1,721,242 research outputs found
HOW DIFFERENT CARBON SOURCES ANDCONDITIONS MAKE AAB “WORKING” STRAINS:ACETOBACTER PASTEURIANUS STRAIN AB0220IN SUPERFICIAL ACETIFICATION SYSTEM ASCASE STUDY
No full textMetabolic potential of acetic acid bacteria (AAB) is ofgreat interest for several fields of the bio-industry.Acetobacter pasteurianus species accounts strains relevantfor the production of both conventional and innovativefermented beverages. Strain AB0220 was isolated in2002 during a large spectrum of isolation work aimed tobuild up an AAB collection from superficial vinegar acetificationsystems. It was preserved for 9 years by shortand long time methods. Ethanol oxidation to acetic acidwas stable and confirmed, as well as acetate assimilationduring preservation. The strain do not produced cellulose.Cultivability checks showed persistence of phenotypictraits over the extended preservation time. Stability ofsubcultures related to the culture age and subcultures frequencyconfirmed the suitability of preservation at leastover a period of 9 years. Strain performance during superficialacetification, both in laboratory and industrial scale,was assayed. To this aim, the acetification ability wastested on different carbon sources and conditions mimingthe basic unit operation of superficial acetification technology.The performance of AB0220 during processeswas evaluated implementing a molecular and analyticalcontrol system. Under the experimental conditions, aceticacid, ethanol and pH were the main parameters dictatingthe conduction of scaling-up procedure. When fixingethanol content between 1 and 3% as upper and lowerlimits and 3% as the lower limit for acetic acid, suitableacidity (6-7%) was reached. The persistence of AB0220as starter over the time was evaluated after biofilm-enrichmentcultures on GYC plates. The biofilm, totally recoveredfrom plates, was processed for genomic DNAextraction. PCR/DGGE and ERIC/PCR were successfullyused to assess species and strain persistence respectively,during 178 days of acetification
Isolation and cultivation of acetic acid bacteria from high selective sources
No full textCultivable acetic acid bacteria (AAB) are used as oxidising bacteria in several biotechnological applications (e.g vitamin C, dihydroxyacetone, gluconate, ketogluconates synthesis) as well as in fermentative processes (vinegar). Troubles about their isolation and cultivation in laboratory media has been well reported. The viable but not cultivable state seems mainly influenced by environmental stress conditions and current isolation methods allow to access only a small subset of AAB population. Also the handling and preservation of strains isolated from high selective sources is still a hard practice. Among vinegars, traditional balsamic vinegar is made through cooking the grape must, in which spontaneous alcoholic fermentation and acetic oxidation take place, then it is aged to be bottled. Cooked grape must is characterized by very low pH and high sugars content. In previous works we observed high selective pressure of cooked grape must on AAB growth and the loss of strains viability under laboratory conditions. Moreover culture independent studies by PCR/DGGE, highlighted that only easier cultivable strains are isolated from cooked grape must by conventional culture-dependent methods. In this study AAB strains were isolated from cooked grape musts by plating system using three isolation media, molecular characterized by PCR/RFLP analysis and partial sequencing of rDNA region. To test the ability to carry out the oxidation process in high selective substrates, cooked grape must, wine and “Passmore and Carr” medium, with different pH, titrable acidity, soluble solids and ethanol content, were used as substrates. The results showed the high soluble solids parameter as the main limiting factor of AAB growth and activity in cooked grape must. Improvement of isolation and cultivation methods could provide recognition of new species, a better preservation system of strains, allowing an AAB strains selection of biotechnological interest
Isolamento e selezione di batteri acetici per aceto balsamico tradizionale
