Biomedical subjects

Y Ma

Publications and source records attributed to Y Ma.

At least 55 records · Page 3Linked to original sources

PubMed2005

Gland ducts and multilayered epithelium in mucosal biopsies from gastroesophageal-junction region are useful in characterizing esophageal location.

SUMMARY. There is controversy as to whether oxynto-cardiac mucosa (OCM), cardiac mucosa (CM) and intestinal metaplasia (IM) found in the gastroesophageal-junction region line the anatomic stomach, esophagus or both. A total of 785 retroflex biopsies taken at the endoscopic gastroesophageal junction in 244 patients were evaluated for the presence of gland ducts and multilayered epithelium which are two recognized markers of esophageal mucosa. Oxyntic mucosa was found in 287 biopsies, OCM in 283, CM in 158, IM in 30 and squamous epithelium in 53 (some biopsies had more than one epithelial type). Esophageal gland ducts and multilayered epithelium were absent in all biopsies with oxyntic mucosa. Sixty-four (13.6%) of 471 biopsies with OCM, CM and IM contained esophageal gland ducts, and 68 of 471 (14.4%) contained multilayered epithelium. Ninety-eight of 471 (20.8%) biopsies contained either gland ducts or multilayered epithelium. This study shows that 20.8% of biopsies at the gastroesophageal junction with OCM, CM and IM can be definitively characterized as lining the anatomic esophagus by the finding of gland ducts and multilayered epithelium. The absence of these markers in oxyntic mucosa confirms this epithelium as gastric. The presence of gland ducts and multilayered epithelium can be used by pathologists to objectively ascribe an esophageal or gastric location to a biopsy from the gastroesophageal junction.

Biopsy↗

PubMed2005

Fuzzy control of nitrogen removal in predenitrification process using ORP.

In order to meet increasingly stringent discharge standards, new applications and control strategies for the sustainable removal of nitrogen from wastewater have to be implemented. In the past years, numerous studies have been carried out dealing with the application of fuzzy logic to improve the control of the activated sludge process. In this paper, fuzzy control strategies of predenitrification systems are presented that could lead to better effluent quality and, in parallel, to a reduction of chemicals consumption. Extensive experimental investigations on lab scale plant studies have shown that there was excellent correlation between nitrate concentration and ORP value at the end of the anoxic zone. Results indicated that ORP could be used as an on-line fuzzy control parameter of nitrate recirculation and external carbon addition. The optimal value of ORP to control nitrate recirculation and external carbon addition was - 86 +/- 2 mV and - 90 +/- 2 mV, respectively. The results obtained with real wastewater also showed the good performance and stability of the fuzzy controllers independently from external disturbances. The integrated control structure of nitrate recirculation and external carbon addition in the predenitrification system is also presented.

Bioreactors↗

PubMed2004

Severe allergy to sharon fruit caused by birch pollen.

BACKGROUND: Allergy to sharon fruit (persimmon) has been only rarely reported. Cross-reactivity with pollen (profilin and Bet v 6) appeared to be involved, but Bet v 1 has not been implicated previously. OBJECTIVE: It is our aim to identify whether Bet v 1 sensitization is linked to sharon fruit allergy. METHODS: Two patients with a reaction upon first exposure to sharon fruit were included in the study, as well as 7 patients with birch-pollen-related apple allergy. Sensitivity was assessed by skin prick testing (SPT), a radio-allergosorbent test (RAST) and immunoblotting. RAST analysis was performed for Bet v 1, Bet v 2 and Bet v 6. Cross-reactivity was evaluated by RAST and immunoblot inhibitions. Biological activity of IgE was measured by basophil histamine release. Sharon fruit allergy was evaluated by double-blind placebo-controlled food challenge (DBPCFC) or open challenge (OC). RESULTS: Both sharon-fruit-allergic patients demonstrated positive reactions in the RAST (8.6 and 6.2 IU/ml, respectively) and SPT (wheal area 37 and 36 mm2). Sharon fruit allergy was confirmed by DBPCFC in 1 patient. The second patient refused a challenge because of the severe initial reaction. Sera from both patients were reactive to Bet v 1 and Bet v 6, which was cross-reactive with sharon fruit by inhibition assays. The patient with the severest reactions was reactive to profilin on immunoblotting. However, profilin did not induce significant histamine release, nor did Bet v 6. Bet v 1 induce approximately 60% histamine release. An OC with sharon fruit in 7 patients allergic to birch pollen and apple, who had not eaten sharon fruit previously, was positive in 6/7 cases. CONCLUSIONS: Birch-pollen-related allergy to sharon fruit is mediated by the known cross-reactive pollen allergens including Bet v 1 and may become more of a problem should sharon fruit consumption increase.

