气体射流冲击干燥无核紫葡萄及品质分析

Drying Monukka grapes with air-impingement jet technique and quality analysis

采用气体射流冲击干燥技术设计的葡萄干燥试验装置,可实现温度自动控制,风速、热介质湿度的控制和数据采集与存储。利用该装置对无核紫葡萄干燥工艺和干燥品质进行研究,试验发现,气体射流冲击干燥无核紫葡萄存在预热阶段、恒速干燥阶段和降速干燥阶段,随着风温和风速的提高,恒速段干燥速率明显增加,干燥时间缩短,而降速段干燥速率提高不明显。试验风温和风速范围内所得葡萄干理化成分差异不显著;试验还针对Vc降解进行了动力学分析。在试验装置的基础上,开发设计了中试设备并投产运行,其最佳工艺参数为风温65℃,风速20m/s,耗时为29h。制得葡萄干含水率(干基)17.1%,可溶性固形物77.8%,可滴定酸2.3%,Vc6.74×10-2mg/g。

An experimental device for drying grapes was designed according the principle of air-impingement jet technology. For this device, the hot air temperature and velocity were automatically controlled, the relative humidity of heat media could be monitored, and moreover, all of the data could be collected and saved. Based on this device, the drying technique and drying quality of Monukka grapes were studied. Experimental results showed that the drying curves of Monukka included three stages of pre-heating, constant rate drying and retarded drying. As the increasing of impingement temperature and hot air velocity, the drying rate of constant rate drying stage was improved, the drying time of this stage was shortened, but those factors were insignificant in retarded drying stage. There were no significant differences in the quality indexes of raisins at the range of experimental drying temperatures and velocities. The kinetics of the degradation of ascorbic acid was also studied under various drying temperatures. The pilot equipment of air-impingement jet dryer was developed and put into operation. The optimum technological parameters were air temperature of 65℃ , air velocity of jet nozzle at 20 m/s, drying for 29 h. The moisture content （dry matter, %） of raisins is 17.1%, soluble solid content is 77.8%, titratable acidity is 2.3%, and ascorbic acid content is 6.74×10-2 mg/g.