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Temperature control in severe acute brain injury (SABI) is a key component of acute management. This manuscript delves into the complex role of temperature management in SABI, encompassing conditions like traumatic brain injury (TBI), acute ischemic stroke (AIS), intracerebral hemorrhage (ICH), aneurysmal subarachnoid hemorrhage (aSAH), and hypoxemic/ischemic brain injury following cardiac arrest. Fever is a common complication in SABI and is linked to worse neurological outcomes due to increased inflammatory responses and intracranial pressure (ICP). Temperature management, particularly hypothermic temperature control (HTC), appears to mitigate these adverse effects primarily by reducing cerebral metabolic demand and dampening inflammatory pathways. However, the effectiveness of HTC varies across different SABI conditions. In the context of post-cardiac arrest, the impact of HTC on neurological outcomes has shown inconsistent results. In cases of TBI, HTC seems promising for reducing ICP, but its influence on long-term outcomes remains uncertain. For AIS, clinical trials have yet to conclusively demonstrate the benefits of HTC, despite encouraging preclinical evidence. This variability in efficacy is also observed in ICH, aSAH, bacterial meningitis, and status epilepticus. In pediatric and neonatal populations, while HTC shows significant benefits in hypoxic-ischemic encephalopathy, its effectiveness in other brain injuries is mixed. Although the theoretical basis for employing temperature control, especially HTC, is strong, the clinical outcomes differ among various SABI subtypes. The current consensus indicates that fever prevention is beneficial across the board, but the application and effectiveness of HTC are more nuanced, underscoring the need for further research to establish optimal temperature management strategies. Here we provide an overview of the clinical evidence surrounding the use of temperature control in various types of SABI.
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Lesões Encefálicas , Hipotermia Induzida , Humanos , Hipotermia Induzida/métodos , Lesões Encefálicas/terapia , Lesões Encefálicas/fisiopatologia , Febre/etiologia , Febre/terapiaRESUMO
To investigate the extent of adoption of more efficient coding strategies, pigeons learned, in three experiments, a symbolic matching-to-sample task that featured an asymmetric sample-comparison mapping. In all experiments, one comparison was correct following one of the samples (one-to-one mapping), and another comparison was correct following the remaining samples (many-to-one mapping). The experiments differed in sample number; Experiment 1 featured three samples, Experiment 2 five samples, and Experiment 3 seven samples. Our goal was to assess the adoption of a single-code/default coding strategy, which establishes two response rules: one rule specific to the sample mapped one-to-one (the single code), and another rule to be applied following any other sample (the default rule). Alternatively, the animals could establish more response rules, one per sample. Thus, the single-code/default strategy allows learning a task via a reduced number of response rules, and the more samples are mapped many-to-one, the greater the savings it allows. As such, the three experiments should progressively be more amenable to the adoption of this strategy. Overall, the adoption of a single-code/default strategy was not widespread. When taken together with previous results, the present study suggests that the amount of training may affect the coding strategy pigeons adopt. Additionally, our results underscore that individual differences are a fundamental aspect to consider when studying learning flexibility.
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Spores from the fungus Pithomyces chartarum are commonly found on Azorean pastures. When consumed by cattle along with the grass, these spores cause health issues in the cattle, resulting in animal suffering and financial losses. For approximately two years, we monitored meteorological parameters using weather stations and collected and analyzed grass samples in a laboratory to control for the presence of spores. The data confirmed a connection between meteorology and sporulation, enabling the prediction of sporulation risk. To detect the presence of spores in pastures rather than predict it, we employed field spectrometry and Sentinel-2 reflectance data to measure the spectral signatures of grass while controlling for spores. Our findings indicate that meteorological variables from the past 90 days can be used to predict sporulation, which can enhance the accuracy of a web-based alert system used by farmers to manage the risk. We did not detect significant differences in spectral signatures between grass with and without spores. These studies contribute to a deeper understanding of P. chartarum sporulation and provide actionable information for managing cattle, ultimately improving animal welfare and reducing financial losses.
