Effects of protein–lipid and starch–lipid complexes on textural characteristics of extrudates based on wheat flour with the addition of oleic acid

The knowledge of biopolymer changes by extrusion is very important for a wide range of industrial applications that spreads from extruded food to biodegradable packaging. In this article, the formation of starch–lipid and lipid–protein complexes that occurred during the extrusion cooking of wheat flour with the addition of fatty acids was studied. Results showed that the highest barrel temperature (128.3 °C) promoted the formation of starch–lipid complexes in samples made up of wheat starch and wheat flour with the addition of fatty acids. The maximum formation of protein–lipid complexes (68% fatty acid bound to protein) was observed at the highest barrel temperature and water feed content (<22%). This study is a prerequisite for the optimisation of production of expanded extrudates made up of wheat flour and fatty ingredients and for the study of a biodegradable packaging based on by‐product of milling wheat (and fat).     

Understanding high pressure-induced changes in wheat flour–water suspensions using starch–gluten mixtures as model systems

The effect of high pressure (HP) on wheat flour–water suspensions was investigated. Suspensions were treated for 10 min at 200–600 MPa. HP-treatment significantly increased the consistency of the flour suspensions, as studied by frequency sweep tests. Temperature sweeps revealed that HP-induced starch gelatinisation, with a sigmoidal-shaped correlation between degree of gelatinisation and treatment pressure. Analysis of protein solubility in different buffers indicated the HP-induced formation of urea-insoluble complexes and/or disulphide bonds. Furthermore, the effects of HP on the isolated components wheat starch and gluten were studied, and starch–gluten mixtures were used as a model system for flour. A negative effect of gluten on the consistency increase of starch suspension was observed. Comparing the rheological parameters of HP-treated wheat flour suspensions to those of starch suspensions, confirmed the weakening effect of gluten. However, the presence of gluten in flour could not fully explain the differences between starch and flour suspension.     

Study of starch-lipid complexes in model system and real food produced using extrusion-cooking technology

The formation of starch-lipid complexes during extrusion of model system (rice starch added with oleic acid) and real food (rice starch added with pistachio nut flour) was evaluated. Both formulas were extruded at the same processing conditions (temperature profiles, screw speed and water feed content).The formation of starch-lipid complexes in real food, is strongly dependent on water feed content. In fact, at barrel temperature of 128 °C, the highest melting enthalpy of real food (6.7 J/g) was obtained only at 21% of water feed content whereas in the model system it was obtained both at 16 and 21%.These results point out the importance to consider all components present in the extruded food in order to study biopolymers modifications that occur during processing.

Industrial relevance

Additions of lipids alter the physical and chemical properties of starchy foods. The changes brought about by them in starchy foods have been attributed to the formation of complexes between amylose and lipids. These changes in the functionality of starch are of interest to the food industry and for human nutrition. Lipid complexation with starch is a very important reaction in extrusion cooking that affects structure formation and texture of the extruded products. Most studies on the starch-lipid complex formation during extrusion of model systems like starch and free fatty acids have been carried out, instead very little is known about starch-lipid complex formation during extrusion of flour blends containing fatty meal. This paper points out the importance to consider all components present in the food extruded in order to study biopolymers modifications that occur during processing. For this reason it is very important to use model systems that are not very different to real food and anyhow it would be advisable to verify the obtained results on real food, above all when a relation between macromolecular modifications and quality characteristics of extruded products would be studied.     

Protein nutritional value of extrusion-cooked wheat flours

The effect of extrusion cooking on the protein nutritional value of wheat flour and whole-grain wheat flour was studied. Amino acid analysis showed lysine retention between 63 and 100%. The retention was positively affected by an increase in feed rate, and negatively by an increase in screw speed. The prominent lysine damage under severe conditions was probably due to formation of reducing carbohydrates through hydrolysis of starch. The loss of other amino acids was small. The BV of extruded wheat flours was significantly reduced in the products showing the most prominent lysine loss. However, no effect was seen in TD. In contrast, a decrease in BV of extruded whole-grain flour was accompanied by a significant reduction in TD. Extrusion cooking of wheat starch did not affect the nitrogen balance in rats given casein/starch diets containing raw or extruded starch.     

