Highest Acetic Acid Production Research Articles

Bioaugmentation with Enterococcus casseliflavus: A Hydrogen-Producing Strain Isolated from Citrus Peel Waste

To isolate, identify and characterize an anaerobic strain from in natura CPW, in relation to the consumption of different carbon sources, growth kinetics and H2 production after bioaugmentation. Several substrates were evaluated (glucose, fructose, sucrose, xylose, starch, cellobiose, cellulose and lactose), and its optimal concentration was evaluated by Experimental Design method, besides the application of the isolated strain in citrus peel waste (CPW). A facultative anaerobic strain, similar (99%) to Enterococcus casseliflavus, was isolated from in natura citrus pulp and bagasse. Xylose was the monomer from which there was greater H2 production (10.3 mmol L−1). For 0.5 to 6.5 gxylose L−1, 3.0 to 12.9 mmol H2 L−1 was obtained, respectively. Generation time (Tg) of 0.35 h and specific growth (µ) of 1.98 h−1 for pH 7.0, 37 °C and 2 g glucose L−1 was obtained for E. casseliflavus. In bioaugmentation assays (CPW + E. casseliflavus), highest maximum H2 production potential (P = 13.9 mmol L−1), maximum H2 production rate (Rm = 1.09 mmol h−1) and time to start the H2 production (λ = 2.12 h−1) was observed when compared to glucose (P = 9.1 mmol L−1; Rm = 1.99 mmol h−1; λ = 4.08 h−1). From glucose, there was prevalence of butyric acid pathway (759 mg L−1) in relation to acetic acid (303 mg L−1). From CPW, there was higher production of acetic acid (878 mg L−1) in relation to butyric (147 mg L−1). The application of E. casseliflavus by bioaugmentation is an alternative for biodigestion of complex substrates, such as CPW, to obtain products of biotechnological interest.

Enhanced fermentative hydrogen production from industrial wastewater using mixed culture bacteria incorporated with iron, nickel, and zinc-based nanoparticles

The present study assessed the efficiency of utilizing mixed culture bacteria (MCB) incorporated with individual nanoparticles (NPs), i.e., hematite (α-Fe2O3), nickel oxide (NiO), and zinc oxide (ZnO), dual NPs (α-Fe2O3 + NiO, α-Fe2O3 + ZnO, and NiO + ZnO), and multi-NPs (α-Fe2O3 + NiO + ZnO) for hydrogen production (HP) from industrial wastewater containing mono-ethylene glycol (MEG). When MCB was individually supplemented with α-Fe2O3 (200 mg/L), NiO (20 mg/L), and ZnO NPs (10 mg/L), HP improved significantly by 41, 30, and 29%, respectively. Further, key enzymes associated with MEG metabolism, such as alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), and hydrogenase (hyd), were rapidly and substantially enhanced in the medium. NiO and ZnO NPs notably promoted ADH and ALDH activities, respectively, while α-Fe2O3 exhibited superior impact on hyd activity. Maximum hydrogen production rate was concomitant with higher acetic acid production and lower residual acetaldehyde and ethanol. HP using MCB supplemented with individual NiO (20 mg/L) and ZnO NPs (10 mg/L) further improved by 8.0%–14% when dual and multi-NPs were used; the highest HP was recorded when multi-NPs were used. In addition, NPs incorporation resulted in substantial increase in the relative abundance of Clostridiales (belonging to family Clostridiaceae; > 83%). Overall, this study provides significant insights into the impact of NPs on hydrogen production from MEG-contaminated wastewater.

