Freeze drying and structure effects on in vitro protein digestion of some plant foods

IntroductionPlant proteins have recently gained attention in research and industrial areas by their relatively modestenvironmental, ethical and economic impact.ObjectiveFood structure associated to food processing are known to generally impact sensitivity of proteinsto digestive enzymes.MethodologyFour plant-based foods produced from different protein sources (soy, pea or wheat) and offeringdifferent structure and their corresponding concentrate or isolate were digested following the INFOGESTprotocol. Since tofu and seitan cannot be stored without structure degradation, the impact offreeze drying on protein digestion was also studied. Proteolysis progress was followed by monitoringthe release of free amino-groups and proteolysis degree was assessed. Multi-scale characterizationof foods was performed to allow data interpretation.Main findingsPea emulsion exhibited similar droplet size and lipid content than soymilk, only the protein sourcechanged. Final proteolysis degree was higher with pea (60 %) than soy (45 %). When comparingthe same source, protein digestion of tofu was more extensive than that of soymilk. This could beexplained by differences in macrostructure since tofu is obtained through soy protein coagulation,but also by differences in the origin of beans. Indeed, proteolysis degrees at the end of the intestinalphase were different between protein isolates created from beans used for tofu vs soymilk (15% vs 40 %). Proteins of tofu isolate were less hydrolyzed than tofu (15 % vs 26 %), that could beexplained by different protein denaturation levels. Comparing a simple solubilization of commercialpea isolate with its emulsion with soy lipids, proteolysis was twice higher for the emulsion (60 % vs30 %).ConclusionUltimately, freeze-drying effect of protein digestion was highlighted for seitan, increasing final proteolysisrate from 9 % to 22 %, but not for tofu explained through enzymatic accessibility improvedafter freeze drying in the case of seitan.