The effect of sugars on the extrusion of maize grits: I. The role of the glass transition in determining product density and shape

The effects of sugars (sucrose, glucose, fructose, xylose, lactose and maltose) on both sectional (radial) and longitudinal expansion and subsequent shrinkage of maize extrudates have been investigated. Sugars reduced the sectional expansion, monosaccharides more than disaccharides. Reduced sectional expansion and increased density with sugar content was interpreted as a combination of a reduction in bubble growth and an increase in the degree of shrinkage on leaving the die. The decrease in bubble growth was considered to be the result of a temperature reduced driving force for bubble growth and reduced bubble wall extension before rupture caused by less starch conversion with increasing sugar content. Shrinkage stops when the temperature decreases to approximately T_g+ 30°C, where T_g is the glass transition temperature. The addition of sugars and water will reduce the glass transition temperature (T_g) of the melt and hence increase the temperature range over which the extrudate will shrink. The driving force for shrinkage is the release of stored elastic energy following bubble rupture and the pressure difference between the interior of closed cells in the product and atmospheric pressure.     

Investigation of Growth and Shrinkage Mechanisms in Vapor-Induced Expansion of Extrusion-Cooked Corn Grits

The development of expansion models with good predicting capabilities requires experimental data and a more fundamental understanding of the vapor-induced expansion behavior in extrusion cooking. In this study, we used a conventional and also a high-speed camera to observe the radial and axial expansion behavior of extrusion-cooked corn grits. Image processing was performed with an automated evaluation code. The experimental setup consisted of a novel high-speed extruder, which enabled the determination of the influence of high screw speeds of up to 1,200 rpm on extrudate growth and shrinkage. In addition to optical measurement of the expansion, moisture content and temperature development during growth and shrinkage were determined. Three distinct stages of expansion were observed: extrudate growth, short-term shrinkage, and long-term shrinkage. The initial extrudate growth rate fitted well with a linear regression. Especially the second stage of shrinkage occurring in a time range of 24 h after the experiment showed that shrinkage is often underestimated in existing models. Furthermore, total shrinkage increased at higher screw speeds. The data obtained deliver new insight into expansion phenomena and can support the development of predicting models.     

Assessing Changes in Enriched Maize Flour Formulations After Extrusion by Means of FTIR,XRD, and Chemometric Analysis

Spectral analysis employing multivariate techniques was employed to differentiate plain maize flours from formulations containing maize with added milled chia or quinoa seeds for producing cereal breakfast extrudates. The physicochemical changes of the enriched formulations due to processing stages and formulation were evaluated by using FTIR and chemometric analysis, which allowed a rapid and non-destructive discrimination between sample processing and compositional aspects. Specific IR frequencies were selected which provided highest sample discrimination. Selected IR absorbance relationships at those specific wavenumbers were useful to track changes promoted by extrusion for carbohydrates, proteins, and lipids. The complexes between amylose and lipids, that takes place during extrusion, underwent distinctive changes as confirmed by XRD. The crystallinity loss, after extrusion (with an average value of 50%), shows evidence of amylose-lipid complexes formation of type E_h and V_h. Correlations between the textural behavior, composition, and selected FTIR indices were obtained.     

Properties of extruded whole grain cereals and pseudocereals flours

Common cereals such as wheat are widely used worldwide in extruded products. Nevertheless, other locally available grains would be beneficial for local consumers regarding taste preference, nutritional needs and sustainability. Locally available cereals, that is millet, teff, sorghum and pseudocereals, that is quinoa and amaranth flours were extruded at the same processing conditions, and the resulting properties were compared to those of extruded refined wheat flour. Amaranth flour contained the highest protein content (16%). Sorghum was the highest in calories because of its high lipid content (10%). The extrusion process greatly increased a water solubility index (WSI) of amaranth from 11% to 61%, while the WSI level of quinoa was almost not affected (WSI of 4%). The expansion properties varied differently among grain types. These grains had a sectional expansion index (SEI) ranging between 11 and 13, which could not achieve the performance of the refined wheat (SEI of 22). The lowest expansion was observed for amaranth flour which contained the lowest starch content. Sorghum extrudates, interestingly, provided comparable stress at rupture value to that of wheat. For the mechanical properties, none of these local grains could fully replace refined wheat at the employed extrusion conditions.     

