Fine-Stranded and Particulate Aggregates of Heat-Denatured Whey Proteins Visualized by Atomic Force Microscopy

Abstract

beta-Lactoglobulin and whey protein isolate (WPI) were heated in aqueous solutions at pH 2 and 7 at 80 degrees C, spread onto freshly cleaved mica surfaces, and visualized under butanol using atomic force microscopy. Fine-stranded aggregates were formed at pH 2, the diameter of strands being ca. 4 nm for beta-lactoglobulin and 10 nm for WPI. At pH 7, aggregates were composed of ellipsoidal particles, regardless of the concentration of added NaCl. This observation supports the previously proposed two-step aggregation model at neutral pH (Aymard, P.; Gimel, J. C.; Nicolai, T.; Durand, D. J. Chim. Phys. 1996, 93, 987-997), consisting of the formation of primary globular particles and the subsequent aggregation of those primary particles. The AFM provides the first direct evidence for the anisotropic shape of these primary particles. The heights of primary particles increased from ca. 11 to 27 nm with increasing concentrations of added NaCl from 0 to 0.3 M in the case of WPI. The rate of aggregation was also accelerated with increasing NaCl concentrations, which appeared to induce transitions in gel networks from fine-stranded toward particulate networks. The present study provides structural information essential for understanding the diverse physical properties of heat-induced whey protein gels.

Improvement of barrier and mechanical properties of whey protein isolate based food packaging films by incorporation of zein nanoparticles as a novel bionanocomposite

“…Fig. 4 shows globular microstructure of the pure WPI as reported previously in the literature (Ikeda & Morris, 2002). The local aggregations in the pure WPI may be a result of the heat denaturation of proteins.…”

Production of Whey Protein-Based Aggregates Under Ohmic Heating

“…WPI, due mostly to the presence of β-lactoglobulin (β-lg), can form particulate networks in the pH range of 4-6, while fine-stranded networks are formed above and below this region (Stading et al 1992;Ikeda and Morris 2002;Nicolai et al 2011). Production and development of β-lg and WPI hydrogels have been studied extensively during the latest de-cades (Bryant and McClements 1998;Kavanagh et al 2000;Lefevre and Subirade 2000;Phan-Xuan et al 2013;Hermansson 1990, 1991;Stading et al 1992).…”

Understanding amyloid aggregation by statistical analysis of atomic force microscopy images

“…Studies devoted to the characterization of fibril structures based on light, neutrons and X-ray scattering methods, being bulk techniques, have only provided an average ensemble picture of the fibrils 23 . Single-molecule techniques such as atomic force microscopy (AFM) and transmission electron microscopy (TEM) have recently emerged to probe amyloid fibrils at the molecular level [24][25][26][27] . Nevertheless, so far, a fully comprehensive picture of the aggregation behaviour among different amyloid fibrils has not yet been achieved.…”