Progress 10/01/07 to 09/30/08
Outputs
OUTPUTS: Supercritical fluid extrusion process (SCFX) is an innovative food processing technology that offers sub-100C expansion using direct supercritical fluid carbon dioxide (SC-CO2) injection. Its distinct low-temperature and low-shear conditions due to high moisture allow for the retention of heat sensitive ingredients. The delicate balance of temperature and shear during SCFX processing permits controlled modification of WP conformation. Addition of SC-CO2 provides additional acidic environment and also serves as blowing agent for surface modification of WP matrices. It was hypothesized that reactive SFCX process in highly acidic environment combined with controlled shear and heat in the presence of mineral salts (CaCl2 and NaCl) and SC-CO2 would favorably alter the gelling and functional properties of WPC. Several investigations were undertaken to optimize operating conditions and process variable and their influence have been the subject of several technical presentations made at professional society meetings. PARTICIPANTS: Syed Rizvi, PI. Khanitta Manoi, Graduate student TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
A powder blend comprising 94 wt. percent whey protein concentrate (WPC80), 6 percent pre-gelatinized corn starch, 0.6 percent CaCl2, and 0.6 percent NaCl was texturized using a supercritical fluid extrusion (SCFX) system currently available in our laboratory. The blend was extruded at 90C in a pH range of 2.89 to 8.16 with one percent (db) supercritical carbon dioxide and 60 percent moisture content. The texturized WPC-based (tWPC) samples were dried, grounded into powder, reconstituted in water, and evaluated using a range of rheological studies. Most tWPC samples exhibited shear thinning behavior and their mechanical spectra were typical of weak gel characteristics. The tWPC produced under extremely acidic condition of pH 2.89 with SC-CO2 yielded the highest complex viscosity of 10,049 Pa s) and storage modulus of 9,885 Pa compared to the unprocessed WPC at 0.083 Pa s and 0.036 Pa, respectively. The SCFX process rendered WPC into a product with cold-setting gel characteristics that may be suitable for use as a food texturizer over a wide range of temperatures.
Publications
- Manoi, K. and Rizvi, S.S.H. 2008. Rheological characterizations of texturized whey protein concentrate-based powders produced by reactive supercritical fluid extrusion. Food Res. International, 41(8):786-796.
- Manoi, K. and Rizvi, S.S.H. 2008. Characterization of cold gel-like emulsion produced from texturized whey protein concentrate. Institute of Food Technologists Annual Meeting, June 28-July 01, New Orleans, Book of Abstracts, No. 050-30.
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Progress 10/01/06 to 09/30/07
Outputs
Supercritical fluid extrusion (SCFX) as a novel technology for generation of uniquely textured extrudate was studied and its typical time-delayed expansion characteristic, not observed in steam-based cooking extrusion, was investigated via video analysis. Using a typical feed formulation, the cross-sectional, longitudinal and volumetric expansion characteristics were evaluated at varying SCFX process conditions such as SC-CO2 injection rate and die size. The results showed that the initial cross-sectional expansion of SCFX extrudate was time, SC-CO2 concentration, and pressure drop rate dependent. The growth time of SCFX extrudates was approximately 30-200 fold longer compared to a typical growth time of steam-based extrudates. Die-swell in SCFX extrusion accounted for 32-45percent of the maximum cross-sectional expansion but had insignificant effect on volumetric expansion. The pressure drop profile in the die was found to be critical in controlling not only the
extent of volumetric expansion of SCFX extrudates but also the rate of SCFX expansion via cell nucleation and cell growth. Rapid initial cross-sectional and volumetric expansion of SCFX extrudates promoted faster structure collapse and strategies to enhance the volumetric expansion, which determines the textural and mechanical properties of expanded products, were studied. Post-extrusion treatment such as drying rate and handling were observed to be crucially important in maintaining the morphological integrity of the final product.
