Effects of formulation and extrusion cooking conditions on furfural and hydroxymethylfurfural content

The objective of this research was to investigate the effects of different ingredients (reducing sugars, leavening agents, citric acid), processing conditions (feed moisture content, exit die temperature), and extrusion cooking methods (with/without CO₂ injection) on furfural and 5-hydroxymethylfurfural (HMF) formation in corn-based extrudates. The decrease in furfural levels was 16% upon addition of sodium-bicarbonate, while the increase was 12% upon addition of ammonium-bicarbonate for extrudates produced at 150 °C and feed moisture content of 22%. The furfural concentration of extrudates produced at 150 °C and feed moisture content of 22% without leavening agents was 810 μg/100 g and increased to 11,901 μg/100 g upon citric acid addition (about a 15-fold increase). Furthermore, both low feed moisture and high exit die temperature had promoting effects on furfural and HMF contents. The CO₂ injection method did not have considerable effect on furfural and HMF levels of the extrudates; however, it positively affected the physical properties of extrudates.     

Triticale extrudates – Changes of macrostructure,mechanical properties and molecular water dynamics during hydration

The effect of hydration (in the range of aw 0.981–0.090) on changes of macroscopic and mechanical features of triticale snacks produced in different conditions (feed moisture - 16 and 20%; extrusion temperature - 135 and 175 °C) was analysed. Changes of snacks depended both on the hydration level and the extrusion process conditions.As a result of storage at the highest hydration level (aw = 0.981) contraction of snacks was observed. The shrinkage was more pronounced in case of extrudates obtained from raw material containing 16% of water regardless of the extrusion temperature. The hardness of extrudates depended both on the feed moisture and hydration. Samples obtained from the raw material containing 20% moisture were harder than those prepared at the feed moisture of 16%. Based on the results of molecular dynamics study by low field NMR technique, a model of hydration was developed and critical hydration value of extruded snacks was calculated. Higher values of the critical hydration were obtained for snacks extruded at temperature 135 °C than for those obtained at 175 °C. The feed moisture level affected critical hydration values to a lesser extent. Obtained results suggest that the state of water in extrudates depends on extrusion process conditions.     

Physicochemical and antioxidant properties of extruded corn grits with corn fiber by CO2 injection extrusion process

Corn grits and corn fiber mixed at different mass ratios (0/100, 15/85 and 30/70) were extruded at different melt temperature (90, 105 and 120 °C) using extrusion with and without CO₂ injection. The L value, reducing sugar content and antioxidant properties decreased after extrusion with or without CO₂ injection. The color and antioxidant properties were relatively stable in the extrusion with CO₂ injection at higher melt temperature (120 °C) in comparison with the extrusion without CO₂ injection. Higher corn fiber content resulted in less loss of total phenolic content. The b, ΔE values and water absorption index increased after extrusion. The increase of the water absorption index was higher after the extrusion process with the CO₂ injection especially at the lower melt temperature. The addition of corn fiber decreased L, b, and ΔE values, but significantly increased antioxidant properties under the same extrusion conditions.     

Effect of extrusion cooking on chemical structure,morphology, crystallinity and thermal properties of sorghum flour extrudates

The effect of feed moisture content (10, 14 and 18%) and die temperature (110 and 160 °C) on functional properties, specific mechanical energy (SME), morphology, thermal properties, X-ray diffraction pattern (XRD), Fourier transform infrared spectroscopy (FTIR) and amylose-lipid complex formation of extruded sorghum flour was investigated. Results showed that the extrusion cooking significantly changed the functional properties of extruded sorghum flour. Increasing feed moisture increased the peak gelatinization temperature (T_p), the degree of gelatinization (%) and starch crystallinity (%) while it decreased the gelatinization temperature ranges (T_c - T₀), starch gelatinization enthalpy (ΔH_G) and amylose-lipid complex (%) formation. With increasing die temperature, the degree of gelatinization and amylose-lipid complex formation increased and the starch T_p, T_c-T₀, ΔH_G and crystallinity decreased. The FTIR spectra also showed that the extrusion cooking did not create new functional groups or eliminate them in sorghum protein, whereas the sorghum extrudate protein had random coil conformation.     

