Functional Properties of Polylactic Acid Starch‐Based Loose‐Fill Packaging Foams

In this study, attempts were made to improve the characteristics of starch‐based plastic foams by blending starch with polylactic acid (PLA), a biodegradable polymer made from renewable sources. Formulations of the foams (types of starch, ratio of starch to polymer, and moisture content) were optimized. Physical and mechanical properties of the foams, including expansion, unit density, bulk density, water solubility index (WSI), spring index, and compressibility on both single piece and bulk samples were determined. The addition of the PLA polymer to regular (25% amylose) and waxy corn starches significantly improved the physical and mechanical properties of the extruded foams. Foams made from waxy starch had better radial expansions, higher WSI, higher compressibilities, and lower spring indices than those of regular starch foams. Both regular and waxy starches produced foams with similar unit and bulk densities, bulk compressibilities, and bulk spring indices. Increasing PLA polymer contents increased the radial expansions and spring indices and significantly reduced the unit and bulk densities and bulk compressibilities. Changing the PLA content had no significant effect on WSI, compressibilities, and bulk spring indices. Increasing the moisture content adversely affected foam characteristics. The formulation containing waxy starch, 40% PLA, and 19% moisture produced a loose fill foam with the best physical characteristics and mechanical properties.     

Melt‐Intercalated Starch Acetate Nanocomposite Foams as Affected by Type of Organoclay

Starch acetate nanocomposite foams with four organoclays (Cloisite 30B, 10A, 25A, and 20A) were prepared by melt‐intercalation methods. The structural properties, thermal behaviors, and mechanical properties were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetry analyses (TGA), and Instron universal testing machine. XRD results indicated that the intercalation of starch acetate into the nanoclay layers occurred for all four clays. The extent of intercalation depended on the type of organoclay and was exhibited in the sequence of Cloisite 30B >10A >25A >20A. SEM results indicated a decrease in cell size in the starch acetate foam matrix with the addition of nanoclay. Glass transition temperature (T_g) and onset temperatures of thermal degradation increased with the addition of organoclay into the starch acetate matrix. The incorporation of organoclays decreased significantly the compressibilities of starch acetate nanocomposites and did not substantially affect their spring indices.     

Role of Blowing Agents in Expansion of High‐Amylose Starch Acetate During Extrusion

High‐amylose starch acetate (DS 2) was processed in a Brabender twin‐screw extruder with ethanol and isopropanol as blowing agents at concentrations of 0, 2, 5, 10, 15, and 25%. A constant temperature of 150°C, a constant screw speed of 140 rpm, and a die nozzle with diameter of 4.0 mm and length of 16.2 mm were used to study the role of blowing agents on the expansion of the extrudates. Extrudates without blowing agent shrunk considerably after exiting the die as the cells collapsed drastically after expansion. Stable radial expansion of the extrudates increased with increase in the ethanol concentration to an optimum value of 18.0 at 5% (db) ethanol concentration and decreased with further increase in the ethanol concentration. Stable radial expansion increased to a maximum of 17.0 as the concentration of isopropanol was increased to 25% (db), though the rate of increase in expansion decreased with the increase in isopropanol concentration >10%. Flashing off of blowing agents aided in removing the heat generated during extrusion. The faster the extrudate cooled, the less likely it was to shrink. SEM were used to observe the effects of concentration of blowing agents on cell morphology. Various phenomena involved during the expansion are discussed. To obtain an extrudate with high expansion and low density, isopropanol at 15–25% (db) was found most suitable in this study.     

Twin-Screw Extrusion Processing of Feed Blends Containing Distillers Dried Grains with Solubles (DDGS)

