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Biomedical subjects

T K Singh

Publications and source records attributed to T K Singh.

18 recordsLinked to original sources
PubMed2004

Characterization of nutty flavor in cheddar cheese.

The objectives of this study were to determine the volatile components responsible for the sensory perception of nutty flavor in Cheddar cheese. Cheddar cheeses with and without nutty flavors were selected by descriptive sensory analysis. Volatile aroma components from Cheddar cheeses with and without nutty flavors were isolated and characterized using solvent extraction with high vacuum distillation, dynamic headspace analysis, gas chromatography-olfactometry, and gas chromatography-mass spectrometry. More than 50 aroma-active compounds were detected in Cheddar cheeses. Consistent differences were observed between nutty and not nutty Cheddar cheeses. Strecker aldehydes were detected in higher amounts in Cheddar cheeses with nutty flavors compared with Cheddar cheeses without nutty flavors. Strecker aldehydes, dimethyl sulfide, and propionic acid were evaluated in young and aged Cheddar cheese models for nutty flavor by descriptive sensory analysis. Dimethyl sulfide and propionic acid did not contribute to nutty flavor in Cheddar cheese. The addition of Strecker aldehydes to young (<4 mo old) Cheddar cheese models resulted in nutty/malty flavor perceived by sensory analysis. When Strecker aldehydes were incorporated into aged (>9 mo old) Cheddar cheese models, nutty flavor perception increased. Strecker aldehydes contribute to nutty flavor in aged Cheddar cheese.

Aldehydes↗
PubMed2000

Modification of cysteine residues by N-ethylmaleimide inhibits annexin II tetramer mediated liposome aggregation.

A role of cysteine residues in annexin II tetramer (AIIt)'s function was investigated using the sulfhydryl reagent N-ethylmaleimide (NEM). Incubation of AIIt with NEM resulted in a dose-dependent inhibition of AIIt-mediated liposome aggregation and loss of sulfhydryl groups of AIIt. The concentration effecting 50% inhibition was 0.18 mM. The inhibition was observed in all Ca2+ concentrations tested (1-1000 microM). NEM had no effects on liposome aggregation mediated by other annexins (I, III, and IV), indicating that the inhibitory effect caused by NEM modification is specific to AIIt. The NEM-treated AIIt still can bind to liposomes. However, once AIIt was bound to membrane, the cysteine residues were protected from NEM modification. Our results suggest that cysteine residues are critical for AIIt-mediated liposome aggregation.

Animals↗
PubMed1997

Isolation and identification of further peptides in the diafiltration retentate of the water-soluble fraction of Cheddar cheese.

Several peptides were isolated from the diafiltration retentate, prepared using 10 kDa membranes, of the water-soluble extract from a commercial mature Cheddar cheese and identified by amino acid sequencing and mass spectrometry. Most of the peptides were from the N-terminal half of the beta-casein, but peptides from alpha s1- and alpha s2-caseins were also identified; the extract also contained alpha-lactalbumin. Identified peptides showed the important role played by lactococcal cell envelope proteinases in the degradation of primary proteolytic products from alpha s1- and beta-caseins, produced by chymosin and plasmin respectively. Plasmin seemed to be involved in the hydrolysation of alpha s2-casein. Several phosphopeptides were identified and the action of phosphatase on these peptides was evident.

Amino Acid Sequence↗
PubMed1996

Direct agglutination test for early diagnosis of Indian visceral leishmaniasis.

In a prospective study, 80 cases of fever with hepatosplenomegaly, anemia and leucopaenia coming from the hyperendemic zones for visceral leishmaniasis of North-Bihar, India were screened and subjected to bone marrow or splenic puncture for demonstration of Leishman-donovan bodies (LDB) and DIRECT AGGLUTINATION TEST (DAT) with antigen prepared by Harith et al. 59 cases were confirmed for Visceral Leishmaniasis (VL) by demonstration of LDB in which DAT was also positive in different titres ranging from 1:1600 onwards. Out of 21 cases in which the bone marrow was negative for parasite, DAT was positive in 10 cases. 8 Out of 10 cases responded to WHO regimen of treatment with sodium stibogluconate (SSG). Remaining two cases who did not respond to this therapy became positive for parasites on subsequent splenic aspirate. They were treated with pentamidine isethionate and were cured. 11 out of 80 cases showing a titre of 1:400 or lower in DAT, 6 proved to be cases of enteric fever and 5 of malaria. Thus DAT using Harith's antigen was found to be 100% sensitive and specific in detection of early cases of Indian VL.

Adult↗
PubMed1995

Water-soluble peptides in Cheddar cheese: isolation and identification of peptides in the diafiltration retentate of the water-soluble fraction.

The water-soluble extract of Cheddar cheese was fractionated by diafiltration using 10 kDa cut-off membranes. Peptides were isolated from the diafiltrate retentate by chromatography on DEAE-cellulose with a linear NaCl gradient in 50 mM-Tris-HCl. pH 8.6, and reversed-phase HPLC or electroblotting from urea-PAGE gels. Peptides were identified by determining N-terminal amino acid sequences and mass spectrometry. Most (45) of the total 51 peptides identified in the diafiltrate retentate originated from beta-casein, especially from a short region in the N-terminal half of the molecule. Only six peptides originated from alpha s1-casein; beta-lactoglobulin was also identified in the retentate. The origin of most of these peptides could be explained on the basis of known specificities of lactococcal cell envelope proteinases.

