Waxy flour degradation – Impact of screw geometry and specific mechanical energy in a co-rotating twin screw extruder

Impact of tamarind seed gum on the viscosity behavior, thermal properties, and extrusion characteristics of native corn starch

Tamarind seed gum (TSG) is a cold-swelling hydrocolloid with remarkable processing stability and starch synergy. Its use in direct expanded extruded foods has not been documented. The thermal and pasting viscosity properties of six TSG (0%, 0.5%, 1.0%, 2.5%, 5.0%, and 7.5% TSG) and native corn starch blends were characterized by differential scanning calorimetry and ViscoQuick, respectively. These same blends were extruded using a corotating twin-screw extruder at four screw speeds (SSs) (150, 300, 450, and 600 rpm). System back pressure, motor torque, and specific mechanical energy (SME) were measured. Extrudate quality metrics, such as expansion ratio (ER), water absorption index (WAI), and water solubility index (WSI), were also measured. The pasting viscosities indicated that TSG inclusion increases viscosity but also makes the starch-gum paste more susceptible to permanent shear degradation. The thermal analysis indicated that TSG inclusion narrowed the melting endotherms and lowered the energy required for melting (p < 0.05) at higher inclusion levels. Extruder back pressure, motor torque, and SME decreased with increasing TSG levels (p < 0.05) as the TSG effectively lowered the melt viscosity at high usage rates. The ER reached a maximum of 3.73 with a 2.5% TSG level extruded at 150 rpm (p < 0.05). The WAI of extrudates increased with TSG inclusion rate at equivalent SSs, whereas WSI behaved oppositely (p < 0.05). Small inclusions of TSG can improve the expansion properties of starch, whereas larger inclusions result in a lubrication effect that mitigates the shear-induced depolymerization of starch. PRACTICAL APPLICATION: The impact of cold-water soluble hydrocolloids, including tamarind seed gum, on the extrusion process, is poorly understood. From this work, tamarind seed gum effectively modifies the viscoelastic and thermal characteristics of corn starch in a way that enhances the direct expansion characteristics of the starch during extrusion processing. The effect is more beneficial at lower gum inclusion levels as higher levels result in reduced capabilities to translate shear from the extruder into useful transformations of the starch polymers during processing. Small amounts of tamarind seed gum could be used to improve the quality of extruded starch puff snacks.

Exploration of physicochemical properties and molecular interactions between cellulose and high-amylose cornstarch during extrusion processing

Incorporating fiber at high levels (>10%) into direct-expanded products with acceptable texture is challenging. Fundamental explanations for the interaction of starch and fiber and the cause of expansion reduction need further understanding for the effective incorporation of fiber into expanded products. This study aims to explain how cellulose content impacts the physicochemical properties of starch-based extrudates and the long-range and short-range molecular changes of starch. Mixtures of cornstarch (50% amylose) and cellulose were extruded using a co-rotating twin-screw extruder. Thermal and pasting properties of the raw mixtures were evaluated, and the physicochemical properties and microstructure of extrudates were determined. Long-range and short-range molecular changes of starch-cellulose mixtures before and after extrusion were observed by X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. The expansion ratio of extrudates reduced significantly as the cellulose content increased and had a strong negative correlation with crystallinity. Cell structures of starch-cellulose extrudates had a smaller and more uniform pore size but possessing a more ruptured matrix. FTIR spectra suggested that there was no covalent bonding interaction between starch and fiber after extrusion. Extrusion reduced the overall crystallinity compared to the raw mixtures. XRD showed that the crystallinity of the starch-cellulose extrudates increased as the cellulose content increased, and the XRD peaks representing cellulose remained unchanged. Cellulose could interfere with starch chain reassociation through intermolecular hydrogen bonding during the expansion process. Phase separation of starch and cellulose is likely to occur at high cellulose content, which could be another reason for the reduced expansion.

Whole seed lentil flours from different varieties (Brewer, Crimson, and Richlea) demonstrated significant variations in their expansion characteristics during extrusion

The properties of flours and extrusion characteristics, of three lentil varieties (Brewer, Crimson, and Richlea) were studied. The effects of barrel temperature (110, 125, and 140 °C) and screw speed (150, 200, and 250 rpm) on process responses and extrudate characteristics were evaluated using a corotating twin-screw extruder. The three varieties of lentils had significant differences (p < 0.05) in their starch (48.7% to 50.9%), protein (20.4% to 22.7%), and fat content (1.3% to 1.9%), gelatinization temperature (71.7 to 74.6 °C), peak viscosity (123.3 to 179.7 mPa.s), and melting temperature (113.6 to 119.7 °C). The lentil variety, barrel temperature, and screw speed significantly impacted the process responses and extrudate properties. Whole lentil flours exhibited the highest expansion ratio (3.0 to 3.6) at the lowest temperature (110 °C) and the highest screw speed (250 rpm). Richlea variety had the highest expansion ratio (3.6) and the highest water solubility index (45.4%) as it had the highest starch content and peak viscosity, and the lowest protein content and melting temperature. Meanwhile, Brewer variety exhibited the lowest expansion ratio (1.9 to 3.0) compared to Richlea (2.5 to 3.6) and Crimson (2.4 to 3.0) in most of the extrusion conditions studied. Richlea variety was the most suitable for making direct-expanded extrudates among the varieties studied. The significant differences in the properties of flours from the three varieties of lentils resulted in significant impacts on the properties of their extrudates. Therefore, determining the properties of flours of different varieties is useful to select the appropriate varieties for extrusion processing. PRACTICAL APPLICATION: The information from this study is useful for the food industry to select the appropriate lentil varieties and processing conditions for the development of direct-expanded products. The data prove the importance of understanding the chemical composition, pasting, and thermal properties to select the appropriate varieties for extrusion processing.

