Fabrication of novel casein gel with controlled release property via acidification, spray drying and tableting approach.

In this work, casein has been acidified at a pH of 1.0, forming a shampoo/lotion-like gel. It has been further processed by spray drying and tableting for controlled-release applications. The engineered casein gel shows higher moisture contents and lower Tg /dehydration temperatures compared with the non-gelled casein, based on the DSC and FTIR analysis. Casein is sensitive to thermal exposure (DSC), and no significant change in the casein was observed during acidification (FTIR). The particle size of the spray-dried casein gel increased as the spray-drying temperature decreased. The particles that were spray-dried at high temperatures were more likely to have wrinkled surfaces (raisin-like). For the microencapsulation of ascorbic acid (vitamin C), the spray-dried powders had lower moisture contents and higher Tg /dehydration temperatures as the spray-drying temperature was increased. By increasing the inlet temperature (100-190 °C), the retention of ascorbic acid decreased (80-60%) while the yield increased (0-70%). The DMA analysis showed that the casein gel tablet was elastic, and its stiffness was measured to be 0.8 N/mm. For controlled release, the casein gel tablet gave a slow release of ascorbic acid for 24 h at pH of 2 or 12 h at pH of 7.4. High compression pressure (320 MPa) resulted in slightly slower release than a compression pressure of 80 MPa.