Amino Acid Sequence↗
PubMed1995

Use of amphotericin B in drug-resistant cases of visceral leishmaniasis in north Bihar, India.

Thirty-four multidrug-resistant cases of Indian visceral leishmaniasis (kala-azar) were treated with amphotericin B. A complete hemogram, liver and renal function tests, determination of serum electrolyte levels, a chest radiograph, and an electrocardiogram were done before, during, and after completion of therapy. Assessment for clinical and parasitologic cure was done weekly. Thirty-one patients who completed treatment had full cure after receiving 10-15 injections at six-months follow up. One patient died of myocarditis. A febrile reaction was observed in all cases, while thrombophlebitis was found in six cases (18.75%). Anorexia, nausea, and vomiting were found in seven cases (21.88%). No significant nephrotoxicity or electrolyte disturbances were observed. It is concluded that amphotericin B is an effective second-line drug for Indian visceral leishmaniasis, but unpredictable drug-induced myocarditis remains a problem.

Adolescent↗
PubMed1994

Effect of phospholipase C and apolipophorin III on the structure and stability of lipophorin subspecies.

Four distinct subspecies of the insect hemolymph lipoprotein, lipophorin, that range in diacylglycerol (DAG) content from approximately 100 to 1000 molecules per particle, were treated with phospholipase C. Lipid analysis demonstrated that both phosphatidylcholine and phosphatidylethanolamine were hydrolyzed to DAG. Phospholipase C was used to remove 74-82% of the phospholipid of different lipophorins and these were analyzed for aggregation. Low density lipophorin (LDLp), the largest subspecies, with a diameter of approximately 23 nm, developed turbidity (monitored by sample absorbance at 340 nm) suggesting the formation of lipoprotein aggregates. High density lipophorin-adult (HDLp-A) and high density lipophorin-wanderer 1 (HDLp-W1) also displayed an increase in A340 when incubated with phospholipase C, although the maximal increase observed was considerably less than that for LDLp on a per particle basis. Phospholipase C caused only a minimal increase in A340 in a fourth subspecies, high density lipophorin-wanderer 2 (HDLp-W2), which contains an even lower amount of DAG. Electron microscopy was used to evaluate changes in particle morphology as a result of phospholipid depletion. HDLp-W2 and HDLp-W1 showed signs of progressive aggregation and particle fusion. A similar aggregation/fusion was seen in the case of high density lipophorin adult (HDLp-A) while LDLp samples contained multiple aggregation/fusion foci and resultant very large particles. In the presence of exogenous apolipophorin III (apoLp-III), phospholipase C-induced lipophorin aggregation/fusion was prevented. Electron microscopy of LDLp and HDLp-A samples revealed that apoLp-III-stabilized, phospholipase C-treated particles had a morphology similar to that of control particles.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Conversion of human low density lipoprotein into a very low density lipoprotein-like particle in vitro.

The lipid substrate specificity of Manduca sexta lipid transfer particle (LTP) was examined in in vitro lipid transfer assays employing high density lipophorin and human low density lipoprotein (LDL) as donor/acceptor substrates. Unesterified cholesterol was found to exchange spontaneously between these substrate lipoproteins, and the extent of transfer/exchange was not affected by LTP. By contrast, transfer of labeled phosphatidylcholine and cholesteryl ester was dependent on LTP in a concentration-dependent manner. Facilitated phosphatidylcholine transfer occurred at a faster rate than facilitated cholesteryl ester transfer; this observation suggests that either LTP may have an inherent preference for polar lipids or the accessibility of specific lipids in the donor substrate particle influences their rate of transfer. The capacity of LDL to accept exogenous lipid from lipophorin was investigated by increasing the high density lipophorin:LDL ratio in transfer assays. At a 3:1 (protein) ratio in the presence of LTP, LDL became turbid (and aggregated LDL were observed by electron microscopy) indicating LDL has a finite capacity to accept exogenous lipid while maintaining an overall stable structure. When either isolated human non B very low density lipoprotein (VLDL) apoproteins or insect apolipophorin III (apoLp-III) were included in transfer experiments, the sample did not become turbid although lipid transfer proceeded to the same extent as in the absence of added apolipoprotein. The reduction in sample turbidity caused by exogenous apolipoprotein occurred in a concentration-dependent manner, suggesting that these proteins associate with the surface of LDL and stabilize the increment of lipid/water interface created by LTP-mediated net lipid transfer. The association of apolipoprotein with the surface of modified LDL was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, and scanning densitometry revealed that apoLp-III bound to the surface of LDL in a 1:14 apoB:apoLp-III molar ratio. Electron microscopy showed that apoLp-III-stabilized modified LDL particles have a larger diameter (29.2 +/- 2.6 nm) than that of control LDL (22.7 +/- 1.9 nm), consistent with the observed changes in particle density, lipid, and apolipoprotein content. Thus LTP-catalyzed vectorial lipid transfer can be used to introduce significant modifications into isolated LDL particles and provides a novel mechanism whereby VLDL-LDL interrelationships can be studied.

