Food Structure


B. E. Brooker


A new rapid method for the preparation of milk foams for transmission electron microscopy is described . The air-serum interface of foams made from skimmed milk consists of a uniform electron dense layer (5 nm thick) to which casein micelles become secondarily attached . Changes in bubble volume lead to the formation of folds of excess interfacial material which project into the aqueous phase. Using collapsed bubble ghosts to study the attachment of micelles to the airserum interface it was concluded that neither disulphide bridge formation nor hydrophobic interactions were of major importance. Similar preparations of interfacial material but without casein micelles attached were prepared from milk plasma and solutions of ~- lactoglobulin. The former fragmented slowly into small particles at room temperature but very rapidly when heated to 55° C whereas material derived from~- lactoglobulin was quite stable. The destruction of bubble ghosts in skimmed milk by heating is attributed to interface breakdown rather than to micelle detachment. The air-serum interface, of which casein micelles do not form an integral part, probably consists of a mixture of globular whey proteins and some soluble caseins . Thus, using high pressure liquid chromatography, foamed milk plasma from which bubble ghosts had been removed was shown to be depleted in both a- lactalbumin and ~- lactoglobulin.

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