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Citric Acid Assay Kit

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Citric Acid Assay Kit K-CITR Scheme
Product code: K-CITR

72 assays (manual) / 720 assays (microplate) / 840 assays (auto-analyser)

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Content: 72 assays (manual) / 720 assays (microplate) / 840 assays (auto-analyser)
Shipping Temperature: Ambient
Storage Temperature: Short term stability: 2-8oC,
Long term stability: See individual component labels
Stability: > 2 years under recommended storage conditions
Analyte: Citric Acid
Assay Format: Spectrophotometer, Microplate, Auto-analyser
Detection Method: Absorbance
Wavelength (nm): 340
Signal Response: Decrease
Linear Range: 1.0 to 100 µg of citric acid per assay
Limit of Detection: 0.491 mg/L
Reaction Time (min): ~ 5 min
Application examples: Grape juice, wine, beer, fruit juices, soft drinks, tea, dairy products (e.g. cheese), meat, processed meat, vegetable and fruit products, bakery products, paper, pharmaceuticals, cosmetics and other materials (e.g. biological cultures, samples, etc.).
Method recognition: Methods based on this principle have been accepted by MEBAK, OIV, EU, ISO2963, AOAC and IFU22 (NOTE: If the enzyme oxaloacetate decarboxylase is present in the sample, some of the oxaloacetate product is converted to pyruvate. Therefore, to ensure citric acid is measured quantitatively, D-lactate dehydrogenase (D-LDH) is employed to efficiently convert any pyruvate produced into D-lactate and NAD+).

The Citric Acid test kit is a flexible and simple method for the rapid and reliable measurement and analysis of citric acid (citrate) in foods, beverages and other materials.

Note for Content: The number of manual tests per kit can be doubled if all volumes are halved.  This can be readily accommodated using the MegaQuantTM  Wave Spectrophotometer (D-MQWAVE).

View our full list of organic acid test kits.

Scheme-K-CITR CITR Megazyme

  • Extended cofactors stability. Dissolved cofactors stable for > 1 year at 4oC.
  • Reconstituted citrate lyase stable for 4 weeks at 4oC / 6 months below -10o
  • Buffer / cofactor / enzyme tablets for efficient use of kit components 
  • PVP incorporated to prevent tannin inhibition 
  • Very competitive price (cost per test) 
  • Mega-Calc™ software tool is available from our website for hassle-free raw data processing 
  • Standard included
  • Suitable for manual, microplate and auto-analyser formats
Megazyme publication

Megazyme “advanced” wine test kits general characteristics and validation.

Charnock, S. J., McCleary, B. V., Daverede, C. & Gallant, P. (2006). Reveue des Oenologues, 120, 1-5.

Many of the enzymatic test kits are official methods of prestigious organisations such as the Association of Official Analytical Chemicals (AOAC) and the American Association of Cereal Chemists (AACC) in response to the interest from oenologists. Megazyme decided to use its long history of enzymatic bio-analysis to make a significant contribution to the wine industry, by the development of a range of advanced enzymatic test kits. This task has now been successfully completed through the strategic and comprehensive process of identifying limitations of existing enzymatic bio-analysis test kits where they occurred, and then using advanced techniques, such as molecular biology (photo 1), to rapidly overcome them. Novel test kits have also been developed for analytes of emerging interest to the oenologist, such as yeast available nitrogen (YAN; see pages 2-3 of issue 117 article), or where previously enzymes were simply either not available, or were too expensive to employ, such as for D-mannitol analysis.

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Megazyme publication

Grape and wine analysis: Oenologists to exploit advanced test kits.

Charnock, S. C. & McCleary, B. V. (2005). Revue des Enology, 117, 1-5.

