414 research outputs found
KOMBUCHA TEA: A BIORESOURCE FOR ACETICACID BACTERIA
No full textKombucha or Tea fungus is a traditional fermented beverageobtained during sweetened tea fermentation conductedby acetic acid bacteria (AAB) and yeasts. Historically,Kombucha appeared first in Asia and thereafter its usesand consumption spread from Russia, central Europe andthen over the world. It is composed of a cellulose floatingpellicle and a sour slightly and sparkling broth. However,in spite of vinegar, kombucha remained not well exploredmainly as a niche of AAB strains exploitable in biotechnologicalapplications. The aim of this study was to overviewthe occurrence of AAB in kombucha samples fromliquid and pellicle phases. Kombucha from black andgreen tea was obtained by inoculating a previously grownculture into a freshly prepared tea infusion containing10% of sucrose, 3% (w/v) of cellulose pellicle and 10%(v/v) of broth and led to fermentation up to 15 days in abatch system under aerobic condition. Titrable acidity reacheda maximum of 12 g/L at the end of fermentation inblack kombucha and 6 g/L in green one. pH dropped fromapproximately 3.7 until 2.75 for both samples as a resultof acids formation. Maximum ethanol accumulated at theday 15 did not exceed 0.5% (v/v) for both samples.Cellulose layer become thicker during fermentation, startingfrom 2-3 mm until 10 mm. AAB strains were isolatedfrom pellicle and liquid phases by sampling each 3 daysusing GYC and ACBS media. A total of 93 strains werecollecting during 15 days of fermentation of which 50 arecellulose producing. The majority of strains were tolerantto 5% (v/v) of ethanol and to 30% (w/v) of glucose. Thiswork opens an issue to explore the diversity of AAB fromKombucha focusing their ability to produce cellulose andto grow in low-acidic and sugary environment
DIVERSITY AND DYNAMICS OF CULTIVABLEPOPULATION OF ACETIC ACID BACTERIA ANDYEASTS IN KOMBUCHA
No full textIn recent years functional foods promoted with healthclaims have attracted increasing attention on the market.Among them kombucha is a fermented beverage widelyconsumed in Eastern Asian countries, but little is knownabout its constituent microbial communities. In this studytwo 12 days benchmark kombucha fermentations fromgreen and black tea were carried out. A culture-dependentapproach was applied both on exopolysaccharidic andliquid phases to monitor dynamics and diversity of aceticacid bacteria (AAB) and yeasts community. Among AABone main profile was observed (86% of strains); remainingstrains were grouped in 4 profiles by 16S/RFLPbasedanalysis. Whereas by (GTG)5/PCR typing sixteenclusters were obtained. 16S rRNA gene sequencing confirmedthe occurrence of Gluconacetobacter xylinus as predominantboth in green and black samples at 0, 6 and 12days of fermentation. Mainly on ACB medium minor bacterialgroups often colonizating tea leaves (Paenibacillusspp.), plants (Plantibacter spp.) and moisturing environments(Williamsia spp.), were detected starting from 6thfermentation day. Yeast population consisted of a restrictednumber of dominant species: Dekkera sp., Schizo -saccharomyces sp., Zygosaccharomyces sp., Dekkera sp.and Pichia sp. D. anomala was prevailing in both phasesthough all black and green kombucha fermentation times.Sc. pombe was detected only within 6 days of both greenand black tea and it was not isolated after 9 days, when the high ethanol-producing species D. bruxellensis was detected.Z. bailii was isolated from exopolysaccharidic ofblack tea from 6 to 12 days. Finally P. membranifacienswas detected occasionally at the end of the fermentativeprocess. For each species the degree of diversity wasdetermined by combined M13 and OPA20-based RAPDmethod. Cluster analysis showed that one to two prevailingbiotypes occurred through all the process
Composition of the essential oils in various organs at different developmental stages of Ammi visnaga (L.) Lam. from Tunisia
No full textThe composition of the essential oils isolated by hydrodistillation from various organs at different development stages of Ammi visnaga (L.) Lam. growing in Tunisia was determined by GC/MS analysis. In particular, the oil profiles of the leaves, stems, flower buds, roots, umbels, and fruits have been examined during the whole life cycle. The oil from the flowering aerial parts was characterized by a high content of isoamyl 2-methylbutanoate. After flowering and during desiccation and fructification, the umbels and fruits expressed a high content of linalool. The oils, extracted from the roots collected in the vegetative, buds floral, and floral stages, were rich in monoterpene aldehydes, oxygenated monoterpenes, and monoterpene hydrocarbons. The highest level of non-terpene hydrocarbons was found at the flowerbud stage, represented by 61.3% of nonane. Among the monoterpenes, sabinene (12.5%) and β-pinene (8.5%) were identified in the flower buds
Glacial Mediterranean sea surface temperatures based on planktonic foraminiferal assemblages
No full textWe present a new reconstruction of Mediterranean sea surface temperatures (SST) during the last glacial maximum (LGM). A calibration data set based on census counts of 23 species of planktonic foraminifera in 129 North Atlantic and 145 Mediterranean core top samples was used to develop summer, winter and annual average SST reconstructions using artificial neural networks (ANNs) and the revised analogue method (RAM). Prediction errors determined by cross-validation of the calibration data set ranged between 0.5 and 1.1 °C, with both techniques being most successful in predicting winter SSTs. Glacial reconstructions are based on a new, expanded data set of 273 samples in 37 cores with consistent minimum level of age control.The new LGM reconstructions suggest that the east–west temperature gradient during the glacial summer was 9 °C, whereas during the glacial winter, the gradient was 6 °C, both some 4 °C higher than that existing today. In contrast to earlier studies, our results tend to suggest much cooler SST estimates throughout the glacial Mediterranean, particularly in the eastern basin where previous SST reconstructions indicated a decrease of only 1 °C. Our new SST reconstructions will provide the modelling community with a detailed and updated portrayal of the Mediterranean Sea during the LGM, setting new targets on which glacial simulations can be tested
