Cellulose, composition fermentation products

It is a commonly held view that cellulase is an inducible enzyme, and that cellulose is the best inducer. In solid-state fermentation for cellulase production, cellulosic materials act as either the carbon source or the inducer. Some of the raw materials for solid-state fermentation and their composition are listed in Table 1. From Table 1 it is very clear that the raw materials for cellulase production using solid-state fermentation are abundant and cheap. Proper pretreatment of raw materials is generally required. The nitrogen source for solid-state fermentation includes inorganic compounds, such as urea and (NH4)2SO4, or natural products, such as bran. 

Fermentability using human fecal inoculum ranges from a high of 91% (cabbage) to a low of 0% (Maillard product) demonstrating the sensitivity of human microflora to different fiber sources. Fermentability of cellulose by human fecal microflora (23Z) is substantially less than rumen microflora (94%). The microflora in the human intestine may be more affected by fiber composition than rumen microflora. Work by Bryant (19) and Jeraci (11) leads to speculation that variation among inoculum sources in humans on a particular substrate could be greater than in other species. 

Additional experiments are needed to relate not only the monosaccharide composition of the fibers fed to fecal output but also the structures of those fibers and how they may have been modified In the digestive tract even If not fermented. The effect of fiber particle size and pretreatment should be studied. Free sugar, starch, cellulose and uronlc acid measurements should be made in order to obtain a more complete picture of what survives and what is metabolized. The effect of dietary fibers on the digestion and utilization of other polysaccharides and other food components should be studied. This Information, together with fermentation data. Including gas and VFA production, will provide a better understanding of the role and value of different dietary fibers and their effects on nutrient bloavallablllty. 

The effectiveness of microbial cellulose production depends mainly on the strain, the composition of the culture medium (the C source used being very significant), the fermentation temperature, oxygen supply, and the implementation of static or agitated systems. The cost of the media is an important factor for cost-effective BNC production, and therefore its composition and volume as well as the fermenter surface area should all be considered. 

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. 

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