A viscometric study of the flocculation of the components in stored homogenized ultra-heat-treated cream

Abstract

SUMMARYThe apparent relative viscosity (ηr) of stored homogenized ultra-heat-treated ‘coffee’ cream increased with time (t) at a rate which was a function of mean fat globule diameter (d) and fat volume fraction (ø); the rate was also influenced by Na2CO3and Na citrate when present as stabilizing additives. Viscosity increases were attributed to the progressive flocculation of fat globules and to the strengthening of the structure formed by the gradual accretion of casein micelles on to globule surfaces and their points of contact (bridging). The expressionwheretis in days anddin μm, was found to hold over a 12-week storage period for a batch of creams (ø = 0·143) of differentdvalues prepared from the bulk cream containing carbonate and citrate stabilizers; η0is the relative viscosity att= 0 andkis a rate parameter. In the absence of stabilizers the parameterkassumed a smaller value and so appeared to be a function of chemical composition of the cream and of forces of particle interaction; seasonal factors were also suspected of influencingk. The effect of the fat volume fraction on storage behaviour was not fully resolved, but there was some evidence that the proportionality log ηrα1/ø½ was appropriate.