Proximate composition and some functional properties of extrusion cooked soybean and sweet potato blends

Mixtures of sweet potato flour and soy flour were made in a pilot mixer. They were moisturized with 18, 25, and 30% water and extruded in a single screw extruder at 80 rpm, using a die of 6mm. Extrusion temperature was maintained at 100 ± 3^°C. Effects of adding soy flour into sweet potato flour, as well as variation in feed moisture on the composition and some functional properties of the extrudates were investigated. Increase in sweet potato content increased carbohydrate values. Protein increased with increase in soy flour. Feed moisture did not significantly ( p 0.05) affect extrudate composition. Increase in sweet potato content and feed moisture increased expansion ratio. Bulk density decreased with decrease in feed moisture, but increased with increase in soy flour. Starch content increased as sweet potato content increased. Degree of gelatinization increased with sweet potato content. Lower feed moisture enhanced gelatinization. Water absorption index (WAI) increased as sweet potato content increased. Feed moisture had a slight effect on WAI and water solubility index (WSI). Amylose increased with increase in sweet potato content. Increase in soy flour led to an increase in yellowness (b^*) of extrudates.     

Characteristics of destarched corn fiber extrudates for ethanol production

The effect of extrusion on characteristics of destarched corn fiber was investigated. Extrusion was conducted at a screw speed of 300 rpm, feed rate of 100 g/min, feed moisture content of 30%, melt temperature of 140 °C and die diameter of 3 mm. After extrusion, characteristics of raw and extruded destarched corn fiber were compared. Raw and extruded destarched corn fibers were enzymatically saccharified and fermented using Saccharomyces cerevisiae (ATCC 24858). Extrusion pretreatment resulted in low crystallinity index, significant decrease in degree of polymerization and microstructure disruption of destarched corn fiber for enzymatic saccharification. This provides a significant increase in xylose yield for fermentation. Significant increase in protein digestibility and free amino nitrogen were additional benefits of extrusion for yeast nutrient in fermentation. Therefore, extruded destarched corn fiber significantly increased (p < 0.05) ethanol yield (29.08 g/L) and higher conversion (88.79%) by improving the physiochemical and functional properties for saccharification and fermentation.     

Extrusion of a model sorghum-barley blend: Starch digestibility and associated properties

Blending cereals can maximise their food values, and understanding material-processing-property relationships guides this. A sorghum-barley (60:40) blend was extruded at different conditions to investigate the effects on extruder responses and extrudate properties. Starch digestion in the extrudates was more than in the non-extrudates, but extrusion feed rate did not significantly (P > 0.05) affect the digestibility. Specific mechanical energy reduced with the feed rate, which suggested suppressed molecular and/or structural transformations in a full extruder. Extrudate properties essentially exhibited a significant (P < 0.05) quadratic relationship with the moisture, with 30 ± 4.3% as the critical moisture, above which, the extrusion was high moisture, rate of starch digestion reduced, indices of water binding and solubility reduced, and extrudates were denser. Extrusion temperature had no significant (P > 0.05) effects on starch digestibility, but with more supplied heat as the temperature increased, water binding properties and transverse expansion increased. The increased frictional heat with the screw speed enhanced the transverse expansion also, and the browning, rate of starch digestion and rapidly digestible starch of the extrudates. There were significant Pearson correlations between the extrudate properties and with the extruder responses, which can assist in selecting conditions for desirable extrudate properties.     

Proximate composition and some functional properties of extrusion cooked soybean and sweet potato blends.

Mixtures of sweet potato flour and soy flour were made in a pilot mixer. They were moisturized with 18, 25, and 30% water and extruded in a single screw extruder at 80 rpm, using a die of 6mm. Extrusion temperature was maintained at 100 +/- 3 degrees C. Effects of adding soy flour into sweet potato flour, as well as variation in feed moisture on the composition and some functional properties of the extrudates were investigated. Increase in sweet potato content increased carbohydrate values. Protein increased with increase in soy flour. Feed moisture did not significantly (p < or = 0.05) affect extrudate composition. Increase in sweet potato content and feed moisture increased expansion ratio. Bulk density decreased with decrease in feed moisture, but increased with increase in soy flour. Starch content increased as sweet potato content increased. Degree of gelatinization increased with sweet potato content. Lower feed moisture enhanced gelatinization. Water absorption index (WAI) increased as sweet potato content increased. Feed moisture had a slight effect on WAI and water solubility index (WSI). Amylose increased with increase in sweet potato content. Increase in soy flour led to an increase in yellowness (b*) of extrudates.     