Adult↗

PubMed2004

Phosphorylcholine-polycation diblock copolymers as synthetic vectors for gene delivery.

A novel 2-(dimethylamino)ethyl methacrylate-block-2-(methacryloyloxyethyl phosphorylcholine) (DMAEMA-MPC) diblock copolymer was synthesized and investigated as a new non-viral vector for gene delivery. The attractive perspective of this phosphorylcholine (PC)-based material is its propensity to condense DNA efficiently via the cationic DMAEMA block, as previously demonstrated for the respective homopolymer, with the MPC block acting as a biocompatible steric stabilizer. Two series of DMAEMA-MPC diblock copolymers were synthesized for evaluation, varying independently and systematically either MPC or DMAEMA block length. Markedly different DNA-copolymer complexes were observed depending on the copolymer molecular composition. Certain polymeric structures led to formation of highly condensed, sterically stabilized DNA complexes of 120-140 nm diameter, while some resulted in partly condensed DNA-polymer complexes with 'spaghetti' structures, indicating the importance of a copolymer composition to balance condensing and steric stabilization effect. A low level of non-specific cellular association of the complexes with optimized physicochemical properties was seen, indicating the role of MPC surface layer in the interactions with biological membranes and important property in preventing promiscuous interactions with tissues in the body and potentially allowing for cellular specific delivery of the condensates following the attachment of a targeting ligand.

Buffers↗

PubMed2004

Phase III trial of gemcitabine plus tipifarnib compared with gemcitabine plus placebo in advanced pancreatic cancer.

PURPOSE: To determine whether addition of the farnesyltransferase inhibitor tipifarnib (Zarnestra, R115777; Johnson and Johnson Pharmaceutical Research and Development, Beerse, Belgium) to standard gemcitabine therapy improves overall survival in advanced pancreatic cancer. PATIENTS AND METHODS: This randomized, double-blind, placebo-controlled study compared gemcitabine + tipifarnib versus gemcitabine + placebo in patients with advanced pancreatic adenocarcinoma previously untreated with systemic therapy. Tipifarnib was given at 200 mg bid orally continuously; gemcitabine was given at 1,000 mg/m(2) intravenously weekly x 7 for 8 weeks, then weekly x 3 every 4 weeks. The primary end point was overall survival; secondary end points included 6-month and 1-year survival rates, progression-free survival, response rate, safety, and quality of life. RESULTS: Six hundred eighty-eight patients were enrolled. Baseline characteristics were well balanced between the two treatment arms. No statistically significant differences in survival parameters were observed. The median overall survival for the experimental arm was 193 v 182 days for the control arm (P =.75); 6-month and 1-year survival rates were 53% and 27% v 49% and 24% for the control arm, respectively; median progression-free survival was 112 v 109 days for the control arm. Ten drug-related deaths were reported for the experimental arm and seven for the control arm. Neutropenia and thrombocytopenia grade > or = 3 were observed in 40% and 15% in the experimental arm versus 30% and 12% in the control arm. Incidences of nonhematologic adverse events were similar in two groups. CONCLUSION: The combination of gemcitabine and tipifarnib has an acceptable toxicity profile but does not prolong overall survival in advanced pancreatic cancer compared with single-agent gemcitabine.

