Rheological behaviour of tomato concentrate (Hot Break and Cold Break)

Abstract Knowledge of the rheological properties of agricultural products undergoing industrial transformation is of great importance in the design of industrial equipment in which these changes take place and as an index of quality of the finished products. The rheological behaviour of two samples of tomato concentrate (from the same tomato lot) which were treated, during industrial processing, by two different procedures — ‘Hot Break’ and ‘Cold Break’ — have been studied. Using a rotational viscometer the rheological curves of both concentrate samples were obtained at different concentration and temperature conditions, the corresponding values of K (consistency coefficient) and n (flow behaviour index) indicating a typically pseudoplastic behaviour. From the experimental results, the influence of using variable values of n and K has been studied. Finally, equations were derived to represent the apparent viscosity of tomato concentrate at any concentration and temperature within the range investigated. ‘Hot Break’ samples showed (at the same temperature and concentration) higher μ a and K values and lower n values than ‘Cold Break’ samples, which fully agrees with the logical deductions if it is taken into account that during the ‘Hot Break’ process enzymic inactivation occurs which prevents pectin degradation whereas in the ‘Cold Break’ process, enzymes are not inactivated, allowing the pectins present in the ground tomato to be degraded.