Effect of temperature, time and wheat gluten moisture content on wheat gluten network formation during thermomolding

A plastic-like material can be obtained by thermomolding wheat gluten protein which consists of glutenin and gliadin. We studied the effect of molding temperature (130-170 °C), molding time (5-25 min) and initial wheat gluten moisture content (5.6-18.0%) on the gluten network. Almost no glutenins were extractable after thermomolding irrespective of the molding conditions. At the lowest molding temperature, the extractable gliadin content decreased with increasing molding times and moisture contents. This effect was more pronounced for the α- and γ-gliadins than for the ω-gliadins. Protein extractabilities under reducing conditions revealed that, at this molding temperature, the cross-linking was predominantly based on disulfide bonds. At higher molding temperatures, also non-disulfide bonds contributed to the gluten network. Decreasing cystine contents and increasing free sulfhydryl and dehydroalanine (DHA) contents with increasing molding temperatures and times revealed the occurrence of β-elimination reactions during thermomolding. Under the experimental conditions, the DHA derived cross-link lanthionine (LAN) was detected in all gluten samples thermomolded at 150 and 170 °C. LAN was also formed at 130 °C for gluten samples containing 18.0% moisture. Degradation was observed at 150 °C for samples thermomolded from gluten with 18.0% moisture content or thermomolded at 170 °C for all moisture contents.     

Quality evaluation of commercial chile-based salsas

A standardized extrusion cooking process was developed for production of a high protein weaning food based on peanuts, maize and soybeans. Major factors evaluated included the effects of blend formulation, extrusion temperature and feed moisture content on ease of extrusion and product quality characteristics. Results showed bulk density and hardness increased while expansion index decreased with increase in feed moisture content. At a fixed range of feed moisture content, product bulk density and firmness decreased while expansion index increased with increasing extrusion temperature. For ease of extrusion and best product quality in terms of sensory attributes and cooking properties, the following extrusion parameters were established for a blend formulation of 75% maize, 10% peanut and 15% soybean: feed particle size of 300–400 m extruded using a screw speed of 500 rpm, with a feed rate of 4.6 kg/min, feed moisture content of 16–18%, and extrusion temperature of 100 ,°C–105,°C. Pair-wise comparison of the sensory attributes of porridges prepared from milled samples of the weaning foods showed significant differences between extruded products and existing traditional counterparts, with very high scores for all sensory attributes of the extruded products, especially extruded raw (non-roasted) blend samples. In the Home-Use-Test, at least 92% of respondents in two out of the three major ecological zones of Ghana placed overall sensory and functional characteristics of extruded raw blend samples as highly acceptable. About 7% of respondents scored sensory and functional quality attributes as acceptable.     

An innovative approach for significantly increasing enzyme resistant starch type 3 content in high amylose starches by using extrusion cooking

In this study effects of extrusion cooking on enzyme resistant starch (RS) formation in high amylose corn starches (Hylon V and VII) and the functional properties of RS preparations were investigated. Native starches were extruded at 50, 60, 70% feed moisture contents, at constant screw speed (100 rpm) and barrel temperature (140 °C). Among these samples, the highest RS contents were observed at 60% feed moisture. Therefore, feed moisture in the second and third extrusion cycles was set at 60%. There were significant increases in RS contents of both Hylon V and Hylon VII after the second extrusion cycle (p < 0.05). After the third extrusion, the RS levels reached to 40.0 and 45.1% for Hylon V and Hylon VII, respectively. Substantial loss of birefringence in these samples indicated that the increases in RS were mainly due to RS3 formation. The RS samples produced by extrusion did not have high emulsion capacity, but the ones produced from Hylon VII had high emulsion stability. Although, decreases in L* and increases in b* values of extruded samples were significant as compared to respective native starches, the changes were not substantial. Therefore, their incorporation is not expected to cause major changes in the colour of end-products.     

