Effect of oat bran fractions on extrudates made of defatted oats

Oats are rich in dietary fibre (DF) especially in ß-glucan which has several health-promoting effects. Oats are not commonly used in extruded snacks because they often result in a poor expansion and hard structure. In the present study, defatted wholegrain oat flour (WF) and defatted endosperm oat flour (EF) were used as starch sources for extrudates. Five differently treated oat bran fractions (untreated, ultra-fine ground, enzymatically hydrolysed and hot water-extracted solubles and residue) were added to EF (10 or 20 %), and their influence on the chemical, textural and structural properties of extrudates was investigated. Extrudates made of WF had a poor expansion (151 %) and hard texture (399 N), whereas EF formed a better expanded (199 %) and less hard product (149 N). Addition of oat bran concentrate (OBC) decreased the expansion (171-176 %) and resulted in a harder texture (200-265 N) compared to that of EF 100 % extrudates. The lower expansion of WF and OBC-enriched extrudates was due to the higher content of insoluble fibre. However, no statistical differences were detected between the untreated, ultra-fine ground and enzyme-hydrolysed OBC. The water-insoluble (WIS-OBC) and water-soluble (WS-OBC) fractions had opposite effects on the EF-based extrudates: 10 % addition of WIS-OBC fraction significantly decreased the expansion (163 %) and increased the hardness (313 N), whereas the addition of WS-OBC (10 or 20 %) enhanced the expansion (218-226 %) and resulted in less hard textures (131-146 N). The soluble fibres and low protein content in WS-OBC fraction were hypothesised to cause the improved expansion and decreased hardness. The results demonstrated that extrudates with acceptable expansion and hardness can be produced with defatted oat endosperm flour and oat bran fractions. However, the water-insoluble bran components had a negative effect on the textural properties of extrudates.