High Levels Of Acetate Research Articles

Analysis of Liver Toxicity Markers in Danio rerio following Ethanol Exposure

Zebrafish have been used for many years in developmental and reproductive biology, yet little is still known about the adult zebrafish liver. Additionally, many of the mammalian liver cell types have yet to be characterized in zebrafish, including Kupffer cells, oval cells, and stellate cells. Also, there is minimal information available regarding zebrafish liver transporters and nuclear receptors. Therefore, it is important to understand the mechanism of xenobiotic metabolism in zebrafish to support their use as a model organism for studying the fate and biological effects of xenobiotics. The value of zebrafish as a model organism is based on a broad set of gene similarities (among fish species and humans) involved in metabolism and transportation of endogenous and exogenous chemicals. While there are molecular similarities between zebrafish and humans, there are also differences that may impact how compounds are metabolized. Therefore, it is absolutely necessary to investigate and validate the assumptions that zebrafish possess conserved genes, enzymes, and processes involved in all stages of metabolism. This study investigates the impact of ethanol exposure on liver toxicity markers in adult Danio rerio. Liver tissue from sham and ethanol injected fish were collected, pooled and RNA was isolated for qPCR. Relative expression levels for each gene were determined and normalized to βactin. Of the seventeen genes that were assessed, our results demonstrate a significant upregulation of the following genes following ethanol treatment: abcb4 (mdr3), abcc1(mrp1), abcc4(mrp4), abcc9(sur2), abcg5, mate1, oatp1 and slc4a2(ae2). Alcohol metabolism increases acetate production, a precursor for cholesterol and fatty acid synthesis. Historically, this increase in acetate levels driven by alcohol, is a contributor of hepatic steatosis (fatty liver). In a previous study conducted in the lab, zebrafish chronically exposured to ethanol displayed hallmark signs of hepatic steatosis. An upregulation in slc4a2, a sterol and cholesterol transporter aimed to eliminate dietary cholesterol, was found, consistent with the digestion of high levels of acetate. Furthermore, upregulation of abcc4, a prostaglandin transporter, is indicative of oxidative stress within the liver, caused by ethanol metabolism. Additionally, the upregulation of the other liver transporters would be consistent with normal hepatic ion flow during xenobiotic methabolism.Support or Funding InformationQuinnipiac University: College of Arts and Sciences

Breeding of a sake yeast mutant with enhanced ethyl caproate productivity in sake brewing using rice milled at a high polishing ratio

Sake yeast produces a fruity flavor known as ginjo-ko-which is mainly attributable to ethyl caproate and isoamyl acetate-during fermentation in sake brewing. The production of these flavor components is inhibited by unsaturated fatty acids derived from the outer layer of rice as raw material. We isolated three mutants (hec2, hec3, and hec6) with enhanced ethyl caproate productivity in sake brewing using rice milled at a high polishing ratio from a cerulenin-resistant mutant derived from the hia1 strain, which shows enhanced isoamyl acetate productivity. The hec2 mutant had the homozygous FAS2 mutation Gly1250Ser, which is known to confer high ethyl caproate productivity. When the homozygous FAS2 mutation Gly1250Ser was introduced into strain hia1, ethyl caproate productivity was increased but neither this nor intracellular caproic acid content approached the levels observed in the hec2 mutant, indicating that a novel mutation was responsible for the high ethyl caproate productivity. We also found that the expression of EEB1 encoding acyl-coenzyme A:ethanol O-acyltransferase (AEATase) and enzymatic activity were increased in the hec2 mutant. These results suggest that the upregulation of EEB1 expression and AEATase activity may also have contributed to the enhancement of ethyl caproate synthesis from ethanol and caproyl-CoA. Our findings are useful for the brewing of sake with improved flavor due to high levels of isoamyl acetate and ethyl caproate.

Unexpected competitiveness of Methanosaeta populations at elevated acetate concentrations in methanogenic treatment of animal wastewater.

