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Almeida G, Magalhães R, Carneiro L, Santos I, Silva J, Ferreira V, Hogg T, Teixeira P. Foci of contamination of Listeria monocytogenes in different cheese processing plants. Int J Food Microbiol 2013; 167:303-9. [PMID: 24184608 DOI: 10.1016/j.ijfoodmicro.2013.09.006] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2013] [Revised: 09/14/2013] [Accepted: 09/16/2013] [Indexed: 12/14/2022]
Abstract
Listeria monocytogenes is a ubiquitous bacterium widely distributed in the environment that can cause a severe disease in humans when contaminated foods are ingested. Cheese has been implicated in sporadic cases and in outbreaks of listeriosis worldwide. Environmental contamination, in several occasions by persistent strains, has been considered an important source of finished product contamination. The objectives of this research were to (i) evaluate the presence of L. monocytogenes within the factory environments and cheeses of three processing plants, artisanal producer of raw ewe's milk cheeses (APC), small-scale industrial cheese producer (SSI) and industrial cheese producer (ICP) each producing a distinct style of cheese, all with history of contamination by L. monocytogenes (ii) and identify possible sources of contamination using different typing methods (arsenic and cadmium susceptibility, geno-serotyping, PFGE). The presence of markers specific for 3 epidemic clones (ECI-ECIII) of L. monocytogenes was also investigated. Samples were collected from raw milk (n = 179), whey (n = 3), cheese brining solution (n = 7), cheese brine sludge (n = 505), finished product (n = 3016), and environment (n = 2560) during, at least, a four-year period. Listeria monocytogenes was detected in environmental, raw milk and cheese samples, respectively, at 15.4%, 1.1% and 13.6% in APC; at 8.9%, 2.9% and 3.4% in SSI; and at 0%, 21.1% and 0.2% in ICP. Typing of isolates revealed that raw ewe's milk and the dairy plant environment are important sources of contamination, and that some strains persisted for at least four years in the environment. Although cheeses produced in the three plants investigated were never associated with any case or outbreak of listeriosis, some L. monocytogenes belonging to specific PFGE types that caused disease (including putative epidemic clone strains isolated from final products) were found in this study.
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Affiliation(s)
- G Almeida
- CBQF - Centro de Biotecnologia e Química Fina, Laboratório Associado, Escola Superior de Biotecnologia, Universidade Católica Portuguesa/Porto, Rua Dr. António Bernardino Almeida, 4200-072 Porto, Portugal
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Silva I, Campos FM, Hogg T, Couto JA. Wine phenolic compounds influence the production of volatile phenols by wine-related lactic acid bacteria. J Appl Microbiol 2011; 111:360-70. [PMID: 21575111 DOI: 10.1111/j.1365-2672.2011.05052.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
AIMS To evaluate the effect of wine phenolic compounds on the production of volatile phenols (4-vinylphenol [4VP] and 4-ethylphenol [4EP]) from the metabolism of p-coumaric acid by lactic acid bacteria (LAB). METHODS AND RESULTS Lactobacillus plantarum, Lactobacillus collinoides and Pediococcus pentosaceus were grown in MRS medium supplemented with p-coumaric acid, in the presence of different phenolic compounds: nonflavonoids (hydroxycinnamic and benzoic acids) and flavonoids (flavonols and flavanols). The inducibility of the enzymes involved in the p-coumaric acid metabolism was studied in resting cells. The hydroxycinnamic acids tested stimulated the capacity of LAB to synthesize volatile phenols. Growth in the presence of hydroxycinnamic acids, especially caffeic acid, induced the production of 4VP by resting cells. The hydroxybenzoic acids did not significantly affect the behaviour of the studied strains. Some of the flavonoids showed an effect on the production of volatile phenols, although strongly dependent on the bacterial species. Relatively high concentrations (1 g l(-1) ) of tannins inhibited the synthesis of 4VP by Lact. plantarum. CONCLUSIONS Hydroxycinnamic acids were the main compounds stimulating the production of volatile phenols by LAB. The results suggest that caffeic and ferulic acids induce the synthesis of the cinnamate decarboxylase involved in the metabolism of p-coumaric acid. On the other hand, tannins exert an inhibitory effect. SIGNIFICANCE AND IMPACT OF THE STUDY This study highlights the capacity of LAB to produce volatile phenols and that this activity is markedly influenced by the phenolic composition of the medium.
