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PubMed2002

Prandtl number and thermoacoustic refrigerators.

From kinetic gas theory, it is known that the Prandtl number for hard-sphere monatomic gases is 2/3. Lower values can be realized using gas mixtures of heavy and light monatomic gases. Prandtl numbers varying between 0.2 and 0.67 are obtained by using gas mixtures of helium-argon, helium-krypton, and helium-xenon. This paper presents the results of an experimental investigation into the effect of Prandtl number on the performance of a thermoacoustic refrigerator using gas mixtures. The measurements show that the performance of the refrigerator improves as the Prandtl number decreases. The lowest Prandtl number of 0.2, obtained with a mixture containing 30% xenon, leads to a coefficient of performance relative to Carnot which is 70% higher than with pure helium.

Journal Article↗
PubMed2000

Performance measurements on a thermoacoustic refrigerator driven at high amplitudes

Since the power density in a thermoacoustic device is proportional to the square of the acoustic Mach number, there is strong motivation to design thermoacoustic refrigerators to operate at larger pressure amplitudes. Measurements are reported of a modified version of the Space Thermo-Acoustic Refrigerator (STAR), driven at peak-to-mean pressure ratios up to 6%. This pressure ratio corresponds to 30 W of cooling power-five times as large as reported for STAR in 1993. The results of these measurements are compared to a DELTAE computer model of the low-amplitude (linear) performance that matches experimental conditions on a point-by-point basis. It is found that there is a small but measurable deviation in heat pumping power from the power predicted with a linear acoustic computer model at moderate amplitudes. This deviation in heat pumping power at 6% pressure ratio is about 23%. A large disagreement in the acoustic power needed to attain a specific pressure ratio is found between measured data and DELTAE results. An overview of the instrumentation, including a measurement of exhaust heat with an absolute accuracy of 65 mW, is also presented.

Journal Article↗
PubMed1989

Changes in fatty acid composition in sardines (Sardinops melanosticta) with cooking and refrigerated storage.

The influence of cooking and later storage in a refrigerator for 7 days on the fatty acid composition of lipids in sardines (Sardinops melanosticta) was studied. The total lipid and triacylglycerol (TG) levels did not change and the phospholipid (PL) level decreased somewhat with cooking or during storage. The fatty acid composition of the total lipids and TG fractions was little changed and that in the PL fractions was somewhat changed by the cooking. The composition of the polyunsaturated fatty acids (PUFA) in lipids of sardine precooked at 100 or 170 degrees C for 30 min changed from 42.7 to 38.3 or 33.5%, respectively, for total lipids and from 51.5 to 38.4 or 37.6%, respectively, for PL fractions during storage. The fatty acids in lipids from the ordinary meat of sardine was stable and those in the dark meat were extremely unstable during storage after cooking. We concluded that the PUFA in the lipids of sardines were stable to cooking, but unstable to oxidation during storage in a refrigerator. The PUFA of lipids in the dark meat of sardine were extremely unstable to oxidation.

Animals↗
PubMed2003

Bactericidal effects of Lactobacillus reuteri and allyl isothiocyanate on Escherichia coli O157:H7 in refrigerated ground beef.

Two naturally occurring antimicrobial agents were tested in packages of refrigerated ground beef for their ability to reduce the viability of Escherichia coli O157:H7 during storage. Allyl isothiocyanate (AITC) and Lactobacillus reuteri were tested separately and together for their action against a cocktail of five strains of E. coli O157:H7 in ground beef held at 4 degrees C for 25 days. Ground beef prepared from whole, raw inside round beef roasts was inoculated with low (3 log CFU/g) or high (6 log CFU/g) levels of the E. coli O157:H7 mixture. The beef was treated with AITC (about 1,300 ppm), L. reuteri, or both, along with 250 mM of glycerol per kg of meat at two levels (3 and 6 log CFU/g) and according to a design that yielded 8 controls plus 10 different treatments. Samples were analyzed for E. coli O157:H7 survivors, numbers of total bacteria, and lactic acid bacteria on days 0 to 25 at 5-day intervals. L. reuteri at both input levels with glycerol killed E. coli O157:H7 at both inoculated levels before day 20. AITC completely eliminated E. coli O157:H7 at the low-inoculum level (3 log CFU/g) and reduced viability >4.5 log CFU/g at the high-inoculum level (6 log CFU/g) by the end of the storage period. The combination of L. reuteri and AITC did not yield an additive effect against E. coli O157:H7 viability. L. reuteri in the presence of glycerol was highly effective against E. coli O157:H7 in ground beef during refrigerated storage (4 degrees C) in modified atmosphere packages. Sensory testing is planned to evaluate effects of treatments.