Starch–lipid complex formation during extrusion-cooking of model system (rice starch and oleic acid) and real food (rice starch and pistachio nut flour)

The formation of starch–lipid complexes during extrusion-cooking of model system (rice starch and oleic acid) and real food (rice starch and pistachio nut flour) was evaluated. Both formulas were extruded at the same processing conditions (temperature profiles, screw speed, and water feed content). The obtained data showed that in model system and real food, the formation of starch–lipid complexes occurred under different processing conditions. In particular, the highest formation of starch–lipid complexes, that is, the highest melting enthalpy value (ΔH _m = 1.18 J/g), was obtained at the middle values of barrel temperature (100 °C) and water feed content (19%) in the model system. Yet, the only processing variable that had a significant effect on the formation of starch–lipid complexes in the real food was barrel temperature. In particular, the highest melting enthalpy of starch–lipid complexes (ΔH _m = 9.28 J/g) was obtained at the highest values of barrel temperature (130 °C). These results point out the importance of considering all components present in the raw materials submitted to extrusion-cooking in order to study biopolymer modifications, which occur during processing.     

Dynamic mechanical properties and fractal analysis of texturized soybean protein/wheat gluten composite produced by high moisture extrusion

Texturized soybean protein (TSP) and wheat gluten were prepared at high moisture using a twin-screw extruder. Effects of feed moisture content, extrusion temperature and wheat gluten content on the dynamic mechanical properties, microstructures and fractal analysis of texturized soybean protein/wheat gluten composite were investigated. All extruded samples were well fitted with Burger's model in creep-recovery tests (R² ≥ 0.978). The creep-recovery rate decreased with an increasing extrusion temperature. The addition of wheat gluten increased the resistance to creep and the unrecoverable deformation of TSP samples. The extrusion parameters affected the microstructure and morphology of extruded products. The fractal dimension of TSP products decreased with an increase in moisture content and wheat gluten content. Texturized soybean protein (TSP) and wheat gluten composite could form well-structure products.     

Effect of semolina and absorption level on extrusion of spaghetti containing non‐traditional ingredients

Specific mechanical energy (SME), mechanical energy, extrusion rate and temperature of extruded spaghetti were monitored to determine the effects of semolina, hydration level and non‐traditional ingredients on pasta extrusion using a semi‐commercial pasta press with a fixed screw speed of 25 rpm. SME transferred to the dough during extrusion and the temperature of extruded spaghetti were greater with strong than with weak gluten semolina and at low than at high absorption levels. When compared with semolina hydrated to 300 g kg^?1 absorption, SME transferred to the dough was 13 kJ kg^?1 lower for semolina mixed with buckwheat (Fagopyrum esculentum Moench.) bran flour, 47 kJ kg^?1 lower for semolina mixed with flaxseed (Linum usitativissimum L.) flour and 7 kJ kg^?1 lower for semolina mixed with wheat (Triticum turgidum var. durum L.) bran. Weak gluten semolina, high absorption levels and non‐traditional ingredients reduced the mechanical energy required for extrusion more than they reduced extrusion rate. The target temperature for extruded spaghetti was 45 °C. The temperature of extruded spaghetti containing flaxseed flour was below 45 °C whereas the temperature of spaghetti containing wheat bran was above 45 °C, regardless of semolina type or absorption level. Copyright © 2006 Society of Chemical Industry     

Resistant Starch Derived from Extruded Corn Starch and Guar Gum as Affected by Acid and Surfactants: Structural Characterization

Corn starches with and without guar gum [10% (w/w)] and 2% (w/w) of diacetyl tartaric acid ester of monoglyceride, sodium stearoyl‐2‐lactylate or citric acid, respectively, were extrusion‐cooked in a twin‐screw extruder at 18% moisture, 150 °C and 180 rpm screw speed. The content of resistant starch was determined by sequential enzymatic digestion. The formation of resistant starch in extruded corn starch was strongly affected by the addition of gum and the different food additives. X‐ray diffraction of the extruded starches gave a V diffraction pattern indicating the effect of extrusion cooking and amylose‐lipid complexes. Enzymatic digestion did not affect the V‐structure, which could apparently be attributed to extrusion cooking. Similarly, differential scanning calorimetric thermograms indicated that all isolated resistant starches exhibited endothermic transitions between 71—178 °C signifying a complex formation between amylose and the emulsifiers and possibly the melting of amylose crystallites in the resistant starch. Purification of the isolated resistant starches by size exclusion‐high performance liquid chromatography showed a dependence of molecular weight on the added additives. Results of differential scanning calorimetry and X‐ray diffraction suggest that amylose‐lipid complexes could also be involved in the formation of resistant starch in extruded cornstarch.     

