1. The material presented here is based upon work supported by the National Science Foundation under Award No. EEC-1004227. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation, nor of Iowa State University.
2013 NSF REU: Sustainable Biomass Production & Processing
Department of Agricultural & Biosystems Engineering
Extrusion of Gluten-Free Snack Foods
Caitlin Gearhart, Dr. Kurt Rosentrater
Iowa State University
Project Rationale & Goals
• The overall goal of this project was to utilize quinoa and amaranth to produce gluten-free snack
foods.
• This is an issue of importance because an increasing number of people are choosing gluten free
diets for medical or personal reasons and the production of snack foods in this category has great
potential.
• The specific objectives included successfully extruding each of the grains, then measuring color,
unit density, expansion ratio, and pellet durability of the products.
Materials & Methods
• The ingredients used were quinoa and amaranth.
• A portion of each grain was left raw. The rest was ground to particle sizes of 1mm and 2mm
using a laboratory mill (Wiley).
• Each ingredient was mixed to moisture contents of 20% and 40% db.
• Extrusion was completed using a single-screw extruder (Brabender).
• Each ingredient was extruded at screw speeds of 50rpm and 100rpm, resulting in 12 different
treatments.
Acknowledgements
• We would like to thank the National Science Foundation for making this research project
possible by funding the Sustainable Production and Processing Systems for Biomass-Derived
Fuels of the Future Research Experience for Undergrads program.
• Acknowledgements also to Dr. Raj Raman and Dr. Michelle Soupir for directing, and to
MaryAnn Moore for coordinating this program.
Conclusions
• Particle size and moisture content of the raw product affect the properties of the
extrudates.
• Screw speed of the extruder also has an effect on the properties of the products.
• Quinoa and amaranth are both capable of individually forming a cohesive product via
extrusion processing.
Results & Discussion
As the particle size
decreased:
• The a* and b* values
decreased in the
extrudates.
As the moisture content
increased:
• The a* value of the extrudates
increased.
• There was a decrease in the
extrudates’ expansion ratio.
As the screw speed
increased:
• The extrudates’ L* value
decreased.
• There was in increase in b*
for the extrudates.
Figure 1: Raw quinoa (above) and extrudates
(below) for treatments 2, 6, and 10, respectively
Table 1: Experimental protocol including treatment numbers and
dependent variables.
As the particle size
decreased:
• There was a decrease in
the extrudates’ a* and b*
values.
As the moisture content increased:
• The expansion ratio of the
extrudates decreased.
• The extrudates’ unit density and
durability increased.
As the screw speed
increased:
• The L* and b* values of
the extrudates increased.
Figure 4: Raw amaranth (above) and extrudates
(below) for treatments 2, 6, and 10, respectively
Figure 2: Brabender single-screw extruder used to
extrude blends. Conditions included a 3 mm die and
a screw compression ratio of 1:1.
Table 4: Temperatures
measured at the die,
transition, and feed zones
for the extrusion of quinoa.
Table 5: Temperatures
measured at the die,
transition, and feed zones
for the extrusion of amaranth.
Table 3: Amaranth Properties
Table 2: Quinoa Properties
Figure 3: Infrared picture of the extruder’s
temperature. All heat was caused solely by
friction, as no additional heat was added.
Figure 5: Relationships among all dependent variables. Some clustering was evident due to
the different moisture contents. The behavior of quinoa was different than that of amaranth.
Quinoa Extrudates Amaranth Extrudates