Food Structure


The colloidal precipitate known as tea cream, which separates when a hot aqueous infusion of black tea is cooled, is investigated by electron microscopic (EM) techniques of shadowing, sectioning, freeze-etching and scanning and also by optical microscopy. These indicate tea cream to be an association colloid, the morphology of which depends on overall solids concentration. Dilute infusions (0.1% w/w) produce macromolecular aggregates of about 50 run, but at higher tea solids concentrations secondary aggregation of the initial particles results in ill-defined clusters of approximately 1 um in diameter. At 5% w/w, clear , spherical liquid droplets, typically 1-2 um in diameter are observed . Increasing concentration to 40% w/w causes an increase in size of the individual colloidal droplets and an increase in the phase volume of this disperse phase. The colloidal phase contains 55 - 65% solids by weight, the total solids content appearing to be independent of overall composition of the solutions from which it is formed. The colloid may be separated from cooled tea infusions by centrifugation but individual particles display strong resistance to coalescence. At high tea cream phase volumes phase inversion can occur and dispersions of the dilute phase in a continuous cream phase are then observed.

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