Effects of acetylation and succinylation on the physicochemical and functional properties of the canola 12S globulin
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The canola 12S globulin was isolated by the protein micellar mass (PMM) procedure and acylated through acetylation and succinylation in order to obtain a canola protein concentrate with optimal functional properties and low levels of antinutritional factors. Changes in molecular weight were determined by gradient PAGE. Alterations in protein conformation were examined by differential scanning calorimety (DSC), UV/vis and fluorescence spectoscopy. The isoelectric points of the PMM and acylated concentrates were established by isoelectric focusing. In addition, changes in surface hydrophobicity, amino acid profile and levels of antunutritional factors were also monitored. Several functional properties of the PMM and acylated concentrates, specifically protein solubility, foaming and emulsifying properties, fat and water absorption, colour and gelation were also studied. Acylation was found to cause dissociation of the protein structure, which was evidenced by a decrease in molecular weight and enthalpy of denaturation with increasing modification. The isoelectric points of the acylated concentrates differed from the value of 7.1 observed in the PMM with ranges of 4.9-6.1 for rhe acylated concentrates, and 4.6-5.5 for the succinylated concentrates. Extensive changes in protein conformation were also indicated by alterations in the UV/vis and fluorescence spectra, as well as changes in surface hydrophobicity. Generally, these structural changes were more pronounced in the succinylated concentrates as compared to the acetylated concentrates. There was a slight decrease in lysine following acylation and proline following succinylation, but otherwise the amino acid profile remained unchanged. Both acetylation and succinylation resulted in an overall decrease in the levels of phytic acid and glucosinolates. Acetylation also caused a decrease in the phenolics content. The solubility profile of the acylated concentrates differed from that of the PMM in that solubility below the isoelectric point was impaired, but solubility at neutral and alkaline pH values was greatly enhanced. Foaming and emulsifying capacities were significantly increased by acylation. Form stability declined upon acylation. Emulsion stability increased initially, then decreased at the highest levels of modification. Following acylation, the water holding capacity was reduced dramatically, but the fat absorption capacity was elevated. Gelling properties of canola proteins were also improved by acylation. Furthermore, the acylated concentrates were significantly lighter in colour than the original PMM. Overall, the acylated concentrates possessed improved functionality and lower levels of antinutritional factors as compared to the PMM, making them more suitable as a food or cosmetic ingredient.