Effect of wheat bran on the mechanical properties of extruded starchy foams

Incorporation of wheat bran has a significant effect on the texture of extruded starchy products. This can be explained by changes in the mechanical parameters of the products. The stress at rupture and elastic modulus of wheat flour-based solid foams, obtained at different extrusion conditions and bran concentration, were measured using a three-point bending test. Both parameters were positively correlated with the foam relative density according to the Gibson–Ashby model. At same relative densities and bran concentration, finer structures with higher density of small cells led to a higher mechanical strength of the foams. The stress at rupture of the unexpanded material was decreased when increasing the bran concentration. Nevertheless, expanded foams with added bran at an intermediate level showed increased mechanical strength. This was attributed to the finer cellular structures obtained. The effect of increasing the bran to a higher concentration on the mechanical properties was depending on the cell wall thickness and bran particle dimensions. At high relative density, the strength of the foams was further increased due to the even finer structures obtained. At low relative density, even though finer structures were also obtained, the stress at rupture of the foams was decreased. This may be explained by the lower cell wall thicknesses and low adhesion properties between bran and starch favoring rupture of the cell walls.     

Effect of extruded wheat bran on dough rheology and bread quality

Bran extrusion is mainly under study and works should be performed to know the effect on dough and bread. This study was designed to investigate the effect of bran extrusion (addition of 2.5 g/100 g to 20 g/100g bran) on the rheological characteristics of bread dough, behaviour during fermentation, and bread quality. Extruded bran increased dough development time and tenacity to a greater extent than non-extruded bran, and minimized the loss of stability if over-mixing occurred. Extruded bran, due to its greater gas production, also reduced loss of dough height during fermentation to a greater extent than untreated bran. However, breads with extruded bran showed a higher volume and lower initial firmness than breads with normal bran if improver was added. However, no differences were found in the organoleptic evaluation. Bran extrusion therefore modified dough rheology but did not negatively affect bread quality. It could even improve the quality of breads with bran when improvers are added.     

Elastic properties of extruded starchy melts containing wheat bran using on-line rheology and dynamic mechanical thermal analysis

Addition of wheat bran reduces the expansion volumes of extruded cereals. This may be explained by the influence wheat bran has on the elastic properties of the melt. The elastic properties of extruded refined wheat flour supplemented with wheat bran were investigated using a complementary on-line and an off-line rheological technique. The Bagley pressure (end pressure), reflecting extensional properties of the melt, was measured on-line using the orifice die method (dies with different lengths). The storage modulus of the extruded samples was measured using dynamic mechanical thermal analysis (DMTA). Increasing the bran concentration to an intermediate level significantly increased the Bagley pressure likely due to a reduced mobility of starch molecules. Further increasing the bran concentration significantly decreased the Bagley pressure. This might be caused by physical rupture of the melt at the die exit due to the low adhesion properties between starch and bran particles. This change in Bagley pressure indicates that the elastic properties of the composite melt may be reduced by bran particles. The storage modulus measured by DMTA was decreased when increasing the bran concentration, further supporting a potential decrease of the elastic properties of the melt with bran.     

Supplementation of extruded foams with wheat bran: Effect on textural properties

The objective of this study was to investigate the effect of wheat bran concentrations on the mechanical properties determining the texture of extruded carbohydrate matrices. For this wheat flour was extruded under different conditions with an increasing concentration of wheat bran. The mechanical properties were assessed using a threepoint bending test and the cellular structure was determined by micro-computed X-ray tomography. Regardless of the bran concentration, the stress at rupture of the extruded foams was positively correlated with their relative density according to the Gibson-Ashby model. At same relative densities and bran concentration, finer structures with higher density of small cells led to a higher mechanical strength of the foams. Expanded foams with added bran at an intermediate level showed increased mechanical strength. This was attributed to the finer cellular structures obtained.The effect of increasing the bran to a higher concentration on the mechanical properties was depending on the cell wall thickness and bran particle dimensions.     

