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The effects induced by heat on <i>Depurple</i> and <i>Cheddar</i> (<i>Brassica oleracea</i> L. var. botrytis) during boiling, steaming, and <i>sous-vide</i> were investigated to elucidate the role of the basic cellular elements in softening and extractability of sterols and tocopherols. With this aim, an elastoplastic mechanical model was conceptualized at a cell scale-size and validated under creep experiments. The total amount of the phytochemicals was used to validate multivariate regression models in forecasting. Boiling was the most effective method to enhance the softening mechanisms causing tissue decompartmentalization through cell wall loosening with respect to those causing cell separation, having no impact on the phytochemical extractability. <i>Sous-vide</i> showed the lowest impact on cell wall integrity, but the highest in terms of cell separation. Steaming showed an intermediate behavior. Tissue of the <i>Depurple</i> cauliflower was the most resistant to the heat, irrespectively to the heating technology. Local heterogeneity in the cell wall and cell membrane, expected as a plant variety-dependent functional property, was proposed as a possible explanation because sterol extractability under lower heat-transfer efficiency, i.e., steaming and <i>sous-vide</i>, decreased in <i>Depurple</i> and increased in <i>Cheddar</i> as well as because the extractability of sterols and tocopherols was greater in <i>Cheddar</i>.