Effect Of Microwave On Paddy Quality

Paddy is one of the main food crops in China. Every year, billions of paddy was damaged by deterioration, pest or mildew during storage. Although chemical fumigation and conventional methods such as low temperature and controlled atmosphere could achieve certain effect, they could result in some environmental problems, insect resistance and so on. In order to resolve this problem an efficient, safety, environmental protection method was required. Microwave treatment shows considerable potential for killing insect and preventing mildew in food. However, few studies have attempted to explain how microwaves influence the quality of paddy. In this study, the effects of microwave treatment on milling quality, edible and storage quality of paddy were investigated. The aim was to provide optimal processing parameters for the industrial application of microwaves to control the growth of pests and mildew in paddy. The results were as follows:1. Microwave could influence the characteristics of paddy. Paddy temperature linearly increased with processing time of microwave treatment. The velocity constant of temperature slowed with decreasing microwave dose. The effects of microwave treatment on paddy qualities depended on treatment conditions, under the optimal microwave conditions, kernel cracking and broken yield were relatively low, which were beneficial for improving brown rice recovery and head yield. Additionally, the optimal microwave treatment reduced the contents of water and free fatty acid, improved the water solubility of protein and starch, and reduced the activity ofα-amylase, amylase, protease, lipase, active debranching enzyme and debranching enzyme. The optimal microwave treatment improved milling and storage qualities of paddy and edible quality of rice.Microwave could influence the composition of fatty acid. The main acid in paddy was unsaturated fatty acid, the contents of octadecadienoic acid, hexadecanoic acid, octadecenoic acid, octadecanoic acid in raw paddy were 67.00%, 17.74%, 4.69% and 3.41% respectively; while they were 58.86%, 20.83%, 12.63% and 2.56% respectively in paddy treated by microwave. The other acids were hardly influenced by microwave. Meanwhile the texture characteristics of rice were hardly influence by microwave.2. Microwave could influence the storage stability. During storage, the significantly decreased indexes were brown rice recovery, head yield, water-soluble protein content, dissolution ratio of albumin, globulin and glutelin, water content and kinds of enzyme activity, and the significantly increased indexes included BV and free fatty acid content. After storage for six months, the content of octadecenoic acid declined, the contents of octadecanoic acid and hexadecanoic acid increased. Cooked rice from storaged paddy owned higher hardness, and lower viscidity and elasticity than cooked rice from raw paddy.Compared with the paddy without microwave treatment, the treated paddy remained higher enzyme activity and lower water content, and higher BV and free fatty acid content. The treated paddy had less unsaturated fatty acid and more saturated fatty acids than untreated paddy. Microwave treatment hardly influenced milling quality of paddy. There was no significant difference in hardness, viscidity and elasticity of cooked rice from treated and untreated paddy.3. There were significant correlations among milled quality (brown rice recovery and head yield), edible quality (water soluble protein and BV) and storage quality (free fatty acid content and kinds of enzyme activity). Equilibrium elastic modulus (E₀) of cooked rice from storaged paddy was negatively to enzyme activity in paddy. Smaller retarded elastic modulus (E₁) and higher relaxation time (Ï„) resulted in higher head yield. Higher nonlinear exponential(n) resulted in higher head yield and BV, and lower activity of debranching enzyme.