Extrusion trials were conducted with varying levels of distillers dried grains with solubles (DDGS) along with soy flour, corn flour, fish meal, vitamin mix, mineral mix, and net protein content adjusted to 28% using a Wenger TX-52 twin-screw extruder. The properties of extrudates were studied in experiments conducted using a full-factorial design with three levels of DDGS content, two levels of moisture content, and two levels of screw speed. Increasing the DDGS content from 20 to 60% resulted in a 36.7% decrease in the radial expansion, leading to a 159 and 61.4% increase in the unit density and bulk density of the extrudates, respectively. Increasing the DDGS content resulted in a significant increase in the water absorption index (WAI) but a significant decrease in the water solubility index (WSI) of the extrudates. Changing the screw speed and moisture content had no significant effect on the radial expansion ratio but resulted in a significant difference in the bulk density of the extrudates, which may be due to the occurrence of longitudinal expansion. Even though changing the moisture content and screw speed had no significant effect on the WSI of the extrudates, significant differences in the WAI of the extrudates were observed. The ingredient components in the blend and moisture content had an influence on the color changes of the extrudates, as did the biochemical changes occurring inside the barrel during processing. Overall, it was determined that DDGS could be included at a rate of up to 60% using twin-screw extrusion, and that viable pelleted floating feeds can be produced.     

Effects of Gelatinization and Moisture Content of Extruded Starch Pellets on Morphology and Physical Properties of Microwave‐Expanded Products

Extruded pellets were prepared from normal corn starch using a corotating twin‐screw extruder (25:1 L/D ratio, 31 mm diameter screw), and then expanded by heating in a conventional microwave oven for 70 sec. The effects of gelatinization level and moisture content of the extruded pellets on the morphology and physical properties of the microwave‐expanded products such as puffing efficiency, expansion bulk volume, and bulk density were investigated. The expanded shape and air cell structure differed according to the degree of gelatinization of the pellets. Maximum puffing efficiency and expansion volume with the pellets containing 11% moisture were achieved at 52% gelatinization. For this level of gelatinization, starch was extruded at 90°C barrel temperature. In addition, the moisture content of the pellets critically affected the expansion behavior. The maximum puffing efficiency and expansion volume were achieved in a moisture range of 10~13%. For optimum product shape and uniform air cell distribution, the pellets should undergo sudden release of the superheated vapor during the microwave‐heating. The expansion by microwave‐heating was optimized at ≈50% gelatinization.     

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

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

Effects of Steam,Moisture, and Screw Speed on Physical Properties of DDGS‐Based Extrudates

A fractional factorial design with a replicated central composite point was used to investigate the effects of extrusion processing on physical properties of distillers dried grains with solubles (DDGS) based aquafeeds using a twin‐screw extruder. Extrusion cooking trials were performed with a nutritionally balanced ingredient blend for Nile tilapia, with two levels of screw speed (350 and 450 rpm), two levels of extruder water (0.236 and 0.302 kg/min), and two levels of conditioner steam (0.1 and 0.15 kg/min). The central point was 400 rpm screw speed, 0.271 kg/min extruder water, and 0.12 kg/min conditioner steam. Effects of these processing conditions on extrudate characteristics were extensively analyzed and included moisture content, water activity, thermal properties, expansion ratio, unit density, bulk density, color, water stability, sinking velocity, water absorption and solubility indices, and pellet durability index. Increasing the extruder water and conditioner steam resulted in a 5.3% decrease and nearly 8.6% rise in mass flow rate, respectively. As screw speed increased from 350 to 400 rpm, water stability and water activity increased by 13 and 58%, respectively. Increasing extruder water from 0.236 to 0.302 kg/min led to a significant increase in water stability by 12.5% and decreases in water absorption index, water activity, and expansion ratio by 13, 21, and 5.5%, respectively. As conditioner steam increased from 0.1 to 0.15 kg/min, sinking velocity and water absorption index decreased by 25 and 15%, respectively. Increasing conditioner steam from 0.1 to 0.12 kg/min resulted in 20, 5.5, 10, and 3% decreases in moisture content of the extrudates, brightness (L*), water stability, and expansion ratio, respectively. It also increased bulk density by 5.8% and unit density by 4.2%. Overall, all trials produced viable extrudates with properties appropriate for Nile tilapia feeding.     

Effects of Extrusion Variables and Chemicals on the Properties of Starch-Based Binders and Processing Conditions

The effects of extrusion variables (moisture, screw speed, and temperature) and chemicals (urea and sodium bicarbonate) on the properties of starch-based binders (water absorption, bulk density, binder yield, expansion ratio, solubility, pH) and processing conditions (die temperature and pressure, feed rate, and specific mechanical energy) were studied using a central composite design. All quadratic regression models, except the models for bulk density and pH, were significant at the P ≤ 0.06 level. These models can predict the binder properties and processing conditions when extrusion variables and the chemical concentrations are known. Optimum combinations of the chemical concentrations (g/100 g of starch) and extrusion variables to achieve high water absorption in the binders were 15–20 g of urea /100 g of starch, 0–4 g of sodium bicarbonate/100 g of starch, 35–40 g of moisture/100 g of starch, 100–120 rpm screw speed, and 185–215°C barrel temperature. The molecular degradation of the starch occurred during extrusion, especially when the moisture content of starch was <30 g/100 g of starch.     

