Temperature and water-associated changes of cereal starch monitored by TD-NMR and Microimaging

Abstract

International audienceTime domain NMR (TD-NMR) method has been widely used to characterize starch, the major storage carbohydrate of cereals, as evidenced by the numerous relaxometry and diffusometry studies available in literature [Kovrlija, R. and Rondeau-Mouro C. Food Chemistry, 2017]. When starch is heated and then cooled in the presence of water, it undergoes a series of changes known as swelling, gelatinization and retrogradation that induce variations in water distribution, in starch structure and interactions between them. These biochemical transformations can be investigated and quantified using TD-NMR, also convenient for the continuous monitoring of products during processing up to their final structure. Magnetic Resonance microImaging (MRµI) is a complementary technique that can be applied to investigate, with a spatial resolution, the water penetration in cross-linked starch blends and cereal foodstuffs. NMR and MRI techniques could help cereal scientists to better understand the behaviors of macro-molecules in baked products and their interaction with each other and water, and to make products with better quality and shelf-life. This presentation will be focused on the applications of these two methods for characterizing at molecular or millimetric scales, cereal starch-water systems under hydration and/or heating and cooling. We will show TD-NMR results on starch-water systems and dough at various water levels (40-55% wb). Relaxometry measures permitted to simultaneously quantify water transfers and starch changes induced by a thermal processing between 20 and 90°C (10°C steps) followed by a cooling at ambient temperature. In another hand, the application of MRµI to monitor the water sorption kinetics in starch-glycerol extrudates allowed going ahead in the multi-scale approaches by distinguishing between various water diffusion behavior (Fickian or case II case), in relation with different physical and mechanical properties of starch-based products