Rye brans are high-fibre (39−48%) ingredients containing 13−28 % starch and 14−18 % protein, which are by-products of the cereal processing industry and mainly used as animal feed. Due to the high fibre content, it is difficult to use rye brans in extruded foods. High-fibre e.g., brans tend to give lower expansion, harder texture and less crispy end-products thus not acceptable by the consumer. In this paper, Syed Ariful Alam and his co-authors have focused on to the interrelation between mechanical (e.g., hardness and crispiness), macro- (expansion, specific length and piece density) and micro (porosity, T/D ratio and FI index)-structural properties of healthy extruded products with high dietary fibre content.
The aim of this study was to investigate the effects of particle size reduction on the structural and mechanical properties of rye bran extrudates processed under various extrusion conditions using a co-rotating twin screw extruder. This study also aimed to demonstrate how extrusion processing of rye bran with varying particle sizes (coarse: 440; medium: 143 and fine: 28 μm) affects the soluble and insoluble fibre fraction.
Effects of extrusion processing on rye bran were highly dependent on particle size of the raw material. Decreasing the particle size of the rye bran from 440 to 28 μm significantly improved the physical and mechanical properties of the extrudates. Decreasing the particle size improved the crispiness of rye extrudates by increased expansion, air cell size and porosity with reduced hardness. Expansion properties of extruded products contributed to textural attributes such as crispiness which is one of the most important quality control parameter for consumers. The physical properties of rye bran extrudates were also dependent on extrusion process parameters such as screw speed. Regardless of particle size, high screw speed (500 rpm) gave expanded and less hard extrudates in all extrusion experiments. Extrusion process did not have significant effect on the soluble dietary fibre content but the insoluble dietary fibre content for medium and fine bran extrudates increased after extrusion. The results of this research could be applied for the utilisation of rye brans for the development of new products in the growing snack-food markets.
For more information:
Alam SA, Järvinen J, Kirjoranta S, Jouppila K, Poutanen K, Sozer N. 2013. Influence of particle size reduction on structural and mechanical properties of extruded rye bran. Food and BioprocessTechnology (in press).DOI using the URL:http://dx.doi.org/10.1007/s11947-013-1225-2