Study On Hot-air Drying Characteristics And Heat-moisture Migration Law Of Bamboo Shoot Slices

Bamboo shoots are rich in nutrients and are widely consumed around the world as a healthy vegetable.Fresh bamboo shoots have a high moisture content and are prone to browning and woody conditions within a short period of time after harvesting,resulting in a high loss of fresh shoots.Hot air drying is currently the most widely used drying method due to its low cost and high yield,but there are currently problems with hot air drying of bamboo shoots such as time consumption and poor quality,therefore,it is of great importance to study the hot airdrying process of bamboo shoots.The effect of hot air temperature,hot air velocity and slice thickness on the hot air drying quality of bamboo shoot slices was investigated by single-factor experiments.It was found that the increase of hot air temperature and hot air velocity,and the decrease of slice thickness were conducive to the improvement of drying rate,but the increase of all three was not conducive to the improvement of rehydration ratio and the retention of chromatic color,and it was also found that when the air velocity was lower than 1m/s,the change of air velocity did not have a significant effect on the color,and when the slices were too thin,it also led to the deterioration of color.Based on the results of single-factor experiments,a three-factor,three-level response surface optimization experiment was conducted to establish a quadratic polynomial model of hot air temperature,hot air velocity and slice thickness in relation to the experimental indexes,and the comparison of the response values on the significance of the indexes yielded that the influence of each factor on the indexes in the hot air drying process of bamboo shoots slices were hot air temperature > slice thickness > hot air velocity.The optimized process parameters for hot air drying of bamboo shoot slices were determined to be 60.43°C,0.41 m/s and a thickness of 2mm,at which point the optimum indicators were 9.42 rehydration ratio,14.62 chromatic aberration and 10.3%/h drying rate,respectively.A three-dimensional hot air drying model of bamboo shoots slices was established to analyze the internal heat and moisture migration pattern of bamboo shoots slices during hot air drying,and it was found that the heat migration occurring during the drying process of bamboo shoots slices was a process that proceeded from front to back and from surface to inside.The drying rate at the end of the slices was significantly greater than that at the end,with the high moisture content area inside the slices first exposed to the hot air migrating almost parallel and gradually decreasing from the front end,while the moisture in the other slices gradually migrated outwards from the two corners of the end,contracting from outside to inside to a certain area at the end.