High Concentrations Of Acetic Acid Research Articles

Study of two-phase anaerobic digestion of corn stover: Focusing on the conversion of volatile fatty acids and microbial characteristics in UASB reactor

Methanogenic performance and microbial communities including both bacteria and archaea in UASB reactor treating acidogenic metabolites from acidification of ensiled corn stover (ECS) were investigated. Gradient organic loading rates (OLRs) were adopted to study the conversion of volatile fatty acids (VFAs) characterized by high concentration of acetic acid and propionic acid. The removal rate of chemical oxygen demand (COD) reached above 80.0 % at OLR of 8 g/L·d and volumetric methane production rate improved significantly as the OLR increased. When OLR was 10 g COD/L·d, acetic and propionic acids in effluent were accumulated and failure of methane production occurred. Compared with the control, the methanogenic inhibition was caused by the presence of high concentration of propionic acid. The profile of conversion of individual VFAs in UASB reactors was investigated at different OLRs. Furthermore, microbial communities in anaerobic sludge at OLR of 8 g COD/L·d were compared with those in inoculum and the shift of bacteria and archaea were analyzed. The abundances of some representative acetogenic bacteria such as Proteobacteria (14.18 %) and Bacteroidetes (11.16 %) increased obviously, which contributed to the oxidation and decomposition of organic acids. Acetotrophic methanogen (Methanosaeta) and hydrogenotrophic methanogen (Methanobacterium) played synergistic roles with acetogens to efficiently complete the VFAs conversion. This study will be of great importance to guide the application of two-phase AD of agricultural waste in full-scale plant.

Sequential fed batch extractive fermentation for enhanced bioethanol production using recycled Spathaspora passalidarum and mixed sugar composition

The simultaneous ethanol production and removal during sequential cell recycle fed batch fermentation provides a complementary route to produce this biofuel from sugar mixtures, which may greatly improve yields and productivity from lignocellulosic hydrolysates. Spathaspora passalidarum is a wild-type strain able to naturally convert glucose, fructose, xylose and arabinose into ethanol. Therefore, the present work has focused on 2G bioethanol production by S. passalidarum aiming at the consumption of all sugars released after pre-treatment and enzymatic hydrolysis of sugarcane bagasse in a single fermentation step. The fermentation strategy with sequential cell recycle, fed-batch mode and ethanol removal in situ was performed on a hemicellulosic hydrolysate medium supplemented with molasses. This strategy gave improved fermentation performance and enabled the co-fermention of all sugars under microaerobic conditions. The maximum ethanol yield and productivity was 0.482 g.g−1 and 9.5 g·L-1·h−1, respectively, showing a process efficiency of 94.3%. The selective ethanol removal enables the operation of the bioreactor at low levels of ethanol (20–30 g·L-1), even with high sugar concentration inputs, accelerating the fermentation performance and avoiding inhibitory effects on yeast metabolism. Applying the cell recycle strategy, S. passalidarum was able to increase its robustness, as shown by a 10-fold increase in ethanol productivity, and it was also able to tolerate a high acetic acid concentration (4.5 g·L-1) during long-term fermentations. These results demonstrate that the bioprocess strategy has a strong potential to improve bioethanol production of rich mixed sugar from lignocellulosic hydrolysates in a single fermentation step.

Dietary Alaska pollock protein attenuates liver steatosis and alters gut microbiota in leptin-deficient ob/ob mice

• Alaska pollock protein attenuated liver steatosis in leptin-deficient ob/ob mice. • Alaska pollock protein activated liver fatty acid oxidation through PPARα pathway. • Alaska pollock protein enhanced acetic acid production in cecal contents. • Alaska pollock protein improved the structure of the microbiota in cecal content. This study examined the effects of dietary Alaska pollock ( Theragra chalcogramma ) protein (APP) on nonalcoholic fatty liver disease (NAFLD) and gut microbiota in leptin-deficient ob/ob mice. Mice were fed with high-fat diet containing either casein or APP for six weeks. Then, lipid accumulation and mRNA expression levels in the liver and the composition and metabolites of the gut microbiota were evaluated. Dietary APP attenuated liver steatosis in part through the enhancement and suppression of gene expression involved in liver fatty acid oxidation and synthesis, respectively. The enhancement of liver peroxisome proliferator-activated receptor alpha mRNA expression level by APP consumption may be partly due to the high acetic acid content in cecal contents. Moreover, APP consumption modified the structure of the microbiota and high relative abundance of probiotic bacteria and low relative abundances of Bacteroides and Blautia in cecal content. Therefore, APP consumption could help prevent NAFLD development.

