Keryl K. Jacobi

Postharvest heat disinfestation treatments of mango fruit

Postharvest heat disinfestation treatments have emerged over the past decade as viable non-chemical control methods for fruit flies in mango fruit around the world. The physiological responses of mango fruit both during and following a heat treatment determine the eventual eating quality of the fruit. This review describes the methods used to heat treat mango varieties for insect disinfestation. The physiological effects of heat treatments, particularly pretreatment conditioning and hot water treatments, on the fruit are covered in detail.

Effect of fruit maturity on quality and physiology of high-humidity hot air-treated ‘Kensington’ mango (Mangifera indica Linn.)

Abstract Mature and immature ‘Kensington’ mangoes ( Mangifera indica Linn.) were treated with an experimental high humidity hot air treatment (HT) to a fruit core temperature of 46.5 °C for 10 min for disinfestation purposes and to test for fruit injury reportedly associated with fruit immaturity. Two methods of determining fruit maturity were examined with fruit harvested over two different seasons, in order to gain a broad range of maturities. No internal or external injury was caused to fruit at any maturity stage by the treatment. Mature HT fruit softened faster and had increased skin colour development compared to immature HT fruit. HT shows commercial potential since the physiological changes associated with treatment and maturity can be managed with careful postharvest handling practices. We recommend only mature fruit be harvested and treated since quality and market performance will be maximised.

Lychee (Litchi chinensis Sonn.) fruit quality following vapour heat treatment and cool storage

Abstract Vapour heat treatment (VHT) was used as a possible disinfestation treatment against fruit flies for lychee fruit. On the basis of an optimum core temperature of 45°C for variety ‘Tai So’, this and two other varieties ‘Kwai May Pink’ and ‘Wai Chee’, were exposed to this temperature for various lengths of time. ‘Tai So’ and ‘Wai Chee’, but not ‘Kwai May Pink’, tolerated this temperature for 42 min. without significant reduction in fruit appearance, eating quality and disease control following 2 weeks storage at 5°C, during which transport to distant markets could be undertaken. Preliminary results suggest that 45°C for only 30 min. is sufficient to kill all stages of the Queensland fruit fly, Bactrocera tryoni , so at least two of the three varieties tested could safely survive these conditions without quality reduction.

The influence of hot benomyl dips on the appearance of cool stored lychee (Litchi chinensis Sonn.)

Abstract Three cultivars of lychee (Litchi chinensis Sonn., ‘Tai So’, ‘Kwai May Pink’ and ‘Wai Chee’) were dipped in hot benomyl (Benlate®, 50 wettable powder (WP) 1 g l−1 at 48, 50 and 52°C) for times from 0.5 to 18 min. Appearance and disease incidence were assessed after storage at 5°C for 2 and 4 weeks. Treatments at 48°C for 1–3 min and at 50°C for 1–2 min were found to give the best disease control and most acceptable fruit appearance. ‘Tai So’ was the least affected by heat treatment and showed the greatest storage potential. A previous recommendation for cultivar ‘Bengal’ of 52°C for 2 min was found to be unsuitable for the cultivars tested. Conditions of 48–50°C for 2 min are recommended as providing the best control of disease with minimal loss of skin colour.

Postharvest quality of zucchini (Cucurbita pepo L.) following high humidity hot air disinfestation treatments and cool storage

Abstract Zucchini ( Cucurbita pepo L.) were disinfested by a high humidity hot air treatment (HT) to a fruit core temperature of 45 °C for 30 min, and then stored at 7–8 °C. Skin yellowing (indicated by percentage yellowing and hue angle) generally increased with storage time, and was exacerbated by HT. While zucchini quality can be maintained for up to 11 days following HT, it appears that chilling injury prior to such treatment reduces the ability of the fruit to withstand this method of disinfestation.

Loss of heat tolerance in ‘Kensington’ mango fruit following heat treatments

Abstract Conditions that promote loss of heat tolerance, or dehardening, of ‘Kensington’ mango fruit ( Mangifera indica Linn.) were investigated. Fruit were conditioned at 40°C for 8 h, and then placed at 22°C (dehardened) for 8, 16, 24 or 48 h prior to hot water treatment (HWT) (47°C held for 15 min). The greatest reduction in fruit heat tolerance occurred in fruit placed at 22°C for 16 h. Compared with the other conditioned fruit, these fruit had the highest incidence and severity of skin scalding, external cavities, starch layer, increased F 0 values and a lack of recovery in F V / F M ratios after HWT. It was concluded that the loss of heat tolerance in ‘Kensington’ fruit occurred at a slower rate than the increase in heat tolerance brought about by the 40°C conditioning treatments. Exposure of fruit to 22°C for 24 h or longer accelerated fruit ripening, and induced some protection against heat injury.