Pasting,thermal, gel texture,resistant starch and colour properties of unripe banana flour from 10 desert banana varieties cultivated in South Africa

Unripe banana flour is a potential commercial ingredient in various food products for increased resistant starch and reduced gluten contents. In the present study, the pasting (rapid visco-analysis), gel texture (penetration test), thermal (differential scanning calorimetry), colour (tri-stimulus colour indices) and the resistant starch properties of unripe banana flour produced from different dessert banana varieties (n?=?10) cultivated in South Africa, were analysed and juxtaposed to wheat and maize flour. The functional properties varied significantly (p?≤?0.05) between banana varieties, and from wheat and maize flours, to various extents. Selected functional property ranges of unripe banana, wheat and maize flours, respectively included; flour colour index (63.16–76.42, 77.34 and 80.96), paste viscosity (405.5–556.6, 124.7 and 115.6 RVU), gelatinization temperature (64.67–71.21, 71.11 and 69.95?°C), gel firmness (7.24–11.44?×?10^??2 N, 3.49?×?10^??2 N and 6.56?×?10^??2 N) and resistant starch content (19.9–47.4, 2.8 and 2.2% w/w). Multivariate analysis (principle component analysis) showed that the unripe banana flours from different varieties were distinguished from each other based on the pasting temperature. The unripe banana flours were distinguished from both wheat and maize flour based on breakdown and peak paste viscosities. The breakdown viscosity was the most positively related measure to the resistant starch content with a linear regression R-squared value of 0.898, indicating a significant role played by granule structure in resistance to enzymatic hydrolysis. The present research demonstrates that selection of appropriate dessert banana variety is important when replacing staple flours (wheat and maize) with unripe dessert banana flour as a functional ingredient.     

Process dynamics of starch-based microcellular foams produced by supercritical fluid extrusion. I: model development

Supercritical fluid extrusion (SCFX) has been used successfully to produce biopolymeric foams with bubble size in the range of 50–200 microns, and bubble density to the order of 10⁶ per cm³. Final bubble size and expansion ratio of extrudates depend on process and material parameters like CO₂ injection rate, nozzle temperature, oven temperature, melt viscosity, melt yield stress, etc. The objective of this study was to describe SCFX process dynamics and post-extrusion drying mechanism by using a mathematical model for bubble growth at the microscopic level in conjunction with a macroscopic model for flow of starch melt through the extruder nozzle, bulk diffusion of CO₂ and water to the atmosphere and heat transfer in the extrudate. The model was written in Visual Basic. The model provided the basis for a good understanding of the mechanisms of bubble growth and collapse, post-extrusion drying and open cell formation during SCFX processing, and is the only such one developed so far for extrusion puffed products. Simulation results and comparison with experimental data are presented in Part II of this paper.     

Critical bubble radius for expansion in extrusion cooking

Strong wheat flour, weak wheat flour and rice flour were expanded by sudden reduction in pressure at the discharge port of an extruder. Their micropore-volume distributions were measured by nitrogen adsorption isotherms. The results were compared with the theoretical critical radius for expansion calculated from the balance of forces acting inside and outside a bubble. The micropore volume near the theoretical critical radius for expansion of an extrudate decreased remarkably after extrusion cooking, indicating that the theoretical critical radius for expansion almost coincided with the experimental one.     

Flour lipids and their effects in baking

Wheat flour lipid was separated into five fractions by selective elution from silica gel. The two earlier eluted fractions, which contained mainly non-polar components, depressed loaf volume when added to defatted flour. The three other fractions contained polar components and these maintained or increased loaf volume. The effects of the fractions as foam stabilizers paralleled their effects on loaf volume, supporting the theory that flour lipids exert their action in baking through their role as surfactants in stabilizing or destabilizing the gas bubble structure during expansion of the loaf. Evidence points to a classification of flour lipids into three groups according to their effects in baking. The polar galactolipids and phospholipids increase loaf volume, compounds of intermediate polarity depress loaf volume while the more non-polar compounds such as triglycerides have little effect in the absence of other lipids but have beneficial effects when other lipids are present. Thin-layer chromatography showed clear differences in composition between lipid extracts from wheat, rye and maize flours and these could be correlated with effects on the baking behaviour of defatted wheat flour.     