Impact of Guar and Wheat Bran on the Physical and Nutritional Quality of Extruded Breakfast Cereals

Two non‐starch polysaccharides, guar gum and wheat bran, were used at 15% replacement level in a cereal base to produce an extruded breakfast cereal product from both wholemeal and high‐ratio wheat flour mixes. The inclusion of the non‐starch polysaccharides into the flour bases had no significant effect on the expansion ratio of the products. However, the product density and bulk density of the extruded products increased with guar gum and wheat bran addition. The pasting properties of the raw flour and polysaccharide base as well as the extruded products were altered with the incorporation of polysaccharides, with guar gum‐enriched products showing elevated peak and final viscosity readings. This appeared to be related to moisture manipulation and hence the regulation of gelatinisation. In vitro starch hydrolysis of the raw bases and the extruded samples illustrated that the extrusion process significantly increased the availability of carbohydrates for digestion. Additionally, the inclusion of non‐starch polysaccharides in the raw bases significantly reduced the rate and extent of carbohydrate hydrolysis. This potentially glycaemic reducing action was also evident in the extruded products where the incorporation of guar gum at 15% yielded a reduction of starch hydrolysis of 36% in the wholemeal base and 32% in the high‐ratio white wheat flour base.     

Effect of the addition of whole‐grain wheat flour and of extrusion process parameters on dietary fibre content,starch transformation and mechanical properties of a ready‐to‐eat breakfast cereal

This study evaluates the effect of the incorporation of whole‐grain wheat flour (WGWF) and of extrusion process parameters on the nutritional and technological quality of breakfast cereals. The corn flour‐based breakfast cereals were elaborated in a twin‐screw extruder following a rotatable central composite design with varied WGWF (0–100%), feed moisture (14–24%) and zones 3 and 4 barrel temperature (76–143 °C). Dietary fibre and resistant starch were significantly increased with WGWF addition. Total and digestible starch showed a decrease when WGWF increased. The RVA parameters were significantly affected by all the extrusion conditions and WGWF content. The cell structure of the extrudates was dependent of WGWF and moisture.     

Laboratory‐scale Dry/Wet‐Milling Process for the Extraction of Starch and Gluten from Wheat

A laboratory‐scale process is presented for the manufacture of starch and gluten from wheat. Main feature of this process is that whole wheat kernels are crushed dry between smooth rolls prior to wet disintegration in excess water in such way that gluten formation is prevented and fibres can be removed by sieving. Centrifugation of the endosperm suspension yields a dough which can be separated into starch and gluten using an established batter process. The results suggest that starch recovery is increased in comparison to a conventional wheat flour process without a concomitant decrease in protein recovery. Although starch purification was omitted, a total starch with a low protein content is obtained. On the other hand, the protein content of the gluten fraction is rather low due to difficulties in removing the starch. Despite this, the effect on dough mechanical properties by the addition of gluten obtained from wet‐milled wheat is comparable to the effect of gluten from flour.     

Influence of gluten on the viscoelastic properties of starch pastes and gels

Viscoelastic properties of dispersions (60–300 g kg⁻¹) of gluten (G) and wheat starch (S) blends (0 < G/S < 0·20) and wheat flour have been studied during heating and cooling. In both cases, the moduli followed power law relationships with concentration. The temperature at which the transient network development began, caused by granule–granule interactions, decreased as the concentration increased and increased with an increase in the proportion of gluten. Moreover, gluten weakened the strength of both starch pastes and gels, as shown by the lower values of the moduli. The viscoelastic behaviour of flour samples reflected the role played by internal lipids. A structural model is proposed in order to explain the influence of gluten on the rheological behaviour of starch pastes and gels. © 1998 Society of Chemical Industry.     