It is without doubt that testing plays a pivotal role throughout the whole of the vinification process. To produce the best possible quality wine and to minimise process problems such as “stuck” fermentation or troublesome infections, it is now recognised that if possible testing should begin prior to harvesting of the grapes and continue through to bottling. Traditional methods of wine analysis are often expensive, time consuming, require either elaborate equipment or specialist expertise and frequently lack accuracy. However, enzymatic bio-analysis enables the accurate measurement of the vast majority of analytes of interest to the wine maker, using just one piece of apparatus, the spectrophotometer (see previous issue No. 116 for a detailed technical review). Grape juice and wine are amenable to enzymatic testing as being liquids they are homogenous, easy to manipulate, and can generally be analysed without any sample preparation.

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Polylactose exhibits prebiotic activity and reduces adiposity and nonalcoholic fatty liver disease in rats fed a high-fat diet.

Abernathy, B. E., Schoenfuss, T. C., Bailey, A. S. & Gallaher, D. D. (2021). The Journal of Nutrition, 151(2), 352-360.

Background: Prebiotic dietary fibers change the intestinal microbiome favorably and provide a health benefit to the host. Objectives: Polylactose is a novel fiber, synthesized by extrusion of lactose. We evaluated its prebiotic activity by determining its fermentability, effect on the microbiota, and effects on adiposity and liver lipids in a diet-induced obesity animal model. Methods: Male Wistar rats (4-5 wk old) were fed normal-fat (NF, 25% fat energy) or high-fat (HF, 51% fat energy) diets containing different fibers (6% fiber of interest and 3% cellulose, by weight), including cellulose (NFC and HFC, negative and positive controls, respectively), polylactose (HFPL), lactose matched to residual lactose in the HFPL diet, and 2 established prebiotic fibers: polydextrose (HFPD) and fructooligosaccharide (HFFOS). After 10 wk of feeding, organs were harvested and cecal contents collected. Results: HFPL animals had greater cecum weight (3 times greater than HFC) and lower cecal pH (∼1 pH unit lower than HFC) than all other groups, suggesting that polylactose is more fermentable than other prebiotic fibers (HFPD, HFFOS; P < 0.05). HFPL animals also had increased taxonomic abundance of the probiotic species Bifidobacterium in the cecum relative to all other groups (P < 0.05). Epididymal fat pad weight was significantly decreased in the HFPL group (29% decrease compared with HFC) compared with all other HF groups (P < 0.05) and did not differ from the NFC group. Liver lipids and cholesterol were reduced in HFPL animals when compared with HFC animals (P < 0.05). Conclusions: Polylactose is a fermentable fiber that elicits a beneficial change in the gut microbiota as well as reducing adiposity in rats fed HF diets. These effects of polylactose were greater than those of 2 established prebiotics, fructooligosaccharide and polydextrose, suggesting that polylactose is a potent prebiotic.

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The pH-Responsive Transcription Factor PacC Governs Pathogenicity and Ochratoxin A Biosynthesis in Aspergillus carbonarius.

Barda, O., Maor, U., Sadhasivam, S., Bi, Y., Zakin, V., Prusky, D. & Sionov, E. (2020). Frontiers in Microbiology, 11, 210.

Pathogenic fungi must respond effectively to changes in environmental pH for successful host colonization, virulence and toxin production. Aspergillus carbonarius is a mycotoxigenic pathogen with the ability to colonize many plant hosts and secrete ochratoxin A (OTA). In this study, we characterized the functions and addressed the role of PacC-mediated pH signaling in A. carbonarius pathogenicity using designed pacC gene knockout mutant. ΔAcpacC mutant displayed an acidity-mimicking phenotype, which resulted in impaired fungal growth at neutral/alkaline pH, accompanied by reduced sporulation and conidial germination compared to the wild type (WT) strain. The ΔAcpacC mutant was unable to efficiently acidify the growth media as a direct result of diminished gluconic and citric acid production. Furthermore, loss of AcpacC esulted in a complete inhibition of OTA production at pH 7.0. Additionally, ΔAcpacC mutant exhibited attenuated virulence compared to the WT toward grapes and nectarine fruits. Reintroduction of pacC gene into ΔAcpacC mutant restored the WT phenotype. Our results demonstrate important roles of PacC of A. carbonarius in OTA biosynthesis and in pathogenicity by controlling transcription of genes important for fungal secondary metabolism and infection.

