Drying characteristics of diced potato with thin-layer by hot-wind based on Weibull distribution function

Abstract: Potato, which is widely regarded as a total nutrient food, is the fourth major food crop after wheat, corn and rice in the world. In the same time, potato is one of the most highly productive food crops in China with potentiality of further development in the future and has been widely used in the food, feedstuffs and pharmaceutical industry. So it has also been endowed with the properties of both food crops and commercial crops. The preservation techniques in China, the largest potato producer, are so lagging that the loss amount is estimated to be over 15% each year, which is far above that of developed countries in Europe and America. The potato drying process is an important step as it plays a crucial role in reducing the moisture of agricultural products, extending the storage period and improving the additional values. As the most extensive method among all artificial drying processes, hot air drying has the properties of easy manipulation, low cost, and fewer demands for the environment, space and equipment. Research on the property of hot air drying, development of drying models and determination of water transfer parameters has great importance to the effectiveness in predicting, regulating and optimizing of the drying process. In this paper, the drying curves, the material temperature, the moisture effective diffusivity velocity and the activation energy are discussed at the different hot-air temperature, air velocity and dice length based on the thin layer drying experiments. The hot air temperatures are taken as 40, 50, 60, 70, 80 and 90 ℃. The air velocities are 0.5, 1.0, 1.5, 2.5 and 3.5 m/s. The potato dices have the cross section of 10 mm × 10 mm, and the lengths are classed as 2.5, 5, 10 and 15 mm. The main results are as follows. The hot air drying of fresh diced potatoes has typical characteristics of the Weibull distribution with the falling rate. The process can be divided into 2 phases, i.e. the stage at first increase phase and then the deceleration phase. The drying time is shortened with the rising of the hot air temperature and the decreasing of the dice length, and the air velocity has a little effect on the time except the early stages when the increasing air velocity can give the promotion of drying rate. The hot-air drying process of fresh diced potatoes obeys the Weibull function, and the value of R2 ranges from 0.991 to 0.999, which means the hot-air drying process is in good agreement with the Weibull distribution function. The scale parameter in the model grows with the increase of hot-air temperature and air velocity, and decreases with the rise of dice length. The shape parameter in the model has positive correlation with the dice length and air velocity, while air temperature causes little impact on the shape parameter. The moisture effective diffusivity velocity, which is between 1.859×10-9 and 12.509×10-9 m2/s, is significantly (P<0.05)correlated to the hot-air temperature and air velocity, but the dice length is not significantly (P>0.05). The geometric dimension parameter is relevant to the dice length and air velocity, which increases with the rise of air velocity and dice length). The activation energy of hot-air potato drying is found to be 19.107 kJ/mol, which is lower than the average activation energy of diced or chipped fruit and vegetable, and thus hot-air potato drying is easier to accomplish. This research will help to provide theoretical and technical foundation to the hot-air drying of the fresh diced potato.