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Tecnologia de Sensoriamento Remoto , Esporos Fúngicos , Animais , Bovinos , Tecnologia de Sensoriamento Remoto/métodos , Esporos Fúngicos/isolamento & purificação , Poaceae/microbiologia , Açores , Internet das CoisasRESUMO
The continued functioning of tropical forests under climate change depends on their resilience to drought and heat. However, there is little understanding of how tropical forests will respond to combinations of these stresses, and no field studies to date have explicitly evaluated whether sustained drought alters sensitivity to temperature. We measured the temperature response of net photosynthesis, foliar respiration and the maximum quantum efficiency of photosystem II (Fv /Fm ) of eight hyper-dominant Amazonian tree species at the world's longest-running tropical forest drought experiment, to investigate the effect of drought on forest thermal sensitivity. Despite a 0.6°C-2°C increase in canopy air temperatures following long-term drought, no change in overall thermal sensitivity of net photosynthesis or respiration was observed. However, photosystem II tolerance to extreme-heat damage (T50 ) was reduced from 50.0 ± 0.3°C to 48.5 ± 0.3°C under drought. Our results suggest that long-term reductions in precipitation, as projected across much of Amazonia by climate models, are unlikely to greatly alter the response of tropical forests to rising mean temperatures but may increase the risk of leaf thermal damage during heatwaves.
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Complexo de Proteína do Fotossistema II , ÁrvoresRESUMO
Generalization allows responses acquired in one situation to be transferred to similar situations. For temporal stimuli, a discontinuity has been found between zero and non-zero durations: responses in trials with no (or 0-s) stimuli and in trials with very short stimuli differ more than what would be expected by generalization. This discontinuity may happen because 0-s durations do not belong to the same continuum as non-zero durations. Alternatively, the discontinuity may be due to generalization decrement effects: a 0-s stimulus differs from a short stimulus not only in duration, but also in its presence, thus leading to greater differences in performance. Aiming to reduce differences between trials with and without a stimulus, we used two procedures to test whether a potential reduction in generalization decrement would bring performance following zero and non-zero durations closer. In both procedures, there was a reduction in the discontinuity between 0-s and short durations, supporting the hypothesis that 0-s durations are integrated in the temporal subjective continuum.
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Aprendizagem por Discriminação , Percepção do Tempo , Animais , Columbidae , Percepção do Tempo/fisiologia , Generalização Psicológica , Fatores de Tempo , Generalização do EstímuloRESUMO
Meat constitutes one the main protein sources worldwide. However, ethical and health concerns have limited its consumption over the last years. To overcome this negative impact, new ingredients from natural sources are being applied to meat products to obtain healthier proteinaceous meat products. Algae is a good source of unsaturated fatty acids, proteins, essential amino acids, and vitamins, which can nutritionally enrich several foods. On this basis, algae have been applied to meat products as a functional ingredient to obtain healthier meat-based products. This paper mainly reviews the bioactive compounds in algae and their application in meat products. The bioactive ingredients present in algae can give meat products functional properties such as antioxidant, neuroprotective, antigenotoxic, resulting in healthier foods. At the same time, algae addition to foods can also contribute to delay microbial spoilage extending shelf-life. Additionally, other algae-based applications such as for packaging materials for meat products are being explored. However, consumers' acceptance for new products (particularly in Western countries), namely those containing algae, not only depends on their knowledge, but also on their eating habits. Therefore, it is necessary to further explore the nutritional properties of algae-containing meat products to overcome the gap between new meat products and traditional products, so that healthier algae-containing meat can occupy a significant place in the market.
