Yeast-Free Doughs by Zymomonas mobilis: Evaluation of Technological and Fermentation Performances by Using a Metabolomic Approach

This research focuses on the leavening performances and development of volatile compounds of three strains of Zymomonas mobilis in the production of yeast-free doughs. Z. mobilis DSM 3580, 424, and 473 were used in doughs supplemented with glucose and with or without NaCl. Z. mobilis produced about 10 mg ethanol/g dough, with maximum dough volumes (640\u2013680 mL) being reached after 2 h leavening. NaCl addition postponed this parameter up to 6 h. Among organic acids, hexanoic acid resulted the highest produced compound; DSM 424 and 473 formed more propanoic, butanoic and pentanoic acid, being both negatively affected by NaCl. Esters were mainly discriminated on NaCl addition, with octanoic acid (DSM 3580), butanoic acid (DSM 424), and propanoic acid (DSM 473) ethyl esters as main components. DSM 3580 specifically produced 2-heptanal, DSM 424 2-hexadecenal, (E) and DSM 473 octanal, while DSM 424 and DSM 473 produced 2-butanone-4-hydroxy better than DSM 3580. Z. mobilis unique signatures were the production of nonanoic and undecanoic acids, 2-hexadecenal, (E), L(+)-tartaric acid diethyl ester and 3-decen-5-one, 4-methyl, (E). This outcome can pave the way for using Z. mobilis in baking goods, providing innovation possibilities in the area of yeast-free leavened products

Zymomonas mobilis: biomass production and use as a dough leavening agent

Zymomonas mobilis ferments only glucose, fructose and sucrose via the Entner-Doudoroff pathway, providing an equimolar mixture of ethanol and CO2 and theoretically, as for Saccharomyces cerevisiae, the gas evolved can be used to leaven a dough. However, the capability of Z. mobilis to produce CO2 has rarely been exploited. In the present study we first evaluated the growing performance of two Z. mobilis strains (DSMZ 424 and 3580) in a culture medium lacking yeast extract, with added glucose or fructose (20 and 50 g/L) comparatively; the results demonstrated that biomass yield is 50 % higher with glucose. The best conditions were up-scaled, obtaining a biomass yield of 1.3–1.4 g dcw/L in a 14-L fermenter. Leavening trials performed in a model system with the biomass collected from fermenters after 9 or 16 h incubation evidenced that Z. mobilis can leaven a model dough as S. cerevisiae does, and showing a CO2 production rate (9–11 mL g dcw−1 min−1) statistically higher than that of S. cerevisiae (6–7 mL g dcw−1 min−1), especially when using 9-h-grown biomass. Bakery products leavened with Z. mobilis could thus be available to people with adverse responses to the ingestion of bakery food, providing innovation in the area of yeast-free leavened baked goods

Mild Pretreatments to Increase Fructose Consumption in Saccharomyces cerevisiae Wine Yeast Strains

The present research investigates the effect of different pretreatments on glucose and fructose consumption and ethanol production by four Saccharomyces cerevisiae wine strains, three isolated and identified from different wine regions in Turkey and one reference strain. A mild stress temperature (45 °C, 1 h) and the presence of ethanol (14% v/v) were selected as pretreatments applied to cell cultures prior to the fermentation step in synthetic must. The goodness fit of the mathematical models was estimated: linear, exponential decay function and sigmoidal model were evaluated with the model parameters R2 (regression coefficient), RMSE (root mean square error), MBE (mean bias error) and χ2 (reduced Chi-square). Sigmoidal function was determined as the most suitable model with the highest R2 and lower RMSE values. Temperature pretreatment allowed for an increase in fructose consumption rate by two strains, evidenced by a t90 value 10% lower than the control. One of the indigenous strains showed particular promise for mild temperature treatment (45 °C, 1 h) prior to the fermentation step to reduce residual glucose and fructose in wine. The described procedure may be effective for indigenous yeasts in preventing undesirable sweetness in wines

Zymomonas mobilis in Bread Dough: Characterization of Dough Leavening Performance in Presence of Sucrose

Zymomonas mobilis, because of its fermentative metabolism, has potential food applications in the development of leavened baked goods consumable by people with adverse responses to Saccharomyces cerevisiae. Since Z. mobilis is not able to utilize maltose present in flour, the effect of sucrose addition (2.5 g/100 g flour) on bread dough leavening properties was studied. For comparison purposes, leavening performances of S. cerevisiae with and without sucrose were also investigated. Doughs leavened by Z. mobilis without sucrose addition showed the lowest height development (14.95 ± 0.21 mm) and CO2 production (855 ± 136 mL). When sucrose was added, fermentative performances of Z. mobilis significantly (p < 0.05) improved (+80% and +85% of gas production and retention, respectively), with a dough maximum height 2.6 times higher, results indicating that Z. mobilis with sucrose can be leavened in shorter time with respect to the sample without addition. S. cerevisiae did not benefit the sucrose addition in terms of CO2 production and retention, even if lag leavening time was significantly (p < 0.05) shorter (about the half) and time of porosity appearance significantly (p < 0.05) longer (about 26%) with respect to S. cerevisiae alone. Results demonstrate that in the presence of sucrose, Z. mobilis can efficiently leaven a bread dough, thus providing innovation possibilities in the area of yeast-free leavened products