Effect of extrusion pretreatment on extraction,quality and antioxidant capacity of oat (Avena Sativa L.) bran oil

Extrusion is an alternative pretreatment for oil extraction from cereal resource. The objective of this study was to assess the feasibility of extrusion pretreatment of oat bran for oil extraction. The effects of extrusion conditions including feed moisture content, screw speed and die temperature on the extraction, quality and antioxidant capacity of oat bran oil were investigated. The results showed that the extraction yield of oat bran oil varied from 3.93% to 8.43% under different extrusion conditions. A feed moisture content of 25% had an important effect on the extraction of oil from oat bran. Extrusion pretreatment could increase oil extraction efficiency by increasing expansion index and porosity of oat bran extrudates. Extrusion processing had no positive or adverse effect on the fatty acid compositions, and acid, peroxide and iodine values. Meanwhile, extrusion processing did not affect the phytochemical components and antioxidant capacity of oat bran oil. But refining process could result in decrease of phytochemical components and antioxidant capacity of oat bran oil. These results indicated that extrusion is a feasible and potential pretreatment procedure for oil extraction from oat bran.     

Structural characteristics of corn starches extruded with soy protein isolate or wheat gluten

Commercially available corn starches containing 0, 25, 50 and 70% amylose were extruded with 10, 20 and 30% soy protein isolate (SPI) or wheat gluten (WG) at 22% moisture content (dry basis) in a C.W. Brabender single screw laboratory extruder using a 140°C barrel temperature and a 140 rpm screw speed. True, solid and bulk densities; percent total, closed and open pores; and shear strengths of the extrudates were determined. The microstructures of the extrudates were studied by scanning electron microscopy (SEM). The total pores of the extrudates were affected significantly (p < F=0.0001) by type of protein (SPI or WG) and starch amylose. The open or closed pores, were affected by protein type only. The interaction between amylose and protein contents was highly significant <(p < F=0.0001). In general, the total pores and bulk densities were higher for WG-starch extrudates compared to SPI-starch extrudates. These values decreased as amylose content increased from 0 to 25% and then increased thereafter. The open pores, on the other hand, increased with increasing protein content from 10 to 20% and then decreased. Extrudates containing WG had higher shear strengths than those containing SPI.     

Use of amaranth,quinoa and kañiwa in extruded corn-based snacks

Amaranth (Amaranthus caudatus), quinoa (Chenopodium quinoa) and kañiwa (Chenopodium pallidicaule) are pseudocereals regarded as good gluten-free sources of protein and fiber. A co-rotating twin screw extruder was used to obtain corn-based extrudates containing amaranth/quinoa/kañiwa (20% of solids). Box–Behnken experimental design with three independent variables was used: water content of mass (WCM, 15–19%), screw speed (SS, 200–500 rpm) and temperature of the die (TEM, 150–170 °C). Milled and whole samples were stored in open headspace vials at 11 and 76% relative humidity (RH) for a week before being sealed and stored for 9 weeks in the dark. Hexanal content was determined by using headspace gas chromatography. Extrudates containing amaranth presented the highest sectional expansion index (SEI) (p < 0.01) while pure corn extrudates (control) presented the lowest SEI and greatest hardness (p < 0.01). SEI increased with increasing SS and decreasing WCM. In storage, whole extrudates exposed to 76% RH presented the lowest formation of hexanal. This study proved that it was possible to increase SEI by adding amaranth, quinoa and kañiwa to pure corn flour. The evaluation of lipid oxidation suggested a remarkable stability of whole extrudates after exposure to high RH.     

Effect of fibre–protein additions and process parameters on microstructure of corn extrudates

A study was conducted on the application of high-fibre components (everlasting pea wholemeal, oat bran) for the modification of microstructure and physical properties of corn extrudates. The extrusion was conducted using a single screw extruder type S-45 (Metalchem, Poland). The effect of the material blend composition and of the variable process parameters: material blend moisture (11, 13.5, 16%), barrel temperature distribution profile (120/145/115, 130/155/115, 140/165/115 °C) on the microstructure and the physical properties of the extrudates was analysed. All extrudates obtained were characterised by typical cellular structure and “crunchy” texture characteristic of the “ready to eat” type products. The microstructure of the products obtained was determined both by the material composition of the blend and by the process parameters. The differences observed in the size, number of shapes of air cells and in the cell wall thickness indicate extensive possibilities of modification of the physical properties and sensory traits of extrudates.     

