Добірка наукової літератури з теми "Ultrahigh temperature milk"

A laboratory-scale, indirect, ultrahigh-temperature (UHT) system was constructed using stainless steel tubing (6.35 mm) as the barrier between the heating agent and the product. Nitrogen gas under 80 psi pressure propelled milk through the tubing of the system. The milk was preheated in a hot water bath, brought to sterilization temperature in an oil bath, and held at this temperature in a holding tube. After leaving the holding tube, the milk was cooled rapidly in an ice-water bath and aseptically collected in 250-ml amber colored glass bottles in a glove box. The system effectively sterilized milk with carefully controlled temperature and time.

Nonthermal technologies are emerging as promising alternatives to heat treatment for food processing. Ultrasound, defined as sound waves with a frequency greater than 20 kHz, has proven bactericidal effects, especially when combined with other microbial-reduction strategies such as mild heating. In this study, ultrasound treatment (sonifier probe at 20 kHz, 100% power level, 150 W acoustic power, 118 W/cm2 acoustic intensity) with or without the effect of mild heat (57°C) was effective at reducing microbial levels in raw milk, Listeria monocytogenes levels inoculated in ultrahigh-temperature milk, and Escherichia coli O157:H7 in apple cider. Continuous flow ultrasound treatment combined with mild heat (57°C) for 18 min resulted in a 5-log reduction of L. monocytogenes in ultrahigh-temperature milk, a 5-log reduction in total aerobic bacteria in raw milk, and a 6-log reduction in E. coli O157:H7 in pasteurized apple cider. Inactivation regressions were second-order polynomials, showing an initial period of rapid inactivation, eventually tailing off. Results indicate that ultrasound technology is a promising processing alternative for the reduction of microorganisms in liquid foods.

The aim of this work was to evaluate the bactericidal efficacy of ultrahigh-pressure homogenization (UHPH) against Listeria innocua ATCC 33090 inoculated into milk and orange juice. We also intended to study the effect of inlet temperature on the lethality and production of sublethal injuries in this microorganism and its ability to survive, repair, and grow in refrigerated storage after UHPH treatment. Samples of ultrahigh-temperature whole milk and ultrahigh-temperature orange juice inoculated at a concentration of approximately 7.0 log (CFU per milliliter) were immediately pressurized at 300 MPa on the primary homogenizing valve and at 30 MPa on the secondary valve, with inlet temperatures of 6.0 ± 1.0°C and 20 ± 1.0°C. L. innocua viable counts and injured cells were measured 2 h after UHPH treatment and after 3, 6, and 9 days of storage at 4°C for milk and after 3, 6, 9, 12, 15, 18, and 21 days of storage at 4°C for orange juice. Both the inlet temperature and the food matrix influenced significantly (P < 0.05) the inactivation of L. innocua, which was higher in whole milk at the 20°C inlet temperature. The UHPH treatment caused few or no sublethal injuries in L. innocua. During storage at 4°C after treatments, counts increased by approximately 2 logarithmic units from day 0 to 9 in whole milk, whereas in orange juice counts diminished by approximately 2.5 logarithmic units from day 0 to 18.

The role of dissolved oxygen as a contributor to flavor deterioration in sterile milk during storage was investigated. Before processing, a concentrated aqueous solution of Tenox-2 was added to half of a batch of pasteurized-homogenized milk to give a final concentration of 400 ppm BHA on a fat basis in the milk. The other half was untreated. Half of each of those batches was treated to reduce oxygen concentrations by a combination of nitrogen sweep and sonication. The remaining two samples (Tenox-2 added and no-Tenox-2) did not receive the deoxygenation treatment. Oxygen levels in the preprocessed deoxygenated milk were lower (4.6 ppm) than those in the untreated milk (6.9 ppm). All four lots were UHT-sterilized at 135°C for 5 s in an indirect UHT system constructed at Kansas State University. Sterilized milk was collected aseptically in a glove box in 250-ml amber glass bottles, which were closed with either Teflon-lined caps or sterile cotton plugs. Samples from each treatment were stored at 7° and 32°C for 4 months. Samples in capped bottles maintained relatively low (<4 ppm) dissolved oxygen concentrations, whereas those in cotton-plugged bottles had relatively high (7–7.5 ppm) dissolved oxygen concentrations. Dissolved oxygen affected the rate of stale flavor development. Sterile milk in bottles with cotton plugs, which had relatively high concentrations of dissolved oxygen during storage, developed a stale flavor sooner and with greater intensity than milks with lower levels of oxygen. However, acetaldehyde, propanal, n-pentanal, and n-hexanal, which are most likely products of lipid oxidation, did not appear to be principal contributors to staling in sterile milk during storage in this study. Furthermore, the stale flavor development did not parallel changes in thiobarbituric acid (TBA) values. Although antioxidant (40 ppm BHA on fat basis from Tenox-2) did retard oxidation slightly, it did not control staling. A decrease in the concentration of several volatile materials throughout the storage period probably was caused by dissipation of the volatile material through the cotton plug or by their interaction with other compounds in the milk. Acid degree values increased in sterile milk at 32°C during prolonged storage, but changes in ADVs did not parallel development of the stale flavor.