Cold Temperature↗
PubMed2006

Irradiation inactivation of Listeria monocytogenes in low-fat ground pork at freezing and refrigeration temperatures.

Gamma radiation effectively controls Listeria monocytogenes in uncooked and in ready-to-eat foods. This study was conducted to determine if gamma radiation could be used to control L. monocytogenes in ground pork. Ground pork was contaminated with L. monocytogenes, kept at refrigeration (4 degrees C), chilling (0 degrees C), and freezing (-18 degrees C) temperatures overnight, exposed to gamma radiation and stored at 4 degrees C for 7 days, and at 0 and -18 degrees C for 60 days. Following irradiation, the meat was assayed for L. monocytogenes viable counts and lipid oxidation. A triangle test was performed to determine if sausage made from the irradiated and nonirradiated ground pork differed in sensory quality. It was observed that a 5-log reduction of L. monocytogenes viable counts would require a 3.0-kGy radiation dose. The results of a 60-day storage study of ground pork inoculated with 10(5) to 10(6) CFU of L. monocytogenes per gram indicated that counts for nonirradiated meat remained fairly constant at refrigeration, chilling, and freezing temperatures. However, irradiation of ground pork at 3.0 kGy could inactivate L. monocytogenes totally in ground pork subsequently held at all the temperatures used in this study. Lipid oxidation measurements, as determined by the thiobarbituric acid-reactive substance assay, ranged from 0.16 nmol/g for nonirradiated ground pork and 0.20 nmol/g for meat irradiated at 3.0 kGy. Sensory panelists could distinguish between irradiated and nonirradiated sausage but were divided on whether irradiation adversely affected the sausage quality. Our results suggest that gamma radiation could be useful to control L. monocytogenes in ground pork and improve the safety of ground pork products.

Animals↗
PubMedDate not supplied

Ultra-rapid freezing and storage of rat embryos in an electric refrigerator at -130 degree C without liquid cryo-agents, with ultra-short exposure in the freezing medium and direct rehydration after thawing.

An ultra-rapid freezing technique for embryos has been developed. This procedure involves: ultra-short exposure to cryoprotectants; freezing of embryos in a metallic powder pre-cooled in an electric refrigerator at -130 degree C; storage of embryos ina refrigerator at -130 degree C; direct rehydration after thawing.

Journal Article↗
PubMed2002

Effect of prolonged water storage and repeated thermocycling on the reinforcing ability of refrigerated Amalgambond Plus/High Performance Additive in third molars with large mesio-occlusodistal amalgam restorations.

OBJECTIVE: This in vitro investigation examined what effect prolonged water immersion and repeated thermocycling had on the fracture strength of extracted third molars restored with refrigerated Amalgambond Plus with High Performance Additive (AB+/HPA) and Tytin amalgam. MATERIALS AND METHODS: Mesio-occlusodistal (MOD) channels were prepared in one member from each of 19 contralateral pairs. After restoration, specimens were stored in water for 6 months, with thermocycling repeated every 2 months. Specimens were fractured in a universal testing machine, and the data were analyzed. Secondary effects of tooth location and tooth size were also examined. RESULTS: Fracture strengths of prepared/restored teeth were not statistically different from those of intact contralateral pairs (p > 0.05). Maxillary teeth had lower fracture strengths than mandibular teeth, and tooth size had no effect on fracture strength. CONCLUSIONS: Extracted molars with large MOD amalgam restorations bonded with refrigerated AB+/HPA had fracture strengths equivalent to those of intact contralateral pairs after 6 months of water storage and repeated thermocycling.

Compressive Strength↗
PubMed1998

Changes in physical and chemical constituents of crab meat during storage at refrigerator temperature (7+/-2 degrees C).

