Simultaneous determination of macronutrient digestibility of two model foods: Introduction of an integrated preparation method harmonized with the INFOGEST protocol

There have been attempts for standardisation of INFOGEST-linked analytical protocols in order to provide more comprehensive data on nutrient digestibility. Centred around the commonly shared aspects of these methodologies, an integrated sample preparation method - based on the selective isolation of the Bligh and Dyer extraction - has been proposed, tested for several analytes on four matrices (blank digesta (water, protein-free biscuit), canned chickpeas, wholewheat cereal) using various analytical techniques and established to determine endpoint digestibility and kinetics of nutrient release of the two food matrices. Mechanistic considerations for determination of bioaccessible protein and carbohydrate content were evaluated using HPLC-SEC and HPLC-RID, respectively and data showed appropriate separation of the bioaccessible analytes. The results of the recovery experiments (70-120 % yield for all bioaccessible analytes) have provided a valid ground for the use of the selective isolation. Canned chickpeas showed high protein (91-93 %), and medium carbohydrate (35-47 %) and lipid digestibility (48 %), and wholewheat cereal showed high protein (83-107 %) and carbohydrate (70-89 %), and medium lipid digestibility (57-61 %). Moreover, results showed that digestibility of cysteine and tryptophan are largely dependent on the food matrix however other amino acids show similar release which could be modelled by the release of leucine. Fatty acid (FA) specific results showed that despite the difference in the gastric release of saturated and unsaturated FAs overall release is not influenced by this effect.