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Biomedical subjects

M H Tunick

Publications and source records attributed to M H Tunick.

12 recordsLinked to original sources
PubMed2005

Effect of frozen storage on the proteolytic and rheological properties of soft caprine milk cheese.

Freezing and long-term frozen storage had minimal impact on the rheology and proteolysis of soft cheese made from caprine milk. Plain soft cheeses were obtained from a grade A goat dairy in Georgia and received 4 storage treatments: fresh refrigerated control (C), aged at 4 degrees C for 28 d; frozen control (FC), stored at -20 degrees C for 2 d before being thawed and aged in the same way as C cheese; and 3-mo frozen (3MF), or 6-mo frozen (6MF), stored at -20 degrees C for 3 or 6 mo before being thawed and aged. Soft cheeses had fragile textures that showed minimal change after freezing or over 28 d of aging at 4 degrees C. The only exceptions were the FC cheeses, which, after frozen storage and aging for 1 d at 4 degrees C, were significantly softer than the other cheeses, and less chewy than the other frozen cheeses. Moreover, after 28 d of aging at 4 degrees C, the FC cheeses tended to have the lowest viscoelastic values. Slight variation was noted in protein distribution among the storage treatment, although no significant proteolysis occurred during refrigerated aging. The creation and removal of ice crystals in the cheese matrix and the limited proteolysis of the caseins showed only slight impact on cheese texture, suggesting that frozen storage of soft cheeses may be possible for year-round supply with minimal loss of textural quality.

Animals↗
PubMed2002

Molten globule structures in milk proteins: implications for potential new structure-function relationships.

Recent advances in the field of protein chemistry have significantly enhanced our understanding of the possible intermediates that may occur during protein folding and unfolding. In particular, studies on alpha-lactalbumin have led to the theory that the molten globule state may be a possible intermediate in the folding of many proteins. The molten globule state is characterized by a somewhat compact structure, a higher degree of hydration and side chain flexibility, a significant amount of native secondary structure but little tertiary folds, and the ability to react with chaperones. Purified alpha(s1)- and kappa-caseins share many of these same properties; these caseins may thus occur naturally in a molten globule-like state with defined, persistent structures. The caseins appear to have defined secondary structures and to proceed to quaternary structures without tertiary folds. This process may be explained, in part, by comparison with the architectural concepts of tensegrity. By taking advantage of this "new view" of protein folding, and applying these concepts to dairy proteins, it may be possible to generate new and useful forms of proteins for the food ingredient market.

Animals↗
PubMed2002

Torsion gelometry of cheese.

Torsion gelometry, a fundamental rheological test in which specimens are twisted until they fracture, was applied to several different cheese varieties to determine its suitability for measuring their textural properties. Fresh and aged Brick, Cheddar, Colby, Gouda, Havarti, Mozzarella, and Romano cheeses were subjected to torsion analysis, and the results were compared with those from small amplitude oscillatory shear (SAOS) tests and texture profile analysis (TPA). Strong relationships (correlation coefficients > 0.8) were found between torsion shear stress and TPA hardness, and between torsion shear strain and TPA cohesiveness. SAOS, which measures rheological properties of intact samples, did not correlate well with torsion or TPA. A map showing trends during aging toward brittle, mushy, rubbery, and tough texture was drawn using the torsion data. The findings show that torsion gelometry provides fundamental rheological data on cheese at the fracture point. The information can be used to compare textural qualities of cheese samples as they are being cut.

Cheese↗
PubMed2001

Heat treatment adaptations in Clostridium perfringens vegetative cells.

Vegetative cells of Clostridium perfringens enterotoxigenic strains NCTC 8679, NCTC 8238. and H6 were grown at 37 degrees C followed by a 60-min exposure to 28 degrees C or 46 degrees C. D10-values, as a measure of thermal resistance at 60 degrees C, were significantly lower for 28 degrees C exposures as compared with cultures given 37 and 46 degrees C exposures. Following refrigeration at 4 degrees C for 24 h, D10-values for the 37 and 46 degrees C samples could not be differentiated from 28 degrees C samples. Western immunoblot analyses of lysates from heat-adapted cells also detected the increased expression of proteins reacting with antiserum directed against the molecular chaperonins from Escherichia coli; GroEL, DnaJ, and the small acid soluble protein from Bacillus subtilis, SspC. Differential scanning calorimetry (DSC) identified thermal transitions corresponding to ribosomal protein denaturations at 72.1 +/- 0.5 degrees C. Any cellular heat adaptations in the DSC profiles were lost following refrigeration for several days to simulate minimally processed food storage conditions. Further analyses of high-speed pellets from crude cell extract fractions using two-dimensional gel electrophoresis detected the differential gene expression of at least four major proteins in heat-adapted vegetative cells of C. perfringens. N-terminal amino acid analyses identified two of the proteins as glyceraldehyde 3-phosphate dehydrogenase and rubrerythrin. Both appear to have roles in this anaerobe under stressful conditions.

