Effect of shear stress extrusion intensity on plasticized corn flour structure: Proteins role and distribution

Plasticized corn flour‐based materials were prepared by extrusion and injection molding. Extrusion of corn flour blends (75% wet basis (wb)—glycerol (5 or 10% wb)—water) was performed in a twin‐screw extruder with either one or three shearing zones. Native corn flour is mainly composed of corn starch granules surrounded by proteins layers. Therefore, the destructuration of corn flour by thermomechanical treatments was analyzed (i) by techniques essentially allowing to monitor corn starch amorphization (differential scanning calorimetry, X‐ray diffractometry, determination of water sorption isotherms, susceptibility to hydrolysis by amylolytic enzymes) (ii) and via proteins layers role and distribution observed by confocal scanning laser microscopy and comparing the susceptibility of corn starch to hydrolysis by amylolytic enzymes in the presence or not of a protease. Both corn starch granules amorphization and proteins dispersion and aggregation were more pronounced for materials extruded in a screw profile with three shearing zones. For materials extruded in a screw profile with one shearing zone, the amorphization of starch was higher in materials made with 5% wb glycerol, whereas the proteins dispersion and aggregation was more pronounced in materials made with 10% wb glycerol. A barrier role of proteins to hydrolysis of corn starch by amylolytic enzymes was demonstrated and discussed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Physico-chemical evaluation of products extruded with sorghum-corn-soybean blends

Yellow corn grits (M), brown sorghum (SM), white sorghum (SB) and full fat soy flour (S) blends were extruded in an autogenous Brady Crop Cooker extruder at 195-200 degrees C and 11% moisture content. Binary blends (70:30) made up of M:S, SM:S and SB:S; and ternary blends (30:40:30) made up of SM:M:S and SB:M:S were extruded. Under these conditions, extrudates contained about 19% protein and 6% fat, which are within the specifications given for cereal/oil seed blends. Raw and extruded samples were analyzed for ES, WQI, WSI, MD and paste viscosity. All blends underwent modifications in the starch fraction at granular and molecular level. Brown sorghum extrudates presented higher degradation than those of white sorghum and corn:soy blends, although the last ones gave similar responses to analitical techniques. Extrudates greatly increased their ES, SWI and MD values, suggesting that degradation products, like dextrins, were present. Cooked paste low viscosities (50 degrees C) and micrographs support these findings. Because of their functional characteristics, extrudates could be used in beverages.     

Biodegradable and functionally superior starch–polyester nanocomposites from reactive extrusion

Biodegradable starch‐polyester polymer composites are useful in many applications ranging from numerous packaging end‐uses to tissue engineering. However the amount of starch that can form composites with polyesters without significant property deterioration is typically less than 25% because of thermodynamic immiscibility between the two polymers. We have developed a reactive extrusion process in which high amounts of starch (approx. 40 wt%) can be blended with a biodegradable polyester (polycaprolactone, PCL) resulting in tough nanocomposite blends with elongational properties approaching that of 100% PCL. We hypothesize that starch was oxidized and then crosslinked with PCL in the presence of an oxidizing/crosslinking agent and modified montmorillonite (MMT) organoclay, thus compatibilizing the two polymers. Starch, PCL, plasticizer, MMT organoclay, oxidizing/crosslinking agent and catalysts were extruded in a co‐rotating twin‐screw extruder and injection molded at 120° C. Elongational properties of reactively extruded starch‐PCL nanocomposite blends approached that of 100% PCL at 3 and 6 wt% organoclay. Strength and modulus remained the same as starch‐PCL composites prepared from simple physical mixing without any crosslinking. X‐ray diffraction results showed mainly intercalated flocculated behavior of clay at 1,3,6, and 9wt% organoclay. Scanning electron microscopy (SEM) showed that there was improved starch‐PCL interfacial adhesion in reactively extruded blends with crosslinking than in starch‐PCL composites without crosslinking. Dynamic mechanical analysis showed changes in primary α‐transition temperatures for both the starch and PCL fractions, reflecting crosslinking changes in the nanocomposite blends at different organoclay contents. Also starch‐polytetramethylene adipate‐co‐terephthalate (PAT) blends prepared by the above reactive extrusion process showed the same trend of elongational properties approaching that of 100% PAT. The reactive extrusion concept can be extended to other starch‐PCL like polymer blends with polymers like polyvinyl alcohol on one side and polybutylene succinate, polyhydroxy butyrate‐valerate and polylactic acid on the other to create cheap, novel and compatible biodegradable polymer blends with increased toughness. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1072–1082, 2005     

