Protein extraction from oat: Isoelectric precipitation and water-based extraction
Sandie Ha, Wouter J.C. de Bruijn, Gijs J.C. Vreeke, Marieke E. Bruins, Maaike Nieuwland, Atze Jan van der Goot, Julia K. Keppler
Abstract
• Water-based extraction yields similar proteins as isoelectric precipitation. • Water-based extraction of oat protein limits off-colour formation. • Isoelectric precipitation has a higher yield than water-based extraction. • A nitrogen-to-protein conversion factor of 5.12 was established for oat protein. • Extracted oat protein consisted of approximately 60 % globulins and 40 % prolamins. Protein extraction by alkaline extraction-isoelectric precipitation (AE-IEP) uses alkaline conditions that contribute to off-colour formation, through auto-oxidation of inherent phenolic compounds. We aimed to develop an alternative protein extraction process yielding comparable protein content to AE-IEP while avoiding alkaline conditions. It was hypothesised that a water-based extraction (WBE) of oats would yield lightly coloured native proteins. Protein contents and yields were determined using a newly established nitrogen-to-protein conversion factor of 5.12, based on the amino acid composition. WBE led to a comparable protein content to AE-IEP (69.5 % vs 70.1 % dry matter (DM)), but a 2.5 times lower yield (0.27 g/g protein DM). SDS-PAGE and quantitative proteomics revealed a protein composition of 60 % globulins and 40 % prolamins in both concentrates. A similar protein nativity was observed using differential scanning calorimetry. The WBE yielded in a lighter-coloured protein powder. The low protein yield of water-based extraction is currently a limitation for industrial applications. Nevertheless, this simple process can be used as a pre-treatment for AE-IEP to produce a more neutral-coloured powder. This study expands the knowledge on protein extraction from oats by comparing novel extraction methods with classic AE-IEP and establishing the nitrogen-to-protein conversion factor for oats.