Vulnerability of different life stages of Sitophilus oryzae insects in stored rice grain to ozone treatment and its effect on physico-chemical properties in rice grain

Abstract

Ozone has emerged as a reactive gas with insecticidal activity with the capability to manage insect pests in stored grains. The study focused on the effect of moisture content with exposure time and ozone concentration in achieving mortality of different life stages of Sitophilus oryzae. The ozonation process was done with a moisture content (MC) of 12%–16%, ozone concentration of 1.0–2.0 g/m3 and exposure time of 2–6 h. The responses studied were percentage mortality of eggs, larvae, pupae, and adults. The ozone effect on rice physico-chemical, spectral FTNIR (Fourier transform near infrared spectrophotometer), and morphological attributes (X-ray micro CT) of optimized samples were compared with control sample. The adult stage of S. oryzae was the least vulnerable stage to the ozonation process among eggs, larvae, and pupae, whose mortality ranged from 44.13% to 99.02%. The optimized condition with the desirability of 0.99, MC of 12.31%, ozone of 1.93 g/m3, and time of exposure 5.86 h for mortality of different life stages of S. oryzae was obtained. The standard error mean and SD were in the range of 2.81–1.91 and 3.67–3.21, respectively. Protein, amylose, and MC of ozone-treated rice had lower values in comparison to fresh rice. Microstructural changes in ozonated samples were distinct with X-ray micro CT images and FTNIR peaks. The loss in the micro structure was attributed to the insect infestation and degradation of protein molecules due to oxidation of the disulphide bonds during ozone treatment.