Academic literature on the topic 'Kinetic of acidification'

Measurements of cytosolic pH (pHi) 36Cl fluxes and free cytosolic Ca2+ concentration ([Ca2+]i) were performed in the clonal osteosarcoma cell line UMR-106 to characterize the kinetic properties of Cl-/HCO3- (OH-) exchange and its regulation by pHi and [Ca2+]i. Suspending cells in Cl(-)-free medium resulted in rapid cytosolic alkalinization from pHi 7.05 to approximately 7.42. Subsequently, the cytosol acidified to pHi 7.31. Extracellular HCO3- increased the rate and extent of cytosolic alkalinization and prevented the secondary acidification. Suspending alkalinized and Cl(-)-depleted cells in Cl(-)-containing solutions resulted in cytosolic acidification. All these pHi changes were inhibited by 4',4',-diisothiocyano-2,2'-stilbene disulfonic acid (DIDS) and H2DIDS, and were not affected by manipulation of the membrane potential. The pattern of extracellular Cl- dependency of the exchange process suggests that Cl- ions interact with a single saturable external site and HCO3- (OH-) complete with Cl- for binding to this site. The dependencies of both net anion exchange and Cl- self-exchange fluxes on pHi did not follow simple saturation kinetics. These findings suggest that the anion exchanger is regulated by intracellular HCO3- (OH-). A rise in [Ca2+]i, whether induced by stimulation of protein kinase C-activated Ca2+ channels, Ca2+ ionophore, or depolarization of the plasma membrane, resulted in cytosolic acidification with subsequent recovery from acidification. The Ca2+-activated acidification required the presence of Cl- in the medium, could be blocked by DIDS, and H2DIDS and was independent of the membrane potential. The subsequent recovery from acidification was absolutely dependent on the initial acidification, required the presence of Na+ in the medium, and was blocked by amiloride. Activation of protein kinase C without a change in [Ca2+]i did not alter pHi. Likewise, in H2DIDS-treated cells and in the absence of Cl-, an increase in [Ca2+]i did not activate the Na+/H+ exchanger in UMR-106 cells. These findings indicate that an increase in [Ca2+]i was sufficient to activate the Cl-/HCO3- exchanger, which results in the acidification of the cytosol. The accumulated H+ in the cytosol activated the Na+/H+ exchanger. Kinetic analysis of the anion exchange showed that at saturating intracellular OH-, a [Ca2+]i increase did not modify the properties of the extracellular site. A rise in [Ca2+]i increased the apparent affinity for intracellular OH- (or HCO3-) of both net anion and Cl- self exchange. These results indicate that [Ca2+]i modifies the interaction of intracellular OH- (or HCO3-) with the proposed regulatory site of the anion exchanger in UMR-106 cells.

A new method for the fast and efficient determination of the anaerobic degradability and for the calculation of kinetic parameters is proposed. It is based on the idea that monitoring of the acidification step in the anaerobic degradation cascade is sufficient, as the subsequent steps (acetogenesis, methanogenesis) are well known processes dependent on the intermediate concentrations and not on the original substrate used. The investigation of the acidification is subdivided into two steps. In the first step, biomass is adapted to the new substrate in a continuously operated bioreactor. The second step, the only step monitored, is the acidification of the substrate (or wastewater) in a batch experiment. Three different methods to monitor the acidification were tested: gas chromatography (offline), on-line titration and monitoring of the base consumption (direct titration). The results of these methods were compared to ÒtraditionalÓ batch tests. It is shown that the simplest method (direct titration) revealed the most important information. The investigated substrates were selected pollutants of textile wet processing wastewater.