Glass Transition of Extruded Wheat,Corn and Rice Starch

Commercial wheat, corn and rice starch were extrusion cooked under a specific mechanical energy input (SME) ranging from 81 to 365 Wh/kg (288 to 1314 kJ/kg). Extrusion cooking at low and high SME resulted in products having significant differences in molecular weight distribution and having crystalline structures of the V‐ and E‐type, as determined by gel permeation chromatography and X‐ray diffraction analysis. Differential scanning calorimetry revealed that the glass transition temperature (T_g) of the extruded starches was independent of the botanical source, the degree of extrusion‐induced molecular fragmentation and the formation of the V‐ and E‐type crystalline structures. The obtained master curve, defined by the relationship between water content and T_g of the amorphous starch, may be used as a predictive tool in modelling the extrusion process of starch or starch containing blends, especially with regard to the formation of the morphological structure and texture attributes of directly expanded products.     

Effects of increasing levels of transglutaminase on cooking quality of bran supplemented spaghetti

This study investigated the possibility of incorporating high levels of bran into spaghetti formulation by using transglutaminase (TG)—catalyzed crosslinking, without deterioration in spaghetti quality. Two durum wheat samples and one bread wheat sample were milled to semolina or farina. Ground mixture of coarse and fine brans of each cultivar was substituted for a portion of semolina or farina obtained from the respective cultivar, at the levels of 15 and 30% and then processed into spaghetti. Bacterial TG was added to the spaghetti formula at the levels of 0.2% and 0.4% (w/w). The results indicated that the TOM values and the sensory characteristics of the spaghetti were generally affected by the cultivar, bran supplementation, and TG addition level. The samples with TG exhibited significantly lower scores for TOM and higher sensory scores for firmness, stickiness, and bulkiness when compared with the respective control sample of each cultivar. As a result, transglutaminase addition had a significant improving effect on spaghetti quality which was more obvious in the weaker cultivar and it was possible to overcome the deteriorative effects of bran on spaghetti quality.     

Effects of glucose and acid-hydrolysed vegetable protein on the volatile components of extruded wheat starch

The volatile components produced in wheat starch, and wheat starch combined with 1% glucose, 1% acid-hydrolysed vegetable protein (aHVP) or 1% glucose and 1% aHVP, extruded under different processing conditions (temperatures of 150 or 180 °C and moisture content of 16% or 20%) were identified by gas chromatography-mass spectrometry (GC-MS). Gas chromatography olfactometry (GCO) was used to assess the odour intensity of volatile components present in the starch and starch/glucose/aHVP extrudates obtained at 180 °C. In total, 70 compounds were identified in the eight extrudates. The smallest number (24) was found in the extrudate of the starch/glucose mixture and the largest number (67) in the extrudate of the starch/glucose/aHVP mixture, both processed at 180 °C. Lipid degradation products, such as alkanals, 2-alkanones, 2-alkenals and 2,4-alkadienals, were present in all extrudates in significant quantities. However, in those extrudates containing aHVP, Strecker aldehydes were quantitatively the dominant components. Maillard reaction products, such as pyrroles and pyrazines, were only found in extrudates containing both glucose and aHVP whereas sulphur-containing aliphatic compounds were found in all extrudates containing aHVP. The production of the Maillard reaction products and sulphur-containing compounds were favoured by extrusion at 180 °C. Sensory analyses showed that each of the eight extrudates had different odours, and that the extrudates containing both glucose and aHVP possessed the highest overall odour intensity.     

Thermogravimetric analysis of water release from wheat flour and wheat bran suspensions

Bran is hygroscopic and competes actively for water with other key components in baked cereal products like starch and gluten. Thermogravimetric analysis (TGA) of flour–water mixtures enriched with bran at different incorporation levels was performed to characterise the release of compartmentalised water. TGA investigations showed that the presence of bran increased compartmentalised water, with the measurement of an increase of total water loss from 58.30 ± 1.93% for flour only systems to 71.80 ± 0.37% in formulations comprising 25% w/w bran. Deconvolution of TGA profiles showed an alteration of the distribution of free and bound water, and its interaction with starch and gluten, within the formulations. TGA profiles showed that water release from bran-enriched flour is a prolonged event with respect to the release from non-enriched flour, which suggests the possibility that bran may interrupt the normal characteristic processes of texture formation that occur in non-enriched products.     

