Biorefining of Oilcakes from Peanut Oil Industry: Enhanced Recovery of Proteins and Oil with Improved Protein Technofunctional Properties

The aqueous enzymatic process of producing protein hydrolysates from peanut oil cake is evaluated. Enzymes Alcalase, Neutrase, and Flavourzyme were chosen for the study. Nearly 88.5% of the total protein was extracted by developing a two-tiered extraction process. The optimized processing conditions for the primary extraction were as follows: hydrolysis temperature of 55 °C; pH 8.0 (for Alcalase)/50 °C pH 7.0 (for Neutrase and Flavourzyme); the ratio of raw material/buffer 1:20 (W/V); extraction time, 16 h; enzyme concentration, 2% (v/v). At these conditions, protein extraction for Alcalase was 38.5% ± 3.4, for Neutrase was 39.2% ± 3.2, and for Flavourzyme was 37.4% ± 2.7. The average protein concentrations for Alcalase, Neutrase, and Flavourzyme were 61.7%, 67.5%, 59.2%, respectively. The formation of low molecular weight hydrolysates (0.5-5 kDa) was confirmed by SDS-PAGE, size exclusion chromatography, and MALDI-TOF. The residual protein (∼50%) in the oilcake was extracted in a secondary extraction by employing a mild alkaline enzyme “hybrid” approach at pH 8 and 0.5% enzyme concentration (v/v) and concentrated to 94.3% by ultrafiltration. Moreover, the enzymes used for the second hydrolytic process were recovered and recycled five times, with a ∼10% loss in activity observed post-each-cycle. In vitro digestibility for the hydrolysates was between 94-96%. Excessive hydrolysis however decreased the emulsifying potential, due to the production of smaller peptides. Foaming potential and foam stabilities of hydrolysates were found to be higher than those of unhydrolyzed protein. This research investigates an enzymatic process for the maximal extraction of protein from peanut oilcake for food-based applications, coupled with enzyme and water recovery, with reduced environmental pollution.