Acetoclastic methanogenesis is a key metabolic process in anaerobic digestion, a technology with broad applications in biogas production and waste treatment. Acetoclastic methanogenesis is known to be performed by two archaeal genera, Methanosaeta and Methanosarcina. The conventional model posits that Methanosaeta populations are more competitive at low acetate levels (<1mM) than Methanosarcina and vice versa at higher acetate concentrations. While this model is supported by an extensive body of studies, reports of inconsistency have grown that Methanosaeta were observed to outnumber Methanosarcina at elevated acetate levels. In this study, monitoring of anaerobic digesters treating animal wastewater unexpectedly identified Methanosaeta as the dominant acetoclastic methanogen population at both low and high acetate levels during organic overloading. The surprising competitiveness of Methanosaeta at elevated acetate was further supported by the enrichment of Methanosaeta with high concentrations of acetate (20mM). The dominance of Methanosaeta in the methanogen community could be reproduced in anaerobic digesters with the direct addition of acetate to above 20mM, again supporting the competitiveness of Methanosaeta over Methanosarcina at elevated acetate levels. This study for the first time systematically demonstrated that the dominance of Methanosaeta populations in anaerobic digestion could be linked to the competitiveness of Methanosaeta at elevated acetate concentrations. Given the importance of acetoclastic methanogenesis in biological methane production, findings from this study could have major implications for developing strategies for more effective control of methanogenic treatment processes.

ATP-Citrate Lyase Controls a Glucose-to-Acetate Metabolic Switch

Mechanisms of metabolic flexibility enable cells to survive under stressful conditions and can thwart therapeutic responses. Acetyl-coenzyme A (CoA) plays central roles in energy production, lipid metabolism, and epigenomic modifications. Here, we show that, upon genetic deletion of Acly, the gene coding for ATP-citrate lyase (ACLY), cells remain viable and proliferate, although at an impaired rate. In the absence of ACLY, cells upregulate ACSS2 and utilize exogenous acetate to provide acetyl-CoA for de novo lipogenesis (DNL) and histone acetylation. A physiological level of acetate is sufficient for cell viability and abundant acetyl-CoA production, although histone acetylation levels remain low in ACLY-deficient cells unless supplemented with high levels of acetate. ACLY-deficient adipocytes accumulate lipid invivo, exhibit increased acetyl-CoA and malonyl-CoA production from acetate, and display some differences in fatty acid content and synthesis. Together, these data indicate that engagement of acetate metabolism is a crucial, although partial, mechanism of compensation for ACLY deficiency.

Isolation and characterization of sake yeast mutants with enhanced isoamyl acetate productivity

Isoamyl acetate is an important flavor compound in sake. However, production of isoamyl acetate by Saccharomyces cerevisiae is significantly reduced during sake brewing with rice that has a high polishing ratio, because unsaturated fatty acids derived from the outer layer of rice repress the expression of ATF1, which encodes an alcohol acetyl transferase. Yeast mutants capable of relieving this repression would allow the brewing of rice with high polishing ratios, improving the diversity of taste and flavor of sake. Atf1p is also believed to contribute to biological membrane homeostasis. We isolated four yeast mutants (hia1, hia2, hia4, and hia6) that have high isoamyl acetate productivity and are resistant to aureobasidin A, an inhibitor of sphingolipid biosynthesis. The isoamyl acetate content of sake brewed with the hia1 mutant was 2.6 times higher than that of the parental strain. ATF1 was expressed constitutively in the hia1 mutant during brewing and remained derepressed upon the addition of unsaturated fatty acids. Whole-genome sequence analysis of the hia mutants revealed a homozygous nonsense mutation (Ser706*) in MGA2 in all four mutants. Mga2p, an endoplasmic reticulum (ER) membrane protein, regulates ATF1 transcription. The expression of ATF1 was elevated in BY4743 Δmga2 cells complemented with MGA2 (Ser706*), and this was not completely inhibited by the addition of unsaturated fatty acids. These results indicate that a nonsense mutation in MGA2 induces high levels of isoamyl acetate production in S.cerevisiae. This finding has applications for brewing sake with high levels of isoamyl acetate.

