Abstract
The production of beads by simple extrusion dropwise of an alginate solution in a calcium bath is a simple method. It may be done at room temperature without any toxic compound. However, simple extrusion drop by drop from a needle may result in large capsules and a low flow rate. The solution must be extruded as a jet to get a smaller size and higher flow rate, which breaks into droplets either by vibration or a cutting tool. The present contribution reports jet breakage observations into droplets under vibration by extruding an alginate solution varying some parameters during the study. The droplet formation was observed using a high-speed camera, and images were analyzed. The size, length before breakage, and droplet velocity were obtained by examining 50 droplets, and experiments were repeated three times. The high-speed camera allowed us to observe more precisely the capillary jet breakage. The study showed the importance of selecting a well-designed vibrating system, presented data while varying nozzle size, frequency, and flow rate to get optimum breakage keeping across all the same alginate solution. Further experiments would be interesting, modify the extruded solution concentration and composition, and find a precise criterion to identify optimum conditions.
Highlights
In 1977, Kierstan and Bucke [1] published alginate beads production using a simple extrusion dropwise of an alginate solution in a calcium bath
Bahry [3] utilized alginate beads to immobilize Lactobacillus rhamnosus and explore another efficient way to valorize the residual carbohydrates of carob waste instead of work directly on pods, using Lactobacillus casei in the liquid phase
This method was demonstrated to be effective, mainly because it allows the reuse of microorganism due to easy separation of the biomass from the liquid phase
Summary
In 1977, Kierstan and Bucke [1] published alginate beads production using a simple extrusion dropwise of an alginate solution in a calcium bath. Besides presenting versatility in encapsulation, like core-shell capsules by inverse gelation, the extrusion of calcium suspension in alginate bath [6], or co-extrusion of core solution inside an alginate shell solution [5] These methods were developed based on a simple extrusion drop by drop from a needle. Many articles develop the Rayleigh’s theory, taking into account the rheology of the solution, its surface tension, and the formation of satellite droplets [12,13,14] These models are difficult to apply for daily work. The present contribution reports direct observations of the alginate solution droplet formation with the assistance of fast recording cameras It evaluates the impact of several parameters, such as frequency, type of membrane, nozzle size, and vibration amplitude on droplet size. The study compares and verifies those results with mathematical theories to better understand process optimizing and the importance of selecting a well-designed vibrating system
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