Добірка наукової літератури з теми "High-temperature short-time pasteurization"

Full scare commercial pasteurization equipment operated at 72–73°C with a holding time of 15–16 s was used to determine the ability of commercial thermal processing to inactivate Listeria monocytogenes strain Scott A. Three methods of providing L. monocytogenes concentration in raw milk were employed: freely suspended (extra-cellular), inside bovine phagocytes (in vitro procedure), and inside bovine phagocytes in experimentally infected cows (in vivo). Three enrichment methods were used to assay for L. monocytogenes after pasteurization: cold enrichment (4°C, 28 d), selective enrichment of Lovett et al. (FDA procedure) (17), and the USDA-FSIS two stage enrichment procedure. In addition, a 1-L sample taken just before the vacuum breaker was incubated undiluted in the original sample container (4°C, 4 weeks). None of the four assay methods could detect Listeria in the pasteurized milk.

Modes of pasteurization of raw milk, which are used in the production of hard rennet cheeses, do not destroy all microflora. Even pasteurization of milk at a temperature of 75...76 °C for 20-25 seconds, which corresponds to the upper limit of heat treatment of raw milk in the production of hard rennet cheeses, provides only 94.6% efficiency of heat-resistant bacteria. Adopted modes of short-term pasteurization for most rennet cheeses at the level of 72...76 °C with a holding time of 20-25 s allow to achieve the residual amount of bacterial contamination of milk at 72 °C pasteurization mode - 3.2%, at 76 °C pasteurization mode - 0.7 %

Alkaline phosphatase (AP) is used as the indicator enzyme for proper pasteurization of bovine milk. Predictive modeling of AP inactivation during high-temperature short-time (HTST) pasteurization would support regulations; thus ensuring the safety of heat treated milk. Activation energy (Ea) of AP in milk was measured experimentally using the capillary tube method, and Ea was found to be 429252 J/mol. The Ea was used to develop a nonlinear model to describe the thermal inactivation of milk in a small-scale HTST pasteurizer with a plate heat exchanger. Integrated pasteurization effect (PE) was obtained at different holding temperatures (62–72°C) and holding times (3–25 s), by converting times at different temperatures in various sections of the pasteurizer to the equivalent time at the reference temperature (72°C). A nonlinear function was developed to relate the log(% residual AP activity) to PE. The r2 varied from 0.7488 to 0.8311. The validation trial indicated that the model could predict AP activity accurately for the% residual AP activity >1%.

In order to support regulations directed towards ensuring the safety of heat processed dairy products, data on inactivation of alkaline phosphatase (AP) in whole milk in a pilot plant high-temperature short-time (HTST) pasteurizer were obtained. A Computer program was designed to calculate the integrated lethal effect, or pasteurization effect (PE), at temperatures of 60 to 74°C and with holding tubes for 3 to 60 s. An equation was derived which related values of PE to log % residual activity (r2 of 0.964). These results suggest that predictive equations based on PE could be used to assess the effectiveness of commercial pasteurization processes.

