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Effect of pH and ionic strength on the heat stability of rapeseed 12S globulin (Cruciferin) by the ANS fluorescence method

Folawiyo, Y.L., Owusu Apenten, R.K.
Journal of the science of food and agriculture 1996 v.70 no.2 pp. 241-246
rapeseed oil, heat stability, pH, ionic strength, heat treatment, acid treatment, hydrophobicity, fluorescence, globulins, temperature, inactivation
The heat stability of rapeseed 12S globulin (cruciferin) was examined using 8-anilinonaphthalene-1-sulphonic acid (ANS) as a fluorescence probe. Heating cruciferin (0.06-0.3 mg ml-1 in 10 mM glycyl-glycyl piperizine buffer, pH 7.0, with 0.1-1.0 M NaCl) for 20 min increased its hydrophobicity as monitored by ANS fluorescence measurements. The mid-point temperature for the heat effect (Tm) increased linearly with increasing solvent pH (Tm (degree C) = 4.16 pH + 41 (micro = 0.1)) or sodium chloride concentration (Tm (degree C) = 14.7 [NaCl] + 71 (pH = 7.0)). The range of Tm values for cruciferin was 45-96 degrees C. At 20 degrees C cruciferin was unstable at pH < 3.0 but relatively stable under alkaline conditions (pH 8-10). Though possessing an oligomeric structure, cruciferin appears to heat denature in accordance with the two-stage deactivation model for simple globular proteins.