The Impact of Linseed Oil Lipids on the Physical Properties of Corn Crisps and the Possibility of Obtaining Crisps Enriched with n‐3 Fatty Acids

Linseed oil, also known as flaxseed oil, is obtained from the dried, ripened seeds of the flax plant (Linum usitatissimum). The oil is obtained by pressing, sometimes followed by solvent extraction supported by a refining process. Linseed oil is an edible oil that is in demand as a nutritional supplement, as a source of α‐linolenic acid an n‐3 fatty acid. The aim of this work was to investigate: (1) the influence of the corn crisp extrusion process on the degradation of fatty acids in linseed oil (LO) and some preparations obtained from the linseed oil such as ethyl ester (EE) and free fatty acids (FFA) added to the corn in order to increase the nutritional value of the crisps, (2) influence of the oil and two fatty preparations obtained from it on the quality of corn crisps, (3) interaction of the lipid fraction with starch. The extrusion process did not degrade the fatty acids significantly. Expansion ratio obtained in the corn crisp extrusion process decreased from 620 % down to 153 %, the size of pores/thickness of the starch–protein walls forming the structure of the extruded product decreased from 10 μm down to 4 μm, the hardness of the crisps increased from 20 to 75 N, and number of lipid–starch complexes increased with rising polarity of the lipid fraction. FFA were complexed mostly by starch (about 90 %), to a lesser degree by EE (about 60 %) and to the least extent by triacylglycerols (about 10 %). The studies performed under industrial conditions using the single screw extruder for the production of corn crisps with the application of standard parameters of the extrusion process indicated that the addition of a mass of 5 % of the various lipids (triacylglycerols of linseed oil, ethyl esters and fatty acids obtained from linseed oil) to corn grits prior to the extrusion process significantly affect the quality of corn crisps.     

Soy and corn flour precooked with microwaves and its use in the preparation of arepas]

Unhusked corn and soy grits were used as raw material, with a particle size ranging between 10 and 20 mesh (ASTM). The results obtained in this study reveal that microwave heating is effective in destroying the antinutritional factors present in soybeans. The trypsin inhibitor activity, in effect, was reduced to a 76% inactivation. The hemagglutinating titer was labile to the heating process, showing values of +8 to +3 for the full-fat soy flour and precooked soy flour, respectively. The quality of soy protein was measured by the protein efficiency ratio (PER) showing values of 2.63 for the precooked soy flour, and 2.46 to 2.21 for the precooked corn:soy blends (70:30 and 50:50). These uncooked blends present values of 1.17 and 1.04. The enriched corn:soy flour had a PER value of 1.60, in comparison to casein (PER = 2.90). The microwave heating improved the digestibility of the soy flour and blends. There were no significant differences (P less than or equal to 0.05) in relation to the functionality of the precooked flour and mixtures. The results obtained revealed that the applied process markedly improve the functional properties and nutritional value of the enriched flour, and of the "arepas" prepared from them.     

