Microwave hydrodiffusion and gravity as a sustainable alternative approach for an efficient apple pomace drying

Apple pomace valuation has been impaired by its high perishability and absence of fast drying approaches demanded by industry. This work aimed to assess the feasibility of Microwave Hydrodiffusion and Gravity (MHG) process applied for apple pomace drying using discrete delivery powers (300–900 W) and comparison with hot-air drying (40–100 °C). To dry 0.4 kg of apple pomace (81% moisture), hot-air drying required 3.6–9.9 h with estimated water evaporation flux of 1.0–3.5 mL/min. For MHG, which processed 1.2 kg, these corresponded to 1.0–2.6 h and 5.1–13.9 mL/min. Furthermore, MHG allowed water recovery containing part of apple pomace phenolic compounds and carbohydrates. The dried pomace was stable for 2 years, after which phenolic compounds and polysaccharides were still recoverable by hot water extractions. These results pave the way for MHG to be used for apple pomace and other by-products preservation, boosting their conversion into valuable co-product for valuation of its components.