Effect Of Compound Enzyme Solution Humidification For Brown Rice On Milling Quality

Due to the low moisture content of brown rice(12.0 %~13.0 %) after storage and the structure of brown rice skin is compact and complete, the problem that lots of broken rice is generated and high energy consumption occurs during the rice milling processing exists commonly, which directly affect the economic benefits of rice processing enterprises and restrict the development of the industry. Moisture conditioning treatment for the brown rice, which is an atomization humidifying, is generally used to soften the cortex and improve the milling quality to some extent. However, it does not fundamentally solve the problem caused by the resistant cortex of brown rice. Therefore, the research of enzymatic pretreatment process for brown rice which breaks the limit of cortical properties has an important application value to milling industry.This study combined moisture conditioning treatment with biological enzyme method and proposed a new method of compound enzyme solution humidification with cellulase and xylanase for brown rice which aiming at the main components of brown rice cortex. This method not only improved the moisture content of brown rice, but also degraded the cortex of brown rice selectively, meanwhile, the coarse fiber component of brown rice cortex was degraded more sufficiently and the effect of enzymatic hydrolysis was enhanced with the use of compound enzyme. This method substantially decreases broken rice in the milling process and reduces the milling energy consumption. The main work is as follows:1. Single factor test method was employed to determine the main parameters and parameters range of compound enzyme solution humidification process, and analyze influence on head rice yield and milling energy consumption with the raw material of brown rice in the safe storage period at the moisture content below 15%. Experiment results showed that the parameters of compound enzyme solution humidification had significant impact on the head rice yield and the milling energy consumption.2. A central composite rotatable orthogonal experimental design of response surface methodology was employed to investigate the relationship of percentage of cellulase quality(25~75 %), concentration of compound enzyme solution(10~90 mg/m L), adding liquid proportion(0.6~1.8 %) and enzyme treating time(30~150 min) with milling characteristic, in terms of head rice yield and milling energy consumption, then the optimal combination of process parameters with highest head rice yield and lowest milling energy consumption was concluded. The results showed that the mathematical models for the influences of various parameters on the head rice yield and the milling energy consumption fitted well. The optimized pretreatment parameters were as follows: the cellulose-to-xylanase mass ratio was 1.3:1 g/g, the concentration of composite enzyme solution was 65 mg/m L, the adding liquid proportion was 1.25% and the enzyme treating time was 102 min. Under the optimized parameters, the head rice yield was 80.07 % and the milling energy consumption was 90.72 kJ/kg.3. Contrast validation experiment of different treatments in the same parameters condition based on the test results of optimization was taken. Meanwhile, through the scanning electron microscope test and water absorption test of brown rice to explore the mechanism of compound enzyme solution humidification to improve the milling quality of brown rice from two aspects of the microstructure of the cortex and the ability of water penetration. The storage test of rice under different treatments was taken to validate the stability of head rice yield. Experiment results indicated that the head rice yield and the milling energy consumption were respectively 3.98 % higher and 13.06 % lower than the values from the moisture conditioning treatment, and 0.98 % higher and 5.48 % lower than the values from the cellulase solution humidification. The storage test shows that the head rice yield had stability. Reasons for improvement were as follows: on the one hand, the coarse fiber component of brown rice cortex was degraded more sufficiently by the use of compound enzyme and the local damage and rough structure of the cortex which reduced the hardness of brown rice kernel and decreased the whitening pressure to reduce the milling energy consumption; on the other hand, the loose structure caused by degradation of the cortex facilitated the moisture penetration and increased the grain’s water absorption rate and toughness to reduce broken rice.4. Pilot scale test based on the optimization results of the study was taken, The experimental results confirm the accuracy of the model and the optimization results, and the feasibility of the process.