| There has been considerable interest in applying low-pressure superheated steam to dry various products during the past decade, because it is able to provide dried products with less quality deterioration compared with hot air, no fire danger, no pollution and is applied to various types of heat-sensitive materials. Binlang taro was used as the material in this paper, different pretreatment during low-pressure superheated steam drying were studied; the foundational characteristics and drying dynamic model were discussed; the low-pressure superheated drying conditions were optimized; taro slices undergoing low-pressure superheated drying were compared with three different drying methods. The main results were as follows:1) Pretreatment significantly influenced the quality of raw material and dried taro slices undergoing LPSSD. It gets higher yield with dipping pretreatment and good sensory qualities with freeze drying treatment.2) Factors that influenced dried taro slices moisture condensation were debated and the curves of dried taro chips central temperature and shrinkage were obtained undergoing LPSSD. A drying dynamic model was proposed for estimating the moisture ratio as a function of superheated steam temperature and vacuum degree.3) According to a three-factors and five levels of the quadratic general rotary unitized design, a regression models of shrinkage as a function of vacuum degree, superheated steam temperature, material thickness were set up based on single-factor experiment, the results showed the optimum drying conditions were: vacuum degree of 8KPa, superheated steam temperature of 72.5℃, thickness of 4mm and the rehydration ratio is 2.337 under the optimum conditions.4) Compared the effects on dried slices undergoing low-pressure superheated steam drying with freeze drying, vacuum drying and hot air drying, the result showed low-pressure superheated steam drying is able to provide dried taro with higher quality.
|
PDF Full Text Request