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 °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.