Exploiting synergies of sourdough and antifungal organic acids to delay fungal spoilage of bread

Fungal spoilage of bread remains an unsolved issue in bread making. This work aims to identify alternative strategies to conventional preservatives in order to prevent or delay fungal spoilage of bread. The minimum inhibitory concentration (MIC) of bacterial metabolites and chemical preservatives was evaluated in vitro, and compared to their in situ activity in baking trials. Calcium propionate, sorbic acid, 3-phenyllactic acid, ricinoleic acid, and acetic acid were tested both individually and in combination at their MIC values against Aspergillus niger and Penicillium roqueforti. The combination of acetic acid with propionate and sorbate displayed additive effects against the two fungi. For these reasons, we introduced sourdough fermentation with specific strains of lactobacilli, using wheat or flaxseed, in order to generate acetate in bread. A combination of Lactobacillus hammesii and propionate reduced propionate concentration required for shelf life extension of wheat bread 7-fold. Flaxseed sourdough bread fermented with L. hammesii, excluding any preservative, showed a shelf life 2 days longer than the control bread. The organic acid quantification indicated a higher production of acetic acid (33.8 ± 4.4 mM) when compared to other sourdough breads. Addition of 4% of sucrose to sourdough fermentation with L. brevis increased the mould free shelf-life of bread challenged with A. niger by 6 days. The combination of L. hammesii sourdough and the addition of ricinoleic acid (0.15% or 0.08%) prolonged the mould free shelf-life by 7–8 days for breads produced with wheat sourdoughs. In conclusion, the in vitro MIC of bacterial metabolites and preservatives matched the in situ antifungal effect. Of the different bacterial metabolites evaluated, acetic acid had the most prominent and consistent antifungal activity. The use of sourdough fermentation with selected strains able to produce acetic acid allowed reducing the use of chemical preservatives.

A Growth-Promoting Bacteria, Paenibacillus yonginensis DCY84T Enhanced Salt Stress Tolerance by Activating Defense-Related Systems in Panax ginseng

Panax ginseng (C.A. Mayer) is a well-known medicinal plant used in traditional medicine in Korea that experiences serious salinity stress related to weather changes or incorrect fertilizer application. In ginseng, the use of Paenibacillus yonginensis DCY84T to improve salt stress tolerance has not been thoroughly explored. Therefore, we studied the role of P. yonginensis DCY84T under short-term and long-term salinity stress conditions in a controlled environment. In vitro testing of DCY84T revealed high indole acetic acid (IAA) production, siderophore formation, phosphate solubilization and anti-bacterial activity. We determined that 10-min dip in 1010 CFU/ml DCY84T was sufficient to protect ginseng against short-term salinity stress (osmotic stress) upon exposure to 300 mM NaCl treatment by enhancing nutrient availability, synthesizing hydrolyzing enzymes and inducing osmolyte production. Upon exposure to salinity stress (oxidative and ionic stress), strain DCY84T-primed ginseng seedlings were protected by the induction of defense-related systems such as ion transport, ROS scavenging enzymes, proline content, total sugars, and ABA biosynthetic genes, as well as genes involved in root hair formation. Additionally, ginseng primed with DCY84T and exposed to 300 mM NaCl showed the same metabolite profile as control ginseng plants, suggesting that DCY84T effectively reduced salt stress. These results indicated that DCY84T can be widely used as a microbial inoculant to protect ginseng plants against salinity stress conditions.

Mangrove endophyte promotes reforestation tree (Acacia polyphylla) growth.

Mangroves are ecosystems located in the transition zone between land and sea that serve as a potential source of biotechnological resources. Brazil's extensive coast contains one of the largest mangrove forests in the world (encompassing an area of 25,000 km2 along all the coast). Endophytic bacteria were isolated from the following three plant species: Rhizophora mangle, Laguncularia racemosa and Avicennia nitida. A large number of these isolates, 115 in total, were evaluated for their ability to fix nitrogen and solubilize phosphorous. Bacteria that tested positive for both of these tests were examined further to determine their level of indole acetic acid production. Two strains with high indole acetic acid production were selected for use as inoculants for reforestation trees, and then the growth of the plants was evaluated under field conditions. The bacterium Pseudomonas fluorescens (strain MCR1.10) had a low phosphorus solubilization index, while this index was higher in the other strain used, Enterobacter sp. (strain MCR1.48). We used the reforestation tree Acacia polyphylla. The results indicate that inoculation with the MCR1.48 endophyte increases Acacia polyphylla shoot dry mass, demonstrating that this strain effectively promotes the plant's growth and fitness, which can be used in the seedling production of this tree. Therefore, we successfully screened the biotechnological potential of endophyte isolates from mangrove, with a focus on plant growth promotion, and selected a strain able to provide limited nutrients and hormones for in plant growth.