Abstract We studied the effects of recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSFrh) on the internal pH of granulocytes using the fluorescent probe BCECF. GM-CSFrh did not directly alter the resting pH of granulocytes isolated from the peripheral blood; however, when the cells were preincubated for 90 minutes with the growth factor and then activated with the chemotactic peptide N-formyl met leu phe (fMLP), they exhibited both an acceleration in the initial rate of acidification and a marked delay in realkalinization. The kinetic changes both in initial acidification and in subsequent realkalinization induced by GM-CSFrh priming were not prevented by protein synthesis inhibitors and were observed in granulocytes harvested from patients with both sex-linked and autosomal recessive chronic granulomatous disease (CGD). By directly quantitating H+ ion secretion, by monitoring the effects of sodium repletion on intracellular pH, and through use of the sodium channel inhibitors amiloride and dimethyl amiloride and the Na+/K+-ATPase inhibitor ouabain, we showed that the altered kinetics of intracellular acidification and alkalinization following fMLP stimulation of GM-CSFrh- primed granulocytes could not be accounted for by changes in transmembrane proton exportation regulated by the Na+/H+ antiport channel. Although the initial acidification following fMLP was abrogated by 2-deoxy-D-glucose in both GM-CSFrh-pretreated and GM-CSFrh- untreated granulocytes, retardation of the subsequent phase of alkalinization was observed in GM-CSFrh-primed cells even after inhibition of both glycolytic and mitochondrial metabolism. Our data indicate that the increased cytosolic acidification following fMLP stimulation in granulocytes “primed” with GM-CSFrh does not result from disordered proton excretion but instead from increased release of intracellular free acid which is only partially coupled to glucose catabolism or to the generation of superoxide anion (O2-).

We studied the effects of recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSFrh) on the internal pH of granulocytes using the fluorescent probe BCECF. GM-CSFrh did not directly alter the resting pH of granulocytes isolated from the peripheral blood; however, when the cells were preincubated for 90 minutes with the growth factor and then activated with the chemotactic peptide N-formyl met leu phe (fMLP), they exhibited both an acceleration in the initial rate of acidification and a marked delay in realkalinization. The kinetic changes both in initial acidification and in subsequent realkalinization induced by GM-CSFrh priming were not prevented by protein synthesis inhibitors and were observed in granulocytes harvested from patients with both sex-linked and autosomal recessive chronic granulomatous disease (CGD). By directly quantitating H+ ion secretion, by monitoring the effects of sodium repletion on intracellular pH, and through use of the sodium channel inhibitors amiloride and dimethyl amiloride and the Na+/K+-ATPase inhibitor ouabain, we showed that the altered kinetics of intracellular acidification and alkalinization following fMLP stimulation of GM-CSFrh- primed granulocytes could not be accounted for by changes in transmembrane proton exportation regulated by the Na+/H+ antiport channel. Although the initial acidification following fMLP was abrogated by 2-deoxy-D-glucose in both GM-CSFrh-pretreated and GM-CSFrh- untreated granulocytes, retardation of the subsequent phase of alkalinization was observed in GM-CSFrh-primed cells even after inhibition of both glycolytic and mitochondrial metabolism. Our data indicate that the increased cytosolic acidification following fMLP stimulation in granulocytes “primed” with GM-CSFrh does not result from disordered proton excretion but instead from increased release of intracellular free acid which is only partially coupled to glucose catabolism or to the generation of superoxide anion (O2-).

The kinetic properties of Na+/H+ exchange were investigated in vascular smooth muscle cells (VSMC) in culture from normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Antiport activity was measured in 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein-loaded cells after nigericin-induced cytosolic acidification. Studies were performed without (control) and with pretreatment of the cells with phorbol 12-myristate 13-acetate (PMA; 200 nM). Na+/H+ exchange markedly differed between the two strains with lower Hill coefficients [1.56 +/- 0.17 (SE) vs. 2.62 +/- 0.36] and higher maximal activity (Vmax) values (55.85 +/- 5.24 vs. 31.11 +/- 2.38 mmol H+.l-1.min-1) in SHR compared with WKY cell lines. PMA markedly altered the antiport kinetics in WKY VSMC with a decrease in the Hill coefficient (1.75 +/- 0.14) without affecting Vmax (31.88 +/- 1.55 mmol H+.l-1.min-1). In VSMC from SHR, PMA had no effect on the kinetic variables investigated. Thus two kinetic abnormalities are present with respect to Na+/H+ antiport activity in VSMC from SHR compared with WKY, i.e., increased Vmax and decreased Hill coefficient. The observation that PMA does not affect the kinetics of the Na+/H+ antiport in VSMC from SHR suggests a marked degree of antiporter prestimulation in this animal model of genetic hypertension.

