Effect of Extrusion Variables on Extrudates Properties of Water Yam Flour - A Response Surface Analysis

Abstract

Water yam (Dioscorea alata) flour was processed using standard wet milling procedure prior to the extrusion process, which led to the determination of extrudate properties of the flours. A single‐screw extruder (DCE 330, NJ) was used in evaluating the extrudate properties, which included torque, mass flow rate, residence time, specific mechanical energy and expansion ratio of the flours from the water yam samples. The effect of extrusion and process variables: feed moisture content, screw speed and barrel temperature on the extruder torque, residence time, mass flow rate, specific mechanical energy and expansion ratio for the variety were determined and predictive models were also developed using response surface methodology. It was observed that changing the feed moisture content, barrel temperature and screw speed significantly (P < 0.05) affected expansion ratio, torque, mass flow rate, residence time and specific mechanical energy of all the extrudates. Increasing the feed moisture content (18–28% db) and screw speed (80–180 rpm) resulted in a substantial decrease in expansion ratio (46.6%), residence time (27.5%) and specific mechanical energy (83.6%); whereas, increasing the screw speed significantly increased the mass flow rate (64.5%) of extrudates. Regression analysis indicated that screw speed and feed moisture content were the major process variables showing significant (P < 0.05) linear, quadratic and interaction influences on mass flow rate, expansion ratio and specific mechanical energy. PRACTICAL APPLICATIONS This investigation was conducted with a broad intention of enhancing the value of water yam flours and its suitability for incorporation in the production of noodle‐like products. This was accomplished by varying the feed moisture content, screw speed and barrel temperature, and determining their effects on resulting extrudate properties.

Physicochemical and nutritional properties of extrudates from food grade distiller's dried grains, garbanzo flour, and corn grits

“…As illustrated in Figure a, the ER was high at low moisture content and decreased as the moisture content in the blends increased. According to Oke, Awonorin, Sanni, Asiedu, and Aiyedun (), drag force increases when moisture content decreases; as a result, there is more pressure at the die which leads to greater expansion of the extrudates at the exit. The increase in expansion at higher screw speed can be attributed to the shearing effect of the screw (Singha & Muthukumarappan, ), which causes protein molecules to be stretched farther apart, weakening bonds and resulting in a puffer product (Filli, Nkama, Jideani, & Ibok, ).…”

Effect of feed composition, moisture content and extrusion temperature on extrudate characteristics of yam-corn-rice based snack food

“…Similar trend was observed in this study. Oke et al (2012) studied the effect of moisture content on ER and concluded that decreased moisture content increases the drag force and therefore exerts more pressure at the die resulting in greater expansion of extrudate at the exit. The expansion at higher barrel temperature can be attributed to the starch gelatinization and strengthening of structure (Ali et al 1996;Ainsworth et al 2007).…”

“…The RSM helps in optimizing a set of operational variables of the process (Myers and Montgomery 2002). The RSM approach has widely been applied in extruded food product development (Yagci and Gogus 2009;Oke et al 2012;Seth and Rajamanickam 2012). Among the factorial design Central Composite Design (CCD) and Box-Behnken Design (BBD) are the most common designs adopted in food product development to estimate response surface and subsequent optimization of the process variables.…”

“…The effects of extrusion conditions and feed compositions on functional properties of various cereal and pulse based products have been studied extensively (Balasubramanian et al 2012;Seth and Rajamanickam 2012). Several studies found that increasing feed moisture content increases the bulk density, water solubility index, water absorption index and hardness and decreases the expansion ratio (Chiu et al 2012;Kirjoranta et al 2012;Oke et al 2012). Higher barrel temperature increases the expansion and reduces the hardness of the extrudates (Sebio and Chang 2000).…”

Process optimization of extrusion variables and its effect on properties of extruded cocoyam (Xanthosoma sagittifolium) noodles

“…The mass flow rate (MFR) was determined when steady‐state operation conditions were reached as indicated by constant torque at the different extrusion temperatures (Oke, Awonorin, Sanni, Asiedu, & Aiyedun, 2013). A stopwatch was started immediately, and sample of extrudates flowing out of the extruder die opening was collected as soon as the timer was started at 60‐s interval.…”