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Thesis - University Access Only
Master of Science (MS)
Agricultural and Biosystems Engineering
Com distillers dried grains (DDG) were extruder in a com meal base using single screw extruder and twin screw extruder to study the functional properties of the resulting extrudates. Four different studies were done to see that if formulations were treated differently then there will be significant differences in functional properties of extrudates.
Study 1 was done using single screw extruder at various levels of temperature (120, 135, 150°C), DDG (0, 10, 20 % dry basis) and moisture (14% wet basis) to measure radial expansion (RE), bulk density (BD), peak load (PL), and color (L*, a*, b*) of extrudates. Study 2 was done using single screw extruder with added additives sodium bicarbonate (0, 0.1, 0.25 %) dry basis and sodium aluminum sulfate (0, 0.1, 0.25 % dry basis). Sodium bicarbonate was added to achieve more radial expansion, but it caused browning problem due to higher pH value. Sodium aluminum was used to eliminate the browning problem. Study 3 was done using twin screw extruder at various level of DDG (0, 10, 20, 30 %), screw speed (200,250,300 rpm), water flow rate (0.049, 0.062, 0.077, 0.093, 0.036 kg/min), sodium bicarbonate (0, 0.1%), sodium aluminum sulfate (0, 0.1%). Study 4 was done using single screw extruder to compare pulverized air-dried (PAD) DDG extrusion results with drum dried DDG extrusion results. Study 4 was done using single screw extruder at various levels of DDG (0, 10, 20 %), temperature (120, 150 °C) and sodium bicarbonate (0.1, 0.25, 0.5 %) to measure radial expansion (RE), bulk density (BD), peak load (PL), and color (L*, a*, b*) of extrudates.
For all four studies statistical analyses was done using PROG GLM procedure. Response surface methodology (RSM) was also used for Study 2 to determine optimum temperature, DDG and NaHCO3 for achieving highest RE. RSM was used to investigate the shape of predicted surface and search for region of optimum. RSM uses central composite design. The nonsignificant terms (p>0.05) were withdrawn from model, and new adjustments were made so that only significant terms were included in the final model. Contour and response surface plots were used to see effect of DDG, NaHCO3 on RE, BD, and PL at 150°C. For study 3 we also measured the specific mechanical energy input (SME) which is a good quantitative descriptor in extrusion processes, since it allows the direct comparison of different combinations of extrusion conditions such as screw speed, feeding rate, and torque. Highest SME was observed for formulation of 10% DDG+0.1%NaHC03+0.1% sodium al sulfate.
It can be inferred that radial expansion decreased as DDG% increased. We obtained more expansion at lower temperature i.e. at 120°C than at 150°C. We used 14% moisture com meal and DDG mixture because we saw a significant decrease in radial expansion when higher moisture content mixture was used. As we increased amount of DDG from 0% to 20% and sodium aluminum sulfate + sodium bicarbonate from 0% to 0.25% we got less radial expansion. Increasing amount of DDG results in more dense products that is more bulk density. Proposed model for study 2 was adequate as revealed by diagnostic checking provided by ANOVA. The adequacy of each model is calculated by Lack of Fit and coefficient of determination. So contour plots were employed to study the response surface and locate optimum. Canonical analysis based on coded data and Eigen values showed that stationary point was saddle point. Therefore Ridge analysis was used to estimate max response for dependent variable. The regression model developed for study 2 showed that DDG bad a highly significant effect both in linear and squared terms on RE. The R^ value was 97.83% for RE, which revealed that there was strong correlation between variables and model was appropriate. Highest radial expansion (15.96 mm)was obtained for formulation (10%DDG, 0%NaHCO3 + 0%AlNa(S04)2 I2H2O) at 137°C, screw speed 200 r.p.m using twin screw extruder.
