Impact of emulsifier nature and concentration on the stability of β-carotene enriched nanoemulsions during in vitro digestion
The presence of emulsifiers facilitates the formation of nanoemulsions and assists in their stabilisation. Moreover, behaviour of nanoemulsions along the gastrointestinal tract primarily depends on their composition, affecting the bioaccessibility of the encapsulated compound. The goal of this work was to study how β-carotene-enriched nanoemulsions prepared with different emulsifiers (Tween 20, lecithin, sodium caseinate, sucrose palmitate) at various concentrations (2%–8%) would affect their stability (particle size and zeta potential) during an in vitro gastrointestinal tract (GIT) digestion. In addition, the lipid digestibility and β-carotene's bioaccessibility of nanoemulsions was determined. Nanoemulsions stabilised with Tween 20, lecithin and sodium caseinate did not present any variation in particle size under stomach phase. After the intestinal GIT phase, all nanoemulsions experienced physical changes, i.e. either increase or decrease in their particle size depending on the nature and concentration of the emulsifier used. The zeta potential of all nanoemulsions was maintained negative throughout the GIT digestion; moreover, it was less negative after the stomach GIT phase (between −24.2 and −1.4 mV). Lecithin-stabilised nanoemulsions presented the highest number of free fatty acids when the emulsifier concentration increased from 2% to 8%. In this sense, nanoemulsions containing 8% of lecithin exhibited the highest β-carotene bioaccessibility (23.5%), suggesting that lecithin can enhance lipid digestion and bioaccessibility of β-carotene encapsulated within nanoemulsions. This study elucidates the importance of not only the emulsifier's nature but also the concentration used when designing nanoemulsions as delivery systems for lipophilic compounds.