Dynamic measurements of β-lactoglobulin structures during aggregation, gel formation and gel break-up in mixed biopolymer systems

The kinetics of aggregation and gelation of beta-lactoglobulin/amylopectin microstructures have been studied by using confocal laser scanning microscopy (CLSM) equipped with a temperature stage, transmission electron microscopy (TEM) and dynamic mechanical analysis in shear. The behaviour of the final gels was studied during fracture deformations using a tensile stage adapted to the CLSM. The different types of particulate beta-lactoglobulin (beta-1g) network structures were generated by adding non-gelling antylopectin of varying concentration and viscosity. The results showed that the higher the concentration and the higher the viscosity of the amylopectin, the lower the temperature required for beta-1g to aggregate into particle aggregates and clusters visible in the CLSM. The gelling temperature of the beta-1g, determined by small deformation theological measurements, was also found to decrease with increase in amylopectin concentration. However, although an increased concentration of amylopectin accelerated the particle aggregation of beta-1g, amylopectin with a higher viscosity was found to restrict the aggregated protein aggregates and clusters to form a connected protein network. The result of the difference in connectivity was shown when the gel structures were studied during fracture deformations in tension. In the weaker gel type, where the continued aggregation to a connected network had been obstructed, the fracture was extended more deeply inside the structure than in the stronger gel type with good connectivity, when exposed to the same deformation. The distribution of the protein and the amylopectin in the aggregated structure was visualised by TEM. Amylopectin was found inside the beta-1g aggregates in the gels containing a lower viscosity of the amylopectin. In gels containing amylopectin with higher viscosity, the amylopectin was found in the pores between the protein networks, separated from the protein phase. (C) 2002 Elsevier Science Ltd. All rights reserved.