THE EFFECT OF EXTRUSION CONDITIONS AND CEREAL TYPES ON THE FUNCTIONAL PROPERTIES OF EXTRUDATES AS FERMENTATION MEDIA

FOODBALT 2008
THE EFFECT OF EXTRUSION CONDITIONS AND CEREAL TYPES ON THE
FUNCTIONAL PROPERTIES OF EXTRUDATES AS FERMENTATION MEDIA
Vilma Narbutaite, Tomas Makaravicius, Grazina Juodeikiene, Loreta Basinskiene
Kaunas University of Technology, Faculty of Chemical Technolog Department of Food Technologyy,
Radvilenu pl.-19, LT-50254, Kaunas, Lithuania, e-mail: vilma.narbutaite@stud.ktu.lt
Abstract
Extrusion cooking is used world wide for the production of expanded snack food, modified starch, ready-to-eat
cereal foods. Recently a considerable interest has arisen in the appliance of extruded products, such as raw
materials with specific physical properties, for the production of fermented products. Product quality can vary
considerably depending on the extruder type, screw configuration, feed moisture, temperature profile in the
barrel, screw speed, feed rate and die profile. In this study, the effect of feed moisture content on functional
properties (water solubility index, water absorption index and degree of gelatinization) of different extrudates
was investigated. Different extruded samples were prepared using wheat (flour and meal), rye (flour, meal and
wholemeal), barley, triticale, maize and rice wholemeals, pursuant to selection of fermentation media. Cereal
products were passed through a one-screw extruder using moisture contents of 30% and 50%.
The performed study revealed that functional properties of extrudates are strongly related to the cereal type and
feed moisture content. The higher feed moisture content (50%) influenced the higher water solubility index
(WSI), yet the lower water absorption index (WAI) and degree of gelatinization (DG). The highest values of
WSI, WAI and DG were demonstrated by barley, triticale and rye flour extrudates and were as follows: 10.1%,
2.31 g g-1 and 100%. Meanwhile, the lowest values of functional properties were observed on triticale, rice and
wheat extrudates, and were in the values of 1.8%, 0.63 g g-1 and 6.1%, respectively.
Key words: extrusion, feed moisture content, WAI, WSI, DG.

Introduction
Extrusion is one of the most common industrial processes used to make snacks, and it is
among the most versatile technological processes for making food products, usually from
cereals. Cereals, in turn, are the customary, traditional snack ingredient due to their high
starch content (Perez-Navarrete et al., 2006). Extrusion technology has many advantages,
including its versatility, high productivity, low cost, and the ability to produce unique product
shapes and high product quality (Singh and Smith, 1998; Singh et al., 1999;
Koksel et al., 2004).
Extrusion-cooking is a versatile and feasible alternative for manufacturing snacks and water
reconstitutable foods, and it has been the object of studies to enhance the nutritional and
functional properties of extrudates for the development of products (Sacchetti et al.., 2005;
Shankar and Bandyopadhyay, 2005; Gonzalez-Soto et al., 2006; Hernandez-Diaz et al., 2007).
In extrusion cooking, important parameters for product quality include moisture content of the
material, residence time, which is influenced by feeding rate, screw speed and configuration,
die geometry, temperature and time (Gogoi and Yam, 1994; Obatolu et al., 2005). The results
of extrusion are gelatinization of starch, denaturation of proteins, inactivation of many native
enzymes and antinutritional factors, reduction of microbial counts, and improvement in
digestibility and biological value of proteins (Martin-Cabrejas et al., 1999; Milan-
Carrillo et al., 2002). The suitability of extruded foods for a particular application depends on
their functional properties like water absorption and water solubility indexes, expansion
index, bulk density and viscosity of the dough (Hernandez-Diaz et al., 2007).
The objective of this study was to investigate the effect of feed moisture content as processing
variables on functional and physical quality of extrudates from different cereal types.

Materials and Methods
The extruded samples: wheat (flour and meal), rye (flour, meal and wholemeal), barley,
triticale, maize and rice wholemeals were used throughout this study. Cereal products were
passed through a one-screw extruder using feed moisture contents of 30% and 50%.
Water absorption index (WAI) and water solubility index (WSI). WAI and WSI were
determined in duplicate following the method described by Anderson (1982). Each sample
(1 g) was suspended in 6ml of distilled water and stirred for 30 min at 30 oC temperature.