Impacts
The time-delayed SCFX expansion is very unique and can be utilized for development of novel SC-CO2 expanded products with tailored texture. A fundamental understanding of the mechanics of time dependent SCFX expansion would be useful in creating products of novel morphology and optimizing the post-extrusion drying processes. Knowledge on the pressure profile through the die and its effect on SCFX expansion may be utilized to increase the overall expansion and minimize structure collapse due to the gas loss from the surface. Moreover, it should be possible to increase the blowing agent efficiency resulting in reduced operating cost. New strategies to minimize gas loss and to enhance overall expansion including nucleation time manipulation and surface to volume ratio control have been proposed.
Publications
- No publications reported this period
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Progress 01/01/06 to 12/31/06
Outputs
A continuous system of making bread by SCFX was developed and the effects of varying SC-CO2, pressure and static mixer on the behavior of dough and bread densities were evaluated. The effect of post-extrusion rounding of dough was also studied. Static mixer and some of its interaction terms were significant factors affecting dough and bread densities. Models developed showed that SC-CO2 quantity and pressure were significant factors in determining dough and bread densities. The models developed described 81 and 76 percent of the variability in dough densities, without and with static mixer, respectively; and, 72 and 57 percent of the variability in bread densities, without and with static mixer, respectively. Dough and bread densities increased linearly with pressure. It was inferred that this result was due to the reduced diffusivity of SC-CO2 at higher pressures. The decreasing change in dough and bread densities with increasing SC-CO2 was attributed to the reduced
ability of dough to solubilize SC-CO2 as the saturation point was approached. The effect of the static mixer was varied because of the interaction of its effects with those of SC-CO2 and pressure. Post-extrusion rounding reduced bread density by as much as 20 percent. Delivery of bioactives and other functional foods via SCFX-based bread making is planned for the next phase of research.
Impacts
Supercritical fluid extrusion-based leavening of dough and delivery of bioactives and flavorants offers yet another novel food processing operation. If successful, this process would obviate the need for yeast fermentation or dough leavening by addition of bicarbonate.
Publications
- No publications reported this period
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Progress 01/01/05 to 12/31/05
Outputs
We have developed a novel reactive extrusion process in which starch is compatabilized with a polyester such as polycaprolactone (PCL)in two steps but in a single extrusion process: 1) the partial oxidation of starch by the replacement of hydroxyl groups with carboxyls and carbonyls and 2) the cross-linking of oxidized starch with polyester by the abstraction of hydrogen near the carbonyl groups of oxidized starch and polyester. Both these steps are performed through the addition of a single oxidizing/crosslinking agent and the generation of hydroxyl free radicals. Fentons reagent (hydrogen peroxide with iron and copper catalysts) was used as the oxidizing/cross-linking agent. The crosslinking reaction was catalyzed by the addition of a modified high surface area montmorillonite (MMT) organoclay to ultimately produce tough starch and PCL nanocomposite reactive blends(RBs. Some of the features of RBs produced in this manner are (1) greater toughness and elongation
approaching that of 100% PCL and (2) improved interfacial adhesion between starch and PCL. This concept can be extend to other polymer blends with starch-like polymers, such as poly(vinyl alcohol) and biodegradable and non-biodegradable polyesters.
Impacts
This new reactive extrusion process could be extended to other starch and PCL-like polymer blends with polymers such as poly(vinyl alcohol) on the one side and poly butylene succinate (PBS), poly hydroxy butyrate valerate (PHBV), and poly lactic acid (PLA) on the other to create cheap, novel, and compatible biodegradable polymer blends with increased toughness. Combined with SCFX, it can make lightweight materials.
Publications
- Kalambur, S.B. and Rizvi, S.S.H. 2004. Starch-based nanocomposites by reactive extrusion processing. Poly.Intenational 53:1413.
- Kalambur, S.B. and Rizvi S. S. H. 2005. Biodegradable and functionally superior starch and polyester nanocomposites from reactive extrusion. J. Appl. Poly Sci.96:1072.
