Effect of extrusion temperature on the solubility and molecular weight of lentil bean flour proteins containing low cysteine residues

Lentil flour was extruded at die temperatures of 135, 160, and 175 degrees C. The soluble protein content in the extrudates decreased by 40.1% in the extracting buffer (1% sodium dodecyl sulfate in 50 mM sodium phosphate buffer, pH 6.9) as the extrusion die temperature was increased to 175 degrees C. The most insoluble proteins in the extrudates extruded at die temperatures of up to 175 degrees C could be resolubilized by using sonication. The total disulfide content and sulfhydryl content in the extrudates decreased. The SDS-PAGEs showed that the molecular weight distribution of proteins in the lentil flour changed little before and after extrusion as well as during reduction. The results from this study show that the extrusion temperature had less effect on the solubility and molecular weight of the lentil proteins, which contain a lower level of cysteine residues than wheat proteins.     

Effect of Extruding Wheat Flour at Lower Temperatures on Physical Attributes of Extrudates and on Thiamin Loss When Using Carbon Dioxide Gas as a Puffing Agent

Wheat flour with 0.3% (w/w) thiamin was extruded on a twin‐screw laboratory‐scale extruder (19‐mm barrel) at lower temperatures and expanded using carbon dioxide (CO₂) gas at 150 psi. Extrusion conditions were die temperature of 80°C and screw speed range of 300–400 rpm. Control samples were extruded at a die temperature of 150°C and screw speed range of 200–300 rpm. Dough moisture content was 22% in control samples and 22 and 25% in CO₂ samples. Expansion ratio, bulk density, WAI, and %WSI were compared between control and treatment. CO₂ injection did not significantly increase expansion ratio. Bulk densities in the CO₂ extruded samples decreased when feed moisture decreased from 25 to 22%. The products using CO₂ had lower WAI values than products puffed without CO₂ at higher temperatures. The mean residence time was longer in CO₂ screw configurations than in conventional screw configurations. Thiamin losses were 10–16% in the control samples. With CO₂, thiamin losses were 3–11% at 22% feed moisture, compared with losses of 24–34% at 25% moisture. Unlike typical high‐temperature extrusion, thiamin loss in the low‐temperature samples decreased with increasing screw speed. Results indicate that thiamin loss at lower extrusion temperatures with CO₂ injection is highly dependent on moisture content.     

Immunochemical and Electrophoretic Analysis of the Modification of Wheat Proteins in Extruded Flour Products

Antibodies specific for wheat proteins were used to identify protein fractions modified during extrusion of Hard Red Spring wheat flour (14% protein) under four different combinations of extrusion conditions (18 and 24% feed moisture and 145 and 175°C die temperature). Antibody binding was assessed on immunoblots of proteins extracted from flour and extrudates separated by SDS‐PAGE. Antibodies to high molecular weight glutenin subunits (HMW‐GS) and to B‐group low molecular weight glutenin subunits (LMW‐GS) recognized intact subunits from both flour and extrudates. Antibodies to C‐group LMW‐GS had diminished binding to extruded proteins. Glutenin‐specific antibodies also recognized protein in the extrudates migrating as a smear at molecular weights higher than intact subunits, indicating cross‐linked proteins. Antibodies recognized albumins or globulins in flour but not in extrudates, evidence that these fractions undergo significant modification during extrusion. Acid‐PAGE and antibody reaction of gliadins extracted in 1M urea and in 70% ethanol revealed total loss of cysteine‐containing α, β, γ‐gliadins but no obvious effects on sulfur‐poor ω‐gliadins, suggesting gliadin modification involves replacing intramolecular disulfides with intermolecular disulfide cross‐links. Identifying protein fractions modified during different extrusion conditions may provide new options for tailoring extrusion to achieve specific textural characteristics.     