Insights on Osmotic Tolerance Mechanisms in Escherichia coli Gained from an rpoC Mutation.

An 84 bp in-frame duplication (K370_A396dup) within the rpoC subunit of RNA polymerase was found in two independent mutants selected during an adaptive laboratory evolution experiment under osmotic stress in Escherichia coli, suggesting that this mutation confers improved osmotic tolerance. To determine the role this mutation in rpoC plays in osmotic tolerance, we reconstructed the mutation in BW25113, and found it to confer improved tolerance to hyperosmotic stress. Metabolite analysis, exogenous supplementation assays, and cell membrane damage analysis suggest that the mechanism of improved osmotic tolerance by this rpoC mutation may be related to the higher production of acetic acid and amino acids such as proline, and increased membrane integrity in the presence of NaCl stress in exponential phase cells. Transcriptional analysis led to the findings that the overexpression of methionine related genes metK and mmuP improves osmotic tolerance in BW25113. Furthermore, deletion of a stress related gene bolA was found to confer enhanced osmotic tolerance in BW25113 and MG1655. These findings expand our current understanding of osmotic tolerance in E. coli, and have the potential to expand the utilization of high saline feedstocks and water sources in microbial fermentation.

Antimicrobial Activities of Five Strains Of Lactococcus Isolated from Beef Against Indicator Organisms of Public Health Significance

Five strains of Lactococcus, including L. garviae K2, L. piscium SU4, L. lactis subsp. cremoris E22, L. plantarum L7 and L. lactis subsp. hordinae E91 were screened for production of antimicrobial agents. The strains were also analysed for antimicrobial activities against spoilage and pathogenic organisms, including Staphylococcus aureus, Salmonella Typhimurium, Escherichia coli, Yersinia enterocolitica, Pseudomonas aeruginosa, Klebsiella pneumoniae, Listeria monocytogenes, Bacillus cereus and Pseudomonas fluorescens. Result revealed that L. piscium SU4, L. plantarum L7 and L. lactis subsp. cremoris E22 had lactic acid production (g/107 colony forming units, CFU) of 7.23, 7.20 and 7.19. The value of 6.83 recorded as lactic acid produced by L. garviae K2 was significantly different from those obtained for others. The highest acetic acid production (3.55 g/107 CFU) was recorded for L. garviae K2 while L. piscium SU4 had the lowest (2.99 g/107 CFU). L. lactis subsp. hordinae E91 had diacetyl production of 71.99 (µg/107 CFU), which was higher than those recorded for other Lactococcus strains. Test for antimicrobial activities showed that Escherichia coli NCTC 86, Yersinia enterocolitica NCTC 10460, Pseudomonas aeruginosa NCIMB 10848, Bacillus cereus NCTC 21113 and Pseudomonas flourescens recorded higher susceptibilities to the antimicrobial action of the Lactococcus strains than others; zones of inhibition of 5 mm and above were recorded for the indicator organisms compared to lower values (

Microbial diversity and biochemical characteristics of Borassus akeassii wine.

