Monodisperse aqueous microspheres encapsulating high concentration of l-ascorbic acid: insights of preparation and stability evaluation from straight-through microchannel emulsification

Abstract

Stabilization of l-ascorbic acid (l-AA) is a challenging task for food and pharmaceutical industries. The study was conducted to prepare monodisperse aqueous microspheres containing enhanced concentrations of l-AA by using microchannel emulsification (MCE). The asymmetric straight-through microchannel (MC) array used here constitutes 11 × 104 μm microslots connected to a 10 μm circular microholes. 5–30% (w/w) l-AA was added to a Milli-Q water solution containing 2% (w/w) sodium alginate and 1% (w/w) magnesium sulfate, while the continuous phase constitutes 5% (w/w) tetraglycerol condensed ricinoleate in water-saturated decane. Monodisperse aqueous microspheres with average diameters (d_av) of 18.7–20.7 μm and coefficients of variation (CVs) below 6% were successfully prepared via MCE regardless of the l-AA concentrations applied. The collected microspheres were physically stable in terms of their d_av and CV for >10 days of storage at 40°C. The aqueous microspheres exhibited l-AA encapsulation efficiency exceeding 70% during the storage.

Straight-through microchannel emulsification has ability to produce monodisperse emulsions. l-AA is encapsulated in aqueous microspheres and has encapsulation efficiency of over 70% after 10 days of storage at 40^oC.

Key words:

• monodisperse microspheres
• l-ascorbic acid
• high concentration
• stability
• sodium alginate

Acknowledgments

The first author gratefully acknowledges a scholarship from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan and University of Tokyo Fellowship for study at the University of Tokyo and National Food Research Institute, NARO, of Japan.