Influence of light intensity on glandular trichome density, gene expression and essential oil of menthol mint (Mentha arvensis L.)

The effects of 25, 50, 75 and 100% of light intensity (137, 254, 406 and 543 μmol photons m−2 second−1, respectively) on aspects related to volatile synthesis in menthol mint were investigated. Fresh weight production, glandular trichome density and essential oil content showed a significant linear positive correlation with light intensity. Plants under low light intensity (25%) produced an essential oil with high levels of neomenthol, menthol and menthyl acetate. With 50 and 75% of light intensity plants showed an increase in expression of limonene synthase, limonene hydroxylase, (-)-isopiperitenol dehydrogenase, (+)-pulegone reductase and menthol dehydrogenase genes and an anticipation in oil maturity. With 25% of light intensity plants produced an essential oil with the best commercial profile. However, plants under 100% of light intensity produced more essential oil but with lower levels of menthol and higher levels of pulegone, that can be toxic for humans.

Persistence of Methanosaeta populations in anaerobic digestion during process instability

Anaerobic digestion is a sustainable technology for the treatment of organic waste and production of biogas. Acetoclastic methanogenesis accounts for the majority of methane production in anaerobic digestion. Therefore, sustaining robust acetoclastic methanogens is important for stable process performance. Due to faster growth kinetics at high acetate concentrations, it has been considered that Methanosarcina would be more prevalent than Methanosaeta in unstable anaerobic digestion processes which frequently experience high acetate levels. Methanogen population dynamics were monitored in multiple continuous anaerobic digesters for 500days. Results from quantitative polymerase chain reaction analysis show that Methanosaeta dominated over Methanosarcina in anaerobic digestion at high acetate levels up to 44mM, suggesting the potential of Methanosaeta as a robust and efficient acetoclastic candidate for resilient anaerobic methane conversion. Further efforts are needed to identify mechanisms contributing to the unexpected competitiveness of these methanogens at high acetate levels observed in this study.

Evaluation of an optimal preparation of human standardized fecal inocula for in vitro fermentation studies

This study investigated the optimal preservation approach to prepare human feces as inoculum for in vitro fermentations as an alternative to the use of fresh feces. The four treatments studied were: Treatment 1) fresh feces resuspended in dialysate solution+glycerol; Treatment 2) fresh feces resuspended in dialysate solution+glycerol and then stored at −80°C; Treatment 3) fecal sample frozen with 1.5g glycerol; and Treatment 4) fecal sample frozen. All the treatments contained 8.75g of feces, 3.5ml dialysate and 4.9ml glycerol when inoculated in TIM-2 in vitro system. Treatment 1 (fresh fecal preparation) was used as a reference.The effects were evaluated in terms of i) metabolic activity and ii) composition of the microbiota using fermentation experiments in the TIM-2 in vitro system. In all treatments, high levels of acetate were produced followed by n-butyrate and propionate. However, the metabolic activity of the bacteria, in terms of short-chain fatty acid production, was affected by the different treatments. Microbiota composition was analyzed using the IS-pro profiling technique. Diversity in Actinobacteria, Firmicutes, Fusobacteria and Verrucomicrobia and Proteobacteria groups seemed to be preserved in all treatments whereas it was observed to decline in the Bacteroidetes group. Preparing a human fecal inoculum resuspended in dialysate solution with glycerol and then stored at −80°C showed high similarities to the results obtained with fresh feces, and is proposed as the optimal way to freeze fecal material as an alternative to fresh feces for in vitro fermentation studies.