Fine‐tuning ethanol oxidation pathway enzymes and cofactor PQQ coordinates the conflict between fitness and acetic acid production by Acetobacter pasteurianus

The very high concentrations required for industrial production of free acetic acid create toxicity and low pH values, which usually conflict with the host cell growth, leading to a poor productivity. Achieving a balance between cell fitness and product synthesis is the key challenge to improving acetic acid production efficiency in metabolic engineering. Here, we show that the synergistic regulation of alcohol/aldehyde dehydrogenase expression and cofactor PQQ level could not only efficiently relieve conflict between increased acetic acid production and compromised cell fitness, but also greatly enhance acetic acid tolerance of Acetobacter pasteurianus to a high initial concentration (3% v/v) of acetic acid. Combinatorial expression of adhA and pqqABCDE greatly shortens the duration of starting-up process from 116 to 99h, leading to a yield of 69gl-1 acetic acid in semi-continuous fermentation. As a final result, average acetic acid productivity has been raised to 0.99gl-1 h-1 , which was 32% higher than the parental A.pasteurianus. This study is of great significance for decreasing cost of semi-continuous fermentation for producing high-strength acetic acid industrially. We envisioned that this strategy will be useful for production of many other desired organic acids, especially those involving cofactor reactions.

Antioxidant status, chemical composition and fermentation profile of alfalfa silage ensiled at two dry matter contents with a novel Lactobacillus plantarum strain with high-antioxidant activity

The objective of this study was to evaluate the effects of a novel Lactobacillus plantarum strain with high-antioxidant activity on antioxidant status, chemical composition and fermentation profiles of alfalfa silage ensiled at two dry matter (DM) contents. Fresh chopped alfalfa was wilted to two targeted dry matter (DM) contents of approximately 300 (low DM) and 400 (high DM) g/kg fresh weight and treated without or with a strain of L. plantarum 24−7 with high antioxidant activity. Forages were ensiled in vacuum-sealed polyethylene bags containing ∼600 g wilted forage for 60 d, with 5 replicates for each treatment. Alfalfa silage ensiled at low DM had higher concentrations of acetic acid and non-protein nitrogen (NPN) and lower concentrations of lactic acid, propionic acid and water soluble carbohydrates (WSC) than silages with high DM. Inoculation of L. plantarum 24−7 led to lower silage pH and lower concentrations of NPN, neutral detergent fiber (aNDF), acid detergent fiber (ADF), and higher WSC compared to the control silage at two DM contents. Inoculation increased aerobic stability of the forage ensiled at low DM but decreased that ensiled at high DM. In control silages, almost half of the α-tocopherol and β-carotene was degraded during ensiling, whereas inoculation with L. plantarum 24−7 increased α-tocopherol and β-carotene concentrations as well as the proportion of polyunsaturated fatty acids (PUFA) in ensiled alfalfa at both DM contents. Greater concentrations of β-carotene were observed in L. plantarum 24−7 treated-silage at low DM compared to silage at high DM. The application of L. plantarum 24−7 strain also increased total antioxidant capacity (T-AOC), glutathione peroxidase (GSH-Px) and catalase (CAT) activities of the alfalfa silage but decreased superoxide dismutase (SOD) and lipoxygenase (LOX) activities. These results indicate that L. plantarum 24−7 improved the fermentation quality and antioxidant status of ensiled alfalfa forage relative to the control silage.

Effects of Lactobacillus hilgardii 4785 and Lactobacillus buchneri 40788 on the bacterial community, fermentation and aerobic stability of high-moisture corn silage.

To evaluate the capacity of Lactobacillus hilgardii and Lactobacillus buchneri on modifying the bacterial community and improving fermentation and aerobic stability of high-moisture corn (HMC). High-moisture corn was untreated (CTR), treated with L. hilgardii (LH) or L. buchneri (LB) at 600000CFU per gram fresh weight, or with L. hilgardii and L. buchneri at 300000CFU per gram fresh weight each (LHLB), and stored for 10, 30 or 92days. Compared to CTR, inoculated silages had higher Lactobacillaceae relative abundance, lower yeasts numbers and higher aerobic stability. Treatment with LHLB resulted in a higher acetic acid concentration than LH and higher 1,2 propanediol concentration than LB, such differences were numerically greater at 10 and 30days but statistically greater at 92days. At 10days, all inoculated silages were more stable than CTR, but LHLB was even more stable than LB or LH. The combination of L. hilgardii and L. buchneri had a synergistic effect on yeast inhibition, leading to greater improvements in aerobic stability as early as 10days after ensiling. Lactobacillus hilgardii, especially in combination with L. buchneri, can improve the aerobic stability of HMC after a very short period of ensiling.

