Het ontwerpen van innovatieve olie-in-water emulsies om nutriëntenvertering in het gastro-intestinale systeem van vleeskuikens te beïnvloeden

Poultry meat is one of the most consumed types of meat worldwide, with consumption and production still rising yearly. For this reason, feed producers and researchers are constantly looking to optimize broiler performance to improve the sustainability and cost of broiler production. One way to do so is by decreasing the feed conversion ratio, also referred to as FCR. One commonly applied approach to reach this goal is adding emulsifiers to oil-supplemented feed. Young broilers secrete insufficient quantities of bile salts and lipase to efficiently digest lipids. Therefore, emulsifiers are hypothesized to aid (i) emulsification in the gizzard, (ii) mixed micelle formation, and (iii) nutrient absorption, thereby improving the FCR. However, extensive research in food technology revealed the significant improvement in lipid digestion by preparing oil-in-water (o/w) emulsions upfront rather than relying on emulsification in the gastrointestinal system. Additionally, research regarding o/w emulsion design demonstrated the advantage of using multiple emulsifiers to steer in vitro lipid digestion kinetics instead of a singular emulsifier. In doing so, distinct emulsifiers with specific properties (e.g. molecular structure, hydrophobicity, …) can each differently influence processes occurring throughout digestion such as emulsion stability, bile salt and lipase adsorption, and mixed micellization. Therefore, the aim of this PhD was twofold. The first objective was to evaluate and understand the effect of o/w emulsion-supplemented feed on broiler performance in contrast to feed supplemented with oil and emulsifiers separately. The second objective of this PhD was to design o/w emulsions exploring alternative biobased emulsifiers and emulsifier mixes. This PhD project is a collaboration between KU Leuven and Kemin Industries. Therefore, the reference emulsifier mix used in this PhD was Lysoforte extend® (LEX), consisting of three emulsifiers: lysolecithin (LL; 90%), monoolein (MG; 9%), and glyceryl polyethyleneglycol ricinoleate (SYN; 1%). To achieve these objectives, this PhD manuscript was divided into three parts. The first part of this PhD focused on the development of an in vitro digestion model to simulate the broiler gastrointestinal tract. First of all, this PhD aimed to obtain in-depth insights on the effect of feed structural design on the in vitro digestion process resulting in a decreased need for in vivo work. However, a standardized in vitro digestion model simulating the broiler GIT was lacking. Research showed the importance of using appropriate digestive conditions to simulate digestion as they can significantly affect digestion kinetics (i.e. rate and extent). Therefore, Part I of this research focused on determining appropriate digestive conditions, more specifically bile salt concentration and lipase activity, to simulate lipid digestion of starter, grower, and finisher broilers in vitro. Increasing lipase activity significantly increased digestion extents. The digestion rate constant was influenced by both lipase activity and bile salt concentration. Digestion was slowed down by too little bile salts, and hindered by an excess of them. These results showed the significant impact of digestive conditions on lipid digestion kinetics. Consequently, it is strongly suggested to use these adapted in vitro digestive conditions to simulate the broiler GIT in different life stages when possible. Part II of this PhD research focused on understanding the LEX emulsifier blend impact on lipid digestion. In particular, it was aimed to uncover how (i) LEX emulsifiers influence in vitro lipolysis kinetics, and (ii) how LEX-emulsion supplemented feed influences in vivo broiler performance and nutrient digestibility. For this purpose, the dynamic interfacial tension profile of LEX constituents and combinations thereof were evaluated once using a standard pendant drop tensiometer and once using a pendant drop tensiometer equipped with subphase exchange software. Additionally, in vitro lipolysis using both a standardized consensus protocol and limiting starter digestion conditions was simulated. The latter was additionally assessed using the subphase exchange pendant drop tensiometer to evaluate changes in the interfacial tension profile as well as droplet rheology. Simultaneously, microstructural changes in o/w emulsions during in vitro digestion were assessed. These results revealed the substantially different role of each LEX emulsifier in affecting different steps of the lipid digestion process. SYN strongly adsorbed to the interface, provided o/w emulsion stability throughout the simulated GIT, and was strongly hypothesized to aid mixed micellization of lipid digestion products. On the contrary, MG adsorbed weakly to the interface and negatively affected emulsion stability throughout in vitro digestion when present in higher quantities. LL adsorbed relatively strongly to the interface and largely impacted LEX in vitro digestion kinetics. Subsequently, a three-week in vivo trial was conducted to assess the impact of feed supplemented with LEX-emulsion on the performance of broilers. Compared to broilers fed conventional feeds containing oil and LEX separately, those fed the emulsion-supplemented feed exhibited a significantly higher body weight gain during the first two weeks and a lower feed conversion rate. Complementary in vitro digestion experiments of the identical in vivo diets showed differences in in vitro starch, protein, and lipid digestion kinetics. This implied that emulsification affected in vitro starch and protein digestion kinetics in addition to in vitro lipid digestion kinetics, presumably adding to the positive impact on in vivo broiler performance. Therefore, this part of the PhD demonstrated how LEX components influenced different in vitro digestion parameters and in vivo performance. These insights can be used to further optimize emulsifier mixes to steer in vitro digestion relevant for broilers and consequently in vivo performance. The last part, Part III, of this PhD research evaluated the potential of alternative biobased emulsifiers, more specifically glycolipids. Six glycolipids were assessed by evaluating their effect on the dynamic interfacial tension as well as on starter and grower in vitro lipid digestion kinetics. Simultaneously, potential microstructural changes occurring during in vitro digestion were evaluated. Although molecular differences were small, they substantially affected their affinity for the oil-water interface. Three characteristics increased their affinity for the interface: (i) a higher number of acetyl groups, (ii) a lower area per molecule needed on the interface, and (iii) a lower tendency for self-assembly. However, in vitro lipid digestion kinetics were mainly influenced by emulsion stability during in vitro digestion. More hydrophobic glycolipids were unstable at the lower pH 3 during simulated gastric digestion, resulting in lower in vitro small intestinal lipid digestion extents. The understanding of how minor molecular differences significantly impact interfacial properties can be further investigated to design o/w emulsions and, as a result, steer in vitro lipid digestion kinetics, perhaps in mixes including LL mentioned above. In conclusion/overall, this PhD work showed how the different LEX emulsifiers played a role in affecting in vitro lipolysis kinetics. Additionally, it demonstrated the potential of using glycolipids to steer the interfacial composition. Hence, this work provides perspectives for further research to explore alternative emulsifier mixes to modulate in vitro lipolysis kinetics. These insights could subsequently be used to design o/w emulsions to further improve broiler performance using o/w emulsion-supplemented feeds. Lastly, the work provided a foundation for the in vitro simulation of digestion in animals with substantially different digestive conditions. Therefore, it creates opportunities for an increased use of in vitro feed structural design research.