Microstructure formation of maltodextrin and sugar matrices in freeze-dried systems

Properties of freeze-dried foods are governed by ice formation during freezing. This study investigated the effects of freezing temperature and solids composition on the microstructure and mechanical properties of freeze-dried solids. Maltodextrin and maltodextrin-sugars (glucose, fructose and sucrose) systems were used as solid components. The glass transition and onset temperatures of ice melting for maximally freeze-concentrated systems (T-g' and T-m') were measured using differential scanning calorimetry. Freezing was carried out at -20, -40 or -80 degrees C prior to freeze-drying. Microstructural analyses and measurements of mechanical strength in compression were performed using scanning electron microscope and texture analyzer, respectively. The pore size and wall thickness of freeze-dried solids were dependent on the freezing temperature and molecular size of carbohydrates. Sugars depressed the T-g' and T-m' and affected collapse during freeze-drying, but controlled microstructure of non-collapsed solids. The data show differences for freezing processes and compositions that may lead to varying levels of stability of dispersed substances in freeze-dried matrices. (c) 2012 Elsevier Ltd. All rights reserved.