Bacterial metabolites reduce intestinal permeability to protect against food allergen sensitization (MUC8P.724)

Abstract Food allergies are a growing public health concern. Our laboratory has recently identified a consortium of Firmicutes from the Clostridia class that can protect germ free (GF) or antibiotic (Abx)-treated mice against sensitization to peanut. This Clostridia consortium induces an early innate cytokine response in the colonic lamina propria that is characterized by the production of the barrier protective cytokine IL-22. By measuring the concentrations of two immunodominant peanut allergens, Ara h 2 and Ara h 6, in serum post gavage we demonstrated that Clostridia-induced IL-22 is necessary and sufficient to reduce intestinal permeability in neonatal Abx-treated mice. Administration of FITC-labeled dextran molecules of different sizes has further interrogated the effect of Clostridia colonization on intestinal permeability to food allergens. Treatment of GF mice with heat-killed Clostridia did not induce IL-22 or reduce intestinal permeability, suggesting a role for bacterial metabolites in mediating protection. Metabolomic analysis revealed that our Clostridia consortium produces high levels of the short chain fatty acids acetate and butyrate. Administration of acetate or butyrate to GF mice showed that only butyrate induced IL-22 and reduced the concentration of peanut allergen in the blood after challenge. We propose that production of butyrate is one mechanism by which Clostridia can influence intestinal permeability and host susceptibility to allergic sensitization.

1H nuclear magnetic resonance-based extracellular metabolomic analysis of multidrug resistant Tca8113 oral squamous carcinoma cells

A major obstacle of successful chemotherapy is the development of multidrug resistance (MDR) in the cancer cells, which is difficult to reverse. Metabolomic analysis, an emerging approach that has been increasingly applied in various fields, is able to reflect the unique chemical fingerprints of specific cellular processes in an organism. The assessment of such metabolite changes can be used to identify novel therapeutic biomarkers. In the present study, 1H nuclear magnetic resonance (NMR) spectroscopy was used to analyze the extracellular metabolomic spectrum of the Tca8113 oral squamous carcinoma cell line, in which MDR was induced using the carboplatin (CBP) and pingyangmycin (PYM) chemotherapy drugs in vitro. The data were analyzed using the principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) methods. The results demonstrated that the extracellular metabolomic spectrum of metabolites such as glutamate, glycerophosphoethanol amine, α-Glucose and β-Glucose for the drug-induced Tca8113 cells was significantly different from the parental Tca8113 cell line. A number of biochemicals were also significantly different between the groups based on their NMR spectra, with drug-resistant cells presenting relatively higher levels of acetate and lower levels of lactate. In addition, a significantly higher peak was observed at δ 3.35 ppm in the spectrum of the PYM-induced Tca8113 cells. Therefore, 1H NMR-based metabolomic analysis has a high potential for monitoring the formation of MDR during clinical tumor chemotherapy in the future.

Behaviour of Listeria monocytogenes in raw milk Cantal type cheeses during cheese making, ripening and storage in different packaging conditions

The aim of this study was to run challenge tests to investigate the behaviour of Listeria monocytogenes in raw milk Cantal type uncooked pressed cheeses throughout the cheese process and during storage in different packagings (stretch film, vacuum packs and kraft paper) at 6 °C during two-thirds of the storage period, then at 10 °C; for kraft paper the last five days were at 15 °C. Whatever the weight of the cheese (10 or 40 kg), L. monocytogenes only increased during the first 24 h of cheese making and decreased significantly in both cores and rinds during ripening at 9 °C from day 45 to day 360. In cores, decay rate can depend on milk properties and in our experiment were associated with high levels of lactate and acetate during ripening. The decrease continued significantly in the cores during storage in all three packagings, more rapidly than during ripening. The populations of the pathogen were usually similar whatever the packaging. In rind, L monocytogenes decreased most significantly during storage in kraft paper; after 45 days of storage the counts were significantly lower in kraft paper than under vacuum whereas Gram positive non lactic acid bacteria and yeasts were at higher counts. The low aw (<0.90) in the rinds of kraft wrapped portions may be responsible for this decrease. High pH (6 < pH < 8) in the rind during ripening and storage did not hinder the decrease. This study provides data for developing models of L. monocytogenes inactivation and for attributing by food safety authorities the appropriate category for Cantal type cheeses with regard to European regulation.

