Extrusion cooking is an important food processing technique, which is increasingly being used for generating a wide range of snack foods and breakfast cereals.
The authors of the study published in Food Chemistry claim that successful incorporation of gluten-free cereals, vegetables and fruits into gluten-free extruded products that deliver physiologically active components could enable food processors to provide healthy dietary fibre-enriched products, currently lacking in the gluten-free market.
The objective of this study was to increase the level of total dietary fibre in gluten-free snack products by using extrusion technology and by incorporating a number of different fruits and vegetables and gluten-free Teff flour.
According to the authors, in order to produce extrudates with a high nutritional quality, it is important to understand the changes that occur in the physical and chemical properties during extrusion, and, as such, they investigated the relationships and interactions between raw ingredients, extrusion processing and resulting extrudate properties.
They explained that they chose cranberry as an ingredient because of its high essential nutrients, such as anthocyanins, proanthocyanins, organic acids, vitamins, minerals and its strong antioxidant properties.
In addition, said the authors, apple and beetroot were used because of their high level of total dietary fibre in dry matter. Carrot was chosen due to its high vitamin and fibre contents and finally, Teff flour was used, the researchers added, because it is gluten-free and contains more iron, calcium and zinc than other cereal grains.
The authors said that the different materials were added at the level of 30 per cent into the gluten-free balanced formulation (control) made from rice flour, potato starch, corn starch, milk powder and soya flour.
According to the researchers, different process conditions were employed during the study including a water feed rate at 12 per cent, solid feed rate at 15 to 25 kg/h, screw speed of 200–350 rpm, and barrel temperatures of 80 °C at feed entry and 80–150 °C at die exit.
Pressure, material temperature and torque were monitored during extrusion runs, they added.
The authors have determined that under optimal conditions, extrusion technology is a suitable method for the preparation of gluten-free products with high levels of dietary fibre, and gluten-free expanded products with high dietary fibre levels can be achieved by controlling extrusion conditions, such as temperatures, solid feed rate and screw speed combinations and the selection of appropriate raw ingredients.
They noted a greater increase in dietary fibre content with Teff samples, followed by apple, cranberry, carrot and beetroot, while samples containing carrots were the most stable during extrusion, in terms of crude PC and texture.
“Due to their good textural properties, these gluten-free extrudates may be consumed directly or used as breakfast cereals or as additives in other gluten-free products,” said the researchers.
Source: Food Chemistry
Published online ahead of print
Title: The advantage of using extrusion processing for increasing dietary fibre level in gluten-free products Authors: V. Stojceska, P. Ainsworth, A. Plunkett, Ş. İbanoğlu