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.     

Starch affecting anti-staling agents and their function in freestanding and pan-baked bread

Anti-staling agents with different mechanisms were added to a normal white wheat bread to investigate the relation between bread staling, amylopectin retrogradation and water-related properties (i.e. water content and distribution between crumb and crust). Bread was baked both as pan-baked and freestanding loaves. The anti-staling agents maltogenic α-amylase, distilled monoglyceride and lipase had a direct influence on starch retrogradation, whereas gluten and waxy wheat flour diluted the amylopectin content or changed the ratio between amylose and amylopectin. The degree of staling was measured as the firmness and springiness, together with two new methods, crumbliness and cutability. In addition, the degrees of amylopectin retrogradation and amylose–lipid complex formation were analyzed by differential scanning calorimetry, and the water content, water loss and water migration were measured. The addition of α-amylase improved most staling parameters, although the changes were not as large as expected. Furthermore, monoglyceride and lipase increased the formation of amylose–lipid complexes, but only lipase gave better results regarding the specific volume and firmness. Increased amylose–lipid complex formation was seen to increase water migration from crumb to crust. Adding 10% waxy wheat flour appeared to lead to a slight overall improvement i.e. lower water migration and better cutability. Adding gluten or 3% waxy wheat flour only improved the specific volume. The method of baking the loaves, i.e. freestanding or pan-baked, had a greater influence than the anti-staling agents, which shows that bread quality is not always improved by starch affecting anti-staling agents without process changes.     

Macromolecular Changes in Extruded Starch‐Films Plasticized with Glycerol,Water and Stearic Acid

Native corn starch, plasticized with water, glycerol and stearic acid, was extruded in a conical twin‐screw extruder and sheeted into 0.4–0.6 mm thick films. The effects of extrusion and plasticizers on gelatinization, as well as the molecular and structural changes, in thermoplastic starch were analyzed. The onset and peak gelatinization temperatures of extruded starch varied from 42–46°C and 52.9–56.9°C, respectively, depending on the glycerol content. The enthalpy of gelatinization of extruded thermoplastic starch in excess water varied from 3.6–7.6 J/g, which also increased with plasticizer content. Amylose‐lipid complexes were formed during extrusion, and their enthalpies depended on the initial stearic acid and moisture contents. High‐performance size‐exclusion chromatography (HPSEC) data revealed that the starch underwent fragmentation during extrusion even under highly plasticized conditions, but the degradation was not severe as compared to previous findings. The relative percentages of amylopectin and amylose in native starch were 76.9 and 23.1%, respectively, which were changed to 71.3–76.6% and 23.4–28.7% in the extrudates. The average molecular weights of amylopectin and amylose in the extrudates ranged from 1.55×10⁷–2.07×10⁷ and 4.35×10⁵–7.39×10⁵, respectively. On the other hand, the molecular weights of amylopectin and amylose in native corn starch were observed as 2.27×10⁷ and 4.68×10⁵, respectively. Cross‐polarization magical angle spinning (CP/MAS) and high‐power decoupling (HP‐DEC) nuclear magnetic resonance (NMR) spectra of thermoplastic starch revealed the characteristics of amylomaize starch, confirming HPSEC results that the amylopectin macromolecules underwent fragmentation into amylose‐like fractions. In the extrudates, glycerol was found to be less mobile and entrained within the starch network.     

Changes of chemical composition and dough rheology in two fractions of sieve‐classified Polish spring wheat flour

The study of chemical composition and dough rheology changes in sieve‐classified two fractions (up to 60 and 60–240 μm particles) of wheat flour was the subject of this study. The straight grade flours were obtained by the milling of three Polish varieties of spring wheat, differing in ?? abbreviation? (PSI) values. The flours were separated with the use of a SZ‐1 laboratory sifter. The yield of fine fraction was in the range 50.0–55.7%. The obtained fractions were assayed for the content and composition of free lipids, gluten proteins, damaged starch, ash, water absorption and amylograph viscosity. Dough rheology (extrusion in OTMS cell, alveograph and farinograph tests) and baking trials were also performed. The content of free lipids, including the non‐polar and phospholipids was lower and the content of glycolipids was higher in fine flours. Those fractions were more rich in linoleic acid but the lower content of oleic and linolenic acids resulted in a higher oxidizability index of free lipids. Fine flours contained less ash and significantly more damaged starch. At the same time, they were characterized by a higher content of wet gluten, water absorption, amylograph viscosity and better dough parameters. This was reflected in the bread volume, which was higher by 6.3–10.7%. The influence of the changes in composition and the content of free lipids upon the rheology of the dough after the 90 days flour storage has not been defined unambiguously and requires further research.     

