Candida Humilis Research Articles

Response of wheat sourdough parameters to temperature, NaCl and sucrose variations

Fermentation temperature, NaCl level and sucrose level of a wheat sourdough were varied according to a Box–Behnken response surface design. The effect on yeast increase, lactic acid bacteria (LAB) increase and sourdough acidity was investigated. Yeast and LAB growth increased with temperature in the range from 15°C to 27°C. Optimum growth temperature of two Candida milleri strains, isolated earlier from the same sourdough as used in this study, was between 26°C and 28°C in pure culture. Decreasing temperature affected yeast growth to largely the same extent as LAB. Increasing NaCl addition had a negative effect on yeast growth throughout the range (0–3.2%). A low level of NaCl (up to 0.7%) stimulated LAB growth but higher levels decreased LAB growth drastically, and to a much greater degree than yeast growth. Sucrose addition had a stimulatory effect on both yeast and LAB growth. Sourdough TTA increased with sucrose addition throughout the range (0–6%) and was largely due to the increase in acetic acid accumulation.

Candida humilis—dominant species in sourdoughs for the production of durum wheat bran flour bread

Yeasts present in the sourdough that is generally used for the production of durum wheat bran flour bread were isolated and identified. Samples were taken during the rebuilding phase and at different intervals of time in order to monitor the population dynamics. The results obtained from the phenotypic studies were further confirmed by the molecular studies and enabled us to affirm that most of the strains, more than 95%, belong to the species Candida humilis. The dominance of C. humilis was steady in time. The isolations were carried out at sufficiently long intervals so that it was possible to ascertain that the conditions in which the sourdough is kept are fundamental to the microbiological stability of the dough.

Yeast communities in a natural tequila fermentation.

Fresh and cooked agave, Drosophila spp., processing equipment, agave molasses, agave extract, and fermenting must at a traditional tequila distillery (Herradura, Amatitan, Jalisco, México) were studied to gain insight on the origin of yeasts involved in a natural tequila fermentations. Five yeast communities were identified. (1) Fresh agave contained a diverse mycobiota dominated by Clavispora lusitaniae and an endemic species, Metschnikowia agaveae. (2) Drosophila spp. from around or inside the distillery yielded typical fruit yeasts, in particular Hanseniaspora spp., Pichia kluyveri, and Candida krusei. (3) Schizosaccharomyces pombe prevailed in molasses. (4) Cooked agave and extract had a considerable diversity of species, but included Saccharomyces cerevisiae. (5) Fermenting juice underwent a gradual reduction in yeast heterogeneity. Torulaspora delbrueckii, Kluyveromyces marxianus, and Hanseniaspora spp. progressively ceded the way to S. cerevisiae, Zygosaccharomyces bailii, Candida milleri, and Brettanomyces spp. With the exception of Pichia membranaefaciens, which was shared by all communities, little overlap existed. That separation was even more manifest when species were divided into distinguishable biotypes based on morphology or physiology. It is concluded that crushing equipment and must holding tanks are the main source of significant inoculum for the fermentation process. Drosophila species appear to serve as internal vectors. Proximity to fruit trees probably contributes to maintaining a substantial Drosophila community, but the yeasts found in the distillery exhibit very little similarity to those found in adjacent vegetation. Interactions involving killer toxins had no apparent direct effects on the yeast community structure.

Microbial flora and some chemical properties of ersho, a starter for teff (Eragrostis tef) fermentation

Ersho is a clear, yellow liquid that accumulates on the surface of fermenting teff-flour batter and is collected to serve as an inoculum for the next fermentation. The pH of ersho samples was about 3.5 and titratable acidity ranged between 3.1% and 5.7%. The mean aerobic mesophilic counts from four households varied between 6.9×10(6) and 1.3×10(8) c.f.u./ml and the aerobic bacterial flora consisted of Bacillus spp. Mean yeast counts ranged between 5.2×10(5) and 1.8×10(6) c.f.u./ml and comprised, in order of abundance, Candida milleri, Rhodotorula mucilaginosa, Kluyveromyces marxianus, Pichia naganishii and Debaromyces hansenii. Candida milleri was the most dominant isolate in all samples. About 90% of the teff flour samples had aerobic mesophilic counts ≥10(5) c.f.u./g and Gram-positive bacteria constituted about 71% of the total isolates. About 80% of samples had Enterobacteriaceae counts of 10(4) c.f.u./g.

Candida milleri sp. nov.

Three strains of yeast previously identified as Torulopsis holmii were found to have a considerably higher guanine-plus-cytosine content than the type and other strains of this species and are described as a new species, Candida milleri.