Characterization of pre-gelatinized kidney bean (Phaseolus vulgaris L.) produced using microwave hot-air flow rolling drying technique

This study aims to develop a pretreatment and drying process for kidney beans to improve their cooking efficiency. Hot air drying (HD) and microwave hot air rolling drying (MHRD) were analyzed for the drying of pre-cooked kidney beans, and the effect of hot air and microwave on structure and gelatinization properties of kidney beans starch were investigated. The result indicated that the drying time was significantly reduced by approximately 27% (p < 0.05) with the increase of hot air temperature by 10 °C in the HD-processed material. Based on the incorporation of microwave radiation, drying time was further decreased by 2.5 times at the same hot air temperature. The microstructure, crystalline structure, thermal behavior and FTIR spectra of the kidney bean starch suggested the positive correlation between the hot air temperature/microwave radiation and destruction of their crystalline structure/gelatinization degree. The cooked dried kidney beans exhibited significantly decreased hardness, gumminess and chewiness and increased springiness, compared with the untreated kidney beans, suggesting an improved cooking efficiency. Base on the results of drying efficiency, color profile, gelatinization of kidney bean starch and texture profile analysis of the cooked beans, MHRD-70 was the optimum drying process.