Difusão e sorção do isotiocianato alilo e o seu efeito no controle de Sitophilus zeamais e na qualidade do milho / Diffusion and sorption of allyl isothiocyanate and its effect on the control of Sitophilus zeamais and quality of maize

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

This study was done to evaluate allyl isothiocyante (AITC) transport through the grain bulk of maize, and determine its fumigant effect on different developmental phases of Sitophilus zeamais Motsch. (Coleoptera: Curculionidae) and on maize quality. The study was done in three steps at the Universidade Federal de Viçosa, in Viçosa, MG. In the first, the AITC transport was evaluated by studying sorption mechanisms and diffusion through the grain bulk. In all studies the grains with 13% moisture content and 40% bulk porosity, at 25 oC were used. The sorption was determined by injecting saturated vapors of AITC in to a hermetically sealed glass jar containing the grains. The pressure alterations were monitored at 10-minute interval for 130 minutes with use of a liquid column manometer. This procedure took place without the presence of AITC. The sorption rate constant was estimated by adjusting the kinetic models of the zero, first and second order to the AITC concentration data. An apparatus having a gas chamber attached to a cylindrical grain column was used to determine diffusion pattern. After the gas release, the samples were collected after 110 minutes, from the gas chamber and from seven heights of the grain column, and immediately injected into a gas chromatograph. With the use of sorption rate constant and AITC concentration, AITC effective diffusion coefficient through the grain bulk was calculated by use of the mathematical models describing transient diffusion, by adding the term about the sorption rate. In the second step, the maize grains were infested with immature phases (egg, third instar larvae and pupa) and adults of S. zeamais and subjected to AITC fumigation for 6, 12, 18, 24, 30, 36, 42, 48, 54 or 60 h at concentration of 0; 1.25 or 1.87 L L-1. The mortality of adult insects was determined after 48h of each exposure period and that of immature phases after 42 days of posture by counting the number of emerged adult insects. The lethal time (LT50 <95) of the immature phases and the adults of S. zeamais were estimated by Probit analysis. In the third step, the fumigated grains were used to evaluate moisture content, electrical conductivity and germination. The sorption data fitted the first order the kinetic model and sorption rate constant was estimated to be 6.26x10-4 s-1. The effective diffusion coefficient of AITC through the bulk grain was estimated to be 7.2x10-3 cm2 s-1. The efficacy of AITC fumigation on the insect-pest mortality increased with increasing exposure period independent of the developmental phase. The egg phase required longer exposure period, while the third instar larvae required the least for 50 or 95% mortality. The eggs and pupa were most tolerant phases, while the adults and larvae were most sensitive to AITC. The fumigation for 60 h did not affect grain quality. It was concluded that AITC transport through the bulk of maize grain is slow due to low effective diffusion coefficient and high grain sorption rate. However, the capacity of AITC to control all phases of S. zeamais and not affecting grain quality indicates that it has the potential as a good grain fumigant.

ASSUNTO(S)

pre-processamento de produtos agricolas effective diffusion coefficient lethal time mustard essential oil coeficiente efetivo de difusão tempo letal Óleo essencial de mostarda

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