Effects of drying methods on colour, amino acids, phenolic profile, microstructure and volatile aroma components of Boletus aereus slices

This study is to investigate the effects of hot air drying (HD) at 60-80 degrees C (HD-60, HD-70 and HD-80), microwave pretreatment combined with HD (MHD), ultrasound pretreatment combined with HD (UHD) and vacuum freeze drying (FD) on the quality of Boletus aereus slices. Key characteristics, including colour, free amino acids, microstructure, volatile aroma components, phenolic profile and antioxidant activity, were studied. Amongst these drying methods, FD was the best way to preserve colour and volatiles of Boletus aereus slices. Fifteen amino acids were detected in Boletus aereus slices, and HD-60 showed a higher content of total amino acids than other drying regimes. Two phenolic acids were identified in Boletus aereus slices, namely, protocatechuic acid and p-hydroxybenzoic acid. MHD presented the highest content of phenolic compounds, followed by FD. Antioxidant capacity was positively correlated with phenolic compounds of Boletus aereus slices. Moreover, the cell structure of Boletus aereus slices was damaged after drying, and FD had a more porous structure than other drying methods. These results will be beneficial to the further industrial production of Boletus aereus slices.