In this study, the effect of different isolation techniques on the isolated proteins from pigeon pea was investigated. Water, methanol, ammonium sulfate, and acetone were used for the precipitation of proteins from pigeon pea. Proximate composition, and antinutritional and functional properties of the pigeon pea flour and the isolated proteins were measured. Data generated were statistically analyzed. The proximate composition of the water‐extracted protein isolate was moisture 8.30%, protein 91.83%, fat 0.25%, ash 0.05%, and crude fiber 0.05%. The methanol‐extracted protein isolate composition was moisture 7.87%, protein 91.83%, fat 0.17%, and ash 0.13%, while crude fiber and carbohydrates were not detected. The composition of the ammonium sulfate‐extracted protein isolate was moisture 7.73%, protein 91.73%, fat 0.36, ash 0.13%, and crude fiber 0.67%. The acetone‐extracted protein isolate composition was moisture 8.03%, protein 91.50%, ash 0.67%, and fat 0.30%, but crude fiber and carbohydrates were not detected. The isolate precipitated with ammonium sulfate displayed the highest foaming capacity (37.63%) and foaming stability (55.75%). Isolates precipitated with methanol and acetone had the highest water absorption capacity (160%). Pigeon pea protein isolates extracted with methanol and ammonium sulfate had the highest oil absorption capacity of 145%. Protein isolates recovered through acetone and methanol had the highest emulsifying capacity of 2.23% and emulsifying stability of 91.47%, respectively. The proximate composition of the recovered protein isolates were of high purity. This shows the efficiency of the extraction techniques. The isolates had desirable solubility index. All the isolation techniques brought significant impact on the characteristics of the isolated pigeon pea protein.
This study examined how application of ultrasound pretreatment (UP) (400 W, 20 kHz for 5, 10 min) influenced the structural characteristics, molecular weight distribution, amino acid composition and biological activity of hydrolysate prepared from lupin protein using protamex enzyme. Circular dichroism (CD) and Fourier transform infrared (FTIR) techniques revealed changes in secondary structure after UP, while changes in molecular weight pattern were revealed by SDS-PAGE and MALDI-TOF analyses. Also, the crystallinity and surface hydrophobicity of the hydrolysates were affected by UP. The amino acid compositions of the hydrolysate varied, especially glutamic acid, arginine and aspartic acid. In vitro biological assays showed that antioxidant, α-glucosidase, α-amylase and ACE inhibitory activities significantly improved in sonicated hydrolysates compared with non-sonicated samples, and this may be linked to the structural modifications caused by UP. Hence, the application of UP to lupin protein could en hance the biological activity of its hydrolysate.
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