Effects of selected processing parameters on rehydration and texture of freeze-dried compressed carrot bars

Abstract

The effect of moisture content, microwave plasticization time, compression force and dwell time on texture of freeze-dried compressed carrots was determined. Response Surface Methodology demonstrated that moisture was the main variable affecting textural quality. Microwave radiation was found to be an excellent means of plasticization. Optimum processing conditions determined were 50% moisture content, 40 second microwave time, 500 psi compression force and 20 second dwell time. Histological examination of freeze-dried carrot tissue with the scanning electron microscope illucidated structural differences as a result of compression moisture level. Cellular disruption from compression at low moisture was found to be the main reason for rehydration and texture differences. Sensory texture evaluation of high moisture compressed carrots was comparable to a freshly cooked product. The ratio of outer wall to core and the sugar-starch content of the tissues were found not to be correlated to rehydration or the parameters of a three-element Maxwell model. A three-element Maxwell model describing stress-relaxation behavior of carrots processed at 50% moisture, 40 seconds microwave, 500 psi compression force and 20 second dwell time was developed.