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Progress 01/01/04 to 12/31/04
Outputs
Our objectives in this phase of the study were to incorporate high level of WPC-34 in starch based formulation and to examine the effect of WPC level on its microcellular morphology and mechanical properties. The physico-chemical attributes of SCFX products were also compared with those of their commercial counterparts. Base formulation used comprised of pre-gelatinized corn starch (49.5 pct), pre-gelatinized potato starch (24 pct), sugar (24 pct), dough conditioner (1.5 pct), and salt (1 pct). Six levels of WPC-34 in the range of 12- 37 pct of the base formulation were examined. SC-CO2 (0.5 pct d.b.) and water (55 pct d.b.) were added. The extrudates were dried post-extrusion at 75C. The effects of WPC on the cellular structure and mechanical properties of the SCFX extrudates were determined. As the WPC level increased from 12 to 37 pct, the expansion ratio decreased from 6 to 3.8, and the cell size decreased from 413 to 142 microns. The piece density increased from
0.28 to 0.37-g/cm3. The crushing strength of the SCFX extrudates increased from 18.5 to 35 kg/g and was comparable to those of commercial samples. The compression modulus increased from 12.6 to 31.1 MPa and had a linear relationship with the relative density. Beyond 37 pct WPC level the change in expansion ratio was not substantial.
Impacts
Results obtained to date have clearly established that the SCFX process is very amenable to production of expanded starch-based extrudates with high concentrations of WPC without compromising the product expansion charactristics or texture.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
To meet the challenge of low-carbohydrate snack foods, the effects of high level (40-70 wt. percent) added whey protein concentrate (WPC) on expansion, cellular structure and mechanical properties of starch-based extrudates made by supercritical fluid extrusion (SCFX) were quantified. Below 0.4 wt. percent SC-CO2 level, extrudate was more expanded but had less uniform cell distribution. Between 0.7 wt. percent and 1.0 wt. percent CO2 level, expanded extrudates did not show statistically significant difference in expansion ratio and bulk density. In terms of other ingredients, addition of pre-gel cornstarch enhanced expansion and formed more rigid cell structure than when masa flour was used. Injection of 0.7 wt. percent to 1.0 wt. percent supercritical CO2 with 70 wt. percent added WPC provided expanded crispy protein based snack of excellent quality. Depending on the WPC level used, the expansion ratio ranged from 4 to 11, piece density from 0.25 to 0.35 g/cm3. The
crushing strength of the extrudates varied from 18.5 to 35 kg/g and was comparable to commercial samples. Results indicated that SCFX process is suitable for production of expanded starch-based extrudates containing high concentrations of nutritionally rich whey protein concentrate without compromising the expansion characteristics or texture of the products.
Impacts
As the demand for low carbohydrate and high protein food increases, extrudates containing high concentrations of nutritionally superior whey proteins if adequately developed will be ideal to fill the need. The results obtained to date indicated that SCFX process is ideally suitable for production of high protein, expanded products using low temperatures and low shear, without compromising the expansion characteristics or texture of the products.
Publications
- Chen, K. J., Dogan, E. and Rizvi, S.S.H. 2002. Supercritical Fluid Extrusion of Masa-based Snack Chips. Cereal Foods World. 47(2): 44-51.
- Alavi, S.H., Chen, K.-H., and Rizvi, S.S.H., 2002. Rheological characteristics of intermediate moisture blends of pregelatinized and raw wheat starch. J. Agric. Food Chem., 50 (23), 6740 -6745, 2002.
- Alavi, S.H., Rizvi, S.S.H. and Harriott, P. 2003. Process dynamics of starch-based microcellular foams produced by supercritical extrusion I: model development. Food Res. Intl. 36(4):309-319.
- Alavi, S.H., Rizvi, S.S.H. and Harriott, P. 2003. Process dynamics of starch-based microcellular foams produced by supercritical fluid extrusion II: numerical simulation and experimental evaluation. Food Res. Intl. 36(4):321-330.
