Effect of cultivar and environment on the physicochemical and functional properties of pea protein isolates
The overarching goal of this research was to investigate the effect of cultivar and environment on the physicochemical and functional properties of pea protein isolates using a structure-function approach. Six pea cultivars (Agassiz, CDC Golden, CDC Dakota, CDC Striker, CDC Tetris, Cooper) were collected from two years (2011, 2012) over two locations in Saskatchewan (Saskatoon and Rosthern) from two field replicates. Pea protein isolates were prepared from defatted flours by alkaline extraction (pH 9.0) followed by isoelectric precipitation (pH 4.5), and then neutralized to pH 7.0 prior to freeze-drying. Samples were evaluated for composition (amino acid profile, legumin/vicilin ratio), surface characteristics (zeta potential, surface hydrophobicity), and functional properties (nitrogen solubility, oil holding capacity, foaming capacity, foam stability, emulsion stability). In addition, samples were assessed for seed weight and colour, and compared against the functional characteristics of six commercially produced protein isolates (whey, wheat, egg, pea, and two soy ingredients). The extracted pea protein isolates had protein contents of ~91% (d.b.), as well as isolate and protein yields of ~18% and ~72%, respectively. Although cultivars exhibited a range of legumin/vicilin ratios from 0.36 (Agassiz) to 0.79 (CDC Golden), such differences were not reflected in their amino acid profiles. Differences amongst cultivars, as well as significant cultivar × environment interactions, were found for only surface hydrophobicity (195-267 a.u.), solubility (63-75%), and foaming capacity (167-244%). No differences in either cultivar or environment were observed in other surface (zeta potential = ~-24 mV) or functional (oil holding capacity = ~3.2 g/g; foam stability = ~75%; emulsion stability = ~96%) properties. All functional properties were significantly correlated with legumin/vicilin ratio and/or surface hydrophobicity. However, such relationships were weak (r = -0.19 to -0.20, and r = 0.17 to 0.32). The strongest correlation was observed between the legumin/vicilin ratio and surface hydrophobicity at r = 0.63 for the pea protein isolates. Meanwhile, zeta potential did not display a significant correlation to any property tested. In comparison to commercial protein isolates, the pea protein isolates behaved most similarly to soy except for solubility. Whey and egg were superior in solubility and the foaming properties, whereas wheat and the commercial pea protein product underperformed in almost all functionality tests. These findings suggest that while inherent protein material source may be important to functional behaviours, the method of extraction could pose even greater effects. This was observed between the laboratory- and commercially-prepared pea protein isolates, which at minimum differed in processing (defatting) and method of drying (freeze- vs. spray-dried). Coupled with the weak correlations between physicochemical and functional properties, findings overall indicate that method of protein isolate production play a more significant role in protein functional characteristics than cultivar, environment, or composition. Findings also suggest that secondary processors may not need to specify either cultivar or environment of their raw materials, thus creating advantages in their feedstock sourcing.
DegreeMaster of Science (M.Sc.)
DepartmentFood and Bioproduct Sciences
SupervisorNickerson, Michael T.; Tyler, Robert T.
CommitteeWarkentin, Thomas D.; Tulbek, Mehmet C.; Qiu, Xiao
Copyright DateDecember 2015