The characterization of zein/xanthan gum composite oleogel: A comparative study of bioactive substances in interface and oil phases

Bioactive substances can be strategically positioned in different locations within a system to regulate its functionality. In this study, we investigated the effects of loading curcumin into two different mediums (interface layer (M1O) and corn oil (M2O)) on the macro- and micro-properties of a zein-xanthan gum (XG) oleogel, aimed at utilizing the oleogel as a fat substitute. The results revealed that the oleogel exhibited a spongy porous bridging network structure, particularly prominent in M2O, which showed a higher elastic modulus (G ') and an impressive structural recovery rate, reaching up to 98.50 +/- 0.60%. While the location of curcumin loading had minimal impact on the oleogel's macro-properties (such as rheology, thermal behavior, and oil binding capacity), significant differences were observed in the micro-properties. The oleogel maintained a high encapsulation efficiency (EE), exceeding 85% in both loading locations, with M1O slightly outperforming M2O. Notably, M2O showed lower free fatty acid release and higher bioaccessibility (about 10% greater than M1O), which was attributed to a denser spongy porous network enhanced by electrostatic attraction, hydrogen bonding, and hydrophobic interactions within the zein-XG matrix. Curcumin underwent significant degradation under prolonged UV and alkaline conditions, but showed minimal damage when exposed to heat in both mediums. Additionally, M2O demonstrated superior UV and thermal stability compared to M1O, which showed better pH stability. Cookies made with oleogel as a butter alternative exhibited improved appearance and quality when added at medium or low levels. This study suggests a viable method for manipulating the loading locations of bioactive substances in oleogel according to specific needs, potentially paving the way for the development of zein-XG oleogel as an effective butter substitute.