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Molecules (Basel, Switzerland) May 2022It is well known that organic acids (OAs) could affect the flavour of fruit juices and beverages. However, the molecular mechanism of aroma release is still unclear. In...
It is well known that organic acids (OAs) could affect the flavour of fruit juices and beverages. However, the molecular mechanism of aroma release is still unclear. In this study, the effects of citric acid (CA), L-(-)-malic acid (MA) and L-lactic acid (LA) on the release of six selected esters and their sensory perception were investigated by means of HS-GC-MS analyses and odour detection threshold determination, respectively. Meanwhile, the density functional theory (DFT) calculation was employed to explore the interaction modes between esters and OAs. HS-GC-MS analyses showed that the concentration and the type of OAs regulated the release of esters. The results were basically consistent with the detection threshold change of those esters. The DFT calculation suggested that the main intermolecular interaction was hydrogen bonds, and several esters could form a ternary ring structure with OAs through hydrogen bonds. The interactions can induce the different release behaviours of esters in OAs water solution. The number of carboxyl functional groups in OAs and the spatial conformation of esters appeared to influence the magnitude of the interaction. The above results demonstrated the mechanism of OAs affecting the release of esters and indicated a possible flavour control way by using different OAs and OA concentrations.
Topics: Acids; Esters; Fruit; Odorants; Volatile Organic Compounds; Water
PubMed: 35566293
DOI: 10.3390/molecules27092942 -
Protein Science : a Publication of the... May 2015Using complementary approaches of potentiometry and NMR spectroscopy, we have determined that the equilibrium acid dissociation constant (pKa value) of the arginine...
Using complementary approaches of potentiometry and NMR spectroscopy, we have determined that the equilibrium acid dissociation constant (pKa value) of the arginine guanidinium group is 13.8 ± 0.1. This is substantially higher than that of ∼ 12 often used in structure-based electrostatics calculations and cited in biochemistry textbooks. The revised intrinsic pKa value helps explains why arginine side chains in proteins are always predominantly charged, even at pH values as great as 10. The high pKa value also reinforces the observation that arginine side chains are invariably protonated under physiological conditions of near neutral pH. This occurs even when the guanidinium moiety is buried in a hydrophobic micro-environment, such as that inside a protein or a lipid membrane, thought to be incompatible with the presence of a charged group.
Topics: Acids; Arginine; Binding Sites; Hydrogen-Ion Concentration; Hydrophobic and Hydrophilic Interactions; Kinetics; Lipid Bilayers; Magnetic Resonance Spectroscopy; Proteins
PubMed: 25808204
DOI: 10.1002/pro.2647 -
Journal of Applied Microbiology Aug 2015In this study, the effectiveness of combining each of seven types of acids with 3% salt as a treatment against pathogens was investigated in laboratory media and...
AIM
In this study, the effectiveness of combining each of seven types of acids with 3% salt as a treatment against pathogens was investigated in laboratory media and acidified food.
METHODS AND RESULTS
When 0.5% malic, 0.5% tartaric, 0.5% citric or 0.25% phosphoric acid was combined with 3% salt, there was a higher reduction in Gram-negative bacteria (Escherichia coli O157:H7 and Salmonella Typhimurium) compared to when using acid alone. However, when 0.5% acetic, 0.5% propionic or 0.25% lactic acid was combined with 3% salt, the salt provided protection against the acid treatment. However, the antagonistic effects of acetic, propionic and lactic acid seen with Gram-negative bacteria were not observed in Listeria monocytogenes. Antagonistic effects were similarly observed when E. coli O157:H7 was treated with acetic acid and salt in food.
CONCLUSIONS
These results show that the addition of salt increases the resistance of Gram-negative bacteria to acid treatments when using acetic, propionic and lactic acid.
SIGNIFICANCE AND IMPACT OF THE STUDY
This study shows that antagonistic effects were observed when Gram-negative bacteria were treated with organic acids of simple structure. It may provide useful information for understanding the acid resistance mechanism of Gram-negative bacteria and developing methods for preserving acidified food.
Topics: Acids; Bacteria; Culture Media; Food Microbiology; Food Preservation; Sodium Chloride; Vegetables
PubMed: 25973744
DOI: 10.1111/jam.12845 -
ChemMedChem Feb 2013Chemogenomics methods seek to characterize the interaction between drugs and biological systems and are an important guide for the selection of screening compounds. The...