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Produtos da Carne , Produtos da Carne/análise , Carne/análise , Antioxidantes , Vitaminas , Nível de SaúdeRESUMO
Nannochloropsis oculata is naturally rich in eicosapentaenoic acid (EPA). To turn this microalga into an economically viable source for commercial applications, extraction efficiency must be achieved. Pursuing this goal, emerging technologies such as high hydrostatic pressure (HHP) and moderate electric fields (MEF) were tested, aiming to increase EPA accessibility and subsequent extraction yields. The innovative approach used in this study combined these technologies and associated tailored, less hazardous different solvent mixtures (SM) with distinct polarity indexes. Although the classical Folch SM with chloroform: methanol (PI 4.4) provided the highest yield concerning total lipids (166.4 mglipid/gbiomass), diethyl ether: ethanol (PI 3.6) presented statistically higher values in terms of EPA per biomass, corresponding to 1.3-fold increase. When SM were used in HHP and MEF, neither technology independently improved EPA extraction yields, although the sequential combination of technologies did result in 62% increment in EPA extraction. Overall, the SM and extraction methodologies tested (HHP-200 MPa, 21 °C, 15 min, followed by MEF processing at 40 °C, 15 min) enabled increased EPA extraction yields from wet N. oculata biomass. These findings are of high relevance for the food and pharmaceutical industries, providing viable alternatives to the "classical" extraction methodologies and solvents, with increased yields and lower environmental impact. KEY POINTS: ⢠Et2O: EtOH is a less toxic and more efficient alternative to Folch solvent mixture ⢠HHP or MEF per se was not able to significantly increase EPA extraction yield ⢠Combinations of HHP and MEF technologies increased both lipids and EPA yields.
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Microalgas , Estramenópilas , Ácido Eicosapentaenoico , Solventes , Metanol , Etanol , BiomassaRESUMO
The midsession reversal task involves a simultaneous discrimination between stimuli S1 and S2. Choice of S1 but not S2 is reinforced during the first 40 trials, and choice of S2 but not S1 is reinforced during the last 40 trials. Trials are separated by a constant intertrial interval (ITI). Pigeons learn the task seemingly by timing the moment of the reversal trial. Hence, most of their errors occur around trial 40 (S2 choices before trial 41 and S1 choices after trial 40). It has been found that when the ITI is doubled on a test session, the reversal trial is halved, a result consistent with timing. However, inconsistent with timing, halving the ITI on a test session did not double the reversal trial. The asymmetry of ITI effects could be due to the intrusion of novel cues during testing, cues that preempt the timing cue. To test this hypothesis, we ran two types of tests after the regular training in the midsession reversal task, one with S1 and S2 choices always reinforced, and another with S1 always reinforced but S2 reinforced only after 20 trials when the ITI doubled or 40 trials when the ITI halved. For most pigeons, performance was consistent with timing both when the ITI doubled and when it was halved, but some pigeons appeared to follow strategies based on counting or on reinforcement contingencies.
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The interest in high hydrostatic pressure (HHP) is mostly focused on the inactivation of deleterious enzymes, considering the quality-related issues associated with enzymes in foods. However, more recently, HHP has been increasingly studied for several biotechnological applications, including the possibility of carrying out enzyme-catalyzed reactions under high pressure. This review aims to comprehensively present and discuss the effects of HHP on the kinetic catalytic action of enzymes and the equilibrium of the reaction when enzymatic reactions take place under pressure. Each enzyme can respond differently to high pressure, mainly depending on the pressure range and temperature applied. In some cases, the enzymatic reaction remains significantly active at high pressure and temperature, while at ambient pressure it is already inactivated or possesses minor activity. Furthermore, the effect of temperature and pressure on the enzymatic activity indicated a faster decrease in activity when elevated pressure is applied. For most cases, the product concentration at equilibrium under pressure increased; however, in some cases, hydrolysis was preferred over synthesis when pressure increased. The compiled evidence of the effect of high pressure on enzymatic activity indicates that pressure is an effective reaction parameter and that its application for enzyme catalysis is promising.
