Confined Impinging Jets: An alternative approach to traditional food emulsification techniques

Abstract

In the food sector, the development of innovative manufacturing technologies represents an exciting area of research. Within this context, Confined Impinging Jets (CIJs) offer potential for the large throughput production of tailored emulsion-based microstructures at lower energy inputs than conventional emulsification routes. Overall, this thesis aims to demonstrate that CIJs can be considered as a reliable alternative to existing emulsification methods by assessing its processing capacity and performance in delivering emulsion-based microstructures from a wide range of different formulations. The use of CIJs was initially explored for the production of emulsions with dispersed phase contents of up to 80 wt.%, in both a surfactant-poor and surfactant-rich regime, under varying mass jet flow rates, W$_{jet}$, and residence times. From both a computational and experimental study, it was observed that the CIJs emulsification capacity was strictly dependent on the mass jet flow rate (W$_{jet}$> 176 g/min) and the pre-emulsion droplet size (>10μm). CIJs emulsification performance remained (almost) unaffected by variations in the oil mass fraction. All systems showed the lowest droplet size (~8μm) and similar droplet size distributions under the highest W$_{jet}$. Conditionally onto the Tween20 availability, the emulsion d$_{3,2}$ was primarily determined by formulation characteristics in the surfactant poor-regime and by the CIJs energy dissipation rate in the surfactant-rich regime. CIJs emulsification performance was further assessed at varying energy dissipation rates (ε̅$_{th}$) and residence times for the production of 10 and 40 wt.% oil-in-water emulsions stabilised by an array of particles (Silica) and mixed emulsifier (Tween20-Silica) concentrations. Overall, it was demonstrated that droplet size reduction was promoted as higher energy levels of ε̅$_{th}$ were approached, regardless of the formulation. Following emulsion recirculation under a fixed jet mass flow rate, the residence time associated with two passes was sufficient to ensure no further changes in terms of both average droplet size (d$_{3,2}$) and span of the droplet size distribution. Only when Tween20 and Silica were mixed at low concentrations (0.01 and 0.1 wt.%, respectively), this emulsifier system could not promote any droplet size reduction even during multipassing. All systems showed excellent stability over 40 days of storage and it was possible to demonstrate that the combination of the emulsifiers aided in prolonging emulsion integrity. Finally, a comparison of the emulsification performance of CIJs with that of both high- (high pressure homogeniser, HPH; high-shear mixer, HSM) and low-energy (rotating membrane, RM) emulsification techniques was studied and compared based on a wide range of processing (average energy dissipation rate, ε̅$_{th}$; flow regime; energy density, Ev; and energy efficiency, EF) as well as formulation (dispersed phase content, and type of emulsifier) parameters. It was observed that during HPH, HSM and CIJs processing, emulsions were produced under a turbulent flow regime, contrarily to RM where the flow was laminar. The performance of the HPH was very much dependent on the type of emulsifier used, while all other techniques were practically unaffected by both emulsifier and oil phase content. Overall, the HPH treatment generated the highest ε̅$_{th}$ and comparable Ev to the HSM. The CIJs operated at intermediate ε̅$_{th}$ and Ev conditions, while RM exhibited the lowest values for both these parameters. CIJs and the RM were the most energy efficient processes. For all techniques (with the exception of RM where recirculation was not performed), emulsion recirculation (under fixed hydrodynamic conditions) significantly affected droplet size distribution but only marginally reduced d$_{3,2}$. However, increasing the residence time within the emulsification apparatus (via recirculation), strongly decreased the EF of all processing techniques. The CIJs still remained the most energyefficient method while HPH and HSM processing resulted in lower EFs with their relative values dependent on the type of emulsifier used