Soluble phosphoglycerides were studied in ultrahigh-temperature (UHT) milk by 31P-nuclear magnetic resonance. It was shown that, during storage of UHT milk, manufactured from raw milk with poor microbial quality, glycerophosphocholine and glycerophosphoethanolamine disappeared in parallel with an increase in α-glycerophosphate (GP). Storage at 10, 20, and 30°C showed a faster transformation as the temperature increased. UHT milk samples manufactured from raw milks with better microbial quality and submitted to severe heat processes did not display changes in phosphoglycerides during storage. Screening of commercial UHT milks showed variations regarding the presence of GP, while in pasteurized milk samples, the appearance of GP occurred when the commercial life had been exceeded. Inoculation of sterile milk with Pseudomonas fluorescens NCIB9046 and incubation at 10°C supported that changes in phosphoglycerides could be the consequence of a phosphodiesterase activity of bacterial origin, able to survive UHT processing. A similar behavior was observed between this activity and proteolytic activity. The potential application of the detection of these compounds as spoilage predictor indices is discussed.

Heat treatments of milk between 100 and 145°C produce a new type of product with a shelf life of 15 to 30 days at 7°C, which is termed extended shelf life (ESL) milk. Little information is available on the safety and sensory qualities of this product. Extended shelf life milk is being processed commercially to expand the distribution area of fluid milk products. After arrival at market, this product still has the shelf life of a pasteurized product. In this study milk was processed by direct steam injection at temperatures between 100 and 140°C for 4 or 12 s. Holding time did not significantly affect the sensory quality of the milk. A trained taste panel found cooked flavor and other off flavors varied significantly with increasing processing temperature and storage time. There were no significant differences noted in cooked or off flavors between 132 and 140°C. Psychrotrophic Bacillus species were isolated from milk processed at and below 132°C, while no organisms were isolated from milk processed at temperatures at or above 134°C. Consumer preference panels indicated consumers preferred milk processed at 134°C for 4 s to ultrahigh-temperature (UHT) processed milk, although there was a slight preference for high-temperature short-time processed (HTST) milk compared to milk processed at 134°C for 4 s. Higher temperatures had a less destructive effect on lipase activity, while storage time did not significantly affect lipase activity.

Introduction. The aim of this study was to determine estrone (E1), 17?-estradiol (E2) and progesterone (P4) concentrations in processed milk with different fat contents and to compare the concentrations of these hormones in commercial ultrahigh temperature (UHT) processed milk and commercial pasteurized milk. Materials and Methods. Commercial milks with different fat contents (UHT 0.5 %, UHT 1.5 %, UHT 3.5 % and pasteurized 3.5 % (10 samples of each type of milk)) were purchased in local stores. E1, E2 and P4 concentrations were determined by commercial ELISA kits. Results and Conclusions. E1 concentrations were below the limit of detection (15 pg mL-1) in all milks except in two UHT 3.5 % (out of 10) and two pasteurized 3.5 % (out of 10) milk samples. Mean E2 and P4 concentrations in UHT 3.5 % milk (25.37 ? 1.15 pg mL-1 and 10.76 ? 0.43 ng mL-1, respectively) were significantly higher than in UHT 0.5 % milk (19.38 ? 0.79 pg mL-1 and 7.06 ? 0.26 ng mL-1, respectively). Significant positive correlations were determined between hormone concentrations and milk fat contents. Relatively high E2 and P4 concentrations indicate that the bulk of milk in the commercial milks examined originated from pregnant cows.

ABSTRACT To investigate the drug residue status in commercial liquid milk products in China, 190 samples, including ultrahigh temperature milk (n = 168) and pasteurized milk (n = 22) samples, were collected in 2019. Milk samples were analyzed for the presence of any of the 61 veterinary drugs in them by using a screening assay combined with an ultraperformance liquid chromatography–tandem mass spectrometry analysis. Ten (5.26%) samples were found positive for β-lactams, tetracyclines, and aminoglycosides, and six (3.16%) samples were confirmed residual for penicillin G (n = 6; 3.16%), tetracycline (n = 1; 0.53%), and oxytetracycline (n = 1; 0.53%), with the maximum concentration of 2.85, 40.64, and 12.35 μg kg−1, respectively. Drug residue detection rate in group II (4.55%; the local city domestic brands) was higher than that in group I (2.70%; the major brands of China) and group III (2.78%; the imported brands into China) and higher in domestic samples (3.39%) than that in imported samples (2.78%), and higher in pasteurized milk samples (9.09%) than in ultrahigh temperature milk samples (2.38%). All drug residue levels were far below the regulated maximum residue limits. However, based on some veterinary drug residues detected in the samples, there is a potential veterinary drug risk in liquid milk products in the Chinese market, and this situation deserves the attention of governments and consumers. HIGHLIGHTS

