The purpose of this research was to produce size-controlled polyunsaturated fatty acids (PUFA)-loaded oil-in-water (O/W) emulsions using refined palm oil rich in β-carotene, by microchannel (MC) emulsification. A commercial mixture of long-chain PUFA extracted from Menhaden oil was added to palm oil at a concentration of 45 g/L and used as the to-be-dispersed phase. The continuous phase consisted of a water dispersion of two different emulsifiers, in order to improve droplet stabilization and β-carotene bioavailability: sucrose laurate and β-lactoglobulin (1 wt %, respectively). The effect of various levels of to-be-dispersed phase flux (J d) (10, 20, 40, and 80 L/(m2·h)) and continuous phase flow velocity (V̅ c) (ranging from 0.23 to 2.33 mm/s) on the behavior of droplet formation, average droplet size (d av) and coefficient of variation (CV) were evaluated. The fine carotenoid O/W emulsions loaded with PUFA were prepared using an MC emulsification device. Protein-stabilized monodispersed PUFA-loaded emulsions were successfully produced, with a d av of 27.9 μm and a CV of less than 4%. The d av and CV increased with J d especially above 40 L/(m2·h), and were independent of V̅ c, within the velocity range applied in this study. Analysis of the dimensionless Ca indicated that on increasing the J d up to the critical Ca (0.075), the flow is based on spontaneous transformation, resulting in monodispersed droplets. If Ca exceeds the critical value, viscous force is dominant, the flow is similar to laminar flow, and the to-be-dispersed phase flows out continuously from the MC.

Microchannel (MC) emulsification is a promising technique to produce monodisperse emulsions by spontaneous interfacial-tension-driven droplet generation. The purpose of this study was to systematically characterize the effect of temperature on droplet generation by MC emulsification, which is a major uncharted area. The temperature of an MC emulsification module was controlled between 10 and 70°C. Refined soybean oil was used as the dispersed phase and a Milli-Q water solution containing sodium dodecyl sulfate (1 wt%) as the continuous phase. Monodisperse oil-in-water (O/W) emulsions with a coefficient of variation below 4% were produced, and at all the operating temperatures, their average droplet diameter ranged from 32 to 38 lm. We also investigated the effect of flow velocity of the dispersed phase on droplet generation characteristics. The maximum droplet generation rate (frequency) from a channel at 70°C exceeded that at 10°C by 8.1 times, due to the remarkable decrease in viscosity of the two phases. Analysis using dimensionless numbers indicated that the flow of the dispersed phase during droplet generation could be explained using an adapted capillary number that includes the effect of the contact angle of the dispersed phase to the chip surface. Keywords Microchannel emulsification Á Temperature Á Uniform droplets Á Droplet productivity Á Capillary number List of symbols Variables A disk Initial disk area of a dispersed phase (m 2 ) A drop Droplet surface area (m 2 ) A MC Channel cross-sectional area (m 2 ) Ca d Capillary number of a dispersed phase (-) Ca h d Adapted capillary number of a dispersed phase (-) CV Coefficient of variation (-) d drop Droplet diameter (m) " d Dimensionless droplet diameter (-) d n,drop Number-weighted mean droplet diameter (m) d MC Channel hydraulic diameter (m) f MC Frequency per channel (s -1 ) f MC,max Maximum frequency per channel (s -1 ) g Acceleration due to gravity (m/s 2 ) Dh d Height of a dispersed phase chamber (m) h terrace Terrace height (m) DP d Pressure applied to a dispersed phase (Pa) DP d,bt Breakthrough pressure of a dispersed phase (Pa) T C Celsius temperature (8C) t det Detachment time (s) t gen Droplet generation time (s) U d,MC Flow velocity of a dispersed phase inside a channel (m)Greek symbols c Dynamic interfacial tension (N/m) c 0 Interfacial tension between the two phases in the absence of surfactant (N/m) jRelative rate of surfactant creation (s) s d Diffusion of surfactant molecules (s) c eq Equilibrium interfacial tension (N/m) g c Viscosity of a continuous phase (Pa s)