Plant protein flour microgels: new generation Pickering stabilisers for oil-in-water emulsions

We present a novel plant-based particle i.e. lentil flour-based microgels (LFBMs) to serve as effective Pickering stabilisers for oil-in-water emulsions. The LFBMs were successfully synthesised using a top-down approach, employing a thermal treatment to form an initial flour-based gel, that was broken down to microscopic gel particles using high pressure homogenisation. Dynamic light scattering of the LFBM revealed a monodisperse distribution of microgels with an average particle size of ∼175 nm. The LFBM markedly lowered the interfacial tension of the n-tetradecane-buffer interface at pH 7.0, where LFBMs outperformed traditional plant protein isolate emulsifiers, reducing the interfacial tension to ∼17 mN m⁻¹ compared to ∼19 mN m⁻¹. The LFBM-stabilised oil-in-water (O/W) emulsions prepared using varying n-tetradecane concentrations (10–30 % v/v) displayed limited changes in droplet sizes over a period of 28 days, with the average droplet d32 on day 1 being 12.5 ± 1.8 μm and the average d32 on day 28 being 10.3 ± 1.7 μm. Investigation via confocal laser scanning microscopy confirmed the formation of microgel-laden films at the droplet surface, protecting the droplets from coalescence. Cryogenic scanning electron microscopy was also performed using high pressure freezing (HPF) and plasma focused ion beam (pFIB) milling techniques, this being the first instance that HPF has been used to image microgel-stabilised emulsions. These images confirmed the attachment of LFBM particles to the droplet surfaces, substantiating that the LFBMs stabilise the emulsions via a Pickering-type mechanism. The ability to form stable emulsions at a range of oil concentrations using LFBMs is a significant development in the field, which may allow for use of less refined and sustainable ingredients in the formation of various food emulsions in the future.