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Biomedical subjects

B W Li

Publications and source records attributed to B W Li.

35 records · Page 2Linked to original sources
PubMed1991

[Restriction fragment length differences of genomic repetitive DNA from five sibling species of Anopheles hyrcanus group].

Genomic DNA were prepared from 5 sibling species of Anopheles hyrcanus group including An. sinensis (ASS), An. anthropophagus (ALA), An. liangshanensis (ALS), An. crawfordi (ACW) and An. xiaokuanus (AXK). High molecular weight DNA from each species were cut with three restriction endonucleases (Bgl II, Hae III and Pst I) and the DNA fragments analysed by agarose gel electrophoresis and ethidium bromide staining. Three enzymes (Bgl II, Hae III and Pst I) produced unique fragments in all sibling species tested. A diagnostic restriction fragment length of DNA from 5 sibling species of An. hyrcanus group may be derived from a single restriction enzyme pattern (i.e. Bgl II). The results demonstrated that the restriction fragment length differences of repetitive DNA could used as a tool to distinguish sibling species of An. hyrcanus group.

Animals↗
PubMed1990

[Restriction fragment length differences (RFLDs) of genomic DNA from different geographical strains of Anopheles sinensis and Anopheles anthropophagus].

Total DNA was extracted from three geographical strains of Anopheles sinensis and two geographical strains of Anopheles anthropophagus and digested respectively with three restriction endonucleases (Bgl II, Hae III and Pst I). The restriction fragment length differences (RFLDs) of repetitive DNA detected after agarose gel electrophoretic separation and ethidium bromide staining were compared among the above-mentioned geographical strains of both An. sinensis and An. anthropohagus. The results indicated that the band patterns are species- specific and strain-specific, their main bands being similar while their minor bands being distinctly different. Pst I digestion produced unique fragments for three geographical strains of An. sinensis while Bgl II digestion produced unique fragments for two geographical strains of An. anthropophagus. In view of the variation in repetitive DNA of different geographical strains of both An. sinensis and An. anthropophagus presented, the RFLDs could be used as a means to distinguish various closely related geographical strains of anopheline mosquitoes.

Animals↗
PubMed1987

A nationwide sampling of fast-food fried chicken: starch and moisture content.

A nationwide sampling plan was executed to estimate the nutrient composition of fast-food fried chicken in the United States. Ninety-four composite samples were selected from major chains in 10 cities. Starch contents were determined using a modified American Association of Cereal Chemists method. The amount of glucose formed during enzymatic hydrolysis was quantified either by a gas-liquid-chromatographic or a high-performance liquid chromatographic technique. The starch content ranged from 6% to 13% (wet weight basis). Moisture was determined by both microwave and vacuum oven methods; levels ranged from 38% to 49%. Analysis of variance for both starch and moisture indicated that starch was significantly (p less than .01) higher for light cuts than for dark cuts across all brands. Extra crispy recipes were significantly higher in starch than other recipes. Light cuts were significantly (p less than .01) lower in moisture than dark cuts. In addition, significant differences existed among brands. However, no significant difference was found between samples within a brand obtained from the five regions.

Animals↗
PubMed1977

A study of calcium pump activity of lysosomes from rat renal cortex.

Fractions rich in either primary or secondary lysosomes were prepared from rat renal cortex by differential centrifugation and evaluated for their capacity for net calcium uptake. No uptake was observed in the absence of ATP. A vigorous uptake did take place in the presence of ATP but it was largely prevented by azide and other inhibitors of mitochondrial calcium uptake, suggesting that it was attributable to contamination by mitochondria. Evidence was obtained for an inhibitory influence of the secondary lysosomal fraction on mitochondrial calcium uptake.

Acid Phosphatase↗
PubMedDate not supplied

Paper chromatography hybridization: a rapid method for detection of Onchocerca volvulus DNA amplified by PCR.

Prior studies have shown that Onchocerca volvulus DNA can be detected in skin snips and in black flies after polymerase chain reaction (PCR) with primers specific for repeated "O-150" DNA sequences. We have adapted a paper chromatography hybridization assay (PCHA) to detect amplified O-150 DNA and compared this method to two established methods, namely agarose gel electrophoresis (AGE) and hybridization enzyme-linked immunosorbent assay (ELISA). The minimum amounts of purified O-150 DNA detected by PCHA, AGE, and ELISA were 5, 10, and 2 ng, respectively. The three methods had similar estimated sensitivities for detecting O. volvulus DNA amplified from skin snips from African subjects with onchocerciasis (88%, 84%, and 91%, respectively). No false positive results were observed with skin snips from uninfected control subjects. The paper chromatography hybridization assay detects PCR products in 30 minutes without electricity or special equipment. This technology brings DNA detection a step closer to widespread use in field settings.

Animals↗
PubMedDate not supplied

Simplified method for determination of total dietary fiber in foods.

A simplified method, based on the same principles as the AOAC enzymatic-gravimetric method for determining total dietary fiber (TDF) (43.A14-43.A20), has been tested on 12 food samples which had been used in other collaborative studies. TDF values obtained in our laboratory for these 2 methods were in good agreement (y = 0.96x + 0.39; r = 0.999). The simplified method uses a single incubation period and only 1 enzyme (amyloglucosidase), and thus yields smaller blank and ash corrections but a higher protein correction.

Dietary Fiber↗
PubMedDate not supplied

Determination of total dietary fiber in foods and products with little or no starch, nonenzymatic-gravimetric method: collaborative study.

