Inhibition by yeast strain of tyrosinase activity in must and wine

The course of tyrosinase activity in musts is related to the strain of yeast used; with strain 633 the activity becomes practically non-detectable during the first days of growth. With other strains a drastic drop always occurs during the first 48 hours, followed by a recovery during the exponential phase of growth, in correlation to a substantial fall of phenols and to the exponential rise in colour. The inhibitory power on the tyrosinase in vitro is a widespread character in the yeast, even if quantitatively different: this character is not always associated with colour stability. Such a character, possessed to a remarkable measure by strains 633 and 36, is bound to the biosynthesis, even in synthetical media, of a compound capable of becoming bound to the protein units of enzyme, thus preventing the enzyme activity.Inhibition par la souche de levure de l'activité de la tyrosinase du moût et du vinLe cours de l'activité de la tyrosinase dans les moûts est rélié à la souche de levure employée: la souche 633 rend l'activité pratiquement inexistante pendant les premiers jours de son dévéloppement. D'autres souches provoquent une baisse drastique pendant les premières 48 heures, suivie par un récouvrement de l'activité de la tyrosinase pendant la phase exponentielle de leur dévéloppement en corrélation à une chute substantielle des composés phénoliques totaux et à la hausse exponentielle de la couleur. Le pouvoir inhibiteur sur la tyrosinase in vitro est un caractère diffusé des levures bien que quantitativement différent; ce caractère n'est pas toujours associé à la stabilité de la couleur des vins blancs. Tel caractère, possedé d'une façon remarquable par les souches 633 et 36, est lié à la biosynthèse, même dans les substrats synthétiques, d'un composé capable de se lier aux unités protéiques de l'enzyme, de façon à prévenir l'activité enzymatique

Primi risultati del progetto LIFE+ sulle analisi microbiologiche delle acque nel Parco dei Gessi dell’Emilia Romagna

Dal 2010 è in corso il Progetto Life + 08NAT/IT/000369 “Gypsum” 2, cofinanziato dall’Unione Europea, finalizzato alla tutela e gestione dei principali ambienti gessosi dell’Emilia Romagna. Nell’ambito dell’Azione A3 è previsto un monitoraggio pluriennale dei principali acquiferi carsici sotto l’aspetto chimico e microbiologico. Nel corso del primo anno sono state analizzate le acque carsiche su circa 50 punti di controllo (inghiottitoi, fiumi, torrenti in grotta, e risorgenti). In generale l’obiettivo di questa sperimentazione è quello di valutare l’impatto di sostanze di origine agricola o di altre forme di inquinamento, legate ad insediamenti o attività antropiche o fattori naturali, in acque di grotta. La sperimentazione è stata sviluppata tramite tecniche microbiologiche classiche e di biologia molecolare (PCR 16S rRNA e PCR-DGGE), finalizzate alla caratterizzazione delle popolazioni microbiche presenti nei diversi siti di prelievo e alla determinazione di loro eventuali variazioni e/o evoluzioni. I valori di carica microbica totale determinati oscillavano da un massimo di 3.32 ad un minimo di 0.18 log UFC/ ml e da un massimo di 2.26 fino a valori al di sotto del limite di determinazione (1 log UFC/ml) per quanto riguarda i coliformi totali e fecali. Le analisi genetiche hanno mostrato la presenza di numerosi specie batteriche (Agrobacterium tumefaciens, Pseudomonas spp., Rahnella aquatilis, Stenotrophomonas maltophilia, Pedobacter swuonensis, Enterobacter spp., Aeromonas hydrophila, Citrobacter, Klebsiella and Raoultella). I microrganismi identificati possono avere diverse origini, alcuni provengono dal terreno, altri possono essere comuni contaminanti delle acque ed altri avere un’origine antropica (batteri fecali). Fino a questo step del progetto, l’analisi PCR-DGGE ha evidenziato le evoluzioni ecologiche, in termine di popolazioni microbiche, presenti tra i diversi campioni e i diversi siti di campionamento all’interno di una stessa grotta.The Project Life + 08NAT/IT/000369 “Gypsum” 2, co-financed by the European Union, has started in the spring of 2010. This project aims to protect and manage the main karst caves and sites of Emilia-Romagna region. The A3 action provides a periodic monitoring of the main karst aquifers in terms of chemistry and microbiology. During the first year and a half, karst waters of 50 control points were analysed (sinking streams, rivers and streams in caves, and resurgences). The objective of this study is to evaluate the impact, in the waters of the cave, of agricultural substances or other forms of pollution or settlements related to human activities or natural factors. The experiment was developed using traditional microbiology techniques and molecular biology techniques (PCR and 16S rRNA PCR-DGGE), focused on the characterization of microbial populations in the different sampling sites and determination of their variations and/or changes. The total microbial concentration ranged from a maxiimum of 3.32 or 2.26 to values below the limit of detection (1 log CFU/ml) for total and faecal colifroms, respectively. The genetic analysis showed the presence of numerous bacterial species (Agrobacterium tumefaciens, Pseudomonas spp., Rahnella aquatilis, Stenotrophomonas maltophilia, Pedobacter swuonensis, Enterobacter spp., Aeromonas hydrophila, Citrobacter, Klebsiella and Raoultella). The organisms identified have different origins, some come from the ground, others are common water contaminants and others derive from human activities (faecal bacteria). Up to now, PCR-DGGE revealed the ecological changes, in terms of microbial populations present in the samples, and different sampling sites within the same cave

