| Abstract | Suitability of various methods; gamma irradiation, packing under reduced oxygen and enriched carbon dioxide and combination of the two techniques, to control infestation of maize weevils (S. zeamais) in packaged aromatic rice (KDML-105) was investigated as alternatives to traditional fumigation. Milled rice, which had hidden infestation with maize weevils (S. zeamais), was exposed to phosphine fumigation with doses of 1, 2 and 3 tablets/tonne rice (F1, F2, F3) for 8 days. Irradiation as an alternative to phosphine fumigation was applied to infested rice ranging from 0.2 to 2.0 kGy to determine the optimum dose. For storage study, doses of 0.2, 0.5 and 1.0 kGy (Ir0.2, Ir0.5, Ir1 .0) were selected. In addition, the influence of packaging systems was also investigated by packing infested rice in laminated nylon/PE/LLDPE plastic bags under normal air (AP), vacuum (Vac), and carbon dioxide concentration of 20, 30 and 40% (C20, C30 and C40). To reduce applied irradiation dose, combination of low dose irradiation at 0.1 kGy and reduced oxygen (Llr/L) was applied and compared to low dose irradiation treatment (Llr). Apart from insect control efficiency, changes in physicochemical properties of rice were determined immediately after treatments and during storage at ambient conditions for 1 year. Physicochemical properties such as yellowness (b value), water absorption (WA), total solid in cooking water (TS), cooked rice hardness (HN) and oxidative rancidity (thiobarbuturic number, TBA) were determined to signify the alterations of appearance, color, texture, odor and taste of cooked rice after the treatments and following the storage. These changes contributed to overall perception of consumers when sensory qualities were evaluated. Whereas determination of pasting properties by Rapid Visco Analyzer (RVA) indicated modification of starch molecular structure by irradiation treatment and presummably by ageing effect. All applications were compared in terms of their effects on insect mortality. F1, F2, F3, Ir0.2, Ir0.5, Ir1.0, Vac, C30, C40 and Llr/L samples were proved effecient in controlling insects in packaged rice during storage for 1 year. But insects were not completely killed in AP, C20 and Llr samples. For the control sample, insects emerged from infested rice after storage in PE plastic bags for 1 month and the population rapidly increased with extensive weight loss around 5% during 1 year storage. Treatments were also compared in terms of their effects on rice quality. Physicochemical properties of fumigated rice changed during storage due to ageing effects in terms of increase in b value, HN, and TBA and decrease in WA and TS. For pasting properties, peak viscosity (PV) and breakdown (BD) decreased but final viscosity (FV), consistency (CS) and setback (SB) increased with time. In milled rice damaged by insects, decreased b value and HN and increased WA and TS were observed. There was a distinctive increase in TBA and lowering of FV, CS and SB. Gamma irradiation (0.2 to 2.0 kGy) resulted in decrease in some pasting parameters and HN and an increases in WA and TS. Alteration at granular level of starch was evident by scanning electron microscopy. Increase in b value and decrease in volatile compounds (ACPY, 2-acetyl-1-pyrroline) contributed to changes in and color and aroma of irradiated cooked rice. Panelists responded to these changes with less perception of sensory qualities. Maximum doses of less than 1.0 kGy should be used to disinfest aromatic rice although when considered strictly based on aroma, less than 0.5 kGy would be more suitable. Compared to nonirradiatied rice, greater decreases in WA and TS and less increases in HN during storage was observed in irradiated rice. Higher TBA peak and lower SB were evident in irradiated rice during storage for 1 year. The increase in b value and TBA during storage of AP, Vac, C20, C30, and C40 samples was less than those of rice packed in PE plastic bag (PE). Packaging systems had no effects on WA, TS, HN and pasting properties. However relatively lower b value and lower TBA peak was observed in rice stored in laminated plastic bags compared to those of rice stored in PE plastic bags. Vacuum induced more changes in BD and SB during storage for 1 year compared to other packaging systems. For combination techniques, lower TBA peak in LIr/L than that of LIr sample was also observed. Significant lower SB and CS of LIr sample was seen during storage. Sensory analysis was used to determine shelf life of packaged rice treated with all applications. Alteration in physicochemical properties of rice after treatments and during storage apparently caused the changes in sensory qualities of cooked rice. Considering overall acceptance rating by the panelists, F1, F2 and F3 samples were still preferable during 13-16 months of storage. Due to undesirable flavor and odor and slippery texture, panelists rejected Ir0.2, Ir0.5 and Ir1.0 after 9, 7 and 2 months of storage respectively. Relatively higher scores were obatined after 1 year storage for rice packed under reduced oxygen or enriched carbon dioxide, therefore, their estimated shelf life was longer (19-28 months) compared to rice packed in PE plastic bags (15 months). Combination of techniques had no effect on the acceptance by the panelists on stored pacakged rice. Without any insect control treatments, panelists rejected packaged infested rice after 4 months of storage because of bad smell and off flavor due to insect infestation. Therefore the study recommended irradiation at 0.2 kGy, packing under vacuum and packing with carbon dioxide concentration of 30 and 40% to be the alternatives to phosphine fumigation. |