Evaluating the Microstructure and Bioaccessibility of Bioactive Compounds and Antioxidant Activity After the Dehydration of Red Cabbage

This study aims to examine the effects of various drying methods, namely convective drying (CD), vacuum drying (VD), infrared drying (IRD), low-temperature vacuum drying (LTVD), and freeze-drying (FD), on the microstructure and in vitro bioaccessibility of red cabbage bioactive compounds and antioxidant activity. Total polyphenol content (TPC), total flavonoid content (TFC), total anthocyanin content (TAC), total glucosinolate content (TGC), individual phenolic profile, and antioxidant potential (DPPH, ABTS, FRAP) were examined experimentally in original and digested samples. Overall, SEM images of dried red cabbage showed more porous structures and minimal parenchyma deformation, enhancing bioactive compound bioaccessibility. Specifically, the bioaccessibility of TPC in IRD-dried samples was remarkably higher than that of FD- and LTVD-dried samples, although the latter two proved more TAC and TGC bioaccessible, respectively. Notably, hydroxycinnamic acids, such as ferulic and p-coumaric acids, markedly increased after digestion, especially in FD-dried samples. In vitro digestion revealed that CD-dried samples showed stronger DPPH and FRAP radical scavenging, whereas FD-dried samples had significantly higher ABTS scavenging activity. These findings suggest that LTVD and FD are the most suitable drying methods for red cabbage to enhance relevant bioactive compounds and, to some extent, antioxidant activity after digestion.