Reduction in drying time of taro using pretreatments or posttreatment with hot air drying

Abstract

Taro is a widely cultivated crop, primarily grown for its corm, which serves as a staple food worldwide. However, due to its high moisture content, taro is highly perishable, with an unprocessed shelf life of only 15 to 20 days. Drying has been employed as a method for extending shelf life by reducing moisture content to levels that inhibit microbial growth and prevent moisture-induced deteriorative biochemical reactions. Convective hot air drying (HAD) is the most commonly used method for food drying, but it is associated with prolonged drying times and high energy consumption. This research aimed to reduce the drying time of taro by using pretreatments and posttreatments with hot air drying. HAD without pre- or posttreatments was used as a control, and drying times were compared across four pretreatment methods (microwave, blanching, ultrasonication, and osmotic dehydration) and one posttreatment method (microwave). The results indicated that microwave post-treatment after 1 hour of hot air drying at 50°C reduced total drying time by 85% compared to the control. Similarly, microwave post-treatment after 1 hour of hot air drying at 70°C reduced drying time by 75% when moisture content decreased from 2.4 (dry basis) to 1.3 (dry basis). In contrast, blanching and osmotic dehydration pretreatments at 50°C worsened drying efficiency, increasing drying time relative to the control. Microwave pretreatments at 50°C resulted in slight reductions in drying time compared to the control. Additionally, peeling the skin before drying reduced total drying time by approximately 36% compared to skin-on samples. However, slicing was necessary, as whole peeled samples required longer drying times than sliced ones. Taro, sliced to 8 mm thickness, dried with hot air at 70°C for 1 hour, followed by 20 minutes of microwave post-treatment, reaches 0.10 (dry basis), which is the required final moisture content for taro flour production, and is suitable for industrial scale implementation. Further research is required to assess the energy consumption of microwave post-treatment and hot air drying to determine their economic and sustainable feasibility. Quantifying energy requirements is essential for balancing efficiency with cost-effectiveness.