Chemogenomics methods seek to characterize the interaction between drugs and biological systems and are an important guide for the selection of screening compounds. The acid/base character of drugs has a profound influence on their affinity for the receptor, on their absorption, distribution, metabolism, excretion and toxicity (ADMET) profile and the way the drug can be formulated. In particular, the charge state of a molecule greatly influences its lipophilicity and biopharmaceutical characteristics. This study investigates the acid/base profile of human small-molecule drugs, chemogenomics datasets and screening compounds including a natural products set. We estimate the acid-ionization constant (pK(a)) values of these compounds and determine the identity of the ionizable functional groups in each set. We find substantial differences in acid/base profiles of the chemogenomic classes. In many cases, these differences can be linked to the nature of the target binding site and the corresponding functional groups needed for recognition of the ligand. Clear differences are also observed between the acid/base characteristics of drugs and screening compounds. For example, the proportion of drugs containing a carboxylic acid was 20 %, in stark contrast to a value of 2.4 % for the screening set sample. The proportion of aliphatic amines was 27 % for drugs and only 3.4 % for screening compounds. This suggests that there is a mismatch between commercially available screening compounds and the compounds that are likely to interact with a given chemogenomic target family. Our analysis provides a guide for the selection of screening compounds to better target specific chemogenomic families with regard to the overall balance of acids, bases and pK(a) distributions.
Topics: Acids; Biological Products; Databases, Pharmaceutical; Drug Discovery; Humans; Ions; Pharmaceutical Preparations; Small Molecule Libraries
PubMed: 23303535
DOI: 10.1002/cmdc.201200507 -
International Journal of Biological... Oct 2019Biopolymers have received considerable attention in recent years given the environmental concern related to the incorrect disposal of materials based on synthetic...
Biopolymers have received considerable attention in recent years given the environmental concern related to the incorrect disposal of materials based on synthetic plastics. Starch and chitosan are good examples of raw materials of interest, and its combination can exhibit some newsworthy barrier and mechanical properties. Therefore, this study aimed to determine the impact of the acid type, acetic and lactic solutions (1% v/v), used for chitosan solubilization and the starch:chitosan proportion on the properties of cornstarch/chitosan-based films. The films were prepared by casting and characterized by analyses of water vapor permeability, tensile strength, elongation, elastic modulus, antimicrobial activity, and biodegradability. Mechanical properties analyses showed that the films prepared by using acetic acid presented higher rigidity and lower deformation, giving higher values of Young's Modulus and a smaller percentage of elongation, in comparison to the films fabricated with lactic acid. Besides, starch/chitosan films containing acetic acid also exhibited better water vapor barrier properties, showing smaller water permeation values. Moreover, the antimicrobial activity of the cornstarch-based films containing chitosan was confirmed, obtaining better results for the blended films prepared with lactic acid, indicating a high potential for the development of active packaging. For the biodegradation tests, all samples started the degradation after 15 days.
Topics: Acids; Biodegradation, Environmental; Biopolymers; Chemical Phenomena; Chitosan; Mechanical Phenomena; Membranes, Artificial; Solubility; Spectrum Analysis; Starch; Thermogravimetry
PubMed: 31306704
DOI: 10.1016/j.ijbiomac.2019.07.089 -
Journal of Microbiology and... Jan 2016The new movement towards green chemistry and renewable feedstocks makes microbial production of chemicals more competitive. Among the numerous chemicals, organic acids... (Review)
Review
The new movement towards green chemistry and renewable feedstocks makes microbial production of chemicals more competitive. Among the numerous chemicals, organic acids are more attractive targets for process development efforts in the renewable-based biorefinery industry. However, most of the production costs in microbial processes are higher than that in chemical processes, among which over 60% are generated by separation processes. Therefore, the research of separation and purification processes is important for a promising biorefinery industry. This review highlights the progress of recovery processes in the separation and purification of organic acids, including their advantages and disadvantages, current situation, and future prospects in terms of recovery yields and industrial application.
Topics: Acids; Bacteria; Biomass; Culture Media; Fermentation; Industrial Microbiology
PubMed: 26403818
DOI: 10.4014/jmb.1505.05049 -
The ISME Journal Jul 2015The microbial communities in acid mine drainage have been extensively studied to reveal their roles in acid generation and adaption to this environment. Lacking,...
The microbial communities in acid mine drainage have been extensively studied to reveal their roles in acid generation and adaption to this environment. Lacking, however, are integrated community- and organism-wide comparative gene transcriptional analyses that could reveal the response and adaptation mechanisms of these extraordinary microorganisms to different environmental conditions. In this study, comparative metagenomics and metatranscriptomics were performed on microbial assemblages collected from four geochemically distinct acid mine drainage (AMD) sites. Taxonomic analysis uncovered unexpectedly high microbial biodiversity of these extremely acidophilic communities, and the abundant taxa of Acidithiobacillus, Leptospirillum and Acidiphilium exhibited high transcriptional activities. Community-wide comparative analyses clearly showed that the AMD microorganisms adapted to the different environmental conditions via regulating the expression of genes involved in multiple in situ functional activities, including low-pH adaptation, carbon, nitrogen and phosphate assimilation, energy generation, environmental stress resistance, and other functions. Organism-wide comparative analyses of the active taxa revealed environment-dependent gene transcriptional profiles, especially the distinct strategies used by Acidithiobacillus ferrivorans and Leptospirillum ferrodiazotrophum in nutrients assimilation and energy generation for survival under different conditions. Overall, these findings demonstrate that the gene transcriptional profiles of AMD microorganisms are closely related to the site physiochemical characteristics, providing clues into the microbial response and adaptation mechanisms in the oligotrophic, extremely acidic environments.