Effect of Barley Flour on Development of Rice‐Based Extruded Snacks

This study was conducted to develop a ready‐to‐eat extruded food using a single‐screw laboratory extruder. Blends of Indian barley and rice were used as the ingredients for extrusion. The effect of extrusion variables and barley‐to‐rice ratio on properties like expansion ratio, bulk density, water absorption index, hardness, β‐glucan, L*, a*, b* values, and pasting characteristics of extruded products were studied. A central composite rotatable design was used to evaluate the effects of operating variables: die temperature (150–200°C), initial feed moisture content (20–40%), screw speed (90–110 rpm), and barley flour (10–30%) on properties like expansion ratio, bulk density, water absorption index (WAI), hardness, β‐glucan, L*, a*, b* values, and sensory and pasting characteristics of extruded products. Die temperature >175°C and feed moisture <30% resulted in a steep increase in expansion ratio and a decrease in bulk density. Barley flour content of 10% and feed moisture content of <20% resulted in an increased hardness value. When barley flour content was 30–40% and feed moisture content was <20%, a steep increase in the WAI was noticed. Viscosity values of extruded products were far less than those of corresponding unprocessed counterparts as evaluated. Rapid visco analysis indicated that the extruded blend starches were partially pregelatinized as a result of the extrusion process. Sensory scores indicated that barley flour content at 20%, feed moisture content at 30%, and die temperature at 175°C resulted in an acceptable product. The prepared product was roasted in oil using a particular spice mix and its sensory and nutritional properties were studied.     

Small‐Scale Extrusion of Corn Masa By‐Products

Corn masa by‐product streams are high in fiber and are amenable for utilization in livestock feed rations. This approach is a potentially viable alternative to landfilling, the traditional disposal method for these processing residues. Suspended solids were separated from a masa processing waste stream, blended with soybean meal at four levels (0, 10, 20, and 30% wb), and extruded in a laboratory‐scale extruder at speeds of 50 rpm (5.24 rad/sec) and 100 rpm (10.47 rad/sec) with temperature profiles of 80‐90‐100°C and 100‐110‐120°C. Processing conditions, including dough and die temperatures, drive torque, specific mechanical energy consumption, product and feed material throughput rates, dough apparent viscosity, and dough density, were monitored during extrusion. The resulting products were subjected to physical and nutritional characterization to determine the effects of processing conditions for these blends. Extrudate analysis included moisture content, water activity, crude protein, in vitro protein digestibility, crude fat, ash, product diameter, expansion ratios, unit and true density, color, water absorption and solubility, and durability. All blends were suitable for extrusion at the processing conditions used. Blend ratio had little effect on either processing parameters or extrudate properties; extrusion temperature and screw speed, on the other hand, significantly affected both processing and product properties.     

Effect of Temperature and Screw Speed on Stability of Fumonisin B1 in Extrusion-Cooked Corn Grits

Corn grits spiked with fumonisin B₁ (FB₁) at a level of 5 μg/g were extrusion cooked in a corotating twin-screw extruder at different temperatures (140, 160, 180, and 200°C) and screw speeds (40, 80, 120, and 160 rpm). Good recoveries of FB₁ were obtained from the nonextruded as well as the extruded grits by using high-performance liquid chromatography. Both the barrel temperature and the screw speed significantly (P ≤ 0.05) affected the extent of fumonisin reduction in extruded grits. As expected, the FB₁ recovered decreased with an increase in temperature and a decrease in screw speed. The amount of FB₁ lost from cooking grits at the different extrusion parameters used in this study ranged from 34 to 95%. About 46–76% of the spiked FB₁ was lost when the grits were cooked at temperatures and screw speeds that resulted in acceptable product expansion and color.     

Waxy Soft White Wheat: Extrusion Characteristics and Thermal and Rheological Properties

Waxy wheat flour was analyzed for its thermal and rheological properties and was extruded to evaluate its potential for extruded products. Normal soft white wheat flour was analyzed with the same methods and same extrusion conditions to directly compare differences between the two types of flour. Through DSC analysis, waxy wheat flour was found to have a higher gelatinization peak temperature of 66.4°C than normal wheat at 64.0°C, although the transition required 2.00 J/g less energy. Rapid visco‐analysis indicated that the waxy wheat flour pasted much more quickly and at lower temperatures than the normal wheat flour. Preliminary extrusion experiments were conducted to determine the optimal screw profile for waxy wheat with respect to maximum radial expansion. The optimum screw profile was used for extrusion trials with varying flour moisture (15–25% wb) and extruder screw speed (200–400 rpm) while monitoring process conditions including back pressure and specific mechanical energy. Physical properties of the extrudates were then studied. The radial expansion ratios of the waxy wheat extrudates exceeded those of the normal wheat extrudates by nearly twice as much, and it was observed that the waxy wheat flour took less energy in the form of fewer shear screw elements to expand. The waxy wheat extrudates also exhibited significantly higher water solubility and less water absorption than the normal wheat extrudates owing to solubilizing of the extrudates. The results of our study indicate that waxy wheat flour may be a viable ingredient for creating direct expanded products with less energy.     