Adult↗

PubMed2004

Method for isolating tight-binding inhibitors of rat lens aldose reductase.

Numerous animal studies indicate that aldose reductase inhibitors (ARIs) are beneficial for the prevention or amelioration of diabetic complications such as neuropathy, nephropathy and the ocular complications of cataract, retinopathy and keratopathy. To aid in the identification of novel potent ARIs, we have previously developed a screening method that is based on the formation of a non-covalent ternary tight-binding enzyme-inhibitor-nucleotide (AR-ARI-NADPH) complex that can be isolated using YM-10 filter units. Here, we report a modification of this method that permits us to rapidly identify tight binding ARIs that are isolated by denaturation from AR-ARI-NADPH complexes that are free of possible contamination resulting from the reaction of methanol with the YM-10 filter units. For the development of this procedure, nine structurally diverse ARIs were mixed with purified recombinant rat lens aldose reductase (RLAR) bound with NADPH to form tight-binding RLAR-ARI-NADPH complexes. These complexes were purified by high pressure Sephadex 75 size exclusion chromatography using ammonium acetate buffer and the formation of each complex was confirmed by electrospray ionisation mass spectrometry (ESI-MS). Each of the complexes was then denatured with methanol, rechromatographed on the size exclusion column, and the identity of the bound ARIs was confirmed by ESI-MS. The apparent ARI binding with aldose reductase to form a tight binding ARI complex appeared proportional to their IC50 values. This procedure allows for the rapid identification of tight binding ARIs with apparent IC50s<0.1 microm.

Aldehyde Reductase↗

PubMed2004

N-phosphoryl amino acids and biomolecular origins.

The possible role of phosphoryl amino acids for biomolecular origins is briefly reviewed. Peptide formation, ester formation, ester exchange on phosphorus and N to O migration occurred when the N-phosphoryl amino acid was incubated at room temperature. Short nucleotides and peptides were formed when nucleoside was reacted with N-phosphoryl amino acid at room temperature. Serine and threonine residues in their conjugate with different nucleosides (mediated with phosphorus) showed different self-cleavage activities. N-phosphoryl Histine and Ser-His dipeptide could cleave nucleic acids, proteins and esters in neutral medium. Based on a simple model, a pathway of 'co-evolution of protein and nucleic acid' was proposed.

Amino Acids↗

PubMed2004

Extensive homology between the major immunodominant mitochondrial antigen in primary biliary cirrhosis and Helicobacter pylori does not lead to immunological cross-reactivity.

BACKGROUND: Primary biliary cirrhosis (PBC) is an immune-mediated chronic cholestatic disease characterized by the presence of antibodies directed predominantly against the E2 subunit of the pyruvate dehydrogenase complex (PDC-E2). What provokes tolerance breakdown in PBC remains to be established, though there is evidence to indicate that microbes may induce anti-mitochondrial antibodies (AMA) through a mechanism of molecular mimicry. METHODS: Having found that urease beta (UREB)(22-36) antigen of Helicobacter pylori (HELPY) shares extensive (87%) similarity with PDC-E2(212-226), the major mitochondrial autoepitope, it was hypothesized that this would also lead to cross-reactivity. The UREB/PDC-E2 mimics were thus constructed and tested by ELISA in 112 PBC patients and 114 controls. RESULTS: Reactivity to PDC-E2(212-226) was found in 104 patients but to UREB(22-36) in only 2. In these two patients, the double reactivity was not cross-reactive. The lack of surface antibody accessibility to UREB(22-36), as demonstrated through three-dimensional model prediction analysis, may explain this unexpected finding. There was some speculation on whether HELPY UREB(22-36) might act as a cross-reactive CD4 T-cell epitope. All seven PBC patients, tested in a standard proliferation assay against PDC-E2(212-226), gave a positive response. All seven were unresponsive to HELPY UREB(22-36). The pattern of reactivity to HELPY antigens by immunoblot was similar between anti-PDC-E2-positive and negative PBC cases, as well as between PBC patients and controls. CONCLUSION: Contrary to common belief, extensive sequence homology (molecular mimicry) between self and microbe does not necessarily result in cross-reactivity. It is therefore likely that, when present, cross-reactivity between self and microbes is of biological importance.