Sensorial and biological evaluation of an extruded product made from corn supplemented with soybean and safflower pastes

A puffed product was made by extruding corn flour supplemented with soybean and safflower pastes. Mixes with the following proportions of corn flour, soybean and safflower pastes: (i) 89:8:3, (ii) 83:11:6 and (iii) 80:17:3 were extruded. The corn flour, soybean and safflower pastes used had 6.6%, 45.9% and 32.9% protein content respectively. In addition, the soybean paste contained 11.78 units of inhibited trypsin/mg of sample, which means it was appropriate for human consumption. Sensory evaluation of extruded products showed that there were no significant differences in flavour, crunchiness and acceptance in the case of products 1 and 3, when compared with samples made from corn flour alone. Product 2 had lower scores, as it had a bitter taste because of the greater amount of safflower paste used. Biological testing showed that all the products containing soybean and safflower pastes were superior to the 100% corn diet in terms of food conversion, growth rate and weight gain.     

Pressurised solvent extraction of policosanol from wheat straw,germ and bran

Policosanols (PCs) are a group of long chain aliphatic alcohols that have been reported to have low-density lipoprotein (LDL) cholesterol-lowering properties. Wheat is a good source of these compounds. This study examined the effect of solvent type and temperature on extract yields and PC content and composition in the extracts. Wheat germ, straw and bran samples were extracted with petroleum ether, chloroform, n-hexane and ethanol at various temperatures ranging from 80 to 125 °C.     

Proximate composition and digestibility of fermented and extruded uji from maize-finger millet blend

The proximate composition, amino acid profile and in vitro starch and protein digestibilities of raw; fermented; fermented and cooked; unfermented and extruded; and fermented and extruded maize-finger millet blend was studied. Aspartic acid, glycine, cystine, methionine, tyrosine and lysine increased after fermentation, while contents of all other amino acids showed no significant changes. Greater losses of amino acids occurred when the fermented blend was extruded than when cooked. Fermentation improved protein and starch digestibilities, whereas cooking or extruding the fermented blend reduced the digestibilities. Extruding the unfermented blend increased protein and starch digestibilities and reduced nitrogen solubility index by 50%. Raw flour had 0.41 g/100 g water-soluble starch which declined to 0.05 g/100 g on fermentation but increased to 20-34 g/100 g after extrusion.     

Matrix transformation in fiber-added extruded products: Impact of different hydration regimens on texture, microstructure and digestibility

The objective of this work was to study the effect of three hydration regimens on the extent of matrix transformation, texture, microstructure and digestibility of a corn-based extruded product blended with apple pomace. Blends containing 0%, 17%, 22%, and 28% pomace were hydrated to 17.2% by adding water either into the preconditioner (P), the extruder (E) or dividing half in each (PE). Increasing the opportunity for hydration (P > PE > E) promoted more complete starch gelatinization at all pomace levels. Apple pomace promoted milder extrusion conditions, resulting in less starch gelatinization and solubilization, poor expansion and reduced starch digestibility. Digestible starch was inversely correlated to cell wall thickness/cell size ratio (r = 0.91), which increased with pomace addition. Thus, pomace decreased digestibility by promoting changes in structure and gelatinization. Delayed water addition (E) promoted broader cell size and cell wall thickness distributions, attributed to poor mixing and hydration. Therefore, water incorporation (not just total content) is a key factor in defining extrudate microstructure, texture and digestibility patterns.     