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Affiliation(s)
- I Silva
- CBQF/Escola Superior de Biotecnologia - Universidade Católica Portuguesa, Porto, Portugal
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Bach S, Bombinski T, Daniels M, Gross D, Hogg T, Martin T, McMurray D, Naber E, Perez N, Schulman A, Tucker S, Andera‐Cato S, Arnold A, Blumberg A, Bord M, Feiertag A, Greaves M, Her A, Kennedy E, Orozco C, Rice C, Rodgers A, Sauer A, Schubert J, Tubbs C, Wray T, Vogt G, Shrestha L, Hillard C. Of Mice and MAGL (Monoacylglycerol Lipase). FASEB J 2011. [DOI: 10.1096/fasebj.25.1_supplement.lb158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- S. Bach
- Brown Deer High SchoolMilwaukeeWI
| | | | | | - D. Gross
- Brown Deer High SchoolMilwaukeeWI
| | - T. Hogg
- Brown Deer High SchoolMilwaukeeWI
| | | | | | - E. Naber
- Brown Deer High SchoolMilwaukeeWI
| | - N. Perez
- Brown Deer High SchoolMilwaukeeWI
| | | | | | | | | | | | - M. Bord
- Brown Deer High SchoolMilwaukeeWI
| | | | | | - A. Her
- Brown Deer High SchoolMilwaukeeWI
| | | | | | - C. Rice
- Brown Deer High SchoolMilwaukeeWI
| | | | - A. Sauer
- Brown Deer High SchoolMilwaukeeWI
| | | | - C. Tubbs
- Brown Deer High SchoolMilwaukeeWI
| | - T. Wray
- Brown Deer High SchoolMilwaukeeWI
| | - G. Vogt
- Brown Deer High SchoolMilwaukeeWI
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Poças M, Oliveira J, Pereira J, Hogg T. Consumer exposure to phthalates from paper packaging: an integrated approach. Food Addit Contam Part A Chem Anal Control Expo Risk Assess 2010; 27:1451-9. [DOI: 10.1080/19440049.2010.490790] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Abstract
Phase transitions, similar to those seen in physical systems, are observed in spreading activation networks. Such networks are used both in theories of cognition and in artificial intelligence applications. This result confirms a predicted abrupt behavioral change as either the topology of the network or the activation parameters are varied across phase boundaries.
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Abstract
It is widely believed that a group of cooperating agents engaged in problem solving can solve a task faster than either a single agent or the same group of agents working in isolation from each other. Nevertheless, little is known about the quantitative improvements that result from cooperation. A number of experimental results are presented on constraint satisfaction that both test the predictions of a theory of cooperative problem solving and assess the value of cooperation for this class of problems. These experiments suggest an alternative methodology to existing techniques for solving constraint satisfaction problems in computer science and distributed artificial intelligence.
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Almeida G, Morvan A, Magalhães R, Santos I, Hogg T, Leclercq A, Teixeira P. Distribution and characterization of Listeria monocytogenes clinical isolates in Portugal, 1994-2007. Eur J Clin Microbiol Infect Dis 2010; 29:1219-27. [PMID: 20563829 DOI: 10.1007/s10096-010-0988-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2010] [Accepted: 05/29/2010] [Indexed: 10/19/2022]
Abstract
In recent years, the number of cases of listeriosis has increased worldwide. Ninety-five isolates of Listeria monocytogenes recovered from Portuguese human cases of listeriosis have been characterized by biotyping (cadmium and arsenic sensitivity), polymerase chain reaction (PCR) grouping, and by pulsed-field gel electrophoresis (PFGE) applying the enzymes AscI and ApaI. Isolates were classified into one of three PCR groups; IVb (71.6%), IIb (17.9%), and IIa (10.5%). Four biotypes were differentiated: sensitive to arsenic/cadmium (48.4%), arsenic-sensitive and cadmium-resistant (25.3%), resistant to arsenic and sensitive to cadmium (18.9%), and resistant to both heavy metals (7.4%). Combined analyses of AscI and ApaI patterns yielded a total of 58 PFGE types with five sets (G, Jb, KKa, Me, and U) of Portuguese strains, each of which were indistinguishable by PFGE typing. In the present study, it was demonstrated that there are recurrent pulsotypes and that some were the same pulsotypes linked to outbreaks in France. In addition, there are some pulsotypes spread throughout the country, while others only appear in a restricted region. This study allowed the assembly of a first large pulsotype database of Portuguese clinical strains.
