Heat treatments have been used to control diseases and insect infestation of fruit. The development of heat treatments have been the result of empirical experiments based on the efficacy on the insects coupled with parallel experiments on the phytotoxicity of host fruit. Such heat treatments while approved as quarantine treatments have occasionally produced fruit of poor quality. Thermal processing of foods, an established science, employs kinetics of enzyme inactivation, thermal death times evaluation of various time-temperature relationships to determine the adequacy of the heat process to ensure the safety of the product as well as minimize over-processing to preserve the products quality. There is a need to develop thermo-processing guidelines in the development of quarantine heat treatments and also to enhance product quality. We will report methods that we have developed to determine the thermal death kinetics of insects, fruit pathogens and kinetics for thermotolerance of the fruit.
Harvey T. Chan Jr. and Eric Jang
Harvey T. Chan Jr., Myles H. Taniguchi and Edward S. Linse
Suzanne S. Sanxter, Kate A. Nishijima and Harvey T. Chan Jr.
Chilling injury symptoms were reduced when `Sharwil' avocados (Persea americana Mill.) were held at 37 to 38C for 17 to 18 hours and then air-cooled at 20C for 4 hours before storage at 1.1C for ≥14 days. In contrast, nonheated fruit developed severe surface discoloration and pitting. Chilling injury symptoms were reduced further when the heated fruit were stored in perforated polyethylene bags during 1.1C storage. No treatment equaled or surpassed the quality of fruit in nontreated controls.
Harvey T. Chan Jr., Kate A. Nishijima, Myles H. Taniguchi and Edward S. Linse
Thermal death kinetics, decimal reduction times (D-values), and rate constants, k, at 43 to 49 °C were determined for spore or cell suspensions of Colletotrichum gloeosporiodes (Penz.) Penz. & Sacc. in Penz., Guignardia psidii Ullasa & Rawl, Guignardia sp. Viala & Ravaz., and Enterobacter cloacae (Jordan) Hormaeche & Edwards. D-values for Monilinia fructicola (Wint.) Honey, Rhizopus stolonifer (Ehr.: Fr.) Vuill., and Stemphylium lycopersici (Enjoji) Yamamoto were calculated and extrapolated from published reports. We compared the relative heat resistances of the various postharvest pathogens to their expected survival during quarantine heat treatments and found that Guignardia, Rhizopus, and E. cloacae could be expected to survive quarantine heat treatments.
James D. Hansen, Harvey T. Chan Jr., Arnold H. Hara and Victoria L. Tenbrink
Phytotoxicity from hydrogen cyanide (HCN) fumigation was measured in several varieties of Hawaiian cut flowers and foliage (Zingiberaceae, Heliconia, Orchidaceae, Marantaceae, Lycopodiaceae, Agavaceae, Proteaceae) as a potential disinfestation treatment. Concentrations tested were 2500, 3700, 4600, and 5500 ppm HCN for 30 min. All foliage and most heliconia were undamaged at fumigation levels of 5500 ppm HCN; most protea and `Midori' anthuriums were uninjured at 4600 pm HCN; red and pink ginger were uninjured at 3700 ppm HCN; and all pincushion protea showed phytotoxicity to HCN. Red ginger was quickly damaged when exposed to sunlight immediately after treatment at 2500 ppm HCN. No injury was observed in simulated shipment tests of red ginger and `Ozaki' anthuriums fumigated at 2500 ppm HCN. Wet, red ginger flowers longer than 6 cm were damaged at 2500 ppm HCN, whereas shorter flowers were uninjured. Wet `Ozaki' anthuriums showed phytotoxicity only at 4600 ppm HCN. Wet, treated lycopodium and bamboo orchid foliage was not injured. The number of marketable days and shelf life of the treated plant material were estimated from the visual ratings.
Kate A. Nishijima, Harvey T. Chan Jr., Suzanne S. Sanxter and Edward S. Linse
A reduced heat shock period for `Sharwil' avocado (Persea americana Mill.) before quarantine cold treatment is described. The shortened heat pretreatment period of 8 to 12 hours, rather than the originally recommended 18 hours at 38C, is effective in reducing chilling injury symptoms when the pulp is at ≤2.2C during 16 days of storage. The reduced durations and the range of pretreatment hours affords packinghouses greater efficiency and more flexibility and will reduce handling costs relative to the longer exposure.
M. Seltenrich, W.G. Laidlaw, Harvey T. Chan Jr. and C.F. Hayes
The disinfestation protocol for fruit often requires a delicate balance between suppression of the pest and avoidance of fruit damage. In Hawaii both hot-water and hot-air treatments are used for papaya destined for export. A computer simulation of the heat flow can be used to obtain the temperature Tα(x,t) at every point x in the papaya and every time t for any given heating protocol α. The activity of the ethylene forming enzyme (EFE) has been used as a measure of fruit damage and the “kill” of fruit-fly larvae/eggs as a measure of pest control. The degradation of the EFE measured experimentally for a fixed temperature T and at several times t can be analyzed to yield a rate expression R1(T,t). Similarly the survival of fruit-fly larvae/eggs can be used to establish a rate expression R2(T,t).
The temperature space-time expression, Tα(x,t), for a chosen heating protocol α, and the rate laws R1(T,t) and R2(T,t) can be used to calculate the effect on EFE activity, EFEα(x,t), and pest control, PCα(x,t), at every point in the fruit and time of the protocol. For example the effect of different heating schedules, different heating fluids or even the role of “pre-conditioning” can be assessed.