Physical Characteristics,Nutritional Quality,and Antioxidant Potential of Extrudates Produced with Polished Rice and Whole Red Bean Flours

In Brazil, rice (Oryza sativa L.) and beans (Phaseolus vulgaris L.) are the basis of the population's diet, and their consumption together is a good strategy to improve protein biological value. The aim of this study was to produce extruded products with whole red bean (WRBF) and polished rice (PRF) flours and to evaluate the effects of extrusion temperature (T) and feed moisture content (FM) on technological properties and total phenolic compounds content. The extrudates were elaborated in a twin‐screw extruder following a 2² central composite rotatable design with FM (15–23%) and T (120–160°C) as independent variables. WRBF and PRF were used at a 1:3 ratio. Amino acid content and profile were evaluated in the optimum extrudate (produced at FM = 19% and T = 140°C). The total phenolic content identified in extruded products was provided by the red bean seed coat, and its quantification suggested the release of bound phenolics with the extrusion process (not temperature dependent). The extrusion of PRF and WRBF, in combination, produced extruded products of high protein quality, being complete in essential amino acids for the diets of people at least 48 months old. The results indicate that legume flours such as WRBF incorporated into rice flour can cause a positive impact on technological, nutritional, and functional quality of extrudates.     

SME‐Arrhenius Model for WSI of Rice Flour in a Twin‐Screw Extruder

We have modeled a rice extrusion process focusing specifically on the starch gelatinization and water solubility index (WSI) as a function of extrusion system and process parameters. Using a twin‐screw extruder, we examined in detail the effect of screw speed (350–580 rpm), barrel temperature, different screw configurations, and moisture content of rice flour on both extrusion system parameters (product temperature, specific mechanical energy [SME], and residence time distribution [RTD]) and extrudate characteristics (expansion, density, WSI, and water absorption index [WAI]). Changes in WSI were monitored to reveal a relationship between the reaction kinetics during extrusion and WSI. Reaction kinetics models were developed to predict WSI during extrusion. WSI followed a pseudo first‐order reaction kinetics model. It became apparent that the rate constant is a function of both temperature and SME. We have developed an adaptation of the kinetic model based on the Arrhenius equation that shows better correlations with SME and distinguishes data from different screw configurations. This adaptation of the model improved predictability of WSI, thereby linking the extrusion conditions with the extruded product properties.     

Extrusion Chemistry of Wheat Flour Proteins: I. Free Radical Formation

Electron paramagnetic resonance (EPR) spectroscopy was used to study free radical production in hard red wheat flours extruded according to a two-level fractional factorial experimental design (11 and 14% protein content, 160 and 185°C, 16 and 20% moisture, 300 and 500 rpm screw speed, and mass flow rate of 225 and 400 g/min). All spectra showed dominant broad singlets (g = 2.0053–2.0059) from nitrogen-centered radicals originating from heat-induced peptide scission and reactions of lipid radicals with side-chain amino groups. At 77 K, sulfur-oxyl or peroxyl radicals (g = 2.008–2.018), thiyl radicals (g = 2.025), and disulfide radical species (g = 2.032–2.035 and 2.05–2.06), resulting from intra- and intermolecular electron migration and shear-induced scission of disulfides, sometimes were present. The strongest EPR signals occurred under conditions of maximum free radical production and minimum opportunity for radical recombination: high protein flour (14%), high die temperature (180°C), and low moisture (16%). EPR signals correlated with sulfhydryl and disulfide (SH-SS) levels and physical properties of extrudates, indicating that free radicals are integrally involved in molecular changes that occur during extrusion.     

