Understanding the impact of proteolysis on extractability, physicochemical, and functional properties of proteins and lipids from almond flour

Abstract

The extraction of lipids and proteins from food matrices has been challenged by the use of several sequential unit operations and the frequent use of hazardous and flammable solvents to produce defatted flours for subsequent protein extraction. The effects of aqueous (AEP) and enzymatic extraction (EAEP) on the simultaneous extraction of lipids and proteins from full-fat almond flour, insoluble microstructure, oil recovery from the oil-rich emulsion, and physicochemical and functional properties of the extracted protein were evaluated. Except for the use of 0.5% of protease in the EAEP, extraction parameters were similar for both processes (pH 9.0, 50 ºC, 1:10 solids-to-liquid ratio, and 60 min). Enzymatic extraction significantly improved the oil (from 62 to 67%) and protein (from 67 to 77%) extractability while generating smaller protein fragments and creating a more porous insoluble structure. EAEP followed by enzymatic destabilization of the oil-rich emulsion increased the degree of hydrolysis of the emulsion proteins from 8 to 22% while reducing its hydrophobicity from 1205 to 688, resulting in 93% oil recovery. EAEP also resulted in the production of protein extracts with higher protein content, a more unordered protein secondary structure with reduced surface hydrophobicity, and reduced thermostability. Importantly, proteolysis significantly enhanced the functionality of the hydrolysates at pH values close to the almond protein isoelectric point. At pH 5.0, the hydrolysates had higher solubility (47 vs 23%), emulsification capacity (492 vs 402 g oil/ g protein), emulsification activity index (35 vs 17 m2 40 /g), and foaming capacity (23 vs 41 11%) compared with unhydrolyzed proteins. These results highlight the effectiveness of this flammable solvent-free extraction approach to maximize lipid and protein extractability from almond flour with concurrent improvement in oil recovery and protein functionality, creating new opportunities for their application as food ingredients.