Lactobacillus pentosus is one of the few lactic acid bacteria (LAB) species capable of surviving in olive brine, and thus desirable during table olive fermentation. We have recently generated mutants ...of the efficient strain L. pentosus C11 by transposon mutagenesis and identified five mutants unable to survive and adapt to olive brine conditions. Since biofilm formation represents one of the main bacterial strategy to survive in stressful environments, in this study, the capacity of adhesion and formation of biofilm on olive skin was investigated for this strain and five derivative mutants which are interrupted in metabolic genes (enoA1 and gpi), and in genes of unknown function (“oba” genes). Confocal microscopy together with bacteria count revealed that the sessile state represented the prevailing L. pentosus C11 life-style during table olive fermentation. The characterization of cell surface properties showed that mutants present less hydrophobic and basic properties than the wild type (WT). In fact, their ability to adhere to both abiotic (polystyrene plates) and biotic (olive skin) surfaces was lower than that of the WT. Confocal microscopy revealed that mutants adhered sparsely to the olive skin instead of building a thin, multilayer biofilm. Moreover, RT-qPCR showed that the three genes enoA1, gpi and obaC were upregulated in the olive biofilm compared to the planktonic state. Thus enoA1, gpi and “oba” genes are necessary in L. pentosus to form an organized biofilm on the olive skin.
•L. pentosus C11 prevails in sessile state during olive fermentation.•Mutants were impaired in adhesion to abiotic and biotic surfaces.•oba, enoA1 and gpi genes are required for biofilm formation on the olive skin.•Olive surface is a biotic support for L. pentosus C11 adhesion and biofilm formation.
To detect rate-limiting steps in the production of lactones by studying the combined effect of pH and aeration on their accumulation. A Doehlert experimental design was chosen to evaluate the ...accumulation of four lactones in the pH (3·5-7·3) and KLa (4·1 h⁻¹ to 26 h⁻¹) experimental domain. The accumulation of γ-decalactone was higher at pH around 5 and increased at low aeration reaching 496 mg l⁻¹ at pH 6·35 and KLa 4·5 h⁻¹. The specific accumulation increased at low aeration. The 3-hydroxy-γ-decalactone accumulation was higher at low pH and high aeration conditions: 660 mg l⁻¹ at pH 4·4 and 26 h⁻¹. For dec-2-en-4-olide and dec-3-en-4-olide, lower amounts were reached (104 mg l⁻¹ and 66 mg l⁻¹, respectively). Although the accumulation of the four lactones should be related to catalytic steps requiring oxygen, the accumulation of γ-decalactone was higher in low aeration conditions whereas the one of 3-hydroxy-γ-decalactone was promoted for high aeration. Decenolides accumulate independently of pH or aeration. This study gives new insights into the catabolism of lipids, such as the role of co-factor regulation and the fact that the 3-hydroxylactone dehydration step is insensitive to pH or aeration.
The gamma- and delta-lactones of less than 12 carbons constitute a group of compounds of great interest to the flavour industry. It is possible to produce some of these lactones through ...biotechnology. For instance, gamma-decalactone can be obtained by biotransformation of methyl ricinoleate. Among the organisms used for this bioproduction, Yarrowia lipolytica is a yeast of choice. It is well adapted to growth on hydrophobic substrates, thanks to its efficient and numerous lipases, cytochrome P450, acyl-CoA oxidases and its ability to produce biosurfactants. Furthermore, genetic tools have been developed for its study. This review deals with the production of lactones by Y. lipolytica with special emphasis on the biotransformation of methyl ricinoleate to gamma-decalactone. When appropriate, information from the lipid metabolism of other yeast species is presented.
Consumption of food or feed contaminated with fumonisin B1 (FB1), a mycotoxin produced by Fusarium verticillioides, can lead to disease in humans and animals. The present study was conducted to ...examine the effect of FB1 intake on the intestinal immune system. Piglets were used as a target and as a model species for humans since their gastro-intestinal tract is very similar. The animals were orally exposed to a low dose of FB1 (1 mg/kg body weight FB1) for 10 days which did not result in clinical signs. However, when compared to non-exposed animals, FB1-exposed animals showed a longer shedding of F4+ enterotoxigenic Escherichia coli (ETEC) following infection and a lower induction of the antigen-specific immune response following oral immunization. Further analyses to elucidate the mechanisms behind these observations revealed a reduced intestinal expression of IL-12p40, an impaired function of intestinal antigen presenting cells (APC), with decreased upregulation of Major Histocompatibility Complex Class II molecule (MHC-II) and reduced T cell stimulatory capacity upon stimulation. Taken together, these results indicate an FB1-mediated reduction of in vivo APC maturation.