Effects of soy protein isolate,acid-hydrolysed vegetable protein and glucose on the volatile components of extruded wheat starch

The volatile components produced in wheat starch containing 1% soy protein isolate (SPI), and wheat starch/1% SPI combined with 1% glucose, 1% acid-hydrolysed vegetable protein (aHVP), or 1% glucose and 1% aHVP, extruded under different processing conditions (temperatures of 150 or 180 °C and moisture content of 16% or 20%), were identified by gas chromatography–mass spectrometry (GC–MS). Gas chromatography olfactometry (GCO) was used to assess the odour intensity of volatile components present in the starch/glucose/SPI and starch/glucose/SPI/aHVP extrudates obtained at 180 °C. In total, 94 compounds were identified in the eight extrudates. The smallest number (31) was found in the extrudate of the starch/glucose/SPI feedstock processed at 150 °C and the largest (64) in the extrudate of the starch/SPI feedstock processed at 180 °C. Lipid degradation products, such as alkanals, 2-alkanones, 2-alkenals and 2,4-alkadienals, were present in all extrudates in significant quantities. Strecker aldehydes were also present in all extrudates; however, in those extrudates containing aHVP, these compounds were quantitatively the dominant components. Maillard reaction products, such as pyrroles, pyrazines and oxazoles, were mainly found in extrudates containing aHVP whereas sulphur-containing aliphatic compounds were found in all extrudates. The production of the Maillard reaction products and sulphur-containing compounds was favoured by extrusion at 180 °C. Sensory analyses showed that each of the eight extrudates had different odours, and that the extrudates containing both glucose and aHVP possessed the highest overall odour intensity. In addition, SPI was found to have a modifying effect on the volatile content and odour of extrudates also containing glucose and aHVP.     

Expansion characteristics of a nutritious extruded snack food using response surface methodology

Response surface methodology was used to analyze the effect of screw speed (220–340 rpm), feed moisture (11.0–15.0%, wet basis) and feed rate (22.0–26.0 kg/h, wet basis) on the physical properties (i.e., bulk density, expansion, porosity) of a nutritionally balanced extruded snack food. Regression equations describing the effect of each variable on the responses were obtained. Responses were most affected by changes in screw speed followed by feed moisture and feed rate (P<0.05). Expansion and porosity increased with screw speed and feed moisture whereas the opposite was observed for bulk density. Radial expansion was found to be a better index to measure the extent of expansion than the axial and overall expansions, indicated by a higher correlation coefficient.     

Impact of dietary fibre‐enriched ready‐to‐eat extruded snacks on the postprandial glycaemic response of non‐diabetic patients

Food intervention is a financially sensible way for prevention and treatment of diabetes. Extruded snack foods are considered high glycaemic products. Our previous research illustrated that postprandial glycaemic responses to snacks are manipulated by altering dietary fibre and starch contents. The current research assessed the effect of psyllium and oat bran on postprandial glycaemia and in vitro digestibility. Addition of psyllium fibre to extruded snack products significantly reduced both the in vitro and in vivo glycaemic responses of products compared to a control snack product recipe. Oat bran inclusion reduced in vitro starch digestibility but not in vivo glycaemic response. The inclusion of oat bran into the snack products appeared to extend the glycaemic response of individuals compared to the control snack, suggesting a possibility of prolonging glucose release and potentially affecting satiety responses. The positive effect in attenuating glucose response means that psyllium fibre could be a target for inclusion by the snack food industry to effectively manipulate postprandial glucose response of individuals.     

Film Formation Properties of Potato Starch Hydrolysates

Native and freeze‐dried potato starch granules were partially hydrolysed to produce maltodextrins with dextrose equivalents (DE) 10, 15 and 20. Freeze‐drying greatly improved the enzyme accessibility of the native granules. Film formation properties of the hydrolysates were examined. Films were prepared by water casting. Especially the maltodextrins, which were produced from the native starch, were very sticky materials and could not form any films. But after removing most of the soluble saccharides from the maltodextrins, good quality films were produced by dissolving the hydrolysate in water, casting on a Teflon mould and drying the solution.     

