In Vitro 1h Mt and Cest MRI Mapping of Gastro-Intestinal Milk Protein Breakdown

Abstract

Protein digestion is commonly studied using in vitro models. However, validating these models with in vivo data is challenging. Here, we explore the use of Magnetization Transfer (MT) and Chemical Exchange Saturation Transfer (CEST) MRI for non-invasive monitoring of protein solubilization and hydrolysis during static in vitro digestion using skim milk (SM) as a test food. We measured CEST spectra of unheated and heated SM during gastric digestion, from which a measure for soluble proteins/peptides was obtained by calculating the asymmetric MT ratio (MTRasym).  We also obtained the semi-solid volume (vss), MT ratio (MTR) and MTRasym from the same measurement, within 1.3 min of scan time. The MTRasym area increased with gastric digestion, due to solubilization of the initially-formed coagulum, and a mean difference of 20±7% was found between unheated and heated SM (p<0.005). The vss and MTR decreased during gastric digestion and can be used to monitor changes in the amount and structure of the coagulum, but not for assessment of soluble proteins/peptides. The MTRasym increased for heated SM during gastric and intestinal digestion, proving sensitive to protein solubilization and hydrolysis. Hence, the MTRasym is suitable for in vitro monitoring of protein hydrolysis at later stages of digestion.

Keywords: Magnetic Resonance Imaging, in vitro digestion, protein coagulation, Chemical Exchange Saturation Transfer, Magnetization Transfer