Study of extrusion-cooking as tool to enhance the physicochemical, physiology-related and nutrition-related properties of cereal bran

In line with the growing interest in healthy and high-quality food, there is an increasing interest in food products with a high dietary fibre content. Cereal bran incorporation in food systems as an ingredient or as part of wholemeal may be a solution for this problem. Despite the health effects ascribed to bran consumption, it can be hypothesised that the beneficial physiological and nutritional impact of native millers bran can be further improved. Therefore, the aim of this dissertation was to investigate extrusion-cooking as tool to change the structural and physicochemical characteristics of bran and thereby improve the physiology-related and nutrition-related properties. In this context, it was hypothesised that extrusion cooking can increase the accessibility of minerals and bioactive compounds located in the aleurone cells, improve faecal bulking, increase viscosity in the gastrointestinal tract and increase short-chain fatty acid production during colon fermentation.

To achieve this aim, native bran of different cereal sources was firstly characterised to get an idea about the differences in the physicochemical characteristics and the possibly distinct nutrition-related properties of cereal bran starting materials for extrusion-cooking. Wheat, rye, oat and maize bran were selected. A side-by-side comparison of the characteristics of these bran types is, however, confounded by residual endosperm. Endosperm was therefore removed and composition, structural characteristics and in vitro fermentation characteristics of bran of wheat, rye, oat and maize were compared. The second step to achieve the goal of this dissertation, was to investigate extrusion-cooking as technique to modify the structure and properties of wheat and oat bran.

Changing the types of extrusion-cooking and the extrusion parameters led to bran material with distinct physicochemical characteristics. Modeling showed that the extent of structure degradation mainly depended on the level of specific mechanical energy, which can be increased by increasing the number of work sections in the screw configuration and by decreasing moisture content and barrel temperature. Extrusion parameters can thus be changed to achieve desired bran technofunctionality and physiological effects. In addition, it can also be assumed that different types of extrusion-cooking will lead to differences in technofunctionality and sensory perception.