The effects of TiO2 sol concentration on single- and multiple-scratch damage in electroplated Ni–B-TiO2 sol composite coating
No full textThe electrodeposited sol-enhanced Ni–B–TiO2 composite coatings were elaborated using a novel electroplating process. This coating was assessed in terms of tribological behavior and corrosion resistance. However, the adhesion strength of this coating has not been discussed so far. The aim of this study is to evaluate the adhesion behavior of this coating, considering different TiO2 sol concentration in the plating solution in order to predict its effectiveness and its sustainability when used in mineral crushing process. A progressive load scratch test and multi-pass scratch test were performed on coatings. The morphology of scratched surfaces was analyzed to identify the scratch failure mechanism. The results indicate that the addition of TiO2 sol significantly enhanced the deposit adhesion to the substrate compared to pure Ni–B coating. No spallation failure was observed on the sol-enhanced coatings after progressive load scratch test, contrary to Ni–B coating. Moreover, the multi-pass scratch test demonstrated that the improvement in adhesion strength depends strongly on the quantity of the TiO2 sol added to the plating solution. For the optimal concentration of TiO2 sol (25 ml/L), the sol-enhanced Ni–B–TiO2sol composite coating boasts the best adhesion strength. However, further increase in TiO2 sol concentration results in a deterioration of coating adhesion
Response of the pelagic enviroment to palaeoclimatic changes in the central Mediterranean Sea during the Late Quaternary.
No full textLipid components of olive oil from Tunisian cv. Sayali: characterization and authenticity
No full textThe analysis of the total lipid fraction from the Sayali variety of olive oil was accomplished in the present investigation. Glyceridic, unsaponifiable and flavour fractions of the oil were isolated and identified using several analytical methods. Chromatographic techniques have proven to be suitable for these determinations, especially capillary gas chromatography. Gas chromatography coupled to mass spectrometry was successfully used to identify sterols, triterpenes alcohols, 4-monomethylsterols, aliphatic alcohols and aroma compounds in our samples. Furthermore, solid phase microextraction was used to isolate volatiles from the total lipid fraction. Results from the quantitative characterization of Sayali olive oil showed that oleic acid (77.4%) and triolein (47.4%) were the dominant glyceridic components. However, the main compounds of the unsaponifiable fraction were b-sitosterol (147.5mg/100 g oil), 24-methylene cycloartenol (146.4mg/100 g oil) and hexacosanol (49.3 mg/100 g oil). Moreover, results showed that the aldehydic compounds were the major flavours present in Sayali olive oi
Planification de la distribution de l'énergie électrique avec demande incertaine
No full textDans cette thèse, nous considérons le problème de la planification de la distribution de l'énergie électrique avec demande incertaine. Nous avons élaboré un modèle mathématique détaillé représentant les caractéristiques principales d'un réseau radial de distribution électrique. Dans l'objectif du modèle et en plus des coûts d'installation et d'entretien des équipements (postes, lignes) et des coûts dûs au pertes de puissance dans les lignes, nous avons tenu compte du coût de"la pénalité" dûe à la non satisfaction de la demande. Nous avons proposé une définition de ces coûts de pénalité ainsi qu'une procédure pour les évaluer. Etant donnée la présence de deux types de variables réelles et entières dans notre modèle, nous avons choisi la méthode de décomposition de Benders comme approche de résolution. Le sous problème associé possède une structure particulière et donc sa résolution est assez simple. Dans le cas où ce problème est réalisable, nous avons proposé une façon efficace pour générer des coupes Paréto-optimales. Pour résoudre le problème maître nous avons confronté à deux difficultés majeures: la non linéarité de la fonction économique et la forme implicite du coût de pénalité. Nous avons contourné la première difficulté par l'introduction d'une variable binaire, quant à la deuxième nous avons utilisé des notions de programmation mathématique ce qui nous a permis de trouver une formulation équivalente au problème maître relaxé plus simple à traiter. Pour résoudre ce problème équivalent, nous avons proposé deux approches de résolutions, la méthode de Branch-and-Bound et la relaxation lagrangienne. Nous avons mis au point une version préliminaire d'un logiciel comosé d'un programme écrit en C++ qui fait appel à Cplex pour résoudre le problème maître. Ce logiciel nous a permis de faire des tests numériques et valider l'approche de résolution
Diagenetic Mg-rich calcite in Mediterranean sediments: quantification and impact on foraminiferal Mg/Ca thermometry
No full textMg/Ca ratios in planktonic foraminifera have been developed into a powerful tool in paleoceanography to
reconstruct past sea surface temperatures (SST). However, additional factors that might have an influence on
Mg/Ca, like dissolution, salinity, diagenesis, and carbonate ion effects have come into focus. In this paper, the
occurrence of diagenetic calcification and its potential effects on Mg/Ca have been studied using 20 wellpreserved
core tops recovered from the Mediterranean Sea. Analyses were performed on two planktonic
foraminifer species; Globigerinoides ruber and Globigerina bulloides using ICP-AES Mg/Ca measurements, SEM
observations and X-ray diffractometry analyses.