Orientador: Luiz Francisco Prata
Banca: Angela Cleusa de Fatima Banzatto de Carvalho
Banca: Sandra Ferreira Fukuda
Resumo: Este trabalho buscou definir e padronizar uma metodologia simples e rápida para ser utilizada na indicação da segurança de consumo de leite pasteurizado. Foram analisadas 261 amostras de leite recém-pasteurizado de diferentes marcas comerciais, as quais foram submetidas à prova rápida de redução em tubos, aos métodos microbiológicos oficiais de controle (contagem padrão em placas de mesófilos, determinação do número mais provável (NMP) de coliformes totais e fecais) e às pesquisas de atividade enzimática (peroxidase e fosfatase alcalina). Padronizou-se a prova rápida em tubos partindo de diluições decimais das amostras, misturando-as ao Cloreto de Trifeniltetrazólio (TTC) e a um meio nutritivo à base de leite desnatado. As leituras foram realizadas a cada 30 minutos até completar 8 horas de incubação, observando-se a formação de cor pela redução do TTC. Comparou-se os resultados da prova rápida com os da contagem padrão em placas de mesófilos e com o NMP de coliformes (total e fecal), demonstrando uma elevada correlação linear (r = -0,85). A maioria das amostras que se encontrava fora dos padrÕes regulamentares tinha peroxidase positiva classificadas como reações P++ e P+++. Do total, 134 amostras (51,3%) foram consideradas dentro dos padrões regulamentares para ambos os métodos microbiológicos oficiais, embora oito dessas tenham reduzido o TTC em até 8 horas. Dentre as 127 amostras (49,7%) que estavam fora dos padrões regulamentares, 93 reduziram o TTC em até 8 horas de leitura... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The objective of this study was to define and to standardize a sim pie and rapid methodology to be used in the indication of the security of pasteurized milk consumption. In this work, 261 fresh-pasteurized milk samples, of different commercial brands, were submitted to a rapid test of reduction in tubes and to the official microbiological methods of control (standard plate count of mesophilic aerobic bacteria, determination of the most probable number (MPN) of total and fecal coliforms) and to the research of enzymatic activity (peroxidase and alkaline phosphatase). It was standardized rapid test in tubes leaving of decimal dilutions of the samples, mixing them it the Triphenyltetrazolium Chloride (TTC) and to a nutritional medium containing skimmed milk. The readings were realized to each 30 minutes until completing 8 hours of incubation, observing themselves it formation of color for the reduction of the TTC. The results of the fast test were compared with the ones of the standard plate count of mesophilic and with the MPN of coliforms (total and fecal), demonstrating a high degree of linear correlation (r = -0,85). Most of the samples that was found outside of established pattern had peroxidase positive as reactions P++ and P+++. Of the total, 134 samples (51.3%) were considered inside of the established limits for both the official microbiological methods, even so eight of these have reduced the TTC in up to 8 hours. Amongst the 127 samples (49.7%) that were over the established pattern, 93 had reduced the TTC in up to 8 hours of reading. The fast reduction test in tubes was able to detect bacterial counts loading from 104 UFC/mL of tested sample, with 72,2%... (Complete abstract click electronic access below)
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Este trabalho buscou definir e padronizar uma metodologia simples e rápida para ser utilizada na indicação da segurança de consumo de leite pasteurizado. Foram analisadas 261 amostras de leite recém-pasteurizado de diferentes marcas comerciais, as quais foram submetidas à prova rápida de redução em tubos, aos métodos microbiológicos oficiais de controle (contagem padrão em placas de mesófilos, determinação do número mais provável (NMP) de coliformes totais e fecais) e às pesquisas de atividade enzimática (peroxidase e fosfatase alcalina). Padronizou-se a prova rápida em tubos partindo de diluições decimais das amostras, misturando-as ao Cloreto de Trifeniltetrazólio (TTC) e a um meio nutritivo à base de leite desnatado. As leituras foram realizadas a cada 30 minutos até completar 8 horas de incubação, observando-se a formação de cor pela redução do TTC. Comparou-se os resultados da prova rápida com os da contagem padrão em placas de mesófilos e com o NMP de coliformes (total e fecal), demonstrando uma elevada correlação linear (r = -0,85). A maioria das amostras que se encontrava fora dos padrÕes regulamentares tinha peroxidase positiva classificadas como reações P++ e P+++. Do total, 134 amostras (51,3%) foram consideradas dentro dos padrões regulamentares para ambos os métodos microbiológicos oficiais, embora oito dessas tenham reduzido o TTC em até 8 horas. Dentre as 127 amostras (49,7%) que estavam fora dos padrões regulamentares, 93 reduziram o TTC em até 8 horas de leitura...
The objective of this study was to define and to standardize a sim pie and rapid methodology to be used in the indication of the security of pasteurized milk consumption. In this work, 261 fresh-pasteurized milk samples, of different commercial brands, were submitted to a rapid test of reduction in tubes and to the official microbiological methods of control (standard plate count of mesophilic aerobic bacteria, determination of the most probable number (MPN) of total and fecal coliforms) and to the research of enzymatic activity (peroxidase and alkaline phosphatase). It was standardized rapid test in tubes leaving of decimal dilutions of the samples, mixing them it the Triphenyltetrazolium Chloride (TTC) and to a nutritional medium containing skimmed milk. The readings were realized to each 30 minutes until completing 8 hours of incubation, observing themselves it formation of color for the reduction of the TTC. The results of the fast test were compared with the ones of the standard plate count of mesophilic and with the MPN of coliforms (total and fecal), demonstrating a high degree of linear correlation (r = -0,85). Most of the samples that was found outside of established pattern had peroxidase positive as reactions P++ and P+++. Of the total, 134 samples (51.3%) were considered inside of the established limits for both the official microbiological methods, even so eight of these have reduced the TTC in up to 8 hours. Amongst the 127 samples (49.7%) that were over the established pattern, 93 had reduced the TTC in up to 8 hours of reading. The fast reduction test in tubes was able to detect bacterial counts loading from 104 UFC/mL of tested sample, with 72,2%... (Complete abstract click electronic access below)

