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141.
Determination of acrolein in french fries by solid-phase microextraction gas chromatography and mass spectrometry 总被引:1,自引:0,他引:1
The frying of foods in the home can be a cause of indoor pollution due to the formation of acrolein. The emission of acrolein formed during frying in soybean, corn, canola, sunflower and palm oils was studied. A GC/MS method has been developed to determine acrolein in French fries using SPME as the sampling technique after derivatization with 2,4-dinitrophenylhydrazine (DNPH). Optimum SPME conditions included desorption at 250°C for 2min after an adsorption time of 10min at room temperature. The method presented good resolution, repeatability, detection and quantification limits, and linearity of response. French fries were prepared in five different oils with four frying steps. The results showed that changes in acrolein concentration occurred after frying potatoes in different types of oil and at different frying cycles. Potatoes fried in soybean oil contained the lowest concentration of acrolein. Shoestring potatoes contained a lower concentration of acrolein than potato chips and French fries, respectively, because of the higher surface/volume ratio. 相似文献
142.
Katarína uchov Vladimír Puchart Nikolaj Spodsberg Kristian B. R. Mrkeberg Krogh Peter Biely 《Molecules (Basel, Switzerland)》2021,26(15)
Catalytic properties of GH30 xylanases belonging to subfamilies 7 and 8 were compared on glucuronoxylan, modified glucuronoxylans, arabinoxylan, rhodymenan, and xylotetraose. Most of the tested bacterial GH30-8 enzymes are specific glucuronoxylanases (EC 3.2.1.136) requiring for action the presence of free carboxyl group of MeGlcA side residues. These enzymes were not active on arabinoxylan, rhodymenan and xylotetraose, and conversion of MeGlcA to its methyl ester or its reduction to MeGlc led to a remarkable drop in their specific activity. However, some GH30-8 members are nonspecific xylanases effectively hydrolyzing all tested substrates. In terms of catalytic activities, the GH30-7 subfamily is much more diverse. In addition to specific glucuronoxylanases, the GH30-7 subfamily contains nonspecific endoxylanases and predominantly exo-acting enzymes. The activity of GH30-7 specific glucuronoxylanases also depend on the presence of the MeGlcA carboxyl, but not so strictly as in bacterial enzymes. The modification of the carboxyl group of glucuronoxylan had only weak effect on the action of predominantly exo-acting enzymes, as well as nonspecific xylanases. Rhodymenan and xylotetraose were the best substrates for exo-acting enzymes, while arabinoxylan represented hardly degradable substrate for almost all tested GH30-7 enzymes. The results expand current knowledge on the catalytic properties of this relatively novel group of xylanases. 相似文献
143.
基于气相色谱-质谱(GC-MS)结合正交偏最小二乘判别分析法(OPLS-DA),建立了筛选玉米浆中影响青霉素发酵效价的潜在标志物的方法.利用GC-MS获得玉米浆中44种物质,经过标准化、Pareto预处理后,通过OPLS-DA对样本进行模式识别,根据模型的载荷图和变量重要性因子(VIP)筛选出9个潜在的标志物,即亮氨酸、5-酮脯氨酸、天冬氨酸、柠檬酸、酪氨酸、丝氨酸、赖氨酸、苏氨酸和葡萄糖.结果表明,这些物质与青霉素的初级代谢和次级代谢密切相关,可以作为筛选青霉素发酵优质原料的潜在质量指标. 相似文献
144.
