Current dietary guidelines recommend high dietary fibre (DF), low fat and low glycaemic index (GI) diets as means to prevent or manage diet related chronic diseases which have become increasingly frequent amongst younger individuals. However there is a shortage of such products on the market. This study investigates the behaviour of DF in cereal and dairy systems with the aim to screen for DF ingredients that may lead not only to nutritionally valuable, but also to good quality, palatable functional foods. A range of insoluble and/or soluble DF was used in cereal (bread and pasta) and milk (fresh cheese and yoghurt) formulations and their influences on the structural, textural, rheological and overall quality of the products were assessed. The results indicate that DFs can be successfully used to design good quality functional cereal or dairy products, with acceptable or improved attributes. However, it was shown that there is no generic behaviour, which can be applied for each product. Instead, a careful selection of suitable DFs and levels needs to be carried out in relation to the type of product to be made in order to ensure that such products meet consumer expectation with regards to overall quality and sensory characteristics. In vitro and in vivo studies carried out strongly demonstrate that certain types of DFs significantly lowered the GI of the cereal products studied in comparison to the controls. The reduced rate of starch digestibility in products containing these DFs was found to be the result of a combination of factors: reduced starch swelling, changes in the internal structure by formation of a layer coating starch granules, lengthened path between starch granules and a-amylase, and potential inhibition of a-amylase. DFs used were ranked according to their effect on the GI of cereal foods studied. In the dairy products, interactions between DFs and milk proteins were found to promote significant changes in product structure, with direct influence on their rheological properties; in several cases improved sensory attributes of the final products were obtained. Scanning electron microscopy strongly indicated that various different microstructures can be obtained in milk products depending on the type of DF, level used and also on the fat content of milk. This enables the production of low fat dairy products, with non-compromised quality characteristics and which also bring the added health benefits of DFs.

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