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Affiliation(s)
- G Almeida
- Centro de Biotecnologia e Química Fina, Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Rua Dr António Bernardino de Almeida, 4200-072 Porto, Portugal
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Albano H, Henriques I, Correia A, Hogg T, Teixeira P. Characterization of microbial population of 'Alheira' (a traditional Portuguese fermented sausage) by PCR-DGGE and traditional cultural microbiological methods. J Appl Microbiol 2009; 105:2187-94. [PMID: 19120664 DOI: 10.1111/j.1365-2672.2008.03947.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
AIMS This study evaluates the microbial ecology of 'Alheira' by traditional microbiological analysis and a PCR-denaturing gradient gel electrophoresis (DGGE) protocol. METHODS AND RESULTS Total microbial DNA from 'Alheiras' was extracted directly from the products and subjected to PCR using Eubacterial primers for 16S rDNA. The amplicons were separated by DGGE. The results demonstrated that different products of the same batch display identical profiles, whereas products from different batches of the same producer could display different DGGE profiles. 'Alheiras' from different producers were distinguishable based on the respective DGGE profiles. The obtained sequences from prevalent phylotypes affiliated with order Lactobacillales and order Bacillales and class Gammaproteobacteria. The same samples were subjected to traditional microbiological analysis. In both methods, lactic acid bacteria were dominant and were present together with other organisms, mainly members of the family Micrococcaceae. CONCLUSIONS The approach explored in this study allowed the description of the microbial community present in 'Alheira' in particular the diversity of lactic acid bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY This can be useful for the microbiological characterization of traditional products in order to develop new methods of quality control capable of supporting a standardization of the processes, while preserving their typical traits.
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Affiliation(s)
- H Albano
- Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Porto, Portugal
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Poças M, Oliveira J, Pinto H, Zacarias M, Hogg T. Characterization of patterns of food packaging usage in Portuguese homes. Food Addit Contam Part A Chem Anal Control Expo Risk Assess 2009. [DOI: 10.1080/02652030903046690] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Ferreira V, Barbosa J, Silva J, Gibbs P, Hogg T, Teixeira P. Microbiological profile of Salpicão de Vinhais and Chouriça de Vinhais from raw materials to final products: Traditional dry sausages produced in the North of Portugal. INNOV FOOD SCI EMERG 2009. [DOI: 10.1016/j.ifset.2008.11.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Couto J, Rozès N, Hogg T. Ethanol-induced changes in the fatty acid composition ofLactobacillus hilgardii, its effects on plasma membrane fluidity and relationship with ethanol tolerance. ACTA ACUST UNITED AC 2008. [DOI: 10.1111/j.1365-2672.1996.tb04489.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Felício MTS, Hogg T, Gibbs P, Teixeira P, Wiedmann M. Recurrent and sporadic Listeria monocytogenes contamination in alheiras represents considerable diversity, including virulence-attenuated isolates. Appl Environ Microbiol 2007; 73:3887-95. [PMID: 17449681 PMCID: PMC1932748 DOI: 10.1128/aem.02912-06] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Microbiological characterization of alheiras, traditional smoked meat sausages produced in northern Portugal, had previously shown that more than 60% of the lots analyzed were contaminated with Listeria monocytogenes at levels higher than 100 CFU/g. In order to better understand L. monocytogenes contamination patterns in alheiras, we characterized 128 L. monocytogenes isolates from alheiras using a variety of subtyping techniques (i.e., molecular serotyping; arsenic, cadmium, and tetracycline resistance typing; and pulsed-field gel electrophoresis [PFGE]). Subtyping of isolates from products collected on two separate dates provided evidence for the persistence of specific L. monocytogenes PFGE types in the production and distribution chains of alheiras from four different processors. A subset of 21 isolates was further characterized using ribotyping and Caco-2 cell invasion assays to evaluate the pathogenic potential of L. monocytogenes present in alheiras. Caco-2 invasion assays revealed seven isolates with invasion efficiencies that were less than 20% of that of the control strain 10403S. All seven isolates had premature stop codons in inlA that represented three distinct mutations, which had previously been observed in isolates from the United States or France. Our findings indicate the need for a comprehensive approach to control L. monocytogenes in alheiras, including strategies to reduce persistence. The presence of considerable diversity in invasion phenotypes among L. monocytogenes strains present in alheiras, including the presence of subtypes likely to be virulence attenuated, may provide an opportunity to initially focus control strategies on the subtypes most likely to cause human disease.
