Research background: Various approaches have been used to present functional lipids including lycopene in a palatable food form to consumers. However, being highly hydrophobic, lycopene is insoluble in aqueous systems and has a limited bioavailability in the body. Lycopene nanodispersion is expected to improve the properties of lycopene, but its stability and bioaccessibility are also affected by emulsifier type and environmental conditions such as pH, ionic strength and temperature.
Experimental approach: The influence of soy lecithin, sodium caseinate and soy lecithin/sodium caseinate at 1:1 ratio on the physicochemical properties and stability of lycopene nanodispersion prepared using the emulsification-evaporation methods before and after treatment at different pH, ionic strength and temperature were investigated. The in vitro bioaccessibility of the nanodispersions was also studied.
Results and conclusion: Under neutral pH conditions, nanodispersion stabilized with soy lecithin had the highest physical stability and the smallest particle size (78 nm), the lowest polydispersity index (PDI) value (0.180) and highest zeta potential (-64 mV) but the lowest lycopene concentration (1.826 mg/100 mL). Conversely, nanodispersion stabilized with sodium caseinate had the lowest physical stability. Combining the soy lecithin with sodium caseinate at 1:1 ratio resulted in a physically stable lycopene nanodispersion with the highest lycopene concentration (2.656 mg/100 mL). The lycopene nanodispersion produced by soy lecithin also had high physical stability under different pH range (pH=2-8) where the particle size, PDI and zeta potential remained fairly consistent. The nanodispersion containing sodium caseinate was unstable and droplet aggregation occurred when the pH was reduced close to the isoelectric point of sodium caseinate (pH=4-5). The particle size and PDI value of nanodispersion stabilized with soy lecithin and sodium caseinate mixture increased sharply when the NaCl concentration increased above 100 mM, while the soy lecithin and sodium caseinate counterparts were more stable. All of the nanodispersions showed good stability with respect to temperature changes (30-100 °C) except for the one stabilized by sodium caseinate, which exhibited an increased particle size when heated to above 60 °C. The combination of soy lecithin and sodium caseinate was found to increase the bioaccessibility of the lycopene nanodispersion. The physicochemical properties, stability and extent of the lycopene nanodispersion digestion highly depend on the emulsifier type.
Novelty and scientific contribution: Producing a nanodispersion is considered one of the best ways to overcome the poor water solubility, stability and bioavailability issues of lycopene. Currently, studies related to lycopene-fortified delivery systems, particularly in the form of nanodispersion, are still limited. The information obtained on the physicochemical properties, stability and bioaccessibility of lycopene nanodispersion is useful for the development of an effective delivery system for various functional lipids.
Keywords: bioaccessibility; emulsifier; lecithin; lycopene; nanodispersion; sodium caseinate.