Novel use of Acacia senegal (Super Gum™) and Anogeisus latifolia (Gatifolia SD) as functional ingredients in extruded snack products: Their role in manipulating product characteristics and modulating the potential glycaemic response of snack foods

Acacia senegal (in the form of Super Gum™) and Anogeissus latifolia (in the form of gum Gatifolia SD) were used in the manufacture of ready to eat extruded cereal snack products. Inclusions rates were 0, 5, 10 and 15% w/w replacement levels for wheat flour from a control recipe. The inclusion of Super Gum™ and Gatifolia increased product expansion and reduced product density compared to a cereal flour based control snack product. Inclusion of the gum materials also decreased the hardness of the snack products whilst increasing the crispiness of the product (number of fracture peaks recorded during axial compression of samples). Glucose area under the curve (AUC) measurements obtained using in vitro digestion procedures illustrated that the potential glucose release of snack products was reduced by more than 30% by the inclusion of Gatifolia and Super Gum™ at 15% w/w compared to the control sample. Such a reduction in potential glucose release was not dose responsive. These results illustrate a potential nutritional benefit of the utilisation of Gatifolia and Super Gum™ in the ready to eat snack food sector of the food industry.     

Thermal,textural, and physicochemical analysis of corn extrudates enriched with broccoli or olive paste

The growing consumers’ demand for healthier snacks is of high importance and is driving research and industry towards developing novel ready to-eat expanded products. Thus, it would be interesting to enrich these products with additives that possibly lead to highly nutrient products. In the present study, extruded snacks based on corn flour enriched with broccoli or olive paste were developed and studied. Although the addition of broccoli or olive paste in extruded snacks can improve their nutritional properties, the final properties of these products must also be considered. Textural analysis (compression tests), thermal analysis (glass transition temperature), and moisture sorption measurements (sorption isotherms) were performed. A Guggenheim–Anderson–de Boer model has been applied to describe moisture sorption isotherms. Moreover, simple mathematical models were developed in order to correlate textural properties (maximum stress, maximum strain, elasticity parameter, number of cracks) with the process conditions during the extrusion (screw speed, temperature) and the raw materials’ characteristics (moisture content, concentration of broccoli or olive paste). Regression analysis was used to estimate mathematical models’ parameters. The influence of process conditions and raw materials’ characteristics on the measured properties of corn-based snacks enriched with broccoli or olive paste was presented based on the alterations of the estimated parameters.     

Cellular architecture and its relationship with mechanical properties in expanded extrudates containing apple pomace

Cereal-based puffed foods can deliver significant amounts of fruit and vegetable fiber, however a major hurdle is the accompanying decrease in expansion and poor textural properties. The objective of this work was to develop a comprehensive understanding of the operative rheology, processing conditions, cellular architecture, macrostructure and mechanical properties of high fiber, starch-based expanded matrices produced using extrusion. The combination of phase transition analysis and non-invasive X-ray microtomography provided a unique analytical approach for this purpose. A lab-scale twin screw extruder was used for processing directly expanded products from corn flour and apple pomace blends containing up to 22.5% total dietary fiber. Different levels of pomace (0-28%) and in-barrel processing moisture (17.5-25%) resulted in extrudates with a wide range of microstructures (average cell size 0.05-3.43 mm, wall thickness 0.12-0.34 mm and void fraction 0.53-0.76). Structural anisotropy biased towards radial expansion was observed in foams without pomace, whereas cellular isotropy, higher cell number density and greater longitudinal expansion were favored in the presence of pomace. A conceptual model for foaming and collapse was developed based on flow temperature of blends (123.7-167.6 °C), specific mechanical energy, and anticipated changes in visco-elasticity and extensibility of the high-fiber melt. Cell size was significantly correlated to average crushing force (r = − 0.69), crispness work (r = − 0.69) and number of spatial ruptures (r = 0.74). Microstructure data in combination with standard theory for brittle foams was employed to understand mechanical properties of extrudates under compression.     

Nutritional quality of extruded snacks developed from composite of rice brokens and wheat bran

Wheat bran was mixed with broken rice to develop nutritionally balanced extruded crisp snacks for human consumption. The inclusion of wheat bran enhanced the content of nutrients such as calcium, phosphorus, iron, copper, thiamine, riboflavin, lysine and also of antinutrients like phytic phosphorus and trypsin inhibitor. Extrusion cooking decreased the content of thiamine, riboflavin and lysine. The degradation of phytic phosphorus and inactivation of trypsin inhibitor had an improving effect on the nutritional quality of the extruded snacks as reflected by higher in vitro digestibility of its proteins.