Optimizing infrared wavelengths in food drying: A comprehensive review of standalone and combined techniques

In food processing, infrared drying techniques efficiently remove moisture while preserving quality. Determining the optimal infrared wavelength reduces energy costs and maintains food quality after drying. This review paper summarizes the various wavelengths utilized in infrared drying and explores combined techniques to enhance drying efficiency, reduce drying time, save energy, and maintain food quality. Among infrared drying, far-infrared radiation is the most commonly used for effectively removing moisture and preserving bioactive compounds. However, other infrared wavelengths also have significant applications. For example, near-infrared radiation is prevalent to achieve the Maillard reaction in carbohydrate-rich foods. The combination of mid-infrared (MIR) and far-infrared (FIR) wavelengths, ranging from 2 to 50 μm, covers a broad spectrum of food components, making it a widely used range for infrared drying. In terms of infrared combined techniques, utilizing MIR or FIR in infrared-assisted freeze drying can yield value-added fruit snacks with enhanced crispness. Mid-infrared radiation is sometimes preferred after freeze drying to prevent structural collapse in food products, while near-infrared wavelength (NIR) is favored for expediting drying time, especially for berries. In contrast, infrared-assisted hot air is suitable for seafood, with NIR rarely used due to its potential to deteriorate food quality. This comprehensive review provides researchers with guidance on properly selecting wavelengths for infrared drying and combined techniques.