## 6 Concluding Remarks and Future Research Prospects  
Over the past few decades, it has been widely recognized that the development of nanosized delivery systems is one of the most effective strategies to improve the stability and oral bioavailability of many poorly soluble nutraceuticalals. Among all these nano-delivery systems, SLNs and NLCs seem to be the most appropriate delivery systems for lipophilic or hydrophobic nutraceuticalals, thanks to their good compatibility with lipid matrices. The usage of such nanoparticles as nanovhelics for nutraceuticalals exhibits many advantages over other nano-delivery systems: for example, high loading capacity, good biocompatibility, high stability (especially oxidative stability), prolonged release, high cellular uptake and bioavailability, and easy scale-up. In contrast, NLCs as nanovhelics for nutraceuticalals or bioactives perform better, in terms of loading capacity and inhibition of perfect lipid crystallization, than SLNs. Although SLNs and NLCs have been successfully developed as nano-delivery systems for drugs for several decades, the use of such nanoparticles as food-grade nanovhelics for nutraceuticalals has only come to pass within the past two. To date, such nanoparticles have been confirmed to act as effective nanovhelics for liposome nutraceuticalals, e.g., carotenoids, fat-soluble vitamins, \(\omega\)-3 polyunsaturated fatty acids, and essential oils, as well as for poorly soluble bioactive compounds, e.g., curcuminoids, polyphenols, phytosterols, and phytostanols. Accumulating evidence suggests that SLNs and NLCs exhibit great potential as nanovehicles for functional food formulations with beneficial effects on the brain and human health. In this regard, one successful example is the development of curcumin-loaded SLNs or NLCs for the prevention and improvement of many common central nervous system diseases, including Alzheimer's disease, Parkinson's disease, ischemic stroke, and multiple sclerosis [17, 62]. This is closely associated with the fact that lipid nanoparticles (including SLNs and NLCs) can be directly absorbed by the epithelium cells in the intestinal tract and enter the lymphatic system. Despite their promising potential as nanovehicles for lipophilic or hydrophobic nutraceuticalals, great effort is still needed for the development and utilization of food-biocompatible SLNs and NLCs as effective nanovehicles that will significantly improve their oral bioavailability. Future research prospects for the development of such nanoparticles as food-grade nanovehicles for nutraceuticalals should include, but not be limited to, the following aspects:  
1. elucidating the potential and effectiveness of SLNs and/or NLCs as nanovehicles for nutraceuticalals with specific properties, e.g., heat-labile or lipid-insoluble bioactives;
2. characterizing the stability and absorption of SLNs and/or NLCs during in vitro simulated digestion and unravelling the relationships between the bioaccessibility and bioavailability of encapsulated nutraceuticalals;
3. developing surfactant-free, food-grade SLNs (or NLCs) as oral nanovehicles for the delivery of nutraceuticalals or bioactives;
4. elucidating the health and function-related effectiveness of encapsulated nutraceuticalals, e.g., using in vitro cell models or in vivo animal models;
5. determining the suitability of incorporating SLNs and NLCs into different types of food formulations, e.g., beverages and milks, and investigating effective drying techniques for obtaining powdered products. Conceptualization, C.-H.T. ; methodology, C.-H.T. ; software, J.-R.D. ; validation, C.-H.T., H.-L.C. and J.-R.D. ; resources, H.-L.C. and J.-R.D. ; data curation, J.-R.D. ; writing--original draft preparation, H.-L.C. ; writing--review and editing, C.-H.T. ; visualization, C.-H.T. ; supervision, C.-H.T. ; project administration, C.-H.T. ; funding acquisition, C.-H.T. All authors have read and agreed to the published version of the manuscript.