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Affiliation(s)
- M T S Felício
- Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Porto, Portugal
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Nagarajan K, Hogg T, Herzberg S, Wecke M, Blohmke C, Schmidt C, Hilgenfeld R. Structural analysis of the Plasmodium falciparumcysteine protease falcipain-2. Acta Crystallogr A 2006. [DOI: 10.1107/s0108767306096930] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Pérez-Nevado F, Albergaria H, Hogg T, Girio F. Cellular death of two non-Saccharomyces wine-related yeasts during mixed fermentations with Saccharomyces cerevisiae. Int J Food Microbiol 2006; 108:336-45. [PMID: 16564103 DOI: 10.1016/j.ijfoodmicro.2005.12.012] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2005] [Revised: 09/05/2005] [Accepted: 12/10/2005] [Indexed: 10/24/2022]
Abstract
The early death of two non-Saccharomyces wine strains (H. guilliermondii and H. uvarum) during mixed fermentations with S. cerevisiae was studied under enological growth conditions. Several microvinifications were performed in synthetic grape juice, either with single non-Saccharomyces or with mixed S. cerevisiae/non-Saccharomyces inocula. In all mixed cultures, non-Saccharomyces yeasts grew together with S. cerevisiae during the first 1-3 days (depending on the initial inoculum concentration) and then, suddenly, non-Saccharomyces cells began to die off, regardless of the ethanol concentrations present. Conversely, in both non-Saccharomyces single cultures the number of viable cells remained high (ranging 10(7)-10(8) CFU ml(-1)) even when cultures reached significant ethanol concentrations (up to 60-70 g l(-1)). Thus, at least for these yeast strains, it seems that ethanol is not the main death-inducing factor. Furthermore, mixed cultures performed with different S. cerevisiae/ H. guilliermondii inoculum ratios (3:1; 1:2; 1:10; 1:100) revealed that H. guilliermondii death increases for higher inoculum ratios. In order to investigate if the nature of the yeast-yeast interaction was related or not with a cell-cell contact-mediated mechanism, cell-free supernatants obtained from 3 and 6 day-old mixed cultures were inoculated with H. guilliermondii pure cultures. Under these conditions, cells still died and much higher death rates were found for the 6 days than for the 3 day-old supernatants. This strongly indicates that one or more toxic compounds produced by S. cerevisiae triggers the early death of the H. guilliermondii cells in mixed cultures with S. cerevisiae. Finally, although it has not been yet possible to identify the nature of the toxic compounds involved in this phenomenon we must emphasise that the S. cerevisiae strain used in the present work is killer sensitive with respect to the classical killer toxins, K1, K2 and K28, whereas the H. guilliermondii and H. uvarum strains are killer neutral.