Physiological characterization of a new thermotolerant yeast strain isolated during Brazilian ethanol production, and its application in high-temperature fermentation

BackgroundThe use of thermotolerant yeast strains can improve the efficiency of ethanol fermentation, allowing fermentation to occur at temperatures higher than 40 °C. This characteristic could benefit traditional bio-ethanol production and allow simultaneous saccharification and fermentation (SSF) of starch or lignocellulosic biomass.ResultsWe identified and characterized the physiology of a new thermotolerant strain (LBGA-01) able to ferment at 40 °C, which is more resistant to stressors as sucrose, furfural and ethanol than CAT-1 industrial strain. Furthermore, this strain showed similar CAT-1 resistance to acetic acid and lactic acid, and it was also able to change the pattern of genes involved in sucrose assimilation (SUC2 and AGT1). Genes related to the production of proteins involved in secondary products of fermentation were also differentially regulated at 40 °C, with reduced expression of genes involved in the formation of glycerol (GPD2), acetate (ALD6 and ALD4), and acetyl-coenzyme A synthetase 2 (ACS2). Fermentation tests using chemostats showed that LBGA-01 had an excellent performance in ethanol production in high temperature.ConclusionThe thermotolerant LBGA-01 strain modulates the production of key genes, changing metabolic pathways during high-temperature fermentation, and increasing its resistance to high concentration of ethanol, sugar, lactic acid, acetic acid, and furfural. Results indicate that this strain can be used to improve first- and second-generation ethanol production in Brazil.

Mechanistic interpretation on acidic stress-corrosion cracking of NiCrMoV steam turbine steel

The present work evaluates the acidic stress-corrosion cracking (SCC) of NiCrMoV steam turbine steel. Between a pH of 4.2 and 7, iron oxidises to Fe2O3, whereas iron dissolution (Fe2+) and hydrogen proton (H+) reduction are favoured at lower pH. The corrosion rate increases with the H+ concentration via a linear relationship as well as by a temperature increase. During in-situ constant extension rate testing, both the ductility and strength losses, caused by anodic dissolution and hydrogen embrittlement, increase with a higher acetic acid concentration. Hydrogen embrittlement causes larger embrittled zones with higher acetic acid concentrations as well as stress-corrosion cracking.

Microbial Diversity of Acetic Acid Producing Bacteria from Protein-Rich Residues

Background: Acetic acid bacteria (AAB) are concrete sets of organism which act as precursor for acetic acid production. Acetic acid is a colorless liquid with strong pungent and sour smell. It is synthesized from oxidation of ethanol by AAB. Vast studies have been made from sugary sources in the isolation of AAB.
 Aim: The needs to study and utilize our protein-rich residues (PRR) for AAB presence spurn this study.
 Place and Duration of Study: Department of Microbiology, University of Port Harcourt, between June and December 2018.
 Methodology: The samples (beans, groundnut and powdered milk) used in this study were surface-sterilized, homogenized, pre-enriched (in balsam medium) and serially diluted with inoculum size (0.1ml) inoculated on sterilized glucose yeast peptone agar, Mannitol agar and low glycemic index (LGI) media and incubated at 30oC for 48 h using the spread plate technique. A total of 11 bacterial isolates were obtained and screened for acetic acid production in brain heart infusion and yeast glucose ethanol acetic acid broth at 30oC for 14 days and positive isolates were identified by titration method. AAB isolates with the highest acetic acid concentration were selected for molecular identification and further studies.
 Results: Two Acetic acid bacteria identified in this study were Acetobacter and Gluconobacter. The result of this study indicated that Acetobacter had acetic acid concentration of 3.6g/100ml while Gluconobacter had 1.8g/100 ml. However, molecular identification highlighted Acetobacter as Bacillus cereus with Genbank accession number MK 332142; whereas Gluconobacter was Stenotrophomonas maltophilia MK 332143. The neighbor-joining phylogenetic tree and bioinformatics revealed B. cereus and S. maltophilia as 97% and 96% similarity index, 854 and 883 nucleotide sequencing letters as well as 450 and 410 base pairs.
 Conclusion: This finding implied that “S. maltophilia” and “B. cereus” are predominant Acetic acid bacteria in spoilt beans and groundnut; and can act as potential strains with industrial importance to man and environment.