Lysosomal/vacuolar protein targeting is dependent on compartment acidification. In yeast, sorting of soluble vacuolar proteins such as carboxypeptidase Y is sensitive to acute changes in vacuolar pH. In contrast, the vacuolar membrane protein alkaline phosphatase is missorted only under conditions of chronic deacidification. We have undertaken a temporal analysis to define further the relationship between compartment acidification and sorting of soluble and membrane vacuolar proteins. Depletion of either the Vma3p or Vma4p subunits of the yeast vacuolar ATPase over time resulted in loss of vacuolar ATPase activity and vacuolar acidification. A kinetic delay in processing of carboxypeptidase Y occurred concomitant with these physiological changes while transport of alkaline phosphatase remained unaffected. Carboxypeptidase S, another vacuolar hydrolase that transits through the secretory pathway as an integral membrane protein, displayed a pH sensitivity similar to that of soluble vacuolar proteins. These results indicate that compartment acidification is tightly coupled to efficient targeting of proteins to the vacuole and that there may be multiple distinct mechanisms for targeting of vacuolar membrane proteins.

In the present paper a rapid and simple kinetic method for determination of the biosynthetic activity of glutamine synthetase is described based upon the decomposition of ATP, accompanied with acidification of the slightly buffered medium which can be measured by means of a pH indicator. The method can be used for determination of the enzyme activity in whole permeabilized cells, crude cell extracts, as well as for kinetic studies and studies of the effects of inhibitors on the purified glutamine synthetase.

Waste activated sludge is always used to product methane by two phases anaerobic digestion, but fermenting to accumulate VFAs has seldom reported. This paper deals with the effects of pH value, adding ratio and hydraulic retention time (HRT) on WAS acidification during mesophilic phase in two phases anaerobic digestion (TPAD) system through batch experiments. In order to gain the most amount of VFAs for providing more carbon source, the optimal conditions for WAS mesophilic anaerobic digestion observed in this study are pH=7, adding ratio=12.5%, HRT=4d and TC/TNb value=1.7~2.0. Finally, we analyzed acid production kinetic under the optimal conditions. It can be inferred that the performance of WAS acidification is sensitive to operating conditions.

Sediments from polluted urban streams act as a sink of contaminants. The high content of organic matter and sulphides makes the system appropriate for binding heavy metals. However, changes in the redox potential leads to processes in which sediments acts like a low sulphidic ore in an oxidizing environment, and could generate acid drainages. Human and not human disturbances of the sediments could derive in its oxidation catalyzed by sulphur oxidizing bacteria (SOB). This process leads to acidification and metal release. In this study we analyze the acidification potential of anaerobic sediments of polluted streams near Buenos Aires with static and kinetic methods. The results remark the necessity to consider this process before any sediment management action.

