449–455. Crop Post-Harvest: Science and Technology

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.