Beet Pulp: An Alternative to Improve the Gut Health of Growing Pigs.

Simple SummaryImproving disease resistance in pig is a major challenge faced by the pig industry. Intestinal health plays a critical role in modulating disease resistance in pigs. Dietary fiber has been widely recognized to prevent intestinal disorders in pigs. We found that feeding 5.74% crude fiber (obtained from beet pulp) to growing pigs could modulate gut microbiota composition and increase the short-chain fatty-acid content in the hindgut, suggesting that dietary supplementation with a high dose of fiber derived from beet pulp can help improve the gut health of growing pigs.The present study aimed to investigate the effects of dietary fiber on the gut health of growing pigs. In total, 30 growing pigs with an initial average body weight of 45.8 ± 2.78 kg were divided into three groups with 10 replicates per treatment, and one pig per replicate. The treatments included a corn–soybean meal-based diet (control group, 1.5% crude fiber (CF)), corn–soybean meal + beet pulp-based diet (beet pulp group, 5.74% CF) and corn–soybean meal-based diet (feed intake-pairing group (pairing group); the feed intake was equal to the beet pulp group, 1.5% CF). The whole trial lasted 28 days. The beet pulp group had a longer length of the large intestine, higher weight of the small intestine and whole intestine, greater density of the large intestine and whole intestine, and higher villus height in the jejunum and ileum than the control group (p < 0.05). The messenger RNA (mRNA) expression levels of epidermal growth factor (EGF), glucagon-like peptide 2 (GLP-2), and glucagon-like peptide 2 receptor (GLP-2R) in the duodenum, EGF and GLP-2 in the jejunum, EGF in the ileum, and GLP-2 in the colon were higher in the beet pulp group than in the control group (p < 0.05). Moreover, the apparent total tract digestibility of crude ash, energy, dry matter (DM), and crude protein (CP) was lower in the beet pulp group than in the control group (p < 0.05), while the apparent total tract digestibility of CF, the activity of jejunal lactase, and the mRNA abundance of duodenal GLP-2 were higher in the beet pulp group than in the control and pairing groups (p < 0.05). In addition, the beet pulp group had more goblet cells in the colon, more Bifidobacterium spp. in the cecal digesta, higher concentrations of acetic acid and butyric acid in the cecal digesta, and higher mRNA abundance of duodenal regeneration protein Ⅲγ (REG-Ⅲγ), jejunal mucin 2 (MUC-2), and ileal G protein-coupled receptor 43 (GPR-43) than the control group (p < 0.05). However, these parameters did not differ between the control and pairing groups (p > 0.05). These findings indicate feeding a high-fiber diet (5.74% CF, obtained from beet pulp) to pigs could modulate the gut microbiota composition, increase the short-chain fatty-acid (SCFA) content in the hindgut, and improve gut health, which is independent of the feed intake.

Physicochemical and microbiological quality in the fermentation of different cocoa blends with the addition of coffee and cardamom

Fermentation is an essential step in obtaining good quality almonds. Thus, the present study aimed to evaluate the fermentation process of cocoa almonds and quantify the physicochemical and microbiological quality of different cocoa blends with the addition of coffee and cardamom, aiming at the reduction of the cost of processing, the addition of value to the raw material, and technological and scientific development of the Amazon region. The experimental design used was completely randomized, arranged in a 4 x 2 x 3 factorial scheme, corresponding to four fermentation times, two fermentation, three concentrations of pulp (blends) (pure cocoa, cocoa + coffee, and cocoa + cardamom), and three replicates. The results made it possible to conclude that the temperature inside the mass measured every 48 hours after turning increased with the fermentation time, reaching its maximum on the seventh day of fermentation. The increase in the temperature inside the fermentation mass on the seventh day is due to the higher concentration of acetic acid, evidenced by the reduction in pH value and consequent reduction in °Brix. Fermentation in a greenhouse at a temperature of 40 °C enables the maintenance of stable temperature throughout the fermentation process for blends of cocoa with the addition of coffee and cardamom. It is verified that, when there is a pre-established temperature, as in a greenhouse at 40 °C, there is a decrease in the values of °Brix and soluble solids present in the final product. Temperature, pH, and sugars are determining factors for the duration of the fermentation process and quality of pure cocoa almonds and cocoa almonds with the addition of coffee and cardamom. Under the experimental conditions, fermentation time from seven days is sufficient to ensure the physicochemical and microbiological quality of cocoa blends with the addition of coffee and cardamom, but it should not exceed nine days.

