New bacterial agents to limit Colletotrichum gloeosporioides development on mango

Mango anthracnose disease forms typical irregular-shaped black necrotic spots on the fruit peel of mature fruit and is caused by Colletotrichum gloeosporioides. In order to improve the disease control with a limited use of fungicides, new microbial agents able to limit the growth of the pathogen were searched in the indigenous natural flora of mango surface. In order to find a suitable biocontrol agent, a screening was applied to 305 epiphytic bacteria isolated from the carposphere of 17 mango cultivars sampled from eight locations on Reunion Island. The screening approach involved a first step based on the ability of the isolates to form a biofilm, to grow under fruit storage conditions, and to interfere with the development of C. gloeosporioides. In a second step, the capability of selected isolates to limit C. gloeosporioides in vitro mycelial growth and conidia germination was assessed and species identified. The most effective bacteria belonged to the Enterobacter, Pantoea, Kosakonia and Leuconostoc genera, but for some of them, their safe use has to be demonstrated. Efficacy in vivo, performed on wounded mature mango fruit, was limited, probably because of the wounding inoculation strategy favoring the pathogen. Future biocontrol treatments should focus on preharvest applications to enhance the protective benefit

Influence of temperature, solvent and pH on the selective extraction of phenolic compounds from tiger nuts by-products: Triple-TOF-LC-MS-MS characterization.

The aim of this study was to assess the effect of temperature, solvent (hydroethanolic mixtures) and pH on the recovery of individual phenolic compounds from 'horchata' by-products. These parameters were optimized by response surface methodology and triple-TOF-LC-MS-MS was selected as the analytical tool to identify and quantify the individual compounds. The optimum extraction conditions were 50% ethanol, 35 °C and pH 2.5, which resulted in values of 222.6 mg gallic acid equivalents (GAE)/100 g dry matter and 1948.1 µM trolox equivalent (TE)/g of dry matter for total phenolic content (TPC) and trolox equivalent antioxidant capacity (TEAC), respectively. The extraction of phenolic compounds by the conventional solvent method with agitation was influenced by temperature (p = 0.0073), and more strongly, by the content of ethanol in the extraction solution (p = 0.0007) while the pH did not show a great impact (p = 0.7961). On the other hand, the extraction of phenolic acids was affected by temperature (p = 0.0003) and by ethanol amount (p < 0.0001) but not by the pH values (p = 0.53). In addition, the percentage of ethanol influenced notably the extraction of both 4-vinylphenol (p = 0.0002) and the hydroxycinnamic acids (p = 0.0039). Finally, the main individual phenolic extracted with hydroethanolic mixtures was 4-vinylphenol (303.3 μg/kg DW) followed by spinacetin3-O-glucosyl-(1→6)-glucoside (86.2 μg/kg DW) and sinensetin (77.8 μg/kg DW)

Obtaining antioxidants and natural preservatives from food by-products through fermentation: A review

Industrial food waste has potential for generating income from high-added-value compounds through fermentation. Solid-state fermentation is promising to obtain a high yield of bioactive compounds while requiring less water for the microorganism’s growth. A number of scientific studies evinced an increase in flavonoids or phenolics from fruit or vegetable waste and bioactive peptides from cereal processing residues and whey, a major waste of the dairy industry. Livestock, fish, or shellfish processing by-products (skin, viscera, fish scales, seabass colon, shrimp waste) also has the possibility of generating antioxidant peptides, hydrolysates, or compounds through fermentation. These bioactive compounds (phenolics, flavonoids, or antioxidant peptides) resulting from bacterial or fungal fermentation are also capable of inhibiting the growth of commonly occurring food spoilage fungi and can be used as natural preservatives. Despite the significant release or enhancement of an-tioxidant compounds through by-products fermentation, the surface areas of large-scale bioreactors and flow patterns act as constraints in designing a scale-up process for improved efficiency. An in-process purification method can also be the most significant contributing factor for raising the overall cost. Therefore, future research in modelling scale-up design can contribute towards mitigating the discard of high-added-value generating residues. Therefore, in this review, the current knowledge on the use of fermentation to obtain bioactive compounds from food by-products, emphasizing their use as natural preservatives, was evaluated