Amaranth,millet and buckwheat flours affect the physical properties of extruded breakfast cereals and modulates their potential glycaemic impact

Three non‐traditional pseudo‐cereal flours (amaranth, buckwheat and millet) were used in the manufacture of extruded breakfast cereal products as a replacement for wheat and maize flour. The use of these flours altered the physical and nutritional quality of extruded breakfast cereals. Extruded products made using the flours exhibited an increased product and bulk density. However the extruded products were not significantly different compared to the control sample in terms of expansion ratio (excepting Amaranth at the 65% inclusion rate). All of the extruded products made with the inclusion of pseudo‐cereals showed a significant reduction in readily digestible carbohydrates and slowly digestible carbohydrates compared to the control product during predictive in vitro glycaemic profiling. The results illustrate the potential use of these non‐traditional cereal flours in lowering the glycaemic response to the ingestion of extruded breakfast cereals.     

Optimising process for making pasta from maize in admixture with durum wheat

Processing conditions for making pasta from blends of maize (Zea mays L) flour and durum wheat (Triticum durum Desf) semolina (ratio 66:33 w) were studied. The maize mill stream characteristics determined the quality of the maize pasta; flours with low lipid content and very fine granulometry produced pasta with good colour characteristics and high cooking quality (with especially good surface conditions). The use of white maize varieties was preferred; they produced pasta which, after heat treatment, had colour indices close to those of durum wheat pasta. Extrusion conditions affected the colour characteristics and cooking quality of the pasta. The cooking qualities of macaroni products were better than those of spaghetti. In all cases, heat treatment (90°C for 2 h) improved the cooking quality of the pasta: it reduced cooking losses but did not alter the surface condition and viscoelasticity index.     

小麦面粉的3D打印特性

本实验以8 种不同蛋白质量分数小麦面粉为研究对象，通过测定其理化特性、糊化特性、混合特性、流变特性及3D打印特性，研究小麦面粉不同品质特性与3D打印特性的关系。结果显示，蛋白质量分数对小麦面粉的3D打印特性有显著影响，蛋白质量分数在9%～10%时（ZY原味小麦粉、BN 4199小麦粉和XL中式面点粉）打印效果较好，制品整体形状规则、表面平整、纹路清晰，与模型的符合程度较高。面团的损耗模量（G’’）影响其挤出行为，而储能模量（G’）影响其支撑三维结构的能力，ZY原味小麦粉面团的损耗角正切值（tan δ）较大，有利于面团挤出成型；XL中式面点粉G’较大，有利于面团打印后保持自身的形状。在选用的8 种小麦面粉中，XL中式面点粉的蛋白质量分数为9.33%，与设计的30 mm×30 mm×10 mm模型相比，其打印体积误差仅为0.26%。打印制品蒸制熟化后在X轴和Y轴方向上长度略有增加，但Z轴方向上长度略有减小，且发生一定程度的褐变。综上，小麦面粉作为3D打印材料是可行的，这有利于拓展3D打印技术在食品领域的应用。     

High Lysine Extruded Products of Quality Protein Maize

Extrusion-cooking is used by several food industries to produce expanded snack foods, ready-to-eat cereals and pet foods from corn meal. A snack food utilising normal maize and quality protein maize (QPM) as its main ingredient was developed and characterised. The extrusion process was performed in a Mapimpianti single cooker extruder. Processing conditions were single screw with a screw speed of 150 rpm, and a die with 20 die-nozzle orifices with openings of 2 mm of diameter. The die head zone was heated at 110°C by electrical resistance. Compressed air was circulated around the barrel to maintain precise control of the temperature. Moisture content of samples were 150 and 200 g kg⁻¹. The extruded products showed low density and high expansion degree. Optimum expansion index was obtained with flours processed at 150 g kg⁻¹ of moisture content in both maize samples with better characteristics for QPM extrudates. The white colour values were highest for QPM compared to H-128 extruded products.     

