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

Abstract

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.

Keywords: brassica vegetables; drying kinetics; glucosinolates; simulated digestion.

Figure 1

Graphic representation of the preparation of red cabbage and drying procedure.

Figure 2

Graphic representation of the simulated gastrointestinal digestion and extraction procedure.

Figure 3

Changes in the moisture ratio (MR) of red cabbage dried with different methods. Values are the means of triplicate analyses (n = 3), and error bars are the standard deviation. CD: convective drying; VD: vacuum drying; IRD: infrared drying; LTVD: low-temperature vacuum drying; FD: freeze-drying.

Figure 4

Changes in the microstructure of red cabbage dried with different methods. (A) fresh sample; (B) CD: convective drying; (C) VD: vacuum drying; (D) IRD: infrared drying; (E) LTVD: low-temperature vacuum drying and (F) FD: freeze-drying.

Figure 5

Changes in the antioxidant potential of dried red cabbage using different methods during in vitro gastrointestinal digestion evaluated by (A) DPPH assay, (B) FRAP assay, and (C) ABTS assay. CD: Convective Drying; VD: Vacuum Drying; IRD: Infrared Drying; LTVD: Low-Temperature Vacuum Drying; FD: Freeze-Drying. Values are expressed as mean ± standard deviation (n = 3). Different letters within bars indicate significant differences (p < 0.05) among drying methods. Asterisks (*) indicate significant differences (p < 0.05) among fractions (control, bioaccessible, and non-bioaccessible fraction) within each drying method.

Figure 6

Pearson correlation coefficients between antioxidant activity (DPPH, FRAP, ABTS) and biactive compound variables (TPC, TFC, TAC, TGC, and individual phenolic acids) in red cabbage extracts. Correlations are shown separately for control (non-digested), bioaccessible, and non-bioaccessible fractions. Positive correlations are represented in purple and negative in pink.