Abstract
Due to the poor thermal stability of egg white protein (EWP), important challenges remain regarding preparation of nanoparticles for EWP above the denaturation temperature at neutral conditions. In this study, nanoparticles were fabricated from conjugates of EWP and isomalto-oligosaccharide (IMO) after heating at 90 °C for 30 min. Meanwhile, the effects of protein concentration, temperature, pH, ionic strength and degree of glycation (DG) on the formation of nanoparticles from IMO-EWP were investigated. To further reveal the formation mechanism of the nanoparticles, structures, thermal denaturation properties and surface properties were compared between EWP and IMO-EWP conjugates. Furthermore, the emulsifying activity index (EAI) and the emulsifying stability index (ESI) of nanoparticles were determined. The results indicated that glycation enhanced thermal stability and net surface charge of EWP due to changes in the EWP structure. The thermal aggregation of EWP was inhibited significantly by glycation, and enhanced with a higher degree of glycation. Meanwhile, the nanoparticles (<200 nm in size) were obtained at pH 3.0, 7.0 and 9.0 in the presence of NaCl. The increased thermal stability and surface net negative charge after glycation contributed to the inhibition. The EAI and ESI of nanoparticles were increased nearly 3-fold and 2-fold respectively, as compared to unheated EWP.
Highlights
Egg white protein (EWP) is an important ingredient in food processing, because of its abundant nutritive value and various functional properties
The bands of LZ, OVA and OT shifted to higher MW, and a large number of continuous bands appeared on the top of the conjugate electrophoretic patterns, indicating the formation of protein polymers in glycated EWP
The MW (Figure 1a) and saccharide moieties (Figure 1b) of LZ, OVA and OT gradually increased with the increase of degree of glycation (DG), which further confirmed the formation of conjugates (Table 1)
Summary
Egg white protein (EWP) is an important ingredient in food processing, because of its abundant nutritive value and various functional properties. The main components of EWP are ovalbumin (OVA, 54%), ovotransferrin (OT, 12%), ovomucoid (OM, 11%) and lysozyme (LY, 3.4%) [1] These proteins mainly show a globular structure. It was reported that heat-induced nanoparticles formed from globular proteins could increase their emulsifying capacity and binding ability to hydrophobic bioactive compounds [2,3,4]. Attempts in fabrication of EWP nanoparticles by heat treatment under extremely acidic [7] or alkaline conditions [8] have been successful. This proves that the heat-induced EWP nanoparticles exhibit excellent potential to be a type of delivery system for hydrophobic compounds. The stable heat-induced nanoparticle prepared by commercial EWP at neutral condition was not reported
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