Electron Paramagnetic Resonance (EPR) Spectroscopy to Detect Reactive Oxygen Species in Staphylococcus aureus.

Under aerobic conditions, Staphylococcus aureus (S. aureus) primarily metabolizes glucose to acetic acid. Although normally S. aureus is able to re-utilize acetate as a carbon source following glucose exhaustion, significantly high levels of acetate in the culture media may not only be growth inhibitory but also potentiates cell death in stationary phase cultures by a mechanism dependent on cytoplasmic acidification. One consequence of acetic acid toxicity is the production of reactive oxygen species (ROS). The present protocol describes the detection of ROS in S. aureus undergoing cell death by electron paramagnetic resonance (EPR) spectroscopy. Using 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine (CMH) as a cell permeable spin probe, we demonstrate the detection of various oxygen radicals generated by bacteria. Although standardized for S. aureus, the methods described here should be easily adapted for other bacterial species. This protocol is adapted from Thomas et al. (2014) and Thomas et al. (2010).

Acetate metabolism in cancer cells.

No abstract

Effect of acetate to biomass ratio on simultaneous polyhydroxybutyrate generation and direct microbial growth in fast growing microbial culture

The study investigated the effect of variations in the acetate to biomass ratio on substrate storage potential, and the kinetics of substrate utilization. A series of batch experiments were conducted with biomass taken from the fill and draw reactor operated at a sludge age of 2d. One of the batch reactors duplicated the substrate loading in the main reactor. The others were started with different initial acetate to biomass ratios both in lower and higher ranges. Increasing available acetate did not totally divert excess substrate to storage; the microbial culture adjusted the kinetics of the metabolic reactions to a higher growth rate so that more substrate could be utilized for direct growth at high acetate levels. Conversely, storage rate was increased, utilizing a higher substrate fraction for polyhydroxybutyrate generation when acetate concentration was lowered. The physiological and molecular bases of storage at low substrate levels were discussed.

Metabolomic Profiling of Autoimmune Hepatitis: The Diagnostic Utility of Nuclear Magnetic Resonance Spectroscopy.

Autoimmune hepatitis (AIH) is often confused with other liver diseases because of their shared nonspecific symptoms and serological and histological overlap. This study compared the plasma metabolomic profiles of patients with AIH, primary biliary cirrhosis (PBC), PBC/AIH overlap syndrome (OS), and drug-induced liver injury (DILI) with those of healthy subjects to identify potential biomarkers of AIH. Metabolomic profiling and biomarker screening were performed using proton nuclear magnetic resonance spectroscopy (1H NMR) coupled with a partial least-squares discriminant analysis. Compared with the levels in healthy volunteers and other liver disease patients, AIH patients exhibited relatively high levels of plasma pyruvate, lactate, acetate, acetoacetate, and glucose. Such metabolites are typically related to energy metabolism alterations and may be a sign of metabolic conversion to the aerobic glycolysis phenotype of excessive immune activation. Increased aromatic amino acids and decreased branched-chain amino acids were found in the plasma of AIH patients. The whole NMR profiles were stepwise-reduced, and nine metabolomic biomarkers having the greatest significance in the discriminant analysis were obtained. The diagnostic utility of the selected metabolites was assessed, and these biomarkers achieved good sensitivity, specificity, and accuracy (all above 93%) in distinguishing AIH from PBC, DILI, and OS. This report is the first to present the metabolic phenotype of AIH and the potential utility of 1H NMR metabolomics in the diagnosis of AIH.