Palm wine produced traditionally and consumed by many people in the South-West of Burkina Faso is subject to alteration. In this study, we carried out a follow-up of two palm wines' fermentation during the 10days in which palm wines are classically produced and consumed. We monitored biochemical characteristics of fermenting wines as well as followed the microflora kinetics using culture-dependent and culture-independent methods. The analysis of the acid content and the bacterial population revealed the correlation between the development of Lactic acid bacteria, acetic acid, and total acidity. Ribosomal intergenic spacer analysis and sequencing results revealed different yeast and bacterial populations for the two palm wines. Although Saccharomyces cerevisiae remained the sole yeast species in one fermentation, it was quickly replaced by Clavispora lusitaniae in the second fermentation, which had never been described until now in palm wine. When considering bacteria, the species Corynebacterium sp., Lactobacillus casei, Lactobacillus paracasei and Leuconostoc sp. were detected in both palm wines. But we also detected Acetobacter pasteurianus, Bacillus cereus and Bacillus thuringiensis in the second fermentation. Our results highlight the evolution of palm wine during the 10days separating palm tapping and consumption of the fermented wine. The fermentation step is performed within few hours and completed after 24h. The next days, its acidity increases progressively with the production of lactic and acetic acids by bacteria. The high production of acetic acid is very likely one of the main cause of palm wine degradation during this period. This indicates that the solution to palm wine preservation might be protection against oxygen, as well as the limit of bacterial growth through the use of preservatives.

Social wasp intestines host the local phenotypic variability of Saccharomyces cerevisiae strains.

Nowadays, the presence of Saccharomyces cerevisiae has been assessed in both wild and human-related environments. Social wasps have been shown to maintain and vector S. cerevisiae among different environments. The availability of strains isolated from wasp intestines represents a striking opportunity to assess whether the strains found in wasp intestines are characterized by peculiar traits. We analysed strains isolated from the intestines of social wasps and compared them with strains isolated from other sources, all collected in a restricted geographic area. We evaluated the production of volatile metabolites during grape must fermentation, the resistance to different stresses and the ability to exploit various carbon sources. Wasp strains, in addition to representing a wide range of S. cerevisiae genotypes, also represent large part of the phenotypes characterizing the sympatric set of yeast strains; their higher production of acetic acid and ethyl acetate could reflect improved ability to attract insects. Our findings suggest that the relationship between yeasts and wasps should be preserved, to safeguard not only the natural variance of this microorganism but also the interests of wine-makers, who could take advantage from the exploitation of their phenotypic variability. Copyright © 2016 John Wiley & Sons, Ltd.

High Acetic Acid Production Rate Obtained by Microbial Electrosynthesis from Carbon Dioxide.

High product specificity and production rate are regarded as key success parameters for large-scale applicability of a (bio)chemical reaction technology. Here, we report a significant performance enhancement in acetate formation from CO2, reaching comparable productivity levels as in industrial fermentation processes (volumetric production rate and product yield). A biocathode current density of -102 ± 1 A m(-2) and an acetic acid production rate of 685 ± 30 (g m(-2) day(-1)) have been achieved in this study. High recoveries of 94 ± 2% of the CO2 supplied as the sole carbon source and 100 ± 4% of electrons into the final product (acetic acid) were achieved after development of a mature biofilm, reaching an elevated product titer of up to 11 g L(-1). This high product specificity is remarkable for mixed microbial cultures, which would make the product downstream processing easier and the technology more attractive. This performance enhancement was enabled through the combination of a well-acclimatized and enriched microbial culture (very fast start-up after culture transfer), coupled with the use of a newly synthesized electrode material, EPD-3D. The throwing power of the electrophoretic deposition technique, a method suitable for large-scale production, was harnessed to form multiwalled carbon nanotube coatings onto reticulated vitreous carbon to generate a hierarchical porous structure.

Multivariate analysis of buckwheat sourdough fermentations for metabolic screening of starter cultures