A collaborative study was conducted to validate a nonenzymatic-gravimetric method for the determination of total dietary fiber (TDF) of samples containing little or no starch such as most fruits, and vegetables and many purified polysaccharides. This simple procedure involves suspension of freeze-dried, ground samples in deionized water and incubation at 37 degrees C for 90 min, followed by precipitation with 4 volumes of 95% ethanol. The weight of the dilute alcohol-insoluble residues after correcting for crude protein and ash corresponds to the TDF content of the sample. Six samples in blind duplicate (apples, apricots, cabbage, carrots, onions, and soy fiber) were sent with Celite to 10 laboratories. The reproducibility relative standard deviation (RSDR) of the TDF values for 9 laboratories ranged from 2.92 to 6.25%. The repeatability standard deviation (RSDr) for the 9 laboratories ranged from 1.50 to 2.70%. The method has been adopted first action by AOAC INTERNATIONAL.

Chemistry Techniques, Analytical↗
PubMedDate not supplied

Determination of sugars, starches, and total dietary fiber in selected high-consumption foods.

A general scheme has been developed to determine sugars, starches, and total dietary fiber (TDF) in half-gram freeze-dried subsamples of various foods (or wet samples containing about 0.5 g dry matter). Duplicate subsamples are extracted for free sugars with 80% methanol, dried, derivatized to their trimethylsilylated oximes or ethers, and quantitated by gas-liquid chromatography (GLC). Residues after 80% methanol extraction are incubated with a solution containing amyloglucosidase in acetate buffer. Hydrolyzates are centrifuged, and duplicate aliquots are removed for glucose determination by GLC. Starch content is calculated as glucose (g/100 g) x 0.9. Remaining hydrolyzates are diluted with 4 volumes of 95% ethanol, left at room temperature for 1 h, and then filtered through glass crucibles matted with Celite filter aid. The weight of dry residues are corrected for residual crude protein and ash, and the resulting values are taken to be the TDF content of a sample. A variety of high-consumption foods selected by the Nutrient Data Laboratory of the Agricultural Research Service were analyzed for carbohydrate fractions by this method. Values for total sugar and dietary fiber were compared with those obtained by a commercial laboratory using different methods.

Carbohydrates↗
PubMedDate not supplied

Determination of total dietary fiber in foods and food products by using a single-enzyme, enzymatic-gravimetric method: interlaboratory study.

A simplified enzymatic-gravimetric method for total dietary fiber (TDF) determination has been published and used in the Food Composition Laboratory of the U.S. Department of Agriculture since 1988. THis method gives comparable results to AOAC Official Methods 985.29 and 991.43 but the AOAC methods use 100 degrees C (water bath) to gelatinize the sample and a combination of alpha-amylase and an amyloglucosidase to hydrolyze starches, whereas the simplified method incorporates an autoclaving step (121 degrees C) for gelatinization followed by incubation with only amyloglucosidase. The simplified method omits protease hydrolysis and does not require any pH adjustment. Overall, the simplified method cuts cost and is less labor intensive. An interlaboratory study was conducted to validate this method. Blind duplicates of six sample (baked beans, corn bran, roasted peanuts, cooked potatoes, white bread with reduced calories, and cooked white rice) were sent to 11 laboratories. The reproducibility relative standard deviations of the TDF values (without outliers) ranged from 3.46 to 27.6%. The repeatability standard deviations ranged from 0.91 to 14.6%.

Dietary Fiber↗
PubMedDate not supplied

Effect of lipid extraction methods on total dietary fiber and nonstarch polysaccharide contents of selected nuts and seeds.

Three extraction methods were used to remove lipid materials from 8 edible nuts and seeds before analysis for their total dietary fiber (TDF) and nonstarch polysaccharide (NSP) contents. Portions of ground materials were extracted by: n-hexane, followed by 80% methanol, n-hexane-acetic acid (95 + 5, v/v), and supercritical carbon dioxide. Defatted samples were gelatinized in water and incubated with amyloglucosidase; 95% ethanol was added to the hydrolyzates, and the residues were collected on tared glass crucibles. TDF was calculated according to a simplified enzymatic-gravimetric method developed in our laboratory, and NSP was determined as described by Englyst and coworkers. Dietary fiber values obtained with any of the extraction methods range from 3.47 g/100 g for cashews to 28.56 g/100 g for sunflower seeds. Nonstarch polysaccharide values range from 2.43 g/100 g for pecans to 5.56 g/100 g for peanuts. With the exception of sunflower seeds, samples extracted with supercritical carbon dioxide had lower TDF contents but similar amounts of NSP compared with samples extracted by the other 2 methods.

Acetic Acid↗
PubMedDate not supplied

Comparison of microwave oven and convection oven for acid hydrolysis of dietary fiber polysaccharides.

Hydrolysis of dietary fiber polysaccharides (DFP) is an integral part of any enzymatic-chemical method for dietary fiber analysis. Residues obtained after enzyme treatments of fiber-containing foods are usually suspended in 12 M sulfuric acid and kept at or slightly above ambient temperature for at least 1 h, and then the mixtures are diluted with deionized water to a final concentration of 1 M or 2 M acid, followed by heating at 100 degrees C in a water bath or convection oven for 1 or 2 h. Under these hydrolytic conditions, some degradation of the released monosaccharides generally takes place over the duration of hydrolysis. We investigated the feasibility of using microwave energy as a heat source to reduce time and minimize degradation. Preliminary tests were done on the well-characterized soy polysaccharide Fibrim. With a microwave digestion system equipped with temperature and pressure monitors and control lines, optimum settings of power (5%, 75%), time (up to 3 min and 30 s), temperature (35 degrees-55 degrees C), and pressure (45-65 psi) were determined for different foods depending on the residue weight and volume of acid. Results were comparable for microwave oven and convection oven hydrolysis of DFP from 5 foods with good correlations for neutral sugar values; r2 = 0.997 for arabinose, 0.925 for galactose, 0.981 for glucose, 0.969 for mannose, and 0.990 for xylose.

Arabinose↗