Rapid Diagnosis and Staging of Colorectal Cancer via High-Resolution Magic Angle Spinning Nuclear Magnetic Resonance (HR-MAS NMR) Spectroscopy of Intact Tissue Biopsies

To develop novel metabolite-based models for diagnosis and staging in colorectal cancer (CRC) using high-resolution magic angle spinning nuclear magnetic resonance (HR-MAS NMR) spectroscopy. Previous studies have demonstrated that cancer cells harbor unique metabolic characteristics relative to healthy counterparts. This study sought to characterize metabolic properties in CRC using HR-MAS NMR spectroscopy. Between November 2010 and January 2012, 44 consecutive patients with confirmed CRC were recruited to a prospective observational study. Fresh tissue samples were obtained from center of tumor and 5 cm from tumor margin from surgical resection specimens. Samples were run in duplicate where tissue volume permitted to compensate for anticipated sample heterogeneity. Samples were subjected to HR-MAS NMR spectroscopic profiling and acquired spectral data were imported into SIMCA and MATLAB statistical software packages for unsupervised and supervised multivariate analysis. A total of 171 spectra were acquired (center of tumor, n = 88; 5 cm from tumor margin, n = 83). Cancer tissue contained significantly increased levels of lactate (P < 0.005), taurine (P < 0.005), and isoglutamine (P < 0.005) and decreased levels of lipids/triglycerides (P < 0.005) relative to healthy mucosa (R2Y = 0.94; Q2Y = 0.72; area under the curve, 0.98). Colon cancer samples (n = 49) contained higher levels of acetate (P < 0.005) and arginine (P < 0.005) and lower levels of lactate (P < 0.005) relative to rectal cancer samples (n = 39). In addition unique metabolic profiles were observed for tumors of differing T-stage. HR-MAS NMR profiling demonstrates cancer-specific metabolic signatures in CRC and reveals metabolic differences between colonic and rectal cancers. In addition, this approach reveals that tumor metabolism undergoes modification during local tumor advancement, offering potential in future staging and therapeutic approaches.

Metabolomics analysis reveals large effect of roughage types on rumen microbial metabolic profile in dairy cows

The aim of our study was to determine the effect of diets with different types of roughage on the ruminal microbial metabolite profile in dairy cows. Holstein dairy cows were fed a diet containing either corn stover (CS group) or a mixture of alfalfa hay, Leymus chinensis hay and corn silage (MF group) at 0700 and 1900 h daily. Rumen fluid was sampled from each cow through a ruminal cannula at 0630 and 1030 h, and the mixed ruminal fluid from 3 day in each cow was analysed using nuclear magnetic resonance (NMR) spectroscopy. A multivariate analysis revealed a significant difference between the ruminal metabolome of the CS and MF groups at both time points. The MF group had higher levels of acetate, valerate, hydrocinnamate and methylamine and lower levels of glucose, glycine, propionate and isovalerate than those in the CS group. Our results showed that different types of roughages can significantly influence the ruminal microbial metabolome, especially with regard to organic acids, amines and amino acids. The microbial metabolites in the rumen provide nutritional precursors that are critical for general health and milk production in dairy cows. However, studies of the effect of diet on ruminal microbial metabolism are scant. In our current study, we analysed the ruminal microbial metabolite profile of cows fed different types of roughage. We found that the ruminal microbial metabolite profile of cows fed a mixed-roughage diet differed significantly from that of cows fed a single type of roughage. Certain metabolites, such as acetate, hydrocinnamate and methylamine, were closely correlated with specific types of roughage. Our findings provide insight into the effects of different roughages on ruminal microbial fermentation in dairy cows.

Optimizing hydrogen production from a switchgrass steam exploded liquor using a mixed anaerobic culture in an upflow anaerobic sludge blanket reactor