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Pressão Hidrostática , Temperatura , Hidrólise , Catálise , CinéticaRESUMO
The quality standards for the export of chestnuts generate large quantities of rejected fruits, which require novel processing technologies for their safe industrial utilization. This study aimed to investigate the impact of high-pressure processing (HPP) and hydrothermal treatments (HT) on the physicochemical properties of rejected chestnut starch. Chestnuts were treated by HPP at 400, 500, and 600 MPa for 5 min and HT at 50 °C for 45 min. In general, all HPP treatments did not induce starch gelatinization, and their granules preserved the integrity and Maltese-cross. Moreover, starch granules' size and resistant starch content increased with the intensity of pressure. Native and HT chestnut starches were the most susceptible to digestion. HPP treatments did not affect the C-type crystalline pattern of native starch, but the crystalline region was gradually modified to become amorphous. HPP-600 MPa treated starch showed modified pasting properties and exhibited the highest values of peak viscosity. This study demonstrates for the first time that after HPP-600 MPa treatment, a novel chestnut starch gel structure is obtained. Moreover, HPP treatments could increase the slow-digesting starch, which benefits the development of healthier products. HPP can be considered an interesting technology to obtain added-value starch from rejected chestnut fruits.
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Amilose , Amido , Amido/química , Amilose/química , Viscosidade , Nozes/química , Amido Resistente/análiseRESUMO
Urea cycle disorders (UCD) are inherited diseases resulting from deficiency in one of six enzymes or two carriers that are required to remove ammonia from the body. UCD may be associated with neurological damage encompassing a spectrum from asymptomatic/mild to severe encephalopathy, which results in most cases from Hyperammonemia (HA) and elevation of other neurotoxic intermediates of metabolism. Electroencephalography (EEG), Magnetic resonance imaging (MRI) and Proton Magnetic resonance spectroscopy (MRS) are noninvasive measures of brain function and structure that can be used during HA to guide management and provide prognostic information, in addition to being research tools to understand the pathophysiology of UCD associated brain injury. The Urea Cycle Rare disorders Consortium (UCDC) has been invested in research to understand the immediate and downstream effects of hyperammonemia (HA) on brain using electroencephalogram (EEG) and multimodal brain MRI to establish early patterns of brain injury and to track recovery and prognosis. This review highlights the evolving knowledge about the impact of UCD and HA in particular on neurological injury and recovery and use of EEG and MRI to study and evaluate prognostic factors for risk and recovery. It recognizes the work of others and discusses the UCDC's prior work and future research priorities.
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Encéfalo , Eletroencefalografia , Hiperamonemia , Imageamento por Ressonância Magnética , Espectroscopia de Prótons por Ressonância Magnética , Distúrbios Congênitos do Ciclo da Ureia , Animais , Encéfalo/diagnóstico por imagem , Encéfalo/metabolismo , Encéfalo/fisiopatologia , História do Século XXI , Hiperamonemia/diagnóstico por imagem , Hiperamonemia/história , Hiperamonemia/metabolismo , Hiperamonemia/fisiopatologia , Distúrbios Congênitos do Ciclo da Ureia/diagnóstico por imagem , Distúrbios Congênitos do Ciclo da Ureia/história , Distúrbios Congênitos do Ciclo da Ureia/metabolismo , Distúrbios Congênitos do Ciclo da Ureia/fisiopatologiaRESUMO
OBJECTIVE: Children with CHD may be at increased risk for epilepsy. While the incidence of perioperative seizures after surgical repair of CHD has been well-described, the incidence of epilepsy is less well-defined. We aim to determine the incidence and predictors of epilepsy in patients with CHD. METHODS: Retrospective cohort study of patients with CHD who underwent cardiopulmonary bypass at <2 years of age between January, 2012 and December, 2013 and had at least 2 years of follow-up. Clinical variables were extracted from a cardiac surgery database and hospital records. Seizures were defined as acute if they occurred within 7 days after an inciting event. Epilepsy was defined based on the International League Against Epilepsy criteria. RESULTS: Two-hundred and twenty-one patients were identified, 157 of whom were included in our analysis. Five patients (3.2%) developed epilepsy. Acute seizures occurred in 12 (7.7%) patients, only one of whom developed epilepsy. Predictors of epilepsy included an earlier gestational age, a lower birth weight, a greater number of cardiac surgeries, a need for extracorporeal membrane oxygenation or a left ventricular assist device, arterial ischaemic stroke, and a longer hospital length of stay. CONCLUSIONS: Epilepsy in children with CHD is rare. The mechanism of epileptogenesis in these patients may be the result of a complex interaction of patient-specific factors, some of which may be present even before surgery. Larger long-term follow-up studies are needed to identify risk factors associated with epilepsy in these patients.
