Biomedical subjects

D J McMahon

Publications and source records attributed to D J McMahon.

At least 19 recordsLinked to original sources

PubMed2006

Determinants of bone mineral density in Chinese-American women.

SUMMARY: Few data are available regarding bone mineral density (BMD) and its determinants among Chinese Americans. We identified determinants of BMD among 359 Chinese-American women in order to identify risk factors for low BMD in this burgeoning population. BMD in Chinese-American women is influenced by a number of factors, including immigration. INTRODUCTION: Osteoporosis and low BMD are common among Chinese women, including Chinese Americans, who are a growing population at risk for osteoporosis in the US. Few data are available regarding BMD and its determinants among Chinese-American women. METHODS: In this study, we examined predictors of BMD in 359 ambulatory Chinese-American women, ages 20-90, using stepwise multiple regression analysis. Variables in the model included age, weight, height, menarche age, years since menopause, immigration age, years in US, percentage of life in US, number of pregnancies, oral contraceptive use, family history of osteoporosis, family history of hip fracture, daily calcium intake, exercise, time outdoors, alcohol consumption and tobacco use. RESULTS: Among premenopausal women, weight was the strongest predictor of BMD, accounting for 10.5% of the variance at the lumbar spine (LS), 15.2% at the total hip (TH) and 16.6% at the femoral neck (FN). Time outdoors was also a positive predictor of BMD (1.4% at LS, 2.8% at TH and 1.6% at FN), while family history of osteoporosis (1.4% at TH) and age (3.7% at FN) were negative predictors. Among postmenopausal women, greater BMD at the LS and TH was associated with greater weight and earlier immigration age. Weight accounted for 16.4% of the variance at the LS and 19.8% at the TH; immigration age accounted for 3.1% of the variance at the LS and 4.1% at the TH. At the FN, years since menopause and weight were predictors of BMD, accounting for 14.4% and 8.7% of the variance, respectively. While older age at immigration had a negative effect on BMD, years in and proportion of life in the United States were not significant predictors of BMD. CONCLUSIONS: Bone mineral density in Chinese-American women is influenced by a number of biological and lifestyle factors, including immigration. The results of this study provide new insights into risk factors for low bone density as they relate to environmental determinants in the growing population of Chinese-American women.

Adult↗

PubMed2006

Milk and cheese from cows fed calcium salts of palm and fish oil alone or in combination with soybean products.

Twenty cows were used in a randomized block design experiment for 6 wk to determine the influence of feeding partial ruminally inert Ca salts of palm and fish oil (Ca-PFO), alone or in combination with extruded full-fat soybeans or soybean oil, on milk fatty acid (FA) methyl esters composition and consumer acceptability of milk and Cheddar cheese. Cows were fed either a diet containing 44% forage and 56% concentrate (control) or a diet supplemented with 2.7% Ca-PFO (FO), 5% extruded full-fat soybeans + 2.7% Ca-PFO (FOESM), or 0.75% soybean oil + 2.7% Ca-PFO (FOSO). Total dietary FA content in the control, FO, FOESM, and FOSO diets were 4.61, 6.28, 6.77, and 6.62 g/100 g, respectively. There was no difference in nutrient intake, milk yield, or milk composition among treatments. Conjugated linoleic acid (CLA) C(18:2) cis-9, trans-11 isomer, C(18:1) trans-11 (VA), and total n-3 FA in milk from cows on the control, FO, FOESM, and FOSO treatments were 0.56, 1.20, 1.36, and 1.74; 3.29, 4.66, 6.34, and 7.81; 0.62, 0.69, 0.69, and 0.67 g/100 g of FA, respectively. Concentrations of CLA, VA, and total n-3 FA in cheese were similar to milk. A trained sensory panel detected no difference in flavors of milk and cheese, except for acid flavor below a slightly perceptible level in cheese from all treatments. Results suggest that feeding Ca-PFO alone or in combination with extruded full-fat soybeans or soybean oil enhanced the CLA, VA, total unsaturated and n-3 FA in milk and cheese without negatively affecting cow performance and consumer acceptability characteristics of milk and cheese.

