of the flesh after prolonged storage Chisosto et al. 2002. Table 12.1 Kiwifruit production MT in 2000 and 2001. Region 2000 2001 Asia 62 775 62 000 CentralNorth America 31 074 20 640 Europe 512 402 533 700 Oceania 257 197 268 197 South America 115 500 120 000 Source: Fresh Produce Deskbook 2003.