Heat‐induced gelation of rapeseed proteins: Effect of protein interaction and acetylation

Abstract

The gel-forming abilities of a rapeseed protein isolate, composed of 70% globulin (cruciferin) and 30% albumin (napin), and their individual protein components, were investigated. The influence of acetylation upon the gelation properties was also studied. Highest gel strength (measured as shear modulus) of the isolate was obtained at pH values around 9, which is between the isoelectric points of both major proteins. Purified cruciferin gave the highest shear modulus values, with maxima at pH 6 and 8. Weak and poorly stable gels exhibiting strong hysteresis were obtained with isolated napin. Acetylation resulted in a pH shift of the shear modulus maximum of the protein isolate to about 6. The gelation temperature of the acetylated isolate had the highest pH and concentration dependence compared with the other proteins. JAOCS 75, 83-87 (1998).The ability to form gels is a key functional property in utilizing plant proteins. The gel-forming properties of proteins from soybeans and other legume and oilseed crops have been extensively studied (1-7).Gill and Tung (8) first demonstrated the ability of a highly glycosylated 12S rapeseed protein to form gels on heating at pH > 4. The strongest gels were formed at high pH and ionic strength. The high level of carbohydrate (12.9%) led the authors to assume protein-carbohydrate interaction during gel formation. Thompson et al. (9) observed increased viscosity of a hexametaphosphate-extracted rapeseed protein isolate on heating to 80˚C but did not obtain a gel. Paulson and Tung (10) studied thermally induced gelation of a rapeseed (canola) protein isolate on heating to 72°C. Gels formed only at high pH (>9.5).Léger and Arntfield (11) studied gelation of 12S canola globulin. Gels prepared with 6% protein under alkaline conditions were superior to gels prepared from acidic solutions. The effects of pH, salts, and denaturing and reducing agents on gelation properties led the authors to conclude that hydrophobic forces and electrostatic interactions were responsible for establishing the gel network, while gel stabilization and strengthening were attributed to disulfide bonding, electrostatic interactions, and hydrogen bonding.Succinylation has been used to improve the gel-forming properties of a canola protein isolate by Paulson and Tung (10). In this way, the pH range of gel formation was extended from the alkaline region (pH > 9.5) to 5.0.Comparison of the gel-forming properties of the different rapeseed protein preparations is difficult owing to differences in protein composition and purity. Moreover, data on the protein composition of the isolates studied are scanty.The present paper deals with the influence of the major protein components of rapeseed protein isolate [12S globulin "cruciferin" and 2S protein "napin" (12)] and of acetylation on the gel-forming properties of the isolate. The pH and concentration dependencies on the gelation temperature and the shear modulus of purified cruciferin and napin as well as nonmodified and acetylated isolates containing both proteins...

Comparison of biological value and technological properties of oil seed proteins

“…It could be resulted by presence of polypeptides with higher molecular weight in soy protein isolates, which abounded by polypeptides with molecular weight from 30 to 76 kDa [42], whereas sunflower protein isolates − by polypeptides with molecular weight from 20 to 45 kDa [34,43,44] and rape protein isolates − by polypeptides with molecular weight 12-50 kDa [45]. Similar values of soy proteins isolate solubility were obtained by Molina Ortiz and Cristina An [46].…”

Canola/rapeseed protein-functionality and nutrition

“…The maximum gelation temperature of cruciferin and napin depends on the concentration and pH (Schwenke et al, 1998). Increase in protein concentration resulted in earlier onset of gelation of cruciferin (72…”

“…• C at pH 10 and formed a gel network that showed extreme synerisis (Schwenke et al, 1998). Napin is resistant to form a gel network between pH 4 and 8 (Folawiyo and Apenten, 1997).…”

“…Canola protein products that contain both cruciferin and napin form heat-induced gels, especially the gels formed at alkaline pH were more stable (Kim et al, 2016;Léger and Arntfield, 1993;Schwenke et al, 1998;Tan et al, 2014b). A range of temperatures has been observed for maximum gelation temperature of mixed canola albumin and globulin containing protein products; 69…”

“…• C for 70% globulins and 30% albumins (15% w/v protein slurry) at pH 9.0 (Schwenke et al, 1998), 88…”