UHT milk is gaining market share worldwide for being a healthy, safe and convenient food product with a long shelf life at room temperature. However, the UHT treatment (usually 140- 150 °C for 2-10 s) contributing to its long shelf life may induce some changes, which may make it unstable during storage. Considerable levels of sedimentation (up to 1 % dry weight basis) of proteinaceous material at the bottom of the storage container, or formation of a gel (age-gelation), or both, can mark the end of shelf life of UHT milk, and hence affect its market potential and incur financial losses to the UHT dairy processors. Irrespective of a mechanism, gelation or sedimentation appears to be governed and preceded by changes in the extent and nature of interactions among milk proteins leading to their aggregation. Though recent investigations have added significantly to the understanding of the different protein interactions, the exact mechanism involving changes in these molecular interactions leading to sedimentation and gelation, is not clear yet. Moreover, less is known about the role of proteinlipid interactions in the development of a storage instability. In addition, the need of a rapid technique which can detect the shelf life of UHT milk has been emphasised in recent years. This is mainly because applying full-length shelf life tests in a product such as UHT milk would be time- and resource-intensive. Thus, the overall objective of this project was to understand and rapidly predict the storage stability of UHT milk. Accelerated shelf life testing is one such rapid alternative applied to a variety of food products to save time. The industry has not been successful in applying this approach to ultrahigh temperature (UHT) milk because of the chemical and physical changes in the milk proteins that take place during its processing and storage. Thus, the first objective of the study was to investigate the feasibility of applying accelerated shelf life principles to UHT milk samples with different fat levels to elucidate changes in interactions of milk proteins at ambient temperature using electrophoretic analysis (Native- and Sodium dodecyl sulfatepolyacrylamide gel electrophoresis). Samples of UHT skim (SM) and whole milk (WM) were stored at 20, 30, 40, and 50 °C for 28 days. Irrespective of fat content, UHT treatment had a similar effect on the electrophoretic patterns of milk proteins. At the start of testing, proteins were bonded mainly through disulphide and noncovalent interactions. However, storage at and above 30 °C enhanced protein aggregation via covalent interactions. The extent of aggregation appeared to be influenced by fat content, implying aggregation via melted or oxidized fat, or both. Based on the reduction in loss in the absolute quantity of individual proteins, covalent crosslinking in WM was facilitated mainly by products of lipid oxidation. Whereas, Maillard and dehydroalanine products appeared to be the main contributors to protein changes in SM. Protein crosslinking appeared to follow a different pathway at higher temperatures (≥40 °C), making it difficult to extrapolate these changes to lower temperatures. The changes identified under the accelerated shelf life conditions using electrophoretic analysis assisted in evaluating the potential of using another rapid technique, Fourier transform infrared spectroscopy (FTIR) in detecting changes in structure and interactions of milk proteins (the second objective). The feasibility of using FTIR to detect changes in conformational rearrangements, protein-protein and protein-lipid interactions was studied with accelerated shelf life protocols. WM and SM were stored at 20, 30, 40 and 50 °C for 28 days. The changes in FTIR spectra were observed concomitant with increased sedimentation in SM (by 50 %) and WM (by 20 %) at higher temperatures (40 °C) after 14 days of the storage period. Milk samples stored at 40 and 50 °C showed marked changes in the bands corresponding to the conformations of milk lipids and formation of intermolecular β-sheets, indicating protein-lipid interactions and aggregation. Dried sediment contained fat confirming protein-lipid participation in the sedimentation. FTIR was also able to detect changes that led to increased sedimentation in SM at temperatures lower than 40 °C, but only after 28 days. However, to establish appropriateness of accelerated shelf life testing and FTIR as a tool for prediction of stability of UHT milk, the observed correlation between spectral changes and sediment formation at accelerated temperatures has to align with that at normal storage temperature (third objective of the study). SM and WM were stored at 20 °C for 9 months to investigate the feasibility of using FTIR to predict sedimentation in UHT milk. Identified spectral marker variables corresponding to changes in the structure and interactions of lipids, proteins and carbohydrates successfully predicted sedimentation in SM (R2 -0.92) and WM (R2 - 0.60). Low predictability in WM may be due to the influence of fat. These markers were similar to those observed during accelerated shelf life testing, hence implying that the accelerated shelf life testing could be used in UHT milk. Among several changes in milk protein interactions during its heating and storage, conformational changes specific to an interaction remain largely unknown. Hence, the fourth objective of the project evaluated the possibility of fingerprinting two selected changes, i.e., deamidation and dephosphorylation, using FTIR. Enzymatic deamidation and dephosphorylation were carried out prior to heat treatment. Principal component analysis revealed that the heat treatment induced different changes in the secondary structure of control, deamidated and dephosphorylated milk samples. In contrast to a significant (P<0.05) decrease in β-sheet (1624 cm-1) and a rise in β-turns (1674 cm-1) in heated control samples, both deamidation and dephosphorylation of SM before heat treatment created more ordered secondary structure (significant (P<0.05) increase in α-helix (1650-52 cm-1) and β-sheet at the expense of 310-helix (1661 cm-1), random (1645-46 cm-1) and β-turn (1674 cm-1). The only difference between heated deamidated and dephosphorylated samples was decrease in large loops (1656 cm-1) in the latter opposed to the increase in the former. The project therefore established that the accelerated shelf life testing in combination with FTIR spectroscopy has a potential as a rapid tool to forecast sedimentation and other instabilities in UHT milk, and hence the shelf life of UHT milk. Further, a complete understanding of the conformational changes affecting the storage stability of UHT milk could also be attained by studying the structural changes specific to different known interactions using FTIR spectroscopy

