Evaluation of microwave vacuum drying combined with explosion puffing drying and compared with microwave vacuum drying and hot-air drying by the quality of the dried apple slices

The objective of the study was to whether the microwave vacuum drying system, which makes positive contributions to the quality characteristics in food drying, would have positive effects on the existing quality criteria by using explosion puffing drying after microwave vacuum drying and microwave vacuum drying after hot air drying. In this study, apple slices were dried in four single drying; air drying (AD) (70 °C, 2 m/s), microwave vacuum drying (MWVD) (1.5, 3 and 4.5 W/g) and six combined drying; the first 3 of 6 combined drying; AD (70 °C, 2 m/s) + MWVD (1.5, 3 and 4.5 W/g), the second 3 of 6 combined drying; MWVD (1.5, 3 and 4.5 W/g) + Explosion puffing drying (EPD) (0.6 MPa, 70 °C). It was determined that the apparent volumes of MWVD samples (1.5, 3 and 4.5 W/g) were 9, 17, and 51% higher than AD samples, respectively. With the MWVD and EPD processes applied after AD, a product structure with expanded and increased porosity was obtained, which increased the rehydration rate of the dried product. This was confirmed by the image analysis method, and the geometric structure, dimensions, and depth map of the porous material were examined using the MATLAB program for SEM images of dried products. We believe that a verification approach that is not available in the literature will contribute to the literature by providing an innovative approach for validation purposes in the evaluation of SEM images in drying studies. The total phenolic content (TPC), 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2.2’ azinobis 3-ethylbenzothiazoline-6-sulfonic acid (ABTS) contents were higher in the MWVD samples than in the MWVD + EPD samples. TPC and antioxidant capacity were higher 2–1.87 times and 1.98–1.74 times for 4.5 W/g MWVD and 4.5 W/g MWVD + EPD dried apple as compared to air-dried apple slice. With the increase in power density per product in MWVD, the porosity, rehydration, total phenolic, DPPH and ABTS values of the product increased The MWVD and EPD methods prevent shrinkage and volume loss of the dried products, and a low bulk density product was obtained. Therefore, we can conclude that both puff drying and microwave -vacuum drying are successful methods for the production of dried apple slices.