Animals↗

PubMed2005

Consumer acceptability of conjugated linoleic acid-enriched milk and cheddar cheese from cows grazing on pasture.

Two experiments were conducted to study the consumer acceptability attributes of conjugated linoleic acid (CLA)-enriched milk and cheese from cows grazing on pasture. In experiment 1, 15 cows were fed either a diet containing 51% alfalfa hay plus corn silage and 49% concentrate [total mixed ration (TMR)], were grazed on pasture, or were grazed on pasture and received 3.2 kg/d of a grain mix. The grain mix contained 75% full-fat extruded soybeans (FFES), 10% corn, 10% beet pulp, and 5% molasses. During the final 3 wk of the 6-wk experiment, milk was evaluated for sensory attributes. In experiment 2, 18 cows were fed similar diets as in experiment 1, except replacing the group of cows grazed on pasture and receiving the grain mix was a group of cows grazed on pasture and receiving 2.5 kg/d per cow of the FFES; Cheddar cheese was manufactured from milk. Average CLA contents (g/100 g of fatty acid methyl esters) were 0.52, 1.63, and 1.69 in milk and 0.47, 1.47, and 1.46 in cheese from cows fed a TMR, grazed on pasture, and grazed on pasture and fed the grain mix, respectively. An open and trained panel evaluated CLA-enriched milk for mouth-feel, color, flavor, and quality and evaluated cheese for color, flavor, texture, and quality. Open and trained panel evaluations of milk and cheese showed no differences among treatments for any of the attributes, except that the trained panel detected a more barny flavor in milk from cows grazing pasture compared with milk from cows fed the TMR only. Results suggest that consumer acceptability attributes of CLA-enriched milk and cheese from cows grazing pasture is similar to those of milk and cheese with low levels of CLA.

Animals↗

PubMed2005

Influence of calcium, pH, and moisture on protein matrix structure and functionality in direct-acidified nonfat Mozzarella cheese.

Influence of calcium, moisture, and pH on structure and functionality of direct-acid, nonfat Mozzarella cheese was studied. Acetic acid and citric acid were used to acidify milk to pH 5.8 and 5.3 with the aim of producing cheeses with 70 and 66% moisture, and 0.6 and 0.3% calcium levels. Cheeses containing 0.3% calcium were softer and more adhesive than cheeses containing 0.6% calcium, and flowed further when heated. Cheeses with the same calcium content (0.6%), the same moisture content, but set at different pH values (pH 5.3 and 5.8), exhibited no significant differences in melting or firmness. Increasing cheese moisture content from 66 to 70% produced a softer cheese but did not increase meltability. Such differences in functionality corresponded with differences in structure and arrangement of proteins in the cheese protein matrix. Microstructure of cheese with 0.6% calcium had an increase in protein folds and serum pockets compared with the 0.3% calcium cheeses that had a more homogeneous structure. Protein matrix in the low-calcium cheese appeared less dense indicating the proteins were more hydrated. In the 0.6% calcium cheeses, the proteins appeared more aggregated and had larger spaces between protein aggregates. Thus, between pH 5.3 and 5.8, calcium controls cheese functionality, and pH has only an indirect affect related to its influence on the calcium in cheese.

Acetic Acid↗

PubMed2003

Effect of salt on structure-function relationships of cheese.