In 1980, high-performance computing was becoming limited by the heat dissipated in semiconductor chips. IBM was introducing a new chip packaging technology that featured a specific thermal conductance of about 5000 W/m2·°C and occupied approximately 1 liter of space in order to cool 300 W. IBM was also developing a superconducting computer technology to circumvent the thermal problem posed by continued scaling of semiconductor chips. The following year, two of us (DBT and RFWP) showed theoretically and experimentally that by scaling down the dimensions of a conventional plate-fin liquid-cooled heat sink to a channel width of ∼50 μm, operating in the laminar flow regime, and integrated within the silicon chip, we could achieve in a laboratory demonstration at least a 20-fold improvement in specific thermal conductance, and more than 1000-fold greater volumetric heat removal. The reception of this advance was mixed, but what really stalled its adoption was the emergence of high-speed low-power CMOS semiconductor circuitry. Two decades later even scaled CMOS circuitry was getting too hot, and various commercialization attempts were then undertaken; some were successful, others not. New commercialization opportunities are now appearing including ones that enable society’s more efficient use of energy. A specific example of one such opportunity will be described, i.e., the use of microchannels in a novel, highly efficient regenerative heat-exchanger configuration, intended for heat-treating low-viscosity liquids for purposes such as pasteurization. Water was successfully heat-treated in continuous-flow tests of an experimental scaled-down prototype ultrahigh-temperature (UHT) pasteurizer incorporating a linear counterflow microchannel (50 μm parallel-plate channel separation) heat exchanger having an integrated electric heater at the hot end. The use of an integral electric heater permitted a unique manifold-less arrangement for reversing the flow directions at the hot end, wherein perfect local mass balance was enforced locally (i.e., between every pair of adjacent counter-flowing microchannels), eliminating a major potential source of flow maldistribution that would have otherwise reduced heat-exchanger effectiveness. Water entered the device at room temperature, steadily heated to 135°C in about 2.5 s, was maintained at 135°C for ∼2.5 s, and then cooled in ∼2.5 s, exiting at no more than 2°C above its original temperature, indicative of high heat-exchanger effectiveness. Heat leaks to ambient air required an excess of heater power, but those could be mostly eliminated in a scaled-up design and with proper attention to exterior insulation. Subsequent tests with milk flowing in heated microchannels revealed that fouling can be a severe problem (perhaps exacerbated by the long-tailed residence-time distribution characteristic of laminar flow), limiting continuous use to less than 2 hours for UHT pasteurization conditions. Conventional high-temperature short-time (HTST) milk pasteurization employs much lower peak temperatures and it is more likely that a practical microchannel system could be constructed for that application.

Hot forming die quenching (HFDQ) is used to transform ultrahigh strength steel blanks into martensitic body-in-white components that are lighter than parts made from traditional mild steels, without sacrificing crash performance. The part is sometimes locally reinforced by spot-welding patches to the blanks, but the increased thickness of the patched blanks sometimes results in incomplete austenitization, which can compromise the strength of as-formed parts. This paper presents an integrated thermo-metallurgical model of the austenitization of Al-Si coated 22MnB5 within a roller hearth furnace. While previous models account for the latent heat of austenitization by heuristically adjusting the specific heat, the present model explicitly simulates austenite formation using a first-order metallurgy submodel derived from dilatometry measurements. The model is validated by comparing predicted temperatures to measurements carried out on coupons heated within a lab-scale muffle furnace and full-sized blanks heated in an industrial-scale roller hearth furnace. Finally, the model is used to optimize roller speed based on zone temperatures.