Adult↗

PubMed2004

Complete sequence of virulence plasmid pEIB1 from the marine fish pathogen Vibrio anguillarum strain MVM425 and location of its replication region.

AIMS: The aim of this study was to determine the whole DNA sequence of pEIB1, one pJM1-like virulence plasmid from Vibrio anguillarum MVM425 and locate the replication region. METHODS AND RESULTS: DNA sequence of virulence plasmid pEIB1 from V. anguillarum MVM425 was determined using the methods of restriction endonuclease digestion, subcloning, and primer walking. The whole nucleotide sequence of pEIB1 comprises 66,164 bp, encoding 44 open reading frames (>400 bp) containing the genes of DNA replication, biosynthesis and regulation of the siderophore anguibactin and transport of ferric-anguibactin complexes. With no demonstrated replication origin, the Sau3AI partial digested plasmid DNA fragments of pEIB1 were ligated into the BamHI-fragment containing the kanamycin-resistance gene (Kmr). For there is no effective transformation in V. anguillarum, the ligated DNA was first introduced into E. coli JM83, and the transfomants were selected for resistance to kanamycin. It was demonstrated with southern blotting and DNA sequencing that plasmid pEIB7 containing the Sau3AI DNA fragment of pEIB1 (from 12516 to 13957) has the ability to replicate in E. coli JM83 and V. anguillarum MVM425sh. The segregational stability of plasmid pEIB7 kept in 100 and 4% in E. coli JM83 and V. anguillarum MVM425sh respectively when the cells were cultured in 200th generation. In following experiments, we also found that plasmid pEIB7 replicated at a middle-copy number of 10-40 in JM83, while at a high-copy number of 100-300 in MVM425sh. Moreover, pEIB7 can survive in V. alginolyticus, another fish pathogenic. CONCLUSIONS: With the whole DNA sequence of pEIB1 determining, it was found that pEIB1 showed microheterogeneity in its restriction endonuclease patterns with pJM1 though their DNA sequences had slight difference. According to the complete DNA sequence of pEIB1, its replication region was located from 12516 to 13957. And this replication region is compatible to pUC18 (pMB1), pKA3 (pSC101) and p15A: caiE (p15A). SIGNIFICANCE AND IMPACT OF THE STUDY: The worldwide vibriosis marine pathogen V. anguillarum strains contain common virulence, pJM1-like plasmids, independent on the geographical source. The pEIB1 was the second common virulence plasmid, which sequence was determined. Its sequence is highly homologous to pJM1 as they both encode biosynthesis and regulation of the siderophore anguibactin and transport of ferric-anguibactin complexes. Some interesting features as in pJM1 were also identified, such as transposon-like structures. So it can be deferred that the whole DNA sequences of virulent plasmid pEIB1 will be great helpful to future revealing these V. anguillarum virulence-related genes derived during evolution from transposition events or horizontal transfer of genes potentially originating in other organisms. Another result, replication region of pEIB1 locating is the first report about replication of pJM1-like plasmid. This work will be useful for researching pJM1-like plasmid replication mechanism in V. anguillarum.

Animals↗

PubMed2004

Natural community structure of cyanobacteria in the South China Sea as revealed by rpoC1 gene sequence analysis.