Orientador: Flavio Luis Schmidt<br>Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos<br>Made available in DSpace on 2018-08-14T15:45:20Z (GMT). No. of bitstreams: 1 Quast_Ernesto_M.pdf: 1820232 bytes, checksum: 30904cbd0aa1ec3f045d21ff606867b5 (MD5) Previous issue date: 2009<br>Resumo: A garantia da segurança microbiológica de alimentos prontos para o consumo é essencial para a sua comercialização. Alimentos sensíveis ao calor, como o palmito, podem ser conservados com tratamentos térmicos brandos, adição de conservantes químicos, diminuição do pH ou por métodos combinados. Aliando-se a pasteurização com a acidificação adequada é possível impedir a germinação de Clostridium botulinum. A difusão de ácido até o interior do tecido vegetal deve ocorrer durante um intervalo de tempo que não seja suficiente para permitir a germinação de esporos, multiplicação das células e conseqüente formação de toxina botulínica. A cinética de acidificação dos diferentes tecidos que compõe o tolete de palmito foi estudada, observando-se uma diferença significativa do tempo necessário para o abaixamento do pH dos mesmos. O tempo para a acidificação de toletes de com diferentes comprimentos também foi avaliado, sendo observado o desenvolvimento de esporos de C. sporogenes (PA3679) em toletes de palmito pupunha com comprimento maior que 3 cm, com pH de equilíbrio de 4,41, indicando a possibilidade da formação de toxina botulínica em toletes com tamanho comercial em pH de equilíbrio = 4,5 desde que exista a presença de esporos de C. botulinum no seu interior. O palmito não é um meio rico para o desenvolvimento de esporos de PA3679, fato observado pela não germinação destes esporos em suspensão de palmito triturado e misturado, com pH < 5,2. Isto mostra que o pH no interior do tolete deve atingir pH < 5,2 para impedir o desenvolvimento de esporos microbianos<br>Abstract: Ready to eat food must have their food safety guaranteed. Heat sensible food, such as heart of palm, can be preserved using mild heat treatment, chemical preservatives addition and acidification or combined methods. Germination of Clostridium botulinum can be inhibited by combining mild heat treatment and lowering of pH. The diffusion of the acid to the interior of the vegetable tissue must be fast enough not to permit spores germination, multiplication of the vegetative cells and consequent botulinum toxin formation. Study of the acidification of heart of palm showed a significant difference between the tissues regarding to the time necessary for lowering the pH. Hearts of palm Bactris gasipaes were evaluated and were observed the growth of C. sporogenes (PA3679) spores in stems with length larger than 3 cm in equilibrium pH of 4.41, indicating the possibility of botulism toxin formation in commercial heart of palm preserves with pH = 4.5 if spores of C. botulinum are present in the vegetable tissue. Heart of palm is not rich growing medium as observed that spores of PA3679 did not grow in suspension of triturated heart or palm with pH < 5.2. This fact shows that pH in the interior of heart of palm should reach pH < 5.2 to inhibit bacteria spores development<br>Mestrado<br>Mestre em Tecnologia de Alimentos

Acidification of low acid vegetables reduces their pH level to below 4.5 thereby facilitating their processing below 100 degrees Celsius, thus reducing thermal damage, and yielding better product quality. We sought to determine the acidification kinetics of turnip and radish in acetic or citric acid solutions, specifically the time for the treated tissue to reach pH 4.5, and the concurrent percent acidity of the tissue. The two vegetables' response to acidification with citric acid were compared. Experiments followed a central composite rotatable design, with three process variables (temperature, acid concentration and sample: solution ratio), each at five levels. All process variables showed significant effects (P ≤ 0.05) on both time to pH 4.5 and concurrent tissue acidity. Higher acid concentration, temperature or solution: sample ratio resulted in a shorter response time, and higher sample acidity. Optimum processing conditions (shortest time to reach pH 4.5) and the corresponding acidity were determined using a response surface methodology. This acidification process was successfully completed in practice.<br>L'acidification de légumes hypoacides réduit leur pH en dessous de 4.5, facilitant ainsi leur transformation à des températures n'excédant pas 100degrees celsius, réduisant les dommages thermiques, et donnant un produit de plus grande qualité. Nous avons étudié la cinétique d'acidification avec acide acétique ou acide citrique de morceaux de navet ou de radis, en particulier le temps requis pour que les tissues atteignent un pH de 4.5, ainsi que le pourcentage d'acidité à ce moment. La réponse des deux légumes à une acidification par acide citrique fut comparée. Les expériences suivirent un plan central composé rotatif avec trois variables de transformation (température, teneur en acide, et rapport échantillon:solution), chacun à cinq niveaux. Toutes les variables de transformation eurent un effet significatif (P ≤ 0.05) sur le temps pour atteindre un pH de 4.5, ainsi que l'acidité des tissus à ce moment. Une concentration en acide, température, ou rapport échantillon:solution plus élevé donna un temps de réponse plus court, et une acidité du tissus plus élevé. Les conditions de transformation idéales (temps le plus court pour atteindre pH = 4.5) et l'acidité correspondante des tissus, furent déterminés grâce à une méthode de surface de réponse. Cette transformation par acidification fût mise en pratique.