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Affiliation(s)
- F Pérez-Nevado
- Area de Nutrición y Bromatología, Departamento de Zootecnia, Univ. de Extremadura, Badajoz, Spain
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Abstract
AIMS The development of a simple and reliable procedure, compatible with routine use in wineries, for the presumptive detection of Brettanomyces/Dekkera from wine and wine-environment samples. METHODS AND RESULTS The method of detection of these yeasts employs a selective enrichment medium. The medium contains glucose (10 g l(-1)) as carbon and energy source, cycloheximide (20 mg l(-1)) to prevent growth of Saccharomyces, chloramphenicol (200 mg l(-1)) to prevent growth of bacteria and p-coumaric acid (20 mg l(-1)) as the precursor for the production of 4-ethyl-phenol. After the inoculation with wine, the medium is monitored by visual inspection of turbidity and by periodic olfactive analysis. Contaminated wines will develop visible turbidity in the medium and will produce the 4-ethyl-phenol off-odour, which can be easily detected by smelling. CONCLUSIONS A selective enrichment liquid medium was developed to differentially promote the growth and activity of Brettanomyces/Dekkera. The method is simple to execute, employing a simple-to-prepare medium and a periodic olfactive detection. SIGNIFICANCE AND IMPACT OF THE STUDY The characteristics of the procedure make it particularly applicable in a wine-making environment thus presenting important advantages to the wine industry.
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Affiliation(s)
- J A Couto
- Escola Superior de Biotecnologia, Universidade Católica Portuguesa, R. Dr António Bernardino de Almeida, Porto.
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Oliveira C, Silva Ferreira AC, Mendes Pinto M, Hogg T, Alves F, Guedes de Pinho P. Carotenoid compounds in grapes and their relationship to plant water status. J Agric Food Chem 2003; 51:5967-5971. [PMID: 13129303 DOI: 10.1021/jf034275k] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The aim of this work was to study the relationship between carotenoid contents in grapevine berries and plant water status. For this purpose, a black grapevine variety, Vitis vinifera L. cv. Touriga Nacional, was studied. The experiments were carried out in the same Douro vineyards, with plants of the same age, in two different water retention soils. A higher water retention capacity soil, soil A, and a lower water retention capacity soil, soil B, were both in a 1.2 m deep silt-loam schist-derived soil. The training system was the double cordon trained and spur pruned. A first range was nonirrigated (NI) and a second one was irrigated (I), 60% of evapotranspiration (ET(0)). For soil B, a 30% of ET(0) treatment was also applied. The plant water status was estimated by predawn leaf water potential. The effects of plant water status on berry growth were studied by measurement of the berry weight and total soluble solids (degrees Brix). The carotenoid profile was quantitatively determined by high-performance liquid chromatography/diode array. Carotenoids determined were beta-carotene, lutein, neoxanthin, violaxanthin, and luteoxanthin. The comparison between irrigated and nonirrigated grapes was followed from 2 weeks before veraison until the ripe stage. Results showed that at harvest time, berries exposed to the NI had a lower weight than those exposed to the irrigated treatment (60% of ET(0)), 0.89 vs 1.36 g/berry and 0.94 vs 1.34 g/berry, for soils A and B, respectively. The irrigated treatment contributed to a higher sugar concentration in both soils. However, depending on the soil water retention capacity, the carotenoid contents were different in soils A and B. For soil A, the total carotenoid content was similar for both NI and I treatments. However, with regard to soil B, in irrigated treatment, levels of carotenoids were approximately 60% lower than those found for the NI. It seems to be possible to produce higher weight berries (with higher sugar levels) with similar carotenoid contents. On the other hand, soil characteristics had a larger influence than irrigation on the concentration of carotenoids in grapes, resulting in an important viticultural parameter to take into account in aroma precursor formation.
