Comparative Antibacterial Activity of Cabbage Varieties Against Thermophilic Bacillus spp. Isolated from Wheat Grains

The microbiological safety of whole wheat flour remains a critical issue due to its susceptibility to contamination by spore-forming thermophilic bacteria. In this study, two thermophilic species, Bacillus subtilis and Bacillus mesentericus, were isolated from locally produced wheat grains and used as target microorganisms to evaluate the antibacterial potential of freshly pressed cabbage juices. Juices obtained from five cabbage varieties-red cabbage, white cabbage, napa (Chinese) cabbage, broccoli, and cauliflower-were comparatively assessed using the broth dilution method to determine their minimum inhibitory and bactericidal effects (n = 3). The results revealed pronounced differences in antibacterial efficacy among the tested samples. White cabbage juice exhibited selective inhibitory activity against B. subtilis at a dilution of 1:4, whereas napa cabbage and broccoli juices demonstrated the highest antibacterial activity against both Bacillus species at a dilution of 1:3. Importantly, napa cabbage juice showed no inhibitory effect on Saccharomyces cerevisiae, indicating its compatibility with dough fermentation processes. Spectroscopic analysis of the bioactive fraction obtained from napa cabbage juice revealed characteristic absorption bands at 3422 cm^-1 (O-H stretching), 2907-2840 cm^-1 (aliphatic C-H stretching), 1740 cm^-1 (ester carbonyl group), and 1641 cm^-1 (C=C stretching). The predominance of lipophilic compounds, including fatty acid esters, terpenes, and sulfur-containing compounds (734 cm^-1), suggests a molecular basis for the observed antibacterial activity against Bacillus spp. Overall, these findings identify napa cabbage as a promising source of selective natural antimicrobial agents capable of enhancing the microbiological safety of whole wheat flour-based bakery products without compromising yeast activity.