Fermentation improves the nutritional and sensory properties of food. Despite the challenges of fermenting algae individually, incorporating it into vegetable matrices offers a great opportunity for the development of new products. This study aimed to investigate changes in the antioxidant capacity and total phenolic content of Chinese, white, and red cabbages supplemented with Undaria pinnatifida throughout controlled fermentation. These values were then compared to those for the respective spontaneous process (mixed models), as well as to previously published data on cabbage fermentation without algae (simple models). Controlled fermentation was carried out in a two-step process using previously selected autochthonous starter cultures. Antioxidant activity was measured using the DPPH scavenging assay and the CUPRAC assay. The total phenolic content was determined using the Folin-Ciocalteu method. The total phenolic content varied across the different fermentation processes depending on the vegetable matrix. The antioxidant capacity was significantly higher in the controlled process than in the spontaneous one in all mixed models. Red cabbage with algae exhibited higher total phenolics and antioxidant capacity than white and Chinese cabbages with algae. Furthermore, all the mixed models showed higher or comparable total phenolics and antioxidant capacity compared to the respective simple models under similar controlled fermentation and extraction conditions, except for Chinese cabbage with Undaria under the CUPRAC method. Controlled fermentation of the studied cabbages improved their antioxidant capacity to a greater extent than spontaneous in all mixed models. In general, the mixed models showed higher nutritional properties than the simple models.