Browsing by Author "Maumela, Pfariso"

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    Development of integrated processes for the coproduction of inulin, protein, and ethanol from Jerusalem artichoke tubers in a biorefinery
    (Stellenbosch : Stellenbosch University, 2021-03) Maumela, Pfariso; Gorgens, Johann F.; Chimphango, Annie F. A.; Van Rensburg, Eugene; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Biorefining is an attractive approach to simultaneously address food supply, energy security and global warming. Furthermore, biorefining offers a sustainable strategy to utilise biomass, for energy production, thereby, reducing overreliance on fossil resources. The principal aim of the study was to evaluate the feasibility of a Jerusalem artichoke (JA) tuber-based biorefinery by integrating protein extraction to the conventional inulin extraction process, and subsequently hydrolysing the tuber residues with an enzyme cocktail of crude inulinases and commercial Cellic® CTec3 and Pectinex, for ethanol fermentation. The tuber mash was pressed for protein extraction from the juice and water extraction from the solid residues. Sequential water-extraction was used for protein and inulin, in the first and second step, respectively. The resulting tuber residues from the sequential extraction was hydrolysed and fermented into ethanol. Fed-batch culture was used to optimise the bioprocess conditions for recombinant endoinulinases production by Aspergillus niger. Comparison of sequential extraction sequences demonstrated that protein extraction in the first and second step, respectively, maximised the selectivity of the extraction and product yields. Both extraction steps utilised water as a solvent, and were optimised with respect to pH, solids loading and temperature for the selective extraction from each dedicated step from tubers. The soluble protein fraction contained a cumulative 71.8% of the protein present in tubers, while 17.1% was present in the inulin extracted in the subsequent step. The inulin yield was 67.6% of the inulin in the tubers, while 11.8% was co-extracted with the protein product. The protein extract was augmented by protein present in the press juice, obtained from tubers prior to the water extraction steps. High cell density fermentation of Aspergillus niger for recombinant endoinulinase production, was achieved through an exponential fed batch method. Endoinulinase production was growth associated at higher growth rates, achieving the highest volumetric activity (670 U/ml) and biomass concentration (33 g/L) at a growth rate (μ) of 0.07 h-1. Moreover, the significant decrease in enzyme activity (506 U/ml) and biomass substrate yield (0.043 gbiomassDW/gglucose) at low μ (0.04 h-1) was due to the high maintenance energy requirement. High biomass concentrations resulted in broth viscosity, which necessitated increased agitation for mixing and oxygen transfer. However, this led to pellet disruption and biomass growth in mycelial. Moreover, enzyme production profiles, product (Yp/s) and biomass (Yx/s) yield coefficients were not affected. High gravity simultaneous saccharification and fermentation (SSF) of the extraction residues, enriched in cellulose and inulin, was achieved with an optimised cocktail of enzymes. A combined inulin and cellulose conversion yield of 74% was achieved during fermentation at 21% w/v solids loading. The optimised enzyme cocktail improved the saccharification and fermentation of the residues, with an ethanol concentration and yield of 38 g/L and 83%, respectively, compared to an unoptimized cocktail with the same protein dosage, with 32 g/L and 59%, respectively, both at the maximum attainable solids loading of 21% w/v. Therefore, the current data demonstrated the potential of integrating a protein extraction with conventional inulin extraction from JA tubers and fermenting the residues into ethanol with an optimised enzyme cocktail.
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    Sequential extraction of protein and inulin from the tubers of Jerusalem artichoke (Helianthus tuberosus L.)
    (Springer Nature, 2020-02) Maumela, Pfariso; Van Rensburg, Eugéne; Chimphango, Annie FA; Gorgens, Johann F
    An increase in inulin and plant-protein based nutraceutical demand ultimately puts pressure on available resources. Therefore, there is a need to prospect for supplementary feedstocks and sustainable ways to exploit them. The aim of this study was to explore the technical feasibility of sequential extraction of inulin and protein from Jerusalem artichoke tubers and understand the interrelationships between processes and product functional properties. The response surface methodology was used to determine the optimal parameters for sequential extraction. Protein functional properties analysis was done to identify the effects of the extraction process. The extraction approach adopted in this study was preceded by mechanical pressing of the tuber to yield a protein-rich juice. However, only 40.8% of the protein was recovered from the juice, therefore a subsequent solvent extraction step followed to extract the residual protein and inulin retained in the solids. Selective extraction was achieved when protein was solubilised in the first step of solvent extraction. The overall protein and inulin yields from pressing and both sequential extraction steps were 71.88 and 67.6%, respectively. The inulin yields were substantially higher than the maximum overall yields when inulin extraction, from the pressed tuber, was performed first thus improving yields from 57.3 to 67.6%. Consequently, mechanical pressing improved the overall protein yield. Sequential extraction resulted in an inulin extract with minimal protein contamination compared to the conventional method. Therefore, sequential extraction was efficient in yielding extracts with reduced impurities and good functional properties.