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Subsequently, the dispersions were centrifuged at 4000 g for 20 min using Heraeus Labofuge
200 Centrifuge (Thermo Electron LED GmbH, Langenselbold, Germany). The supernatants
were poured into dry test tubes and stored overnight at 110 oC for the process of evaporation.
WAI and WSI were calculated using following equations:
WAI = weight of sediment / weight of dry solids
WSI = weight of dissolved solids in supernatant x100/weight of dry solids
Degree of gelatinization (DG). Degree of gelatinization was determined by comparing
OD values of a particular extrudate to its control (non-extruded) sample. OD values of the
samples in triplicate were measured using Spectrophotometer Genesys 10 (Thermo Electron
LED GmbH, Langenselbold, Germany) at a wavelength of 608 nm. Calculations were made
using the following equation:
DG=optical density of extrudate x100/optical density of control sample.

Results and Discussion
Water solubility and water absorption indexes. Water solubility index (WSI) is used as a
measure for starch degradation; it means that at lower WSI there is minor degradation of
starch and such condition leads to less numbers of soluble molecules in the extrudates
(Hernandez-Diaz et al., 2007). Higher moisture content in extrusion process can diminish
protein denaturation and starch degradation. The experimental results show that WSI of all
examined extrudates (excluding maize) decreased with increasing moisture levels. The effect
of feed moisture content on WSI is illustrated in Figure 1 (A).
The highest WSI under 50.0% feed moisture content in extrusion process were determined in
barley and maize extrudates, being 8.7% and 5.9%, respectively. Whereas the lower WSI
under same conditions were measured in rye meal and triticale extrudates, with the values of
2.0% and 1.8%, respectively. In the case of 30.0% feed moisture content, barley extrudate had
the highest WSI, yet in triticale extrudate was measured the lowest WSI, being 10.1% and
3.6%, correspondingly.

Figure 1. Effect of feed moisture content on WSI (A), WAI (B) and extrudates
from different cereal types

WAI, an indicator of the ability of flour to absorb water, depends on the availability of
hydrophilic groups which bind water molecules and on the gel-forming capacity of
macromolecules. The results of the effect of feed moisture content on WAI of extrudates from
different cereal types are demonstrated in Figure 1 (B).
The higher feed moisture content influenced higher WAI for all but rice, barley and maize
extrudates. The highest WAI was determined in triticale extrudate (2.31 g g-1) along with the
lowest WAI in rice extrudate (0.63 g g-1), both under 50.0% feed moisture content. Badrie and
Mellowes (1991) and Hernandez-Diaz (2007) reported similar findings where WSI of several
extrudates decreased and WAI increased with increasing moisture levels.

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Degree of gelatinization. Degree of gelatinization was mainly affected by different cereal
types. It was observed that lower feed moisture enhanced gelatinization in all except rye flour
and wheat flour extrudates. The effect of feed moisture content on DG of different extrudates
is illustrated in Figure 2.

Figure 2. Effect of feed moisture content on DG and extrudates from
different cereal types

Nevertheless the highest DG was examined under 50.0% feed moisture content in rye flour
extrudate where all starch was gelatinized, yet in the wheat meal extrudate only 6.1% of
starch gelatinization showing the lowest DG was achieved.

Conclusions
1. The effect of moisture content in extrusion process on functional properties of different
cereal types was examined throughout this study. Experimental data indicate that the
extrudate type had a significant influence on water solubility index (WSI), water
absorption index (WAI) and degree on gelatinization (DG). Extrusion conditions have to
be chosen considering cereal type of extrudate in order to get the preeminent functional
properties for fermentation process.
2. Samples with higher degree of gelatinization resulted in lower water solubility and higher
water absorbability. Therefore, extrudate samples with a higher degree of gelatinization
have a higher gelling capacity and could be incorporated into foods as thickeners or in
dough where retaining the moisture is important for the maintenance of the texture.

Acknowledgements
This research was supported by the Eureka project FERMFOOD E13966.

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Document Outline

• THE EFFECT OF EXTRUSION CONDITIONS AND CEREAL TYPES ON THE FUNCTIONAL PROPERTIES OF EXTRUDATES AS FERMENTATION MEDIA / Vilma Narbutaite, Tomas Makaravicius, Grazina Juodeikiene, Loreta Basinskiene
• Abstract
• Key words
• Introduction
• Materials and Methods
• Results and Discussion
• Conclusions
• Acknowledgements
• References

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