Gelation of Pre-Renneted Milk Concentrate During Spray Drying and Rehydration for Microcapsule Formation

Abstract

The gelation behavior of pre-renneted skim milk concentrate during and after spray drying is investigated in this work, which forms the basis for an encapsulation process. This process consists of renneting at 4 °C prior to drying, an initial gelation during drying and a final gelation under controlled rehydration conditions. The aim of this study was to gain a deeper understanding of the gelation process during spray drying by rheological and film and spray drying experiments. For this purpose, steep temperature gradients were applied to assess gelation time and maximal gel strength under fast up-heating conditions to temperatures typical for spray drying. Additionally, the drying behavior during film drying was varied by different dry matter concentrations of the gelling solutions and air temperatures, resulting in different times for the first drying stage. All results were correlated with the degree of aggregation (DA), the characteristic parameter for the state of gelation. The results of the film drying experiments are comparable to the gelation experiments. The gelation process takes more time than spray drying, but it is faster than film drying. Moreover, the gelation only takes place within the first drying stage and, therefore, the drying of SMCs (skim milk concentrate) with lower TS (total solid) contents results in better gelled capsules after spray drying.