Our objective was to determine the effect of salt on structural and functional properties of cheese. Unsalted Muenster cheese was obtained on 1 d, vacuum packaged, and stored for 10 d at 4 degrees C. The cheese was then cut into blocks that were vacuum packaged. After 4 d of storage at 4 degrees C, cheese blocks were high-pressure injected one, three, or five times, with a 20% (wt/wt) sodium chloride solution. Successive injections were performed 24 h apart. After 40 d of storage at 4 degrees C, cheese blocks were analyzed for chemical, structural, and functional attributes. Injecting sodium chloride increased the salt content of cheese, from 0.1% in the control, uninjected cheese to 2.7% after five injections. At the highest levels, salt injection promoted syneresis, and, after five injections, the moisture content of cheese decreased from 41 to 38%. However, the increased salt content caused a net weight gain. Cheese pH, soluble nitrogen, and total and soluble calcium content were unaffected. Cheese injected five times had a 4% increased area of cheese occupied by protein matrix compared with uninjected cheese. Hardness, adhesiveness, and initial rate of cheese flow increased, and cohesiveness decreased upon salt injection. However, the final extent of cheese flow, or melting was unaffected. We concluded that adding salt to cheese alters protein interactions, such that the protein matrix becomes more hydrated and expands. However, increasing the salt content of cheese did not cause an exchange of calcium with sodium. Therefore, calcium-mediated protein interactions remain a major factor controlling cheese functionality.

Calcium↗

PubMed2003

Effect of calcium and water injection on structure-function relationships of cheese.

Our objectives were to determine the effect of calcium and water injection on cheese structure and to relate changes in structure to changes in functional properties of cheese. Cheese with fat and moisture content similar to that of low-moisture part-skim Mozzarella was made according to a direct-acid, stirred/pressed-curd procedure. The cheese was then cut into blocks that were high-pressure-injected from one to five times, with either water or a 40% calcium chloride solution. Successive injections were performed 24 h apart. After 42 d of refrigerated storage, cheese microstructure and functionality were analyzed. When injected three or more times, water tended to increase cheese weight. The control, uninjected cheese, had the typical structure of a stirred/pressed-curd cheese: protein matrix interspersed with areas that originally contained fat and/or serum. Injecting water increased the area of cheese matrix occupied by protein, but it did not affect textural properties or melting of cheese. In contrast, when calcium was injected, a decrease in cheese weight was observed that was manifested through syneresis. The moisture content and pH of the cheese decreased as well. Calcium injection also decreased the area of cheese matrix occupied by protein. Cheese hardness increased, and cohesiveness and melting of cheese decreased upon calcium injection. We concluded that adding calcium to cheese alters how the proteins interact, which is manifested as changes in cheese microstructure. Such changes in cheese structure provide an understanding of changes in functional attributes of the cheese.

Calcium↗

PubMed2003

Biochemistry, genetics, and applications of exopolysaccharide production in Streptococcus thermophilus: a review.

Many strains of Streptococcus thermophilus synthesize extracellular polysaccharides. These molecules may be produced as capsules that are tightly associated with the cell, or they may be liberated into the medium as a loose slime (i.e., "ropy" polysaccharide). Although the presence of exopolysaccharide does not confer any obvious advantage to growth or survival of S. thermophilus in milk, in situ production by this species or other dairy lactic acid bacteria typically imparts a desirable "ropy" or viscous texture to fermented milk products. Recent work has also shown that exopolysaccharide-producing S. thermophilus can enhance the functional properties of Mozzarella cheese, but they are not phage-proof. As our understanding of the genetics, physiology, and functionality of bacterial exopolysaccharides continues to improve, novel applications for polysaccharides and polysaccharide-producing cultures are likely to emerge inside and outside the dairy industry. This article provides an overview of biochemistry, genetics, and applications of exopolysaccharide production in S. thermophilus.

Animals↗

PubMed2003

Effect of Lactobacillus helveticus and Propionibacterium freudenrichii ssp. shermanii combinations on propensity for split defect in Swiss cheese.

One of the least controlled defects in Swiss cheese is development of splits that appear during refrigerated storage after cheese is removed from the warm room. Such fissures, or cracks, in the body of the cheese can be as short as 1 cm, or long enough to span a 90-kg block. A 2 x 2 x 2 factorial experiment was used to determine the effect of different Lactobacillus helveticus/Propionibacterium freudenreichii ssp. shermanii starter culture combinations on the occurrence of split defect in Swiss cheese. Eights vats of cheese were made in summer and eight in winter. Each 90-kg block of cheese was cut into twenty-four 4-kg blocks and graded based on the presence of splits. Only small variations were found in the composition of cheeses made during the same season. There were no correlations between moisture, pH, fat, protein, calcium, lactose contents, D/L lactate ratio, or protein degradation that could be used to predict splits after 90 d of storage. However, cheese made in the summer had 2% higher moisture content and a greater prevalence of splits. There was a sixfold increase in amount of downgraded cheese between the best and worst culture combinations used during cheese manufacture. After 90-d storage, 14 to 90% of cheese had splits in the summer, and 1 to 6% in the winter. Split formation increased with time from 60 to 120 d of storage and extent of split formation was influenced by both the lactobacilli and propionibacteria cultures used.

