Improved coalescence and creaming stability of structured oil-in-water emulsions and emulsion gels containing ovalbumin amyloid-like fibrils produced by heat and enzymatic treatments

Abstract

Proteins are well known stabilisers for emulsions, gels and foams. Hereby, the protein (supra)molecular structure may play an important role. In order to investigate that effect, 0.5% unheated (UH), heated (H) and combined heat and trypsin treated (H TT) ovalbumin (OVA) dispersions were evaluated for their capacity to stabilize 20–60% oil-in-water (O/W) emulsions. Such emulsions contained native OVA (UH OVA), amorphous and short fibrillar aggregates (H OVA) or long fibrils and peptides (H TT OVA). The experimental results indicated that emulsions containing UH OVA showed larger droplet sizes than those containing H OVA or H TT OVA and revealed a high extent of oiling-off. Although the emulsions containing H OVA contained smaller oil droplets, still a remarkable amount of oil separated upon centrifugation. In contrast, the H TT OVA stabilized emulsions did not display any oiling-off upon centrifugation, which was suggested to be due to the increased viscosity of the (gelled) H TT OVA dispersions used as continuous phase. Nevertheless, the viscosity of the latter emulsions was negatively affected by breakdown of the fibrillary (gel) structure during emulsification. When 60% O/W emulsions containing 1.6% H OVA were subjected to tryptic treatment only after emulsification, the emulsion gels were significantly stronger than the H TT OVA emulsions. Both emulsion types only showed the onset of creaming after several hours of centrifugation, whereas only the emulsions submitted to the enzymatic treatment after emulsification showed no evidence of coalescence. Overall, the experimental results show that emulsions containing long OVA fibrils, as obtained by trypsin treatment after heating, hold great promise for structured food applications.