Ripening responses of 'Forelle' pears

[摘要] ENGLISH ABSTRACT:'Forelle' is one of three blushed pear cultivars produced in South Africa. A mandatoryminimum cold storage duration of 12 weeks at -0.5°C to ensure even ripening,prevents 'Forelle' from being marketed earlier. Since earlier marketing can result inpremium prices (in excess of 50% morê per carton) research in recent years has beendirected at reducing this 12 week cold storage period. Intermittent warmingtreatments, controlled atmosphere (CA) storage in combination with regularatmosphere (RA) storage intervals, and ethylene treatments, have been tested asalternatives to the 12 week cold requirement. However, none of these treatmentsdelivered a better internal quality in terms of mealiness and astringency.Fruit harvested from the Warm Bokkeveld and Theewaterskloof areas at commercialmaturity were stored at -0.5°C for up to 21 and 22 weeks, respectively, to understandthe changes in ripening and mealiness of 'Forelle' pears after cold storage (Paper 1).Samples were removed every third weev, placed at 15°C, and maturity factors, totalACC concentration, ethylene production and respiration rates monitored every thirdday for 12 days. Fruit from the Warm Bokkeveld and the Theewaterskloof areasripened after 6 and 7 weeks at -0.5°C, respectively. However, after 6 weeks of coldstorage followed by 6 days at 15°C, all fruit harvested in the Warm Bokkeveld, and70 % of the fruit harvested in the Theewaterskloof area, were mealy. With extendedstorage at -0.5°C (> 15 weeks) the incidence of mealiness declined in fruit from bothareas, but never disappeared, when evaluated at 15°C over 12 days.Since harvest maturity affects the incidence of mealiness in other pear cultivars, theeffect of harvest maturity on 'Forelle' pears with regard to mealiness developmentwas examined (Paper 2). Fruit were harvested from the Ceres area, in weeks 8 (preoptimum),10 (optimum), 12 and 14 (both post optimum). Maturity indices, juicecontent, mealiness, total ACC content, ethylene production and internal ethylene weremonitored at harvest, after 6 weeks of storage at -0.5°C and again after 7 days at15°C. Fruit harvested 2 weeks before commercial harvest (week 8) had the highesttotal ACC concentration, ethylene production and the potential to ripen, but alsodeveloped the highest incidence of mealiness (80%). However, fruit of all harvestmaturities (except where contamination with 1-MCP occurred) were mealy. It would appear that factor(s), other than harvest maturity, play a more important role in theinitiation of mealiness in 'Forelle' pears.Although ethylene has been shown to shorten the cold requirement of 'Forelle', thereare conflicting reports as to its effectiveness in reducing mealiness. Consequently, theaim of the third paper was to evaluate the effect of ethylene on ripening and mealinessof 'Forelle' pears. Fruit harvested from the Elgin area at commercial maturity werestored for 3 weeks at -0.5°C, treated with ethylene (100 Jl L.L·l, 24h, 20°C) and held at20°C for a further 2 days (without ethylene). Control fruit were held at 20°C for 3days. Fruit were returned to -0.5°C for a further 3 weeks. After a subsequent 3 days at20°C, flesh firmness was 4.6 kg in treated fruit compared to 6.1 kg for control fruit.At this point all fruit treated with ethylene were mealy. Control fruit all exhibitedmealiness after a further 3 weeks at -0.5°C followed by 7 days at 15°C. Ethylenetreatment advanced fruit maturity, but did not prevent or alleviate mealiness.Mealiness is a textural disorder recognized by a dry soft pulp. This has previouslybeen recorded in 'd'Anjou' pears, as a result of storing the fruit for too long at -1.1°C,but has also been the result of a chilling injury in fruit like nectarines, kiwi andpersimmon. The role of storage temperature on ripening, and specifically mealiness,of 'Forelle' was thus investigated (Paper 4). Fruit harvested from the Elgin area atcommercial maturity were stored at -0.5°C, 4.0°C and 7.5°C for 0, 3 and 6 weeks.Samples were removed every third week, placed at 15°C, and maturity indices,extractable juice content, mealiness, total ACC content, internal ethyleneconcentration and ethylene production were monitored on removal and after 7 days.Flesh firmness of the 4°C stored fruit was 0.5 kg lower than fruit stored at -0.5°C, onremoval from storage. Fruit stored at 4°C and 7.5°C ripened with little to nomealiness (0 and 8% respectively) in contrast to fruit stored at -0.5°C (70% mealy).Total ACC accumulation and ethylene production were higher for fruit stored at 4°Cand 7.5°C than fruit stored at -0.5°C. Storage temperature appears to playa role in thedevelopment of mealiness.Although storage temperatures influenced mealiness development, this researchshould be repeated before this can recommended as a commercial treatment. The underlying mechanism of action in the development of mealiness should beinvestigated.By examining fruit grown in different climatical areas, harvested at differentmaturities, treated with exogenous ethylene and stored at different temperatures, thisresearch has helped to a better understanding of the role of factors affecting ripeningand development of mealiness in 'Forelle'.

[发布机构] Stellenbosch University