Effect of extrusion cooking on β-glucan and fructan in wheat and rye bran

Sammanfattning: In cereal industry, when cereal grains are milled to extract the starchy endosperm for white flour, large quantities of bran are classed as by-products and end up in animal feed. Bran, depending on the extraction rate, comprises of small amount of germ and endosperm along with aleurone layer, nucellar epidermis, seed coat and fruit coat. Bran is rich in dietary fibre, phytochemicals like phytic acid, phenolic components, lignans and flavonoids which is important in healthy human diet. To make use of all the nutrients present in this fraction of the cereal by-product could be a new value added product. This thesis aims at investigating if twin screw extrusion cooking of wheat (n=18) and rye bran (n=18) has an effect on β-glucan and fructan content. The total β-glucan content and fructan content was analysed using enzymatic assay kits available from Megazyme ltd. Then using HPSEC and Calcoflour detection method, molecular weight analysis using area under the curve of the peaks was done along with extractable β-glucan content analysis. Un-extruded reference for each cereal grain was used in all the analyses. The results from the different analyses were tested for significance with every varying extrusion parameter. The three varying extrusion parameters were temperature, moisture content and screw speed. Total β-glucan content in both extruded wheat and rye bran samples had an slight increase. In case of extruded wheat, the average overall increase was about 17% compared to un-extruded wheat bran. In extruded rye bran, total β-glucan content was 4% higher than its un-extruded reference. Of all extrusion parameters, temperature had the most influence on total β-glucan content in extruded wheat and rye. Fructan content in both extruded wheat and rye samples showed an increase compared to their references. In case of extruded wheat, there was a 9% increase from reference and 8% in case of extruded rye. Except for varying moisture in rye samples, no extrusion parameter had a statistical difference in the fructan content in both cereals. Molecular weight analysis of β-glucan in extruded wheat revealed that there was a 2.8 fold increase in extruded samples compared to the reference with statistical differences recorded with varying temperature and screw speeds (90% confidence interval). In extruded rye bran samples, the average molecular weight decreased by 7% with no statistical difference among varying extrusion parameters. The extractable β-glucan content in extruded wheat bran samples showed an average increase of 16% from reference and an 8% decrease in case of extruded rye samples. While there was a significant difference in extractable β-glucan content with varying moisture content for extruded wheat samples, changing speeds seemed to influence the extractable β-glucan content in extruded rye samples. While individual extrusion parameters seemed to have an effect on β-glucan and fructan content, it is still unclear so as to what combination is best for improving the functionality of β-glucan (molecular weight) and fructan.