Transglutaminase modification affects in vitro gastric digestion of pea protein and duodenal lipolysis of emulsions.

The objective of the present work was to assess if the degree of crosslinking of pea proteins (PPI) by transglutaminase (TG) affects the in vitro gastric digestion of pea proteins in the bulk and at the oil-water interface as well as the duodenal lipolysis of the emulsions. PPI samples were prepared at protein concentrations of 10-18 % w/w and 1 % TG at 37 °C and characterized by small deformation tests and texture measurements. The degree of crosslinking linearly decreased with the increase of protein concentration and at the same time a loss of elasticity occurred. However, both the storage modulus G' and gel hardness increased with increasing protein concentration. These three crosslinked proteins were tested regarding their susceptibility to be hydrolysed by pepsin as well as the behaviour of their emulsions during in vitro gastroduodenal digestion. As the degree of crosslinking of the samples increases and they are more homogeneous (lower PPI concentration), they are more rapidly hydrolysed by pepsin in the bulk because the enzyme and the acid may easily diffuse into the gel microparticles. At the interface, lower degrees of PPI crosslinking would allow a higher structural flexibility, exposing peptide bonds that pepsin can more easily cleave. The rate of lipolysis increased as the degree of crosslinking decreased but at the end of duodenal digestion they converged to similar values. A correlation was found between the kinetics of gastric proteolysis of emulsions mediated by pepsin and the kinetics of duodenal lipolysis.