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Progress 01/01/02 to 12/31/02
Outputs
A new generation of expanded whey protein-based nutritious snack chips with cracker-like crispy texture and unique product appearance was made by supercritical fluid extrusion (SCFX). These SC-CO2 expanded extrudates possess smooth nonporous surface and uniform interior closed cell structure with average cell sizes of 100-250 microns. Use of SC-CO2 is attributed to the development of expanded internal structure and the elimination of the hard, glassy-like texture characteristics of the typical masa corn-based taco and tortilla chip products. Extruded product temperature was at 85-90oC, below 100oC to prevent steam expansion. SCFX shear-temperature treatment induced starch conversion, critical to enhance gas retention capacity for dough expansion. The end-point gelatinization was, however, similar to what is typically achieved for tortilla chips through conventional process. SC-CO2 injection rates of 0.8-2.0 wt percent of feed produced expansion ratio of 1.1-1.6 times
upon die exit and further expanded to 2.0-2.5 times by frying and 1.5-1.8 times by baking. When compared to range of commercial crackers and chips, SCFX samples had comparable breaking strength but higher compression and flexure moduli values, corresponding to a crispier texture since a faster breakage than commercial chips can be achieved with same applied force. This novel processing technology could offer a commercially viable alternative using extruders only, effectively eliminates the need for sheeting and equilibration steps in conventional process.
Impacts
Results obtained to date indicated that SCFX process is suitable for production of expanded starch-based extrudates containing high concentrations of nutritionally rich whey protein concentrate without compromising the expansion characteristics or texture of the products. The product categories of breakfast cereals as well as snack chips are very amenable to manufacturing by this process.
Publications
- Chen, K. J., Dogan, E. and Rizvi, S.S.H. 2002. Supercritical Fluid Extrusion of Masa-based Snack Chips. Cereal Foods World. 47(2): 44-51.
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Progress 01/01/01 to 12/31/01
Outputs
The effects of 7 to 37% added whey protein concentrate (WPC) on expansion, cellular structure and mechanical properties of starch-based extrudates made by supercritical fluid extrusion (SCFX) were quantified. Depending on the WPC level used, the expansion ratio ranged from 7.9 to 11.7, piece density from 0.28 to 0.37 g/cm3 and cell size from 244 to 445 mm. Expansion of extrudates with WPC level as high as 37% was comparable with steam-based extrudates. The products with 12% and 17 % WPC showed the most expansion. The crushing strength of the extrudates varied from 18.5 to 35 kg/g and was comparable to commercial samples. The compression modulus (Ec) of the expanded samples ranged between 12.6 and 31.1 MPa and had a linear relationship with the relative density of the products. Above 17%WPC the piece density, crushing strength and the compressive moduli of the extrudates (Ec) increased and the expansion ratio decreased as the %WPC added in the formulation was
increased. The whiteness of the sample decreased by only 14% on addition of up to 37% WPC, indicating that Maillard browning was not as pronounced as in steam-based extrusion. Oat flour was also added to mimic commercial cereal formulation. Addition of 5% and 10% oat flour to the formulation with 12% and 17% WPC made the starch-based melt highly adhesive and adequate expansion was not achieved.
Impacts
Results obtained to date indicate that SCFX process is suitable for production of expanded starch-based extrudates containing high concentrations of nutritionally rich whey protein concentrate. The extruded product is expected to be superior to steam-based products because of low-temperature and low-shear SCFX processing.