Made available in DSpace on 2014-06-11T19:27:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-11-29Bitstream added on 2014-06-13T19:14:41Z : No. of bitstreams: 1 silva_lf_me_sjrp.pdf: 986291 bytes, checksum: e879f8c79aac66ac197646cb214878eb (MD5)<br>Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)<br>No Brasil, o queijo Mussarela elaborado com leite de búfala, tem uma boa aceitação pelos consumidores e mercado em expansão. Entretanto, poucas são as pesquisas em âmbito nacional sobre a microbiota e influência das bactérias ácido-láticas utilizadas na produção, sobre a qualidade tecnológica deste queijo. O objetivo deste trabalho foi compor um banco de culturas representativo da microbiota isolada de queijo Mussarela fabricado com leite de búfala e efetuar a caracterização das bactérias ácido-láticas (BAL). Foram realizadas três coletas em dois laticínios (Laticínios A e B), em diferentes etapas do processo de fabricação, assim como no produto acabado (queijo Mussarela e soro de conservação) recém processado e com 14 e 28 dias de estocagem. Foi feita a contagem de colônias viáveis, isolamento dos mesófilos e termófilos, caracterização morfológica por coloração de Gram e teste de catalase. Foram obtidos 313 isolados que apresentaram características de BAL. As culturas isoladas das amostras do queijo do Laticínio B foram identificadas pela técnica de RAPD e sequenciamento do gene 16S rRNA e caracterizadas quanto à atividade acidificante, capacidade de utilizarem o citrato, atividade proteolítica e capacidade de produzirem compostos voláteis precursores de aromas. Para os dois laticínios, a população de microorganismos termófilos prevaleceu sobre os mesofilos. Os isolados foram identificados como Lactobacillus fermentum, Lactobacillus casei, Lactobacillus delbrueckii, Lactobacillus delbrueckii subsp. bulgaricus e Leuconostoc mesenteroides. A velocidade máxima de acidificação para os isolados variou de 0,0005 e 0,0305 unidades de pH por minuto após 20 min e 18 h 50 min do início do processo de fermentação, respectivamente para termófilos e mesófilos. O tempo...<br>In Brazil, the Mozzarella cheese prepared with buffalo milk has a good acceptance and market expansion. However, there are few national studies about microflora and influence of lactic acid bacteria, used in production, on the technological quality of this cheese. The aim this study was to compose a representative bank of the microbial cultures isolated from Mozzarella cheese produced with buffalo milk and to characterize the lactic acid bacteria (LAB). Three collections were performed in two dairy (Dairy A and B) at different stages of the manufacturing process as well as the finished product (Mozzarella cheese and whey conservation) newly processed and with 14 and 28 days of storage. It was followed a count of viable colony, isolation of mesophiles and thermophiles, morphological characterization by Gram staining and catalase test. It was obtained 313 isolates that exhibited characteristics of LAB. The cultures isolated of the cheese samples of the cheese from the Dairy B were identified by RAPD and 16S rRNA gene sequencing and characterized by acidifying activity, ability to utilize citrate, proteolytic activity and ability to produce volatile compounds that are flavor precursors. At two dairies, the population of thermophilic microorganisms was higher than mesophylic. The isolates were identified as Lactobacillus fermentum, Lactobacillus casei, Lactobacillus casei, Lactobacillus delbrueckii, Lactobacillus delbrueckii subsp. bulgaricus and Leuconostoc mesenteroides. The top speed of acidification for the isolates ranged from 0.0005 and 0.0305 pH units per minute after 20 minutes and 18:50 of the beginning of the fermentation process, respectively for thermophiles and mesophiles. The time required to reach the pH 5.0 ranged from 4h50min to 60h the beginning of... (Complete abstract click electronic access below)