Adaptation, Physiological↗
PubMed2000

Cold shock and its effect on ribosomes and thermal tolerance in Listeria monocytogenes.

Differential scanning calorimetry (DSC) and fatty acid analysis were used to determine how cold shocking reduces the thermal stability of Listeria monocytogenes. Additionally, antibiotics that can elicit production of cold or heat shock proteins were used to determine the effect of translation blockage on ribosome thermal stability. Fatty acid profiles showed no significant variations as a result of cold shock, indicating that changes in membrane fatty acids were not responsible for the cold shock-induced reduction in thermal tolerance. Following a 3-h cold shock from 37 to 0 degrees C, the maximum denaturation temperature of the 50S ribosomal subunit and 70S ribosomal particle peak was reduced from 73.4 +/- 0.1 degrees C (mean +/- standard deviation) to 72.1 +/- 0.5 degrees C (P < or = 0.05), indicating that cold shock induced instability in the associated ribosome structure. The maximum denaturation temperature of the 30S ribosomal subunit peak did not show a significant shift in temperature (from 67.5 +/- 0.4 degrees C to 66.8 +/- 0.5 degrees C) as a result of cold shock, suggesting that either 50S subunit or 70S particle sensitivity was responsible for the intact ribosome fragility. Antibiotics that elicited changes in maximum denaturation temperature in ribosomal components also elicited reductions in thermotolerance. Together, these data suggest that ribosomal changes resulting from cold shock may be responsible for the decrease in D value observed when L. monocytogenes is cold shocked.

Calorimetry, Differential Scanning↗
PubMed2000

Rheology of dairy foods that gel, stretch, and fracture.

Casein gels are found in hard and soft dairy foods such as cheese and yogurt, and their rheological properties can be analyzed with various instrumental techniques. Empirical tests of cheese have been used since cheese making began, and imitative tests have been conducted in laboratories since the 1930s. Texture profile analysis is now the most frequently used imitative test. Fundamental tests provide a better representation of cheese and yogurt rheology because of the systematic mathematical treatment involved. Uniaxial compression and stress and strain relaxation tests are among the fundamental tests performed on cheese, and viscosity data are often used to investigate the physical characteristics of yogurt. Small amplitude oscillatory shear measurements are applicable to both products. Food scientists can acquire a clearer picture of the structure of dairy foods by performing appropriate rheological studies of the casein matrix.

Caseins↗
PubMed2000

Effect of carbon dioxide under high pressure on the survival of cheese starter cultures.

A new processing method that rapidly forms curds and whey from milk has the potential to improve cheesemaking procedures if cheese starter cultures can tolerate the processing conditions. The survival of Lactobacillus delbrueckii ssp. bulgaricus, Lactococcus lactis ssp. lactis, or Streptococcus thermophilus through this new process was evaluated. Inoculated milk containing 0, 1, or 3.25% fat or Lactobacillus MRS broth or tryptone yeast lactose broth (depending on microorganism used) was sparged with CO2 to a pressure of 5.52 MPa and held for 5 min at 38 degrees C. Broth contained 7.93 to 8.78 log CFU/ ml before processing and 7.84 to 8.66 log CFU/ml afterward. Before processing, milk inoculated with L bulgaricus, L. lactis, or S. thermophilus contained 6.81, 7.35, or 6.75 log CFU/ml, respectively. After processing, the curds contained 5.68, 7.32, or 6.50 log CFU/g, and the whey had 5.05, 6.43, or 6.14 log CFU/ml, respectively. After processing, the pHs of control samples were lower by 0.41 units in broth, 0.53 units in whey, and 0.89 units in curd. The pH of the processed inoculated samples decreased by 0.3 to 0.53 units in broth, 0.32 to 0.37 units in whey, and 0.93 to 0.98 units in the curd. Storing curds containing L. lactis at 30 degrees C or control curds and curds with L. bulgaricus or S. thermophilus at 37 degrees C for an additional 48 h resulted in pHs of 5.22, 5.41, 4.53, or 4.99, respectively. This study showed that milk inoculated with cheese starter cultures and treated with CO2 under high pressure to precipitate casein-produced curds that contained sufficient numbers of viable starter culture to produce lactic acid, thereby decreasing the pH.

Animals↗
PubMed1987

Calcium in dairy products.

Increasing attention has been given to the nutritional role of calcium because many Americans do not consume their Recommended Dietary Allowance of this nutrient and because calcium deficiency may lead to the development of osteoporosis or other disorders. Calcium is absorbed in the intestines with the aid of a vitamin D metabolite and is used in the body for many essential functions. There are several ways to obtain calcium in the diet, but the best sources are milk and other dairy products because of their low cost and high bioavailability of this mineral. Some manufacturers have responded to the concern over lack of calcium in the diet by increasing its levels in milk. The amount of calcium in cheese and yogurt also can be elevated.

Animals↗