Yiqin Wan Paul Chen Bo Zhang Changyang Yang Yuhuan Liu Xiangyang Lin Roger Ruan 《Journal of Analytical and Applied Pyrolysis》2009,86(1):161-167
This study was intended to evaluate the effects of catalysts on product selectivity of microwave-assisted pyrolysis of corn stover and aspen wood. Metal oxides, salts, and acids including K2Cr2O7, Al2O3, KAc, H3BO3, Na2HPO4, MgCl2, AlCl3, CoCl2, and ZnCl2 were pre-mixed with corn stover or aspen wood pellets prior to pyrolysis using microwave heating. The thermal process produced three product fractions, namely bio-oil, gas, and charcoal. The effects of the catalysts on the fractional yields were studied. KAc, Al2O3, MgCl2, H3BO3, and Na2HPO4 were found to increase the bio-oil yield by either suppressing charcoal yield or gas yield or both. These catalysts may function as a microwave absorbent to speed up heating or participate in so-called “in situ upgrading” of pyrolytic vapors during the microwave-assisted pyrolysis of biomass. GC–MS analysis of the bio-oils found that chloride salts promoted a few reactions while suppressing most of the other reactions observed for the control samples. At 8 g MgCl2/100 biomass level, the GC–MS total ion chromatograms of the bio-oils from the treated corn stover or aspen show only one major furfural peak accounting for about 80% of the area under the spectrum. We conclude that some catalysts improve bio-oil yields, and chloride salts in particular simplify the chemical compositions of the resultant bio-oils and therefore improve the product selectivity of the pyrolysis process. 相似文献
145.
Claudia I. Ishizawa Tina Jeoh William S. Adney Michael E. Himmel David K. Johnson Mark F. Davis 《Cellulose (London, England)》2009,16(4):677-686
It has previously been shown that the improved digestibility of dilute acid pretreated corn stover is at least partially due
to the removal of xylan and the consequent increase in accessibility of the cellulose to cellobiohydrolase enzymes. We now
report on the impact that lignin removal has on the accessibility and digestibility of dilute acid pretreated corn stover.
Samples of corn stover were subjected to dilute sulfuric acid pretreatment with and without simultaneous (partial) lignin
removal. In addition, some samples were completely delignified after the pretreatment step using acidified sodium chlorite.
The accessibility and digestibility of the samples were tested using a fluorescence-labeled cellobiohydrolase (Trichoderma reesei Cel7A) purified from a commercial cellulase preparation. Partial delignification of corn stover during dilute acid pretreatment
was shown to improve cellulose digestibility by T. reesei Cel7A; however, decreasing the lignin content below 5% (g g−1) by treatment with acidified sodium chlorite resulted in a dramatic reduction in cellulose digestibility. Importantly, this
effect was found to be enhanced in samples with lower xylan contents suggesting that the near complete removal of xylan and
lignin may cause aggregation of the cellulose microfibrils resulting in decreased cellulase accessibility. 相似文献
146.
Extraction and characterization of native heteroxylans from delignified corn stover and aspen 总被引:1,自引:0,他引:1
Radnaa Naran Stuart Black Stephen R. Decker Parastoo Azadi 《Cellulose (London, England)》2009,16(4):661-675
Dimethylsulfoxide-solubilized polysaccharides from delignified corn stover and aspen were characterized. The biomass was delignified
by two different techniques; a standard acid chlorite and a pulp and paper QPD technique comprising chelation (Q), peroxide
(P), and acid-chlorite (D). Major polysaccharides in all fractions were diversely substituted xylan. Xylan acetylation was
intact after chlorite delignification and, as expected, xylan from QPD-delignified fraction was de-acetylated by the alkaline
peroxide step. The study of DMSO-extractable xylans from chlorite-delignified biomass revealed major differences in native
acetylation patterns between corn stover and aspen xylan. Xylan from cell walls of corn stover contains 2-O- and 3-O-mono-acetylated xylan and [MeGlcA-α-(1 → 2)][3-OAc]-xylp units. In addition, aspen xylan also contains 2,3-di-O-acetylated xylose. 1,4-β-d-xylp residues substituted with MeGlcA at O-2 position are absent in chlorite-delignified aspen xylan. Sugar composition in accord with NMR-spectroscopic data indicated
that corn stover xylan is arabinosylated while aspen xylan is not. We have shown that corn stover xylan has similar structure
with xylans from other plants of Poales order. No evidence was found to indicate the presence of 1,4-β-d-[MeGlcA-α-(1 → 2)][Ara-α-(1 → 3)]-xylp in corn stover xylan fractions. 相似文献
147.
