Fish oil is a rich source of omega-3 polyunsaturated fatty acids (PUFAs), crucial for human health. However, its strong odor, susceptibility to oxidation, and limited bioavailability pose challenges. While encapsulation in nanoparticles offers protection against oxidation and enhances bioavailability, existing methods often involve multiple steps or expensive equipment. This study explores the use of a vortex fluidic device (VFD), a continuous flow thin film microfluidic platform, as a novel, scalable, and cost-effective method for encapsulating fish oil. The VFD leverages high shear forces, intense micro-mixing, and high mass transfer to overcome limitations of traditional batch processing. Previous research demonstrated the VFD's effectiveness in encapsulating fish oil at low concentrations; this study extends that work to high concentrations, making the process more industrially relevant. The research also investigates the simultaneous encapsulation of water-insoluble bioactive polyphenols (curcumin and quercetin) and introduces a real-time SANS method to study the encapsulation process.

Existing literature extensively explores the encapsulation of fish oil to address its inherent limitations. Several methods have been developed, including encapsulation in liposomes and electrospun zein fibers. However, these techniques often involve multiple steps, high surfactant-to-oil ratios, or expensive equipment, hindering their industrial scalability and economic feasibility. Studies on nano-encapsulation highlight the benefits of smaller particle sizes for improved stability and bioavailability. Previous work by the authors demonstrated the potential of the VFD for encapsulating fish oil at low concentrations, showing the formation of smaller particles compared to homogenization. This laid the groundwork for the current study, which aims to address the limitations of existing methods by applying the VFD to high-concentration fish oil encapsulation and the co-encapsulation of other bioactive compounds.

The study utilized a vortex fluidic device (VFD) for fish oil encapsulation. A 1:1 (w/w) ratio of fish oil to Tween 20 surfactant was used at a total concentration of 0.2 g/mL. The VFD was operated at optimized conditions (9000 rpm, 0.3 mL/min flow rate, 45° tilt angle, 25°C). Conventional homogenization served as a control. Particle size and stability were analyzed using dynamic light scattering (DLS) and epi-fluorescence microscopy. Omega-3 fatty acid content was determined using gas chromatography. Sensory evaluation was performed on apple juice enriched with encapsulated and unencapsulated fish oil. For co-encapsulation of curcumin and quercetin, 30 mg of each compound was mixed with fish oil and Tween 20, processed in the VFD, and analyzed using DLS and confocal microscopy. Real-time SANS measurements were conducted on the Bilby instrument at ANSTO to study the effects of VFD processing on the size and geometry of Tween 20 micelles, both alone and with fish oil, at different rotational speeds (0, 4000, 7000, and 9000 rpm). Data analysis involved fitting various models to the SANS data using non-linear least squares to determine particle size and polydispersity.

The VFD method produced significantly smaller fish oil particles (sub-300 nm) compared to homogenization (3-4 µm), leading to greater stability. The VFD-encapsulated fish oil exhibited higher omega-3 fatty acid content after 14 days of storage (approximately 62%) than the raw fish oil (approximately 31%). The VFD-encapsulated fish oil successfully enriched apple juice with omega-3s without compromising sensory quality. Panelists preferred apple juice with encapsulated fish oil over apple juice with free fish oil. The VFD effectively encapsulated both curcumin and quercetin into fish oil particles, with encapsulation capacities of 67.9% and 51.2%, respectively, creating homogenous suspensions in water. The real-time SANS data revealed that the VFD processing influenced the size and polydispersity of the Tween 20 micelles. At higher rotational speeds, the micelles with fish oil generally increased in size and decreased in polydispersity, indicating increased homogenization. However, at 7000 rpm, the micelles exhibited a decrease in size and an increase in polydispersity, potentially due to the formation of strong eddy currents. The SANS data confirmed that the VFD treatment led to a more uniform particle size distribution and enhanced encapsulation efficiency.

The results demonstrate that the VFD provides a superior method for encapsulating fish oil compared to conventional homogenization. The smaller particle size and increased stability of the VFD-encapsulated fish oil result in improved bioavailability and reduced oxidation. The successful enrichment of apple juice and the co-encapsulation of water-insoluble bioactive compounds showcase the versatility of the VFD for food applications. The real-time SANS observations provide valuable insights into the dynamic self-assembly processes occurring during VFD-mediated encapsulation. The findings highlight the importance of controlling shear stress to optimize particle size and stability. The observation of micelle breakup at 7000 rpm suggests the existence of an optimal shear rate for achieving the desired particle size distribution.

This study successfully demonstrated the use of a VFD for efficient, single-step encapsulation of fish oil at high concentrations, significantly improving stability and preserving omega-3 fatty acids. The VFD's ability to co-encapsulate water-insoluble bioactive compounds expands its potential applications in food and nutraceutical industries. The in situ SANS technique provided valuable real-time insights into the encapsulation process. Future research could focus on exploring other surfactants and optimizing VFD parameters for different bioactive compounds and food matrices. Further investigation into the effects of different shear rates and the influence of eddy currents on the encapsulation process is also warranted.

The study focused on a specific surfactant (Tween 20) and a limited set of bioactive compounds. The generalizability of the findings to other surfactants and compounds needs further investigation. The sensory evaluation was limited to apple juice; more diverse food applications should be explored. The study is limited to one type of fish oil, and future studies should look at using the VFD on other fish oils.