THE EFFECT OF GENOTYPE AND THE ENVIRONMENT ON THE PHYSICOCHEMICAL AND FUNCTIONAL ATTRIBUTES OF FABA BEAN PROTEIN ISOLATES
Abstract
The overarching goal of this research was to investigate the differences in the physicochemical and functional properties of protein isolates produced from seven different faba bean genotypes (CDC Fatima, Taboar, SSNS-1, FB9-4, FB18-20, Snowbird and CDC Snowdrop) grown at different locations in Canada (Saskatchewan, Alberta and Manitoba) in 2011 and 2012. The protein isolates were prepared by alkaline extraction (pH 9.5) followed by isoelectric precipitation at pH 4.5. The isolates had an average protein content of ~94% and average protein and isolate yields of ~77% and ~25%, respectively. The physicochemical properties assessed in this study included surface charge/zeta potential (ZP), surface hydrophobicity (SH), and surface and interfacial tension (ST and IT). The functional properties tested included foaming capacity (FC) and foam stability (FS), emulsion capacity (EC) and creaming stability (CS), emulsion activity index (EAI) and emulsion stability index (ESI), oil holding capacity (OHC), and protein solubility.
The findings indicated that all physicochemical properties for all isolates were independent of genotype. Overall, an average ZP of + 22.1 mV, SH of 47.2 arbitrary units, and ST and IT of 65.0 mN/m and 10.7 mN/m, respectively, were observed. However, with the exception of ZP considerable differences were observed due to the effect of environment. The ratio of the major globulin protein fractions [legumin:vicilin (L/V)] was found to shift during processing, from 3.8 (range: 3.4-4.6) in the flour to 4.5 (range 4.0-4.9) in the isolates. The L/V ratio for faba bean flour and isolate samples was also found to be independent of genotype. For all genotypes, with the exception of the zero-tannin varieties (Snowbird and CDC Snowdrop), the L/V ratio was affected by the environment.
Similar to the physicochemical properties, all functional attributes were found to be independent of genotype. However, environmental effects were observed for all functional properties with the exception of EAI and ESI. Average values for FC of 162.0%, for FS of 65.0%, for EC of 184.0 g/g, for CS of 94.0%, for OHC of 5.7 g/g, for EAI of 13.0 m2/g, for ESI of 10.7 min and for solubility of 81.0% were reported. Zeta potential was observed to be positively correlated with CS (r = 0.46; p<0.05) and FS (r = 0.54; p<0.01), whereas SH and L/V ratio were not. The L/V ratio in the isolate, however, was correlated positively with SH (r = 0.40; p<0.05) and negatively with ZP (r = -0.39; p<0.05). Moreover, the solubility of faba bean isolates was found to be positively correlated with ZP (r = 0.44; p<0.05) and negatively correlated with both IT (r = -0.38; p<0.05) and OHC (r = -0.38; p<0.05).
The functional properties of some commercial protein isolates (soy, pea, whey, egg and wheat) were evaluated for comparative purposes. The OHC of the faba bean isolate was found to be higher than that of any of the commercial isolates. With the exception of CS (soy and pea) and FC (egg), all of the emulsifying (EC, EAI and ESI) and foaming (FC and FS) properties of the faba bean protein isolates were comparable to those of soy, pea and egg isolates. In contrast, values for most of the other functional properties were greater for faba bean isolates than for the pea and wheat isolates, but lower than for the whey isolate. For example, the solubility of the protein isolates was observed to decrease in the following order: whey (89.0%) = egg (88.1%) > faba bean (81.0%) > soybean (30.5%) > pea (20.1%) > wheat (10.7%).