Application of radio frequency treatments to control insects in in-shell walnuts.
Authors:
Mitcham, E.J. Veltman, R.H. Feng, X. Castro, E. de Johnson, J.A. Simpson, T.L. Biasi, W.V. Wang, S. Tang, J. USDA, ARS
Source:
Postharvest biology and technology. 2004 July, v. 33, no. 1, p. 93-100.
NALT Subjects:
walnuts insect control Cydia pomonella Amyelois transitella Plodia interpunctella disinfestation radio waves heat treatment postharvest treatment temperature mortality moisture content heat tolerance food quality stored product protection
Other Subjects:
lethal temperature radio frequency heating heating rate
Issue Date:
Jul-2004
Abstract:
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 postharvest treatments. 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 walnut quality, 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.
