Antioxidant activity of lactic-fermented Chinese cabbage

Lactic-fermented cabbage, similar to Kimchi in Korea, is a very popular fermented vegetable product in Taiwan and China. In this study, fermented cabbage prepared by a dry-salt method was first extracted with water and methanol. Antioxidant activity such as DPPH radical scavenging effects, reducing power and Fe2+-chelating ability of the solvent extracts of fermented cabbage was determined and the effect of fermentation on the change of antioxidant activity, total phenolic and total flavonoid content was also investigated. Results revealed that antioxidant activity observed on the Chinese cabbage mixture may vary with extraction solvents and fermentation. Generally, the methanol extract of the cabbage mixture showed a higher DPPH radical scavenging activity and reducing activity than the water extract. Although, fermentation did not alter the Fe2+-chelating ability and reducing activity of the methanol extract of the cabbage mixture, it reduced these same antioxidant activities in the water extract. Amongst the various extracts examined, the methanol extract of fermented cabbage showed the highest DPPH radical scavenging effect. On the other hand, the highest Fe2+-ion chelating and reducing activities were exerted by the methanol extracts of both the cabbage mixture and the fermented cabbage, which showed no significant difference (p < 0.05). Additionally, the type of solvent and fermentation were also found to affect the total phenolic and flavonoid content of the extracts. Fermentation increased the total phenolic content of the methanol extract, whilst reducing the total flavonoid content of the water extract. Furthermore, changes in the antioxidant activity observed on the extracts of the cabbage mixture and fermented cabbage did not coincide exactly with the total phenolic and total flavonoid content.