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Deletion of Voltage-Dependent Anion Channel 1 knocks mitochondria down triggering metabolic rewiring in yeast.

Magri, A., Di Rosa, M. C., Orlandi, I., Guarino, F., Reina, S., Guarnaccia, M., Morello, G., Spampinato, A., Cavallaro, S., Messina, A., Vai, M. & De Pinto, V. (2020). Cellular and Molecular Life Sciences, 77(16), 3195-3213.

The Voltage-Dependent Anion-selective Channel (VDAC) is the pore-forming protein of mitochondrial outer membrane, allowing metabolites and ions exchanges. In Saccharomyces cerevisiae, inactivation of POR1, encoding VDAC1, produces defective growth in the presence of non-fermentable carbon source. Here, we characterized the whole-genome expression pattern of a VDAC1-null strain (Δpor1) by microarray analysis, discovering that the expression of mitochondrial genes was completely abolished, as consequence of the dramatic reduction of mtDNA. To overcome organelle dysfunction, Δpor1 cells do not activate the rescue signaling retrograde response, as ρ0 cells, and rather carry out complete metabolic rewiring. The TCA cycle works in a “branched” fashion, shunting intermediates towards mitochondrial pyruvate generation via malic enzyme, and the glycolysis-derived pyruvate is pushed towards cytosolic utilization by PDH bypass rather than the canonical mitochondrial uptake. Overall, Δpor1 cells enhance phospholipid biosynthesis, accumulate lipid droplets, increase vacuoles and cell size, overproduce and excrete inositol. Such unexpected re-arrangement of whole metabolism suggests a regulatory role of VDAC1 in cell bioenergetics.

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Engineering of the citrate exporter protein enables high citric acid production in Aspergillus niger.

Steiger, M. G., Rassinger, A., Mattanovich, D. & Sauer, M. (2019). Metabolic Engineering, 52, 224-231.

Aspergillus niger was engineered using a gene responsible for citric acid transport, which has a significant impact on citric acid secretion when overexpressed. The transport gene was identified by a homology search using an itaconic acid transporter from Ustilago maydis as template. The encoding homologous protein CexA belongs to the major facilitator superfamily subclass DHA1 and members of this family work as drug-H+ antiporter. The disruption of this gene completely abolishes citric acid secretion, which indicates that this protein is the main citric acid transporter in A. niger. In the disruption strain, the metabolism is re-routed mainly to oxalic acid, which is a known by-product during citric acid production. The gene can be heterologously expressed in Saccharomyces cerevisiae, which leads to the secretion of citric acid during the growth on glucose. These results confirm the functionality of CexA as the main transporter for citric acid of A. niger. Overexpression of cexA leads to a significant increase in secreted citric acid. Thereby, striking differences between a strong constitutive expression system using pmbfA as a promoter and an inducible expression system using ptet-on can be observed. The inducible system significantly outcompetes the constitutive expression system yielding up to 109 g/L citric acid, which is 5 times higher compared to the parental wild-type strain and 3 times higher compared to the constitutive expression system. These results demonstrate the importance of the cellular transport system for an efficient production of metabolites. By overexpressing a single gene, it is possible to significantly improve the citric acid secretion capability of a moderately producing parental strain.

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Systems analysis of metabolism in platelet concentrates during storage in platelet additive solution.

Jóhannsson, F., Guðmundsson, S., Paglia, G., Guðmundsson, S., Palsson, B., Sigurjónsson, Ó. E. & Rolfsson, Ó. (2018). Biochemical Journal, BCJ20170921.

