Influence of a hybrid drying combined with infrared and heat pump dryer on drying characteristics, colour, thermal imaging and bioaccessibility of phenolics and antioxidant capacity of mushroom slices

An infrared-assisted heat pump drying (IR-HPD) was designed and used for drying of mushroom slices at three different infrared (IR) powers (50, 100, and 150 W) and a fixed drying temperature of 40°C and air velocity of 1 m/s. The changes in total phenolic content (TPC), total antioxidant capacity (TAC) and individual phenolic contents bioaccessibility, drying characteristics, and colour values of mushroom slices were investigated. IR-HPD provided 13.11 to 30.77% higher energy savings than HPD and reduced drying time between 9.48 and 26.72%. Page, Modified Page models were considered the best for predicting the thin layer drying behaviour of mushroom slices. The effective moisture diffusivity (Deff) value increased with IR power and ranged between 6.491x10-10 and 9.023x10-10 m2s-1. The contents of TPC, TAC, and individual phenolics in mushroom slices were significantly reduced (p<0.05) after drying. In vitro the bioaccessibility of phenolic compounds and TAC generally decreased, whereas TPC bioaccessibility was increased. Colour values were decreased except for a* value that increased after drying. Thermal imaging results showed that IR lamps increase the temperature of the products in the middle close to the lamp by approximately 1.5°C. In addition, thermal imaging gave a better understanding and visualised the effect of different power IR lamps on the temperature distribution of the products according to their distance from the lamp. As a result, drying mushrooms with a hybrid drying system combined with IR and heat pump dryer provided higher energy savings than HPD, reduced drying time, and maintained the physical and nutritional characteristics of mushrooms. Overall, the use of IR-HPD is an alternative tool that allows us to obtain high-quality dried mushrooms with good nutritional attributes and a high amount of bioaccessible polyphenols.