Extrusion of Cross‐Linked Hydroxypropylated Corn Starches II. Morphological and Molecular Characterization

A series of cross‐linked hydroxypropylated corn starches were extruded with a Leistritz micro‐18 co‐rotating extruder. Extrusion process variables including moisture (30, 35, and 40%), barrel temperature (60, 80, and 100°C), and screw design (low, medium, and high shear) were investigated. Scanning electron microscopy (SEM) of extruded starches showed a gel phase with distorted granules and granule fragments after extrusion at 60°C. After extrusion at 100°C only a gel phase was observed with no granular structures remaining. High performance size exclusion chromatography (HPSEC) equipped with multiangle laser light‐scattering (MALLS) and refractive index (RI) detectors showed extruded starches degraded to different extents, depending on extrusion conditions. The average molecular weight of the amylopectin of unextruded native corn starch was 7.7 × 10⁸. Extrusion at 30% moisture, 100°C, and high shear reduced the molecular weight of amylopectin to 1.0 × 10⁸. Hydroxypropylated normal corn starch extruded at identical conditions showed greater decreases in amylopectin molecular weight. With the addition of cross‐linking, the amylopectin fractions of the extruded starches were less degraded than those of their native and hydroxypropylated corn starch counterparts. Similarly, increasing moisture content during extrusion lowered amylopectin degradation in the extruded starches. Increasing temperature during extrusion of cross‐linked hydroxypropylated starches at high moisture content (e.g., 40%) lowered amylopectin molecular weights of the extruded starches, whereas increasing extrusion temperature at low moisture content (30%) resulted in less degraded molecules. This difference was attributed to the higher glass transition temperatures of the cross‐linked starches.     

Effect of l‐Cysteine on the Rheological Properties of Wheat Flour

Extrudate expansion of cereal‐based products is largely dependent on the molecular interactions and structural transformations that proteins undergo during extrusion processing. Such changes strongly influence the characteristic rheological properties of the melt. It is possible to modify rheological properties of wheat flour during extrusion processing, in particular shear viscosity, with cysteine. The objective of this work was to further develop an understanding of the molecular interactions and structural transformations of wheat flour from dynamic oscillatory rheological measurements. Temperature and frequency sweeps were conducted in the linear viscoelastic range of the material. Changes in the storage modulus (G′), the loss modulus (G″) and the loss tangent (tan δ) of 25% moisture wheat flour disks as a function of cysteine concentration (0–0.75%) were monitored. Molecular weight between cross‐links (M_c) and the number of cross‐links (N_c) per glutenin molecule were determined from frequency sweep data. Increasing cysteine concentration broke cross‐links by decreasing G′ maximum and increasing tan δ values. Molecular weight between cross‐links increased and the number of cross‐links decreased. G′ values from temperature sweeps showed a similar trend. This information leads to a better understanding of the viscoelastic behavior of wheat flour doughs during extrusion cooking and elucidation of protein‐protein reaction mechanisms and other interactions in extruded cereal‐based snack foods.     

Extrusion of Wheat Gluten Plasticized with Glycerol: Influence of Process Conditions on Flow Behavior,Rheological Properties,and Molecular Size Distribution

Gluten-glycerol dough was extruded under a variety of processing conditions using a corotating self-wiping twin-screw extruder. Influence of feed rate, screw speed, and barrel temperature on processing parameters (die pressure, product temperature, residence time, specific energy) were examined. Use of flow modeling was successful for describing the evolution of the main flow parameters during processing. Rheological properties of extruded samples exhibited network-like behavior and were characterized and modeled by Cole-Cole distributions. Changes in molecular sizes of proteins during extrusion were measured by chromatography and appeared to be correlated to molecular size between network strands, as derived from the rheological properties of the materials obtained. Depending on operating conditions, extrudates presented very different surface aspects, ranging from very smooth-surfaced extrudates with high swell to completely broken extrudates. The results indicated that extrudate breakup was caused by increasing network density, and some gliadins may have acted as cross-linking agents. Increasing network density resulted in decreasing mobility of polymeric chains, and “protein melt” may no longer have been able to support the strain experienced during extrusion through the die. Increasing network density was reflected in increased plateau modulus and molecular size of protein aggregates. Increasing network structure appeared to be induced by the severity of the thermomechanical treatment, as indicated by specific mechanical energy input and maximum temperature reached.     