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Isquemia Encefálica , Epilepsia , Cardiopatias Congênitas , Acidente Vascular Cerebral , Criança , Epilepsia/complicações , Epilepsia/epidemiologia , Cardiopatias Congênitas/complicações , Cardiopatias Congênitas/epidemiologia , Cardiopatias Congênitas/cirurgia , Humanos , Incidência , Lactente , Estudos Retrospectivos , Fatores de Risco , ConvulsõesRESUMO
Honey is a value-added product rich in several types of phenolic compounds, enzymes, and sugars recently explored in biomedical and food applications. Nevertheless, even though it has a low water activity (aW ≈ 0.65) that hinders the development of pathogenic and spoilage microorganisms, it is still prone to contamination by pathogenic microorganisms (vegetative and spores) and may constitute harm to special groups, particularly by immunosuppressed people and pregnant women. Thus, an efficient processing methodology needs to be followed to ensure microbial safety while avoiding 5-hydroxymethylfurfural (HMF) formation and browning reactions, with a consequent loss of biological value. In this paper, both thermal (pressure-assisted thermal processing, PATP) and nonthermal high-pressure processing (HPP), and another pressure-based methodology (hyperbaric storage, HS) were used to ascertain their potential to inactivate Bacillus subtilis endospores in honey and to study the influence of aW on the inactivation on this endospore. The results showed that PATP at 600 MPa/15 min/75 °C of diluted honey (52.9 °Brix) with increased aW (0.85 compared to ≈0.55, the usual honey aW) allowed for inactivating of at least 4.0 log units of B. subtilis spores (to below detection limits), while HS and HPP caused neither the germination nor inactivated spores (i.e., there was neither a loss of endospore resistance after heat shock nor endospore inactivation as a consequence of the storage methodology). PATP of undiluted honey even at harsh processing conditions (600 MPa/15 min/85 °C) did not impact the spore load. The results for diluted honey open the possibility of its decontamination by spores' inactivation for medical and pharmaceutical applications.
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Bacillus subtilis , Mel , Feminino , Temperatura Alta , Humanos , Preparações Farmacêuticas , Gravidez , Esporos Bacterianos , Açúcares , ÁguaRESUMO
In experimental tasks that involve stimuli that vary along a quantitative continuum, some choice biases are commonly found. Take, for instance, a matching-to-sample task where animals must, following the presentation of sample stimuli (that differ in duration), choose between two or more comparison stimuli. In tests where no sample is presented there is usually a bias towards the comparison that is correct following the shortest sample. To examine some aspects of these choice biases, pigeons were trained in a symbolic matching-to-sample task with two durations of keylight as samples, where key pecking had to be maintained during sample presentation. Firstly, even though animals were required to attend to the sample, a preference for the "short" comparison in no-sample testing was found. This result disproves an account where this effect was hypothesized to happen due to non-programmed learning resulting from the animals failing to attend to some trials. Secondly, even though a bias for "short" was found in both no-sample and delay testing, the extent of the biases differed between tasks, thus suggesting that forgetting the sample presented during a delay does not necessarily land the animal in a state similar to presenting no sample at all to begin with.