Effects of selected extrusion parameters on physicochemical properties and in vitro starch digestibility and β-glucan extractability of whole grain oats

Whole grain oat flour was extruded under different moisture contents (15%, 18%, 21%), barrel temperatures (100 °C, 130 °C), and screw speeds (160 rpm, 300 rpm, 450 rpm), and selected physicochemical properties, in vitro starch digestibility, and β-glucan extractability of the extrudates were analyzed. An increase in screw speed resulted in an increase in radial expansion index, water absorption index, and water solubility index. Screw speed significantly affected slowly and rapidly digestible starch. Moderate screw speed (300 rpm) led to higher slowly digestible starch with an accompanying decrease in rapidly digestible starch. Low moisture conditions (15%) resulted in the highest resistant starch and water-extractable β-glucan. Under the conditions used in this study, extrusion did not result in changes in water-extractable β-glucan molecular weight. Thus, extrusion might be beneficial in improving functionality and consumer acceptability by affecting physicochemical properties, in vitro starch digestibility, and β-glucan extractability of oat extrudates.     

Sodium hydroxide and trimetaphosphate levels affect properties of starch extrudates

In addition to being consumed as food, starch is considered for replacement of petroleum-based plastics, but imparts negative effect like water absorption and solubilization in water. In this study, the effects of sodium hydroxide and sodium trimetaphosphate concentrations on the water absorption and solubility indices of starch cross-linked by sodium hydroxide and sodium were evaluated. Starch was granulated, and 0.3 kg granulated starch was mixed with 65 ml sodium hydroxide at three concentrations (0.2, 0.6, and 1.0 M), sodium trimetaphosphate at two levels (0.015 and 0.045 kg sodium trimetaphosphate corresponding to 5 and 15% of starch), and water to adjust moisture content to 40% (dry basis). The samples were extruded in a single-screw extruder at a barrel temperature of 130 °C and screw speed of 140 rpm. Phosphorus content and pasting viscosity of starch extrudates showed that starch was cross-linked with phosphorus that was incorporated into starch during extrusion. The extrusion and cross-linking of starch with 5% sodium trimetaphosphate reduced water absorption index, and increasing sodium trimetaphosphate percentage reduced water absorption index further at high levels of sodium hydroxide. On the other hand, the reduction in water solubility of starch extrudates required the extrusion of starch with more than 5% sodium trimetaphosphate, but increasing the sodium hydroxide level increased the water solubility index of extrudates.     

Rheological properties of starches with different amylose/amylopectin ratios

The rheological properties of corn starches with different amylose/amylopectin ratios (80/20, 50/50, 23/77, and 0/100) were systematically studied by Haake rheometry. The starches were initially pre-compounded with water to designated moisture content levels using a twin-screw extruder. A single-screw extruder with a slit capillary die was then used to characterize the shear stress and melt viscosity characteristics of sample pellets, as a function of both moisture content (19–27%) and extrusion temperature (110–140 °C). The melts exhibited shear thinning behavior under all conditions, with the power law index (0 < n < 1) increasing with increasing temperature and moisture content in the majority of cases. The higher the amylose content, the higher is the viscosity (for example, η increases from 277 Pa s to 1254 Pa s when amylose content increases from 0% to 80% under a certain condition), which is opposite to the sequence of molecular weight; amylopectin-rich starches exhibited increased Newtonian behavior. These rheological behaviors are attributed to the higher gelatinization temperature of amylose-rich starches, and in particular the multiphase transitions that occur in these starches at higher temperatures, and the gel-ball structure of gelatinized amylopectin.     

Process,structure and texture of extruded whole wheat

Whole wheat is well known by consumers as a health-providing ingredient. Nevertheless, in extruded products it leads to textures that are less favorable to consumer preference compared to its refined flour. An understanding of the effect of extrusion on whole wheat properties is therefore necessary to improve its texture. Whole wheat flour was extruded under varying conditions of water content (18 or 22%), screw speed (400 or 800 rpm) and barrel temperature (140 or 180 °C) and its physicochemical properties were measured. Changing the extrusion conditions significantly modified the volumetric expansion index (between 9.1 and 20.6) and longitudinal expansion (between 0.93 and 2.98) of the samples. Interestingly, changing the extrusion conditions did not significantly modify the sectional expansion. Increasing barrel temperature, water content or screw speed decreased the shear viscosity of the melt. This can be explained by plasticizing effects and modification of starch properties. The change in shear viscosity at the die can mostly explain the effect of process conditions on volumetric expansion of the extruded whole wheat. The stress at rupture of the extruded samples was varied between 0.49 and 1.86 MPa depending on process conditions. It was the lowest at high water content and low screw speed.