As bactérias ácido-láticas (BAL) são micro-organismos que auxiliam nas características organolépticas, funcionais e de bioconservação de produtos fermentados. A utilização do soro de leite como meio de cultivo natural enaltece o conceito da produção de biomoléculas de alto valor agregado, como bacteriocinas, já que é um subproduto gerado por indústrias de laticínios e considerado um agente poluidor. A inulina é um ingrediente prebiótico que promove seletivamente o crescimento de culturas probióticas. Nesse âmbito, o objetivo deste estudo foi avaliar o efeito da composição da cultura de Lactococcus lactis (LL) em cocultura com Streptococcus thermophilus (ST) e da suplementação da base de soro de leite com inulina: (i) nos parâmetros cinéticos de acidificacão, (ii) no crescimento celular, (iii) na viscosidade do produto e (iv) na atividade antimicrobiana da nisina. A fermentação do soro de leite com Lactococcus lactis em cocultura com Streptococcus thermophilus proporcionou a maior taxa de acidificação (Vmax=7,93x10-3 upH/min), assim como apresentou o menor tempo para atingir a velocidade máxima de acidificação (Tvmax=1,13 h). A adição de 2% de inulina ao soro de leite fermentado pela cocultura binária fez com que o tempo para completar o cultivo fosse o mais curto (TpH4,5=4,43 h) quando comparado aos demais ensaios. Quanto ao crescimento celular, pode-se observar que a inulina não afetou significativamente a contagem microbiológica, quando as cepas ST e LL foram utilizadas separadamente no processo fermentativo. Em particular, a adição de 4% de inulina reduziu em 1,2 LogUFC/mL e 0,92 LogUFC/mL a contagem de ST e LL (em monocultura), respectivamente. Por outro lado, em coculturas binárias (ST-LL), percebeu-se ganho na contagem microbiológica nos ensaios que receberam suplementação do ingrediente prebiótico, ou seja, quando adicionados 2% e 4% de inulina, houve aumento de 1 LogUFC/mL e de 1,34 LogUFC/mL na contagem de ST, respectivamente. No caso da cepa LL em cocultura com ST, a suplementação de 2% e 4% do prebiótico aumentou em 0,31 LogUFC/mL e 0,75 LogUFC/mL, respectivamente. A concentração de ácido lático também foi mais elevada nos cultivos realizados com a cocultura binária, sendo 4,56 g/L (na ausência de inulina), 5,28 g/L (com adição de 2% de inulina) e 5,71 g/L (com suplementação de 4% de inulina). A viscosidade foi influenciada tanto pela adição de inulina como pelo efeito sinérgico da cocultura, sendo que o maior valor (7,38 mPas) foi obtido pela cocultura ST-LL e pela adição de 4% do ingrediente prebiótico. Quanto à produção de nisina, observou-se que, no cultivo em cocultura (ST-LL), a concentração de 2% de inulina aumentou em 102% a atividade antimicrobiana quando comparada com a cultura pura LL. Vale ressaltar que ambas as cepas satisfizeram os requisitos tecnológicos relativos à produção de laticínios funcionais.<br>Lactic acid bacteria (LAB) are microorganisms that help in the organoleptic and functional characteristics and in the biopreservation of fermented products. The use of milk whey as a culture medium extols the concept of the production of high value-added biomolecules, such as bacteriocins, since it is a by-product generated by the dairy industry and considered a pollutant. Inulin is a prebiotic ingredient that promotes selectively the growth of probiotic cultures. In this context, the aim of this study was to evaluate the effect of culture composition Lactococcus lactis (LL) in co-culture with Streptococcus thermophilus (ST) and the supplementation of milk whey with inulin on: (i) the acidification kinetic parameters, (ii) the cell growth, (iii) the product viscosity, and (iv) the antimicrobial activity of nisin. The fermentation of milk whey by Lactococcus lactis in coculture with Streptococcus thermophilus provided the highest acidification rate (Vmax = 7.93x10-3 upH/min) and the shortest time to reach the maximum acidification rate ( TVmax = 1.13 h). The addition of 2% inulin in the binary coculture binary led to the shorter time to complete the fermentation (TpH4,5 = 4.43) compared to the other tests. With regard to cell growth, it can be observed that the addition of inulin did not affect the microbiological count of pure cultures of ST and LL strains in the fermentation process. In particular, the addition of 4% inulin reduced by 1.2 Log CFU/mL and 0.92 Log CFU/mL the counts of ST and LL (monoculture), respectively. In the other hand, the binary co-cultures cultivations (ST-LL) with the addition of 2% and 4% inulin increased by 1 LogCFU/mL and 1.34 Log CFU/mL in the case of the ST counts and 0.31 log CFU/mL and 0.75 log CFU/mL the counts of LL, respectively. Lactic acid concentration was higher in cultivations carried out by binary cocultures, thus being 4.56 g/L (in the absence of inulin), 5.28 g/L (with addition of 2% inulin) and 5.71g/L (supplemented with 4% inulin). The viscosity was influenced by the addition of prebiotic ingredient and by the synergistic effect of binary coculture, being the highest value (7.38 mPas) obtained by the addition of 4% inulin. Finally, as regards the production of nisin noted that in the binary coculture cultivations (ST-LL), the concentration of 2% inulin increased at 102% the antimicrobial activity when compared to the pure culture LL. It is worth mentioning that both strains met the technological requirements as regards the production of functional dairy products.

