Effects of freeze‐thawing, blanching, and ultrasound pretreatments on drying efficiency and quality of quince peels

This study investigated the effects of freeze-thawing (FT), blanching (BL), and ultrasound (US) pretreatments on the drying characteristics and quality of quince peels before hot air drying (HAD) at 60°C. All three pretreatments could decrease the moisture ratio (MR) at any drying time point and increase the effective moisture diffusivity (D_eff). The maximum drying rate (DR) of the peels pretreated with BL and US was 1.4 times that of unpretreated peels. The MR-t curves of the peels were highly fitted to the Midilli model. The drying time to reach equilibrium dry basis moisture content for peels pretreated with FT, BL, and US was reduced by 33.33%, 58.33%, and 66.67%, respectively, compared to 4 h for unpretreated peels. The color of US pretreatment peels was closest to that of fresh peels. The total phenolics content and total flavonoids content in the peels were in the order of US > unpretreated > BL > FT. Notably, the rutin content of US pretreatment peels was 4.15 ± 0.10 mg/g DW, which was 15% higher than that of unpretreated peels. In summary, US is the most recommended pretreatment to improve the drying efficiency and quality of HAD quince peels.