Casein micelle iota carrageenan interactions in milk: influence of temperature

The behaviour of iota carrageenan/skim milk mixtures was studied at 60 degr ees C and on cooling. At 60 degrees C, iota carrageenan flocculates casein micelles by depletion. Comparison of the gelling properties of iota carrage enan in skim milk and permeate during cooling and heating shows that the pr esence of micelles increases the gelation temperature, the gel rigidity, an d the gel melting temperature. These observations lead to the hypothesis th at a double network is formed. It is suggested that the first is because of casein micelles bridged by adsorbed carrageenan. This network is responsib le for the differences in properties between gels in permeate and skim milk . The second network requires a minimum carrageenan concentration and has p roperties very similar to those of an iota carrageenan gel in permeate. The apparent micelle size was determined as a function of temperature in milk 100-fold diluted in permeate in the presence of iota carrageenan or guar gu m. These measurements confirm the existence of a specific attractive intera ction between carrageenan and casein micelles. The interaction seems to req uire a certain charge density on the polymer. An attractive interaction bet ween casein micelles and iota carrageenan only occurs when the latter is at least partially in the more densely charged helical form. (C) 1999 Elsevie r Science Ltd. All rights reserved.