Microwave assisted drying of short-cut (ditalini) macaroni: Drying characteristics and effect of drying processes on starch properties

摘要

Macaroni samples were dried by conventional hot air, microwave alone and hot air followed by microwave drying methods. The drying of macaroni samples took place in the falling rate period. Higher drying rates were observed with a higher microwave power level. A diffusion model was employed to fit the experimental drying data in order to characterize the drying rate of samples. Drying only with microwave energy (70 and 210 W) or hot air-microwave energy (70 and 210 W) resulted in substantial shortening of the drying time. The reduction was 61.8%, 87.3%, 61% and 78%, respectively, of the time to dry with hot air. All starch granules of semolina and hot air dried macaroni displayed a clear "Maltese cross" under polarized light. Starch granules of macaroni samples dried with microwave (70-210 W) and combined hot air-microwave (70-210 W) had irregular shapes but retained birefringence in about half or whole of each granule. The starch gelatinization enthalpies of macaroni samples dried with hot air, microwave alone (70 and 210 W) and combined hot air and microwave (70 and 210 W) drying were lower than that of semolina sample. This confirms that starch is not completely gelatinized during drying.