Scientific contact: Corinne Rondeau
Water is often the main component in food products. Water has an impact on technological transformation parameters and the physical and organoleptic characteristics of products as well as their stability over time. As starch is also a key ingredient in many food products and cereal products in particular, it seems essential to understand water transportation phenomena in starchy systems, especially as water is also known to play a structural role in these systems. The research carried out by the MRI-Food team confirms that NMR and MRI techniques make it possible to measure the compartmentalization of water in starch grains along with the changes it undergoes (decompartmentalization/exchange) when cooking and cooling cereal products (gelatinization/retrogradation).
Recently, the team developed two-dimensional acquisition methods using low field NMR (NMR 2D T1-T2) that provide additional information to traditional NMR 1D methods (Rondeau-Mouro et al., (2016) JMR 265 :16-24). This method has been used to reveal chemical exchange phenomena coupled to dipolar interactions between water and starch (or its components), thereby facilitating the interpretation of the T1 and T2 relaxation times traditionally measured in 1D. Similar methods using DSC (partnership with INRA Nantes) clearly demonstrated that only NMR can differentiate the various thermokinetic phenomena measured by DSC, specifically the thawing of amylopectin crystals, while quantifying the phenomena and specifically characterizing water transfers linked to the hydrothermal transformation of starch. These NMR developments are supported by specific data processing methods based on entropy maximization without data compression (partnership with Irccyn JRU, Ecole Centrale de Nantes). We have developed original code using Matlab to reconstruct 2D T1-T2 maps as well as Diffusion-T2 maps that should help interpret water diffusion measurements in this type of porous and very heterogeneous system from a structural and compositional perspective. In addition to molecular mobility across several microns, water profile measurements using micro-imaging indicate that the method could be used to quantify transportation diffusion phenomena such as water sorption in extruded starch produced across several millimeters over 24 hours.