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Comportamento de Escolha , Columbidae , Animais , Aprendizagem por DiscriminaçãoRESUMO
From 2012, the preservation of food products under pressure has been increasingly studied and the knowledge acquired has enlarged since several food products have been studied at different storage conditions. This new food preservation methodology concept called Hyperbaric Storage (HS) has gain relevance due to its potential as a replacement or an improvement to the conventional cold storage processes, such as the traditional refrigeration (RF), or even frosting, from the energetic savings to the reduction of the carbon foot-print. Briefly, HS is capable to inhibit the microbial proliferation or its inactivation which results in the extension of the shelf-life of several food products when compared to RF. Moreover, the overall quality parameters seem not to be affected by HS, being the differences detected on samples over storage similar to lower when compared to the ones stored at RF. This review paper aims to gather data from all studies carried out so far regarding HS performance, mainly at room temperature on fruit juices, meat and fisheries, as well on dairy products and ready-to-eat meals. The HS advantages as a new food preservation methodology are presented and explained, being also discussed the industrial viability and environmental impact of this methodology, as well its limitations.
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Armazenamento de Alimentos , Refrigeração , Microbiologia de Alimentos , Conservação de Alimentos , Carne/análise , TemperaturaRESUMO
Embryo vitrification involves exposure to high concentrations of cryoprotectants and osmotic stress during cooling and warming in the cryopreservation process. Many of these factors can potentially affect gene expression. In this study, invitro-produced bovine embryos at the blastocyst stage were subjected to vitrification. Four recipients each were used for transferring non-vitrified (n=80) and vitrified (n=80) embryos. A total of 12 non-vitrified and 9 vitrified viable day-14 (D14) embryos were recovered by uterine flushing. RNA-seq analysis of the whole embryo or isolated trophectoderm (TE) from vitrified and fresh recovered D14 embryos revealed a total of 927 and 4376 genes with changed expression in embryos and TE isolates, respectively, as a result of vitrification. In addition, we found 671 and 61 genes commonly up- or downregulated in both vitrified whole embryos and TE. Commonly upregulated pathways by vitrification included epithelial adherens junctions, sirtuin signalling, germ cell-sertoli cell junction, ATM signalling, NER and protein ubiquitination pathways. The commonly downregulated pathways included EIF2 signalling, oxidative phosphorylation, mitochondrial dysfunction, regulation of eIF4 and p70S6K signalling and mTOR signalling pathways. Our analysis identified specific pathways and implicated specific gene expression patterns affecting embryo developmental competence that are important to cryopreservation.
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Blastocisto/metabolismo , Bovinos/embriologia , Criopreservação/veterinária , Expressão Gênica , Animais , Transferência Embrionária/veterinária , Embrião de Mamíferos/química , Embrião de Mamíferos/metabolismo , Desenvolvimento Embrionário/fisiologia , Feminino , Fertilização in vitro/veterinária , Regulação da Expressão Gênica no Desenvolvimento , Análise de Sequência de RNA , Transdução de Sinais/genéticaRESUMO
Honey is a natural product rich in several phenolic compounds, enzymes, and sugars with antioxidant, anticarcinogenic, anti-inflammatory, and antimicrobial potential. Indeed, the development of honey-based adhesives for wound care and other biomedical applications are topics being widely investigated over the years. Some of the advantages of the use of honey for wound-healing solutions are the acceleration of dermal repair and epithelialization, angiogenesis promotion, immune response promotion and the reduction in healing-related infections with pathogenic microorganisms. This paper reviews the main role of honey on the development of wound-healing-based applications, the main compounds responsible for the healing capacity, how the honey origin can influence the healing properties, also highlighting promising results in in vitro and in vivo trials. The challenges in the use of honey for wound healing are also covered and discussed. The delivery methodology (direct application, incorporated in fibrous membranes and hydrogels) is also presented and discussed.
