Effect Of Far-infrared Drying On Characteristics And Quality Of Agaricus Bisporus

Agaricus bisporus have tender texture, and then their freshness decreased rapidly after harvest, so it is not easy to keep in storage. Drying of the Agaricus bisporus is beneficial to extension its storage period, which is convenient for storage and transportation. The drying methods, pretreatments, moisture distribution and rehydration rate of Agaricus bisporus were investigated in this paper. Main research results are listed below:The effects of 5 drying methods (including hot air drying, vacuum microwave drying, far infrared drying, vacuum microwave-far infrared combination drying and hot air-far infrared combination drying) on the physical properties and VC content of Agaricus bisporus were studied. The results showed that the hardness decreased according to the order of hot air drying, hot air-far infrared combination drying, far infrared drying, vacuum microwave-far infrared combination drying, vacuum microwave drying; crispness increased according to the order of hot air drying, hot air-far infrared combination drying, far infrared drying, vacuum microwave-far infrared combination drying, vacuum microwave drying; rehydration rate decreased according to the order of far infrared drying, hot air-far infrared combination drying, hot air drying, vacuum microwave-far infrared combination drying, vacuum microwave drying; shrinkage rate decreased according to the order of vacuum microwave-far infrared combination drying, hot air drying, hot air-far infrared combination drying, far infrared drying, vacuum microwave drying; the color value increased according to the order of far infrared drying, hot air-far infrared combination drying, hot air drying, vacuum microwave drying, vacuum microwave-far infrared combination drying; VC content value decreased according to the order of far infrared drying, vacuum microwave-far infrared combination drying, vacuum microwave drying, hot air-far infrared combination drying, hot air drying; Overall, far infrared drying can be used as a suitable processing method for the development of Agaricus bisporus in consideration of above data.The effects of pretreatments, namely, blanching, ultrasonic-assisted blanching and ultrasound on hardness, crispness, color, VC content and microstructure of Agaricus bisporus dried products during far infrared drying were investigated. Results showed that ultrasound pretreatment induced a reduction in drying time. By compared with untreated dried Agaricus bisporus products, ultrasonic pretreated samples showed an obvious decrease of hardness value, and a significant increase of crispness value. Ultrasound pretreatment significantly improved the rehydration rate and reduced the shrinkage rate of dried products. In addition, ultrasonic-assisted blanching and blanching pretreatments induced loss of color, rehydration rate and Vc content, and an increase of shrinkage rate. These changes may mainly be due to destructive effect of high temperature on Agaricus bisporus cell structure.The moisture distribution and change of Agaricus bisporus during far infrared drying was analyzed by low-field nuclear magnetic resonance (NMR) technology. The Agaricus bisporus slices (3,5,7mm) were dried at three temperatures (50,60,70℃). Results showed that the water state within Agaricus bisporus were free water, immobilized water and bound water. The contents of free water (M23) had the highest ratio during three water state, which were 9048.26,12038.71,17532.27, respectively, in 3,5,7 mm of Agaricus bisporus slices. The removal of free water and immobilized water were the fastest when the thickness of Agaricus bisporus was 3 mm at the same temperature. The free water and immobilized water within Agaricus bisporus were decreased gradually with increasing temperature. The content of bound water within Agaricus bisporus had no obvious downtrend at different temperature. These findings indicated that the free water and partial immobilized water were mainly removed during the drying process, and bound water was hardly removed. Thus the content of bound water had no significant effect on Agaricus bisporus during far infrared drying.The rehydration process of Agaricus bisporus dried products had been studied. With dried products slice thickness, water temperature and water consumption as an index, analyze the rehydration rule and effect. What’s more, the data has been fitted by first order kinetic model, Peleg model and Weibull model. Results showed that rehydration rate was the highest when the thickness of Agaricus bisporus was 3 mm. The rehydration rate of Agaricus bisporus was increased gradually with increasing temperature. Under the 80℃ conditions, rehydration rate of dried products was the highest. Water consumption has little effect on the rehydration rate of dried product, The rehydration rate of Agaricus bisporus was increased gradually with increasing water consumption. Model fitting results show that Weibull model is the most suitable to describe the rehydration process of far infrared drying Agaricus bisporus.