This study investigated the metabolic activity of 35 strains of lactic acid bacteria (LAB), which were able to grow in buckwheat sourdoughs and delivers a detailed explanation of LAB metabolism in that environment. To interpret the high-dimensional dataset, descriptive statistics and linear discriminant analysis (LDA) were used. Heterofermentative LAB showed a clear different metabolism than facultative (f.) heterofermentative and homofermentative LAB, which were more similar. Heterofermentative LAB were mainly characterized by high free SH groups and acetic acid production; they were also able to consume arabinose and glucose. Homofermenters were mainly characterized by lower free amino nitrogen content and they did not show a good capacity to consume arabinose and fructose. Except for the heterofermentative Weissella cibaria strain, only homofermentative strains showed high ornithine yields. Some f. heterofermentative strains differed from homofermentative due to the high lactic acid production as well as low glucose and arginine consumption. LAB containing more genes encoding peptidase activities and genes involved in aroma production showed a high consumption of free amino acids. Strain-dependent activities could be clearly distinguished from group dependent ones (homofermentative, f. heterofermentative and heterofermentative), e.g., some Lactobacillus paracasei and Lactobacillus plantarum strains showed the highest carbohydrate consumption. However, some microbial activities were more strain-dependent than group-dependent. Multivariate analysis of raw data delivered a detailed and clear explanation of LAB metabolism in buckwheat sourdough fermentations.

Interactions between Bifidobacterium and Bacteroides Species in Cofermentations Are Affected by Carbon Sources, Including Exopolysaccharides Produced by Bifidobacteria

Cocultures of strains from two Bifidobacterium and two Bacteroides species were performed with exopolysaccharides (EPS) previously purified from bifidobacteria, with inulin, or with glucose as the carbon source. Bifidobacterium longum NB667 and Bifidobacterium breve IPLA20004 grew in glucose but showed poor or no growth in complex carbohydrates (inulin, EPS E44, and EPS R1), whereas Bacteroides grew well in the four carbon sources tested. In the presence of glucose, the growth of Bacteroides thetaiotaomicron DSM-2079 was inhibited by B. breve, whereas it remained unaffected in the presence of B. longum. Ba. fragilis DSM-2151 contributed to a greater survival of B. longum, promoting changes in the synthesis of short-chain fatty acids (SCFA) and organic acids in coculture with respect to monocultures. In complex carbohydrates, cocultures of bifidobacterium strains with Ba. thetaiotaomicron did not modify the behavior of Bacteroides nor improve the poor growth of bifidobacteria. The metabolic activity of Ba. fragilis in coculture with bifidobacteria was not affected by EPS, but greater survival of bifidobacteria at late stages of incubation occurred in cocultures than in monocultures, leading to a higher production of acetic acid than in monocultures. Therefore, cocultures of Bifidobacterium and Bacteroides can behave differently against fermentable carbohydrates as a function of the specific characteristics of the strains from each species. These results stress the importance of considering specific species and strain interactions and not simply higher taxonomic divisions in the relationship among intestinal microbial populations and their different responses to probiotics and prebiotics.

Isolation of a high malic and low acetic acid-producing sake yeast Saccharomyces cerevisiae strain screened from respiratory inhibitor 2,4-dinitrophenol (DNP)-resistant strains

We isolated 2,4-dinitrophenol (DNP)-resistant sake yeast strains by UV mutagenesis. Among the DNP-resistant mutants, we focused on strains exhibiting high malic acid and low acetic acid production. The improved organic acid composition is unlikely to be under the control of enzyme activities related to malic and acetic acid synthesis pathways. Instead, low mitochondrial activity was observed in DNP-resistant mutants, indicating that the excess pyruvic acid generated during glycolysis is not metabolized in the mitochondria but converted to malic acid in the cytosol. In addition, the NADH/NAD(+) ratio of the DNP-resistant strains was higher than that of the parental strain K901. These results suggest that the increased NADH/NAD(+) ratio together with the low mitochondrial activity alter the organic acid composition because malic acid synthesis requires NADH, while acetic acid uses NAD(+).

