Influence of Particle Size, Extraction Solvent and pH on the Protein Recovery from Defatted Kusum (Schleichera oleosa (Lour.) Oken) Seed Cake

This study evaluated the influence of three key extraction parameters, particle size, solvent type and precipitation pH, on protein recovery to identify optimal extraction conditions. Two particle size classes (<0.5 mm and 0.5-1.0 mm) and three solvent systems, namely distilled water (alkaline adjusted), 0.25 M sodium hydroxide (NaOH) and 0.2 M potassium hydroxide (KOH), were assessed across precipitation pH values ranging from 2 to 5. Protein recovery varied markedly across extraction treatments. The highest yield (26.15%) was recorded when the fine particle fraction (<0.5 mm) was extracted using 0.2 M KOH and precipitated at pH 5, suggesting enhanced solubility and precipitation behavior under alkaline-assisted extraction near the protein’s isoelectric point. In contrast, the lowest protein yield (15.66%) occurred in the coarse particle fraction (0.5-1.0 mm) extracted using distilled water and precipitated at pH 2, demonstrating limited solubilization under non-alkaline conditions. Across all solvent systems, the finer particle fraction consistently produced higher yields than the coarser fraction, reflecting improved solvent accessibility and reduced mass transfer resistance. Alkaline solvents (NaOH and KOH) outperformed distilled water, confirming the critical role of pH-induced protein ionization and structural disruption in enhancing solubility and extractability. Overall, the results demonstrate that protein recovery from Kusum seed cake is not material-fixed but process-dependent. Optimization of particle size, solvent strength and precipitation pH significantly improves extraction efficiency and supports the potential utilization of Kusum protein in food, feed and bioprocessing applications.