AIMS: To examine the community structure of cyanobacterial populations of the South China Sea on the surface and at depth of 80 m. METHODS AND RESULTS: Direct PCR amplification of RNA polymerase (rpoC1) genes from environmental DNAs extracted from seawater, and cloning of the fragments and sequence analysis were used. A great diversity of Prochlorococcus and Synechococcus were detected at the investigation site. Genetically related Prochlorococcus were found in both layers while Synechococcus were found only on the surface. Prochlorococcus were clustered with the known high-light adapted II genotypes, and further divided into seven groups. Synechococcus could be divided into two groups, and the second group could be further subdivided into several clades. CONCLUSION: The dominant genotype of Prochlorococcus was high-light adapted II genotype, and Synechococcus were distributed basically on the surface. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report about the cyanobacterial community structure in the South China Sea, and an important supplement to the current understanding of the relationship between genetic and ecological diversity and environments.

China↗

PubMed2003

PET imaging of 5-HT1A receptor binding in patients with temporal lobe epilepsy.

BACKGROUND: Activation of central serotonin (5-HT)1A receptors, found in high density in brainstem raphe, hippocampus, and temporal neocortex, exerts an anticonvulsant effect in various experimental seizure models. To test the hypothesis that 5-HT1A receptor binding is reduced in human epileptic foci, PET imaging was performed using the radioligand [18F]trans-4-fluoro-N-2-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl]-N-(2-pyridyl)cyclohexanecarboxamide ([18F]FCWAY), a selective 5-HT1A receptor antagonist, in patients with temporal lobe epilepsy and normal controls. METHODS: MRI and PET were performed using [15O]water and [18F]FCWAY in 10 controls and in 12 patients with temporal lobe epilepsy confirmed on ictal video-EEG; patients also underwent [18F]fluorodeoxyglucose PET. Using quantitative PET image analysis, regional values were obtained for [18F]FCWAY volume of distribution (V), cerebral blood flow (CBF), and glucose cerebral metabolic rate (CMRglc). Hippocampal volume (HV) was also measured with MRI. [18F]FCWAY V PET and MR measures were compared within patients and controls using paired t-tests; grouped comparisons were made with two sample t-tests. RESULTS: Lower [18F]FCWAY V was found ipsilateral than contralateral to the epileptic focus in inferior medial (IMT) and lateral (ILT) temporal regions of patients (ILT 47.4 +/- 6.1 vs 61.8 +/- 6.1, p < 0.01; IMT 52 +/- 4.6 vs 67.0 +/- 6.0, p < 0.01). [18F]FCWAY V was 29% lower in raphe and 34% lower in the ipsilateral thalamic region of patients than controls. In ILT, mean [18F]FCWAY V asymmetry index (AI) was significantly greater than mean CBF and mean CMRglc AI. Mean [18F]FCWAY V AI in IMT was greater than mean HV AI, but the difference was not significant. CONCLUSION: These findings support the hypothesis of reduced serotonin receptor binding in temporal lobe epileptic foci.

Adult↗

PubMed2003

Microbial activity during composting of anthracene-contaminated soil.

Microbial activity of an anthracene-spiked soil mixed with kitchen waste during laboratory composting at 56-59 degrees C was studied using an in-vessel technology. The effect of old compost containing acclimated microorganisms on the composting efficiency was also investigated. Microbial succession, microbial enzyme activity, microbial diversity and anthracene removal rate were analyzed during 42 days of composting. The results demonstrated that inoculating with old compost increased the amounts of thermophilic microorganisms, but did not significantly increase anthracene removal. A microbial succession from mesophilic bacteria to thermophilic bacteria and thermophilic actinomycetes was observed during composting. Polyphenol oxidase activity decreased while catalase activity varied irregularly. Microbial diversity increased drastically when temperature elevated from 35 to 56 degrees C, but decreased when temperature maintained at 56-59 degrees C.

Anthracenes↗

PubMed2003

Association between the primary biliary cirrhosis specific anti-sp100 antibodies and recurrent urinary tract infection.

