It is widely believed that natural antioxidants found in food are significantly lost during processing. Nevertheless, it was recently demonstrated that processed fruits and vegetables may retain their antioxidant activity. In the present work, the changes in the overall antioxidant properties as a consequence of fermentation of cabbage and/or heat treatment of cabbage juices and extracts were studied. Fermentation processes as well as heat treatment increased the initial values of antioxidant activity. While a decrease in the antioxidant potential of sauerkraut juice was found for short heat treatments, a partial recovery of these properties was observed by prolonging heating periods. The TLC analysis showed that during fermentation and thermal processes, some substances with reactivity towards Folin–Ciocalteu reagent, hence with possible antioxidant activity, were released. We demonstrated that in contrast to common expectation, typical culinary processing of cabbage increases its antioxidant potency. The gain in antioxidant activity of heated samples coincided with the formation of both F–C reagent reactive compounds as well as brown early Maillard reaction products. This information may encourage the consumption of heat processed cabbage, especially that the release of antioxidants during heating may prevent oxidation of other food components, e.g. fats.