Extraction of water-soluble polysaccharides from lupin beans and their function of protein dispersion and stabilization under acidic conditions

In the current environment whereby new sources of proteins are extracted from plant material, it is also important to study the potential use of the resulting side streams. Although a number of studies have been conducted on various polysaccharides extracted from plant raw material, a polysaccharide fraction extracted from lupin bean is yet to be explored, in spite of the emerging interest in this crop as a source of food ingredients. In this work lupin soluble polysaccharide (LuPS) was obtained with a recovery as high as 46 % by extraction at pH 8, 120 °C, for 90 min. This fraction, named LuPS-8, was composed of a mostly linear pectic polysaccharide with a weight average molecular mass of 6608 kg/mol, and containing 71.0 % galactose, with minor amounts of arabinose (16.0 %), glucuronic acid 4.6 %, and galacturonic acid 4.1 %. When added to an acid milk dispersion, LuPS-8 improved its dispersibility, providing storage stability against sedimentation over a wider pH range than a HM-pectin reference, between 3.6-4.4. This research demonstrated the potential for upcycling of a side stream of lupin protein production, by the creation of value-added novel functional polysaccharide.

Molecular structures of high- and low-methoxy water-soluble polysaccharides derived from peas and their functions for stabilizing milk proteins under acidic conditions

The structural and functional properties of two different pea water-soluble polysaccharides, a high methyl-esterified (HM-SPPS; degree of methyl esterification (DMe): 71.0 %) and low methyl-esterified SPPS (LM-SPPS; DMe: 25.2 %) were investigated. The two extracts did not vary in composition and showed a weight average molecular mass of about 1,000 kDa, as measured by size exclusion chromatography equipped with a multi-angle light scattering detector. Both HM-SPPS and LM-SPPS had similar sugar compositions, with arabinose 42.2-47.1 %, glucose 26.6-31.0 %, and galacturonic acid 17.5-18.0 %, as their main sugars. Their charge varied as a function of pH. The molecular structure was observed by a scanning probe microscope and showed a straight chain structure with small branches. The structure was similar to that already reported for polysaccharides from kidney bean. SPPS molecules interact with acidified milk protein particles at pH < 4.4. There were differences between the two SPPS. LM-SPPS could stabilize a model acidified milk dispersion with minimal aggregation between pH 3.6-4.4, while HM-SPPS showed the presence of bridging flocculation caused by polysaccharide's entanglements. It was concluded that SPPS stabilizes acidified protein by steric and electrostatic repulsion.

Dynamics of carbohydrate strands in water and interactions with clay minerals: influence of pH, surface chemistry, and electrolytes

Carbohydrate hydrogels are extensively used in pharmaceuticals and engineered biomaterials. Molecular conformations, assembly, and interactions of the carbohydrate strands with stabilizers such as clay minerals in aqueous solution are difficult to quantify in experiments and the hydrogel properties remain largely a result of trial-and-error studies. We analyzed the assembly of gellan gum in aqueous solution and interactions with dispersed clay minerals in all-atomic detail using molecular dynamics simulation, atomic force microscopy (AFM), and comparisons to earlier measurements. Gellan strands associate at low pH values of 2 and gradually disassemble to double strands with weak association of -0.4 kcal per mole carbohydrate ring as the pH values increases to 9. Ionization of the carbonic acid side groups in the backbone extends the chains and accelerates the conformational dynamics via rapidly changing intramolecular ion bridges. Gellan interactions with clay minerals depend on the strength of electric triple layers between clay, cations, and anionic polymer strands, as well as weaker hydrogen bonds along the edges, which are tunable as a function of the clay surface chemistry, local ionic strength, and pH values. Interaction energies range from -4 to +6 kcal per mol carbohydrate ring and were most favorable for electric triple layers with high charge mobility, which can be achieved for intermediate cation exchange capacity of the clay mineral and high pH values to increase ionization of the clay edges and of the polymer. The findings provide understanding and help control the dynamics and stabilization of carbohydrate hydrogels by clay minerals.

Purification, Rheological Characterization, and Visualization of Viscous, Neutral, Hetero-exopolysaccharide Produced by Lactic Acid Bacteria

Viscous exopolysaccharide (EPS)-producing lactic acid bacteria (LAB) have received increasing interest in the dairy industry because of their capability to improve the texture and mouthfeel of fermented dairy products. To date, enormous efforts have been made to reveal the relationship between texture and EPS production in fermented milk products such as yogurt. However, the structure-rheology relationship of EPSs themselves is not yet well understood due to their low yields in general and their wide variety of chemical structures. In this chapter, we describe common techniques for the purification, visualization, and rheological analysis of viscous EPSs produced by LAB.

Rheological characteristics and supramolecular structure of the exopolysaccharide produced by Lactobacillus fermentum MTCC 25067

Rheological properties and supramolecular structure of the exopolysaccharide (EPS) secreted by Lactobacillus fermentum MTCC 25067 were investigated. The critical concentration representing the lower-limit of the semi-dilute regime was estimated to be 0.71 g/L from the concentration dependence of zero-shear specific viscosity. The storage modulus (G') of a 20 g/L EPS solution was greater than the loss modulus (G″) at 0.1-25 Hz. Approximately linear increases in G' and G″ determined at a frequency of 1 Hz and a strain of 0.01 during cooling from 80 to 25 °C were an indication that the EPS did not undergo thermally-induced cooperative conformational transitions typical of gelling polysaccharides. Atomic force microscopy images revealed that EPS molecules were not completely dissociated into individual molecules in an aqueous solution but remained to form three-dimensional networks. The gel-like dynamic viscoelasticity of the 20 g/L EPS solution was thus attributed to the existence of supramolecular assemblies resulting from significant degrees of intermolecular association of the EPS in the solution.