INVESTIGATION OF CONTINUOUS AND INTERMITTENT HEATING ON FAR-INFRARED ASSISTED FREEZE-DRYING

Freeze-drying of sweet potato was studied using continuous and intermittent jar-infrared (FIR) assisted heating in this study. Intermittency levels of alpha = 0, 0.25, 0.5, 0.75, and 1. were applied with a cycle time of 30 min, and it was found that the optimum intermittency level was alpha = 0.5. The continuous (alpha = 1.) and intermittent (alpha = 0.5) FIR-assisted freeze-drying processes were then performed using a three-level, three-factor experimental design and analyzed by response surface methodology (RSM). For both continuous and intermittent freeze-drying, the response variable of drying time was affected by drying temperature (X-1) and sample thickness (X-3) at the 5% significance level; total color difference was affected by distance (X-2) at a 95% confidence level. In addition, rehydration ratio was significantly affected by drying temperature (X-1) and sample thickness (X-3) in continuous heating, and by thickness (X-3) at a 0.1% level of significance. lit both continuous and intermittent FIR-assisted treatments, the coefficients of determination (R-2) of surface response models of drying time, rehydration ratio, and total color difference were all found to be greater than 0.90. Determination of optimum conditions was based on comparison between the control and FIR-assisted treatments. lit both continuous and intermittent treatments, optimum drying conditions could be established at 20 nun distance front FIR radiator to sample, and controlling the drying temperature in the range of 34 degrees C to 37 degrees C with 6 to 7 min sample thickness. Verification tests indicated that the generated second-order polynomial models were acceptable.