Calcium↗

PubMed2003

Effect of pH on the chemical composition and structure-function relationships of cheddar cheese.

The objectives of this study were to determine the effect of pH on chemical, structural, and functional properties of Cheddar cheese, and to relate changes in structure to changes in cheese functionality. Cheddar cheese was obtained from a cheese-production facility and stored at 4 degrees C. Ten days after manufacture, the cheese was cut into blocks that were vacuum-packaged and stored for 4 d at 4 degrees C. Cheese blocks were then high-pressure injected one, three, or five times with a 20% (wt/wt) glucono-delta-lactone solution. Successive injections were performed 24 h apart. Cheese blocks were then analyzed after 40 d of storage at 4 degrees C. Acidulant injection decreased cheese pH from 5.3 in the uninjected cheese to 4.7 after five injections. Decreased pH increased the content of soluble calcium and slightly decreased the total calcium content of cheese. At the highest level, injection of acidulant promoted syneresis. Thus, after five injections, the moisture content of cheese decreased from 34 to 31%, which resulted in decreased cheese weight. Lowered cheese pH, 4.7 compared with 5.3, also resulted in contraction of the protein matrix. Acidulant injection decreased cheese hardness and cohesiveness, and the cheese became more crumbly. The initial rate of cheese flow increased when pH decreased from 5.3 to 5.0, but it decreased when cheese pH was further lowered to 4.7. The final extent of cheese flow also decreased at pH 4.7. In conclusion, lowering the pH of Cheddar cheese alters protein interactions, which then affects cheese functionality. At pH greater than 5.0, calcium solubilization decreases protein-to-protein interactions. In contrast, at pH lower than 5.0, the acid precipitation of proteins overcomes the opposing effect caused by increased calcium solubilization and decreased calcium content of cheese, and protein-to-protein interactions increase.

Calcium↗

PubMed2003

Effect of sodium citrate on structure-function relationships of Cheddar cheese.

The objective of this study was to determine the effect of sodium citrate on the structure and functionality of Cheddar cheese. The hypothesis was that citrate (sodium citrate) injection would affect cheese properties mainly through its effect on bound calcium (calculated as the difference between total calcium and the water-soluble calcium content of a cheese extract). A 9-kg block of Cheddar cheese was made, vacuum-packaged, and then stored for 2 wk at 4 degrees C. After storage, the cheese was cut into 0.5- to 0.6-kg blocks that were vacuum-packaged and stored for 1 wk at 4 degrees C prior to injection. Cheese blocks were then high-pressure injected with a buffer solution (pH 5.27) containing 40% (wt/ wt) citric acid trisodium dihydrate and 6.25% (wt/wt) anhydrous citric acid, from zero (control) to five times (successive injections performed 24 h apart). Increased citric acid content of cheese from 0.22 (uninjected) to 1.39% (after five injections) caused phosphate solubilization. Thus, the calculated bound phosphate content of cheese decreased from 0.54 to 0.45 mmol/g of protein. However, unexpectedly, the soluble calcium content decreased from 0.34 (control) to 0.28 mmol/g of protein (after five injections), whereas the bound calcium content remained unchanged (0.42 mmol/g of protein). The decrease in soluble calcium probably resulted from the formation and concentration of crystals in the cheese surface, which was not included in samples for analysis, and from the expulsion of serum from within the cheese. Higher concentration of solutes in the water phase of cheese would increase the volume of serum, but the cheese had limited holding capacity and serum was expelled. Citrate injection increased the sodium content of cheese from 0.63 to 0.93%, but it had no effect on cheese pH (5.2). After five injections, the protein matrix expanded, occupying an increased area of cheese matrix (83 vs. 78%). Even though citrate injection had no effect on bound calcium, and thus the rate and extent of cheese flow were unaffected, increased phosphate solubilization, and possibly decreased ionic calcium content, resulted in expansion of the protein matrix and increased cheese hardness.

