Emulsion-based delivery systems as a strategy to improve functionality of β-carotene

Resumen

Bioactive compounds are of great interest for consumers, food industries and researchers due to their potential health benefits. However, the low aqueous solubility, stability and bioavailability of some lipophilic bioactive compounds, such as β-carotene, greatly compromise successful incorporation within foodstuffs. Recent advancements in encapsulation and protection of bioactive compounds has opened new possibilities for the development of enriched novel food products, with special attention to emulsion-based delivery systems. However, composition of these systems clearly determines their physicochemical properties and functionality. Thus, the main goal of this Doctoral Thesis was to use stabilisers of different nature to formulate emulsion-based systems for a successful β-carotene delivery. β-carotene nanoemulsions formulated with different emulsifiers (Tween 20, lecithin, sodium caseinate and sucrose palmitate) at various concentrations (2-8%) were subjected to an in vitro gastrointestinal tract (GIT) and their physicochemical properties were also determined. Lecithin-stabilised nanoemulsions at 8% presented the highest release of free fatty acids (100%) after lipid digestion, and in turn, exhibited the highest β-carotene bioaccessibility (23.5%). Furthermore, the permeability across two intestinal barrier models (Caco-2 and Caco-2/HT29-MTX co-cultures) was evaluated. Nanoemulsions stabilised with lecithin had a β-carotene concentration in Caco-2 cells lysates significantly higher (2.28%) compared with those containing sodium caseinate (1.72%). On the contrary, the concentration of β-carotene was significantly lower in Caco-2/HT29-MTX co-cultures cell lysates (≥0.74%), with no significant differences between both emulsifiers. Different mandarin fiber concentrations (0-2%) were added to β-carotene-enriched nanoemulsions. Although nanoemulsions exhibited similar physicochemical properties along the different phases of the in vitro gastrointestinal tract (GIT), similar lipid digestibility and β-carotene bioaccessibility was obtained among nanoemulsions. However, a significant increase in β-carotene bioaccessibility was observed for those nanoemulsions containing until 1% of mandarin fiber. Tertiary emulsion (lactoferrin/alginate/ε-poly-L-lysine) was developed as a β-carotene carrier. Its physical stability and β-carotene content under external stresses (temperature, pH and ionic strength changes), as well as functionality were evaluated. Tertiary emulsion presented a great particle size after extreme temperatures (≥70ºC), acidic conditions (≤4) or with salt addition (≥0.1M), while a small particle size was observed at basic pH. In addition, β-carotene content in tertiary emulsions decreased only 40% when emulsions were subjected at temperatures <70 °C, in acidic conditions and below 0.3 M NaCl. Finally, tertiary emulsions exhibited higher lipid digestibility (83.59%) and β-carotene bioaccessibility (70.10%) compared with primary and secondary emulsions. Results obtained in the present Doctoral Thesis provide useful information about how composition of emulsion-based systems enriched with β-carotene might have an influence on their physicochemical properties, stability under in vitro GIT and stress conditions, as well as, lipid digestibility and β-carotene delivery. These systems can be considered as promising vehicles for lipophilic compounds, which might open new perspectives for designing functional food products with outstanding benefits for consumers.