Application of radio frequency treatments to control insects in in-shell walnuts
E. J. Mitcham , R. H. Veltman, X. Feng, E. de Castro, J. A. Johnson, T. L. Simpson, W. V. Biasi, S. Wang and J. Tang
Postharvest Biology and Technology Volume 33, Issue 1 , July 2004, Pages 93-100
2004
บทคัดย่อ
Codling moth (Cydia pomonella [L.]), navel orangeworm (Amyelois transitella [Walker]), and Indianmeal moth (Plodia interpunctella [Hübner]) are common insect pests in walnuts (Juglans regia [L.]). Currently, exported in-shell walnuts are disinfested using methyl bromide fumigation. Restrictions on methyl bromide use have increased interest in developing alternative postharvesttreatments. Radio frequency (RF) heating is such an alternative. Our tests have shown that heating walnuts with radio frequency energy to temperatures lethal to these important insect pests has no negative effects on walnutquality,and may even reduce the susceptibility of walnuts to becoming rancid in storage. Radio frequency treatments provided acceptable rates of heating (5–6 °C min-1) for in-shell walnuts to lethal temperatures. Heating walnuts to 55 °C or higher resulted in 100% mortality of fifth instar navel orangeworm, which is the most resistant of the three insect pests. Moisture content of walnuts is an important factor affecting heating rates during radio frequency treatments. The relationship between average moisture content and average heating rate was linear, and the variability in moisture content and heating rates was higher with a higher average moisture content. Radio frequency treatments reduce the moisture content of walnuts. A combined system of radio frequency heating with hot air has the potential to accelerate or even replace batch drying of walnuts in the future.