Raw, heated and frozen-thawed apple parenchyma of the 'Golden Delicious' and 'Granny Smith' varieties were subjected to leaching and phenolic compounds were analysed by high performance liquid chromatography (HPLC). Fick's second law was applied for the determination of the apparent diffusivity (D-e) of individual polyphenols. Further information was obtained histochemically by means of toluidine blue O staining and image analysis. No difference in phenolic quantification existed between the biochemical and histochemical approaches. The histochemical analysis revealed cell structure changes and the interaction of procyanidins with the cell wall during the leaching process. The D-e values of the total polyphenols were 0.30 and 0.26 x 10(-9) m(-2) s(-1) for the 'Golden Delicious' and 'Granny Smith' raw apple matrix, respectively. The D-e values (and leaching yields) increased after treatments that degraded the plant tissue matrix. After freeze-thaw, the D-e values became 0.39 and 0.40 x 10(-9) m(2) s(-1), while after heating they were 0.92 and 0.38 x 10(-9) m(2) s(-1). There was also an influence of the phenolic compound nature. (C) 2015 Elsevier Ltd. All rights reserved.