BACKGROUND AND AIMS: Recurrent urinary tract infections (rUTI) have been suggested to be involved in the induction of anti-mitochondrial antibodies (AMA), the serological hallmark of primary biliary cirrhosis (PBC), in view of the presence of AMA in rUTI women without liver disease and conversely of a high prevalence of rUTI in women with PBC. This prompted us to investigate whether PBC-specific anti-nuclear antibodies (ANA) to sp100, gp210 and lamin B receptor (LBR) antigens may also be related to rUTI. METHODS AND SUBJECTS: PBC-specific ANA reactivities were investigated in 20 women with rUTI but without liver disease, some of whom were AMA-seropositive; 40 women with PBC, with or without rUTI; and 104 pathological and 23 healthy controls. RESULTS: Among the women with rUTI but without liver disease, 8 (80%) of 10 AMA-positive women reacted with sp100 compared with none of the 10 AMA-negative women. Among the PBC patients, 14 (74%) of 19 with rUTI and 1 (4.8%) of the 21 without rUTI reacted with sp100. None of the rUTI women without liver disease reacted with gp210 or LBR. None of 127 pathological and healthy controls had PBC-specific ANA reactivity. CONCLUSIONS: Anti-sp100 reactivity strongly correlates with AMA seropositivity in rUTI women, with or without evidence of primary biliary cirrhosis. These findings provide additional support to the notion that E. coli infection is involved in the induction of PBC-specific autoimmunity. Additional factors must be involved in the progression to overt autoimmune disease.

Adult↗

PubMed2003

Mimicry between the hepatitis C virus polyprotein and antigenic targets of nuclear and smooth muscle antibodies in chronic hepatitis C virus infection.

Autoantibodies to smooth muscle (SMA) and nuclear components (ANA) arise in the natural course of chronic infection with hepatitis C virus. In view of the growing evidence for 'molecular mimicry' as a mechanism of autoimmunity we investigated whether cross-reactive immune reactions between host smooth muscle/nuclear components and HCV antigens may contribute to the formation of SMA and ANA in chronic HCV infection. Computer-assisted protein database search methods were used to identify three smooth muscle (smoothelin698-717, myosin1035-1054, vimentin69-88) and three nuclear (matrin722-741, histone H2A11-30, replication protein A133-152) host antigens with the highest local sequence similarity to the HCV polyprotein and 20-mer peptides corresponding to these regions were constructed. Sera from 51 children with chronic HCV infection [median age: 8 (2-16); 27 boys], 26 SMA positive and five ANA positive, were tested for reactivity to the synthesized HCV peptides and their human homologues by enzyme linked immunosorbent assay (ELISA). Sera from patients with HBV infection and chronic liver disease of different aetiologies were used as controls. 'Double reactivity' to HCV peptides and smooth muscle/nuclear homologues was associated strongly with HCV infection (P < 0.001 for both). Humoral cross-reactivity was established as the basis for double recognition by competition ELISA. Double-reactivity to smooth muscle and HCV peptide antigens correlated with SMA positivity by indirect immunofluouresence (P = 0.05). Of 15 patients double-reactive to myosin1035-1054 and its HCV homologue, 13 recognized whole myosin by immunoblot. These results suggest that ANA and SMA in chronic HCV infection may arise, at least in part, as a consequence of cross-reactive immune responses to HCV and host smooth muscle/nuclear antigens.

Adolescent↗

PubMed2003

Effect of temperature of CO2 injection on the pH and freezing point of milks and creams.

