The effect of heat- and acid-treatment on the structure of rapeseed albumin (napin)

The effect of heat and/or acid treatment on rapeseed albumin (napin) structure was monitored, using the hydrophobic fluorescence probe anilinonapthalene-8-sulfonate (ANS), at 20–90 °C and pH 1–10. Heat-treatment of napin at T > 40 °C (20 min) led to an increase in the protein surface hydrophobicity. The mid-point temperature for the irreversible heat-modification of napin at pH 7 (Tm) was 60–67 °C depending on NaCl concentration. The Tm value for napin was independent of pH over the range pH 4–8. At pH≤4.0, napin undergoes an acid-induced structural modification leading to a greater change in the apparent surface hydrophobicity compared to the effect of heating alone. These results are discussed in terms of the effect of solvent pH and temperature on the heat-resistance and heat-stability of napin.