Micelle Dispersions Research Articles

Microscopic observation of the effect of some reagents on the physical state of casein

SummaryObservations were made by anoptral phase-contrast microscopy of the effect of various reagents on the state of dispersion of casein micelles in skim-milk and in lactic acid and rennet coagula. Among the hydrogen-bond-breaking reagents, urea at higher (4M) concentration dispersed the casein micelles in skim-milk and in acid and rennet coagula. Sodium salicylate was effective at low (M) concentration. Guanidine hydrochloride at low concentration caused aggregation of the micelles in skim-milk but at high concentration caused dispersion, while at both concentrations it dispersed acid and rennet coagula. Lithium iodide and potassium thiocyanate flocculated the casein in skim-milk, but dispersed it in both types of coagula. Flocculation in skim-milk by these reagents was followed by slow coalescence of the casein.At substantially lower molar concentrations, sodium dodecyl sulphate, an anionic detergent, which attacks either the hydrophobic bonds or the salt linkages in proteins, dispersed micelles and both types of coagula. Sodium thioglycollate, a disulphide-bond-breaking reagent, had no visible effect on the casein.In rennet coagulum in which the calcium bridges have been destroyed by the sequestering action of EDTA or in lactic acid coagulum, urea at low concentrations caused a quick and almost complete coalescence of casein. Fibres were formed in the rennet coagulum when the coalesced material, which presumably consists of randomly coiled chains of unfolded casein macromolecules, was subjected to stretching or flowing. Similar chemical and physical conditions would appear to prevail when fibre formation takes place in cheddaring cheese curd.

Dispersion of Cellulose Strands in Cell Walls

IN a recent letter in NATURE1 Prof. Frey-Wyssling directs attention to the importance in cell wall studies of the angular dispersion of the constituent cellulose micelles and refers to my papers as ignoring this property. Cell wall physics is a study in which there is already much controversy, and it seems therefore a pity to give the impression of a difference of opinion where none actually exists. The question centres round the desirability of taking into account not only the parallel texture said to be typical of fibres but also the so-called 'dispersed' or 'reticul' texture present in some other cell types. So far as I am concerned, the difference between 'parallel' and 'dispersed' textures is one of degree only and actually, far from taking “... only parallel textures into account...”, I have yet to investigate a single cell in which I am convinced that this texture does occur in anything like a strict sense. In some fibres2 and wood cells3, for example, where Frey-Wyssling himself supports parallel texture, and in some collen-chyma4, my collaborators and I have shown that the angular dispersion of the cellulose micelles about the extinction direction may be considerable and is probably of importance in explaining certain optical properties of the wall. These latter papers have apparently not been available to Prof. Frey-Wyssling since his citations of my papers cease in 1939.