Brassica oleracea var. acephala, or kale, is a leafy green vegetable and a group of cultivars of cabbage (B. oleracea). It was once the most common green vegetable in European history, and cultivation was encouraged in the UK during World War II because it is easy to grow and provides important nutrients. Kale leaves contain lots of vitamins A, C, and K, and dietary minerals, as well as beneficial fiber.

The significant anti-oxidant capacity of kale is due to numerous polyphenols derived from kaempferol, quercetin, and hydroxycinnamic acid derivatives. Another research showed that phenolic fractions extracted from kale leaves effectively inhibited the growth of several bacteria, including Moraxella catarrhalis, a major respiratory pathogen in humans.