Levulinic acid cosubstrate

Biomass and P(3HB-co-3HV) yields for shake-flask cultures of Burkholderla cepacia grown on 2.2% (w/v) xylose and various concentrations of levulinic acid. Composition of the copolymers, expressed asthemol%3HV,is also plotted as a function of the levulinic acid cosubstrate concentration... 

Compositionally relevant chemical shift expansions of 300 Hz NMR spectra obtained from P(3HB-co-3HV) samples, illustrating a progressive increase in the mol% 3HV fraction of copolymers produced by Burkholderia cepacia through regulation of the ratio of levulinic acid (cosubstrate) to xylose (substrate) added to the fermentation medium. Chemical structure schematic of P(3HB-co-3HV) displays the methyl side-chain residues of the corresponding monomers, represented quantitatively by the integrated areas of the 3HB doublet (1.27 ppm) and the 3HV triplet (0.88 ppm) (Keenan eta ., 2004). 

In this communication we extend our prior observations and demonstrate the use of xylan-rich, hemicellulosic residual fractions of wood for the production of P(3HB-co-3HV) by B. cepacia. Levulinic acid, the secondary carbon source utilized in this bioconversion process, can be produced cost-effectively from a vast array of renewable carbohydrate-rich resources including cellulose-containing forest and agricultural waste residues 24,25). This five-carbon cosubstrate (4-ketovaleric acid) serves as a precursor to the 3-hydroxyvalerate (3HV) component of the B. cepacia-dtnved P(3HB-co-3HV) copolymer (Figure 1). Further, the mol % 3HV composition and associated physical/mechanical properties of the copolymer can be manipulated as a function of the substrate concentrations provided in the fermentation. Physical-chemical characterizations of such PHA copolymers are reported herein, as evidence supporting the potential of these biodegradable thermoplastics to serve as viable replacements for conventional, environmentally recalcitrant commodity plastics. 

The use of levulinic acid as a cosubstrate in PHA fermentations has also been shown to exhibit a growth and PHA enhancing effect in shake-flask cultures of Alcaligenes sp. SH-69 and B, cepacia ATCC 17759 with glucose or xylose as primary carbon sources, respectively (22,20), For cultures of Alcaligenes sp. SH-69, concentrations of 0.05 % (w/v) levulinic acid resulted in... 

The P(3HB-co-3HV) polymer has been a primary focus, because compared to P(3HB), the copolymer has physical and mechanical properties more conducive to melt-processing and subsequent commercial application. Investigators (Keenan et al, 2005 Nakas et al, 2004) have demonstrated the conversion of steam-exploded (aqueous) and organic solvent-extracted ( organosolv ) hemicellulosic hydrolysates (National Renewable Energy Laboratory, NREL, Golden, CO) to P(3HB-co-3HV) copolymers using levulinic acid as a cosubstrate (see Table 9.3). 

Levulinic acid has been identified as a potentially forest-based, P(3HB-co-3HV) cosubstrate (Bozell et al, 2000), which can be combined with xylose to produce P(3HB-co-3HV) (Keenan et al., 2004). Jang and Rogers (1996)... 

Table9.3 Physical-chemical characteristics of P(3HB-co-3HV) copolymers produced by shake-flask cultures of Burkholderia cepacia from hemicellulosic hydrolysate and levulinic acid as renewable, forest-based substrates and cosubstrates, respectively...

C5 hemicellulosic hydrolysates, produced by the NREL Clean Fractionation procedure, have been detoxified by methods related to the TVA detoxification procedure (Strickland and Beck, 1984). With the appropriate addition of an organic acid cosubstrate, levulinic acid, also produced from renewable feedstocks, we have produced P(3HB-co-3HV) copolymers possessing physical and chemical properties that are potentially useful for application as industrial bioplastics. Thermal characteristics and viscosity-derived molecular masses of a set of P(3HB-co-3HV) samples produced microbially from detoxified hemicellulosic hydrolysate and levulinic acid, are presented in Table 9.3. 

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