Technoeconomic analysis has been used to guide the research and development of lignocellulosic biofuels production processes
for over two decades. Such analysis has served to identify the key technical barriers for these conversion processes so that
research can be targeted most effectively on the pertinent challenges. The tools and methodology used to develop conceptual
conversion processes and analyze their economics are presented here. In addition, the current process design and economic
results are described for dilute acid pretreatment followed by enzymatic hydrolysis and fermentation. Modeled ethanol costs
of $1.33/gallon (in consistent year 2007 dollars) are being targeted for this commercial scale corn stover conversion process
in 2012. State of technology models, which take actual research results and project them to commercial scale, estimate an
ethanol cost of $2.43/gallon at present. In order to further reduce costs, process improvements must be made in several areas,
including pretreatment, enzymatic hydrolysis, and fermentation. As the biomass industry develops, new fuels and new feedstocks
are being researched. Technoeconomic analysis will play a key role in process development and targeting of technical and economic
barriers for these new fuels and feedstocks.
相似文献
Andy AdenEmail: |
148.
There exist large amounts of detergent fiber analysis data [neutral detergent fiber (NDF), acid detergent fiber (ADF), acid
detergent lignin (ADL)] for many different potential cellulosic ethanol feedstocks, since these techniques are widely used
for the analysis of forages. Researchers working in the area of cellulosic ethanol are interested in the structural carbohydrates
in a feedstock (principally glucan and xylan), which are typically determined by acid hydrolysis of the structural fraction
after multiple extractions of the biomass. These so-called dietary fiber analysis methods are significantly more involved
than detergent fiber analysis methods. The purpose of this study was to determine whether it is feasible to correlate detergent
fiber analysis values to glucan and xylan content determined by dietary fiber analysis methods for corn stover. In the detergent
fiber analysis literature cellulose is often estimated as the difference between ADF and ADL, while hemicellulose is often
estimated as the difference between NDF and ADF. Examination of a corn stover dataset containing both detergent fiber analysis
data and dietary fiber analysis data predicted using near infrared spectroscopy shows that correlations between structural
glucan measured using dietary fiber techniques and cellulose estimated using detergent techniques, and between structural
xylan measured using dietary fiber techniques and hemicellulose estimated using detergent techniques are high, but are driven
largely by the underlying correlation between total extractives measured by fiber analysis and NDF/ADF. That is, detergent
analysis data is correlated to dietary fiber analysis data for structural carbohydrates, but only indirectly; the main correlation
is between detergent analysis data and solvent extraction data produced during the dietary fiber analysis procedure. 相似文献
149.
150.
R. Torget M. Himmel J. D. Wright K. Grohmann 《Applied biochemistry and biotechnology》1988,17(1-3):89-104
A preliminary process design for dilute sulfuric acid pretreatment of aspen wood chips in order to obtain fermentable sugars
has been prepared and subjected to an economic evaluation. The process design was prepared according to experimental data
on the kinetics of dilute sulfuric acid prehydrolysis and particle size effects obtained in this study and our previous work.
The initial economic evaluation shows woodchips are 56% of the cost of production, whereas the reactor is only 4%, and the
comminution operation is just under 10%, indicating that the process economics are extremely vulnerable to feedstock costs
and are thus yield-sensitive. Although chances for major cost improvements by modification of the reactor design and finding
alternatives to dry milling of aspen chips to small (20–80 mesh) particles needed for acid penetration and enzymatic saccharification
are not great, design improvements of the process will necessitate development of a cheaper acid resistant pretreatment reactor
and a less energy intensive comminution system. Experimental results on effects of particle size on the dilute acid pretreatment
design are presented. 相似文献