Effect of Batter Solids and Starch Type on the Structure of Baked Starch Foams

The effects of starch type on the properties of baked starch foams were investigated. Starch types used for baking were normal corn, normal potato, waxy corn, high-amylopectin potato, wheat, and tapioca. Solids content of the starch batters used to bake foam trays ranged from 25 to 45%. Processing parameters and physical properties of the foams were examined. Starch-foamed trays were formed by heating a starch batter inside a closed mold. Scanning electron micrographs showed that the thin-walled foamed trays have a dense outer skin and a less dense interior with large cells. The weight of the foamed trays and density of the foam depended on the amount of batter cooked inside the mold, the percent solids of the batter, and the type of starch used. The high-amylopectin starches made the lightest trays, while the normal cereal starches made the heaviest trays. Baking time depended on percent solids of the batter, the batter volume added to the mold, and starch type. The normal cereal starches had the longest baking times and the high-amylopectin starches had the shortest baking times Strength and flexibility of the trays are correlated with tray weight and foam density. Heavier trays had greater strength and less flexibility than did lighter trays. Physical properties of the trays can be tailored to meet specific criteria by changing the starch type used and the batter solids.     

Effects of Extruder Screw Speeds on Physical Properties and In Vitro Starch Hydrolysis of Precooked Pinto,Navy, Red,and Black Bean Extrudates

Precooked pinto, navy, red, and black bean flours were extruded at different screw speeds (320, 380, and 440 rpm) with a twin‐screw extruder. Effect of speed on physical properties and in vitro starch hydrolysis was investigated. Increasing screw speeds reduced water activity, expansion index, and texture. Extrudates could not be obtained from pinto bean flour at 440 rpm because of the high shear effect. Water absorption index and water solubility index were not significantly affected by screw speed but were significantly higher than for unextruded precooked flour. A significant change in color was observed in navy beans, characterized by increasing b values on the Hunter color scale. Resistant starch ranged from 3.65 to 4.83% db and was not significantly affected by screw speed. Glycemic index of all extrudates was high, ranging from 81.3 to 86.9.     

Effect of Single‐Screw Extruder Die Temperature,Amount of Distillers' Dried Grains With Solubles (DDGS), and Initial Moisture Content on Extrudates

Corn distillers' dried grains with solubles (DDGS) was extruded with corn meal in a pilot plant single‐screw extruder at different extruder die temperatures (100, 120, and 150°C), levels of DDGS (0, 10, 20, and 30%) and initial moisture contents (11, 15, and 20% wb). In general, there was a decrease in water absorption index (WAI), water solubility index (WSI), radial expansion, and L* value with an increase in DDGS level, whereas a* value and bulk density increased. Increase in extruder die temperature resulted in an increase in WSI and WAI but a decrease in L* and bulk density. Peak load was highest at 30% DDGS as compared with 0, 10, and 20% DDGS extrudates. Die temperature of 120°C and initial moisture content of 20% resulted in least peak load. The a* value remained unaffected by changes in extruder die temperature. Radial expansion was highest at extruder die temperature of 120°C. Maximum WAI, WSI, radial expansion, and L* value were obtained at 15% initial moisture content. An increase in initial moisture content, in general, decreased L* value and bulk density but increased a* value of extrudates.     

Physical Properties of Poly(Lactic Acid) and Starch Composites with Various Blending Ratios

Two‐phase polymer blends of poly(lactic acid) (PLA) and corn or wheat starches at various ratios were prepared by using a laboratory‐scale twin‐screw extruder and compression molding. The blends were characterized for thermal transitions, mechanical properties, and water absorption. Starch and PLA were immiscible polymers, and the thermal behavior of PLA was not affected by starch. Crystallinity of the blends decreased in some degree as starch content increased 20–40%. Tensile strength and elongation of the blends decreased as starch content increased, but modulus increased as starch content increased up to 70%. As starch content increased to >60%, the PLA phase became discontinuous, and water absorption of the blends increased sharply. Blends made from wheat starch gave slightly better mechanical properties than those made from corn starch, and no differences in other properties were observed.     

