Process efficiency of electromagnetic radiation (EMR)‐assisted hybrid drying in spearmint ( Mentha spicata L. )

Abstract

Spearmint (Mentha spicata L.) leaves were dried using four different methods, namely, infrared-hot air (IR-HA) drying, radiofrequency-hot air (RF-HA) drying, low-humidity air (LHA) drying, and hot air (HA) drying at three different temperatures (30, 40, and 50°C). The effect of the methods on time required for drying, product quality in terms of chlorophyll, total carotenoids, essential oil yield and its composition, color, browning index (BI), and rehydration ratio was evaluated. The IR-HA hybrid drying at 50°C resulted in faster process with nearly 62% lesser drying time, as compared to HA drying, and also resulted in higher retention of essential oil (85.7%), carvone (79.6%), and lower BI (50.4). The specific energy requirement of IR-HA hybrid drying reduced by 60% as compared to HA drying at 50°C. The results showed that hybrid drying involving IR could be effectively used to obtain good quality of dried spearmint leaves in a shorter time with better energy efficiency. Practical applications Spearmint is popular for essential oil, and carvone is the major volatile compound present in the oil, giving its characteristic odor. This study explored the effect of drying methods (IR-HA, RF-HA hybrid drying, and LHA drying) on drying characteristics, quality of dried spearmint and its comparison with HA drying. The study showed that IR-HA drying resulted in shorter processing time with a higher yield of essential oil, carvone retention, and energy efficiency than other drying methods. The results indicated that IR-HA hybrid drying technique could be explored as an alternative to HA drying of heat-sensitive herbs like spearmint.