Microbiological quality of filled pasta in relation to the nature of heat treatment.

The microbial population present in 49 samples of Italian industrially processed filled pasta was characterized and its changes during refrigerated storage were evaluated. The most frequently isolated species belonged to the genus Bacillus. No pathogenic organisms were isolated from the processed industrial pasta. As a consequence of the diversity of composition and thermal treatment a wide variability was observed (from less than 3 days to more than 1 month) in the shelf life at 4 degrees C of the industrial "fresh filled pasta." However, the results obtained suggested that the shelf life of the processed products depend not only on the number of surviving cells but also on the textural or microstructural changes induced by the heat treatment. Challenge tests using Staphylococcus aureus showed that even pasteurization values (P 70(10), expressed as an equivalent process time, in minutes, necessary to obtain at 70 degrees C the same lethal effect as during the actual process) not exceeding 2 were able to remarkably reduce the cell load of this organism. Subsequent growth of the surviving S. aureus cells occurred only at temperatures > 7 degrees C, particularly when the water activity (aw) values were higher than 0.97

Recherche sur l'étiologie d'une nouvelle maladie de la grappe: la pourriture acide

Les espèces et la fréquence d'isolement des levures associées à la pourriture acide ont été determinées.Les genres les plus fréquemment isolés ont été Candida, Pichia et Hanseniaspora, qui sont à même de reproduire in vivo les symptômes de la maladie. Néanmoins d'autres espèces, bien que moins fréquentes, se sont révélées être capables de provoquer la pourriture acide in vitro et de reproduire des profils GLC des composants volatils de l'espace de tête très semblables à ceux des grappes infectées naturellement. Les activités enzymatiques extracellulaires lytiques et leur fréquence dans la population des levures isolées sur les raisins pourris ont été étudiées.Research on the etiology of a new disease of grapes: sour rotThe species of the yeasts associated with sour rot and the frequency of their isolation were determined. The most frequent genera were Candida, Pichia and Hanseniaspora. Species belonging to these genera were able to induce the symptoms of the disease in vivo when inoculated into table grapes. However, other species less frequent have also been found able to induce the rot in vitro and to reproduce GLC profiles of volatile compounds of head space very similar to those of naturally infected grapes. The extracellular lytic enzyme activity of isolated strains and their frequency in the population of infected grapes were studied

Assessment of the chemical composition and in vitro antimicrobial potential of extracts of the liverwort Scapania aspera.