Platelets deteriorate over time when stored within blood banks through a biological process known as platelet storage lesion (PSL). Here we describe the refinement of biochemical network of platelet metabolism iAT-PLT-636 and its application to describe and investigate changes in metabolism during platelet storage. Changes to extracellular acetate and citrate were measured in buffy coat and apheresis platelet units over 10 days of storage in the platelet additive solution T-Sol. Metabolic network analysis of these data was performed alongside our prior metabolomics data to describe the metabolism of fresh (days 1-3), intermediate (days 4-6), and expired (days 7-10) platelets. Changes to metabolism was studied by comparing metabolic model flux predictions of iAT-PLT-636 between stages and between collection methods. Extracellular acetate and glucose contribute most to central carbon metabolism in platelets. The anticoagulant citrate is metabolized in apheresis stored platelets and is converted to aconitate and, to a lesser degree, malate. The consumption of nutrients changes during storage and reflects altered platelet activation profiles following their collection. Irrespective of collection method, a slowdown in oxidative phosphorylation takes place, consistent with mitochondrial dysfunction during PSL. Finally, the main contributors to intracellular ammonium and NADPH are highlighted. Future optimization of flux through these pathways provides opportunities to address intracellular pH changes and reactive oxygen species which are both of importance to PSL. The metabolic models provide descriptions of platelet metabolism at steady state and represent a platform for future platelet metabolic research.

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An accurate description of Aspergillus niger organic acid batch fermentation through dynamic metabolic modelling.

Upton, D. J., McQueen-Mason, S. J. & Wood, A. J. (2017). Biotechnology for Biofuels, 10(1), 258.

Background: Aspergillus niger fermentation has provided the chief source of industrial citric acid for over 50 years. Traditional strain development of this organism was achieved through random mutagenesis, but advances in genomics have enabled the development of genome-scale metabolic modelling that can be used to make predictive improvements in fermentation performance. The parent citric acid-producing strain of A. niger, ATCC 1015, has been described previously by a genome-scale metabolic model that encapsulates its response to ambient pH. Here, we report the development of a novel double optimisation modelling approach that generates time-dependent citric acid fermentation using dynamic flux balance analysis. Results: The output from this model shows a good match with empirical fermentation data. Our studies suggest that citric acid production commences upon a switch to phosphate-limited growth and this is validated by fitting to empirical data, which confirms the diauxic growth behaviour and the role of phosphate storage as polyphosphate. Conclusions: The calibrated time-course model reflects observed metabolic events and generates reliable in silico data for industrially relevant fermentative time series, and for the behaviour of engineered strains suggesting that our approach can be used as a powerful tool for predictive metabolic engineering.

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Compromised Lactobacillus helveticus starter activity in the presence of facultative heterofermentative Lactobacillus casei DPC6987 results in atypical eye formation in Swiss-type cheese.

O’Sullivan, D. J., McSweeney, P. L. H., Cotter, P. D., Giblin, L. & Sheehan, J. J. (2016). Journal of dairy science, 99(4), 2625-2640.

Nonstarter lactic acid bacteria are commonly implicated in undesirable gas formation in several varieties, including Cheddar, Dutch-, and Swiss-type cheeses, primarily due to their ability to ferment a wide variety of substrates. This effect can be magnified due to factors that detrimentally affect the composition or activity of starter bacteria, resulting in the presence of greater than normal amounts of fermentable carbohydrates and citrate. The objective of this study was to determine the potential for a facultatively heterofermentative Lactobacillus (Lactobacillus casei DPC6987) isolated from a cheese plant environment to promote gas defects in the event of compromised starter activity. A Swiss-type cheese was manufactured, at pilot scale and in triplicate, containing a typical starter culture (Streptococcus thermophilus and Lactobacillus helveticus) together with propionic acid bacteria. Lactobacillus helveticus populations were omitted in certain vats to mimic starter failure. Lactobacillus casei DPC6987 was added to each experimental vat at 4 log cfu/g. Cheese compositional analysis and X-ray computed tomography revealed that the failure of starter bacteria, in this case L. helveticus, coupled with the presence of a faculatively heterofermentative Lactobacillus (L. casei) led to excessive eye formation during ripening. The availability of excess amounts of lactose, galactose, and citrate during the initial ripening stages likely provided the heterofermentative L. casei with sufficient substrates for gas formation. The accrual of these fermentable substrates was notable in cheeses lacking the L. helveticus starter population. The results of this study are commercially relevant, as they demonstrate the importance of viability of starter populations and the control of specific nonstarter lactic acid bacteria to ensure appropriate eye formation in Swiss-type cheese.

