FOOD MATRIX INFLUENCES THE APPLICATION OF SOLUBLE PEA PROTEIN-GUM ARABIC MICROCAPSULES AND THEIR IN VITRO DIGESTION

During digestion, the food is broken down into small molecules to be absorbed by the organism. However, the molecules' absorption kinetics depend on the composition and structure of the food matrix. In addition, incorporating delivery systems (i.e., microcapsules obtained from complex coacervation) into food products can play a role in the controlled release of compounds during digestion. Hence, flaxseed oil microcapsules were obtained by complex coacervation using soluble pea protein (SPP) and gum arabic (GA) as wall materials, followed by spray and electrostatic spray drying, and they were applied in liquid yoghurt and sourdough bread. The semi-dynamic in vitro digestion of these products was studied. Three formulations of liquid yoghurt and three formulations of bread were prepared, as follows: Y-SD or B-SD: yoghurt or bread with spray-dried microcapsules; Y-ES or B-ES: yoghurt or bread with electrospray-dried microcapsules; Y or B: yoghurt or bread with free ingredients used in the encapsulation. A standardised semi-dynamic in vitro digestion method (INFOGEST) was employed to study the gastrointestinal digestion of the samples. Digested yoghurt and bread were analysed according to their structure by confocal laser scanning microscopy (CLSM), cumulated protein release, cumulated free NH2 release, fatty acids composition, and total and cumulated free fatty acids release. According to CLSM, stable microcapsules were observed during gastric digestion for yoghurt, but they were visible only until the middle of gastric digestion for bread. Regarding cumulated protein and free NH2 release, there was no significant difference among yoghurt samples until 55 minutes of gastric digestion. However, the Y formulation showed less protein release after 74 minutes of gastric digestion, which was not expected. One hypothesis for this behaviour is that the free SPP was available and positively charged at pH 2-4, resulting in interactions with other constituents of the yoghurt, delaying its release and hydrolysis. When comparing microcapsules formulations, Y-SD showed higher NH2 release than Y-ES, showing that spray-dried capsules were more susceptible to breakdown and to be digested than electrostatic spray-dried ones. Regarding the bread, there was no statistical difference among formulations for protein digestion, but there was a tendency for higher protein release/digestion for formulation with free ingredients. Concerning fatty acids (FAs), 31 and 18 FAs were identified in yoghurt and bread, respectively. More free fatty acids were released during digestion from yoghurt with free flaxseed oil than in formulations with the encapsulated one. Hence, the microcapsules promoted the controlled release of encapsulated oil in the yoghurt samples. A similar behaviour was observed in bread but with no statistical difference. The solid structure of bread promoted the protection of the oil (encapsulated and free), resulting in similar lipid digestion with and without microcapsules. In summary, the incorporation of protein-polysaccharides-based microcapsules into food products resulted in different digestion behaviour, delaying the digestion of encapsulated lipids but accelerating digestion of protein from the microcapsules, especially in liquid food, suggesting a promising approach for various food applications, i.e., intended for weight management by controlling satiety or the feeling of fullness.