Abstract
Extensive purification of plant proteins is probably not a prerequisite for their emulsifying properties, however, details of the interfacial stabilization mechanism of less purified protein extracts are not sufficiently known. Phenolic compounds present in less purified plant protein extracts can interact with proteins, inducing protein aggregation, impeding their interfacial properties. Here, we show that when a rapeseed protein mixture (RPM) containing 40 wt% proteins and 6 wt% sinapic acid is used to form oil-in-water emulsions (10.0 wt% oil) at pH 3.8 and at different protein concentrations (0.2–1.5 wt%), emulsion droplets of 2.0–0.6 μm are formed and large protein aggregates are randomly attached to the droplet interface. By reducing the sinapic acid content to 2.5 wt% to produce a rapeseed protein concentrate (RPC) (65 wt% proteins), smaller emulsion droplets are formed (0.4–0.5 μm) at the same protein concentrations, and no large proteins aggregates are present at the droplet interface. According to our findings, in both RPM- and RPC-stabilized emulsions, napins primarily adsorb at the interface, while cruciferins form a secondary layer which protects the droplets against coalescence during homogenization. However, in RPM, the higher sinapic acid content possibly induces aggregation of cruciferins, which hinders the formation of a sufficient secondary layer. As a result, during homogenization, the colliding droplets coalesce, resulting in emulsions with larger droplets. Our findings show that sinapic acid affects the emulsification mechanism of rapeseed proteins at acidic pH, and recommend that plant protein purification might be necessary for the application of plant proteins in emulsion food products.
Highlights
The effect of protein purification on the functionality of plant pro teins is currently a topic of intense research in food science, both in academia and in industry
The two rapeseed protein extracts with a different degree of protein purity were extracted using a previously developed protocol (Ntone et al, 2020); The rapeseed protein mixture (RPM) -recovered as a serum after centrifugation, composed of 39.4 ± 0.4 wt% proteins
As the higher sinapic acid content in RPM did not affect the ability of napins to adsorb at the interface at pH 3.8, we suggest that the larger oil droplets in RPM-stabilized emulsions emerge from the impact of the higher sinapic acid content on the secondary layer formed by crucifer ins
Summary
The effect of protein purification on the functionality of plant pro teins is currently a topic of intense research in food science, both in academia and in industry. Several studies using various plant protein sources (Fuhrmeister & Meuser, 2003; Geerts, Nikiforidis, van der Goot, & van der Padt, 2017; Karefyllakis, Octaviana, van der Goot, & Nikiforidis, 2019; Kornet et al, 2021; Ntone et al, 2021; Peng, Kersten, Kyriakopoulou, & van der Goot, 2020; Sridharan, Meinders, Bitter, & Nikiforidis, 2020a; (Yang, Faber, et al, 2021)) have shown that exten sive purification of plant proteins is not a prerequisite for functionality, such as interfacial and emulsifying properties. Under these pH conditions, the free sinapic acid present in the protein extracts does not impact the inter facial properties of the proteins (Ntone et al, 2021; J.; Yang et al, 2021)
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