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Affiliation(s)
- C Oliveira
- Escola Superior de Biotecnologia, Universidade Católica Portuguesa, R. Dr. António Bernardino de Almeida, 4200-072 Porto, Portugal
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Silva Ferreira AC, Oliveira C, Hogg T, Guedes de Pinho P. Relationship between potentiometric measurements, sensorial analysis, and some substances responsible for aroma degradation of white wines. J Agric Food Chem 2003; 51:4668-4672. [PMID: 14705894 DOI: 10.1021/jf034217z] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Oxidative degradation of white wines can be described sensorially as developing from a loss at positive aroma characteristics, through the development of negative aromas to a linel stage of chromatic alterations. This work attempts to relate the oxidation "status" evaluate by potentiometric titrations, with sensorial degradation and the levels of substances responsible for "off-flavors", such as methional and phenylacetaldehyde. The potentiometric titration employed measures the most powerful antioxidants of white wines (e.g., those which more rapidly consume oxygen). Considering that aromatic precedes chromatic degradation, resistance to oxidation (ROX) constitutes a useful indicator of resistance to oxidation. Sensorial degradation (ID), potentiometric measures, and volatiles were determined both in samples submitted to a "forced aging" protocol and normal aged white wines. High correlation values were observed between ROX and the ID, in both sets (r > 0.87). ID is better explained by ROX values than by the indicated wine age or by the "degree of browning" (Abs = 420 nm). It was also observed that in samples with ROX values higher than 10, the concentration of methional and phenylacetaldehyde were above their respective odor threshold. Finally, it was observed that there is a relationship between oxygen consumption and the respective ROX. Although these results seem very promising, they needed to be further complemented in order to estimate the shelf life of a white wine using potentiometric titrations.
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Affiliation(s)
- A C Silva Ferreira
- Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Rua Dr. Bernardino de Almeida, 4200-072 Porto, Portugal.
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Moreira N, Mendes F, Pereira O, Guedes de Pinho P, Hogg T, Vasconcelos I. Volatile sulphur compounds in wines related to yeast metabolism and nitrogen composition of grape musts. Anal Chim Acta 2002. [DOI: 10.1016/s0003-2670(01)01618-x] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Azevedo Z, Couto JA, Hogg T. Citrulline as the main precursor of ethyl carbamate in model fortified wines inoculated with Lactobacillus hilgardii: a marker of the levels in a spoiled fortified wine. Lett Appl Microbiol 2002; 34:32-6. [PMID: 11849489 DOI: 10.1046/j.1472-765x.2002.01045.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
AIMS The aim of this study was to investigate the production of ethyl carbamate (EC) precursors by Lactobacillus hilgardii in model and Douro fortified wines and to determine the relationship between these compounds and EC levels in this type of wine. METHODS AND RESULTS Several model fortified wines and fortified wine inoculated with L. hilgardii were analysed for citrulline and EC formation. A good correlation (R > 0.9) was obtained between citrulline and potential EC (that EC which is formed during heating of sample at 80 degrees C for 48 h). CONCLUSIONS This correlation allowed us to calculate the potential EC formed during lactic acid bacteria activity in fortified wine. SIGNIFICANCE AND IMPACT OF THE STUDY A good correlation was obtained (R=0.92) between measured and calculated EC in spoiled fortified wines, citrulline apparently being the main EC precursor produced by Lact. hilgardii thus contributing to the potential EC in this type of wine.
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Affiliation(s)
- Z Azevedo
- Departamento de Química da Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal
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Abstract
Since the pioneering discovery of the inhibitory effects of kirromycin on bacterial elongation factor Tu (EF-Tu) more than 25 years ago [1], a great wealth of biological data has accumulated concerning protein biosynthesis inhibitors specific for EF-Tu. With the subsequent discovery of over two dozen naturally occurring EF-Tu inhibitors belonging to four different subclasses, EF-Tu has blossomed into an appealing antimicrobial target for rational drug discovery efforts. Very recently, independent crystal structure determinations of EF-Tu in complex with two potent antibiotics, aurodox and GE2270A, have provided structural explanations for the mode of action of these two compounds, and have set the foundation for the design of inhibitors with higher bioavailability, broader spectra, and greater efficacy.
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Affiliation(s)
- T Hogg
- Department of Structural Biology and Crystallography, Institute of Molecular Biotechnology, Beutenbergstrasse 11, D-07745 Jena, Germany
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Couto JA, Hogg T. Evaluation of a commercial fluorochromic system for the rapid detection and estimation of wine lactic acid bacteria by DEFT. Lett Appl Microbiol 2002. [DOI: 10.1046/j.1365-2672.1999.00477.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- J. A. Couto
- Escola Superior de Biotecnologia, Universidade Cato´lica Portuguesa, Porto, Portugal
| | - T. Hogg
- Escola Superior de Biotecnologia, Universidade Cato´lica Portuguesa, Porto, Portugal
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Abstract
Quantum computation holds promise for the solution of many intractable problems. However, since many quantum algorithms are stochastic in nature they can find the solution of hard problems only probabilistically. Thus the efficiency of the algorithms has to be characterized by both the expected time to completion and the associated variance. In order to minimize both the running time and its uncertainty, we show that portfolios of quantum algorithms analogous to those of finance can outperform single algorithms when applied to the NP-complete problems such as 3-satisfiability.