Orientador: Ana Lúcia Barretto Penna<br>Banca: Kátia Sivieri<br>Banca: Eleni Gomes<br>Resumo: No Brasil, o queijo Mussarela elaborado com leite de búfala, tem uma boa aceitação pelos consumidores e mercado em expansão. Entretanto, poucas são as pesquisas em âmbito nacional sobre a microbiota e influência das bactérias ácido-láticas utilizadas na produção, sobre a qualidade tecnológica deste queijo. O objetivo deste trabalho foi compor um banco de culturas representativo da microbiota isolada de queijo Mussarela fabricado com leite de búfala e efetuar a caracterização das bactérias ácido-láticas (BAL). Foram realizadas três coletas em dois laticínios (Laticínios A e B), em diferentes etapas do processo de fabricação, assim como no produto acabado (queijo Mussarela e soro de conservação) recém processado e com 14 e 28 dias de estocagem. Foi feita a contagem de colônias viáveis, isolamento dos mesófilos e termófilos, caracterização morfológica por coloração de Gram e teste de catalase. Foram obtidos 313 isolados que apresentaram características de BAL. As culturas isoladas das amostras do queijo do Laticínio B foram identificadas pela técnica de RAPD e sequenciamento do gene 16S rRNA e caracterizadas quanto à atividade acidificante, capacidade de utilizarem o citrato, atividade proteolítica e capacidade de produzirem compostos voláteis precursores de aromas. Para os dois laticínios, a população de microorganismos termófilos prevaleceu sobre os mesofilos. Os isolados foram identificados como Lactobacillus fermentum, Lactobacillus casei, Lactobacillus delbrueckii, Lactobacillus delbrueckii subsp. bulgaricus e Leuconostoc mesenteroides. A velocidade máxima de acidificação para os isolados variou de 0,0005 e 0,0305 unidades de pH por minuto após 20 min e 18 h 50 min do início do processo de fermentação, respectivamente para termófilos e mesófilos. O tempo... (Resumo completo, clicar acesso eletrônico abaixo)<br>Abstract: In Brazil, the Mozzarella cheese prepared with buffalo milk has a good acceptance and market expansion. However, there are few national studies about microflora and influence of lactic acid bacteria, used in production, on the technological quality of this cheese. The aim this study was to compose a representative bank of the microbial cultures isolated from Mozzarella cheese produced with buffalo milk and to characterize the lactic acid bacteria (LAB). Three collections were performed in two dairy (Dairy A and B) at different stages of the manufacturing process as well as the finished product (Mozzarella cheese and whey conservation) newly processed and with 14 and 28 days of storage. It was followed a count of viable colony, isolation of mesophiles and thermophiles, morphological characterization by Gram staining and catalase test. It was obtained 313 isolates that exhibited characteristics of LAB. The cultures isolated of the cheese samples of the cheese from the Dairy B were identified by RAPD and 16S rRNA gene sequencing and characterized by acidifying activity, ability to utilize citrate, proteolytic activity and ability to produce volatile compounds that are flavor precursors. At two dairies, the population of thermophilic microorganisms was higher than mesophylic. The isolates were identified as Lactobacillus fermentum, Lactobacillus casei, Lactobacillus casei, Lactobacillus delbrueckii, Lactobacillus delbrueckii subsp. bulgaricus and Leuconostoc mesenteroides. The top speed of acidification for the isolates ranged from 0.0005 and 0.0305 pH units per minute after 20 minutes and 18:50 of the beginning of the fermentation process, respectively for thermophiles and mesophiles. The time required to reach the pH 5.0 ranged from 4h50min to 60h the beginning of... (Complete abstract click electronic access below)<br>Mestre