Heat expanded starch-based compositions

A heat expansion process similar to that used for expanded bead polystyrene was used to expand starch-based compositions. Foam beads made by solvent extraction had the appearance of polystyrene beads but did not expand when heated due to an open-cell structure. Nonporous beads, pellets, or particles were made by extrusion or by drying and milling cooked starch slurries. The samples expanded into a low-density foam by heating 190-210 degrees C for more than 20 s at ambient pressures. Formulations containing starch (50-85%), sorbitol (5-15%), glycerol (4-12%), ethylene vinyl alcohol (EVAL, 5-15%), and water (10-20%) were studied. The bulk density was negatively correlated to sorbitol, glycerol, and water content. Increasing the EVAL content increased the bulk density, especially at concentrations higher than 15%. Poly(vinyl alcohol) (PVAL) increased the bulk density more than EVAL. The bulk density was lowest in samples made of wheat and potato starch as compared to corn starch. The expansion temperature for the starch pellets decreased more than 20 degrees C as the moisture content was increased from 10 to 25%. The addition of EVAL in the formulations decreased the equilibrium moisture content of the foam and reduced the water absorption during a 1 h soaking period.     

Processing of novel elevated amylose wheats: functional properties and starch digestibility of extruded products

Different types of novel wheat lines with different starch contents and amylose/amylopectin ratios, relating to defined alterations in the number and activity of starch synthase IIa genes, were processed by pilot-plant extrusion. Two types of products were produced: pure wholemeal products and breakfast cereals made from wholemeal/maize blends. Lower apparent shear viscosity was obtained in the extruder with lower starch content and higher amylose/amylopectin ratio flours (SSIIa-deficient line). The bulk density of the products decreased with increasing extrusion temperature and was always higher for the triple-null line. The bulk density was not completely explained by the melt shear viscosity, suggesting the importance of the fillers (fibers, brans) in the process of expansion and structure acquisition. The different mechanical properties were explained by the density and by the material constituting the cell walls. Enzyme-resistant starch (RS) content and hydrolysis index (HI) were not correlated to the extrusion temperature, but RS was higher in pure wholemeal products and in the SSIIa-deficient line. These results are discussed in terms of starch molecular architecture and product microstructure.     

Extrusion Processing of Rice‐Based Breakfast Cereals Enhanced with Tocopherol from a Chinese Medical Plant

Brown rice flour was mixed with a Chinese medical plant (Euryale ferox Salisb.) and processed to make ready‐to‐eat breakfast cereals using twin‐screw extrusion. Levels of 15 and 20% feed moisture in flour, and 200 and 250 rpm screw speed were set, and the physicochemical properties and content of α‐, β‐, γ‐, and δ‐tocopherols were determined. The data showed that 15% feed moisture gave a low bulk density and water absorption index but a high expansion ratio and water solubility index. High screw speed (250 rpm) produced a result similar to that of 15% feed moisture. A sample with 85% brown rice flour with 15% E. ferox Salisb. retained the highest content of α‐, β‐, γ‐, and δ‐tocopherols (125, 6, 78, and 9 μg/g), respectively. The optimum extrusion conditions determined were 15% E. ferox Salisb. mixed with brown rice at 15% feed moisture and at 250 rpm screw speed.     

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

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

Effects of Extrusion on Dietary Fiber and Isoflavone Contents of Wheat Extrudates Enriched with Wet Okara

Okara is the residue left after soymilk or tofu production. In North America, okara is used either as animal feed, fertilizer, or landfill. The purpose of this study was to use wet okara to produce and enrich extruded cereal products and to study the effects of extrusion on the dietary fiber and isoflavone contents. Wet okara was combined with soft wheat flour to produce two different formulations (33.3 and 40% okara) and extruded using four combinations of two screw configurations and two temperature profiles. Various physicochemical properties, dietary fiber by enzymatic-gravimetric method, and isoflavone content by HPLC were analyzed. The radial expansion ratio decreased as fiber content increased. On the other hand, both bulk density and breaking strength increased as fiber content increased. Combining okara with soft wheat flour resulted in increased protein, dietary fiber, and isoflavone contents compared with soft wheat flour alone. Extrusion of the formulations resulted in decreased insoluble fiber (≤25.5%) and increased soluble fiber (≤150%) contents of extrudates. Extrusion decreased the total detectable isoflavones (≤20%) and altered the distribution of the six detected isoflavones.     

