We discuss the p- and hp-versions of the virtual element method for the approximation of eigenpairs of elliptic operators with a potential term on polygonal meshes. An application of this model is ...provided by the Schrödinger equation with a pseudo-potential term. As an interesting byproduct, we present for the first time in literature an explicit construction of the stabilization of the mass matrix. We present in detail the analysis of the p-version of the method, proving exponential convergence in the case of analytic eigenfunctions. The theoretical results are supplied with a wide set of experiments. We also show numerically that, in the case of eigenfunctions with finite Sobolev regularity, an exponential approximation of the eigenvalues in terms of the cubic root of the number of degrees of freedom can be obtained by employing hp-refinements. Importantly, the geometric flexibility of polygonal meshes is exploited in the construction of the hp-spaces.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Cinnamon essential oil (CEO) was encapsulated in chitosan nanoparticles.•Encapsulated and free CEO reduced greatly microbial population and lipid oxidation.•Red color stability was more pronounced ...in patties containing encapsulated CEO.•Sustained release of CEO maintains its preservative effects until end of storage.•PCA could clearly discriminate different formulations of beef patties.
In this study cinnamon essential oil-incorporated chitosan nanoparticles (CEO-CSNPs) were produced by an emulsion-gelation method. Size, zeta potential and polydispersity index of the formed nanoparticles were 235.6nm, 25.1mV and 0.33, respectively. In vitro release evaluation showed an initial burst effect, followed by a slow CEO release during 104h (at pH∼5). Different formulations of patties including control, samples containing free and encapsulated CEO and ascorbic acid were analyzed for physicochemical characteristics, microbial growth and sensorial attributes during 8days of storage at 4°C. Both free and encapsulated CEO decreased the microbial population of patties compared to the control (p<0.05) throughout the experiment. On the 8th day, the best formulations in TBARS test were AA-0.05 (0.05% of ascorbic acid) and 0.1-EN-CEO (0.1% of encapsulated CEO). During storage, the color parameters of the patties containing encapsulated CEO changed slightly whereas color and metmyoglobin content significantly decreased in samples containing free CEO and control. Free CEO had an unfavorable impact on color and odor but the incorporation of encapsulated CEO improved the consumer acceptability. The principle component analysis clearly distinguished 6 formulation groups based on physicochemical characteristics.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In long-ripened cheese, flavor formation occurs during ripening. The metabolism of lactic acid bacteria (LAB) leads to the production of different compounds that contribute to the flavor of cheese. ...The contribution of LAB to the formation of cheese flavor has previously been studied. However, the specific nonstarter LAB (NSLAB) metabolic reactions in ripened cheese that lead to the formation of flavor compounds remain unclear. In ripened cheese, the nutrient sources available include small peptides or amino acids, citrate, lactate, free fatty acids, and starter LAB cell lysis products. Thus, the aim of this study was to evaluate the ability of NSLAB to produce volatile flavor compounds by using an in vitro system that used only the nutrients available in ripened cheese as the energy source. Moreover, the potential contribution of the NSLAB volatilome on total cheese flavor is discussed. For this purpose, the production of volatile compounds on cheese-based medium (CBM) and on starter LAB lysed cell medium (LCM) by 2 Lactobacillus casei and 2 Lactobacillus rhamnosus strains, previously isolated from ripened Parmigiano Reggiano cheese, was investigated. The generated volatile compounds were analyzed with head-space gas chromatography mass spectrometry. Overall, ketones, aldehydes, alcohols, and acids were the most abundant compounds produced. Differences in volatilome production were found between NSLAB grown in LCM and CBM. The catabolic metabolism of amino acids and fatty acids were required for NSLAB growth on LCM. Conversely, pyruvate metabolism was the main catabolic pathway that supported growth of NSLAB in CBM. This study can be considered a first step toward a better understanding of how microbiota involved in the long ripening of cheese may contribute to the development of cheese flavor.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The aim of this study was the evaluation of the effects of pure citral and citron essential oil on microbial spoilage and growth and survival of pathogenic microorganisms during storage. They were ...added in the syrup of industrial ready‐to‐eat fruit salads stored at 9 °C. Both citral (25 to 125 ppm) and citron essential oil (300, 600, 900 ppm) were able to prolong the microbial shelf life of the fruit‐based salads. The essential oil gave excellent results, avoiding the undesirable effects attributable to the cytotoxicity of citral. Citron essential oil doubled the time needed for the wild microflora to reach concentrations able to produce a perceivable spoilage in condition of thermal abuse (9 °C). The same essential oil had reduced effects on the survival of Gram‐negative species Salmonella Enteritidis and Escherichia coli, but showed a strong inhibition toward the Gram‐positive pathogen Listeria monocytogenes.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Aims
The tyraminogenic potential of the strains Enterococcus faecalis EF37 and ATCC 29212 was investigated in a synthetic medium containing defined amounts of tyrosine and phenylalanine at different ...temperatures.