Precooked bran-enriched wheat flour using extrusion: dietary fiber profile and sensory characteristics

ABSTRACT:  The effect of precooking by extrusion processing on the dietary fiber profile of wheat flour substituted with 0%, 10%, 20%, and 30% wheat bran was evaluated. Depending on the level of bran, total dietary fiber (TDF) and soluble dietary fiber (SDF) in uncooked flours ranged from 4.2% to 17.2% and 1.5% to 2.4%, respectively. Precooking by extrusion significantly increased SDF in flours (by 22% to 73%); although in most cases it also led to a significant decrease in TDF. Cookies and tortillas produced from uncooked and precooked flours with 0% and 20% substituted bran were evaluated for consumer acceptability using a 9-point hedonic scale. With a few exceptions, all cookies had scores ranging from 6 to 7 ("like slightly" to "like moderately") for each attribute, including overall acceptability, appearance, texture, crumbliness, and flavor. Tortillas were rated for the same attributes except for crumbliness, which was replaced with chewiness. In most cases, tortilla scores ranged from 5 to 7 ("neither like nor dislike" to "like moderately"). Consumer acceptability scores of cookies from uncooked flour did not change significantly with increase in bran substitution from 0% to 20%. However, consumer scores for tortillas did decrease significantly with increase in bran level. Extrusion precooking of the flours did not improve the consumer acceptability of cookies and tortillas; however, it did improve their dietary fiber profile by increasing the SDF significantly.     

Twin-screw extrusion cooking of starches: Flow behaviour of starch pastes,expansion and mechanical properties of extrudates

Several starches, corn and durum wheat semolina, and wheat flour were extruded with a twin-screw, pilot-scale machine (Creusot-Loire BC 45). After grinding, pastes of the extruded samples were made and flow curves were obtained at 60°C with a coaxial-cylinder viscometer: a power law can be used to describe them from about 20 to 2600 s^?1. Apparent Young's moduli and rupture strengths of extrudates were evaluated with an Instron, and their diametral and longitudinal expansion measured. The following variables were studied: corn semolina water content, barrel temperature and the corn starch amylose/amylopectin ratio. When water content and barrel temperature vary within certain limits, the values of the constants in the power law equation describe a characteristic line which depends on the amylose and lipid contents of the starch. The formation of an amylose-lipid complex during extrusion is suggested as a key factor in the flow properties of pastes and probably also in the rupture strength of extrudates. There is generally a negative correlation between longitudinal and diametral expansion. It is considered that volume expansion phenomena are mainly dependent on viscous and elastic properties of melted starch.     

Selected properties of native or modified maize starch/soy protein mixtures extruded at varying screw speed

Mixtures of soy protein isolate and native or modified (crosslinked) maize starch were extruded in a twin‐screw extruder at screw speeds of 80, 120 and 160 rpm and a moisture content of 250 g kg^?1 (dry basis). Increasing screw speed did not affect the specific mechanical energy and water solubility and absorption indices but did affect the sectional expansion index and bulk density, as the flow rate of the feed was not held constant during extrusion. The sectional expansion indices of modified starch/soy protein mixtures were higher than those of native starch/soy protein mixtures, suggesting an effect of feed material in addition to phase transition on the expansion of extrudates containing soybean. Since the bulk densities of modified starch/soy protein mixtures were lower than those of native starch/soy protein mixtures, it appears that bulk densities of extrudates containing high percentages of soy protein can be reduced by the presence of crosslinked starch in the feed. Copyright © 2005 Society of Chemical Industry     