Extrusion of Cross‐Linked Hydroxypropylated Corn Starches I. Pasting Properties

A series of cross‐linked (0, 0.014, 0.018, 0.024, and 0.028% POCl₃, dry starch basis) hydroxypropylated (8%) corn starches were extruded using a Leistritz micro‐18 co‐rotating extruder. Process variables included moisture, barrel temperature, and screw design. Differential scanning calorimetry and X‐ray diffraction studies showed the level of starch crystallinity decreased with increasing severity of extrusion conditions. Pasting properties of the extruded starches were examined using a Rapid Visco Analyser. Pasting profiles of starches extruded at different conditions displayed different hot paste viscosity and final viscosity. Increasing starch moisture content during extrusion and level of cross‐linking increased starch viscosity (P < 0.0001), whereas increasing extrusion temperature and shear decreased starch viscosity (P < 0.0001). Interactions were found between level of cross‐linking and screw design and between extrusion temperature and starch moisture content (P < 0.0001).     

Empirical Modeling of Mean Residence Time in a Co‐Rotating Twin‐Screw Extruder with Rice Flour

Mean residence time of rice flour in a twin‐screw extruder was determined using a blue tracer. Variables studied included moisture content, screw speed, barrel temperature, and screw configuration. Mean residence time increased with the increase of the barrel temperature and with the addition of reverse and kneading elements. Mean residence time was significantly related to screw speed, moisture content, die pressure, and screw configuration (P < 0.05). An empirical model was developed to predict mean residence time with the ability to reflect the changes of the barrel temperature and screw configuration. The effects of different extrusion operating conditions including screw speed, moisture content, barrel temperature, and screw geometry on the mean residence time were considered in the model. The validity of the developed model was extensively evaluated and verified using different screw geometries and other processing variables. The mean residence times predicted by the developed model are in good agreement with the experimental data.     

Effect of Extrusion Process Parameters on the Quality of Buckwheat Flour Mixes

A response surface analysis using a second-order central composite design was used to study the effect of extrusion process parameters on the extrudate quality of three blends containing buckwheat flour. The extrudates were prepared as three blends. Blend 1 was a 55:40:5 (w/w) mix of light buckwheat flour, wheat flour, and nonfat dry milk (NFDM). Blend 2 was a 40:55:5 mix of light buckwheat flour, corn meal, and NFDM. Blend 3 was a 30:60:10 mix of light buckwheat flour, corn meal, and NFDM. The blends were processed in a twin-screw extruder with factorial combinations of the parameters including: process temperatures of 95–150°C, dough moisture of 15–22%, and screw speeds of 260–390 rpm. The linear components alone significantly explained most of the variation of expansion index, bulk density, water absorption, and breaking strength. The greatest amount of variability was explained by process temperature for blend 1. Dough moisture accounted for the greatest amount of variation for blends 2 and 3. Maximum predicted expansion index values and high water absorption percentages were obtained at low dough moisture levels. Dough moisture and process temperatures were the most important factors predicting bulk density. Sensory evaluation of texture, color, flavor, and general acceptability scores of selected samples ranked blend 3 > blend 2 > blend 1. The in vitro protein digestibility values ranked blend 1 > blend 2 > blend 3. An increase of up to 9.5% units in the protein digestibility values was observed when compared to the nonextruded raw blends.     

Detoxification of Rapeseed Meal by Extrusion with an Added Basic Salt

A commercial, high-glucosinolate, rapeseed meal with no added salt or mixed with 2, 5, or 10% NH₄HCO₃ was extruded under different processing conditions using the Wenger TX-52 twin-screw extruder. Male Wistar rats were fed 13 diets containing 15% rapeseed meals (including nonextruded) or a casein-based control diet. After six weeks, blood samples were taken, and serum was analyzed for thyroid hormones. Extrusion processing under all salt and steam conditions tested reduced glucosinolate levels in the meal, but no significant correlation was found between intensity of the treatment conditions and glucosinolate reduction. Higher weight gains, feed efficiencies, and thyroid hormone profiles were observed with use of the extruded meals; but no treatment completely detoxified the meal. Histopathological evaluation showed that thyroid and other tissue abnormalities occurred in all animals except those fed the casein diet. Antinutrients, including glucosinolates and probably volatile nitriles, in the meal were reduced by extrusion processing under the basic conditions of this experiment.     

