Effects of different pretreatments on the drying, energy and physicochemical properties of Nepeta racemosa Lam by infrared hot air drying

• A comparative, systematic evaluation of five pretreatments—FD, BL, MW, ET, US—prior to IR-HAD of NrLF • All pretreatments significantly shortened drying time by ∼21.2–48.4% relative to the untreated control. • SEC decreased markedly for all pretreatments (∼18.6–67.1% reduction vs. control). • Freeze–thaw samples most closely resembled fresh material in appearance • Retention of TPC and antioxidant activity followed: Fresh > US > FT > BL > ET > MW > Control, Nepeta racemosa Lam (commonly abbreviated as NrLF) is recognized as a valuable source of bioactive compounds with significant therapeutic potential. In this study, five pretreatment strategies—freeze–thaw (FT), blanching (BL), microwave (MW), ethanol immersion (ET), and ultrasound (US)—were applied prior to infrared-assisted hot air drying (IR-HAD) of NrLF leaves. The influences of these pretreatments on drying kinetics, specific energy consumption (SEC), physicochemical attributes, and antioxidant properties were comprehensively assessed, while mathematical modeling was employed to describe the drying behavior. The results indicated that All pretreatments shortened IR–HAD drying time by 21.2–48.4% relative to the untreated control and reduced specific energy consumption (SEC) by 18.6–67.1%, with MW achieving the lowest SEC (2.01 MJ/kg). Notably, MW pretreatment yielded the most pronounced enhancements in D eff and drying rate, alongside the lowest SEC, attributable to the formation of extensive porous microstructures within the tissue. Moisture ratio–time (MR–t) data for NrLF leaves across all treatments were optimally described by the Midilli model. Colorimetric analysis revealed that freeze–thaw pretreated samples most closely resembled fresh material in appearance. Furthermore, FT pretreatment achieved the highest rehydration ratio (RR) and the lowest water activity (a w ). Retention of antioxidant activity and total phenolic content (TPC) followed the order: fresh material > US > FT > BL > ET > MW > control (untreated dried). In conclusion, the integration of ultrasound or freeze–thaw pretreatment with infrared-hot air drying emerges as a highly effective approach for enhancing both processing efficiency and product quality in NrLF, offering considerable promise for scalable industrial application.