Dietary fibre composition and sensory analysis of heat treated wheat and rye bran

Abstract: When grains of wheat and rye are conventionally milled, large quantities of bran classified as by-products are left and are mainly used for animal feed. Bran is a complex material composed of the aleurone layer, nucellar epidermis, a seed coat, a fruit coat and a small proportion of the germ and endosperm depending on extraction rate. The bran fraction consists of approximately 40-50 % dietary fibre which can contribute to increase the nutritional quality of human cereal food. It would also be valuable for the food industry to convert by-products as bran to products with higher commercial values. The aim of this thesis was to analyse the content and composition of dietary fibre of heat treated wheat and rye bran according to the Uppsala method with some modifications in order to analyse soluble and insoluble dietary fibre separately. Half of the bran samples were precooked, dried and roasted and the other half dried and roasted (uncooked). The aim was also to perform a sensory test according to a line scaling test to evaluate the flavour intensity between selected wheat bran samples and determine the particle size of all bran samples. The results in this thesis showed that the total dietary fibre (TDF) content decreased with increasing roasting temperature and the uncooked bran samples had a higher content than the precooked. TDF ranged between 41.3-44.8 % for the wheat bran samples (untreated 42.5 %). For the rye bran samples TDF ranged between 43.7-46.6 % (untreated 43.0 %). The insoluble dietary fibre content decreased with increasing roasting temperature which can be due to fragmentation of polysaccharides during the heat treatment. The pre-treated, precooked and uncooked, samples had though a slight increased content of insoluble dietary fibre compared to the untreated wheat and rye bran. The content of soluble dietary fibres was not significantly affected by temperature or pre-treatment in either wheat or rye bran. The precooked wheat bran samples had a more roasted flavour than the uncooked, where higher roasting temperature led to a more intense flavour. The uncooked samples were sweeter and had a more rancid flavour than the precooked samples. The particle size was in general larger for the wheat bran, especially in the precooked samples, than in the rye bran samples.