Abstract
The effect of (−)-epigallocatechin-3-gallate (EGCG) on protein structure and emulsion properties of glycosylated black bean protein isolate (BBPI-G) were studied and compared to native black bean protein isolate (BBPI). The binding affinity of BBPI and BBPI-G with EGCG belonged to non-covalent interaction, which was determined by fluorescence quenching. EGCG attachment caused more disordered protein conformation, leading to a higher emulsification property. Among the different EGCG concentrations (0.10, 0.25, 0.50 mg/mL), the result revealed that the highest level of the emulsification property was obtained with 0.25 mg/mL EGCG. Therefore, the BBPI-EGCG and BBPI-G-EGCG prepared by 0.25 mg/mL EGCG were selected to fabricate oil-in-water (O/W) emulsions. After the addition of EGCG, the mean particle size of emulsions decreased with the increasing absolute value of zeta-potential, and more compact interfacial film was formed due to the higher percentage of interfacial protein adsorption (AP%). Meanwhile, EGCG also significantly reduced the lipid oxidation of emulsions.
Highlights
The native protein has been widely used as an emulsifier to prepare O/W emulsions on account of good surface activity [1]
black bean protein isolate (BBPI) was grafted with glucose-forming BBPI-G conjugates, which could be confirmed by the high molecular weight bands which appeared on the top of the stacking gel. This result indicated that the amino group of BBPI formed a covalent bond with the carbonyl group of glucose and a new covalent complex was formed by Maillard reaction [24]
EGCG interacted with BBPI or BBPI-G through non-covalent interaction
Summary
The native protein has been widely used as an emulsifier to prepare O/W emulsions on account of good surface activity [1]. In order to enhance the physical stability and oxidation stability of emulsion, modification of native proteins was often carried out to inhibit the flocculation, fat floating and lipid oxidation [2]. The protein–polysaccharide complex can effectively promote the protein to adsorb to the oil–water interface more firmly through the hydrophilic groups of polysaccharides and improve the emulsion stability [3]. Yang et al [4] obtained the conjugates via the Maillard reaction between soybean protein isolate and the soybean-soluble polysaccharide, which showed higher physical stability of O/W emulsion-containing citrate. EGCG has Polymers 2019, 11, 1688; doi:10.3390/polym11101688 www.mdpi.com/journal/polymers
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