Methods and Results
Enterococci growth and the production of biogenic amines (BA) were evaluated in relation to their pre‐growth in medium containing tyrosine. Significant differences between the two strains were evidenced at metabolic level. Both the pre‐adapted strains grew faster in all the tested conditions, independently of the presence of the precursor. Temperatures of 30 and 40°C positively affected the growth parameters. The tyrosine decarboxylase (tyrDC) activity of the strain EF37 was positively affected by pre‐adaptation, while ATCC 29212 showed a faster and higher tyramine accumulation with not‐adapted cells. The expression analysis of the gene tyrDC confirmed the influence of the growth conditions on gene transcription.
Conclusions
The small differences found between the two strains in the maximum transcript level reached rapidly after the inoculum and the different behaviour in the tyramine accumulation suggested the possible involvement of complex regulation mechanisms on the tyrDC or on the membrane transport systems, which could affect the different BA accumulation trend.
Significance and Impact of the Study
This study gives deeper insight into the metabolic regulation of tyrDC activity of enterococci.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
In this paper we discuss the stability of some Stokes finite elements. In particular, we consider a modification of Hood–Taylor and Bercovier–Pironneau schemes which consists in adding piecewise ...constant functions to the pressure space. This enhancement, which had been already used in the literature, is driven by the goal of achieving an improved mass conservation at element level. The main result consists in proving the inf-sup condition for the enhanced spaces in a general setting and to present some numerical tests which confirm the stability properties. The improvement in the local mass conservation is shown in a forthcoming paper (Boffi et al. In: Papadrakakis, M., Onate, E., Schrefler, B. (eds.) Coupled Problems 2011. Computational Methods for Coupled Problems in Science and Engineering IV, Cimne,
2011
) where the presented schemes are used for the solution of a fluid-structure interaction problem.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Minimally processed fruits are an important area of potential growth in rapidly expanding fresh cut produce. However, the degree of safety obtained with the currently applied preservation methods ...seems to be not sufficient. The interest in the possible use of natural compounds to prevent microbial growth has notably increased in response to the consumer pressure to reduce or eliminate chemically synthesized additives in foods. The aim of this work is to give an overview on the application of natural compounds, such as hexanal, 2-(E)-hexenal, hexyl acetate and citrus essential oils, to improve the shelf-life and the safety of minimally processed fruits as well as their mechanisms of action.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The aim of this work was to assess if a sub-lethal high pressure homogenization (HPH) treatment could modulate in vitro functional and biological properties of probiotic bacteria. Lactobacillus ...paracasei A13, Lactobacillus acidophilus 08 and Dru, Lactobacillus delbrueckii subsp. lactis 200 and bile-resistant derivatives L. acidophilus Dru+ and L. delbrueckii subsp. lactis 200+ were suspended in phosphate buffered saline solution and treated at 50 MPa. Data obtained showed that HPH can modulate hydrophobicity and auto-aggregation without modification of viability and decarboxylase activity. Resistance to simulated gastric conditions resulted strain-dependent. High resistance was observed for treated L. paracasei A13, L. acidophilus Dru and 08 and L. delbrueckii subsp. lactis 200. The HPH-treatment reduced the resistance to simulated stomach duodenum-passage of L. acidophilus Dru while increased it for L. paracasei A13.