Results from study 4 revealed that pulverized air-dried DDG (PAD) expanded more than drum dried DDG even when all parameters were held constant. It was observed that there was decrease in radial expansion from 8.31 mm for PAD DDG at 0% and 150°C to 7.7 mm for drum dried DDG at 0% and 150°C. Study 4 revealed that as sodium bicarbonate percentage increased from 0.1% to 0.25% expansion decreased from 6.9 mm to 6.47 mm regardless of DDG content. Highest bulk density was observed for 20% DDG. From studies using single screw extruder it was observed that highest bulk density (327.3 kg/m3) was obtained at 20%DDG, 120°C, 0.25% sodium aluminum sulfate+ 0.25% NaHCO3. Study 2, 3, 4 revealed that bulk density increased with increase in NaHCO3 content. Highest bulk density (183 kg/m3) was obtained for formulation (30% DDG, 0% NaHCO3 + 0% AlNa (S04)2- I2H2O) in case of twin screw extruder. Bulk density was highest (406 kgW) for 20% PDA DDG at 120°C. Highest peak load (0.62 kg) was obtained at 0% DDG 0% sodium aluminum sulfate+0% NaHCO3 150°C. Peak load was higher for Drum dried DDG than PDA DDG at both temperatures i.e. at 120°C and 150°C. L*(Luminosity) value increased with increase in NaHCO3 content from 0.1% to 0.25%. The regression model in study 2 showed that NaHCO3 had a highly significant effect both in linear and squared terms on L*. a* (redness) value increased with increase in DDG content and temperature. Interaction effect of die temperature and sodium bicarbonate was not significant (P>0.05) for a*. Highest b* value (38.66) was obtained at 10% DDG, 0% NaHCO3+0% sodium aluminum sulfate using single screw extruder.
Thus all studies revealed that radial expansion decreased as DDG% increased. Bulk density decreased with increase in RE. Study 1 revealed that RE decreased with increase in temperature this might be due to starch degradation and dextrinisation at higher temperature. Peak load increased with increase in RE. This can be ascribed to more starch content and thicker cell walls, a* value decreased with increase in temperature. This could be because at higher temperature DDG did not bind well with matrix. Luminosity increased with increase in RE. More expansion imparts sheen on extrudates and therefore luminosity increases. Study 2 revealed that RE increased with increase in temperature. Peak load decreased with decrease in RE. This was also true for study 3 and study 4. Sodium bicarbonate might have reacted with starch to form acids which reacted to produce CO2 at higher temperature and assisted in expansion of extrudates. Sodium bicarbonate and sodium aluminum sulfate improved expansion at 0.1% but decreased as it moved from 0.1 % to 0.25 %. Bulk density increased with increase in sodium bicarbonate and sodium aluminum sulfate. a*(redness) value decreased with increase in sodium bicarbonate and sodium aluminum sulfate. L*(Luminosity) increased with increase in sodium bicarbonate and sodium aluminum sulfate. Highest radial expansion was obtained at 200 rpm for study 3. This could be due to less residence time and optimum gelatinization of starch. Increase in screw speed decreased radial expansion. Extrudates produced at lower screw speed were darker in color and higher in redness. Bulk density increased with increase in DDG. In study 4 it was observed that radial expansion was more for PAD DDG than drum dried DDG. This could be due to the fact that small particles are more easily hydrated and cooked than larger particles. Peak load was higher for drum dried DDG than PAD DDG. This could be attributed to larger size particles.
Thus it can be concluded that if the formulations were treated differently then there will be significant differences in functional properties of extrudates. If extrudates appeal is enhanced it will dramatically increase value of extrudates. Extrusion can be used to produce pet foods. DDG being cheap and a good source of essential minerals potassium and phosphorus. It also has an enhanced palatability and is an excellent source of linoleic acid, methonine, cystine and vitamin E. Therefore it can also be consumed by humans provided the production of DDG meets GRAS standards.
Library of Congress Subject Headings
Includes bibliographical references (75-83)
Number of Pages
South Dakota State University
Copyright © 2007 Murali Krishna Rai. All rights reserved
Rai, Murali K., "Understanding the Role of Extrusion Processing Parameters on Functional Properties of Distillers Dried Grains Extruded Using Single and Twin Screw Extruder" (2007). Theses and Dissertations. 636.