Investigation of potential drying strategies for quality maintenance of carrot

Convective drying of carrots is a non-linear and unsteady-state process with simultaneous mechanism of heat and mass transfer leading to time varying quality changes along the process and finally causing irreversible quality modification. Inappropriate drying condition will generate many qualities related problems such as destruction of physical properties and discoloration of carrots causing by mechanical and thermal damage due to over-drying or extended drying periods. Inconsistent quality of the product was also observed in dried carrots due to variation in process parameters and different drying techniques. Inadequate process control during drying also will cause non-uniform moisture and temperature distribution on the surface area and negatively impacting quality degradation. All these existing problems during drying of carrots require new approach to minimize the quality loss with the main objective is to maximize quality retention by introducing new drying strategies. Most of the previous research approach was concentrating on ‘input-output’ or black box concept which relies on initial and final values of quality attributes without considering the time varying transition of specific quality attributes at different exposure time during drying. This common practice effectuates the process performance since quality profile at the entire drying periods is unknown leading to variation in the quality of the product. In view of this, the current research is undertaken to understand the trend of dynamic changes of color and total carotenoids at different temperatures of 50 °C, 60 °C and 70 °C in order to develop a degradation profile of quality attributes in carrots during convective drying. The information is useful for identifying the exact inflection point and moisture level in which the quality parameters are prone to rapid degradation so that specific drying strategies can be designed for process improvement and dynamic optimization. Based on this, a new drying strategy of intermittent drying was tested in this study with the aim to investigate the combined effects of temperature, moisture levels and tempering periods on quality retention and to promote the new concept of inflection point based non-stationary drying for quality maintenance of carrots. This new technique has proven to be effective in increasing the retention of total carotenoids up to 77% with significant improvement in color attribute and noticeable reduction in effective drying time and energy consumption when drying at 60 °C with 3 hours tempering period at 30% moisture level. Furthermore, the possibility to use hyperspectral imaging for non-destructive quality measurement during drying of carrots was also conducted in this study. The results obtained demonstrate excellent predictive performance for moisture content with moderate prediction accuracy for color and total carotenoids content in carrots during drying.