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N H Low

Publications and source records attributed to N H Low.

11 recordsLinked to original sources
PubMed2002

Purification and characterization of beta-glucosidase from honey bees (Apis mellifera).

beta-glucosidase has been purified from the ventriculus and honey sac of Apis mellifera using a combination of anion- and cation-exchange, hydroxyapatite and gel-permeation chromatography. In addition, beta-glucosidase from the hypopharyngeal glands has been partially purified using anion-exchange and gel-permeation chromatography. The purified beta-glucosidase gave a positive result by glycoprotein staining. This beta-glucosidase consists of only one subunit and has M(r) of 72 kDa as determined by SDS-PAGE. IEF-PAGE showed several bands with pIs ranging from 4.5 to 4.8. These multiform proteins have been proposed as having different degrees of glycosylation. The pH optimum of the purified beta-glucosidase from the ventriculus and honey sac are 5.0. These enzymes were stable at temperatures up to 50 degrees C and have a relatively wide pH stability range of 4.0 to 9.0. MALDI-TOF-MS peptide mass maps of purified beta-glucosidase from the ventriculus, honey sac and hypopharyngeal glands showed six matching masses. These results indicate that the beta-glucosidase isolated from the hypopharyngeal glands, honey sac and ventriculus is the same. It is proposed that beta-glucosidase is produced in the hypopharyngeal glands, secreted into the mouth during feeding and then passes to the honey sac. From the honey sac, this enzyme is transferred into honeycomb cells and the ventriculus.

Animals↗
PubMed1999

Analysis of food oligosaccharides using MALDI-MS: quantification of fructooligosaccharides.

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a powerful new technique that will have a great impact on food analysis. This study demonstrates the applicability of MALDI-MS performed directly on an aqueous food extract for qualitative and quantitative analysis of food oligosaccharides. 2', 4',6'-Trihydroxyacetophenone was found to be the best matrix for analysis of oligosaccharides in the foods examined. The relationship between laser strength, resolution, and the response factors of individual oligosaccharides using MALDI-MS was investigated. A MALDI-MS method for quantitative analysis of fructooligosaccharides with standard addition of a pure fructooligosaccharide was developed. High performance anion exchange chromatography with pulsed amperometric detection was compared to MALDI-MS for the analysis of fructooligosaccharides. The fructooligosaccharide analyses were performed on red onions, shallots, and elephant garlic.

Carbohydrate Conformation↗
PubMed1999

Capillary gas chromatographic detection of invert sugar in heated, adulterated, and adulterated and heated apple juice concentrates employing the equilibrium method.

The equilibrium method is introduced for the detection of invert sugar addition to apple juice. The method consists of a pre-equilibration of the sample with dry pyridine at 50 degrees C for 20 min followed by the addition of trimethylsilylimidazole and heating at 75 degrees C for 40 min. The resulting derivatized carbohydrates are then analyzed by capillary gas chromatography. This method was successfully used by independent laboratories to distinguish heated pure, intentionally adulterated (with invert sugar), and intentionally adulterated and then heated apple juice concentrates. The equilibrium method was shown to give significantly lower coefficients of variation for this sample set when compared to the original capillary gas chromatographic method. In addition, these results indicate that it may also be an effective method for the detection of medium invert sugar, depending on the level of the fingerprint oligosaccharides in this sweetener.

Beverages↗
PubMed1998

Nectar-carbohydrate production and composition vary in relation to nectary anatomy and location within individual flowers of several species of Brassicaceae.