Effects of ball‐milling on the glass transition of wheat flour constituents

BACKGROUND: Starch and gluten, the major components of wheat flour, greatly influence the structural characteristics of food products made with wheat flour. The effects of ball‐milling on the change in the semicrystalline structure of starch granules to the amorphous state have been reported. However, the effects of ball‐milling of native wheat flour on physicochemical changes in wheat flour constituents have not been elucidated. Therefore in this study the effects of ball‐milling on the glass transition of wheat flour constituents were investigated. RESULTS: Crude gluten, non‐gluten proteins and separated starch were obtained from wheat flour ball‐milled for 0–10 h, and the glass transition temperature (T_g) of these constituents was evaluated. The T_g of all wheat flour constituents decreased with increasing ball‐milling time. Sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed that changes in band position and intensity did not occur for gluten but did occur for non‐gluten proteins. X‐ray diffraction revealed decreased crystallinity and greater plasticisation by water in separated starch as the ball‐milling time was prolonged. CONCLUSION: The results showed that the ball‐milling process decreased the T_g of wheat flour constituents as a function of milling time. The decrease in T_g was probably due to changes in conformation of protein subunits in gluten and depolymerisation of the non‐gluten protein fraction. The information obtained here about the physical alteration of wheat flour constituents may enhance the ability to successfully use ball‐milled wheat flour in food applications. Copyright © 2008 Society of Chemical Industry     

Component Interactions in the Extrusion Cooking Process: Influence of Process Conditions on the Functional Viscosity of the Wheat Flour System

Wheat starch, vital gluten and wheat flour solubles were processed in combination, in a single screw extruder. The paste viscosity profile and degree of cook of the starch component were used to assess interactive effects. The composite of all 3 components, simulating a wheat flour, was more cooked and gave thicker pastes than wheat flour itself when processed under the same extrusion conditions. The data suggest that the integral structure of wheat flour particles imparts a greater resistance to water penetration and cooking than when the individual components exist at random in a composite formulation.     

Cooking quality characterisation of ‘spaghetti’ based on soft wheat flour enriched with oat flour

The cooking quality of pasta based on soft wheat flour and supplemented with three percentages of oat flour was studied. Results showed that oat flour modified deeply the cooking quality of spaghetti in comparison with samples based on only soft wheat flour. These effects were attributed to both starch‐lipid complex formation and presence of β‐glucans that weak gluten network. An increase in optimal cooking time with increase in oat percentages was observed (480 vs. 630 min). Samples enriched with oat flour showed a good‐quality cooking total organic matter (TOM values ranged from 1.4 to 2).     

Effect of extrusion conditions on resistant starch formation from pastry wheat flour

Pastry wheat flour was extruded under various conditions of feed moisture (20%, 40%, and 60%) and screw speed (150, 200, and 250 rpm), at constant barrel temperature profile (40, 60, 80, 100, and 120 °C, feed port to exit die). The extruded samples were stored at 4 °C for 0, 7, or 14 days, at which times resistant starch (RS) formation was analyzed. Thermal and pasting properties of extruded samples stored for 14 days were analyzed using a differential scanning calorimeter and rapid visco analyzer (RVA), respectively. The RS content increased after extrusion compared to non-extruded pastry wheat flour. High significant positive correlations of feed moisture (P < 0.01) and storage period (P < 0.05) with RS formation were observed. The RS derived from extrusion and storage showed higher thermal stability with decreasing feed moisture and screw speed. Statistically significant differences in pasting properties were observed with feed moisture or screw speed. In particular, the setback value from RVA of the sample was significantly increased with increasing feed moisture. These results indicate that feed moisture and storage time were both important factors for the formation of RS from pastry wheat flour during extrusion.