Yield and functional properties of air-classified protein and starch fractions from eight legume flours

Eight legumes were pin-milled and air-classified into protein (fine) and starch (coarse) fractions and their functional properties compared with those of soybean and lupine flours. The fine material which represented 22.5 to 29% of the original flours contained from 29 to 66% protein as well as a high proportion of the flour lipids and ash. The coarse material contained 51 to 68% starch and much of the crude fiber which was dense and concentrated in the starch fraction. Generally legumes which showed highly efficient starch fractionation gave lower recoveries of protein in the fine material. High values for oil absorption, oil emulsification, whippability and foam stability were characteristics of the protein fractions, while starch fractions gave high water absorptions, peak and cold viscosities. Gelation occurred in both air-classified fractions. Pea and northern bean, chickpea and lima bean flours, and airclassified fractions gave generally higher values in the functional property tests, while fababean, field pea, mung bean and lentil gave high protein fractionation in the air classification process.     

Biodegradable packaging foams of starch acetate blended with corn stalk fibers

Starch acetate–corn fiber foams were prepared by extrusion. Corn starch was acetylated (DS 2) to introduce thermoplastic properties. Corn stalks were treated with sodium hydroxide to remove the lignin and to obtain purified cellulose fibers. Starch acetate was blended with treated fiber at concentrations of 0, 2, 6, 10, and 14% (w/w) and extruded in a corotating twin‐screw extruder with 12 to 18% w/w ethanol content and 5% talc as a nucleating agent. The samples were extruded at 150°C and selected physical and mechanical properties were evaluated. Micrographic properties were analyzed using scanning electron microscopy to observe the interaction of fiber and starch. Fiber incorporation at the lower concentrations enhanced the physical properties of the foams. Fiber contents greater than 10% decreased expansion and increased density and shear strength. Good compatibility between starch and corn fiber was observed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2627–2633, 2004     

Extruded rice flour as a gluten substitute in the poduction of rice bread

Research regarding the production of gluten-free bread (GFB) is very important nutritionally, technically and economically speaking, both to celiac patients and to developing countries who import wheat. The main technological problem in the production of GFB is obtaining a gluten substitute that is both inexpensive and capable of retaining gas during bread fermentation and baking. The use of gelatinized starch as an alternative for gluten seems promising. In this project, rice bread was made using pregelatinized extruded rice flour as a gluten substitute. Pre-gelatinized rice flours (PRF) were manufactured in a single screw Brabender extruder, varying extrusion temperature (108-192 degrees C) and the moisture of the raw material (19.2 - 24.8%), and were used in a proportion of 10 g for every 100 g of raw rice flour, in the production of gluten-free bread. Results showed that rice flour extruded at a high temperature (180 degrees) and low moisture content (20%), rendered bread with the best technological characteristics, presenting crust and crumb color similar to those of conventional wheat bread, although with volume and texture not as satisfactory in the same comparison.     

Flour of hard bean (Phaseolus vulgaris) in the preparation of bread]

In order to utilize hardened beans, we proposed to find the method most indicated for the preparation of bean flour to determine their nutritional value, and to make bread of high industrial, nutritional quality, and good sensory characteristics, using blends of bean and wheat flours. Two types of flour were prepared, testing four soaking temperatures (22, 30, 40 and 50 degrees C) and two methods to remove the testa (under moist and dry conditions). At laboratory level, the dry testa removal method gave the best flour yields (mean = 85.8%) and the highest protein content (mean = 23.7%). Comparison between soaking temperature at 30 and 50 degrees C was not significant (alpha = 0.05). At pilot plant level, with soaking at 50 degrees C the flour yields were 58.0% for moist testa removal (H1) and 74.0% for dry removal (H2), with a protein content of 22.6% for H1 and 23.0% for H2. The H1 and H2 flours were added to wheat flour at 5, 10 and 15% for bread making. The addition of 5.0% gave breads with similar protein content and sensory characteristics to those of the control, wheat. A diet based on bean-flour bread resulted in greater weight gains than that with casein for gold hamsters. The study also demonstrated the importance of heat-treating of the bean flours, because when flour without previous heat treatment was administered, the animals lost weight and died. This effect was overcome by the process of baking the flours at 140 degrees C for four hours.     