Nectar-carbohydrate production and composition were investigated by high-performance liquid chromatography and enzymology in nine species from five tribes of the Brassicaceae. In six species (Arabidopsis thaliana (L.) Heynh., Brassica napus L., B. rapa L., Lobularia maritima (L.) Desv., Raphanus sativus L., Sinapis arvensis L.) that produced nectar from both lateral nectaries (associated with the short stamens) and median nectaries (outside the long stamens), on average 95% of the total nectar carbohydrate was collected from the lateral ones. Nectar from these glands possessed a higher glucose/fructose ratio (usually 1.0-1.2) than that from the median nectaries (0.2-0.9) within the same flower. Comparatively little sucrose was detected in any nectar samples except from Matthiola bicornus (Sibth. et Sm.) DC., which possessed lateral nectaries only and produced a sucrose-dominant exudate. The anatomy of the nectarial tissue in nectar-secreting flowers of six species, Hesperis matronalis L., L. maritima, M. bicornus, R. sativus, S. arvensis, and Sisymbrium loeselii L., was studied by light and scanning-electron microscopy. Phloem alone supplied the nectaries. However, in accordance with their overall nectar-carbohydrate production, the lateral glands received relatively rich quantities of phloem that penetrated far into the glandular tissue, whereas median glands were supplied with phloem that often barely innervated them. All nectarial tissue possessed modified stomata (with the exception of the median glands of S. loeselii, which did not produce nectar); further evidence was gathered to indicate that these structures do not regulate nectar flow by guard-cell movements. The numbers of modified stomata per gland showed no relation to nectar-carbohydrate production. Taken together, the data on nectar biochemistry and nectary anatomy indicate the existence of two distinct nectary types in those Brassicacean species that possess both lateral and median nectaries, regardless of whether nectarial tissue is united around the entire receptacle or not. It is proposed that the term "nectarium" be used to represent collectively the multiple nectaries that can be found in individual flowers.

Brassica↗
PubMed1990

Carbohydrate Storage in the Entomopathogenic Fungus Beauveria bassiana.

The entomopathogenic fungus Beauveria bassiana was grown in 1% (wt/vol) gelatin-liquid media singly supplemented with a monosaccharide (glucose or fructose), a disaccharide (maltose or trehalose), a polyol (glycerol, mannitol, or sorbitol), or the amino sugar N-acetyl-d-glucosamine. The relative contributions of the carbohydrate, protein, and water contents in the fungal biomass were determined. Carbohydrates composed 18 to 42% of the mycelial dry weight, and this value was lowest in unsupplemented medium and highest in medium supplemented with glucose, glycerol, or trehalose. Biomass production was highest in liquid cultures supplemented with trehalose. When liquid cultures were grown in medium supplemented with 0 to 1% (wt/vol) glucose, trehalose, or N-acetyl-d-glucosamine, there was an increase in the biomass production and the contribution of carbohydrate to mycelial dry weight. Regardless of the glucose concentration in the culture, water content of the mycelia remained about 77.5% (wt/wt). Mycelial storage carbohydrates were determined by capillary gas chromatography. In gelatin-liquid medium supplemented with 1% (wt/vol) glucose, B. bassiana stored glycogen (12.0%, wt/dry wt) and the polyols mannitol (2.2%), erythritol (1.6%), glycerol (0.4%), and arabitol (0.1%). Without glucose, B. bassiana stored glycogen (5.4%), mannitol (0.8%), glycerol (0.6%), and erythritol (0.6%) but not arabitol. To our knowledge, this is the first report of carbohydrate storage in an entomopathogenic fungus, and the results are discussed in relation to other fungi and the potential implications to commercial formulation and insect-fungus interactions.

Journal Article↗
PubMedDate not supplied

Identification of hydrolyzed inulin syrup and high-fructose corn syrup in apple juice by capillary gas chromatography: PVM 4:1999.