O Mycobacterium bovis causa a tuberculose zoonótica, doença que afeta os animais e o homem podendo causar a morte, sendo o leite uma importante via de transmissão da doença para o homem. A pasteurização do leite é a principal medida para quebrar essa cadeia de transmissão, cujos parâmetros de tempo e temperatura foram definidos através de experimentos que datam desde o fim do século XIX, com base na resistência térmica do M. bovis e da Coxiella burnetti, então considerados os mais resistentes patógenos não formadores de esporos que contaminam o leite. No Brasil são aprovados os binômios 62ºC a 65ºC por 30 minutos e 72ºC a 75ºC por 15 a 20 segundos. Entretanto, com o passar dos anos e surgimento de novas tecnologias (PCR, Spoligotyping e outras técnicas biomoleculares) foi possível observar diferenças genéticas intra-espécie. Assim, este projeto tem por objetivo avaliar e comparar o comportamento de dois espoligotipos de M. bovis (SB0120 e SB1033) frente aos dois protocolos de pasteurização utilizados no país. Para tanto, leite integral UHT foi contaminado com esses espoligotipos e submetido aos dois processos térmicos, em Banho-Maria. O leite foi semeado em meio sólido Stonebrink-Leslie e a contagem de colônias foi feita após 45 dias de incubação a 37ºC. Não houve neste experimento diferença entre as resistências térmicas dos dois espoligotipos, no entanto detectou-se uma maior importância da fase de aquecimento na redução do agente do que da fase de manutenção da temperatura, para os dois espoligotipos, nos dois processos.
Mycobacterium bovis causes zoonotic tuberculosis disease that affects animals and humans and can cause death, the milk is an important route of disease transmission to humans. The pasteurization of milk is the main measure to break the transmission chain, whose time and temperature parameters were defined by experiments dating from the late nineteenth century, based on thermal resistance of M. bovis and Coxiella burnetti, considered then the most resistant non-spore-forming pathogens that contaminate the milk. In Brazil, there are two approved binomials 62ºC to 65ºC for 30 minutes and 72ºC to 75ºC for 15 to 20 seconds. However, over the years and the emergence of new technologies (PCR, spoligotyping and other biomolecular techniques) was observed genetic differences intra-species. Thus, this project aims to evaluate and compare the behavior of two spoligotypes of M. bovis (SB0120 and SB1033) compared to the two pasteurization protocols used in the country. To this end, UHT milk was contaminated with these spoligotypes and subjected to two thermal processes in a water bath. The milk was streaked on solid medium Stonebrink-Leslie and colony counting was done after 45 days of incubation at 37ºC. This experiment showed that there was no difference between the thermal resistances of the two spoligotypes, however it was detected a greater importance of the heating phase in reducing the agent that the maintenance phase of temperature for the two spoligotypes, in both cases.