Topics: Acidithiobacillus; Acids; Bacteria; Biodiversity; Environmental Microbiology; Hydrogen-Ion Concentration; Metagenomics; Mining
PubMed: 25535937
DOI: 10.1038/ismej.2014.245 -
Angewandte Chemie (International Ed. in... Jul 2022Photoacids show a strong increase in acidity in the first electronic excited state, enabling real-time studies of proton transfer in acid-base reactions, proton...
Photoacids show a strong increase in acidity in the first electronic excited state, enabling real-time studies of proton transfer in acid-base reactions, proton transport in energy storage devices and biomolecular sensor protein systems. Several explanations have been proposed for what determines photoacidity, ranging from variations in solvation free energy to changes in electronic structure occurring along the four stages of the Förster cycle. Here we use picosecond nitrogen K-edge spectroscopy to monitor the electronic structure changes of the proton donating group in a protonated aromatic amine photoacid in solution upon photoexcitation and subsequent proton transfer dynamics. Probing core-to-valence transitions locally at the amine functional group and with orbital specificity, we clearly reveal pronounced electronic structure, dipole moment and energetic changes on the conjugate photobase side. This result paves the way for a detailed electronic structural characterization of the photoacidity phenomenon.
Topics: Acids; Amines; Electronics; Protons; Spectrum Analysis
PubMed: 35325500
DOI: 10.1002/anie.202200709 -
Analytical and Bioanalytical Chemistry Jun 2022The Sr/Sr isotope ratio can, in principle, be used for provenancing of cement. However, while commercial cements consist of multiple components, no detailed...
The Sr/Sr isotope ratio can, in principle, be used for provenancing of cement. However, while commercial cements consist of multiple components, no detailed investigation into their individual Sr/Sr isotope ratios or their influence on the integral Sr/Sr isotope ratio of the resulting cement was conducted previously. Therefore, the present study aimed at determining and comparing the conventional Sr/Sr isotope ratios of a diverse set of Portland cements and their corresponding Portland clinkers, the major component of these cements. Two approaches to remove the additives from the cements, i.e. to measure the conventional Sr/Sr isotopic fingerprint of the clinker only, were tested, namely, treatment with a potassium hydroxide/sucrose solution and sieving on a 11-µm sieve. Dissolution in concentrated hydrochloric acid/nitric acid and in diluted nitric acid was employed to determine the Sr/Sr isotope ratios of the cements and the individual clinkers. The aim was to find the most appropriate sample preparation procedure for cement provenancing, and the selection was realised by comparing the Sr/Sr isotope ratios of differently treated cements with those of the corresponding clinkers. None of the methods to separate the clinkers from the cements proved to be satisfactory. However, it was found that the Sr/Sr isotope ratios of clinker and cement generally corresponded, meaning that the latter can be used as a proxy for the clinker Sr/Sr isotope ratio. Finally, the concentrated hydrochloric acid/nitric acid dissolution method was found to be the most suitable sample preparation method for the cements; it is thus recommended for Sr/Sr isotope analyses for cement provenancing.
Topics: Hydrochloric Acid; Isotopes; Nitric Acid
PubMed: 35029692
DOI: 10.1007/s00216-021-03821-7 -
International Journal of Molecular... Oct 2021A daily consumption of cranberry juice (CJ) is linked to many beneficial health effects due to its richness in polyphenols but could also awake some intestinal...
A daily consumption of cranberry juice (CJ) is linked to many beneficial health effects due to its richness in polyphenols but could also awake some intestinal discomforts due to its organic acid content and possibly lead to intestinal inflammation. Additionally, the impact of such a juice on the gut microbiota is still unknown. Thus, this study aimed to determine the impacts of a daily consumption of CJ and its successive deacidification on the intestinal inflammation and on the gut microbiota in mice. Four deacidified CJs (DCJs) (deacidification rates of 0, 40, 60, and 80%) were produced by electrodialysis with bipolar membrane (EDBM) and administered to C57BL/6J mice for four weeks, while the diet (CHOW) and the water were . Different parameters were measured to determine intestinal inflammation when the gut microbiota was profiled. Treatment with a 0% DCJ did not induce intestinal inflammation but increased the gut microbiota diversity and induced a modulation of its functions in comparison with control (water). The effect of the removal of the organic acid content of CJ on the decrease of intestinal inflammation could not be observed. However, deacidification by EDBM of CJ induced an additional increase, in comparison with a 0% DCJ, in the family which have beneficial effects and functions associated with protection of the intestine: the lower the organic acid content, the more bacteria of the family and functions having a positive impact on the gut microbiota.
Topics: Acids; Animal Nutritional Physiological Phenomena; Animals; Biodiversity; Dialysis; Female; Fruit and Vegetable Juices; Gastrointestinal Microbiome; Hydrogen-Ion Concentration; Inflammation; Intestines; Mice; Mice, Inbred C57BL; Vaccinium macrocarpon
PubMed: 34768966
DOI: 10.3390/ijms222111537