Biotechnology of Wine Yeasts

International audienceThe story of biotechnology of wine yeasts started a long time ago. The selection of yeasts from wineries for commercial purposes was developed from the 1970s. The aim was to display satisfactory fermentation profi les and to ensure product quality. From the 1980s, classical breeding, interspecifi c breeding and mutagenesis were applied for the improvement of existing strains. This resulted in many developments: for example, better nitrogen assimilation and fermentation kinetics were obtained by random mutagenesis (Salmon and Barre 1998). These classical approaches are still used; EMS (ethyl methyl sulfonate) mutagenesis resulted in the selection of commercial wine strain variants which produce less reduced hydrogen sulfi de due to mutations into genes encoding sulfi de reductase subunits (Cordente et al. 2009). But genomic features of wine yeasts were rapidly identifi ed as strong limitations for these approaches. Indeed, wine strains are mainly diploid, polyploid or aneuploid. They exhibit a chromosomal polymorphism (Bidenne et al. 1992). Chromosomal trisomies or tetrasomies result in impaired sporulation ability and in highly variable spore viability (Johnston et al. 2000). In addition, wine strains are generally homothallic, i.e., able to switch mating type when haploid, and highly heterozygous. All these features confer to wine yeast, high genome plasticity and limit the stability of lineage of variants

Safety and Microbiological Quality

International audienc

Why Are Weissella spp. Not Used as Commercial Starter Cultures for Food Fermentation?

International audienceAmong other fermentation processes, lactic acid fermentation is a valuable process which enhances the safety, nutritional and sensory properties of food. The use of starters is recommended compared to spontaneous fermentation, from a safety point of view but also to ensure a better control of product functional and sensory properties. Starters are used for dairy products, sourdough, wine, meat, sauerkraut and homemade foods and beverages from dairy or vegetal origin. Among lactic acid bacteria, Lactobacillus, Lactococcus, Leuconostoc, Streptococcus and Pediococcus are the majors genera used as starters whereas Weissella is not. Weissella spp. are frequently isolated from spontaneous fermented foods and participate to the characteristics of the fermented product. They possess a large set of functional and technological properties, which can enhance safety, nutritional and sensory characteristics of food. Particularly, Weissella cibaria and Weissella confusa have been described as high producers of exo-polysaccharides, which exhibit texturizing properties. Numerous bacteriocins have been purified from Weissella hellenica strains and may be used as bio-preservative. Some Weissella strains are able to decarboxylate polymeric phenolic compounds resulting in a better bioavailability. Other Weissella strains showed resistance to low pH and bile salts and were isolated from healthy human feces, suggesting their potential as probiotics. Despite all these features, the use of Weissella spp. as commercial starters remained non-investigated. Potential biogenic amine production, antibiotic resistance pattern or infection hazard partly explains this neglecting. Besides, Weissella spp. are not recognized as GRAS (Generally Recognized As Safe). However, Weissella spp. are potential powerful starters for food fermentation as well as Lactococcus, Leuconostoc or Lactobacillus species

Genetic and technological characterization of lactic acid bacteria isolated from tropically grown fruits and vegetables

International audienc

Engineering of the Pyruvate Dehydrogenase Bypass in Saccharomyces cerevisiae: Role of the Cytosolic Mg(2+) and Mitochondrial K(+) Acetaldehyde Dehydrogenases Ald6p and Ald4p in Acetate Formation during Alcoholic Fermentation

