Influence of PEGylation on the ability of carboxymethyl-dextran to form complexes with α-lactalbumin

Effect of high acyl gellan gum and pH on the structural and foaming properties of heated whey protein suspensions

Effects of association between high-acyl gellan gum and whey protein on heat-induced aggregation and foaming properties of aggregates were assessed in aqueous suspensions. Associative complexes were identified by turbidity and colloidal charge below pH 6, and a balance of charge in the complexes was achieved at pH 5 with a 5:1 protein:polysaccharide ratio. As gellan gum content increased, size of aggregates formed by heating at pH 5 decreased (>1000 nm to 200-300 nm). Microscopy showed polysaccharide chains adhered to spherical aggregates at pH 5 and 6. Gellan gum added to protein before heating did not increase foam volume yet doubled foam half-life at pH 5 when used at a 2:1 protein-to-polysaccharide ratio. Microscopy showed that protein aggregates with attached gellan gum were present in drained foams. These findings indicate that gellan gum improves foam stability of heated whey protein at pH 5 by reducing aggregate size and adhering to aggregates.

Effects of high-pressure homogenization and ultrasound on the composition, structure, and physicochemical properties of proteins extracted from Nannochloropsis Oceania

This study examined the effects of high-pressure homogenization (HPH) and ultrasonication pre-treatment on the structural and physicochemical properties of proteins extracted from defatted Nannochloropsis Oceania biomass (DNOB). HPH treatment was found to enhance the solubility of protein extracted from DNOB compared to ultrasound, where samples pretreated with three passes (3P) of HPH exhibited lower solubility than two passes (2P). The morphology of extracted samples was visualized by scanning electron microscopy, which HPH pre-treatment, especially with more passes, were able to breakdown DNOB into fragments. Alternatively, more holes were displayed on the surface of the extracts pretreated with ultrasound especially when higher amplitude applied. The particle size of extracts from HPH3P (129.5 µm) significant dropped from HPH2P (314.25 µm), where samples pretreated with ultrasound at 20 % amplitude (US20) also decreased in particle size compared to 40 % amplitude (US40), from 115.25 µm to 78.22 µm. Protein flexibility of DNOB extracts were enhanced by both HPH2P and HPH3P but decreased for ultrasound samples. β-sheets were found to be the most abundant protein secondary structure for all samples, where samples treated with HPH3P contained the highest percentage of β-sheets (72 %) than control, HPH2P, ultrasonication at 20 and 40 % amplitude (52-62 %). The high percentage of β-sheets found in HPH3P sample also contributed to its outstanding emulsifying properties which stood out among all, especially at concentrations over 1 mg/ml. Results obtained from this study helped to direct the application of DNOB extracts as functional food ingredient for future food innovation.

Rheological Characteristics of Soluble Cress Seed Mucilage and β-Lactoglobulin Complexes with Salts Addition: Rheological Evidence of Structural Rearrangement

Functional, physicochemical, and rheological properties of protein-polysaccharide complexes are remarkably under the influence of the quality of solvent or cosolute in a food system. Here, a comprehensive description of the rheological properties and microstructural peculiarities of cress seed mucilage (CSM)-β-lactoglobulin (Blg) complexes are discussed in the presence of CaCl₂ (2-10 mM), (CSM-Blg-Ca), and NaCl (10-100 mM) (CSM-Blg-Na). Our results on steady-flow and oscillatory measurements indicated that shear thinning properties can be fitted well by the Herschel-Bulkley model and by the formation of highly interconnected gel structures in the complexes, respectively. Analyzing the rheological and structural features simultaneously led to an understanding that formations of extra junctions and the rearrangement of the particles in the CSM-Blg-Ca could enhance elasticity and viscosity, as compared with the effect of CSM-Blg complex without salts. NaCl reduced the viscosity and dynamic rheological properties and intrinsic viscosity through the salt screening effect and dissociation of structure. Moreover, the compatibility and homogeneity of complexes were approved by dynamic rheometry based on the Cole-Cole plot supported by intrinsic viscosity and molecular parameters such as stiffness. The results outlined the importance of rheological properties as criteria for investigations that determine the strength of interaction while facilitating the fabrication of new structures in salt-containing foods that incorporate protein-polysaccharide complexes.

Impact of Chitosan Molecular Weight and Attached Non-Interactive Chains on the Formation of α-Lactalbumin Nanogel Particles

Thermal treatment of protein⁻polysaccharide complexes will form nanogel particles, wherein the polysaccharide controls nanogel formation by limiting protein aggregation. To determine the impact of the chitosan molecular weight and non-interactive chains on the formation of nanogels, mixtures of α-lactalbumin were prepared with selectively-hydrolyzed chitosan containing covalently-attached polyethylene glycol chains (PEG) and heated near the protein's isoelectric point to induce formation of nanogels. Turbidity of heated mixtures indicated the formation of suspended aggregates, with greater values observed at higher pH, without attached PEG, and among samples with 8.9 kDa chitosan. Mixtures containing 113 kDa chitosan-PEG formed precipitating aggregates above pH 5, coinciding with a low-magnitude colloidal charge and average hydrodynamic radii > 400 nm. All other tested mixtures were stable to precipitation and possessed average hydrodynamic radii ~100 nm, with atomic force microscopy showing homogeneous distributions of spherical nanogel aggregates. Over all of the tested conditions, attached PEG led to no additional significant changes in the size or morphology of nanogels formed from the protein and chitosan. While PEG may have interfered with the interactions between protein and the 113 kDa chitosan, prompting greater aggregation and precipitation, PEG did not indicate any such interference for shorter chitosan chains.