Publications
- No publications reported this period
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Progress 01/01/00 to 12/31/00
Outputs
Supercritical fluid extrusion, a low temperature and low shear process, was used to produce pre-gelatinized corn and wheat flour-based extrudates, containing 4-10% thermosetting whey protein concentrate (WPC-34), and dried at 22-100oC. The extrudate expansion was noticeably unstable and collapsed upon exit at the die. When the wheat flour was replaced with potato starch, the extrudate morphology and expansion characteristics improved significantly. To further understand the role of whey proteins in stabilizing the micocellular structure of the extrudates, 4 to 40 wt.% WPC-34 was incorporated in the formulation. A Wenger TX-52 co-rotating twin-screw extruder with 9 heads, a barrel diameter of 52 mm, and length to diameter ratio (L/D) of 27:1 was configured to operate at a screw speed of 100 rpm and feed rate of 9.88 x 10-3 kg/s (35.58 kg/h). The average specific mechanical energy (SME) was 50 kJ/kg. Addition of whey proteins reduced shrinkage of high-moisture
extrudates, as indicated by increases in expansion ratio by up to 140% and 341% when the drying temperatures were 22 and 100oC, respectively. Products containing about 7 wt.% WPC-34 and dried at 85oC expanded best while maintaining an intact structure, with expansion ratio (12) and bulk density (0.10 g/cm3) comparable to steam extrudates. The products had a unique composite and uniform microcellular structure, with average cell sizes in the range of 50-250 mm and cell density of the order of 106 cells/cm3. The classical nucleation theory and a qualitative model for cell growth and shrinkage based on glass transition temperature were used to explain the microcellular structure. Drying at 70 oC resulted in an expanded extrudate, and peak stress dropped on addition of WPC-34. The compressive modulus decreased as the shape of the cells changed from a predominantly spherical to a polyhedral shape. A higher modulus was associated with a larger number average of cell sides and higher % of
closed cells. In general, Ashby's Model (1983) for non-food cellular solids relating mechanical property to bulk density, gave a good fit to our data for SCFX extrudates with WPC-34 added. A linear regression model with bulk density as a predictor was adequate to predict the mechanical strength of starch based SCFX extrudates. The effect of draining of material to the cell edges for food foams and its effect on mechanical strength needs to be further investigate. The mechanical properties were determined precisely by using a dynamic mechanical analyzer in static stress-scan mode. The flexure modulus (Ef) of the extrudates increased from 1.26 to 61.02 MPa and compressive modulus (Ec) from 0.20 to 8.68 MPa as p*/ps increased from 0.07 to 0.26. The cell size, obtained by scanning electron microscopy, ranged from 102 to 243 microns and was in inverse proportion to p*/ps. The Gibson-Ashby model based on cell wall bending was used to successfully predict the compressive modulus as a
function of product structure (R2 = 0.88). The model was further refined to incorporate the effects of compression on entrapped gas and membrane stresses in the cell faces.
Impacts
The mechanical properties of the SCFX extrudates were comparable to those obtained for commercial samples, but the precise control of cellular structure by controlling processing variables such as supercritical CO2 injection pressure, and the homogeneity of the microstructure of SCFX products will allow apriori design of products with desired textural properties. This is another advantage of SCFX technology over conventional steam extrusion, among others like low shear and temperature processing, and the formation of a non-porous skin.
Publications
- No publications reported this period
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Progress 01/01/99 to 12/31/99
Outputs
Cereal is a popular breakfast food that sometimes isn't too appealing with regards to taste and texture. To make a more appealling breakfast cereal which is nutritious. The effects of whey protein content and drying temperature on the expansion and cellular structure of SCFX extrudates were established. Shrinkage of extrudates before oven drying was reduced (expansion ratio increased by up to 140% and bulk density decreased by up to 70%) when 4 to 10% of WPC-34 was added to a starch-based formulation, because the partial gelation of proteins inside the extruder barrel. Expansion ratio of extrudates increased up to 341% and bulk density decreased up to 74% as the drying temperature was raised from 22 to 20C, although drying of extrudates at 100C caused damage to the cellular structure. In general, maximum expansion ratio and minimum bulk density was observed at 7% WPC-34 for all drying temperatures. The products with the best expansion, while maintaining an intact
cellular structure, were those dried at 85C and containing 7% WPC (expansion ratio of around 12 and bulk density of 0.10 g/cm3). These extrudates were comparable to steam puffed products in terms of degree of expansion. Cell size of the extrudates ranged between 56 and 244 um. The polydispersity index of cell size distribution of SCFX extrudates ranged from 0.90 to 0.97 as compared to a value of 0.29 for steam extrudates indicating that the cell size distribution of SCFX extrudates was much more uniform. The cell density of the extrudates, which was the order of 106 cell/cm3, decreased by up to three times on addition of 4 to 10% WPC-34, which was explained on the basis of the classical nucleation theory.
Impacts
(N/A)
Publications
- No publications reported this period
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