Oil Absorption Characteristics of a Multigrain Extrudate During Frying: Effect of Extrusion Temperature and Screw Speed

The oil absorption characteristics of a multigrain extruded and fried snack product were studied as a function of extruder screw speed and cooking temperature using a central composite response surface methodology (RSM). The extruded product was produced using a corotating twin screw extruder, dehydrated to a uniform moisture content, and subsequently deep‐fat‐fried at 192 ± 1°C for 10–40 sec to complete expansion. Significant RSM models were developed for oil absorption and extrudate water absorption index (WAI). According to the lowest oil model, absorption (19.9%) was obtained with an extruder screw speed of 218.6 rpm and a cooking temperature of 117.8°C. WAI reached a maximum at a screw speed of 221.9 rpm and a cooking temperature of 109°C. Oil absorption characteristics and extrudate WAI were significantly correlated (r= ‐0.84, P = 0.0002). The data suggest that extrusion conditions can be optimized to influence the physicochemical structures in the extrudate matrix so that oil absorption can be minimized.     

Twin‐Screw Extrusion Processing of Rainbow Trout (Oncorhynchus mykiss) Feeds Using Various Levels of Corn‐Based Distillers Dried Grains with Solubles (DDGS)

Increasing demand for seafood products and rising demand for fish meal for commercial fish feeds is driving the search for effective alternative protein sources. Twin‐screw extrusion trials were conducted to study the production of nutritionally balanced feeds for rainbow trout fingerlings (Oncorhynchus mykiss). Six isocaloric (≈4.61 kcal/g) ingredient blends with a target protein content of >45% db were formulated with 0, 10, 20, 30, 40, and 50% distillers dried grains with solubles (DDGS) and other feed ingredients. The moisture contents of the diets were initially adjusted to 5–7% db, and then extruded at 250 rpm using dual 1.9 mm dies with varying amounts of steam (7.2–7.7 kg/hr) injected into the conditioner and water (4.3–6.5 kg/hr) into the extruder. Mass flow rates, moisture contents, and temperatures were measured during processing and moisture content, water activity, unit density, bulk density, expansion ratio, compressive strength, compressive modulus, pellet durability index, water stability, and color were analyzed to quantify the effects of varying DDGS content on the extrudate physical properties. Significant differences (P < 0.05) among the blends were observed for color and bulk density for both the raw and extruded materials, respectively, and for the unit density and pellet durability index of the extruded products. There were also significant changes in redness and yellowness, but only minor changes in brightness, among the final products with increasing DDGS content. The compressive strength of the extrudates increased significantly with increasing DDGS. Expansion ratio of all pellets was low. All extruded diets achieved very good water stability.     

Effect of DDGS,Moisture Content,and Screw Speed on Physical Properties of Extrudates in Single‐Screw Extrusion

Three isocaloric (3.5 kcal/g) ingredient blends containing 20, 30, and 40% (wb) distillers dried grains with solubles (DDGS) along with soy flour, corn flour, fish meal, and mineral and vitamin mix, with net protein adjusted to 28% (wb) for all blends, were extruded in a single‐screw laboratory‐scale extruder at screw speeds of 100, 130, and 160 rpm, and 15, 20, and 25% (wb) moisture content. Increasing DDGS content from 20 to 40% resulted in a 37.1, 3.1, and 8.4% decrease in extrudate durability, specific gravity, and porosity, respectively, but a 7.5% increase in bulk density. Increasing screw speed from 100 to 160 rpm resulted in a 20.3 and 8.8% increase in durability and porosity, respectively, but a 12.9% decrease in bulk density. On the other hand, increasing the moisture content from 15 to 25% (wb) resulted in a 28.2% increase in durability, but an 8.3 and 8.5% decrease in specific gravity and porosity, respectively. Furthermore, increasing the screw speed and moisture content of the blends, respectively, resulted in an increase of 29.9 and 16.6% in extruder throughput. The extrudates containing 40% DDGS had 8.7% lower brightness, as well as 20.9 and 16.9% higher redness and yellowness, compared with the extrudates containing only 20% DDGS. Increasing the DDGS content from 20 to 40% resulted in a 52.9 and 51.4% increase in fiber and fat content, respectively, and a 7.2% decrease in nitrogen free extract. As demonstrated in this study, ingredient moisture content and screw speed are critical considerations when producing extrudates with ingredient blends containing DDGS, as they are with any other ingredients.