Extruded cylindrical strands: Mechanical properties correlated with the formation of biodegradable films through blown extrusion

The objective of this study was to determine the mechanical and viscoelastic properties of extruded cylindrical strands from biodegradable polymer blends and to verify the correlation of the blend properties with their capacity to form films in the blown extrusion process. The production of biodegradable films would only occur if the extruded strands showed adequate characteristics. The strands were produced by extrusion with blends containing starch, glycerol, and fatty acids (caproic, lauric, and stearic). These blends were compared with a standard formulation containing poly(butylene adipate‐co‐terephthalate) (PBAT), a biodegradable polymer. From the mechanical tension tests, the extruded strands containing fatty acids differed significantly from the standard one, it was not clear the possibility to establish a comparison between the mechanical properties of the extruded strands and the formation of films. The rheological tests indicated that the polymer blends presented the desired viscoelastic characteristics for the film formation by blown extrusion. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Industrial corn flour enrichment with whole amaranth flour and milling fractions in corn-based products

Whole flour and milling fractions of raw amaranth seeds were used in 90:10, 80:20 and 50:50 mixtures with industrialized corn flour (MINSA) to prepare tortillas and arepas, basic nutritional foods in several Latin American countries. The three corn-amaranth mixtures showed a good protein and fat content as well as amino acid profile, and presented adequate physical characteristics for making tortillas. Amaranth whole flour and commercial corn flour mixtures in the proportion of 80:20 and 50:50 were found suitable for the preparation of arepas. Protein and fat content were substantially improved, with no changes in organoleptic characteristics. The Mexican type of Amaranthus cruentus, selected due to its availability and bromatologic properties, yielded products of excellent nutritional quality, according to their amino acid content and protein efficiency ratio (PER). The protein-rich (1R) and starchy (2-R) fractions obtained by air classification, also yielded good results when substituting amaranth flour. The afore-mentioned flours and air-classified fractions of the 50:50 mixtures proved to be adequate in gruel preparations when used in 1:8 and 1:12 dilutions, as they improved their organoleptic characteristics. Flakes and extrudates were also used, yielding products with a 13.3-15% protein content, 1.7-3.7% fat, and 65.2-74.2% carbohydrates. In addition, extrudates were utilized to prepare snacks of better nutritional quality than existing similar commercial products. Improvement of the tortilla's mineral and fatty acid contents was achieved in every case. Enrichment of this product with whole amaranth flour is, therefore, recommendable for use in programs aimed at improving the nutritional status of the population.     

亚麻纤维/PBS/TPS复合材料的制备及性能研究

以玉米淀粉为原料,通过挤出加工制得热塑性淀粉(TPS)。再将TPS与聚丁二酸丁二醇酯(PBS)共混,加入亚麻纤维强化,制得复合材料。分析了TPS试样和复合材料试样的断面微观结构,研究了PBS含量、纤维添加量和硅烷偶联剂(KH-550)对TPS/PBS共混物力学性能的影响。进一步通过正交试验分析优化了复合材料的制备工艺参数。实验研究表明,丙三醇是制备TPS的合适的增塑剂,挤出加工能够较好地改变淀粉分子结构,使其具有热塑性。共混物的力学性能随着PBS含量的增加而增加。亚麻纤维和KH-550都能够明显地增加复合材料的拉伸强度和弯曲强度,但是复合材料的断裂伸长率降低。对于复合材料的拉伸强度来说,最优化工艺为:PBS质量分数60%、纤维质量分数0.5%、偶联剂质量分数0.2%,注塑加工温度(注塑机温控区温度)为155、160、160、150、145℃。     

Effects of polyethylene‐grafted maleic anhydride (PE‐g‐MA) on thermal properties,morphology, and tensile properties of low‐density polyethylene (LDPE) and corn starch blends

