Processo de ozonização: eficácia biológica, qualidade dos grãos e análise econômica

Abstract

O presente trabalho teve como meta avaliar, além da eficácia da ozonização no controle dos insetos-praga Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) em grãos de milho armazenado sob condições de temperaturas de 20, 30 35 e 40 ºC, com até 168 horas de exposição ao gás, o seu efeito na qualidade dos grãos durante 180 dias de armazenamento, bem como sua viabilidade econômica. O trabalho, conduzido no Setor de Armazenagem de Grãos do Departamento de Engenharia Agrícola da Universidade Federal de Viçosa, foi realizado em três etapas. Na primeira, estimaram-se os tempos letais (TL) de cada espécie em estudo em diferentes períodos de ozonização, pela análise de Probit, utilizando-se o programa SAS versão 6.12 para ambiente Windows. Para obtenção desses dados, seis tubos de PVC, cada um com comprimento de 1,00 m e diâmetro de 0,20 m, foram utilizados na posição vertical, para sustentação dos grãos. A 0,10 m do fundo de cada tubo colocou-se uma tela metálica para formação de uma câmara para melhor distribuição do gás. Nas tampas inferior e superior dos tubos cilíndricos foram instaladas conexões para injeção e exaustão do gás e, no corpo de cada tubo, foi inserido um sensor para o monitoramento da temperatura da massa de grãos. Para comparação dos resultados da ozonização, três tubos receberam apenas ar atmosférico. O ozônio e o ar atmosférico foram injetados em fluxo contínuo com vazão de 8,0 L min-1. Armadilhas contendo 20 insetos de cada espécie foram colocadas na camada mediana dos tubos e, após diferentes períodos de exposição, avaliou-se o número de insetos mortos. Na segunda etapa, os grãos que foram submetidos ao maior período de exposição ao gás ozônio e ao ar atmosférico foram distribuídos em frascos de vidro e, a cada 45 dias de armazenamento, foram avaliados o grau de infestação, o teor de umidade, a massa específica aparente, a condutividade elétrica e a classificação do produto até completar 180 dias de armazenamento. Na terceira e última etapa, com base nos valores de massa específica aparente obtidos ao longo do armazenamento, foi feita uma análise econômica utilizando os parâmetros econômicos de tempo de retorno de capital, valor presente líquido e taxa interna de retorno. Concluiu-se que, em geral, o aumento do período de exposição resultou em aumento da eficácia do tratamento com 50 ppm de ozônio nas diferentes temperaturas da massa de grãos (20, 30, 35 e 40 ºC) para as quais os tempos letais para 50 e 95% dos insetos foram, respectivamente, de 71,39 e 151,85; 59,61 e 115,62; 82,93 e 138,22; 69,52 e 105,12 horas. Com relação aos ensaios qualitativos e quantitativos, o tratamento com o gás ozônio na concentração de 50 ppm, em comparação com o ar atmosférico, durante 168 horas, não afetou a qualidade dos grãos durante o armazenamento. Os resultados de indicadores econômicos sugerem que a utilização do gás ozônio pode ser economicamente viável se for aplicado à massa de grãos armazenada em condições de temperatura de 20 °C e de 35 ºC.

The present work aimed to assess the ozonization efficacy for controlling the insect-pest Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) in maize stored at 20, 30, 35 and 40 ○C temperature in up to 168 hours of gas exposure, its effect on grain quality during 180 days of storage, besides its economical viability. The work carried out at the Storage Grain Sector of the Department of Agricultural Engineering of the Federal University of Viçosa was carried out in three phases. In the first, lethal time (LT) estimates were carried out for each species under investigation using probit analysis. Six PVC tubes (1 m high x 0.20 m diameter) were used to sustain the grains and obtain the data. At 0.10 m of the recipient bottom a metallic net was placed forming a plenum to better distribute the gás. The connexions for gas injection and exhaustion were installed at the cylinder bottom lids and in its body a sensor to monitor grain temperature was installed. Three cylinders received only atmospheric gas to compare with the ozonization results. Ozone and atmospheric gas were injected at a continuous flow of 8.0 L.min-1. Traps with 20 insects of each species were placed at the median height of the cylinders and after different exposure periods the mortality assessment was carried out. In the second phase, the grains were subjected at the highest exposure period and distributed in glass jars for assessment of infestation level, moisture content, apparent specific mass, electrical conductivity and class at every 45 days during a total of 180 days of storage. In the third phase, an economical analysis was carried out using the values of apparent specific mass obtained throughout the storage period of the second phase and the economical parameters of time length for the capital return, present net value and inner return rate. In general there was an increase in ozone fumigation efficacy at 50 ppm with increased temperature and length of exposure with LT50 and LT90 of 71.39 and 151.85 h at 20 ○C, 59.61 and 115.62 h at 30 ○C, 82.93 and 138.22 h at 35 ○C, and 69.52 and 105.12 h at 40 ○C respectively. Regarding the qualitative and quantitative assays, ozone at 50 ppm did not affect grain quality during storage after a 168 h exposure. The results of economical indicators suggest that the ozone use can be economical viable if applied to grain mass at the temperatures of 20 and 35 ○C.The present work aimed to assess the ozonization efficacy for controlling the insect-pest Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) in maize stored at 20, 30, 35 and 40 ○C temperature in up to 168 hours of gas exposure, its effect on grain quality during 180 days of storage, besides its economical viability. The work carried out at the Storage Grain Sector of the Department of Agricultural Engineering of the Federal University of Viçosa was carried out in three phases. In the first, lethal time (LT) estimates were carried out for each species under investigation using probit analysis. Six PVC tubes (1 m high x 0.20 m diameter) were used to sustain the grains and obtain the data. At 0.10 m of the recipient bottom a metallic net was placed forming a plenum to better distribute the gás. The connexions for gas injection and exhaustion were installed at the cylinder bottom lids and in its body a sensor to monitor grain temperature was installed. Three cylinders received only atmospheric gas to compare with the ozonization results. Ozone and atmospheric gas were injected at a continuous flow of 8.0 L.min-1. Traps with 20 insects of each species were placed at the median height of the cylinders and after different exposure periods the mortality assessment was carried out. In the second phase, the grains were subjected at the highest exposure period and distributed in glass jars for assessment of infestation level, moisture content, apparent specific mass, electrical conductivity and class at every 45 days during a total of 180 days of storage. In the third phase, an economical analysis was carried out using the values of apparent specific mass obtained throughout the storage period of the second phase and the economical parameters of time length for the capital return, present net value and inner return rate. In general there was an increase in ozone fumigation efficacy at 50 ppm with increased temperature and length of exposure with LT50 and LT90 of 71.39 and 151.85 h at 20 ○C, 59.61 and 115.62 h at 30 ○C, 82.93 and 138.22 h at 35 ○C, and 69.52 and 105.12 h at 40 ○C respectively. Regarding the qualitative and quantitative assays, ozone at 50 ppm did not affect grain quality during storage after a 168 h exposure. The results of economical indicators suggest that the ozone use can be economical viable if applied to grain mass at the temperatures of 20 and 35 ○C.