Drying and optimization of orange with a vacuum microwave dryer

In this thesis, the drying of Washington Navel and Valencia orange varieties using vacuum microwave drying (VMD) and conventional drying methods was investigated. Optimum drying conditions were determined using the Response Surface Methodology (RSM), and drying was conducted under these optimized conditions. Changes in various quality parameters and bioactive components of the resulting products were then examined. The main objective of the study was to comparatively analyze the drying performance and product quality of both orange varieties and to identify optimal processing conditions and to highlight the differences of the VMD method over conventional drying. A wide range of physical and chemical quality parameters were assessed in the dried samples, including rehydration capacity, color parameters (particularly the b* value), moisture content, water activity, pH, total acidity, total phenolic content, total carotenoid content, antioxidant activity (DPPH assay), hydroxymethylfurfural (HMF), as well as detailed carotenoid and phenolic compound profiles, and sugar and organic acid contents. Additionally, drying kinetics were modeled, and appropriate mathematical models were selected based on the drying method and orange variety. The results demonstrated that VMD significantly reduced drying time compared to conventional tray drying, while providing higher rehydration capacity, less color degradation, and better retention of bioactive compounds. Notably, orange samples dried using the VMD method exhibited higher total phenolic content and antioxidant activity. Moreover, differences in the retention of bioactive compounds were observed depending on the orange variety. In conclusion, this study demonstrates that vacuum microwave drying is a superior alternative in terms of both process efficiency and product quality for drying orange slices. It also confirms that optimizing drying conditions is crucial for preserving the nutritional and functional properties of the product.