The present study was initiated to determine the deteriorative changes occurred in the nutritive quality of crabmeat during storage at refrigerator temperature (7+/-2) for the period of one week. The parameters studied for the assessment of quality are pH, water, total protein and salt soluble protein, TMA-N, TVB-N content. The results indicate a significant increase (p < or = 0.001) in pH, water, TMA. TVB while total protein salt soluble protein, and total lipid contents were significantly decreased (p < or = 0.001) as compared to fresh tissue. Our finding recommended that the quality of crabmeat is acceptable upto one day of storage at refrigerator temperature after that it becomes deteriorated.

Journal Article↗
PubMedDate not supplied

Metabolism in vivo and in vitro of the refrigerant substitute 1,1,1,2-tetrafluoro-2-chloroethane.

Ternary mixtures of hydrochlorofluorocarbons and hydrofluorocarbons are being evaluated as refrigerant substitutes for dichlorodifluoromethane, which is to be banned from further production in 2000. A priori consideration of the similarity between 1,1,1,2-tetrafluoro-2-chloroethane (HCFC-124), a primary component of candidate refrigerant blends, and halothane suggests that metabolism of HCFC-124 might proceed via reactive intermediates. Our data show that rats exposed for 2 hr to approximately 10,000 ppm HCFC-124 excreted both inorganic fluoride (F-) and trifluoroacetic acid (TFA), identified by 9F-NMR, in the urine. Likewise, microsomes produced F- and TFA from HCFC-124 in an NADPH-dependent, CO-inhibited, aerobic reaction. Treatment of rats with pyridine caused about a 20-fold increase in aerobic microsomal metabolism (F- release) of HCFC-124, while the rate of defluorination was slightly decreased by phenobarbital administration. An antibody to cytochrome P450 IIE1 inhibited more than 90% of HCFC-124 metabolism in pyridine-induced preparations. Defluorination of HCFC-124 by microsomes also occurred under conditions of greatly reduced oxygen tension, demonstrating that this halocarbon can be reductively metabolized. Moreover, heat-inactivated, NADPH-reduced microsomes liberated F- and a fluorinated organic product, although not TFA, from HCFC-124. Formation of TFA and F- as products of oxidative HCFC-124 metabolism support the hypothesis that trifluoroacetyl fluoride is formed as an intermediate. Trifluoroacetyl halides are known to adduct tissue proteins. The reductive metabolism of HCFC-124, by analogy to halothane, may produce a radical (CHFCF3) capable of biological interactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Temperature of refrigerated i.v. fluids and admixtures during infusion.

The effects of infusion rate, drop size, and solution composition on the infusion temperature of i.v. fluids and admixtures that had been stored at refrigerated temperatures were determined. Polyvinyl chloride bags containing 5% dextrose injection, 0.9% sodium chloride injection, cefazolin 20 mg/mL in 5% dextrose injection, or total parenteral nutrient (TPN) solution were removed from the refrigerator after 12 hours and hung from i.v. poles. An administration set was attached to each bag, and the distal end of the administration tubing was placed in a beaker-funnel-flask apparatus that served as a collection vessel for effluent during simulated i.v. infusions. Thermo-couples were inserted into each i.v. bag and positioned under the distal end of each administration set to monitor the temperatures of the solution in the bag and of the effluent. 5% Dextrose injection and 0.9% sodium chloride injection were studied at two flow rates (125 and 60 mL/hr) using two different administration sets (60-drops/mL microdrip set and 15-drops/mL primary set); the cefazolin admixture and the TPN solution were studied at both flow rates using the primary set only. The temperatures at each probe were measured in triplicate at the start of each infusion and at 3, 6, 9, 12, 15, and 25 minutes during the infusion; each infusion was repeated three times. All of the solutions warmed significantly as they passed through the administration sets. Throughout all time intervals, the cefazolin admixtures had the smallest proximal-distal temperature increase, and the TPN solutions had the greatest increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Cefazolin↗
PubMed1984

Characterization of erythrocyte quality during the refrigerated storage of whole blood containing di-(2-ethylhexyl) phthalate.