Animals↗
PubMed1992

A turbidimetric assay of lipid transfer activity.

A novel method to assay insect plasma lipid transfer particle (LTP) activity has been developed that employs insect high density lipophorin (HDLp) and human low density lipoprotein (LDL) as donor/acceptor substrate particles. At a 3:1 or greater HDLp:LDL protein ratio, LTP-mediated net vectorial transfer of diacylglycerol from lipophorin to LDL produces destabilized LDL particles that aggregate, causing sample turbidity. Turbidity was measured spectrophotometrically as a function of absorbance at 340 nm. After an initial lag phase, lipoprotein sample turbidity increased as a function of reaction time and LTP concentration. Saturation was observed at longer times or higher LTP concentrations, indicating that a reaction end point had been reached. As the substrate HDLp concentration was increased relative to LDL, a saturable increase in LTP-induced lipoprotein sample turbidity was observed. When the LDL concentration was increased relative to HDLp, however, there was an initial production of turbidity but at higher concentrations the sample did not develop turbidity. Reaction progress was also dependent on temperature over the range 0-37 degrees C. Taken together the results are consistent with the concept that LTP-mediated diacylglycerol transfer from HDLp to LDL creates unstable product LDL particles that aggregate. The assay method is advantageous because it employs relatively abundant, natural lipoprotein substrates, does not require prelabeling of donor lipid particles with radioactive or fluorescent lipids, and does not require separation of donor and acceptor after incubation. This is the first description of a lipid transfer assay that can be measured spectrophotometrically.

Animals↗
PubMed1992

An assessment of serum lipid and lipoprotein levels in patients with ischaemic heart disease.

A total of 166 patients who had one or more attacks of myocardial infarction and those with angina pectoris, forty-five relative of 18 hyperlipidemic survivors of ischaemic heart disease, and 330 healthy persons (controls) were investigated for serum lipid profiles. Fifty-six of the 166 patients were hyperlipidemic. The commonest abnormalities in lipoproteins were Types IIa, IIb and IV. 75.5% of the 45 relatives investigated were hyperlipidemic. The familial studies showed that hyperlipidemias occurred in the family members of persons with ischaemic heart disease suggesting that hyperlipidemia could play an important role in predisposing familial clustering of coronary heart disease. A family history of heart disease may be a useful marker for identifying persons who are more likely to have high levels of blood lipids for possible treatment.

Adult↗
PubMed1992

Serum ceruloplasmin in acute myocardial infarction.

Serum ceruloplasmin levels were estimated in 81 patients within one week after an attack of acute myocardial infarction. A total of 126 healthy subjects were taken as controls and investigated for this copper containing protein. Results showed that there is an elevation in the levels of serum ceruloplasmin in patients as compared to the controls. Ceruloplasmin levels showed a return to almost normal values in 54 follow-up cases of acute myocardial infarction during the fourth week after infarction.

Adult↗
PubMed1991

Lipid transfer particle-catalyzed transfer of lipoprotein-associated diacylglycerol and long chain aliphatic hydrocarbons.

Following injection of [1-14C]acetate into the sphinx moth, Manduca sexta, radiolabel was incorporated into lipid components of the major hemolymph lipoprotein, adult high density lipophorin (HDLp-A). Analysis of the labeled lipids by thin layer chromatography and radiochromatogram scanning revealed incorporation of radioactivity into the diacylglycerol (DAG) and hydrocarbon components as well as a third lipid fraction of unknown identity. Lipid transfer experiments were carried out using 14C-lipid HDLp-A and human low density lipoprotein (LDL) as donor/acceptor substrates and M. sexta lipid transfer particle (LTP) as catalyst. In control incubations lacking LTP, nearly all of the radiolabeled lipid remained associated with HDLp-A. LTP, however, induced a time-dependent vectorial transfer of radiolabeled lipid from HDLp-A to LDL. Lipid analysis of the LDL fraction, reisolated following the transfer reaction, revealed that labeled lipid components originally associated with HDLp-A were present in the acceptor LDL particles. The recovery of radiolabeled hydrocarbon associated with LDL demonstrates the capacity of LTP to facilitate transfer of these long chain, extremely hydrophobic, lipids and suggests LTP may function as a mediator of hydrocarbon transport and metabolism in vivo. When acceptor LDL particles were analyzed prior to complete transfer of HDLp-A-associated lipid it was observed that DAG was transferred preferentially during the initial stages of the reaction after which hydrocarbon transfer increased. This result suggests that LTP may have a lipid substrate preference for DAG versus hydrocarbon. Alternatively the observed preference for DAG may be a function of the relative accessibility of the substrates within the donor lipoprotein. In other experiments it was demonstrated that, unlike other lipids associated with HDLp-A, free fatty acid spontaneously transfers to LDL in the absence of lipid transfer catalyst.

Acetates↗