Optimization of extrusion process parameters for preparing fiber‐rich oat flour

Abstract

AbstractIn this study, the effect of extrusion temperature and screw speed on the nutritional properties of the extrudates was evaluated by using a response surface methodology. The total, soluble, insoluble dietary fiber, beta‐glucan, resistant starch, and total starch contents were evaluated through enzymatic assays. The processing parameters affected the content of all constituents of the flour mixture, except for beta‐glucan. The total starch content, insoluble dietary fiber, and resistant starch were significantly decreased with increasing temperature and screw speed (until 13, 12, and 97%, respectively). The extrusion parameters had a positive effect on total dietary fiber content (increased this parameter up to 29%) when compared with the raw material, that is, oat and rice blend, causing changes from the insoluble to soluble dietary fibers. In the electron microscopic analysis, the structure of all extrudates showed to be homogeneous and compact with irregular surfaces.Practical applicationsThe processing of oats by using extrusion‐cooking technique is challenging due to the high lipid and fiber content. For this reason, expansion agents such as rice or corn flours are commonly mixed to the oats before processing. In addition to changing rheological, physical and chemical properties of the raw materials, the extrusion operating conditions may lead to loss of food nutritional properties. In this study, we used the response surface methodology to understand which processing conditions maximize the food nutritional value. The selection of an optimum operating condition in terms of energy efficiency and thermal quality represent a relevant requirement for the current food industry. The content of β‐glucan was preserved regardless of the processing condition while the insoluble and soluble fiber ratio was significantly affected by screw speed. Once low temperatures could be used for preparing fiber‐rich oat flour, a reduction in energy consumption from the process is expected.