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Mel , Cicatrização , Administração Tópica , Animais , Tecnologia Biomédica , Queimaduras/patologia , Humanos , Nanofibras/químicaRESUMO
BACKGROUND: Raw ewe's milk, as used to manufacture Serra da Estrela Protected Designation of Origin cheese, was pre-treated by high pressure processing (HPP), using previously optimized conditions (121 MPa for 30 min), aiming to evaluate its effect on milk technological properties for subsequent cheese production, namely the impact on resulting curd, whey and cheese throughout ripening. RESULTS: The cheese yield increased 10.4% as a result of milk pre-treated by HPP, which also yielded inactivation of beneficial microbial groups. After 60 days of ripening, both treated and control cheeses showed no significant differences (P ≥ 0.05) with respect to quantified microbial load or basic physicochemical quality parameters. CONCLUSION: HPP appears to be a promising non-thermal treatment for ewes' milk to inactivate contaminant bacteria but with no negative effect on lactic acid bacteria, which is very important for the unique characteristics of Serra da Estrela cheese. © 2020 Society of Chemical Industry.
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Queijo/análise , Manipulação de Alimentos/métodos , Leite/química , Animais , Feminino , Fermentação , Manipulação de Alimentos/instrumentação , Lactobacillales/crescimento & desenvolvimento , Lactobacillales/metabolismo , Leite/microbiologia , Pressão , OvinosRESUMO
Honey is a natural food of worldwide economic importance. Over the last decades, its potential for food, medical, cosmetical, and biotechnological applications has been widely explored. One of the major safety issues regarding such applications is its susceptibility to being contaminated with bacterial and fungi spores, including pathogenic ones, which may impose a hurdle to its consumption in a raw state. Another factor that makes this product particularly challenging relies on its high sugar content, which will lead to the formation of hydroxymethylfurfural (HMF) when heated (due to Maillard reactions). Moreover, honey's bioactivity is known to be affected when it goes through thermal processing due to its unstable and thermolabile components. Therefore, proper food processing methodologies are of utmost importance not only to ensure honey safety but also to provide a high-quality product with low content of HMF and preserved biological properties. As so, emerging food processing technologies have been employed to improve the safety and quality of raw honey, allowing, for example, to reduce/avoid the exposure time to high processing temperatures, with consequent impact on the formation of HMF. This review aims to gather the literature available regarding the use of conventional and emergent food processing technologies (both thermal and nonthermal food processing technologies) for honey decontamination, preservation/enhancement of honey biological activity, as well as the sensorial attributes.
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Mel , Bactérias , Manipulação de Alimentos , Mel/análise , Temperatura AltaRESUMO
With a better balance among good mechanical performance, high freedom of design, and low material and manufacturing cost, chopped carbon fiber chip reinforced sheet molding compound (SMC) composites show great potential in different engineering applications. In this paper, bending fatigue behaviors of SMC composites considering the heterogeneous fiber orientation distributions have been thoroughly investigated utilizing both experimental and computational methods. First, four-point bending fatigue tests are performed with designed SMC composites, and the local modulus is adopted as a metric to represent the local fiber orientation of two opposing sides. Interestingly, SMC composites with and without large discrepancy in local modulus of opposing sides show different fatigue behaviors. Interrupted tests are conducted to explore the bending fatigue failure mechanism, and the damage processes of valid specimens are also closely examined. We find that the fatigue failure of SMC composites under four-point bending is governed by crack propagation instead of crack initiation. Because of this, the heterogeneous local fiber orientations of both sides of the specimen influence fatigue life. The microstructure of the lower side shows a direct influence while that of the upper side also exhibiting influence which becomes more prominent for high cycle fatigue cases. Furthermore, a hybrid micro-macro computational model is proposed to efficiently study the cyclic bending behavior of SMC composites. The region of interest is reconstructed with a modified random sequential absorption algorithm to conserve all the microstructural details including the heterogeneous fiber orientation, while the rest of the regions are modeled as homogenized macro-scale continua. Combined with a framework to capture the progressive fatigue damage under cyclic bending, the bending fatigue behaviors of SMC composites are accurately captured by the hybrid computational model comparing with our experimental analysis.