Production and characterization of two fractions of pyrolysis liquid from agricultural and wood residues

Liquids obtained by fractional condensation of pyrolysis vapors from two types of lignocellulosic biomass, namely Jerusalem artichoke stalk (high cellulose and ash contents) and white birch bark (high lignin and extractive contents), were compared. Using two condensers connected in series, a dark oily fraction rich in phenolic compounds and sugar derivatives was obtained at 90 °C (respectively, 14% of total polyphenols and 11% of total carbohydrates for the oily fraction from the agricultural stalk) followed by aqueous fraction at 0 °C. Stalk yielded a homogeneous oily fraction whereas the bark oily liquid was heterogeneous, due possibly to lignin pyrolysis products. Both yielded clear orange aqueous fractions having a chemical composition close to wood vinegar, > 60% water, and high concentrations of acetic acid, with also a significant content of polyphenols, around 5%. This study showed that fractional condensation could be a vital tool in pyrolysis-based biorefinery producing an oily (application as an energy source or as a chemical feedstock) and an aqueous fraction (applications as biocide or biostimulation in agriculture) by pyrolysis of vastly different lignocellulosic biomasses.

Biosynthesis of myo-inositol in Escherichia coli by engineering myo-inositol-1-phosphate pathway

Myo-inositol is widely used in drug, food and animal feed industries. In this study, the myo-inositol biosynthetic pathway was established in Escherichia coli by introducing the myo-inositol-1-phosphate synthase-encoding gene (INO1) from Saccharomyces cerevisiae SC288. The production of myo-inositol was also investigated in shake flasks. The results showed that gene INO1 was succefully expressed in E. coli as verified by SDS-PAGE analysis. The initial glucose concentrations in M9 media had a positive impact on the production of myo-inositol and acetic acid, OD600 of cells and plasmid stability. The highest concentration of myo-inositol was obtained at the initial glucose concentration of 30 g/L, which reached 887 mg/L. When the initial concentration of glucose was 40 g/L, a lot of acetic acid was accumulated (8.53 g/L), causing slightly decrease in the concentration of myo-inositol. The recombinant plasmid was more unstable at higher initial concentration of glucose as compared to a lower one. 797 mg/L of myo-inositol was ultimately produced in a 1 L shake flask at the initial glucose concentration of 10 g/L. The maximal OD600 of cells and the highest concentration of acetic acid were 7.18 and 3.05 g/L, respectively. This study lays good foundation for understanding the biosynthesis of myo-inositol in E. coli and provides the possibility of applying myo-inositol to the industrial production by recombinant E. coli in future.

Bioconversion in batch bioreactor of olive-tree pruning biomass optimizing treatments for ethanol production

Processes efficiency for second-generation ethanol production depends mainly on the type of lignocellulosic raw material. Therefore, the optimization (considering a central composite design) for each step involved in olive-tree pruning biomass valorization was studied: (1) alkaline pretreatment of the original feedstock, (2) diluted acid hydrolysis of pretreated solids and (3) fermentation of the hemicellulosic hydrolyzates for ethanol production by Scheffersomyces stipitis. The recommended alkaline pretreatment conditions were 30 min, 90 °C and 0.5% w/v NaOH, with losses of 88.3% of acetyl groups from starting biomass, but only 6.9% of D-xylose. Comparing both, in natura and previously treated acid hydrolyzates at the most effective conditions (2.0% w/v H2SO4 and 60 min) revealed more inhibitory effect for non-treated liquor, with 4.8, 2.1 and 1.6 times higher concentrations of acetic acid, furans and phenolic compounds, respectively. A significant improvement in ethanol production was observed in treated hemicellulose liquor (20.4 g dm−3, YP/S = 0.20 g g−1 and QP = 0.21 g dm−3 h−1). In contrast, the yeast could not satisfactorily ferment the reference hydrolyzate. Biomass pretreatment with alkali previously to dilute acid hydrolysis was a suitable strategy for olive-tree pruning biomass biotransformation, substantially decreasing the hydrolyzate toxicity, without requiring an additional detoxification step.

