Formation of Hydrogel Particles by Thermal Treatment of β-Lactoglobulin−Chitosan Complexes

Abstract

Molecular complexes based on proteins and ionic polysaccharides have considerable potential for encapsulation of functional food components, but their widespread utilization is limited because their structure is highly sensitive to pH and ionic strength. We have investigated the possibility of creating stable hydrogel particles by thermal treatment of protein (beta-lactoglobulin) and cationic polysaccharide (chitosan) mixtures. Mixed solutions of beta-lactoglobulin (0.5 wt %) and chitosan (0.1 wt %) were prepared at various pH's (3-8) and were heated (80 degrees C for 20 min). Prior to heating, the biopolymer mixtures formed molecular complexes at pH values where there was an electrostatic attraction between the protein and the polysaccharide: soluble complexes at pH 4.5; complex coacervates at pH 5.0 and 5.5; precipitates at pH>5.5. After heating, relatively small (d approximately 140 nm) and cationic (zeta>+20 mV) hydrogel particles were formed at pH 4.5, but much larger aggregates were formed at pH 5.0 and higher (d>1000 nm). The thermally treated hydrogel particles formed at pH 4.5 maintained their initial particle size when the pH was subsequently adjusted within the range pH 3-5, but they aggregated when the pH was adjusted to >pH 5 because of a reduction in the magnitude of their electrical charge. This study suggests that hydrogel particles can be formed by heating mixed protein-polysaccharide systems under controlled conditions. These hydrogel particles may be useful for encapsulation of functional food components.

Coacervate formation of α-lactalbumin–chitosan and β-lactoglobulin–chitosan complexes

“…1. Hong and McClements (2007b) reported similar results, and concluded that the b-Lg and chitosan formed soluble complexes at pH 4.5 prior to heating, owing to electrostatic attraction between cationic groups on the chitosan, and anionic patches on the b-Lg surface.…”

“…The coacervate exists in equilibrium with a dilute supernatant (Microtek Lab Inc., 2008). Recently, many research articles have been published regarding coacervation between whey proteins and polysaccharides (Cooper, Dubin, Kayitmazer, & Turken, 2005;de Kruif, Weinbreck, & de Vries, 2004;Hong & McClements, 2007a, 2007bSanchez, Mekhloufi, & Renard, 2006;Schmitt, Sanchez, Thomas, & Hardy, 1999;Wang, Lee, Wang, & Huang, 2007). Schmitt et al (1999) previously evaluated the compatibility of b-Lg and acacia gum in aqueous medium as a function of pH values between 3.5 and 5.0, and concluded that as the biopolymer content was increased at pH values of 3.6 and 4.2, the relative solubility of b-Lg increased, probably as the result of the self-suppression of complex coacervation.…”

“…Droplets coated with b-Lg-chitosan exhibited better stability against flocculation than those coated by b-Lg alone at approximately the isoelectric point of the adsorbed proteins (pH 4.5-5.5), which was attributed to increased electrostatic and steric repulsion between the droplets (Hong & McClements, 2007a). Hong and McClements (2007b) suggested previously that hydrogel particles might be formed by the heating of mixed b-Lgchitosan complex systems under controlled conditions, and may prove useful for the encapsulation of functional food components.…”

Biopolymer nanoparticles as potential delivery systems for anthocyanins: Fabrication and properties

“…There has already been a considerable amount of research on the development of this type of biopolymer-based particle. Biopolymer particles have been formed by electrostatic complexation and thermal treatment of -lactoglobulin and chitosan in aqueous solutions (Hong & McClements, 2007), as well as -lactoglobulin and pectin (Jones, Decker, & McClements, 2009;Jones & McClements, 2008). Biopolymer particles formed by electrostatic complexation of proteins and polysaccharides have also been used to encapsulate hydrophobic nutraceuticals.…”

Stability of Biopolymer Particles Formed by Heat Treatment of β-lactoglobulin/Beet Pectin Electrostatic Complexes

“…Recently, it has been shown that biopolymer particles can be formed by heating globular protein-cationic polysaccharide electrostatic complexes above the thermal denaturation temperature of the protein. 14,15 These particles were shown to remain intact when the pH was subsequently adjusted to values where the complexes would be expected to dissociate at ambient temperature. In the present study, we examine the stability of biopolymer particles formed by heating a globular protein (β-lactoglobulin) and an anionic polysaccharide (sugar beet pectin) under conditions where they form an electrostatic complex (pH 5).…”