The effects of polyethylene‐grafted maleic anhydride (PE‐g‐MA) on the thermal properties, morphology, and tensile properties of blends of low‐density polyethylene (LDPE) and corn starch were studied with a differential scanning calorimeter (DSC), scanning electron microscope (SEM), and Instron Universal Testing Machine, respectively. Corn starch–LDPE blends with different starch content and with or without the addition of PE‐g‐MA were prepared with a lab‐scale twin‐screw extruder. The crystallization temperature of LDPE–corn starch–PE‐g‐MA blends was similar to that of pure LDPE but higher than that of LDPE–corn starch blends. The interfacial properties between corn starch and LDPE were improved after PE‐g‐MA addition, as evidenced by the structure morphology revealed by SEM. The tensile strength and elongation at break of corn starch–LDPE–PE‐g‐MA blends were greater than those of LDPE–corn starch blends, and their differences became more pronounced at higher starch contents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2904–2911, 2003     

Nutritional and stability evaluation during storage of blends extruded with sorghum

Binary sorghum:soy (70:30) and ternary sorghum:corn:soy (30:40:30) blends using high and low tannin content dehulled sorghum were extruded. The effectiveness of heat treatment was determined by protein dispersion index (PDI) and ureasic activity (delta PH), indicating that proteins were denatured and antinutritional factors reduced. The nutritional evaluation supported the fact that samples were adequately treated, giving ternary blends true digestibility (TD) and biological values (BV) similar to milk casein. Blend stabilities, expressed as peroxide index (PI), revealed a low lipid oxidation rate during the first seven months, and were acceptable up to a year of storage. Extrudates with incorporated sorghum cover protein and energy demands of the growing infant, and provide a high nutritional value and long-life product.     

Rheological behavior of starch–polycaprolactone (PCL) nanocomposite melts synthesized by reactive extrusion

Rheological behavior of reactively extruded starch–PCL nanocomposite blends was evaluated in an off‐line capillary rheometer. Power law models for blends with different nanoclay volume fractions were developed using appropriate correction factors. Consistency coefficients K for blends containing starch were significantly higher than 100% PCL. Starch–PCL nanocomposite blends showed shear‐thinning behavior with higher pseudoplasticity than did 100% PCL. Viscosities of nanocomposite blends were significantly lower than that of 100% PCL and nonreactive starch–PCL composites synthesized from simple extrusion mixing. Power law coefficients developed in this study will be used to evaluate rheology‐dependent parameters during scaling up the reactive extrusion process from a batch micro‐extruder to a high output continuous twin‐screw extruder. POLYM. ENG. SCI. 46:650–658, 2006. © 2006 Society of Plastics Engineers.     

Wood Flour and Polypropylene or High Density Polyethylene Composites: Influence of Maleated Polypropylene Concentration and Extrusion Temperature on Properties

Abstract

The effects of the concentration of a maleated polypropylene additive (0 to 5 percent by weight) and of extrusion blending temperature (190°C to 250°C) on the mechanical properties of extruded and injection-molded polypropylene-wood flour composites were investigated. The effects of maleated polypropylene additive on similarly processed polypropylene-wood flour and high density polyethylene-wood flour composites were also compared. Both the additive and the high extrusion temperature led to some wood degradation and to a less polar wood surface. The additive led to greater reinforcement of the composites, as indicated by moderate but useful increases in heat deflection temperature, strength, and modulus. The major portion of those improvements was achieved by adding 1 to 2 percent additive. However, both the additive and the high extrusion temperature decreased impact resistance, presumably as a consequence of increased reinforcement by the filler particles and wood degradation. Heat deflection temperature, strength, and modulus of the polypropylene-wood flour system were marginally better than that of the high density polyethylene-wood flour system; impact resistance was marginally poorer.     

