Structural Properties of Cruciferin and Napin of Brassica napus (Canola) Show Distinct Responses to Changes in pH and Temperature

Abstract

The two major storage proteins identified in Brassica napus (canola) were isolated and studied for their molecular composition, structural characteristics and the responses of structural features to the changes in pH and temperature. Cruciferin, a complex of six monomers, has a predominantly β-sheet-containing secondary structure. This protein showed low pH unstable tertiary structure, and distinctly different solubility behaviour with pH when intact in the seed cellular matrix. Cruciferin structure unfolds at pH 3 even at ambient temperature. Temperature-induced structure unfolding was observed above the maximum denaturation temperature of cruciferin. Napin was soluble in a wider pH range than cruciferin and has α-helices dominating secondary structure. Structural features of napin showed less sensitivity to the changes in medium pH and temperature. The surface hydrophobicity (S0) and intrinsic fluorescence of tryptophan residue appear to be good indicators of cruciferin unfolding, however they were not the best to demonstrate structural changes of napin. These two storage proteins of B. napus have distinct molecular characteristics, therefore properties and functionalities they provide are contrasting rather than complementary.

Effect of Dry Heat Temperature and Moist Heat Pressure on Canola Meal for Ruminant Utilisation. Part II: Maillard Reaction Product Formation and Structural Characteristics

“…Native gel electrophoresis affirmed cruciferin solubility reduced with increasing dry heat. Progressive dry heat-induced changes in the structure of cruciferin were similarly reported by Perera et al (2016). Reduced ability to extract protein from MHP meal suggests the formation of irreversible bonds and formation of insoluble high MW protein aggregates in canola meal treated under these conditions.…”

“…The AOF (2004) reported darker meal was beneficial quality for dairy; however, Classen et al (2005) reported early reactions causing colour change negatively impact AA digestibility by poultry and thus are unfavourable for monogastric digestion. (Perera et al, 2016) and aggregation (Davis & Williams 1998). Folawiyo and Apenten (1997) reported heat treatment of rapeseed napin induced irreversible changes in So at 90 o C. At 20 to 120 o C and 140 to 180 o C, MHP meal shifted So from low to high relative to control meal, to suggest at low and moderate processing temperatures MHP induces protein folding events promoting surface hydrophilic conformation; however, at 140 to 180 o C modifications of turning of side-chains outwards, commonly associated with protein unfolding, loss of 2 o and 3 o structure, scrambling of disulphide bonds, and formation of irreversible protein aggregates contribute to increases in protein hydrophobicity (Davis & Williams, 1998).…”

“…In non-reduced conditions, typical storage protein polypeptide bandings were observed for 11S globulin (cruciferin) i.e. trimer (~177), dimer (~118) (Perera et al, 2016), procruciferin subunits (73.5, 76.8), -(26.7, 28.5, 37.1), -(18.3, 21.1, 22.9) (Wanasundara, 2011), and monomer with intact disulfide linkages (41 to 55) (Perera et al, 2016); and 2S albumin (napin) i.e. dimer (27.5) and monomer (14) (Wu & Muir, 2008).…”

Rheological and water holding alterations in mixed gels prepared from whey proteins and rapeseed proteins

“…It should be noted that the DSC results for BLG at 2% w/w WP and for ALA at the range of 2 -8 % w/w WP are not reported because of uncertainties during identification and peak integration at these low concentrations. The thermal transition point of cruciferin was detected at higher temperatures compared to whey proteins in the expected (Kim, Varankovich, & Nickerson, 2016) range of 87 -96 o C. The second protein fraction present in RP, napin, was not detected due to its reportedly high thermo-stability (Perera, McIntosh, & Wanasundara, 2016). The enthalpy of denaturation of BLG and ALA generally did not vary a lot with protein concentration.…”

Monitoring food structure during digestion using small-angle scattering and imaging techniques

“…Cruciferin represents 60% of the total protein content of canola seeds. It is a neutral protein (pI = 7-7.5), made of six sub-units with a high molecular weight around 300 kDa 3 . Each monomer is composed of two polypeptide chains (30 and 20 kDa), linked by a disulfide bond.…”