The objectives of this study were to measure the impact of CO2 injection temperature (0 degree C and 40 degrees C) on the pH and freezing point (FP) of (a) milks with different fat contents (i.e., 0, 15, 30%) and (b) creams with 15% fat but different fat characteristics. Skim milk and unhomogenized creams containing 15 and 30% fat were prepared from the same batch of whole milk and were carbonated at 0 and 40 degrees C in a continuous flow CO2 injection unit (230 ml/min). At 0 degree C, milk fat was mostly solid; at 40 degrees C, milk fat was liquid. At the same total CO2 concentration with CO2 injection at 0 degree C, milk with a higher fat content had a lower pH and FP, while with CO2 injection at 40 degrees C, milks with 0%, 15%, and 30% fat had the same pH. This indicated that less CO2 was dissolved in the fat portion of the milk when the CO2 was injected at 0 degree C than when it was injected at 40 degrees C. Three creams, 15% unhomogenized cream, 15% butter oil emulsion in skim milk, and 15% vegetable oil emulsion in skim milk were also carbonated and analyzed as described above. Vegetable oil was liquid at both 0 and 40 degrees C. At a CO2 injection temperature of 0 degree C, the 15% vegetable oil emulsion had a slightly higher pH than the 15% butter oil emulsion and the 15% unhomogenized cream, indicating that the liquid vegetable oil dissolved more CO2 than the mostly solid milk fat and butter oil. No difference in the pH or FP of the 15% unhomogenized cream and 15% butter oil emulsion was observed when CO2 was injected at 0 degree C, suggesting that homogenization or physical dispersion of milk fat globules did not influence the amount of CO2 dissolved in milk fat at a CO2 injection temperature of 0 degree C. At a CO2 injection temperature of 40 degrees C and at the same total CO2 concentration, the 15% unhomogenized cream, 15% vegetable oil emulsion, and 15% butter oil emulsion had similar pH. At the same total concentration of CO2 in cream, injection of CO2 at low temperature (i.e., < 4 degrees C) may produce a better antimicrobial effect during refrigerated shelf life due to the higher concentration of CO2 in the skim portion of the cream.

Animals↗

PubMed2003

Serum protein and casein concentration: effect on pH and freezing point of milk with added CO2.

The objective of this study was to determine the effect of protein concentration and protein type [i.e., casein (CN) and serum protein (SP)] on pH (0 degree C) and freezing point (FP) of skim milk upon CO2 injection at 0 degree C. CN-free skim milks with increasing SP content (0, 3, and 6%) and skim milks with the same SP content (0.6%) but increasing CN content (2.4, 4.8, and 7.2%) were prepared using a combination of microfiltration and ultrafiltration processes. CO2 was injected into milks at 0 degree C using a continuous flow carbonation unit (230 ml/min). Increasing SP or CN increased milk buffering capacity and protein-bound mineral content. At the same CO2 concentration at 0 degree C, a milk with a higher SP or a higher CN concentration had more resistance to pH change and a greater extent of FP decrease. The buffering capacity provided by an increase of CN was contributed by both the CN itself and the colloidal salts solublized into the serum phase from CN upon carbonation. Skim milks with the same true protein content (3%), one with 2.4% CN plus 0.6% SP and one with 3% SP, were compared. At the same true protein content (3%), increasing the proportion of CN increased milk buffering capacity and protein-bound mineral content. Milk with a higher proportion of CN had more resistance to pH change and a greater extent of FP decrease at the same carbonation level at 0 degree C. Once CO2 was dissolved in the skim portion of a milk, the extent of pH reduction and FP depression depended on protein concentration and protein type (i.e., CN and SP).

Animals↗

PubMed2003

Sensory threshold of off-flavors caused by proteolysis and lipolysis in milk.

