微波-热风联合干燥对高水分稻谷加工品质及微生物量的影响

研究了不同微波有效功率下高水分稻谷的微波干燥特性,以及探讨了微波处理工艺对稻谷加工品质及微生物量的影响。结果表明,在较低的微波功率(485和927 W)下,处理初期稻谷温度迅速升高,水分下降缓慢,当温度达到65℃、含水量达到19. 7%左右时,稻谷升温速度减小,而水分下降速度加快。微波功率增加可显著提高稻谷的升温速度和降水速率,但高功率微波干燥稻谷易产生焦糊现象。采用有效功率927 W的微波条件,2 min可将稻谷加热至60℃,稻谷含水量从21. 58%降低至19. 96%。通过4 h缓苏处理后,稻谷表面细菌量下降3. 6 log CFU/m L,表面霉菌量下降3. 3 log CFU/m L,对稻谷内部霉菌可实现95%灭菌,稻谷的出糙率和整精米率无显著下降(P 0. 05),分别为83. 92%和68. 14%。与自然通风及热风处理稻谷至入仓偏高水分18. 34%相比,微波与热风联合处理只需20 min,其稻谷加工品质较高,杀菌效果也远远高于自然通风及热风处理。因此,适宜的微波处理在保障高水分稻谷加工品质的前提下,可显著缩短干燥时间,并获得高质量的杀菌效果,实现高水分稻谷快速安全入仓处置。

Effects of combined drying by microwave and hot-air on milling quality and microbial biomass of rough rice with high moisture content

The characteristics of microwave heating for rough rice with high moisture content in different microwave effective power and its effects on rough rice milling quality and microbial biomass were studied. Results showed that under the microwave heating with lower power (485 W and 927 W), the rough rice temperature increased rapidly while the moisture content decreased slowly during the initial period of treatment. After the rough rice was heated to approximately 65°C and the dry basis moisture content was decreased to approximately 19.7%, the heating rate reduced while the rate of moisture removal increased. With the increase of microwave power, the heating and moisture removal rate of rough rice could be significantly improved, but high microwave power drying rice might cause burning phenomenon. After microwave heating for 2 min with power of 927 W that the temperature reached 60°C, the dry basis moisture content of rough rice could be removed from 21.58% to 19.96%. Followed by 4 h of tempering and natural cooling, 3.6 log CFU/mL of viable bacterial biomass and 3.3 log CFU/mL of viable mold biomass on rough rice surface, and 95% the internal mold could be sterilized. Furthermore, the total rice yield and head rice yield was well maintained that was 83.92% and 68.14% respectively. Compared with the natural ventilation and hot-air treatment to 18.34%, combination of microwave and hot-air treatment just need 20 min. The milling quality of rough rice was higher, and the sterilizing effect was far higher than the natural ventilation and hot-air treatment. Therefore, the suitable microwave treatment significantly obtain the high sterilizing effect and shorten the drying period thereof on the premise of guaranteeing the good milling quality of rough rice. It can achieve rough rice with high moisture content in warehousing disposal quickly and safely.