Biohydrogen Production from Cheese Whey Wastewater in a Two-Step Anaerobic Process

Cheese whey-based biohydrogen production was seen in batch experiments via dark fermentation by free and immobilized Enterobacter aerogenes MTCC 2822 followed by photofermentation of VFAs (mainly acetic and butyric acid) in the spent medium by Rhodopseudomonas BHU 01 strain. E. aerogenes free cells grown on cheese whey diluted to 10 g lactose/L, had maximum lactose consumption (∼79%), high production of acetic acid (1,900 mg/L), butyric acid (537.2 mg/L) and H(2) yield (2.04 mol/mol lactose; rate,1.09 mmol/L/h). The immobilized cells improved lactose consumption (84%), production of acetic acid (2,100 mg/L), butyric acid (718 mg/L) and also H(2) yield (3.50 mol/mol lactose; rate, 1.91 mmol/L/h). E. aerogenes spent medium (10 g lactose/L) when subjected to photofermentation by free Rhodopseudomonas BHU 01 cells, the H(2) yield reached 1.63 mol/mol acetic acid (rate, 0.49 mmol/L/h). By contrast, immobilized Rhodopseudomonas cells improved H(2) yield to 2.69 mol/mol acetic acid (rate, 1.87 mmol/L/h). The cumulative H(2) yield for free and immobilized bacterial cells was 3.40 and 5.88 mol/mol lactose, respectively. Bacterial cells entrapped in alginate, had a sluggish start of H(2) production but outperformed the free cells subsequently. Also, the concomitant COD reduction for free cells (29.5%) could be raised to 36.08% by immobilized cells. The data suggest that two-step fermentative H(2) production from cheese whey involving immobilized bacterial cells, offers greater substrate to- hydrogen conversion efficiency, and the effective removal of organic load from the wastewater in the long-term.

Efficient Production Process for Food Grade Acetic Acid by Acetobacter aceti in Shake Flask and in Bioreactor Cultures

Acetic acid is one of the important weak acids which had long history in chemical industries. This weak organic acid has been widely used as one of the key intermediate for many chemical, detergent, wood and food industries. The production of this acid is mainly carried out using submerged fermentation system and the standard strain Acetobacter aceti. In the present work, six different media were chosen from the literatures and tested for acetic acid production. The highest acetic acid production was produced in medium composed of glucose, yeast extract and peptone. The composition of this medium was optimized by changing the concentration of medium components. The optimized medium was composed of (g/L): glucose, 100; yeast extract, 12 and peptone 5 and yielded 53 g/L acetic acid in shake flask after 144 h fermentation. Further optimization in the production process was achieved by transferring the process to semi‐industrial scale 16‐L stirred tank bioreactor and cultivation under controlled pH condition. Under fully aerobic conditions, the production of acetic acid reached maximal concentration of about 76 g/L and 51 g/L for uncontrolled and controlled pH cultures, respectively.

Achieving high yield production of acetic acid by Gluconobacter oxydans in bioreactor

Achieving high yield production of acetic acid by Gluconobacter oxydans in bioreactor

Analysis of volatile compounds produced by different species of lactobacilli in rye sourdough using multiple headspace extraction

SummaryProfiles of volatile organic compound (VOC) produced by nine individual lactic acid bacteria (LAB) during rye sourdough fermentation were compared by automated SPME and GC/MS‐Tof. The dough samples were inoculated with individual strains, placed inside the headspace vials and incubated during next 24 h. The production or loss of VOC‐s was followed by adsorbing volatiles onto 85‐m Car/PDMS fibre in every 4 h. Volatile profiles differed among LAB species and divided LAB into two main groups – hetero‐ and homofermentative. Hetrofermentative LAB (Lactobacillus brevis; Leuconostoc citreum; Lactobacillus vaginalis, Lactobacillus panis) showed high production of acetic acid, CO2, ethanol, ethylacetate, producing also hexyl acetate, ethyl hexanoate and isopentyl acetate. Whereas homofermentative LAB species (Lactobacillus helveticus; Lactobacillus casei; Lactobacillus sakei; Lactobacillus curvatus) produced a considerable amount of 2,3‐butanedione. Production of l‐leucine methyl ester was unique for Lb. sakei, Lb. casei and Lb. curvatus strains. Lb. helveticus was the only LAB that produced benzaldehyde.