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Affiliation(s)
- S M Maurer
- Physics Department, Stanford University, Stanford, California 94043, USA
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Rau A, Hogg T, Marquardt R, Hilgenfeld R. A new lysozyme fold. Crystal structure of the muramidase from Streptomyces coelicolor at 1.65 A resolution. J Biol Chem 2001; 276:31994-9. [PMID: 11427528 DOI: 10.1074/jbc.m102591200] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cellosyl is a bacterial muramidase from Streptomyces coelicolor. Similar to other lysozymes, the enzyme cleaves the beta-1,4-glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine units, but it also exhibits a beta-1,4-N,6-O-diacetylmuramidase activity. The latter enables Cellosyl to degrade the cell walls of Staphylococcus aureus, which are not hydrolyzed by chicken-, goose-, or bacteriophage T4-type lysozymes. The enzymatic activity and amino acid sequence of Cellosyl group it with lysozymes of the Chalaropsis type, for which no detailed structural information has been available so far. The crystal structure of Cellosyl from S. coelicolor has been determined to a resolution of 1.65 A and refined to an R-factor of 15.2%. The enzyme is comprised of a single domain and possesses an unusual beta/alpha-barrel fold. The last strand, beta 8, of the (beta/alpha)(5)beta(3)-barrel is found to be antiparallel to strands beta 7 and beta 1. Asp-9, Asp-98, and Glu-100 are located at the active site. The structure of Cellosyl exhibits a new lysozyme fold and represents a new class of polysaccharide-hydrolyzing beta/alpha-barrels.
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Affiliation(s)
- A Rau
- Department of Structural Biology & Crystallography, Institute of Molecular Biotechnology, Beutenbergstrasse 11, 07745 Jena, Germany
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24
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Abstract
A previously developed quantum search algorithm for solving 1-SAT problems in a single step is generalized to apply to a range of highly constrained k-SAT problems. We identify a bound on the number of clauses in satisfiability problems for which the generalized algorithm can find a solution in a constant number of steps as the number of variables increases. This performance contrasts with the linear growth in the number of steps required by the best classical algorithms, and the exponential number required by classical and quantum methods that ignore the problem structure. In some cases, the algorithm can also guarantee that insoluble problems in fact have no solutions, unlike previously proposed quantum search algorithms.
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Abstract
The easy-hard-easy pattern in the difficulty of combinatorial search problems as constraints are added has been explained as due to a competition between the decrease in number of solutions and increased pruning. We test the generality of this explanation by examining one of its predictions: if the number of solutions is held fixed by the choice of problems, then increased pruning should lead to a monotonic decrease in search cost. Instead, we find the easy-hard-easy pattern in median search cost even when the number of solutions is held constant, for some search methods. This generalizes previous observations of this pattern and shows that the existing theory does not explain the full range of the peak in search cost. In these cases the pattern appears to be due to changes in the size of the minimal unsolvable subproblems, rather than changing numbers of solutions.
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Hogg T, Armstrong V, Brown B. The importance of good record-keeping. Nurs Times 1997; 93:52-3. [PMID: 9146297] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
When large numbers of health care staff from different professional groups are involved in the care of individual clients, the need for simple, understandable, uniform casenotes becomes paramount. This article describes how a survey of the different casenotes used by various CPN teams led to the devising of a new system. The aim was to encourage good practice and develop a standardised record-keeping system.
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Affiliation(s)
- T Hogg
- Northumberland Mental Health NHS Trust
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27
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Abstract
A general method for combining existing algorithms into new programs that are unequivocally preferable to any of the component algorithms is presented. This method, based on notions of risk in economics, offers a computational portfolio design procedure that can be used for a wide range of problems. Tested by solving a canonical NP-complete problem, the method can be used for problems ranging from the combinatorics of DNA sequencing to the completion of tasks in environments with resource contention, such as the World Wide Web.
