Optimization of food dye (betanin) retention during hot air drying: Design space calculation with consideration of reaction and substrate transfer kinetics

ABSTRACT

Retention of food dye (betanin) during hot air drying of a model food system was optimized by developing mechanistic model that took into account the kinetics of degradation and the transfer of the substrate in the model food system. Betanin (red glycosidic food dye extracted from beets) degrades through hydrolysis, and this reaction is temperature dependent and involved with the amount of water in a system. Degradation kinetics of betanin/dextrin mixture was first measured under isothermal and isohumidity conditions in order to obtain kinetic constants for the degradation reaction. A packed bed filled with glass beads (mean diameter ca 200 µm) was wetted by a betanin/dextrin aqueous solution, and contacted with hot air at selected temperature and relative humidity. The resultant betanin retention in the drying systems was estimated by using the kinetic parameters of the degradation reaction. When estimation was made with consideration of dynamic change in temperature and moisture content during drying by assuming the uniformity of temperature and solute concentration in the system, calculation results seriously overestimated the resultant retention. It found experimentally that the dextrin and betanin transferred toward the drying interface and this made the concentrated film layer at the interface. And the kinetics of these mass transfers significantly affected the retention of betanin in the drying systems. The mass transfer rates of the dextrin and betanin were thus experimentally measured and applied to predict the retention values in the drying systems. The calculation results were in good accordance with the experimental values. A design space that relate the betanin retention to the drying temperature and air humidity conditions was calculated by a mechanistic model that took into account the kinetics of the degradation reaction and substrate transfer.

KEYWORDS:

• Betanin
• design space
• hot air drying
• hydrolysis
• reaction kinetics