Alkaline Extraction-Synchronous Ultrafiltration: A Green and Efficient Strategy for Preparing Oilseed Protein Isolate

Oilseed meals, which are produced from oilseed oil extraction, are a vital source of high-quality plant protein. Herein, an alkaline extraction-synchronous ultrafiltration method was established for efficient preparation of protein isolate from the meals of rapeseed, flaxseed, and walnut. The results showed that the purity of protein isolates obtained from the three oilseed meals all exceeded 81%, particularly flaxseed protein isolate (> 95%). The protein isolates from walnut meal and flaxseed meal achieved recovery rates of 52% and 68%, respectively. Notably, the proposed protein extracted method could co-enrich multiple oilseed protein fractions, including albumin, globulin, and glutelin. The three obtained protein isolates exhibited excellent functional properties, probably because pH deviation from the isoelectric point of the three proteins throughout ultrafiltration purification process could effectively suppress aggregation of the concentrated protein solution. The foaming capacities of the three protein isolates (1%, w/v) reached 309%, 375%, and 374% at pH 3.0, respectively. Notably, about 2% (w/v) rapeseed protein isolate and 4% (w/v) flaxseed protein isolate could form gels at pH 7.0. The established multi-protein fraction simultaneous preparation method offers an efficient and alternative strategy for the industrial-scale production of functionalizing plant protein isolates. PRACTICAL APPLICATIONS: Ultrafiltration can substitute acidic precipitation to enrich oilseed proteins. The three obtained oilseed proteins all reach the purity of protein isolate (≥ 80%). The obtained oilseed proteins have excellent foaming performance at pH 3.0. Rapeseed protein isolate at pH 7.0 can form gels at a low concentration (2%, w/v).