Auxin regulation and MdPIN expression during adventitious root initiation in apple cuttings

Adventitious root (AR) formation is critical for the efficient propagation of elite horticultural and forestry crops. Despite decades of research, the cellular processes and molecular mechanisms underlying AR induction in woody plants remain obscure. We examined the details of AR formation in apple (Malus domestica) M.9 rootstock, the most widely used dwarf rootstock for intensive production, and investigated the role of polar auxin transport in postembryonic organogenesis. AR formation begins with a series of founder cell divisions and elongation of the interfascicular cambium adjacent to vascular tissues. This process is associated with a relatively high indole acetic acid (IAA) content and hydrolysis of starch grains. Exogenous auxin treatment promoted this cell division, as well as the proliferation and reorganization of the endoplasmic reticulum and Golgi membrane. In contrast, treatment with the auxin transport inhibitor N-1-naphthylphthalamic acid (NPA) inhibited cell division in the basal region of the cuttings and resulted in abnormal cell divisions during the early stage of AR formation. In addition, PIN-FORMED (PIN) transcripts were differentially expressed throughout the whole AR development process. We also detected upregulation of MdPIN8 and MdPIN10 during induction; upregulation of MdPIN4, MdPIN5, and MdPIN8 during extension; and upregulation of all MdPINs during AR initiation. This research provides an improved understanding of the cellular and molecular underpinnings of the AR process in woody plants.

Polygenic analysis of very high acetic acid tolerance in the yeast Saccharomyces cerevisiae reveals a complex genetic background and several new causative alleles

BackgroundHigh acetic acid tolerance is of major importance in industrial yeast strains used for second-generation bioethanol production, because of the high acetic acid content of lignocellulose hydrolysates. It is also important in first-generation starch hydrolysates and in sourdoughs containing significant acetic acid levels. We have previously identified snf4E269* as a causative allele in strain MS164 obtained after whole-genome (WG) transformation and selection for improved acetic acid tolerance.ResultsWe have now performed polygenic analysis with the same WG transformant MS164 to identify novel causative alleles interacting with snf4E269* to further enhance acetic acid tolerance, from a range of 0.8–1.2% acetic acid at pH 4.7, to previously unmatched levels for Saccharomyces cerevisiae. For that purpose, we crossed the WG transformant with strain 16D, a previously identified strain displaying very high acetic acid tolerance. Quantitative trait locus (QTL) mapping with pooled-segregant whole-genome sequence analysis identified four major and two minor QTLs. In addition to confirmation of snf4E269* in QTL1, we identified six other genes linked to very high acetic acid tolerance, TRT2, MET4, IRA2 and RTG1 and a combination of MSH2 and HAL9, some of which have never been connected previously to acetic acid tolerance. Several of these genes appear to be wild-type alleles that complement defective alleles present in the other parent strain.ConclusionsThe presence of several novel causative genes highlights the distinct genetic basis and the strong genetic background dependency of very high acetic acid tolerance. Our results suggest that elimination of inferior mutant alleles might be equally important for reaching very high acetic acid tolerance as introduction of rare superior alleles. The superior alleles of MET4 and RTG1 might be useful for further improvement of acetic acid tolerance in specific industrial yeast strains.

Effects of citric acid residue and lactic acid bacteria on fermentation quality and aerobic stability of alfalfa silage

An experiment was conducted to investigate the effects of citric acid residue (CAR) and lactic acid bacteria (LAB) on fermentation quality and aerobic stability of alfalfa silage. Alfalfa was treated as follows: (1) control without additive (CON); (2) LAB (L); (3) 12 g/kg CAR (C); (4) 12 g/kg CAR + LAB (CL) and fermented for 3, 6, 9, 15, 30 and 45 days. The residual silages ensiled for 45 days were evaluated for aerobic stability. The results showed that addition of CAR with or without LAB inoculant decreased pH, acetic acid, ammonia nitrogen , neutral detergent fibre, hemicellulose contents and Enterobacteriaceae counts (p < .05) and increased dry matter and lactic acid contents (p < .05) after 45 days of ensiling. Whereas, the lower lactic acid and higher acetic acid contents were observed in L silages (p < .05) after 45 days of ensiling. During aerobic exposure, L and CL silages remained stable in pH, lactic and acetic acid contents, while the control and C silages showed higher pH, yeast and mould counts and lower lactic and acetic acid contents. Compared with the control, L and CL improved aerobic stability, whereas the poorer aerobic stability was shown in C silages (p < .05). In conclusion, applying a combination of CAR and LAB inoculant improved both fermentation quality and aerobic stability of alfalfa silage. Highlights Citric acid residue (CAR) was compared with a lactic acid bacteria (LAB) inoculant in ensiling alfalfa. The CAR improved fermentation quality compared to control and LAB treated silages. Aerobic stability improved when CAR was used in combination with LAB but not when used alone.