Characterization of Two <i>Zymomonas mobilis</i> Wild Strains and Analysis of Populations Dynamics during Their Leavening of Bread-like Doughs

Two Zymomonas mobilis wild strains (UMB478 and 479) isolated from water kefir were characterized for their biomass production levels and leavening performance when used as the inoculum of a real bread-like dough formulation. The obtained baked product would be consumable by people with adverse responses to Saccharomyces cerevisiae. In liquid cultures, the two strains reached similar biomass concentration (0.7 g CDW/L). UMB479 showed an interesting resistance to NaCl (MBC 30 g/L), that may be useful in the bakery sector. When inoculated in doughs, UMB479 produced the maximum dough volume (650 mL) after 5 h, glucose was almost consumed and 1 g/100 g of ethanol produced, +200% respective to UMB478. Using S. cerevisiae for comparison purposes, the dough doubled its volume fast, in only 2 h, but reached a final level of 575 mL, lower than that achieved by Z. mobilis. The analysis of bacterial and fungal population dynamics during dough leavening was performed through the Automated Ribosomal Intergenic Spacer Analysis (ARISA); doughs leavened by UMB479 showed an interesting decrease in fungal richness after leavening. S. cerevisiae, instead, created a more complex fungal community, similar before and after leavening. Results will pave the way for the use of Z. mobilis UMB479 in commercial yeast-free leavened products

Comparative performance of enzymatic and combined alkaline-enzymatic pretreatments on methane production from ensiled sorghum forage

This study investigated the effect of enzymatic and combined alkaline-enzymatic pretreatments on chemical composition and methane production from ensiled sorghum forage. Four commercial enzymatic preparations were tested and the two yielding the highest sugars release were added to evaluate any hydrolytic effect on both untreated and alkaline pretreated samples. In the combined alkaline-enzymatic pretreatment trials, the highest sugar release was found with Primafast and BGL preparations (added at a final concentration 0.12 and 0.20 mL/g TS, respectively), with a total monomeric content of 12 and 6.5 g/L. Fibre composition analysis confirmed that the combined alkaline-enzymatic pretreatment led to cellulose (up to 32 %) and hemicelluloses (up to 56 %) solubilisation, compared to the enzymatic pretreatment alone. BMP tests were performed on both untreated and pretreated samples, and time courses of methane production were fitted. Both enzymatic and combined alkaline-enzymatic pretreatment led to a methane production increase (304 and 362 mL CH4/g VS), compared to that of untreated sorghum (265 mL CH4/g VS), as +15 and +37 %, respectively. Moreover, higher specific methane production rates, compared to that of untreated sorghum (20.31 mL CH4/g VS/d), were obtained by applying the enzymatic and combined alkaline-enzymatic pretreatment (33.94 and 31.65 mL CH4/g VS/d), respectively

From Cheese Whey Permeate to Sakacin A: A Circular Economy Approach for the Food-Grade Biotechnological Production of an Anti-Listeria Bacteriocin

Cheese Whey Permeate (CWP) is the by-product of whey ultrafiltration for protein recovery. It is highly perishable with substantial disposal costs and has serious environmental impact. The aim of the present study was to develop a novel and cheap CWP-based culture medium for Lactobacillus sakei to produce the food-grade sakacin A, a bacteriocin exhibiting a specific antilisterial activity. Growth conditions, nutrient supplementation and bacteriocin yield were optimized through an experimental design in which the standard medium de Man, Rogosa and Sharpe (MRS) was taken as benchmark. The most convenient formulation was liquid CWP supplemented with meat extract (4 g/L) and yeast extract (8 g/L). Although, arginine (0.5 g/L) among free amino acids was depleted in all conditions, its supplementation did not increase process yield. The results demonstrate the feasibility of producing sakacin A from CWP. Cost of the novel medium was 1.53 &euro;/L and that of obtaining sakacin A 5.67 &euro;/106 AU, with a significant 70% reduction compared to the corresponding costs with MRS (5.40 &euro;/L, 18.00 &euro;/106 AU). Taking into account that the limited use of bacteriocins for food application is mainly due to the high production cost, the obtained reduction may contribute to widening the range of applications of sakacin A as antilisterial agent

Assessment of anammox, microalgae and white-rot fungi-based processes for the treatment of textile wastewater.

The treatability of seven wastewater samples generated by a textile digital printing industry was evaluated by employing 1) anammox-based processes for nitrogen removal 2) microalgae (Chlorella vulgaris) for nutrient uptake and biomass production 3) white-rot fungi (Pleurotus ostreatus and Phanerochaete chrysosporium) for decolorization and laccase activity. The biodegradative potential of each type of organism was determined in batch tests and correlated with the main characteristics of the textile wastewaters through statistical analyses. The maximum specific anammox activity ranged between 0.1 and 0.2 g N g VSS-1 d-1 depending on the sample of wastewater; the photosynthetic efficiency of the microalgae decreased up to 50% during the first 24 hours of contact with the textile wastewaters, but it improved from then on; Pleurotus ostreatus synthetized laccases and removed between 20-62% of the colour after 14 days, while the enzymatic activity of Phanerochaete chrysosporium was inhibited. Overall, the findings suggest that all microbes have great potential for the treatment and valorisation of textile wastewater after tailored adaptation phases. Yet, the depurative efficiency can be probably enhanced by combining the different processes in sequence