Bacteria possess surface properties, related to their charge, hydrophobicity and Lewis acid/base characteristics, that are involved in the attachment processes of microorganisms to surfaces. ...Fermentation bulks and food matrixes are complex heterogeneous media containing various components with different physicochemical characteristics. The aim of the present study was to investigate whether (i) bacteria present in a food matrix, interacted physicochemically at their surface level with the other constituents and (ii) the diversity of bacterial surface properties could result in a diversity of microbial adhesion to components and thus in a diversity of tolerance to toxic compounds. The surface properties of 20 lactic acid bacteria were characterized by the MATS method showing their relatively hydrophilic and various basic characteristics. The results obtained from a set of representative strains showed that (i) the strains with higher affinity for apolar solvents adsorbed more to lipids and hydrophobic compounds, (ii) the more the strains adsorbed to a toxic solvent, the less they were tolerant to this solvent. A diversity of bacterial surface properties was observed for the strains in the same species showing the importance of choosing bacteria according to their surface properties in function of technological objectives.
In colloidal media such as emulsions or food matrixes, the stability results from physicochemical interactions. The same type of interaction is involved in the attachment processes of microorganisms, ...through their surface properties, to interfaces. When bacteria are present in a food matrix, it is probable that their surface interacts with the other constituents. In this paper, the involvement of bacterial surface properties of
Lactococcus lactis subsp
lactis biovar diacetylactis (LLD) on the stability of model emulsions has been studied. The hydrophobic and electrostatic cell-surface properties were characterized by the MATH method and by microelectrophoresis, respectively. The oil-in-water emulsions were stabilized by various surface-active compounds, CTAB, SDS or Tween 20, giving differently charged droplets. Two strains with different surface characteristics were added to the emulsion. Contrasting with emulsions made with the non-ionic surfactant, for which the stability was not modified by the addition of bacteria, the emulsions made with ionic surface-active compounds were unstable in the presence of bacteria when the bacterial surface charge was opposite to the one of the emulsion droplets. Moreover, aggregation and flocculation phenomena were observed for emulsions stabilized with the cationic surfactant, particularly for more negatively charged bacteria. The effect of bacteria on the emulsion stability depended on the strain which shows the importance of the choice of the microorganism according to of the characteristics of the colloidal media to obtain a stable system. In addition, these results suggest that the interactions between bacteria and other food components can influence the position of bacteria in food matrixes.
Responding to consumer' demand for natural products, biotechnology is constantly seeking new biocatalysts. In the field of hydrophobic substrate degradation, some yeast species known some years ago ...as non-conventional, have acquired their right to be considered as good biocatalysts. These Candida, Yarrowia, Sporobolomyces ... are now used for themselves or for their lipases in processes to produce flavours and fragrances. In this paper we present some examples of use of these biocatalysts to generate high-value compounds and discuss the new trends related to progress in the development of molecular tools or the mastering of the redox characteristics of the medium.
β-Carotene is, when cleaved, an important source of flavor and aroma compounds in fruits and flowers. Among these aroma compounds, the main degradation products are β-ionone, 5,6-epoxy-β-ionone, and ...dihydroactinidiolide (DHA), which are associated by flavorists and perfumers with fruity, floral, and woody notes. These three species can be produced by degradation of β-carotene through an attack by enzyme-generated free radicals and a cleavage at the C9−C10 bond. This study investigated the influence of cis/trans isomerism at the C9−C10 bond on the production of β-carotene degradation compounds, first with a predictive approach and then experimentally with different isomer mixtures. β-Carotene solutions containing high ratios of 9-cis-isomers produced more DHA, suggesting a different pathway than for the transformation of all-trans-β-carotene to ionone and DHA. These results are important in the search for financially viable processes to produce natural carotene-derived aroma compounds. Keywords: β-Carotene isomers; xanthine oxidase; β-ionone; dihydroactinidiolide
Bacteria possess physicochemical surface properties such as hydrophobicity, Lewis acid/base and charge which are involved in physicochemical interactions between cells and interfaces. Moreover, food ...matrices are complex and heterogeneous media, with a microstructure depending on interactions between the components in media (van der Waals, electrostatic or structural forces, etc.). Despite the presence of bacteria in fermented products, few works have investigated how bacteria interact with other food components. The objective of the present study was to determine the effects of the surface properties of lactic acid bacteria on the stability of model food emulsions. The bacteria were added to oil/water emulsions stabilized by milk proteins (sodium caseinate, whey proteins concentrate or whey proteins isolate) at different pH (from 3 to 7.5). The effect of bacteria on the emulsions stability depended on the surface properties of strains and also on the characteristics of emulsions. Flocculation and aggregation phenomena were observed in emulsion at pHs for which the bacterial surface charge was opposed to the one of the proteins. The effects of bacteria on the stability of emulsion depended also on the concentration of cations present in media such as Ca
2+. These results show that the bacteria through their surface properties could interact with other compounds in matrices, consequently affecting the stability of emulsions. The knowledge and choice of bacteria depending on their surface properties could be one of the important factors to control the stability of matrices such as fermentation media or fermented products.
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