No full textMolti alimenti fermentati vengono preparati mediante l’impiego di colture starter selezionate; i vantaggi che ne derivano sono molteplici e volti ad evitare il rischio di fermentazioni spontanee causate da microrganismi non idonei e a garantire la salubrità del prodotto. Nella produzione di aceto a tutt’oggi non vengono impiegate colture starter selezionate, ma l’avvio dell’acetificazione è indotto da masse precedentemente acidificate. Nel caso dell’aceto balsamico tradizionale, questo sistema non sempre fornisce buoni risultati a causa della difficoltà di sviluppo dei batteri acetici in mezzi molto concentrati come il mosto cotto. L’impiego di colture starter di batteri acetici osmotolleranti rappresentaun’innovazione in grado di rendere il processo riproducibile e costante
I batteri acetici
No full textI batteri acetici (BA) sono microorganismi aerobi stretti in grado di compiere ossidazioni parziali di un gran numero di carboidrati, rilasciando i corrispondenti metaboliti nel mezzo circostante (acidi organici, aldeidi e chetoni). Sono gram-negativi o gram-variabili, di forma ellissoidale o a bastoncino e possono presentarsi singoli, in coppia o in corte catene. Non sporigeni, mobili (flagelli in posizione polare o peritrica) o immobili, catalasi positivi e ossidasi negativi. Il pH ottimale per la loro crescita è compreso tra 5 e 6.5, ma hanno un intervallo di crescita molto ampio e possono sviluppare anche a valori inferiori a 3, come negli aceti. La temperatura ottimale di crescita varia tra 28 e 30° C, ma sono state riscontrate anche specie termotolleranti, con temperature ottimali comprese tra 35 e 38°C. Inoltre i BA possono produrre pigmenti solubili e differenti tipologie di esopolisaccaridi, tra cui la cellulosa.
I BA hanno una lunga storia d’uso nei processi alimentari e la maggior parte di essi sono riconosciuti come generalmente sicuri per la salute umana, cioè organismi GRAS (generally recognised as safe). Tuttavia tre specie sono state descritte come patogene umani emergenti: Asaia bogorensis (in un caso di peritonite); Granulibacter bethesdensis (in 3 casi di linfoadenite associata a malattia granulomatosa cronica); e Acetobacter cibinongensis (infezione in paziente dializzato).
I BA appartengono all’ordine Rhodospirillales, membri della classe Alphaproteobacteria, all’interno della famiglia Acetobacteraceae. Attualmente sono raggruppati nei seguenti generi: Acetobacter, Acidomonas, Ameyamaea, Asaia, Gluconacetobacter, Gluconobacter, Granulibacter, Komagataebacter, Kozakia, Neoasaia, Neokomagataea, Saccharibacter, Swaminathania e Tanticharoenia
Succession of Selected Strains of Acetobacter pasteurianus and Other Acetic Acid Bacteria in Traditional Balsamic Vinegar
No full textThe application of a selected Acetobacter pasteurianus strain for traditional balsamic vinegar production was assessed. Genomic DNA was extracted from biofilms after enrichment cultures on GYC medium (10% glucose, 1.0% yeast extract, 2.0% calcium carbonate) and used for PCR/denaturing gradient gel electrophoresis, 16S rRNA gene sequencing, and enterobacterial repetitive intergenic consensus/PCR sequencing. Results suggested that double-culture fermentation is suitable for traditional balsamic vinegar acetification
I campioni del Palio Matildico e gli indicatori di qualità dell'aceto balsamico tradizionale
No full textLa valorizzazione e la tutela dell’Aceto Balsamico Tradizionale, al pari di qualsiasi altro prodotto alimentare tradizionale, non può prescindere dalla conoscenza delle ragioni che lo rendono così specifico e particolare. La ricerca scientifica, oltre ad essere lo strumento di conoscenza necessario alla comprensione della complessità dell’ABT, è anche veicolo di promozione, nel rispetto della chiarezza, dell’autenticità e dell’oggettività, senza ricorrere a spiegazioni fantasiose, che nulla hanno a che fare con la concretezza dell’ABT, frutto dell’acquisizione empirica della conoscenza
Improvement of traditional vinegar production by selected acetic acid bacterium strain: Acetobacter pasteurianus as acetification starter
No full textRecent microbiological studies investigated the acetic acid bacteria microflora of traditional balsamic vinegar (TBV) highlighting the occurrence of Gluconacetobacter europaeus as widespread indigenous species, followed by Acetobacter pasteurianus, Acetobacter aceti and Acetobacter malorum1,2. However no correlation between occurring species and quality of product have been examined. In this study a selected starter culture (SSC) was designed, implemented at laboratory scale and applied to vinegar factory by scale up procedure. A. pasteurianus strain AB0220 was selected as SSC on the basis of phenotypical and technological traits suitable for TBV must oxidation. The SSC was implemented through three stages: starting steps in laboratory conditions (Stage 1); scale-up performed through a tanks system (Stage 2) and a barrels system (Stage 3) in factory conditions. Main analytical parameters were monitored by pH, titrable acidity, ethanol and soluble solids trend. Moreover molecular identification based on 16S rDNA region analysis (PCR-DGGE and sequencing) and ERIC-PCR were performed respectively to assess species occurrence and evaluate strain persistence during the whole process. In particular the dominant AAB species population was estimated by PCR-DGGE analysis allowing to distinguish two different species groups along the 3 stages. 