Co-encapsulation of β-carotene, lutein, zeaxanthin and fish oil: An investigation of drying kinetics, powder properties, in vitro digestion and cellular uptake of carotenoids

Abstract

Carotenoids (β-carotene, lutein, zeaxanthin) and fish oil are beneficial to ocular health because of their provitamin A activity and antioxidant activities. Microencapsulation was reported to be an effective method to preserve and deliver these bioactives However, research on the co-encapsulation of β-carotene, lutein, zeaxanthin, and fish oil has been limited. This research was conducted to fill the research gap, using a microfluidic-jet spray drying (MFJSD) method to co-encapsulate these carotenoids with fish oil. The research aimed to provide a better fundamental understanding on the relation of drying kinetics and wall materials, physicochemical properties of the microcapsules and drying methods, as well as digestion and cellular uptake of the encapsulated bioactives. Wall materials (whey protein isolate (WPI), OSA modified starch and the combination of the two materials) were applied, and a systematic comparison between the MFJSD, two-fluid nozzle spray drying (SD) and freeze drying (FD) were conducted. This was followed by an investigation of the physicochemical properties, storage stability and in vitro digestion behaviours of the microcapsules produced. Thereafter, the cellular uptake of carotenoids in the MFJSD microcapsules was studied using a Caco-2 cell model. Firstly, the potential synergistic effect of β-carotene, lutein, zeaxanthin on antioxidation was studied. The results showed that the combination of β-carotene, lutein, zeaxanthin gave a synergistic antioxidant effect against the fish oil oxidation. Parameters for obtaining stable emulsion were obtained, including homogenisation conditions (12000 psi and three passes), wall material effect and solid content. A thin film drying method was then used to study the drying behaviours of the emulsions containing different wall materials and oil loadings. The results from the thin-film drying experiments revealed that higher drying temperature led to a faster drying rate and lower moisture content at the initial stage of drying. The drying rate of the WPI emulsion was lower than that of the OSA and WPI/OSA emulsions due to the earlier formation of crust. The oil loadings affected the drying behaviours of emulsions due to lower heat transfer coefficient and thermal conductivity of oil than water. Compared to the WPI emulsion, the drying kinetics of the emulsions containing OSA modified starch can be more accurately predicted by the characteristic drying curve (CDC) model. The MFJSD method was used to produce spray-dried microcapsules from the emulsions containing carotenoids-fortified fish oil. The MFJSD microcapsules using WPI as wall material showed a significantly different morphology compared to the microcapsule using OSA modified starch as wall material. From the MFSJD, higher inlet temperature and lower solid content could result in lower moisture content and water activity. The highest microencapsulation efficiency (97.1%) among all samples was obtained at the inlet temperature of 180 °C, solid content of 20%. A higher wall to core ratio (4:1) would lead to a higher microencapsulation efficiency (96.3%), a better reconstitution quality, a higher density (tapped density of 0.37g/cm3) and a higher flowability (Carr’s index of 15.8%). The Tg showed a strong relationship with wall material type while not with the wall-to-core ratio. Comparing the three drying methods (MFJSD, SD and FD), the MFJSD microcapsules presented spherical particles with good uniformity in size and morphology, while the SD and FD microcapsules presented irregular particles with varied sizes and morphology. The MFJSD microcapsules showed higher microencapsulation efficiency (94.0-95.1%), tapped density (0.37-0.65 g/cm3) and flowability (Carr's index of 16.0-30.0%), as well as better reconstitution properties than the SD and FD microcapsules. From the in vitro digestion, the digesta from different drying techniques did not show significant differences in droplet size and zeta potential, the release of free fatty acids, and the bioaccessibility of carotenoids. On the other hand, the digesta produced by different wall materials showed a significant difference in these properties. This indicated that the digestion behaviours were mainly influenced by the wall materials rather than the drying techniques used for co-encapsulation. Results from the Caco-2 cell model showed that lutein (0.52 μg/mg protein) and zeaxanthin (0.54 μg/mg protein) in the MFJSD microcapsules had a higher cellular uptake than β-carotene (0.31 μg/mg protein). The carotenoids encapsulated by the MFJSD had a higher cellular uptake than those delivered by the methylcellulose and xanthan gum systems. This study has systematically investigated the co-encapsulation of β-carotene, lutein, zeaxanthin, and fish oil and explored the powder properties as affected by drying techniques, emulsion formula, and drying conditions. It has provided valuable scientific information on the fabrication of microcapsules containing multiple lipophilic bioactives for functional food application.