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

Abstract

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 dif-fusivity (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 phe- nolic 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 visu-alised 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 phys-ical and nutritional characteristics of mushrooms. Overall, the use of IR-HPD is an alternative tool that allows us to obtain high-qual-ity dried mushrooms with good nutritional attributes and a high amount of bioaccessible polyphenols.