Peracetic acid-induced kraft lignin solubilization and its characterization for selective production of macromolecular biopolymers

This study was conducted to investigate the degradation characteristics of kraft lignin (KL) during peracetic acid (PAA) treatment, and to produce potentially valuable polymers of low molecular weight lignin by controlling the reaction conditions. For the peracetic acid treatment, acetic acid (AA) and hydrogen peroxide (HP) were directly mixed at ratios of 4:1, 1:1, and 1:4 (v/v) and employed as reaction media. After PAA treatment of kraft lignin at 80 °C, complete dissolution of the lignin and reduction in the molecular weight were observed. When the PAA reaction was performed at high HP concentration (1:4, v/v), the aromatic lignin skeleton opened and converted to a structure containing large amounts of carboxyl groups. On the other hand, the treatment at high AA concentration (4:1, v/v) decomposed lignin while maintaining its aromatic structure. Hence, we demonstrated that the selective production of lignin-derived polymers can be controlled depending on PAA and HP concentrations.

Investigation of Acetic Acid Effect on Carbon Steel Corrosion in CO2-H2S Medium: Mechanistic Reaction Pathway and Kinetics.

Potentiodynamic polarization and electrochemical impedance measurements were employed to investigate the effect of acetic acid on the anodic dissolution of carbon steel in a CO2–H2S solution. Both polarization and impedance results unveil that the dissolution rate of carbon steel first increases and then decreases with an increase in acetic acid concentration. At lower concentrations of acetic acid, the corrosion rate increases due to the increase in cathodic current density. While the decrease in corrosion rate at higher acetic acid concentrations is attributed to the decrease in the anodic current density. The reaction mechanism of carbon steel dissolution in the CO2–H2S–acetic acid medium is elucidated along with the retrieval of kinetic parameters using the impedance data acquired at different overpotentials for various concentrations of acetic acid (1, 50, and 500 ppm). Further field emission scanning electron microscopy (FESEM) images confirm that the pitting corrosion occurs on carbon steel surface at higher acetic acid concentrations.

The effects of stage of maturity and lactic acid bacteria inoculants on the ensiling characteristics, aerobic stability and in vitro digestibility of whole‐crop oat silages

AbstractThis study evaluated the effect of three isolated lactic acid bacteria (LAB) inoculants on the ensiling characteristics, aerobic stability and in vitro digestibility of low dry matter whole‐crop oat silages (WCOS). The oats were harvested at two stages of maturity, boot and filling stages, and then inoculated with 1 × 106 cfu/g fresh material of Lactobacillus plantarum (LP), Lactobacillus rhamnosus (LR) and Lactobacillus buchneri (LB). After 45 days of ensiling, the three LAB inoculants increased lactic acid (LA) concentrations (p &lt; .05) and decreased ammonia nitrogen (NH3‐N) content (p &lt; .05) for both of the two stages of WCOS; the LP‐ and LR‐treated silages exhibited lower pH values and higher Flieg's points than the control and LB‐treated silages (p &lt; .05); LB‐treated silages resulted in higher acetic acid contents than in the other treated silages (p &lt; .05). After exposure to air for 7 days, the control and LB treatments had higher aerobic stability than the LP and LR treatments (p &lt; .05). The Flieg's points and aerobic stability at the filling stage were greater than that at the boot stage. With no LAB inoculants, the in vitro dry matter digestibility (IVDMD) at the boot stage was higher than that at the filling stage. At the filling stage, LB‐ and LR‐treated silages had higher IVDMD than the control and LP‐treated silages (p &lt; .05). It was concluded that the fermentation quality and aerobic stability of oats harvested at the filling stage was higher than that at the boot stage. LP and LR inoculants improved the fermentation quality but reduced the aerobic stability of WCOS. The IVDMD of WCOS at the filling stage was improved by adding LB and LR inoculants.