Yield from corn

The most common method to extract xylan is the alkaline extraction. Several pretreatment methods can be used in association in order to break the covalent bonds that exist between xylan and other carbohydrates during the extraction (Wang Zhang, 2006). A number of articles studied the use of ultrasound on the xylan extraction. Hromadkova and coworkers reported that 36.1% of xylan was extracted from corn cobs with 5% NaOH solution at 60°C for 10 min of ultrasonication in comparison with 31.5% of xylan in the classical extraction. Both extractive methods yielded xylan with immunogenic properties (Hromadkova et al., 1999). 

COMPARISON OF FRACTION YIELDS FROM THE ENZYMATIC AND CONVENTIONAL CORN WET MILLING PROCESS IN A 1-KG LABORATORY PROCEDURE... 

FIG. 3 Starch yields obtained with the use of different commercial protease enzymes and their comparison with the starch yield from a conventionally wet milled corn sample. 

Hydrolysate B from corn stover contained 4 g/L of glucose, 17.9 g/L of xylose, 5 g/L of arabinose, and 2.5 g/L of acetic acid. Glucose was readily fermented eighty-three percent of xylose was fermented in 23 h. The production of ethanol by fermentation of the com stover hydrolysate was 9 g/L (Fig. 3). The yield of ethanol from consumed sugars reached 93% of theoretical yield. We did not observe xylitol production and acetic acid consumption. 

The maximal recovery of hemicellulose (83.8%) was obtained following the mildest pretreatment at 190°C for 2 min using 0.5% H2S04. The harsher the conditions, the lower the hemicellulose recovery was reached. The maximum cellulose recovery was 89.7%, following steam pretreatment at 200°C, but the recovery was sufficient, about 75%, even at 210°C. Cellulose and hemicellulose exhibited maximum recovery at different conditions, which was also found in other studies (24,25). However, in the case of softwood, the hemicellulose solubilization needed harsher pretreatment conditions than corn stover, and the maximum mannose yield from wood was obtained at between 200 and 210°C (26). 

We explored the influence of dilution rate and pH in continuous cultures of Clostridium acetobutylicum. A 200-mL fibrous bed bioreactor was used to produce high cell density and butyrate concentrations at pH 5.4 and 35°C. By feeding glucose and butyrate as a cosubstrate, the fermentation was maintained in the solventogenesis phase, and the optimal butanol productivity of 4.6 g/(L h) and a yield of 0.42 g/g were obtained at a dilution rate of 0.9 h1 and pH 4.3. Compared to the conventional acetone-butanol-ethanol fermentation, the new fermentation process greatly improved butanol yield, making butanol production from corn an attractive alternative to ethanol fermentation. 

Optimum AFEX treatment conditions are quite broad. However, the highest glucan and xylan conversions and ethanol yields from AFEX-treated corn stover were achieved at about 1 1 kg of ammonia/kg of dry biomass, 60% (dwb) moisture content, 90°C, and 5-min residence time in a... 

Biomass can also be converted to a liquid fuel, such as ethanol, which is then used as a gasoline blend. Today, the major biofuel is ethanol produced from corn, which yields only about 25 percent more energy than was consumed to grow the corn and make the ethanol.32 The future holds the promise of ethanol from sources other than corn, dedicated energy crops such as switchgrass, which can be grown and harvested with minimal energy consumption so that overall emissions are near zero (see Chapter 8). 

There are continuing efforts to develop cost-effective processes for fuel alcohol production, although the economics are often dependent on the availability of subsidized feedstocks to compete with traditional fuels derived from oil. The pretreatment and fermentation of such feedstocks, derived from corn, sugar cane, and even municipal waste, yields a dilute aqueous solution of ethanol which must be separated from a complex mixture of waste materials and then concentrated by distillation to remove water. Both batch and continuous production processes have been developed, with the requirement for effective bioseparations during both the pretreatment and ethanol recovery parts of the process. 

With both species, small quantities of other hexane-soluble, nonpolar metabolites were Isolated. Some were hydrolyzed In alkali and yielded the respective parent C-surfactants. These metabolites also had very low mobility in reversed-phase (RP) chromatography systems. This suggested they were equivalent to the surfactant fatty acid esters (Figure 1 Ri=fatty acyl, n=5 or 8) whose formation by cell-free homogenates from corn tissues was reported by Frear (11). 

These predictions have caused much concern in North America. Sharp decreases of corn and wheat yield from the major granaries of the mid-west and Great Plains (Abrahamson, 1983) have been seen as a likely outcome, because these crops are already grown at temperatures above their optima,... 

Amylose gives a greater yield of cycloamyloses than amylopectin. Kerr obtained 70% of cycloamyloses from corn amylose and from amylopectin 44%. Cycloamyloses are formed also from glycogen. On the other hand the /8-dextrin yields no cycloamyloses. " The conclusion is inescapable that the cycloamyloses are formed from the simple chains of the amylose and from the end chains of amylopectin and glycogen. 

A comparison of the efficiency of the 2,3-oxidosqualene cyclase from human placenta microsomes with that from rat liver microsomes has led to the conclusion that in human placenta the conversion of squalene into lanosterol is limited by the rate of squalene epoxidation. Tracer from [l- C]-2,3-oxidosqualene was incorporated into cycloartenol (1% yield) by a cell-free system from Alnus glutinosa but none of the triterpenoid glutinone was synthesized from the labelled precursor. When 2,3-oxidosqualene was incubated with cell-free extracts from corn embryos the only product was cycloartenol, whereas when l-trarts-T-nor-2,3-oxidosqualene (9) was the substrate both 31-norcycloartenol and 31-norlanosterol were formed " l-c/s-T-nor-2,3-oxidosqualene (10) gave rise to no detectable cyclization products... 

In addition to ethanol from cellulose, cellulase enzymes play a minor role in the production of ethanol from corn. In this process, most of the glucose is from starch. Cellulase enzymes offer the opportunity to increase the glucose yield by hydrolyzing a portion of the cellulose to glucose, as well as decreasing the viscosity of the ground corn [25]. 

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