Purification, characterization, and the micelle response of the 12S canola globulin

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Burgess, Deborah Ann
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Various steps in the PMM procedure applied to canola meal were examined to optimize protein recovery. In the extraction step, solubilization was achieved with 0.5M NaCl. Using chromatographic and electrophoretic techniques, the predominant extracted protein identified was the 12S globulin under all salt conditions; there was no evidence to indicate the presence of dissociated 7S form. The impact of pH, NaCl concentration, protein concentration and dilution on protein conformation as well as the formation and interaction of protein micelles were evaluated using gel filtration chromatography, differential scanning calorimetry (DSC) and light microscopy. Variations in pH from 6 to 9 and salt concentrations between 0.1M and 0.5M resulted in no major conformational changes (similar enthalpies of denaturation) but higher pH values and salt concentrations were associated with increased denaturation temperatures reflecting increased molecular stability. At pH 4, however, the 12S globulin dissociated into its 2-3S. This dissociation inhibited the formation of protein micelles. To efficiently isolate proteins with the micellar mass procedure, it is desirable to produce highly interactive micelles while keeping protein concentration and dilution ratio to a minimum. Such reactions were obtained at pH 6, with NaCl concentrations of 0.3M and 0.5M, protein concentrations as low as 25mg/mL and a dilution ratio of at least 1:10. Higher dilution ratios and protein concentrations resulted in a more intense reaction. Lower NaCl concentrations resulted in precipitation prior to dilution and reduced interactions between micelles upon dilution. Variations in pH also effected the formation of micelle networks. At pH values away from the isoelectric point (e.g. pH 4, 8 and 9), the increased net charge was detrimental to good micelle interaction in addition high dilution ratios further reduced the micelle rating. Near the isoelectric point (pH 7), the tendency for pre-dilution precipitation was enhanced and the micelle response was more dependent on salt concentration. Networks formed at pH 7 tended to be delicate and required higher protein concentrations and dilution factors than at pH 6.