Ce travail vise à étudier les effets du traitement par champs électriques pulsés (CEP) et par ultrasons (US) sur les cinétiques de croissance et d’acidification des bactéries lactiques, ainsi que sur la viabilité cellulaire après congélation et lyophilisation. Les effets de diverses conditions opératoires (e.g., durée et intensité du traitement, température de congélation, vitesse de congélation, température de stockage, présence ou non de cryoprotecteurs, prétraitement ou non par CEP, etc) ont été étudiés. La bactérie lactique Lactobacillus delbrueckii subsp. bulgaricus CFL1 a été utilisée comme microorganisme modèle dans cette étude. La première partie de ce travail a été consacrée à l’étude des effets de traitement par CEP ou par US sur les cinétiques de croissance et d’acidification de L. bulgaricus CFL1 durant la fermentation sur un milieu MRS. Le traitement par CEP et US pendant la fermentation a entraîné un retard de la croissance cellulaire et une diminution de l'activité d'acidification. Après l'arrêt du traitement, les cellules traitées ont retrouvé une croissance normale, montrant un taux de croissance et d'acidification accéléré par rapport aux cellules non traitées (contrôle). Les cellules ont présenté une croissance biphasique au cours de la fermentation assistée par CEP et assistée par US. La seconde partie du travail a été consacrée à l’étude des conditions opératoires sur la viabilité de L. bulgaricus CFL1 après congélation et lyophilisation. Les résultats ont montré que l'application d'un protocole de congélation approprié et la réduction du soluté extracellulaire (NaCl) sont importants pour maximiser la viabilité cellulaire après congélation. La viabilité la plus élevée était obtenue quand la conservation cellulaire a été effectuée à -80 °C. Les cellules en suspension dans 10% de saccharose avaient une viabilité après lyophilisation plus élevée que celles qui étaient en suspension dans l'eau ultrapure. Lorsque les cellules étaient suspendues dans une solution de saccharose ou une solution de glycérol, puis congelées à -80 °C, elles avaient une viabilité plus élevée que celles qui étaient congelées à -20 °C. Le traitement par CEP n'a montré aucun effet positif sur la viabilité cellulaire après congélation ou lyophilisation<br>This work aims to investigate the effects of pulsed electric fields (PEF) and ultrasound (US) treatments on the growth and acidification kinetics of lactic acid bacteria (LAB), as well as the impact of processing conditions (e.g., freezing medium, freezing kinetics, storage temperature, cryoprotectants, PEF treatment) on the viability of LAB after freezing and freeze-drying. In this work, Lactobacillus delbrueckii subsp. bulgaricus CFL1 was used as a model culture. The first part of this work deals with the effects of PEF and US treatments on the growth and acidification kinetics of L. bulgaricus CFL1 cells during fermentation in MRS medium. The application of PEF and US treatments during fermentation resulted in a delayed growth and a reduced acidification activity of the cells. After suspending the treatment, the treated-cells showed an accelerated growth and acidification rate, and reached at the end of fermentation the same values obtained for to untreated cells (control). It was also demonstrated that L. bulgaricus CFL1 cells exhibited a biphasic growth during PEF-assisted and US-assisted fermentation. The second part of this study was devoted to investigate the influence of processing conditions on the viability of L. bulgaricus CFL1 cells after freezing and freeze-drying. Applying appropriate freezing protocols and reducing the extracellular solute (NaCl) were important to obtain high viability after freezing. The cells had higher viability during storage at -80 °C compared to that at -20 °C. The cells suspended in 10% sucrose had higher viability than those suspended in ultrapure water after freeze-drying. When the cells were suspended in ultrapure water, and in presence of sucrose or glycerol as cryoprotectants, they had higher viability both after freezing and freeze-drying when they were frozen at -80 °C than that at -20 °C. PEF treatment had no positive effect on the viability of cells after freezing or freeze-drying