On‐line rheology of pearl millet flours during extrusion: Effect of native amylose

Abstract

Pearl millet is a micro‐nutrient rich crop grown in arid regions of Asia and Africa. Millet based extruded products can ensure both food and economic security amongst these malnutrition prone areas. The effect of flour crystallinity and amylose content on the rheological attributes during thermo‐mechanical processing of pearl millet cultivars was determined using on‐line rheometer during twin‐screw extrusion. The shear strain measurements indicated shear thinning behavior which was modeled using modified Power law (R2 > 0.8). Upon increase in moisture content and barrel temperature, the consistency index of pearlmillet flour was found to decrease. Higher amylose cultivars demonstrated higher consistency index. The flow behavior index increased with moisture and temperature. Modified Arrhenius model was used to explain the effect of temperature and moisture on consistency index. This study underlines the effect of crystallinity and amylose on the rheology of millets during extrusion. Practical applications The findings of this study shall be helpful in: determining extrusion conditions for processing whole pearl millet flours. screening varieties of pearlmillet suitable for different types of extruded products varying in degrees of polymeric modification.

Effects of extrusion process parameters on cooking characteristics and physicochemical, textural, thermal, pasting, microstructure, and nutritional properties of millet‐based extruded products: A review

“…Lipids involved in the complex formation with amylose are a novel Gulati et al, 2016;Hagenimana et al, 2006;Kharat et al, 2019;Rudra et al, 2018). Narang et al (2018) found a decreased WSI for pearl millet-based extruded snacks as the FM increased.…”

Influence of extrusion conditions on the physical and nutritional properties of snacks from maize and pearl millet

“…Moisture also influences the elasticity characteristics of starchbased materials. During extrusion, in a high-pressure, high-temperature F I G U R E 1 Snacks according to coded variables of central composite experimental design: moisture (horizontal, X 1 ) and temperature (vertical, X 2 ) F I G U R E 2 Surface response of the specific volume of snacks environment, increased moisture reduces the elasticity of a starchbased material due to a change in the molecular structure of amylopectin, thereby reducing the expansion of the product and increasing its density, consequently decreasing its SV (Rudra et al, 2018). Maximum expansion is generally desirable for extruded snacks, as those with high expansion are crispier because the internal structure has larger cells with fine walls (Yagci & Gogus, 2009).…”

“…Moisture also influences the elasticity characteristics of starchmaterials. During extrusion, in a high-pressure, high-temperature tin, thereby reducing the expansion of the product and increasing its density, consequently decreasing its SV (Rudra et al, 2018). Maximum expansion is generally desirable for extruded snacks, as those with high expansion are crispier because the internal structure has larger cells with fine walls (Yagci & Gogus, 2009).…”

“…Snacks are usually produced by extrusion cooking. This food processing method is quite versatile and has the advantage of minimizing nutrient degradation and improving digestibility (Leonard et al, 2020;Rudra et al, 2018). Through processing, starch gelatinization and protein denaturation are brought about (Kumar et al, 2020).…”

“…During the expansion process, a viscoelastic melt expands due to the flashing of moisture at the die exit, followed by bubble growth and collapse(Kharat et al, 2019). According toRudra et al (2018), a high moisture rate has the opposite effect on expansion, as it acts as a plasticizer for starchy materials, thereby reducing their viscosity and the dissipation of mechanical energy in the extruder. Consequently, the product becomes denser and bubble growth is compressed.Rodríguez-Miranda et al (2011) also found a negative linear effect of moisture concerning the rate of expansion in extrudates of taro (Colocasia esculenta) and nixtamalized maize (Zea mays) flour blends.…”