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Allan B. Woolf and Michael Lay-Yee

`Hass' avocados [Persea americana Mill.] were pretreated in water (38 °C for up to 120 min) immediately before 50 °C hot water treatments of up to 10 min. Fruit were stored for 1 week at 6 °C and ripened at 20 °C. External browning was evaluated immediately upon removal from cold storage, and fruit quality evaluated when fruit were ripe. Pretreatments at 38 °C tended to reduce the levels of external browning, skin hardening, and internal disorders, such as tissue breakdown and body rots, that were associated, and increased, with longer hot water treatments. A pretreatment of 60 min was the most effective for eliminating external browning, and reducing hardening of the skin when fruit were ripe following hot water treatment. Examination of heat shock protein (hsp) gene expression in avocado skin tissue, showed that levels of hspl7 and hsp70 homologous mRNA increased with increasing pretreatment duration. The results demonstrate that 38 °C pretreatments increase the tolerance of avocado fruit to subsequent hot water treatments.

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Michael Lay-Yee and Kellie J. Rose

`Fantasia' nectarine fruit [Prunus persica (L.) Batsch var. nectarina (Ait.) Maxim.], held at 0C for ≤ 1 week following harvest, were forced-air heated either immediately after removal from cold storage or after an overnight pretreatment at 20C. Fruit were heated to 41,43, or 46 ± lC for 24,36, or 48 hours. Following treatment, fruit were stored for 3 weeks at 0C, held at 20C for 1 or 5 days, and then assessed for quality. No significant damage, relative to nonheated controls, was observed in pretreated fruit subjected to 41C for 24 hours. Nonpretreated fruit given the same treatment showed only a slight increase in damage relative to controls. Higher temperatures and longer treatment times, however, were associated with an increased incidence of fruit damage (scald, internal browning, or decay). Heat treatment was associated with reduction in ethylene production and titratable acidity of the fruit following storage.

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Michael Lay-Yee, Graeme K. Clare, Robert J. Petry, Robert A. Fullerton and Anne Gunson

Papaya fruit (Carica papaya L. cv. Waimanalo Solo), at color break ripeness, were either not heated (controls) or forced-air heated to center temperatures of 47.5, 48.5, or 49.5 °C, and held at these temperatures for 20, 60, 120, or 180 minutes. Following heat treatment, fruit were hydrocooled until reaching a center temperature of 30 °C, treated or not treated with prochloraz, allowed to ripen at 26 °C and then assessed for quality. Treatment at 48.5 °C or 49.5 °C for ≥60 minutes was associated with skin scalding. No significant scald was observed in other treatments or in the controls. Both control and heat-treated fruit had relatively high levels of decay. Heat treatment increased the incidence of body rots but did not affect the incidence of stem-end rots. Prochloraz treatment significantly reduced the incidence of decay. With the inclusion of a prochloraz treatment to control postharvest decay, fruit tolerated treatments of 47.5 °C for up to 120 minutes, and 48.5 °C and 49.5 °C for 20 minutes with no significant damage. Chemical name used: 1-N-propyl-N-(2-(2,4,6-(trichlorophenoxy)ethyl)-1H-imidazole-1-carboxamide (prochloraz).

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Allan B. Woolf, Christopher B. Watkins, Judith H. Bowen, Michael Lay-Yee, John H. Maindonald and Ian B. Ferguson

`Hass' avocados (Persea americana Mill.) were heated in air at 25 to 46C for 0.5 to 24 hours and stored at 0, 2, or 6C. After storage, fruit were ripened at 20C and their quality was evaluated. In unheated fruit, external chilling injury occurred in fruit stored at 0 or 2C, hut not 6C. Chilling injury was also evident after storage at 2C in fruit heated at 34C, and to a lesser extent in fruit heated at 36C. A heat treatment (HT) of 38C for 3, 6, or 10 hours and 40C for 0.5 hour further reduced external chilling injury induced by storage at 2C. These HTs did not reduce internal fruit quality and resulted in more marketable fruit than unheated fruit stored at 6C. Low-temperature storage and HT slowed avocado ripening, resulting in longer shelf life after storage. In flesh tissue sampled directly after selected HTs, the levels of mRNA homologous to cDNA probes for two plant heat-shock protein (HSP) genes (HSP17 and HSP70) increased to a maximum at 40C and declined at higher temperatures. These increases in gene expression coincided with the extent to which HTs prevented chilling injury. Hot-air HTs confer significant protection against low-temperature damage to avocados.