Expansion mechanism of extruded foams supplemented with wheat bran

Addition of bran reduces the expansion of extruded starchy foams. This may be attributed to changes in parameters driving expansion. Wheat flour was supplemented with wheat bran to achieve two levels of fibers (12.6% and 22.4%) and extruded under different conditions of barrel temperature (120 or 180 °C), water content in the feed (18% or 22%) or screw speed (400 or 800 rpm). Increasing the bran concentration decreased sectional and volumetric expansions and increased longitudinal expansion. Finer cellular structures consisting of an increased number of small cells with more spherical shapes were generated. This may be linked to an increased nucleation at the die. The reduction in volumetric expansion was associated with an increase in shear viscosity only at the highest bran concentration. At same extrusion conditions the glass transition temperature of starch was reduced by down to 15 °C by supplementation with bran. This may induce a decrease in the viscosity of the starch phase and counteract the matrix viscosity increase linked to the properties of bran. A higher surface porosity was observed in the bran containing recipe due to earlier burst of the bubbles during growth.     

Use of low-temperature extrusion for reducing phytohemagglutinin activity (PHA) and oligosaccharides in beans (Phaseolus vulgaris L.) cv. Navy and Pinto

Bean (Phaseolus vulgaris L.) lectins and oligosaccharides are the anti-nutrients that limit dry bean consumption. The objective of this study was to study the effects of low temperature (85 °C) extrusion and steam-cooking (82 °C) on the fate of lectin, analysed as phytohemagglutinin activity (PHA), and the oligosaccharides, raffinose and stachyose. Both extrusion processing and steam-cooking significantly (p ? 0.05) reduced the lectin in bean flour by 85–95% over raw bean flours (control). The stachyose content in extruded navy bean flours was comparable to that in raw and steam-cooked flours while extruded pinto bean flour had significantly lower stachyose content than that found in raw and steam-cooked flour. The raffinose content of both navy and pinto extruded flours, though lower than raw bean flours, was significantly higher than that in steam-cooked flours. The results of this study demonstrated that extrusion processing at relatively lower temperature can be effective in eliminating lectins and reducing oligosaccharides.     

Monitoring and identification of aflatoxins in wheat, gram and maize flours in Bihar state (India).

The occurrence of aflatoxins in some common food commodities: wheat, gram and maize flours is reported. Of the total 416 collections during three years (1987-1989) 162 were recorded to be aflatoxin-positive. The incidence of aflatoxins was maximum in the samples of 1987. Most of the contaminated samples contained aflatoxins at levels above 20 micrograms/kg. The environmental conditions and traditional agronomic and storage practices relating to aflatoxin incidence are discussed.     

Limiting the allowable concentration of zearalenone in processed grain products

The distribution zearalenon (ZL) in products of processing of contaminated wheat, barley and maize grains was is investigated. Results of the data analysis on the investigation of an actual nutrition of the population in Russia is presented; the share of products of processing of contaminated wheat, barley and maize grains as part of the total ration was determined Varied values of Maximum Acceptable Concentration (MAC) of ZL based on the obtained results are offered: 1 mg/kg--for wheat, barley and maize grains; 0.2 mg/kg--for main products of grain processing, viz flour and groats. The application of these MAC-values for ZL ensures the conformity between the ones for raw materials and for products of processing of raw materials, as well as the limitation of the maximum possible ZL--intake within the bounds of Acceptable Daily Intake (ADI) for a man.     

Description of Microstructural Changes in Wheat Flour and Flour Components during Hydration by using Environmental Scanning Electron Microscopy

The initial microstructures of two wheat flours (hard wheat flour and soft wheat flour) and flour components (starch, gluten, soluble pentosans and insoluble pentosans) were observed by scanning electron microscopy (SEM) and the changes in microstructure during hydration were described using environmental SEM (ESEM). SEM images permitted observation of the classical microstructure of wheat flour particles and starch granules. The initial microstructure of the purified fractions of flour components (gluten, soluble pentosans and insoluble pentosans) seemed largely dependent on the purification techniques, and could not thus directly be used to describe their in situ behavior during flour processing. ESEM observations of wheat flours and flour components during hydration first demonstrated slight changes in surface of particles that we associated to apparent swelling effects. The formation of a continuous aqueous phase between particles was observed for long hydration times.