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Valorization of guayule and soy biomass through pretreatment, enzyme production and enzymatic hydrolysis

Islam, S. M. Mahfuzul
http://orcid.org/0000-0002-9938-7692
http://rave.ohiolink.edu/etdc/view?acc_num=akron1525110947568914

Abstract Details

2018, Doctor of Philosophy, University of Akron, Chemical Engineering.
This research aims at developing guayule and soy material (soybean hull and meal) as biorefinery feedstock. Carbohydrate is the main component in guayule and soybean hull, with similar contents of cellulose (27-35%) and hemicellulose (19-22%) but different lignin contents (~36% in guayule and 1-4% in soybean hull). Carbohydrate (30-35%) is the second largest component in soybean meal, next to protein (50%). The main objective is to increase value of these materials through enzymatic carbohydrate hydrolysis to fermentable monomeric sugars. For guayule and soybean hull, CO2-H2O based pretreatment conditions were studied for reducing generation of fermentation inhibitors while enabling high sugar conversion in subsequent enzymatic hydrolysis. The pretreatment condition for guayule was optimized at 1800 psi and 180 °C for 30 min, enabling 82% sugar conversion with low levels of hydroxymethylfurfural (0.07%), furfural (0.25%) and acetic acid (3.0%). The optimal condition for soybean hull was 1250 psi-130 °C-30 min, giving 90+% sugar conversion and negligible inhibitors generation. The better outcomes with gentler pretreatment for soybean hull confirmed the hypothesis that lignin plays the critical role in required pretreatment severity. For soybean meal, additional objectives are to remove indigestible carbohydrates and increase protein content for food and feed uses. The main challenge lies in the complicated enzymes required, containing at least cellulase, xylanase, pectinase, a-galactosidase and sucrase activities, and their optimal composition for complete hydrolysis. A kinetic model was developed to describe the hydrolysis and help optimize the enzyme composition. Pectinase (half-maximum constant, Km = 6.8 U/g) and a-galactosidase (Km = 1.2 U/g) were found to be the most deficient activities produced by the chosen (and other common) enzyme producers. To improve their production, fed-batch Aspergillus niger fermentation conditions were studied and higher pectinase (19.1 ± 0.04 U/mL), a-galactosidase (15.7 ± 0.4 U/mL) and cellulase (0.88 ± 0.06 FPU/mL) activities were achieved. Soybean meal pretreatment and enzymatic hydrolysis was also studied to improve pectin hydrolysis by destabilizing Ca2+-bridged junctures with chelators and to decrease protein loss during the enzymatic hydrolysis. and protein recovery has been improved to 94.8% with only 5.2% protein loss in process. Overall this research has optimized pretreatment and enzymatic carbohydrate hydrolysis for guayule, soybean hull and meal, and increased value of these materials. New knowledge has also been gained in the effect of biomass composition on pretreatment requirement and associated inhibitor generation and in the interactions of mixed enzyme activities on complex carbohydrate structures. The work to further improve the model for enzyme hydrolysis kinetics of complex carbohydrates and the production of very high enzyme titers, along with reduction of protein loss, are the major steps forward for future soybean bioprocessing.
Lu-Kwang Ju, Ph.D. (Advisor)
J. Richard Elliott, Ph.D. (Committee Member)
George Chase, Ph.D. (Committee Member)
Sadhan C. Jana, Ph.D. (Committee Member)
Stephen Duirk, Ph.D. (Committee Member)
Chemical Engineering
Soybean; guayule; enzymatic hydrolysis; pretreatment; biomass; fermentation inhibitors; Aspergillus niger

Recommended Citations

Citations

  • Islam, S. M. M. (2018). Valorization of guayule and soy biomass through pretreatment, enzyme production and enzymatic hydrolysis [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1525110947568914

    APA Style (7th edition)

  • Islam, S. M. Mahfuzul. Valorization of guayule and soy biomass through pretreatment, enzyme production and enzymatic hydrolysis. 2018. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1525110947568914.

    MLA Style (8th edition)

  • Islam, S. M. Mahfuzul. "Valorization of guayule and soy biomass through pretreatment, enzyme production and enzymatic hydrolysis." Doctoral dissertation, University of Akron, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1525110947568914

    Chicago Manual of Style (17th edition)

akron1525110947568914
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This open access ETD is published by University of Akron and OhioLINK.