In this study, the operation of an upflow anaerobic sludge blanket reactor (UASBR) producing hydrogen (H2) from a steam-exploded switchgrass (SWG) liquor was statistically optimized. The factors consider included pH, hydraulic retention time (HRT) and linoleic acid (LA) concentration. Under optimal operational conditions (pH 5.0, 10 h HRT and 1.75 g L−1 LA), which were close to the predicted conditions using the D-optimality index, the maximum H2 and methane yield observed were 99.86 ± 5.6 mL g−1 TVS and 0.5 ± 0.1 mL g−1 TVS, respectively. Under maximum H2-producing conditions, high levels of acetate plus butyrate were observed with low levels of ethanol and lactate. A principal component analysis revealed that clustering of the samples was based on the operating conditions and fermentation metabolites. The microbial profiles revealed that by lowering the HRT from 16 to 8 h or decreasing the pH from 7.0 to 5.0 in the controls caused a 50% reduction in the relative abundance of the terminal restriction fragments belonging to the methanogenic population (Methanobacteria, Methanomicrobia, Methanococci). With LA treatment, H2 producers (Ruminococcaceae and Clostridiaceae) were dominant and methanogens were inhibited and/or washed-out from the UASBR.

Acetate adaptation of clostridia tyrobutyricum for improved fermentation production of butyrate

Clostridium tyrobutyricum ATCC 25755 is an acidogenic bacterium capable of utilizing xylose for the fermentation production of butyrate. Hot water extraction of hardwood lingocellulose is an efficient method of producing xylose where autohydrolysis of xylan is catalysed by acetate originating from acetyl groups present in hemicellulose. The presence of acetic acid in the hydrolysate might have a severe impact on the subsequent fermentations. In this study the fermentation kinetics of C. tyrobutyricum cultures after being classically adapted for growth at 26.3 g/L acetate equivalents were studied. Analysis of xylose batch fermentations found that even in the presence of high levels of acetate, acetate adapted strains had similar fermentation kinetics as the parental strain cultivated without acetate. The parental strain exposed to acetate at inhibitory conditions demonstrated a pronounced lag phase (over 100 hours) in growth and butyrate production as compared to the adapted strain (25 hour lag) or non-inhibited controls (0 lag).Additional insight into the metabolic pathway of xylose consumption was gained by determining the specific activity of the acetate kinase (AK) enzyme in adapted versus control batches. AK activity was reduced by 63% in the presence of inhibitory levels of acetate, whether or not the culture had been adapted.

Characterization of the aromatic profile of the Italia variety of Peruvian pisco by gas chromatography-olfactometry and gas chromatography coupled with flame ionization and mass spectrometry detection systems

Thirty-three commercial pisco samples made with Italia grapes in five different regions in Perú have been evaluated by gas chromatography-olfactometry (GC-O) and chemical quantitative analysis for the first time. The GC-O study has revealed that the Peruvian pisco made from this aromatic variety of grape (Italia) has an aroma profile composed of twenty-five odorants. Only one of them could not be identified (LRIDB-WAX 2313). Most of the odorants are fermentation-related, while guaiacol, β-damascenone, geraniol and linalool come from the grape. A total of sixty-two compounds have been analyzed following two different methods. As a result of these analyses, a volatile profile quite typical of a wine distillate was obtained. Terpenes play a relevant aromatic role in piscos elaborated from aromatic varieties of grapes. Italia piscos are particularly highlighted because of their high levels of linalool. This terpene has exceeded its odor threshold in 28 of the 33 samples, reaching odor activity value (OAV) up to 10units. Other terpenes such as geraniol and β-citronellol have presented OAVs higher than 1 in one and five samples respectively. Compared to the composition of other aromatic piscos, the Italia variety exhibited considerably higher concentrations of some volatile compounds (nerol and acetic acid) and lower levels of some ethyl esters (ethyl lactate, diethyl succinate and ethyl hexanoate). Furthermore, when compared with other distillates it can be concluded that in general aromatic piscos seem to be characterized by high levels of β-phenylethanol and β-phenylethyl acetate (with the exception of some orujo and grappa compositions), and also by low levels of some ethyl esters, 1-hexanol and ethyl acetate. In general, the chemical differences may be sufficient to classify the samples by origin. Quantitative data revealed that samples from Ica are the richest in several aromatic compounds such as terpenes, β-damascenone and β-phenylethyl acetate and samples from Moquegua are the poorest in phenol compounds, which can have an impact from a sensory point of view.