Design and development of a refractance window drying system coupled with vacuum: Production of bioactive apple pomace powder

Abstract

Drying is a widely used technique for food preservation and is continuously advancing to enhance efficiency and product quality. This study focused on developing a hybrid system that merges refractance window technology with vacuum drying (VRW). Apple pomace was dried using refractance window (RW) at 65, 75, and 85 °C under atmospheric pressure, VRW at the same temperatures, under vacuum pressure of 0.15, 0.25, and 0.45 bar, and using freeze-drying (FD) as a quality standard. The drying time, water activity, moisture content, particle size distribution, total soluble solids, color, polyphenol content, antioxidant activity, and dietary fiber content were measured. These results indicate that VRW reduced the drying time by 25 % compared with that of RW at 0.45 bar. RW and VRW showed similar results for water activity, moisture content, particle size distribution, and total soluble solids. Color analysis showed that overall VRW drying resulted in darkening; however, VRW at 85 °C and 0.45 bar achieved a color closer to freeze-drying. The highest polyphenol content was obtained with VRW at 65 °C and 0.45 bar, showing values comparable to those of FD, whereas RW yielded lower results. However, both RW and VRW exhibited antioxidant activities comparable to those obtained after FD.