Foraminiferal Mg/Ca values are higher than those obtained in the open sea. The highest values were found in
the Eastern Mediterranean basin. These anomalies cannot be simply explained by a salinity effect because Mg/
Ca ratios, when corrected for temperature influence, do not display any significant correlation with salinity.
Our results seem to indicate that diagenesis can account for anomalously high Mg/Ca values. Indeed, SEM
observations show aggregates of rhombohedral crystals that could be interpreted as secondary calcite
overgrowths. We note also the occurrence of numerous coccoliths trapped in foraminifer walls and covered
with a secondary mineral phase.
X-ray diffraction diagrams of numerous foraminiferal samples exhibit peak of Mg-rich calcite (10–12%)
associated with the usual foraminifer calcite peak. It has been demonstrated that this calcite highly rich in Mg,
is compatible with an inorganic calcite precipitated directly from seawater.
The deconvolution of the main XRD peak (104) shows that the percentage of Mg-rich calcite can reach up to
~21% of the total foraminiferal calcite in the Eastern basin whereas in the western Mediterranean Sea,
proportions do not exceed 5%. In addition, we demonstrate that, the diagenetic process is very heterogeneous
(even at the sample scale) and is not simply a reflection of ΔCO3 at the sea bottom. Thus, the high Mg/Ca ratios
measured from Mediterranean Sea planktonic foraminifera does not appear to be caused by increased Mg
uptake in a high salinity setting, but instead result chiefly from the presence of Mg rich calcite (10–12%)
deposited during early diagenetic processes
Action des Nématodes Entomopathogènes du genre Heterorhabditis sur les oeufs de criquet, Locusta migratoria (L.) (Orthoptera : acrididae)
No full textLes nématodes entomopathogènes (EPN) ont été décelés pour la première fois sur les oeufs de criquets. Quelques populations d’Heterorhabditis isolées sur les oeufs de Schistocera gregaria Forsskål, de Locusta migratoria L. (Orthoptera : Acrididae) et sur les chenilles de Galleria mellonella L. (Lepidoptera : Pyralidae) ont été isolées. La pathogénie des populations du nématode isolées sur les oeufs est plus importante que celle sur les chenilles. A l’inverse la pathogénie des EPN isolée sur les chenilles est plus importante sur les chenilles de l’insecte modèle. Les potentialités biochimiques des nématodes entomopathogènes et de leurs bactéries symbiontes en rapport avec l’activité protéolytique et chitinase ont été étudiées. Les bactéries mutualistes des nématodes isolées sur les oeufs de criquet montrent une importante activité protéolytique.Mots Clés: Heterorhabditis, nématode entomopathogène, oeuf, criquet, Locusta migratoriaEnglish Title: Effect of entomopathogenic nematode, heterorhabditis on eggs, Locusta migratoria (L.)English AbstractEffect of entomopathogenic nematode, Heterorhabditis on eggs locust, Locusta migratoria (L.) First report of entomopathogenic nematodes have been detected in locusts eggs. Some Heterorhabditis populations isolated on eggs of Schistocera gregaria Forsskål, of Locusta migratoria L. (Orthoptera : Acrididae) and caterpillars of Galleria mellonella L. (Lepidoptera : Pyralidae) were isolated. Nematode populations isolated from insect eggs aremore aggressive on locust eggs than those obtained by greater wax moth traps. Pathogenesis on nematodes isolated on carterpillar larvae bait, is greater on Galleria mellonella, insect model of EPN, than those bait by locust eggs. Biochemical potential of EPN and their symbiotic bacteria is related on proteolytic and kinetics activity. Mutualistic bacteria of nematode isolated on locust eggs show a significant proteolytic activity.Keywords: Heterorhabditis, entomopathogenetic nematode, Egg, locust, Locusta migratori
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