Xiaolin Yao

Complexation of Bovine Serum Albumin and Sugar Beet Pectin: Structural Transitions and Phase Diagram

The complexation between bovine serum albumin (BSA) and sugar beet pectin (SBP) was studied in situ by coupling glucono-δ-lactone (GDL) induced acidification with dynamic light scattering and turbidity measurements. Individual measurements at specific pHs and mixing ratios were also carried out using zeta potentiometry, gel permeation chromatography-multiangle laser light scattering (GPC-MALLS), and isothermal titration calorimetry (ITC). These investigations together enabled the establishment of a phase diagram of BSA/SBP and the identification of the molecular events during protein/polysaccharide complexation in relation to the phase diagram, which showed five regions: (I) a stable region of mixed individual soluble polymers, (II) a stable region of intramolecular soluble complexes, (III) a quasi-stable region of intermolecular soluble complexes, (IV) an unstable region of intermolecular insoluble complexes, and (V) a second stable region of mixed individual soluble polymers, on lowering pH. We found for the first time that the complexation could take place well above the critical pH(c), the value that most previous studies had regarded as the onset occurrence of complexation. A model of structural transitions between the regions was proposed. The borderline between region II and region III represents the BSA/SBP stoichiometry for intramolecular soluble complex at a specific pH, while that between region III and region IV identifies the composition of the intermolecular insoluble complex. Also studied was the effect of NaCl and CaCl(2) on the phase diagram and structural transitions.

Physical and chemical stability of gum arabic-stabilized conjugated linoleic acid oil-in-water emulsions.

Oil-in-water (O/W) emulsions have been used as a delivery system to protect conjugated linoleic acid (CLA), a polyunsaturated fatty acid, from oxidation. Conventional gum arabic (GA) and two matured gum arabic samples (EM2 and EM10) were used as emulsifiers to prepare CLA-in-water emulsions. The emulsions have optimal physical and chemical stability at gum concentrations of 5% for all three gums. Emulsions with higher gum concentrations are more susceptible to lipid oxidation. This is attributed to reduced physical stability at higher gum concentrations because of the coalescence and depletion-induced flocculation of the emulsion droplets. The prooxidants iron and copper intrinsically contained in the gums could also contribute to this instability. Among the three gums, EM10 provides the most effective protection for CLA both physically and chemically, because of its superior interfacial properties over GA and EM2.

Whey protein isolate/gum arabic intramolecular soluble complexes improving the physical and oxidative stabilities of conjugated linoleic acid emulsions

Protein/polysaccharide electrostatic complexes have been widely used in food products to confer structure and stability. Intramolecular soluble complexes (ISCs) have superior emulsifying properties in stabilizing oil-in-water (o/w) emulsions. This paper investigates the potential application of ISCs to stabilize polyunsaturated fatty acids that were difficult to disperse and liable to oxidation. The idea was demonstrated using whey protein isolate/gum arabic (WPI/GA) ISCs and conjugated linoleic acid (CLA). Zeta potential measurements indicated a stoichiometry of r = 1.0 for the electrostatic complexation of WPI/GA. Excess of GA (r 20 mM and therefore seriously reduced the stability of ISCs-stabilized CLA emulsions. The superiority of ISCs in stabilizing polyunsaturated fatty acids is due to the cooperative adsorption of protein and polysaccharide at the emulsion interface, providing strong steric and electrostatic effects against droplet aggregation and coalescence and thus excellent physical stability. The improved oxidative stability should arise from the free radical scavenging ability of the protein at the emulsion interface, reducing lipid oxidation.

Protein/Polysaccharide Electrostatic Complexes and Their Applications in Stabilizing Oil-in-Water Emulsions

Consumers are becoming increasingly fastidious in demanding food products with improved quality and functionality. This largely relies on rational design of food structures. As the two key food ingredients, protein and polysaccharides play important roles in food structuring. The combination of protein and polysaccharide provides rich opportunities for food structure and function designs through molecular interaction and assembly. This paper provides a brief review on the formation and characterization of protein/polysaccharide electrostatic complexes and their applications in stabilizing oil-in-water emulsions, particularly those containing polyunsaturated fatty acids.

Preparation and stability of nano-scaled gel beads of λ-carrageenan bound with ferric ions

Iron-deficiency anemia (IDA) is a major global public health problem, and the iron fortifiers in diet are clearly needed in the prevention and improvement of IDA for humans. A novel nano-scaled gel beads of λ-carrageenan (λ-car) specifically binding with ferric ions was developed to be a promising iron fortifier with no adverse organoleptic changes on food. Turbidity measurement, thermogravimetric analysis and Fourier transform infrared spectroscopy confirmed the successful chelating. The gel beads of λ-car-Fe3+ complex showed good dispersibility and solvent stability. The in vitro cell viability of HepG2 cells treated with λ-car-Fe3+ was over 75% at 5 mg/mL of ferric ions, indicating a significant cytotoxicity reduction of ferric ions. The stability of λ-car-Fe3+ complex powder was obviously increased against browning during 60 d storage with zein coating, which was attributed to the prevention of moisture permeation. Zein coated gel beads also performed a slow release of ferric ions in simulated gastrointestinal juices, resulting from the compact and hydrophobic zein surface delaying the dissociation of λ-car-Fe3+ in acidic environment. This λ-car-Fe3+ complex would have a great potential as a safe iron fortifier and facilitate iron supplementary with the advantage to relieve the side effects of iron ions.