Search

Spontaneous cereal fermentations involve diverse lactic acid bacteria (LAB) and yeasts which may include multifunctional and safe or unsafe strains. This study assessed acidification ability, safety, antifungal activity and free amino acids release ability of LAB and yeasts previously isolated from spontaneously fermented cereal doughs in Benin. Fourteen LAB and thirteen yeast strains were studied in liquid media and/or in a model cereal dough prepared in laboratory conditions. Antifungal activity was assessed against Candida glabrata in liquid medium. Amino acids were determined by pre-column derivatization and separation with reversed-phase HPLC. Antimicrobial susceptibility was analysed by minimum inhibitory concentration determination. The acidification ability was higher for LAB compared to yeast strains. All LAB strains retarded the growth of C. glabrata Cg1 with the highest inhibition recorded for Weissella confusa Wc1 and Wc2. The highest free amino acid content was found in the doughs fermented with Pichia kudriavzevii Pk2 and Pk3. All the LAB strains were susceptible to ampicillin, chloramphenicol, erythromycin, but displayed phenotypic resistance to kanamycin, streptomycin and tetracycline. Positive PCR amplicon of resistance genes were detected in the following cases: 2 LAB strains were positive for kanamycin (aph(3)III), 5 strains were positive for streptomycin (aadA and/or strA and/or strB) and 3 strains were positive for tetracycline (tet (L) and/or tet (M)). For yeasts, most of the P. kudriavzevii strains were resistant to amphotericin B, fluconazole and itraconazole opposite to K. marxianus and Saccharomyces cerevisiae strains which were susceptible. The results obtained are valuable for selecting safe and multifunctional strains for cereal fermentation in West Africa. [ABSTRACT FROM AUTHOR]

A good understanding of the socio-demographic and economic factors which characterize the food value chains (FVC) of traditional African fermented foods is a major prerequisite for developing and implementing scientific evidence-based policies towards the improvement of Africa’s food and nutrition security and sustainable agriculture. This study aims at identifying the key factors which shape the FVC for mawè and its derived products. Mawè is a traditional fermented cereal dough, widely consumed in Benin. The findings of the study show that mawè and its derived products are processed, marketed, and consumed through both ‘traditional’ and ‘traditional-to-modern’ value chains. The traditional chain plays a key role in facilitating food affordability for low-income people. However, the traditional-to-modern value chain is increasingly predominant, especially in an urbanized environment, and consequently offers greater opportunities for value chain upgrading for value-added processing of traditional fermented foods. The study offers insights into policy and research challenges in value chain upgrading. [ABSTRACT FROM AUTHOR]

Fermented cereal doughs constitute a predominant part of West African diets. The environment of fermented doughs can be hostile for microbial survival due to high levels of microbial metabolites such as weak carboxylic organic acids and ethanol. In order to get a better understanding of the intrinsic factors affecting the microbial successions of yeasts during dough fermentation, survival and physiological responses of the yeasts associated with West African fermented cereal doughs were investigated at exposure to relevant concentrations of microbial inhibitory compounds. Three strains each of the predominant species, i.e. Saccharomyces cerevisiae , Kluyveromyces marxianus , Pichia kudriavzevii as well as the opportunistic pathogen Candida glabrata were studied. The strains were exposed to individual stress factors of cereal doughs, i.e. (i) pH 3.4, (ii) 3% (v /v) ethanol (EtOH pH3.4), (iii) 285 mM lactic acid (LA pH3.4) and (iv) 150 mM acetic acid (AA pH3.4) as well as to combinations of these stress factors, i.e. (v) (LA + AA) pH 3.4 and (vi) (LA + AA+EtOH) pH 3.4. Growth and single cell viability were studied by flow cytometry using combined SYTO 13 and propidium iodide (PI) staining. Intracellular pH (pH i), plasma membrane integrity and micro-colony development of stressed cells were studied by fluorescence microscopy using PI and carboxyfluorescein diacetate succinimidyl ester (CFDA-se). Viability of the yeast strains was not affected by pH 3.4 and 3% (v /v) ethanol (EtOH pH3.4). 285 mM lactic acid (LA pH3.4) reduced the specific growth rate (μ max) from 0.27-0.41 h−1 to 0.11–0.26 h−1 and the viability from 100% to 2.6–41.7% at 72 h of exposure in most yeast strains, except for two strains of C. glabrata. 150 mM acetic acid (AA pH3.4) as well as the combinations (LA + AA) pH 3.4 and (LA + AA+EtOH) pH 3.4 reduced μ max to 0.0 h−1 and induced significant cell death for all the yeast strains. Exposed to (LA + AA+EtOH) pH 3.4 , the most resistant yeast strains belonged to S. cerevisiae followed by P. kudriavzevii , whereas C. glabrata and K. marxianus were more sensitive. Strain variations were observed within all four species. When transferred to non-stress conditions, i.e. MYGP, pH 5.6, after exposure to (LA + AA+EtOH) pH 3.4 for 6 h, 45% of the single cells of the most resistant S. cerevisiae strain kept their plasma membrane integrity, recovered their pH i to near physiological range (pH i = 6.1–7.4) and resumed proliferation after 3–24 h of lag phase. The results obtained are valuable in order to change processing conditions of the dough to favor the survival of preferable yeast species, i.e. S. cerevisiae and K. marxianus and inhibit opportunistic pathogen yeast species as C. glabrata. • The intrinsic stress factors of mawè doughs have a synergistic negative impact on yeast survival • Ethanol and pH did not affect yeast survival, while organic acids with ethanol at low pH strongly affected yeast survival • The sensitivity of the examined yeasts was species, strain and cell dependent • Saccharomyces cerevisiae strains were generally the least sensitive • pH i and membrane integrity are key physiological parameters for yeast cell sensitivity [ABSTRACT FROM AUTHOR]