Structure‐Property Relationships of Extruded Starch, 2 Extrusion Products from Native Starch

The supermolecular structure and morphology of extruded flat films from several native starch materials of A‐ and B‐crystal type were investigated by wide‐angle X‐ray scattering and scanning electron microscopy. The degree of crystallinity and crystallite dimensions of both the different starting materials and the extruded films were determined and a scheme of the lattice transformations resulting from extrusion was established. The conditions of structure formation of the extruded starch films were varied in relation to plasticizer composition and extruder zone temperatures. The mechanical properties and biodegradability of the films were also measured. The extruded starches crystallized in the V_H polymorph with crystallinities between 33 and 41% and crystallite sizes of up to 35 nm. An increase in crystallite size was found for all starches (sometimes a doubling) with increasing extruder middle zone temperatures from 120 up to 210°C. For extruded potato and maize starches a steep rise in strength and modulus and a drop in elongation was observed above 190°C. Purified amylopectin from maize showed after extrusion the crystalline A‐type and small amounts of B polymorph with small crystallites (up to 3 nm) and the best mechanical performance with strengths and moduli of about 20 MPa and 1 500 MPa, respectively, for the present extrusion conditions. Native starch films that include 20 to 30% plasticizer biodegrade rapidly in 25 d consuming 90% of the oxygen needed for complete degradation, as analyzed by the Sapromat test.     

Evaluation of cookies enriched with corn germ and soy fiber

The objective of this study was to evaluate four cookie formulations which wheat flour was partially substituted by free-fat corn germ flour and/or soy fiber. Baking quality, protein, fat, ash, dietary fiber, hardness, color, Protein Efficiency Ratio PER and Apparent Digestibility in vivo were determined. A trained panel evaluated color, hardness and fracturability of cookies. Dietary fiber of cookies varied from 8.2 to 24.9% and protein from 11.3 to 12.7%. The source and amount of dietary fiber modified physical, sensory, and nutritional properties of cookies. Cookies formulated with 20% corn germ flour gave the highest PER, Digestibility Aparente in vivo, and acceptance by consumers. This study demonstrated the potential use of free-fat corn germ and soy fiber as functional ingredients.     

Effect of the quality and quantity of dietary proteins on vitamin A depletion rate, and biological availability of vitamin A precursors

The effect of quantity and quality of protein from cereal and legume sources on the rate of vitamin A depletion was evaluated through changes in retinol serum levels and liver stores in male and female Wistar strain rats. A total of 64 animals were distributed into four groups and fed ad libitum with diets adequate in all nutrients, except vitamin A. The protein in the diets was derived from 91% common maize (Diet A); 91% Opaque-2 maize (Diet B), 64% common maize plus 27% precooked common black bean flour (Diet C), and 64% Opaque-2 maize with 27% bean flour (Diet D). The total depletion period lasted 60 days and four rats per group were sacrificed at 15, 30 and 60 days. A total of 4 animals were sacrificed at 0 day to count with a basal serum and hepatic retinol concentration value. The 16 depleted remaining rats were used for the carotene bioavailability study with dehydrated carrots. During the first 15 days the greater rate of depletion was observed in animals fed the highest protein quality diet made from Opaque-2 maize and beans (Diet D), which also caused the greatest weight increase. The least depletion rate and lowest weight gain was obtained with the common corn diet (Diet A). Diets B and C caused intermediate depletion rates, with Diet B (Opaque-2 maize) being more effective than Diet C in spite of its lower protein content. At the end of 60 days all groups presented depletion levels not statistically different. Thus, these results confirm that protein quantity and quality from basic staple foods influence mobilization of retinol liver reserves. The 16 remaining depleted rats were then divided into four groups and fed a standard 14% casein diet to which 25, 50 and 75% of the retinol requirements was added to obtain a reference standard biological response. The fourth group was fed with an amount of dehydrated and ground carrot containing 67.1 mg % of total carotenoids. After seven days, serum and hepatic retinol were obtained, from which a regression equation of liver retinol to diet retinol was calculated (microgram % liver retinol per 100 g of rat) = 2.47 + 0.063 (microgram retinol/g diet) (r = 0.585). From this equation the bioavailability of carrot carotenoids was established with a value of 21.8% comparable to the FAO/WHO value previously reported.