Inclusion of liposoluble bioactive compounds in fortified foods represents a complex challenge due to the labile nature of such compounds and the instability of oil-in-water emulsion-based delivery systems. In the present study, dispersions prepared with 10% (w/w) sunflower oil (SO) or hydrogenated palm kernel oil (HPKO) containing 0.05% (w/w) β-carotene were stabilized by various concentrations of whey protein isolate (WPI) or sodium caseinate (NaCas) (0.1 to 2.0% w/w) in 30% (w/w) sucrose aqueous solutions. Physicochemical characterization of emulsions was done considering the particle size, the particle surface protein coverage, and the physical state of continuous and dispersed phases. Physical stability of the systems and their protection properties on β-carotene were compared. The lipid carrier type and interfacial structure were investigated as the two key factors which regulate the stability of labile lipophilic bioactive molecules in food model systems. Our results showed high β-carotene stability when O/W systems were stable (protein concentration ≥0.8% w/w.) A (partially) solid lipid carrier (HPKO) enhanced protection compared to the liquid carrier (SO) as the bioactive molecules were entrapped in isolated domains within the solid lattice and kept apart from reactive species in the surroundings. NaCas provided a better barrier than WPI due to the different amino acid composition and interface structure which significantly reduced β-carotene degradation rate.
Liposoluble bioactive compounds are often included in foods in emulsified lipid carriers. In the present study, the impact of the physical state of the lipid carrier and the interfacial composition of oil-in-water emulsions on the stability of β-carotene was studied. Emulsions with hydrogenated palm kernel oil (HPKO) concentration of 10% (w/w) dispersing 0.05% (w/w) β-carotene, and a water phase at pH 7 containing 30% (w/w) sucrose, were stabilized by 1%, 1.5%, 2%, and 3% (w/w) whey protein isolate (WPI). Crystallization and melting behavior of emulsified and bulk HPKO were studied by differential scanning calorimetry. The hysteresis of emulsified HPKO crystallization (onset approximately 10 °C; endset approximately 6 °C) and melting (onset approximately 17 °C; endset approximately 45 °C) allowed us to operate at 15 °C on systems with identical compositions but different physical states of the same lipid phase. Surface protein coverage of emulsions was calculated and size of the dispersed particles was characterized by dynamic light scattering. β-Carotene contents of the emulsions during storage at 15 °C was analyzed spectrophotometerically. Results highlighted an impact of the phase of the lipid carrier and of the concentration of WPI on β-carotene degradation. β-Carotene loss showed zero-order kinetics. A liquid dispersed phase resulted in a low degradation rate but a high concentration of protein on a solid lipid carrier was likewise effective for β-carotene protection. Practical Application: The inclusion of lipophilic bioactive compounds, such as carotenoids, is a current trend in the production of functional foods aiming to enhance health and well-being. However, the use of functional ingredients in food products is complicated because of the sensitivity of the active molecules to physical and chemical factors to which they are exposed during processing, storage, and consumption. The present work gives indications of the influence of the lipid carrier physical state and surface structure on ß-carotene stability in formulated oil-in-water liquid food models, suggesting possible strategies for an enhanced stabilization of lipophilic labile compounds.
Stability of oil-in-water emulsions during freezing and thawing is regulated by the phase transitions occurring in the continuous and dispersed phases upon thermal treatments and by the composition of the interfacial membrane. In the present study, the impact of the water phase formulation (0-2.5-5-10-20-30-40% w/w sucrose), the interfacial composition [whey protein isolates (WPI) or sodium caseinate (NaCas) used at different concentrations], and the particle size on the stability of hydrogenated palm kernel oil (30% w/w)-in-water systems was investigated. Phase/state behaviour of the continuous and dispersed phases and emulsion destabilisation were studied by differential scanning calorimetry. System morphology was observed by particle size analysis and optical microscopy. The presence of sucrose in the aqueous phase and reduced particle size distribution significantly improved emulsion stability. WPI showed better stabilising properties than NaCas at lipid to protein ratios of 10:1, 7.5:1, 5:1 and 4:1. Increased WPI concentration significantly improved emulsion resistance to breakdown during freeze-thaw cycling. NaCas showed poor stabilising properties and was ineffective in reducing emulsion destabilisation at 0% sucrose at all the lipid to protein ratios.
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