Controlled release of caffeine from tablets of spray-dried casein gels
The controlled release of caffeine from the casein gel tablets has been achieved over release periods lasting from a few minutes to over a few days. A novel casein gel has been acidified at pH of 1.0 as the insoluble controlled-release matrix and spray-dried with coffee for microencapsulation. The optimal inlet temperature of spray drying for the casein-coffee mixtures has been found to be 150 °C. The elastic casein-coffee tablets have been engineered without denaturing the components (as indicated by DSC and FTIR analysis). Pressure-controlled release has been achieved for the casein-coffee tablets prepared by compression at 8 (with lactose excipient), 80 and 160 MPa. The corresponding releases of over 80% caffeine are about 24, 12 and 3–6 h, respectively. By changing the coffee/casein ratio from 10 to 100%, the release time of 80% caffeine can be controlled from 24 to 0.5 h. The spray-dried casein-coffee particles shown in the SEM images are similar in size (about 10 μm) and shape (raisin-like). No significant interactions between the casein and coffee components have been observed by FTIR analysis.