MOLECULAR CHARACTERIZATION OF PROTEINS IN FOOD MATRICES: HOW THEIR STRUCTURE EVOLVE FROM RAW MATERIALS TO FINISHED PRODUCTS

Proteins have a fundamental importance for their peculiar chemical characteristic, implication in metabolism and structure for all living organisms. In food systems, proteins provide both nutritional and non-nutritional functionalities and, with other macromolecules, contribute in define the characteristics of the food systems. Technological and biotechnological treatments used in food processing are also responsible for the formation of new inter- and intra-molecular interactions, driven by changes in the structure of proteins, often in association with other food components. In the present PhD thesis, the structural evolution of proteins from raw materials to finished products was studied in different food systems, with the aim of connecting protein molecular features - and the changes they undergo upon processing - with their functional properties. This PhD thesis aims at improving the current understanding of the structure/function relationship of macromolecules in various food systems, and of how the new relationships affect their technological properties. The approaches and results presented are of practical relevance for the food industry, that require to understand how to tailor processes in order to fit the nutritional, sensorial and environmental requests from the consumers. The introduction (Chapter 2) provides a review of the current knowledge and of the approaches used to study the structure of proteins in food systems. The gluten network is used as a model system in this context, because of its high level of complexity and of its importance in defining the properties of cereal-based food systems. The first four sections (4.1, 4.2, 4.3 and 4.4) of the Results presents the structural and geometrical events leading to the formation of the gluten-network, and discusses some novel approaches set-up to investigate the three- dimensional rearrangements resulting from a transformation process (such as bread making). These approaches were also applied to clarify the impact of other macromolecules (amylose and amylopectin) in the gluten-network development, that in turn affects the properties of the derived products. Sections 4.5, 4.6 and 4.7 discusses the impact of technological treatments on proteins in gluten-free flours, using lentils as a model and analyzing protein structural changes as a function of different technological treatments. Biochemical characterization was one prong of a multidisciplinary approach (rheology and calorimetry) that showed how the technological treatments affect the protein structure, improving the transformability of lentis flour in gluten- free pasta. Pseudo cereals, such as buckwheat (Section 4.8), represent a suitable system to show how biotechnological treatments like sprouting can positively affect the nutritional properties, also thanks to modification of the protein pattern and structure. The overall features of proteins in sprouted grains made them more suitable for the formation of protein network, useful for appropriate texturing of specific foods, like couscous. The nutritional properties were assessed in couscous fortified with the sprouted flour, after a simulation of an in vivo digestion. Finally, proteins can also impact the flavor of the products acting as a source of reactive and/or bioactive components, often originated by breakdown by endogenous or added proteases. In Sections 4.9, 4.10 and 4.11, the nature and amount of peptides and amino acids released during fermentation of cocoa was related to the selected inoculum and to the flavor of the final product.