16S rDNA sequencing confirmed DGGE results, showing high percentage of sequence homology (99 and 100%) with A. pasteurianus at stage 1 and 2 and Ga. europaeus at Stage 3. Finally, ERIC-PCR fingerprinting assay performed at the end of each acetification stage showed an electrophoretic profile similar to that of AB0220 at stage 1 and 2, whereas a different pattern at stage 3. This result supports DGGE data suggesting a change in the population during the 3 acetification stages. On the basis of these evidences, our hypothesis is that the persistence of inoculated strain during stages 1 and 2 was assured by the scale-up procedure. New must was periodically added to increase the SSC volume and microbial population was not exposed to constant effect of acetic acid. Instead, the static conditions of stage 3 resulted in a constant increase of acetic acid concentration, negatively affected AB0220 growth. In this environment, indigenous Ga. europaeus cells, which is less sensitive to physiological stress caused by acetic acid3, found optimal growth conditions to become dominant. In this study for the first a SSC for TBV production was implemented and applied at factory scale. Results demonstrated that selected A. pasteurianus strains are suitable to start the acetification of TBV ensuring the acetification course in unsuitable conditions for other AAB such as Ga. europaeus. On the contrary, Ga. europaeus strains are able to oxidise cooked must in presence of constant of acetic acid concentration corresponding to the final stages of TBV oxidation. Results suggest that the introduction of SSC could be a valid innovation in TBV production, contributing to safety and quality of the product and improving the reliability and stability of technological process
Oxidation of sugars and polyalcohols by acetic acid bacteria during surface culture fermentation
No full textAcetic Acid Bacteria (AAB) are well known for their ability to oxidize alcohols, aldehydes, sugars, polyalcohols and others molecules with ketonic or aldehydic functional groups. Species of Acetobacter and Gluconobacter lack a functional Embden-Meyerhof-Parnas pathway and are unable to metabolize hexose sugars by this route. Hexose and pentose sugars are oxidatively metabolized by the hexose monophosphate pathway to acetic and lactic acids. In some cases, hexose sugars may be directly oxidized to gluconate and ketogluconates without further catabolism, leading to an accumulation of these end products in the culture medium. Furthermore, Gluconobacter oxydans has been used to oxidize various sugars and sugar alcohols to substances of industrial significance, such as sorbose, gluconic acid and ketogluconic acids. Dihydroxyacetone, 2,3-butanediol, and acetoin are also significant products of carbohydrate metabolism evolved by AAB Our trials of surface static fermentation was carried out on complex media such as base wine (BW) for Traditional Balsamic Vinegar, where sugars and alcohols are present in different amount. In this conditions AAB sequentially oxidized the several carbon sources, first ethanol, then glucose and glycerol. In particular the oxidation of glucose to gluconate occurred when the ethanol was exhausted, then high amount of gluconate was accumulated in the medium. BW had an initial composition of around 7% (v/v) of ethanol and 25% of sugars with glucose and fructose in the ratio 1/1. At the end of the fermentation the glucose/fructose ratio was in favour of fructose, titratable acidity was very high due to the gluconate formed, while volatile acidity decreased. In summary, when surface fermentation is extended afterward the ethanol run out, other substrates are oxidized and give origin to a vinegar with a completely different composition. The extension of the oxidative step is a tool for increasing vinegar’s sweetness and acidity without the acetic acid sensorial pungency. (empty line)Keywords: gluconic acid, sugar oxidation, surface static acetification
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