碩士
國立嘉義大學
動物科學系研究所
95
The purpose of this study was to distinguish between high temperature short time pasteurization (HTST) milk and ultra high temperature treatment (UHT) milk by bovine immunoglobulin G level. Raw milk was pasteurized by HTST and UHT and low temperature long time (LTLT), respectively. The IgG of these samples was analyzed by sodium dodecylsulfate polyacrylamide gel electro-phoresis (SDS-PAGE) and western blot and enzyme-linked immunosorbent assay (ELISA). The results showed that pasteurized milk of 65℃,30min, 75℃,16s, 75℃,32s, 75℃,43s, 75℃,64s and 80℃,16s had been found obviously dyed protein band of IgG, IgG heavy chain (IgG-HC) and IgG light chain (IgG-LC) with SDS-PAGE and western blot, and the IgG contents of these samples were 382.1±17.73, 384.2±11.12, 348.8±19.15, 282.1±10.77, 267.1±9.24 and 256.3±13.01 mg/L, respectively. However, pasteurized milk of 75℃,15min, 80℃,32s, 80℃,43s, 80℃,64s, 85℃,16s, 85℃,32s, 85℃,43s, 85℃,64s and 130℃,2-3s had been found not obvious or faint dyeing protein band of IgG in the SDS-PAGE and the western blot. Nevertheless，the contents of all above treated IgG were below 150 mg/L. In addition, the content of milk IgG 150 mg/L is as a boundary value that can be used distinguish between HTST and UHT milk by the immunodot blot technique.