A peer-verified, gas chromatographic (GC) method is presented for the identification of hydrolyzed inulin syrup (HIS) and high-fructose corn syrup (HFCS) in apple juice. The procedure involves determining the Brix value of the apple juice or apple juice concentrate and preparing a dilution of the test sample to 5.5 degrees Brix. A 100 microL aliquot of the 5.5 degrees Brix test solution is then freeze-dried in a GC autosampler vial. The sugars in the freeze-dried residue are converted to trimethylsilyl derivatives, by the addition of an appropriate silylation reagent, and the vial is heated at 75 degrees C for 30 min. After derivatization, the solution is introduced into a gas chromatograph where the analytes are separated on a 30 m, 0.25 mm id DB-5 column. The method can use hydrogen, helium, or nitrogen as the carrier gas. The analytes and marker compounds are measured by use of a flame ionization detecone of the 2 syrups at 2 levels. Dilution was ascertained by the presence of retrograde sugar markers found in the 2 sugar syrups. All 3 laboratories involved in the study were able to identify the correct diluent in the blind, randomly coded, apple juice test portions. The levels of dilution in the test portions were 0, 6.9% (HIS), 16.0% (HIS), 8.1% (HFCS), and 17.0% (HFCS). No false positive results were reported. Quantitative conclusions can be drawn when the same syrup is used for dilution and as a reference standard.

Beverages↗
PubMedDate not supplied

Detection of orange juice adulteration with beet medium invert sugar using anion-exchange liquid chromatography with pulsed amperometric detection.

Carbohydrate analysis of 5 beet medium invert sugar (BMIS) samples and 10 pure orange juices was carried out using anion-exchange chromatography with a pulsed amperometric detector. This analysis revealed the presence of several oligosaccharides in BMIS that were in either low concentration or nonexistent in the orange juice samples. These oligosaccharides may be naturally present in sugar beets or synthesized during the acid and/or enzyme catalyzed hydrolysis of sucrose during the production of BMIS. BMIS was intentionally added to pure orange juice at levels of 5, 10, 15, and 20%. Subsequent liquid chromatographic (LC) analysis of these intentionally adulterated samples revealed that detection of 5% BMIS in orange juice was possible.

Beverages↗
PubMedDate not supplied

Determination of honey authenticity by anion-exchange liquid chromatography.

Methodology using anion-exchange liquid chromatography with pulsed amperometric detection was developed to determine the addition of invert syrups (beet or cane) and high-fructose corn syrup to honey. The invert syrups used were either chemically (commercially) or enzymatically prepared. Fingerprint oligosaccharides were shown to be present in these sweeteners, which were either not detectable or present at low concentrations in pure honey. Forty-four pure honey samples produced in continental North America, Hawaii, China, and Australia were used in this study.

Chromatography, Ion Exchange↗
PubMedDate not supplied

Normative data for commercial pineapple juice from concentrate.

Normative data for pineapple juice from concentrate were determined for 19 samples, including 5 that had been aseptically processed and representing 4 of the major pineapple growing regions of the world. Values are reported for sugars, organic acids, including isocitric acid, metals (specifically potassium, sodium calcium, and magnesium), delta 13C, and oligosaccharides. Although geographical variation existed, the observed ranges and variances were small enough to be useful in describing authentic pineapple juice. Two concentrates (one aseptically and one nonaseptically processed) were intentionally adulterated (individually) with 3 commercially available inexpensive sweeteners (high fructose corn syrup, cane invert syrup, and beet medium invert syrup). Oligosaccharide analysis of these samples either by liquid chromatography or by capillary gas chromatography yielded oligosaccharide patterns that were useful for the detection of these sweeteners at 10% levels. Principal-component analysis (PCA) was used to represent graphically both the pure and adulterated samples based on their measured chemical parameters.

Beverages↗
PubMedDate not supplied

Determination of fruit juice authenticity by capillary gas chromatography with flame ionization detection.

A method using capillary gas chromatography with flame ionization detection was developed to determine the addition of high-fructose syrup and beet or cane invert syrup to apple or orange juice. Fingerprint oligosaccharides in these inexpensive sweeteners were not detectable (area < 1000) in pure apple or orange juice. One hundred twenty-three pure apple juice and 60 pure orange juice samples representing growing regions around the world were analyzed. Ten samples were intentionally adulterated with each sweetener at levels of 5, 10, and 15%. The detection limit for each sweetener was 5%.

Beverages↗