Aggregates, fibrous

Denaturation and aggregation of whey proteins are affected by the pH of extrusion. When extruding WPI, alkaline conditions increase denaturation and solubility, decrease pasting properties, and produce more pronounced microstructural changes (Onwulata et ah, 2006). Denaturation in the extruder causes whey proteins to form small primary aggregates that combine to form large clusters. The clusters are then aligned by shear to form fibrous structures. 

Figure 5.7 AFM images of fibrous aggregates of D-Glu-8 (1) lying directly on silicon surfaces (a) network of fibers (b) high-resolution phase image of quadruple helices. Reprinted with permission from Ref. 42. Copyright 2000 by the American Chemical Society.

Conversely, flocculation implies those aggregation processes effected by the intertwining of fibrous particles, for example in the wool trade, or the entrapment of silt particles in foul water, as above. 

Based on the same principle, there are monomeric / -helical proteins that carry at their extremities a cluster of helical or nonrepetitive structures that could act as a capping element covering their exposed ends (Emsley et al., 1996 Lietzke et al, 1994 Petersen et al, 1997 Steinbacher et al, 1994). For example, the last 40 residues of pectate lyase C form a large loop that partially covers the surface of the /Hielix (Yoder et al, 1993). The fibrous (or otherwise elongated) domain of these natural /f-stranded proteins is not stable in isolation, as for example in the case of the P22 tailspike where bacterially expressed isolated /Hielix domain, at high concentrations, forms fibrous aggregates that bind Congo red (Schuler et al, 1999). 

Schuler, B., Rachel, R., and Seckler, R. (1999). Formation of fibrous aggregates from a non-native intermediate The isolated P22 tailspike beta-helix domain./. Biol. Chem. 274, 18589-18596. 

A paper by Meijer et al. described the synthesis and electronic properties of a series of PPE-PPV hybrid oligomers. The approach is shown in Scheme 11 [70]. Starting from a brominated stilbene, reaction with a series of diethynyl-benzenes furnished pentameric PE-PV hybrids in yields around 80%. The materials are used as emitters in LEDs and other electrooptical devices. It was noted that fibrous aggregates formed upon melting and recooling of thin films of these pentameric PE-PV hybrids. 

The most common, and certainly the most familiar, inorganic fibers are the mineral fibers known as asbestos. Several minerals have been mined as asbestos (Fig. 1.1 A, C see chapter 2 for a detailed discussion of the asbestos minerals). These minerals are widespread in nature, but mining is economical only when they occur as continuous fibrous aggregates (veins) crosscutting rock masses. The veins are made up of hairlike fibers in parallel array that, on close inspection, appear bent (Fig. I.IB). Not surprisingly, a mineralogical term, asbestiform, has been used to describe this subset of inorganic materials. 

Alternatively, a fiber can be one member of a group or aggregate, as a fibril is one part of a fiber. Spherulites (Fig. 1. IH), fan-shaped fibrous crusts or rosettes, and the veins depicted in Fig. 1.1A are examples of aggregates created when many crystalline fibers grow in close proximity. During fibrous growth, lateral interference may produce planar but irregular bound-... 

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