Bovine milk proteins are a source of high-quality proteins in the human diet. Raw milk is subjected to different processing treatments prior to human consumption to ensure food safety and extend the shelf life. However, the thermal processing including high-temperature short-time (HTST) pasteurization and ultra-high temperature (UHT) treatment and alternative nonthermal methods including application of high pressure (HP) appear to modify the native properties of milk proteins. The processing induced modifications in protein structure, mainly denaturation and aggregation, and associated changes in epitopes can modulate the immunogenicity and potential allergenicity of milk proteins. The severity of some processing conditions appears to alter the native minor proteins including immunoglobulins (Ig), which may otherwise exert immunomodulatory properties in such a way as to prevent occurrence of allergies. Bovine or cow’s milk protein allergy (CMPA) is an abnormal immunological reaction to one or more milk proteins and it is the most prevalent food allergy among infants globally. Hence, the overall aim of this study was to identify the modification of native milk proteins induced by selected thermal (heating at 72 for 15 s and 100 °C for 30 s) and nonthermal processing conditions (application of HP at 400, 500, or 600 MPa for 15 min at 30 °C) and to establish their impact on modulation of in vitro immunogenicity as a means of envisaging potential allergenicity. Processing induced changes in secondary structure of proteins were studied by Fourier transform infrared spectroscopy (FTIR), and protein denaturation and aggregation were mainly examined using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and size exclusion chromatography (SEC). Changes in antigenicity of milk proteins followed by processing was studied by enzyme-linked immunosorbent assay (ELISA). Modulation of in vitro immunogenicity was assessed based on the concentration of several cytokines secreted by human peripheral blood mononuclear cells (PBMCs) in response to native and processed milk proteins. Thermal denaturation of bovine IgG was studied alone and in the presence of major whey proteins. The two heating regimes studied provided the simulated thermal effect compared to HTST (72 °C/ 15 s) and UHT (100 °C/ 30 s equivalent to 140 °C/ 5 s in terms of denaturation of β-lactoglobulin) conditions. Simulated HTST conditions least impacted on the secondary structure of IgG and other whey proteins when they were present either alone or in mixtures of whey proteins. The heating at 100 °C for 30 s caused formation of covalent complexes of IgG alone, as well as in the mixtures, mainly through thiol-disulfide reactions. Under 100 °C /30 s treatment, bovine serum albumin (BSA) did not interact with IgG through thiol-disulfide reactions in a binary mixture of proteins (IgG+BSA). α-Lactalbumin (ALA) appeared to preferentially lead denaturation of whey proteins over β-lactoglobulin (BLG), in a protein mixture (BLG+ALA+IgG+BSA), while native whey contains another component that can inhibit this effect. The presence of other whey proteins did not contribute to thermal stability of IgG at 100 °C for 30 s. Residual antigenicity of a processed protein is a marker of potential allergenicity. Other milk proteins affect thermal denaturation of bovine BLG and modulate its antigenicity. Denaturation of BLG and altered antigenicity were studied in protein mixtures during 72 °C/ 15 s and 100 °C/ 30 s treatments. BLG denaturation, affected by other proteins, correlated with altered antigenicity. The treatment at 72 °C/ 15 s enhanced antigenicity in BLG+ALA mixture possibly due to exposed epitopes in unfolded structure, while it did not affect other protein mixtures. The treatment at 100 °C/ 30 s resulted in BLG-led protein aggregation by thiol/disulphide interactions and declined antigenicity by fragmentation and masking of epitopes to a different extent depending on the mixture. IgG contributed to diminish antigenicity in BLG+ALA+IgG mixture at 100 °C/ 30 s. The protein denaturation governed by ALA over BLG in BLG+ALA+IgG+BSA mixture, was possibly catalysed by BSA at 100 °C/30 s, resulting in a higher retention of antigenicity than other mixtures. In vitro immunogenicity of various native and thermally processed (72 °C / 15 s and 100 °C /30 s) bovine milk protein fractions, their mixtures, whey, and skim milk, was studied by analysing the immune response of T helper (Th) cells in human PBMCs. The secretion of Th types cytokines induced by the protein stimulants was quantified, while determining the heat-induced protein denaturation. Purified whey proteins, caseins and whey fraction, and skim milk, provoked substantial immune responses at various degrees, indicating their potent immunogenicity. The protein mixtures prepared using the fractionated whey proteins with or without caseins appeared less immunogenic in both native and heat-treated forms, implying their potential of producing less immunogenic dairy products. The treatment at 100 °C/ 30 s significantly altered the immunogenicity of most of the potent protein stimulants, which mostly coincided with their levels of protein denaturation. The treatment at 72 °C / 15 s caused least protein denaturation but altered the immunogenicity of several protein stimulants notably including heat-stable caseins and ALA. High pressure processing (HPP), conducted at 400, 500 or 600 MPa for 15 min at 30 °C, of raw skim milk was studied in comparison to HTST pasteurization (72 °C/ 15 s), considering protein denaturation and in vitro immunogenicity. HTST pasteurization least impacted denaturation of native proteins leading to mostly unchanged milk immunogenicity. HPP resulted in denaturation of whey proteins, mostly BLG and IgG, and disturbed structure of the casein micelle. HPP at 600 MPa caused protein aggregation, involving mainly BLG and κ-casein, through thiol disulphide interactions. ALA was least denatured subjected to all HPP conditions. The balance between expression of Th1 and Th2 type cytokines, which is believed to regulate adverse immune response, was initially shifted toward Th1 with increase in HP, then the immunogenic capacity of milk proteins diminished at 600 MPa. This could be related to exposure of T cell-specific linear epitopes followed by unfolding of protein structure firstly and masking of them by protein aggregation subsequently with increase in high pressure. In overall, the conditions applied in raw milk processing should be further optimised in considering modifications of native milk proteins and subsequent modulation of their immunogenicity, in addition to ensuring the food safety, to make the final dairy product both hygienic and hypoallergenic. Mild heat treatments (< 72 °C) or combined mild processing, for instance application of HP below 400 MPa in combination with low temperature (< 50 °C), would be able to fulfil aforementioned requirements.

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.