The objective of this study was to determine the sensory threshold of off-flavor caused by lipolysis in 2% fat milk and to establish the relationship between increased proteolytic activity in milk and the detection of bitter off-flavor. Homogenized raw milk was held at room temperature for 100 min to allow the native milk lipase to release free fatty acids from the triglycerides. Low and high lipolysis pasteurized milk containing 2% fat were blended together in varying amounts to create a series of six milks with increasing free fatty acid (FFA) concentration for sensory evaluation. Sensory threshold for lipolysis in 2% fat milk was determined by ascending forced-choice procedure, with a series of triangle tests in four sessions with 25 panelists in each session. The group best estimated threshold was the geometric mean of the individual thresholds within each of four panel sessions. The geometric mean best estimated detection thresholds for off-flavors caused by lipolysis in 2% fat milk carried out by native milk lipases were 0.320, 0.322, 0.351, and 0.316 meq of FFA/kg milk for panels 1 to 4, respectively. One third of the panelists detected an off-flavor at or below 0.250 meq of FFA/kg milk. To establish the relationship between proteolysis and detection of off-flavor in pasteurized skim milk, 2800 ppm of CO2 were added to pasteurized skim milk, and it was stored for 27 d at 6 degrees C. Another portion of the same milk was frozen on d 1 at -40 degrees C for use as a low proteolysis portion of the same milk. Decrease in casein as a percentage of true protein (CN/TP) was used as an index of proteolysis. After 27 d at 6 degrees C the milk had a decrease in CN/TP of 4.76% and a standard plate count of 430 cfu/ml. The novel approach of storing milk at 6 degrees C for 27 d with added CO2 blocked microbial growth but allowed proteolytic degradation by milk enzymes to proceed. Before sensory analysis, CO2 was removed by vacuum from the high proteolysis milk and the low proteolysis milk was given the same heat and vacuum. Two triangle tests were performed to determine whether panelists could detect off-flavors caused by proteolysis in milk. The threshold detection of off-flavor in skim milk produced by the action of native milk proteases was less than a decrease of CN/TP of 4.76%, but this value is probably near the threshold.

Animals↗

PubMed2003

Effect of CO2 addition to raw milk on proteolysis and lipolysis at 4 degrees C.

Fresh raw milks, with low (3.1 x 10(4) cell/ml) and high (1.1 x 10(6) cells/ml) somatic cell count (SCC), were standardized to 3.25% fat, and from each a preserved (with 0.02% potassium dichromate) and an unpreserved portion were prepared. Subsamples of each portion were carbonated to contain 0 (control, pH 6.9) and 1500 (pH 6.2) ppm added CO2, and HCl acidified to pH 6.2 Milk pH was measured at 4 degrees C. For the preserved low- and high-SCC milks, two additional carbonation levels, 500 (pH 6.5) and 1000 (pH 6.3) ppm, were prepared. Milks were stored at 4 degrees C and analyzed on d 0, 7, 14, and 21 for microbial count, proteolysis, and lipolysis. The addition of 1500 ppm CO2, but not HCl, effectively delayed microbial growth at 4 degrees C. In general, in both the low- and high-SCC unpreserved milks, there was more proteolysis and lipolysis in control and HCl acidified milks than in milk with 1500 ppm added CO2. Higher levels of proteolysis and lipolysis in the unpreserved milks without added CO2 were related to higher bacteria counts in those milks. In preserved low- and high-SCC milks, microbial growth was inhibited, and proteolysis and lipolysis were caused by endogenous milk enzymes (e.g., plasmin and lipoprotein lipase). Compared with control, both milk with 1500 ppm added CO2 and milk with HCl acidification had less proteolysis. The effect of carbonation or acidification with HCl on proteolysis in preserved milks was more pronounced in the high SCC milk, probably due to its high endogenous protease activity. Plasmin is an alkaline protease and the reduction in milk pH by added CO2 or HCl explained the reduction in proteolysis. No effect of carbonation or acidification of milk on lipolysis was observed in the preserved low- and high-SCC milks. The CO2 addition to raw milk decreased proteolysis via at least two mechanisms: the reduction of microbial proteases due to a reduced microbial growth and the possible reduction of endogenous protease activity due to a lower milk pH. The effect of CO2 on lipolysis was mostly due to a reduced microbial growth. High-quality raw milk (i.e., low initial bacteria count and low SCC) with 1500 ppm added CO2 can be stored at 4 degrees C for 14 d with minimal proteolysis and lipolysis and with standard plate count < 3 x 10(5) cfu/ml.

Animals↗