Calcium↗

PubMed2002

Diversity in specificity of the extracellular proteinases in Lactobacillus helveticus and Lactobacillus delbrueckii subsp. bulgaricus.

AIMS: To investigate the diversity in specificity of cell-bound extracellular proteinases in Lactobacillus helveticus and Lactobacillus delbrueckii subsp. bulgaricus. METHODS AND RESULTS: HPLC analysis of whole-cell preparations of 14 Lact. delbrueckii subsp. bulgaricus and eight Lact. helveticus strains incubated with alpha (s1)-casein (f 1-23) detected at least six distinct proteolytic patterns. Differences between groups were found in both the primary and secondary specificity toward alpha(s1)-casein (f 1-23) and its breakdown products. No correlation was found between the o-phthaldialdehyde (OPA) general proteolysis analysis and alpha(s1)-casein (f 1-23) cleavage profiles. CONCLUSIONS, SIGNIFICANCE AND IMPACT OF STUDY: Using the alpha(s1)-CN (f 1-23) method, six patterns of proteolysis were found in the dairy lactobacilli tested. Understanding the influence of Lactobacillus proteinase specificity on casein degradation should facilitate efforts to develop starter cultures that predictably improve the functional properties of Mozzarella cheese.

Chromatography, High Pressure Liquid↗

PubMed2002

Temperature effect on structure-opacity relationships of nonfat mozzarella cheese.

Our objective was to determine the effect of heating on the structure of nonfat Mozzarella cheese and then to relate changes in structure to changes in cheese opacity. Cheese was made according to a direct-acid, stirred-curd procedure. Cheese samples, at 4 degrees C, were taken on d 1 and placed into glass bottles, which were sealed and heated. Once the cheese reached 10 degrees C or 50 degrees C, the bottles were placed on a scanner and color values measured. Samples were also taken on d 1 for chemical, micro, and ultrastructural analyses. Applying heat increased cheese opacity. At 50 degrees C the cheese was more opaque than at 10 degrees C. The increase in temperature induced changes in cheese structure. Larger high-density protein aggregates and increased protein concentration in the protein matrix were observed in cheese at 50 degrees C. Applied heat would favor hydrophobic interactions, and possibly, re-association of beta-casein and calcium with the protein matrix, promoting protein-to-protein interactions. Thus, the protein matrix contracts, occupying less cheese matrix area, and microphase separation occurs, causing serum pockets to grow in size, and microstructural heterogeneity to increase. It is proposed that the increased size of aggregates and heterogeneity of the cheese at 50 degrees C promote light reflection, thus increasing cheese opacity. We concluded that applying heat alters protein interactions in the cheese matrix, manifested as changes in cheese structure. Such changes in structure help provide an understanding of changes in cheese opacity.

Cheese↗

PubMed2002

Proteolytic specificity of Lactobacillus delbrueckli subsp. bulgaricus influences functional properties of mozzarella cheese.

