Grass Pea (Lathyrus sativus L.) Protein Isolate: The Effect of Extraction Optimization and Drying Methods on the Structure and Functional Properties

- Extraction of grass pea protein was successfully optimized based on protein content and extraction yield.
- Foaming properties, emulsion capacity and lightness of optimized grass pea protein isolates (OGPPIs) were different.
- Vacuum oven and freeze drying methods had considerable effect on the protein structure, thermal stability and function of OGPPIs.
- Glutamic acid and aspartic acid were the main amino acids of all samples confirming their acidic isoelectric pH (4.5-5).
- FTIR analysis successfully confirmed different amide regions in all protein isolate samples.

This research focused on the effect of extraction pH (2.5-10), time (20-80 min) and water: flour ratio (WFR) (5:1-30:1 v/w) on extractability and characterizations of grass pea seed (Lathyrus sativus L.) protein. Protein extraction optimization was successfully performed based on protein content and extraction yield using response surface methodology (RSM). The highest protein extractability (92.5%) was found at acidic condition (pH 2.57), 48 min extraction time and WFR of 10 (v/w). The most extraction yield was occurred at alkaline condition (pH 9.96), higher WFR (15 v/w) and longer extraction time (58 min). Besides, high protein content and acidic medium resulted in significantly (p < 0.05) lighter color (L* value of 53) and better foam stability (100%), while optimized grass pea protein isolate based on extraction yield showed higher foam and emulsifying capacities (87% and 87.5%, respectively). There was no significant difference (p < 0.05) between other functional properties of two optimized grass pea protein isolates (OGPPIs). Further investigations were conducted using two different drying methods including freeze drying and vacuum oven drying. The amino acid content, protein solubility, thermal and color properties, FTIR analysis, surface hydrophobicity and SDS- PAGE pattern demonstrated that the OGPPIs resulted from different media and procedures were considerably different. The presence of more ordered structures including α-helix and β-turn in vacuum oven dried grass pea protein isolate powders was in accordance with their higher denaturation temperature in comparison with freeze dried samples.

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