Di-(2-ethylhexyl) phthalate (DEHP) accumulates in blood brought into contact with materials utilizing this compound as a plasticizer. To determine whether this phthalate diester affects red blood cell integrity, we have compared cell morphology, plasma hemoglobin accumulation, micro-vesicle production, and the concentration of intracellular metabolites and electrolytes of erythrocytes from blood stored at 4 degrees C with and without DEHP. When sufficient emulsified DEHP was mixed with blood to give a final concentration of 300 micrograms/mL, plasma hemoglobin accumulation was reduced by an average of 70%, the percentage of cells exhibiting normal morphology was enhanced by at least 20-fold, and the volume of microvesicles released from red blood cells was reduced by 50% after 35 days of refrigerated storage compared to the values obtained from corresponding samples stored without added phthalate. Similar effects were observed regardless of whether blood was stored in nonplasticized polypropylene or tri-(2-ethylhexyl) trimellitate plasticized polyvinylchloride containers and with DEHP solubilized by a variety of emulsifiers. When 300 micrograms/mL DEHP was added to stored blood containing erythrocytes predominantly in the echinocyte conformation, many of the cells reverted to the normal discoid morphology. The addition of this quantity of DEHP to blood had no significant effect on the course of storage-induced changes in erythrocyte adenosine triphosphate (ATP), 2,3-diphosphoglycerate (2,3-DPG), sodium or potassium concentrations. The data are consistent with the hypothesis that DEHP inhibits the deterioration of the red blood cell membrane that results from the refrigerated storage of whole blood.

Blood Preservation↗
PubMed1997

Stability of gamma-glutamyltransferase activity in calf sera after refrigerated or frozen storage.

OBJECTIVES: To examine stability of -glutamyltransferase (GGT) activity in stored serum from neonatal calves. ANIMALS: 10 commercial beef calves between 36 and 60 hours old. PROCEDURE: Serum samples were obtained from the calves, and each sample was divided into 8 aliquots. Serum GGT activity was measured on day 0 (fresh) and days 1, 2, 3, and 4 of refrigerated storage (4 C) and weeks 1, 2, and 3 of frozen storage (-20 C). RESULTS: Serum GGT activities for each of the refrigerated aliquots did not significantly differ from day zero, with serum GGT activity (expressed as a percentage of initial activity) > 99% on all 4 days. Serum GGT activity in frozen aliquots decreased significantly after 1 and 2 weeks of frozen storage, 97 and 98%, respectively; however, this decrease in GGT activity was not biologically significant. The observed GGT activity did not decrease significantly in the samples stored frozen for 3 weeks; these samples retained 99% of initial activity. CONCLUSION: The observed stability of serum GGT activity indicates that serum may be obtained, stored, and batch processed at a later time. This stability during storage is important to the success of a bovine passive transfer monitoring program based on GGT activity.

Animals↗
PubMed1987

Bacterial growth in refrigerated human milk.

Unprocessed breast milk is currently being used as a desirable feeding alternative for premature infants. To assess some of the potential risks of this practice, we studied the bacterial growth in 41 samples of unprocessed human milk for a period of five days. No bacteria were cultured in eight samples of milk; the bacteria that were cultured in the remaining 33 samples were similar to those found on the skin and nipple of the breast. With the exception of three samples, two with Klebsiella and one with Pseudomonas, all identified bacteria have been reported as normal skin flora. The initial concentration of bacteria found in milk was low, with a mean of 10,000 colonies (range, 1000 to 140,000 colonies). Bacterial colony counts progressively decreased throughout the five-day refrigeration period.

Breast↗
PubMed1999

Viable spermatozoa can be recovered from refrigerated mice up to 7 days after death.

To develop a model for utilizing germ cells collected from dead animals, male mice were euthanized and refrigerated for various periods, and the viability of the epididymal spermatozoa was examined by in vitro fertilization, embryo culture, and embryo transfer. Higher proportions of fresh oocytes were fertilized when males had been stored at 4-6 or 8-10 degrees C than at 0 degrees C. By partially dissecting the zona of freshly ovulated oocytes, spermatozoa from ICR male mice could fertilize oocytes (21% fertilization rate) after being stored for 5 days at 4-6 degrees C, and spermatozoa from BDF1 male mice could fertilize oocytes (39%) after being stored for 7 days at 4-6 degrees C. The resulting two-cell embryos had the ability to develop into expanded blastocysts in culture (81-100%) and into live young after transfer (34-47%). With further refinement of this system, it should be applicable not only for rescuing valuable genetic variants in laboratory animals or livestock animals but also for wild species in the future.

