Improving the nutritional properties of Brassica L. vegetables by spontaneous fermentation

Introduction. Brassica L. vegetables are rich in fiber, minerals, and bioactive compounds. Lactic fermentation can improve their nutritional value. The goal of this study was to evaluate phytase, calcium, phytic acid, total phenolic content, and antioxidants during spontaneous fermentation of white cabbage, red cabbage, and Chinese cabbage. Study objects and methods. The research featured samples of water extract, methanol extract, and brine. The procedure involved monitoring lactic bacteria and pH during cabbage fermentation. Diphenyl-1-picrylhydrazyl radical (DPPH) scavenging assay and cupric reducing antioxidant capacity (CUPRAC) assay were used to measure the antioxidant activity and Folin-Ciocalteau method to determine total phenolic content in the water and methanol extracts. In the brine samples, we studied calcium, phytic acid, and phytase activity. Results and discussion. The samples of white and red cabbage displayed the highest phytase activity on days 5–10 and had a maximal decrease of phytic acid and increase of calcium concentration, while in Chinese cabbage these processes occurred gradually throughout the fermentation. The total phenolic content in the brine and extracts was very similar for all the cultivars throughout the fermentation process. A continuous release from the solid phase to brine could be observed during the first ten days of fermentation. DPPH and CUPRAC assays revealed a similar phenomenon for the total phenolic content. The antioxidant capacity decreased in the water and methanol extracts and increased in the brine. At the end of fermentation, the red cabbage samples demonstrated a significant increase in the total phenolic content and total antioxidant activity, which was less prominent in the Chinese cabbage. The samples of white cabbage, on the contrary, showed a decrease in these parameters. Conclusion. Fermentation made it possible to increase the concentration of free calcium in white, red, and Chinese cabbages, as well as improve the antioxidant capacity of red and Chinese cabbages.