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Citrus pectin (CP) and sugar beet pectin (SBP) were demethoxylated and fully characterized in terms of pectin properties in order to investigate the influence of the pectin degree of methyl-esterification (DM) and the pectin type on the in vitro β-carotene bioaccessibility and lipid digestion in emulsions. For the CP based emulsions containing β-carotene enriched oil, water and pectin, the β-carotene bioaccessibility, and lipid digestion were higher in the emulsions with pectin with a higher DM (57%; "CP57 emulsion") compared to the emulsions with pectin with a lower DM (30%; "CP30 emulsion") showing that the DM plays an important role. In contrast, in SBP-based emulsions, nor β-carotene bioaccessibility nor lipid digestion were dependent on pectin DM. Probably here, other pectin properties are more important factors. It was observed that β-carotene bioaccessibility and lipid digestion were lower in the CP30 emulsion in comparison with the CP57, SBP32, and SBP58 emulsions. However, the β-carotene bioaccessibility of CP57 emulsion was similar to that of the SBP emulsions, whereas the lipid digestion was not. It seems that pectin type and pectin DM (in case of CP) are determining which components can be incorporated into micelles. Because carotenoids and lipids have different structures and polarities, their incorporation may be different. This knowledge can be used to engineer targeted (digestive) functionalities in food products. If both high β-carotene bioaccessibility and high lipid digestion are targeted, SBP emulsions are the best options. The CP57 emulsion can be chosen if high β-carotene bioaccessibility but lower lipid digestion is desired.

Protein particles are promising systems for encapsulation purposes and structure building and stabilization in a food context (Arroyo-Maya & McClements, 2015; Oduse, Campbell, Lonchamp, & Euston, 2017). Whey protein isolate (WPI) nanoparticles can be easily produced using liquid antisolvent precipitation. An additional particle hardening step is however often required, since WPI particles tend to disintegrate in aqueous environment. In this study, the potential of different food-grade aldehydes (i.e. cinnamaldehyde, salicylaldehyde, syringaldehyde, vanillin and p-anisaldehyde) to stabilize the protein particle matrix was explored. In general, the largest increase in stability against disintegration was observed for vanillin-treated particles. Incubation with vanillin did not only improve particle stability in aqueous environment, but also during isothermal storage (T = 6, 23 or 37°C for 3 weeks) and thermal treatment (T ≤ 80°C for 30 min). Although less pronounced, an increased particle stability in aqueous environment was also observed after salicylaldehyde or syringaldehyde treatment. All particles however disintegrated at pH values far removed from their isoelectric point (IEP ≈ pH 4.9), while extensive aggregation was observed near the IEP and under variable salt concentrations (0-250 mM NaCl). Vanillin treatment did not induce conformational changes or covalent bond formation within the particle matrix. Therefore, the observed hardening effect presumably results from non-covalent interactions between vanillin and protein molecules. The provided insights will serve as a basis to further optimize the stabilization of protein-based systems, with the eventual goal of increasing their application potential in the food industry.

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