Acetic acid plays a crucial role in the organoleptic balance of many fermented products. We have investigated the factors controlling the production of acetate by Saccharomyces cerevisiae during alcoholic fermentation by metabolic engineering of the enzymatic steps involved in its formation and its utilization. The impact of reduced pyruvate decarboxylase (PDC), limited acetaldehyde dehydrogenase (ACDH), or increased acetoacetyl coenzyme A synthetase (ACS) levels in a strain derived from a wine yeast strain was studied during alcoholic fermentation. In the strain with the PDC1 gene deleted exhibiting 25% of the PDC activity of the wild type, no significant differences were observed in the acetate yield or in the amounts of secondary metabolites formed. A strain overexpressing ACS2 and displaying a four- to sevenfold increase in ACS activity did not produce reduced acetate levels. In contrast, strains with one or two disrupted copies of ALD6, encoding the cytosolic Mg(2+)-activated NADP-dependent ACDH and exhibiting 60 and 30% of wild-type ACDH activity, showed a substantial decrease in acetate yield (the acetate production was 75 and 40% of wild-type production, respectively). This decrease was associated with a rerouting of carbon flux towards the formation of glycerol, succinate, and butanediol. The deletion of ALD4, encoding the mitochondrial K(+)-activated NAD(P)-linked ACDH, had no effect on the amount of acetate formed. In contrast, a strain lacking both Ald6p and Ald4p exhibited a long delay in growth and acetate production, suggesting that Ald4p can partially replace the Ald6p isoform. Moreover, the ald6 ald4 double mutant was still able to ferment large amounts of sugar and to produce acetate, suggesting the contribution of another member(s) of the ALD family

Etude et caractérisation de l'état " Viable mais Non Cultivable " chez Brettanomyces, une levure d'altération des vins (nouvel outil de détection et de quantification spécifique de Brettanomyces en vin)

L état Viable Non Cultivable (VNC) a été observé et décrit chez de nombreuses espèces bactériennes. Mais cet état métabolique a également été suggéré chez certaines cellules eucaryotes, et notamment chez les levures du vin comme Brettanomyces. L état VNC chez cette levure a donc été étudié afin d en déterminer les conditions d entrée et de sortie, ainsi que les modifications morphologiques et métaboliques associées à cet état VNC. Une addition de sulfite (0,8 mg/L de SO2 moléculaire) induit un état VNC chez Brettanomyces, et une inactivation de ce sulfite par modification du pH du milieu permet une sortie de l état VNC de la levure par un regain de cultivabilité. Dans les conditions VNC, la taille moyenne des cellules de Brettanomyces a été déterminée comme diminuée de 22% comparée à leur taille en condition contrôle. Ensuite, la capacité des cellules à produire des phénols volatils, éléments de contamination des vins, est conservée même lorsque les cellules sont en état Viable Non Cultivable. De plus, l étude comparative des protéomes entre cellules de Brettanomyces témoin et cellules en état VNC montre une modification du métabolisme avec une diminution de la synthèse d ATP compensée par une augmentation des protéines impliquées dans d autres voies métaboliques de production d énergie. Cette étude met donc en évidence pour la première fois l existence de l état VNC chez une espèce eucaryote et montre des points communs avec l état VNC chez les cellules procaryotes. L existence de cet état VNC chez Brettanomyces peut également engendrer des erreurs de détection. Un nouvel outil de détection par hybridation in situ et lecture par cytométrie en flux a donc été mis en place. Cette méthode permet ainsi la mise en évidence des cellules de Brettanomyces présentes en vin de façon efficace et rapide.The viable but not culturable (VBNC) state has been studied in detail in bacteria. It has been suggested that the VBNC state also exists in eukaryote cells, such as wine yeasts, including Brettanomyces in particular. We investigated the VBNC state in this yeast, focusing on the conditions for entry and exit, and the morphological and metabolic modifications associated with this state. We added sulfite (0.8 mg.L-1 molecular SO2) to induce the VBNC state. Increasing the pH of the medium inactivated the sulfite, allowing the cells to exit from the VBNC state and to become culturable again. In these conditions, we found that Brettanomyces VBNC cells were smaller than culturable cells, and that spoilage by volatile phenols could persist during VBNC state. Furthermore, according to our proteome comparison, it seems that the blockade of ATP synthesis was compensated by an increase in energy-producing metabolism pathway. This study provides the first insight into the VBNC state in eukaryote cells, showing common trend to the VBNC state of prokaryotic cells. The existence of VBNC state in Brettanomyces cells can also provoke errors of detection. A new tool of detection by fluorescence in situ hybridization and reading by flow cyometry was thus set up. This method allows the revealing of Brettanomyces cells presence in wine in an efficient and fast way.DIJON-BU Doc.électronique (212319901) / SudocSudocFranceF