Optimization of enzyme-assisted alkaline extraction of protein isolate from oilcake of dehulled sunflower (Helianthus Annuus L.) seeds.

Abstract

The oilcake left after mechanical sunflower oil extraction contains substantial amounts of proteins, minerals, and vitamins. These bioactive compounds in the oilcake can be made available for food, cosmetics, and pharmaceutical applications by valorizing the oilcake. This study aimed to determine the optimal protein content and extraction yield of protein isolate obtained from enzyme-assisted alkaline extraction of oilcake residue from mechanical oil extraction of dehulled sunflower seeds. This was done by investigating the effect of extraction conditions: particle size (500µm - 1000µm), temperature (30 °C - 60^oC), extraction time (15 - 90 minutes), and pH (7 - 9) during extraction. Dehulled sunflower seeds were subjected to cold pressing in a domestic oil press. The resultant cake was mixed with distilled water, protease enzyme added, and extraction conducted with continuous stirring. The extracted proteins were centrifuged and iso-electrically precipitated (at pH 4.5), then re-centrifuged before being washed thrice with distilled water, pH adjusted to 7 and freeze-dried, in readiness for protein analysis by Kjeldahl method. Optimization by Box-Behnken design yielded a protein content of 73.99±1.23% and an extraction yield of 62.84±0.12%. These optimal responses were obtained at particle size 750µm, temperature 60 °C, time 52.5 minutes and pH 9 for protein content, and particle size 750µm, temperature 45 °C, time 90 minutes and pH 9 for extraction yield. The polynomial regression models obtained had R² values of 0.9778 and 0.9994 for protein content and extraction yield, respectively. These experimental results agreed with the predicted values by analysis of variance, with a high model fitness. The extracted protein isolate was light-coloured compared to the one obtained without enzyme addition, pointing to its suitability in the food industry. However, only the evaluation of its anti-nutritive components and techno-functional properties can confirm its use in food applications.