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Affiliation(s)
- BA Huberman
- Dynamics of Computation Group, Xerox Palo Alto Research Center, Palo Alto, CA 94304, USA
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28
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Abstract
We introduce an algorithm for combinatorial search on quantum computers that is capable of significantly concentrating amplitude into solutions for some NP search problems, on average. This is done by exploiting the same aspects of problem structure as used by classical backtrack methods to avoid unproductive search choices. This quantum algorithm is much more likely to find solutions than the simple direct use of quantum parallelism. Furthermore, empirical evaluation on small problems shows this quantum algorithm displays the same phase transition behavior, and at the same location, as seen in many previously studied classical search methods. Specifically, difficult problem instances are concentrated near the abrupt change from underconstrained to overconstrained problems.
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Revel G, Capela AB, Hogg T. A pre-spoilage marker for bacterial activity in fortified wine, conversion of L-malic acid to L-lactic acid. Lett Appl Microbiol 1994. [DOI: 10.1111/j.1472-765x.1994.tb00881.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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32
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Abstract
Stability criteria and phase boundaries for complex ecosystems are obtained and contrasted with previously studied scenarios. The stability of such systems is determined by the behaviour of the largest eigenvalue of matrices governing the response of the system to small perturbations. As a result we show that ecosystems with unstructured cooperative interactions between arbitary species can be less stable than had been previously determined. We also examine hierarchical ecologies, and demonstrate their increased stability under certain conditions.
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Affiliation(s)
- T Hogg
- Xerox Palo Alto Research Center, California 94304
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Abstract
Numerous human learning phenomena have been observed and captured by individual laws, but no unified theory of learning has succeeded in accounting for these observations. A theory and model are proposed that account for two of these phenomena: the power law of practice and the problem-solving fan-effect. The power law of practice states that the speed of performance of a task will improve as a power of the number of times that the task is performed. The power law resulting from two sorts of problem-solving changes, addition of operators to the problem-space graph and alterations in the decision procedure used to decide which operator to apply at a particular state, is empirically demonstrated. The model provides an analytic account for both of these sources of the power law. The model also predicts a problem-solving fan-effect, slowdown during practice caused by an increase in the difficulty of making useful decisions between possible paths, which is also found empirically.
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Bernstein AD, Alexandersson M, Benedek M, Bond EL, Eller D, Flink R, Hogg T, Huntley S, Irnich W, Miyoshi A. Report of the policy conference on computer communications in pacing sponsored by the North American Society of Pacing and Electrophysiology. October 13, 1987. Pacing Clin Electrophysiol 1988; 11:784-8. [PMID: 2456559 DOI: 10.1111/j.1540-8159.1988.tb06029.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- A D Bernstein
- Department of Surgery, Newark Beth Israel Medical Center, N.J. 07112
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Hogg T, Huberman BA. Attractors on finite sets: The dissipative dynamics of computing structures. Phys Rev A Gen Phys 1985; 32:2338-2346. [PMID: 9896348 DOI: 10.1103/physreva.32.2338] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Abstract
We experimentally examine the consequences of the hypothesis that the brain operates reliably, even though individual components may intermittently fail, by computing with dynamical attractors. Specifically, such a mechanism exploits dynamic collective behavior of a system with attractive fixed points in its phase space. In contrast to the usual methods of reliable computation involving a large number of redundant elements, this technique of self-repair only requires collective computation with a few units, and it is amenable to quantitative investigation. Experiments on parallel computing arrays show that this mechanism leads naturally to rapid self-repair, adaptation to the environment, recognition and discrimination of fuzzy inputs, and conditional learning, properties that are commonly associated with biological computation.
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Hoets JWVR, Colquhoun J, Wilson NP, Hogg T, Woodward JJ. Section of Orthopaedics and Physical Medicine. Med J Aust 1952. [DOI: 10.5694/j.1326-5377.1952.tb81977.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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