Strain viability and resistance to simulated gastric conditions were evaluated treating at 50 MPa cells suspended in acidified buttermilk (pH 4.6) and stored at 4 °C for 30 days. The highest cell viability loss, after 30 d of refrigerated storage, was observed for L. acidophilus Dru, independently of the application of HPH. However, after 30 days of storage, the resistance of L. paracasei A13 to simulated gastric digestion significantly increased in HPH treated cells.
•HPH treatments could increase some functional characteristics of LAB endowed with in vitro functional properties.•The response to HPH varied according to the characteristics of individual strains.•HPH effect was affected also by the time of storage and media containing strains.•HPH could be exploited to improve the quality and functionality of probiotic foods.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Aims
To evaluate the effect of cultivation (anaerobiosis vs respiration) and Tween 80 supplementation on the production of metabolites and on the composition of membrane fatty acids (FAs) in ...Lactobacillus casei N87.
Methods and Results
Anaerobic and respiratory growth, with or without Tween 80 supplementation, was carried out in a chemically defined medium. Production of biomass, organic acids, volatile organic compounds (VOCs), consumption of amino acids and changes in membrane FAs were investigated.
Respiration altered the central metabolism rerouting pyruvate away from lactate accumulation, while Tween 80 had a minor effect on metabolic pathways. VOCs were mainly affected by growth conditions and significant amounts of diacetyl were produced by respiratory cultures. Respiration increased desaturation of membrane lipids and Tween 80 improved the production of essential polyunsaturated FAs. Palmitic acid decreased in Tween‐supplemented aerated cultures.
Conclusions
Combination of Tween 80 and respiratory growth promoted production of biomass and aroma compounds and affected the composition of membrane FAs in Lact. casei N87.
Significance and Impact of the Study
Respiration might be exploited in Lact. casei as a natural strategy for the enhanced production of aroma compounds.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
High‐pressure homogenization (HPH) has been proposed to be applied directly to lactic acid bacterial cells at sublethal levels to enhance some functional properties. As the principal target of HPH ...are the cell surface envelope structures, the aim of this work was to study the effect of a HPH treatment, applied at 50 MPa, on cell membrane stress responses of already‐known functional strains, isolated from Argentinean products. Specifically, the membrane fatty acid composition of cells before and after the sublethal treatment was investigated, and the results showed that plasma membranes, their level of unsaturation and their composition are involved in response mechanisms adopted by microbial cells when subjected to a sublethal HPH stress. In fact, the data obtained demonstrated that the treatment was able to modify the fatty acid profile of the different strains, although a uniform response was not observed. Further studies are necessary both to elucidate the role of each fatty acid in the cell response mechanisms and to clarify the changes in membrane compositions induced by HPH treatment also in relation to the applicative potential of this technique.
Significance and Impact of the Study
This study contributed to understand the response mechanisms activated in cells exposed to pressure stress. It has been demonstrated that high‐pressure homogenization (HPH) treatments, conducted at sublethal levels, could increase some important functional and technological characteristics of nonintestinal probiotic strains. The findings of this paper can contribute to elucidate the mechanisms through which these treatments can modify these strain probiotic properties that are related to outermost cell structures, also principal target of HPH.
Significance and Impact of the Study: This study contributed to understand the response mechanisms activated in cells exposed to pressure stress. It has been demonstrated that high‐pressure homogenization (HPH) treatments, conducted at sublethal levels, could increase some important functional and technological characteristics of nonintestinal probiotic strains. The findings of this paper can contribute to elucidate the mechanisms through which these treatments can modify these strain probiotic properties that are related to outermost cell structures, also principal target of HPH.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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