Barrier and Mechanical Properties of Starch‐Clay Nanocomposite Films

The poor barrier and mechanical properties of biopolymer‐based food packaging can potentially be enhanced by the use of layered silicates (nanoclay) to produce nanocomposites. In this study, starch‐clay nanocomposites were synthesized by a melt extrusion method. Natural (MMT) and organically modified (I30E) montmorillonite clays were chosen for the nanocomposite preparation. The structures of the hybrids were characterized by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Films were made through casting using granulate produced by a twin‐screw extruder. Starch/MMT composite films showed higher tensile strength and better water vapor barrier properties than films from starch/I30E composites, as well as pristine starch, due to formation of intercalated nanostructure. To find the best combinations of raw materials, the effects of clay content (0–21 wt% MMT), starch sources (corn, wheat, and potato), and amylose content (≈0, 28, 55, 70, 100%) on barrier and mechanical properties of the nanocomposite films were investigated. With increase in clay content, significantly higher (15–92%) tensile strength (TS), and lower (22–67%) water vapor permeability (WVP) were obtained. The barrier and mechanical properties of nanocomposite films did not vary significantly with different starch sources. Nanocomposite films from regular corn starch had better barrier and mechanical properties than either high amylopectin or high‐amylose‐based nanocomposite films. WVP, TS, and elongation at break (%E) of the films did not change significantly as amylose content increased beyond 50%.     

Characteristics of Vegetable‐Based Twin‐Screw Extruded Yellow Perch (Perca flavescens) Diets Containing Fermented High‐Protein Soybean Meal and Graded Levels of Distillers Dried Grains with Solubles

A twin‐screw extrusion study was performed in replicated trials to produce vegetable‐based feeds for juvenile yellow perch. Two isocaloric (3.06 kcal/g) experimental diets were balanced to contain 20 and 40% distillers dried grains with solubles (DDGS) and a constant amount (20%) of fermented high‐protein soybean meal (PepSoyGen) as the fishmeal protein replacers; crude protein content was targeted at 40%. A fishmeal‐based diet was used as a control. Extrusion conditions included conditioner steam (0.11–0.16 kg/min), extruder water (0.11–0.19 kg/min), and screw speed (230–300 rpm). Increasing DDGS from 0 to 40% led to a considerable rise in bulk density, lightness L*), yellowness (b*), and unit density but to decreases in water activity (a_w) and expansion ratio by 12.6, 14.4, 23, 21, 31, and 13%, respectively. The lowest unit density of 791.6 kg/m³ and highest bulk density of 654.5 kg/m³ were achieved with diets containing 20 and 40% DDGS, respectively; changes in DDGS content did not affect extrudate moisture, absorption index, or thermal properties. Raising DDGS from 0 to 40% resulted in an increase in water solubility and redness (a*) by 13.4 and 35%, respectively. All extrudates had high durability (>98%), and low a_w of less than 0.5. Overall, this study yielded viable feeds for yellow perch.     

Effect of Decorticating Sorghum on Ethanol Production and Composition of DDGS

The use of a renewable biomass that contains considerable amounts of starch and cellulose could provide a sugar platform for the production of numerous bioproducts. Pretreatment technologies have been developed to increase the bioconversion rate for both starch and cellulosic‐based biomass. This study investigated the effect of decortication as a pretreatment method on ethanol production from sorghum, as well as investigating its impact on quality of distillers' dry grains with solubles (DDGS). Eight sorghum hybrids with 0, 10, and 20% of their outer layers removed were used as raw materials for ethanol production. The decorticated samples were fermented to ethanol using Saccharomyces cerevisiae. Removal of germ and fiber before fermentation allowed for greater starch loading for ethanol fermentation and resulted in increased ethanol production. Ethanol yields increased as the percentage of decortication increased. The decortication process resulted in DDGS with higher protein content and lower fiber content, which may improve the feed quality.