Animals↗
PubMed1994

Safety assessment of HCFC-141b: use as a blowing agent for insulation in building construction and refrigeration.

We have performed a risk assessment to evaluate potential risk to human health that might be associated with the use of HCFC-141b (1,1-dichloro-1-fluoroethane) in rigid foam insulation boards for home sheathing and in foam insulation for refrigerators. Risks presented by the blowing agent itself and its potential contaminants and breakdown products (HCFC-151a, HCFC-1131a, and vinylidene chloride) were evaluated following the standard procedures outlined by the National Academy of Sciences. HCFC-141b showed an equivocal tumorigenic effect in rats (an increase in benign testicular tumors that was not dose related), while vinylidene chloride was associated with an increase in tumor incidence (kidney tumors in mice) in a single study out of 19 in which its carcinogenicity has been investigated. The other two contaminants have not been tested for carcinogenicity, but do show some evidence of genotoxicity in short-term tests. However, even if all of these substances are treated as potential carcinogens, under the anticipated conditions of human exposure the maximum theoretical risk to a resident is less than one in one million (10(-6)). Also, no other toxic effects would be anticipated.

Animals↗
PubMed1986

The viability of Campylobacter jejuni on refrigerated chicken drumsticks.

Radappertized chicken drumsticks were experimentally contaminated with suspensions of Campylobacter jejuni in two trials. Qualitative analysis on drumsticks with an initial level of contamination of 4.8 X 10(3) CFU/cm2 showed that viability was retained for at least 10 days of storage at either 9 degrees or -12 degrees C. In a second quantitative trial, the level of contamination declined from 9.9 X 10(2) CFU/cm2 to 4.5 X 10(1) CFU/cm2 after 7 days at -20 degrees C. Thereafter, C. jejuni persisted at levels ranging from 1.8 X 10(1) to 0.2 X 10(1) CFU/cm2 through the 26th week of storage. Drumsticks held at 4 degrees C showed a significant decline in count from 9.9 X 10(2) CFU/cm2 to 1.8 X 10(2) CFU/cm2 on day 7. It is concluded that the viability of C. jejuni on chicken parts is maintained under both refrigerated and freezing conditions which approximate commercial storage. This is of significance to the meat industry and consumers.

Animals↗
PubMed1991

Public health implication of refrigerated pasteurized ('sous-vide') foods.

Food that upon pasteurization is stored in hermetically sealed containers at food temperatures not exceeding 3 degrees C could be designated by the generic term Refrigerated Pasteurized Foods of Extended Durability, REPFEDs. If not properly processed or protected against recontamination, or if temperature-abused, REPFEDs may present serious health risks. However, control is readily available. Sound microbial ecology, supported by expert risk assessment, allows the design and introduction of longitudinally integrated manufacture, distribution, handling by outlets and consumers and culinary preparation, which result in the assurance of the wholesomeness of the commodity as eaten. Recent progress, including intrinsic preservation by the incorporation of starter cultures, bacteriocins or particular enzymes, opens vistas for attractive future developments. Once microbiological safety has been built into the REPFED-line, monitoring can be limited to (i) real-time tests particularly applied to the factory environment; and (ii) rapid, simple examination for marker organisms of freshly manufactured products versus those approaching expiration dates. Such audits will allow rapid retrieval of incidental process failure and its rectification. It also serves to substantiate measurements of food temperature and spot checks on intrinsic inhibitory attributes. The application of scientific knowledge and technological expertise should primarily be entrusted to the industry itself, heeding Lord Plumb's strategy of "partnership along the food production chain from farm to fork." It should be supported and validated by Public Health Authorities. At all stages safety communication with the public should be ensured.

Bacteria↗
PubMed1991

Behavior of Aeromonas species at refrigeration temperatures.

The ability of many strains of Aeromonas hydrophila and A. sobria to produce several types of virulence factors has been documented. The presence of Aeromonas in drinking water, as well as in river and saline waters and on various finfish and shellfish taken from them, has caused some concern relative to the role this bacterium plays as a causative agent of human gastroenteritis. The fairly common occurrence of Aeromonas on red meats, poultry and fresh produce and its ability to grow at 4 degrees C gives rise to further concern over public health risks which may be associated with consumption of these foods. A brief overview of the behavior of Aeromonas species at refrigeration temperatures is presented.

Aeromonas↗