Gelatin Hydrolysate Hybrid Nanoparticles as Soft Edible Pickering Stabilizers for Oil-In-Water Emulsions

Abstract

The aim of this study was to fabricate edible gelatin enzymic digest (GED) based gel particles that can stabilize oil-in-water (O/W) microemulsions. The gel particles were generated by covalent crosslinking, with genipin, the individual protein molecules within tannic acid-induced gelatin hydrolysate (GED-TA) particles. The ability of the genipin-treated GED-TA (GP-GED-TA) to stabilize emulsions was evaluated by Turbiscan analysis and droplet-size changes. For comparison, gelatin hydrolysate (GE) and tannic acid-induced gelatin hydrolysate particles (GED-TA) were used as controls. The mean diameters of GED, GED-TA, and GP-GED-TA particles were 0.68 ± 0.1 nm, 66.2 ± 8.4 nm, and 66.9 ± 7.2 nm, respectively. Nanomechanic analysis using atomic force microscopy(AFM) indicated the average Young's modulu of the GP-GED-TA particles was 760.8 ± 112.0 Mpa, indicating the GP-GED-TA were soft particles. The Turbiscan stability indexes (lower values indicate a more stable emulsion) of the emulsions stabilized with GED, GED-TA, and GP-GED-TA, after storage for three days, were 28.6 ± 1.5, 19.3 ± 4.8, and 4.4 ± 1.3, respectively. After one, or 60 days of storage, the volume-weighted mean diameters (D_[4,3]) of oil droplets stabilized by GP-GED-TA were 1.19 ± 0.11 μm and 1.18 ± 0.1 µm, respectively. The D_[4,3] of oil droplets stabilized by GED-TA, however, increased from 108.3 ± 5.1 μm to 164.3 ± 19.1 μm during the storage. Overall, the GP-GED-TA gel particles have considerable potential for stabilization of O/W emulsions in food products.

Keywords: edible pickering stabilizer; emulsifying property; gelatin hydrolysate hybrid; soft gel particles.

Figure 1

Schematic diagram of the preparation of genipin-treated tannic acid-induced gelatin hydrolysate (GP-GED-TA) gel particles.

Figure 2

Size distribution curves, from zeta potential measurements, of particles in 8 mol L⁻¹ urea solutions (A) or in water (B).

Figure 3

Transmission electron microscopy (TEM) images of GP-GED-TA particles. The scale bar is 100 nm.

Figure 4

Distribution of the Young’s modulus of GP-GED-TA particles in Derjaguin-Müller-Toporov (DMT) modulus channels.

Figure 5

Changes in the backscattering intensity (BS) profiles of oil-in-water (O/W) emulsions generated by gelatin enzymic digest (GED) (A), tannic acid-induced gelatin hydrolysate (GED-TA) (B), and GP-GED-TA (C). The inserted photographs were taken 3 days after preparation of fresh emulsions.

Figure 6

Global turbiscan stability index (TSI) of O/W emulsions generated by different stabilizing agents.

Figure 7

Shear-rate dependence of viscosity (A) and shear stress (B) for emulsions prepared with GED-TA or GP-GED-TA.

Figure 8

The size distribution curves of oil droplets stabilized by GP-GED-TA and GED-TA.