Low-moisture part-skim Mozzarella cheeses were manufactured from 2% fat milk and aged for 21 d. Treatments included cheeses made with one of three different strains of Lactobacillus delbrueckii ssp. bulgaricus in combination with a single strain of Streptococcus thermophilus. A fourth, control treatment consisted of cheeses made with only S. thermophilus. Although total proteolytic ability of these strains, as indicated by the o-phthaldialdehyde analysis, was similar in each of the three strains of L. bulgaricus, these strains exhibited different proteolytic specificities toward the peptide, alpha(s1)-CN (f 1-23). On the basis of their alpha(s1)-CN (f 1-23) cleavage patterns and a previously described classification, these strains were assigned to the groups I, III, and V. The objective of this study was to investigate the influence of lactobacilli proteolytic systems, based on specificity toward alpha(s1)-CN (f 1-23), on functionality of part-skim Mozzarella cheese. Moisture, fat, protein, salt-in-moisture, and moisture in nonfat substances content of cheeses made with groups I, III, and V strain were similar. Control cheese had a lower moisture content than did other treatments. Significant differences were observed in functional properties between cheeses manufactured using groups III and V strains. Cheeses made with groups I and III strains were similar in their meltability, hardness, cohesiveness, melt strength, and stretch quality. Meltability and cohesiveness increased with age, while melt strength and stretch quality decreased with age for all cheeses. Additionally, HPLC showed that total peak areas of water-soluble peptides derived from cleavage of alpha(s1)-CN (f 1-23) by different strains of lactobacilli could be highly correlated to meltability and stretch characteristics of cheeses made with those strains.

Amino Acid Sequence↗

PubMed2002

Test for measuring the stretchability of melted cheese.

A test for measuring the stretchability of cheese was developed by adapting a texture-profile analyzer to pull strands of cheese upwards from a reservoir of melted cheese. Seven different cheeses were analyzed using the Utah State University stretch test. The cheeses were also analyzed for apparent viscosity with a helical viscometer, for meltability using a tube melt test, and for stretch using the pizza-fork test. Cheese was placed into a stainless steel cup and tempered in a water bath at 60, 70, 80, or 90 degrees C for 30 min before analysis. The cup was then placed in a water-jacketed holder mounted on the base of the instrument. A three-pronged hook-shaped probe was lowered into the melted cheese and then pulled vertically until all cheese strands broke or 30 cm was reached. This produced a stretch profile as the probe was lifted through the reservoir of melted cheese and then pulled strands of cheese upwards. Three parameters were defined to characterize the stretchability of the cheese. The maximum load, obtained as the probe was lifted through the cheese, was defined as melt strength (F(M)). The distance to which cheese strands were lifted was defined as stretch length (SL). The load exerted on the probe as the strands of cheese were being stretched was defined as stretch quality (SQ). There was a correlation between F(M) and apparent viscosity. There was also some correlation between SL measured by the fork test and SL when the cheese was tested at 90 degrees C, but no correlation occurred at lower temperatures.

Calcium↗

PubMed2001

Appetite is not influenced by a unique milk peptide: caseinomacropeptide (CMP).

The milk protein, caseinomacropeptide (CMP), is a predominant breakdown product of casein in the human stomach, and may aid in the regulation of food intake. Using a human feeding study design, this project assessed the effects of CMP on satiety and satiation by measuring the amount of food consumed at meal times and through subjective motivation to eat questionnaires. The following beverage treatments were prepared: 0.4% CMP solution, 2.0% CMP solution, vehicle alone, and water containing colorant and clouding agent. Twenty male and 32 female adults were enrolled into the study using a Latin Square randomization. Treatment beverages and ad libitum lunches were consumed on four separate occasions at the Study Center. After lunch, subjects left the Study Center, and completed a standardized questionnaire every hour throughout the afternoon and evening to assess hunger and stomach fullness, and kept track of all food and beverages consumed. Under these experimental conditions, CMP had no effect on energy intake or weight of food consumed at lunch or for the remainder of the day. CMP also had no effect on subjective indicators of satiety. Intake of CMP before a midday meal has no effect on regulation of food intake over a short-term period.

Adolescent↗

PubMed2001

Comparison of simple measures of insulin sensitivity in young girls with premature adrenarche: the fasting glucose to insulin ratio may be a simple and useful measure.

