The authors, who published their findings in the Journal of Food Engineering, said they developed simple power model equations to enable the production of extruded snacks with good quality characteristics.
The researchers, based at the National Technical University of Athens, point out that as soybean is the most used legume grain for the production of protein enriched snacks, there is still a lack of knowledge of extrudate properties using legume and legume-cereal blends, especially products obtained from whole legume grains.
They explained that extrusion has been used to develop various types of snack foods, mainly from corn meal, rice, wheat flour, or potato flour, in many shapes and variety of textures but product quality can vary considerably.
According to the authors, factors such as extrusion processing conditions including extruder type, screw configuration, feed moisture, along with temperature profile in the barrel sections, screw speed, and feed rate play a significant role in whether the snack will meet consumer acceptability standards.
They said their aim was to investigate density and expansion ratio, as well as textural and sensorial characteristics of corn–lentil extruded snacks as affected by extrusion conditions and raw material characteristics such as moisture content and lentil to corn ratio.
Lentil was used in mixtures with corn flour at a ratio of 10–50 per cent (legume/ corn).
A co-rotating twin screw extruder was used in the study. The screw geometry, said the authors, was length 40 cm, diameter 16 mm, maximum rotation speed 500 rpm, and die diameter 3 mm. The material was fed into the extruder using a volumetric feeder and the extruder used had five temperature control zones.
The temperature during extrusion was adjusted by varying the temperature in the barrel, screw, and die using electric heaters. The screw speed was set at 200 rpm, continued the authors.
A ten-member trained panel participated in analysis of extrudates’ diameter and texture, said the team.
And they explained that a simple mathematical model was used to predict investigate structural and textural characteristics such as apparent density, expansion ratio, elasticity modulus and number of peaks during compression.
The researchers concluded that, in general, extruded snacks produced at low feed rates and moisture content and intermediate levels of temperature had a crunchy, crispy and soft texture:
“Corn and lentil mixtures processed at low temperature and higher values of feed moisture content and feed rate become more rigid, having increased values of apparent density and elasticity modulus, with thick cell walls.
In contrary, extrudates processed at low feed rates and moisture contents become softer, crispier with thin cell walls.”
Legume pulses are low in sodium and fat, cholesterol-free, as well as being rich in protein and fibre, so they can help reduce the risk of a variety of health problems such as obesity, heart disease, cancer and diabetes.
Thanks to the health and organic trends, sales of cereal bars in the EU have experienced average compound annual growth of 7.2 per cent over the last few years, said a report from Global Business Insights. Back in 2007, the company predicted the European market for snack bars to be worth $4bn (€2.7bn).
Source: Journal of Food Engineering
Published online ahead of print: doi:10.1016/j.jfoodeng.2010.04.024
Title: Structural and textural characterization of corn–lentil extruded snacks
Authors: A Lazou, M. Krokida