An FTIR study of Rh-PtSn/C catalysts for ethanol electrooxidation: Effect of surface composition

The effect of adding various amounts of Rh to a carbon-supported Pt3Sn electrocatalyst for the electrooxidation of ethanol is evaluated by electrochemical methods and single potential alteration infrared reflectance spectroscopy (SPAIRS). This technique was used to identify intermediate species and the final products of ethanol electrooxidation and to track their evolution with the reaction potential. Rh addition to Pt3Sn/C was accomplished by impregnation, and this process resulted in Rh-modified catalysts of controlled composition. The Pt3Sn stoichiometry of the original sample was maintained after Rh addition, as demonstrated by analysis with X-ray diffraction (XRD) and transmission electron microscopy (TEM). The selectivity for partially oxidized products, acetaldehyde and acetic acid is promoted on the Rh-PtSn/C electrocatalysts; however, the electrooxidation of ethanol to CO2 is only marginally promoted by the addition of Rh to PtSn/C. The higher production of acetic acid on the Rh-modified PtSn/C electrodes, rather than the production of CO2, is responsible for the higher current density recorded during the electrooxidation of ethanol on Rh-PtSn/C.

Fermentative capability and aroma compound production by yeast strains isolated from Agave tequilana Weber juice

Five yeast strains isolated from agave juice were studied for their fermentative and aromatic capacity. The experiments were performed using agave juice supplemented with ammonium sulphate, as is commonly done in tequila distilleries. Three strains classified as Saccharomyces cerevisiae showed high biomass and ethanol production, as well as higher ethanol tolerance than those classified as Kloeckera africana and Kloeckera apiculata, which showed scarce growth. The results suggest that Kloeckera strains were affected by nutritional limitation and/or toxic compounds present in agave juice. Agave juice analyses showed a lower amino acid content than those reported in grape juice. S. cerevisiae strains produced predominantly amyl and isoamyl alcohols, n-propanol, 2-phenyl ethanol, succinic acid, glycerol, methanol, isoamyl acetate, ethyl hexanoate, acetaldehyde and isobutanol, whereas Kloeckera strains showed a high production of acetic acid, 2-phenyl ethyl acetate and ethyl acetate. The methanol concentration was significantly different among the yeasts studied. The diversity between three S. cerevisiae strains were higher for the aromatic profile than for genetic level and kinetic parameter. On the other hand, the diversity of Kloeckera yeasts were lower than Saccharomyces yeasts even when belonging to two different species.

Development of alcoholic and malolactic fermentations in highly acidic and phenolic apple musts

This work reports the influence of the high acidity and high phenolic content in apple musts on the development of alcoholic and malolactic fermentations and on the final chemical and microbiological composition of the ciders. Four different musts were obtained by pressing several varieties and proportions of cider apples from the Basque Country (Northern Spain). Specially acidic and phenolic varieties were selected. Three musts were obtained in experimental stations and the fourth one, in a cider factory following usual procedures. The evolution of these musts was monitored during five months by measuring 18 parameters throughout eight samplings. In the most acidic of the three experimental musts, yeasts were added to complete the alcoholic fermentation. In the rest of the musts, alcoholic and malolactic fermentations took place spontaneously due to natural microflora and no chemical was added to control these processes. Malolactic fermentation (MLF) finished before alcoholic fermentation in the three tanks obtained in experimental stations, even in the most acidic and phenolic one (pH 3.18, 1.78 g tannic acid/l). After four months, these ciders maintained low levels of lactic acid bacteria (⩽10 4 CFU/ml) and low content of acetic acid (<0.60 g/l). Both fermentations began simultaneously in the must obtained in the cider factory, but MLF finished 10 days after alcoholic fermentation. Subsequently, this must maintained a high population of lactic acid bacteria (>10 6 CFU/ml), causing a higher production of acetic acid (>1.00 g/l) than in the other ciders. These results show the possible advantages of MLF finishing before alcoholic fermentation.