Extraction and Evaluation of Functional and Colour Properties of Protein Isolate from Sunflower Seed De-oiled Cake

Abstract

Proteins from sunflower de-oiled cake are considered as a valuable alternative food ingredient, since they are low in anti-nutritional compounds and devoid of toxic substances containing around 30- 40% of protein that can be extracted and used in the development of value added food products. An attempt was made to extract the protein from cold pressed de-oiled cake using common salt solution. Three levels of pH (8-10) and NaCl% (8-10) at a sunflower meal to solvent ratio of 1:10 were selected and evaluated. Extraction was carried out at 30°C for 60 minutes. The extracts were centrifuged at 5000 x g for 30 minutes and then the extracted protein was precipitated at pH 3.5 with 1.0 N HCl, further collected by centrifugation. The extracted sunflower protein isolate was washed with distilled water and adjusted to pH 7.0 using 1.0 N NaOH prior to drying. Protein isolate yield was recorded and the protein content of the isolate was determined by Micro-Kjeldahl method. The resulting sunflower protein isolate exhibited favourable functional characteristics, including water-holding capacity (2.38 g/g), oil-holding capacity (1.49 g/g), emulsion capacity (45.27%), emulsion stability (44.46%), foaming capacity (104%), and foaming stability (53.83%). Particle size analysis indicated that the majority of particles ranged between 250 and 499 μm, and the isolate showed a bulk density of 1.007 g/cm³. Sunflower oil cake extract showed chlorogenic acid content of 2.778 mg/L while SPI extract showed 1.277 mg/L. Among the treated samples, lightness (L*) increased with higher pH, especially at pH 10 with 8 and 9% salt concentration. The result indicated that the colour attributes improved with increasing pH, with the highest lightness (L*) value at pH 10 and 9% salt concentration. These findings demonstrate the potential of sunflower protein isolate as a functional ingredient for incorporation into food systems.