EFFECT OF WATER-CONTENT ON THE GLASS-TRANSITION AND CAKING OF FISH-PROTEIN HYDROLYZATES

The glass transition temperature (T(g)) and structure collapse (volume tric shrinkage) of a freeze-dried fish protein hydrolyzate (HFP) were studied. An increase in the water activity from 0 to 0.64 reduced the T(g) of HFP from 79.1 to -42.8-degrees-C. The Gordon-Taylor equation w as a good predictor for the plasticizing effect of water on T(g). At r oom temperature (19-degrees-C), collapse was initiated at a(W)= 0.44 c orresponding to a T - T(g) value of 35.8-degrees-C, and browning was e vident above a(W) = 0.55. Above these critical values several structur al changes occurred: shrinkage, collapse, browning, and setting into a sticky, high-viscosity brown liquid. The viscosity of the matrix at t he onset of collapse was 10(5)-10(7) Pa.s, as estimated using the Will iams-Landel-Ferry equation.