The chemical composition of Scapania aspera extracts was determined by solid phase micro extraction gas chromatography–mass spectrometry (SPME GC-MS) and 96 constituents were identified. The dominant compounds in the methanol extract were β-barbatene (25.1%), o-cymene (14.0%), α-barbatene (5.7%), allo-aromadendrene (4.9%) and β-bourbonene, while in the ethanol extract, o-cymene (17.8%), β-barbatene (17.6%), α-thujene (6.7%), octen-1-ol acetate (4.9%) and β-bazzanene (2.4%) were the major components. In the ethyl acetate extract, β-barbatene (14.3%), undecane (11.8%), 2-methyldecane (11.2%), decane (10.9%) and o-cymene (3.6%) were major components. The antimicrobial activity of the different extracts was evaluated against pathogenic and food spoilage microorganisms using disc diffusion and micro-broth dilution methods. The minimal inhibitory concentration (MIC) of extracts of S. aspera varied from 0.4 to 1.5 mg/mL and 1 to 3 mg/mL for yeast and bacterial strains, respectively. The zone of inhibition of the methanol extract for yeast strains was higher than that for bacterial strains. The results suggest that S. aspera extracts have potential as natural antimicrobial agents

Physiology and Biochemistry of Sourdough Yeasts

The cereal dough is a dynamic system which is characterised by continuous changes in nutrients availability and physic-chemical condition changes. Depending on the type of flour and bread making technology, starvation conditions can be also envisaged. The imbalance between yeast consumption and starch hydrolysis might lead to the rapid depletion of soluble carbohydrates. Overall, microbial starvation induces a quiescent state whose length is conditioned by the presence of the limiting factors. Yeast responds to a changing environment not with a small adjustment in a key control points but with the coherent transcriptional relation as a large set of genes. During fermentation of sourdough yeasts cells may encounter different environmental states. Co-fermentation with lactic acid bacteria and yeasts determines environmental fluctuations not only of availability of nutrients, but also of organic acids concentration, decrease of pH and changes on the texture profile. Maintaining optimal functionality in the presence of such external variability is a central evolutionary constraint. The exposure of microbial cells to stressful and fluctuating conditions during fermentation involves a broad transcriptional response with many induced or repressed genes. The selective pressure exerted by the environmental conditions encountered by yeast cells during sourdough fermentation, accounts for the consolidated dominance of selected yeast species, such as in particular C. milleri and S. cerevisiae. The nutrient availability or limitations are likely the factors that modulate the microbial ecology of sourdough. However, within the sourdough ecosystem there are numerous mechanisms whereby one species may influence the growth of another species. The chapter describe the stress response, of those species, to nutrient availability (starvation), DY, pH (acid stress), presence of sugars, salts and polysaccharides (osmotic stress), oxygen (oxidative stress), temperature fluctuations (heat shock and cold stress) and interactions between lactic acid bacteria and yeasts (e.g., S. cerevisiae, C. milleri and L. sanfranciscensis), and between yeasts (e.g., S. cerevisiae and C. milleri). Moreover, both environmental process parameters and the interaction with lactic acid bacteria affect the metabolism of yeast in terms of fusel alcohols and namely branched chain amino acids metabolites, carbonyl compounds and unsaturated fatty acids oxidation products and induce also the inter-species signalling molecules production. An overview of baker\u2019s yeast in bread making industry is also included. Traditional cultivation methods in combination with phenotypic and genotypic identification adopted to characterize the yeasts of ripe dough revealed the presence of more then 2, 3 species belonging especially to the genera Saccharomyces and Candid

Influence of starch addition and dough microstructure on fermentation aroma production by yeasts and lactobacilli

The work hypothesis of this paper was that during fermentation processes the chemico-physical interactions of the microbial metabolites with food matrix affects not only their retention, but the metabolic activity of the microorganisms. The influence of starch addition to liquid fermentation systems simulating sourdough and inoculated with pure and mixed population of Saccharomyces cerevisiae, Candida milleri and Lactobacillus sanfranciscensis significantly enhanced the production of selected metabolites. Moreover the starch addition interfered with the response of S. cerevisiae, C. milleri and L. sanfranciscencis when exposed to conditioned media of L. sanfranciscensis resulting in an increasing production of alcohols, isovaleric acid and of a key odorant like γ-decalactone. Under real conditions, the microstructure of the dough matrix significantly affected the metabolites production and cell activity