Utilization of Food Processing By-products in Extrusion Processing: A Review

The processing of agricultural products into value-added food products yields numerous by-products or waste streams such as pomace (fruit and vegetable processing), hull/bran (grain milling), meal/cake (oil extraction), bagasse (sugar processing), brewer's spent grain (brewing), cottonseed meal (cotton processing), among others. In the past, significant work in exploring the possibility of the utilization of these by-products has been performed. Most by-products are highly nutritious and can be excellent low-cost sources of dietary fiber, proteins, and bioactive compounds such as polyphenols, antioxidants, and vitamins. The amount of energy utilized for the disposal of these materials is far less than the energy required for the purification of these materials for valorization. Thus, in many cases, these materials go to waste or landfill. Studies have been conducted to incorporate the by-products into different foods in order to promote their utilization and tackle their environmental impacts. Extrusion processing can be an excellent avenue for the utilization of these by-products in foods. Extrusion is a widely used thermo-mechanical process due to its versatility, flexibility, high production rate, low cost, and energy efficiency. Extruded products such as direct-expanded products, breakfast cereals, and pasta have been developed by researchers using agricultural by-products. The different by-products have a wide range of characteristics in terms of chemical composition and functional properties, affecting the final products in extrusion processing. For the practical applications of these by-products in extrusion, it is crucial to understand their impacts on the qualities of raw material blends and extruded products. This review summarizes the general differences in the properties of food by-products from different sources (proximate compositions, physicochemical properties, and functional properties) and how these properties and the extrusion processing conditions influence the product characteristics. The discussion of the by-product properties and their impacts on the extrudates and their nutritional profile can be useful for food manufacturers and researchers to expand their applications. The gaps in the literature have been highlighted for further research and better utilization of by-products with extrusion processing.

Pea starch exhibits good expansion characteristics under relatively lower temperatures during extrusion cooking

Extrusion processing characteristics of pea starch were studied as impacted by various extrusion cooking processing variables, including, moisture content (15%, 17.5%, and 20% w.b.), temperature (120, 135, and 150 °C), and screw speed (150, 200, and 250 rpm), in a co-rotating twin-screw extruder. Physicochemical properties such as radial expansion ratio (ER), unit density (UD), water absorption index (WAI), and water solubility index (WSI) were measured. ER of the extrudates ranged between 2.52 and 3.63. These values of ER were significantly high, although relatively lower compared to the highest values reported in the literature for corn and rice extrudates. The UD values for all the extrudates ranged from 0.12 to 0.35 g/cm3 , WAI, and WSI values ranged from 10.98 to 12.10 g/g and from 0.12% to 7.73%, respectively. Both screw speed and moisture content had significant impacts on the ER (P < 0.01). The highest ER was observed for the extrusion cooking conditions of the lowest moisture content level (15%), lowest barrel temperature (120 °C), and lowest screw speed (150 rpm). The cross-sectional microstructure of the extrudates showed that the samples with a high ER had thick and elongated pores. The results of this study indicate that pea starch is a viable ingredient for making puffed extruded products. PRACTICAL APPLICATION: The food industry can utilize the information generated from this study in the development of extruded expanded food products with pea starch. The specific information related to process conditions can assist the food industry in determining the ideal conditions for extrusion cooking in the production.

Whole faba bean flour exhibits unique expansion characteristics relative to the whole flours of lima, pinto, and red kidney beans during extrusion

Determining the impacts of extrusion conditions on extrudate characteristics of whole beans flours is critical to find the suitable types of beans to use for making direct expanded products. Whole bean flours of four different bean types, faba, lima, pinto, and red kidney, were extruded. The influence of barrel temperature (120, 140, and 160 °C), moisture content (17%, 21%, and 25%), and screw speed (150, 200, and 250 rpm) on process and product responses was studied with a corotating twin screw extruder. The barrel temperature, moisture content, screw speed, and variety of bean had significant influence on process and product responses, back pressure (MPa), torque (N·m), specific mechanical energy (kJ/kg), expansion ratio, water absorption index (g/g), and water solubility index (%) (P < 0.05). Faba bean extrudates had a significantly higher expansion ratio compared to other beans (lima, pinto, and red kidney beans) even though faba bean contained significantly higher protein and higher crude fiber contents (P < 0.05). PRACTICAL APPLICATION: The outputs of this research will be helpful to the food industry in the production of high nutrient-dense food products from whole beans by maintaining the expansion and texture of the products. The data should assist to choose the suitable types of whole bean flours and the optimum processing conditions for making direct expanded extruded products.