Advancements in atmospheric freeze-drying: Innovations, technology integration, quality and sustainability implications for food preservation

Atmospheric freeze-drying (AFD) is a method of freeze-drying conducted at atmospheric pressure and low temperatures below the freezing point of water, using dry air for the preservation of foods and pharmaceutical products. AFD shows promise as a cost-effective alternative to traditional vacuum freeze-drying (VFD), particularly for industrial-scale applications. This review aims to explore recent advancements in AFD over the past two decades, focusing on numerical simulations and novel experimental systems. It highlights the integration of technologies such as Ultrasound (US), Infrared Radiation (IR), and Microwave radiation (MW) to enhance drying kinetics. Key processing parameters, including temperature, air velocity, and product geometry, are examined for their impact on drying kinetics and food quality attributes like texture, colour, and nutritional properties. The review also assesses the economic and environmental impact of AFD. Innovative systems, such as fluidized beds, spray freeze, tunnel freeze, and vibro-fluidized bed drying, have improved the kinetic rate of AFD. The integration of advanced technologies has notably reduced drying time by up to 70% without substantially compromising food quality, depending on the power applied. AFD demonstrates up to 30% less energy consumption compared to vacuum freeze-drying (VFD) and, while slightly lower in quality than VFD, surpasses hot air drying in product attributes. AFD presents a cost-effective, energy-efficient alternative to VFD with promising industrial scalability.