Mod­i­fied rye bran could turn un­healthy ex­truded snacks to healthy ones

Up to 40% rye bran could be included in extruded snacks without affecting their structural and textural properties, or compromising the taste, according to a study carried out at the University of Helsinki. Not only is rye bran a cost-effective ingredient but it is also high in fiber and nutritional value.
Extruded snacks such as cheese puffs are generally made of refined wheat flour and lacking the health benefits associated with dietary fibre, thus may increase the risk for obesity, type II diabetes and cardiovascular diseases. Increasing the dietary fibre content of extruded snacks without compromising structure and taste would not only caliber the nutritional profile of these products but also form new business opportunities in the functional foods sector. The market demand for extruded snacks is expected to reach €55.3 billion by the year 2026.

“Adding rye bran in food products such as extruded snacks is greatly enhancing their nutritional value and assist in, for example, reducing obesity and chronic diseases among the rapidly increasing population. Knowledge obtained in my PhD work on cereal matrix formation and digestion of food structure will help the food industry to develop healthy and appealing products,” says Syed Ariful Alam who carried out his doctoral studies at the Faculty of Agriculture and Forestry, University of Helsinki

Rye bran is an abundant flour processing side-stream, which is a good source of both dietary fibre, 48%, and protein 18% protein. However, current use of rye bran is mainly for animal feed. Therefore, rye bran bran is a promising cost-effective ingredient, a low-cost fibre and protein source in healthy snacks. However, rye bran addition during extrusion is challenging due to its high levels of insoluble dietary fibre, which leads to less expanded products and a hard texture. To overcome these challenges, modification of rye bran prior to extrusion is needed, which would increase the applicability of rye bran in extruded snacks.

In his dissertation, Alam focused on modification of rye bran to produce high fibre extruded products with a good structure and texture. Alam studied bran modification either by particle size reduction or by fermentation to improve the structural and textural properties of rye bran added extruded snacks. He sampled different structure formation of rye-based extrudates, their disintegration behaviour during mastication and linked those results to in vitro starch digestibility.

In his study, Alam demonstrated that bran modification by particle size reduction or fermentation with exopolysaccharide (i.e. sugar polymers such as dextran) producing Weisella Confusa (i.e. food-grade lactic acid bacteria) significantly improved both the structural and textural properties of the extrudates containing rye bran. Optimization of the processing parameters such as increasing the screw speed, lowering the feed moisture and the use of in-barrel hydration regimens also improved the textural properties.

Alam also established that it’s not the matrix composition (neither fibre nor starch) but the structure-texture interplay of the extrudates dictate particle breakdown during mastication and starch digestibility. The extruded food structure and texture had a direct effect on the mastication and bolus formation process in the mouth. A hard and dense extrudate structure required more mastication effort than a crispy structure. Crispy and porous structures easily disintegrated in the mouth and produced smaller bolus particles compared to hard and dense structure. A higher number of smaller particles in the bolus was associated with increased starch hydrolysis. Alam demonstrated that the bolus particle size was more effective than the matrix composition in altering the starch digestibility.

“The applicability of rye bran in extruded products could be improved by particle size reduction and fermentation“ Alam summarises. The outcome of this study will greatly enhance the potential use of rye bran in food products and in turn will assist in reducing obesity and chronic diseases among the rapidly increasing population. The findings of this study will also benefit the food-processing industry by delivering knowledge in understanding the process-structure-physiological functionality relationship, which is very important when designing new dietary fibre rich healthy foods.

Doc­toral de­fence
M. Sc. Syed Ariful Alam will defend his doctoral dissertation in subject “Process-induced structural properties and starch digestibility of high-fibre extruded products” in the Faculty of Agriculture and Forestry, University of Helsinki, on Thursday, 10th of December. Professor Charles Brennan (Lincoln University, New Zealand) will serve as the opponent and Custos is Associate Professor Kati Katina. The doctoral dissertation is held in English.