Insulin resistance is a strong predictor of the development of type 2 diabetes mellitus and cardiovascular disease. Girls with premature adrenarche (PA) or obesity may be at an increased risk for the development of insulin resistance. Recently, in prepubertal girls with PA, a fasting glucose to insulin ratio (FGIR) of less than 7 was found to be predictive of insulin resistance as determined by the frequently sampled iv glucose tolerance test. We sought to compare the FGIR with 2 insulin sensitivity measures, SiM (an adjusted mean measure of insulin sensitivity based on fasting and 2 h post glucose load insulin sensitivity measures) and the composite whole body insulin sensitivity index, ISI(comp), both derived from the 2-h oral glucose tolerance test in 2 groups of children at risk: girls with PA and obese girls. We studied 25 prepubertal girls with PA and/or obesity and further classified them as insulin resistant (IR) or insulin sensitive (IS) based on the FGIR. Four simple measures of insulin sensitivity [FGIR, quantitative insulin sensitivity check index (QUICKI), fasting insulin resistance index, and fasting insulin] were compared with SiM and ISI(comp). Additionally, we characterized the subjects in terms of risk factors associated with insulin resistance according to their insulin resistance status based on the FGIR. In our subjects the strongest correlations overall appeared to be between FGIR and SiM, FGIR and ISI(comp), QUICKI and SiM, and QUICKI and ISI(comp) [correlations (r) ranged from 0.81--0.84]. Furthermore, the IR group had higher body mass index and body mass index z-scores and triglyceride levels than the IS group and were over 3 times more likely to have triglycerides greater than the 95th percentile compared with national norms. We conclude that the FGIR and QUICKI are highly correlated with oral glucose tolerance test measures of insulin sensitivity. An FGIR less than 7 in young girls with PA or obesity may be helpful in the early identification of children at risk for complications of insulin resistance.

Blood Glucose↗

PubMed2001

Telomere associations in interphase nuclei: possible role in maintenance of interphase chromosome topology.

The relative sizes of individual telomeres in cultured human cells under conditions of cell cycling, replicative quiescence, cell transformation and immortalization were determined using quantitative fluorescence in situ hybridization (Q-FISH) with a telomere-specific peptide nucleic acid (PNA) probe. Results obtained from analysis of telomere length profiles (TLPs), which display the distribution of relative telomere lengths for individual cells, confirmed telomere length heterogeneity at the single cell level and proportional shortening of telomere length during replicative aging of virus-transformed cells. TLPs also revealed that some telomeric ends of chromosomes are so closely juxtaposed within interphase nuclei that their fluorescent signals appear as a single spot. These telomeric associations (TAs) were far more prevalent in interphase nuclei of noncycling normal and virus-transformed cells than in their cycling counterparts. The number of interphase TAs per nucleus observed in late-passage E6/E7-transformed cells did not increase during progression to crisis, suggesting that telomere shortening does not increase the frequency of interphase TAs. Furthermore, interphase TAs were rarely observed in rapidly cycling, telomerase-positive, immortalized cells that exhibit somewhat shortened, but stabilized, telomere length through the activity of telomerase. Our overall results suggest that the number of interphase TAs is dependent more on whether or not cells are cycling than on telomere length, with TAs being most prominent in the nuclei of replicatively quiescent cells in which nonrandom (even preferred) chromosome spatial arrangements have been observed. We propose that interphase TAs may play a role in the generation and/or maintenance of nuclear architecture and chromosome positional stability in interphase nuclei, especially in cells with a prolonged G(1)/G(0) phase and possibly in terminally differentiated cells.

Cell Cycle↗

PubMed2001

Reversibility of the temperature-dependent opacity of nonfat mozzarella cheese.

Salted and unsalted nonfat mozzarella cheese was made by direct acidification and stored at 4 degrees C over 60 d. Changes in cheese opacity were measured by using reflectance L* values while the cheese was heated from 10 to 90 degrees C, then cooled to 10 degrees C, and reheated to 90 degrees C. A characteristic opacity transition temperature (T(OP)) was obtained for each cheese. Both salt content and storage time influenced T(OP). Opacity during heating, cooling, and reheating formed a hysteresis. At d 1, the unsalted cheese became opaque when heated to 20 degrees C, but the salted cheese required heating to 40 degrees C. As the salted cheese was aged, its T(OP) increased so that by 60 d the cheese did not become opaque until it was heated to 70 degrees C.

Cheese↗