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Chemical composition and in vitro antimicrobial and cytotoxic activities of plum (Prunus domestica L.) wine.

Miljić, U., Puškaš, V., Velićanski, A., Mašković, P., Cvetković, D. & Vujić, J. (2016). Journal of the Institute of Brewing, 122(2), 342-349.

A moderate intake of wine is associated with a positive impact on human health owing to the effects of important biologically active components present in the wine in large amounts. The aim of this study was to examine the chemical composition and to assess antimicrobial and cytotoxic activities of fruit wines produced from three plum varieties (Čačanska rana, Čačanska lepotica and Požegača) commonly grown in Serbia as an approach to assess the quality and acceptability of these wines as a functional food. Furthermore, the activity of a series of control samples was assessed in order to determine components from the wine that are responsible for its functional properties. The plum wines produced showed considerable antimicrobial activity against six bacterial and two yeast strains used in this study. In addition to antimicrobial activity, the plum wines showed a significant cytotoxic effect (IC50 < 50 µg Ml-1) on the growth of three tested cancer cell lines (Hep2c, RD and L2OB). Regarding the determined activities, Čačanska rana plum wine achieved the best results. The results indicated that the antimicrobial activity of the plum wines was, in large part, based on the effects of the total acids and the pH value, while the contribution of ethanol and the content of the phenolic compounds were not significant. Similar conclusions were drawn regarding the cytotoxic activity of this fruit wine. The results can be seen as a contribution to the global acceptance of fruit wines as a functional food, with the accent placed on moderate consumption. An important advantage of fruit wines (in particular plum wine), compared with traditional grape wine, is their lower alcohol content.

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Genetic mapping of a 7R Al tolerance QTL in triticale (x Triticosecale Wittmack).

Niedziela, A., Bednarek, P. T., Labudda, M., Mańkowski, D. R. & Anioł, A. (2014). Journal of Applied Genetics, 55(1), 1-14.

Triticale (x Triticosecale Wittmack) is a relatively new cereal crop. In Poland, triticale is grown on 12% of arable land ( There is an increasing interest in its cultivation due to lowered production costs and increased adaptation to adverse environmental conditions. However, it has an insufficient tolerance to the presence of aluminum ions (Al3+) in the soil. The number of genes controlling aluminum tolerance in triticale and their chromosomal location is not known. Two F2 mapping biparental populations (MP1 and MP15) segregating for aluminum (Al) tolerance were tested with AFLP, SSR, DArT, and specific PCR markers. Genetic mapping enabled the construction of linkage groups representing chromosomes 7R, 5R and 2B. Obtained linkage groups were common for both mapping populations and mostly included the same markers. Composite interval mapping (CIM) allowed identification of a single QTL that mapped to the 7R chromosome and explained 25% (MP1) and 36% (MP15) of phenotypic variation. The B1, B26 and Xscm150 markers were 0.04 cM and 0.02 cM from the maximum of the LOD function in the MP1 and MP15, respectively and were highly associated with aluminum tolerance as indicated by Kruskal–Wallis nonparametric test. Moreover, the molecular markers B1, B26, Xrems1162 and Xscm92, previously associated with the Alt4 locus that encoded an aluminum-activated malate transporter (ScALMT1) that was involved in Al tolerance in rye (Secale cereale) also mapped within QTL. Biochemical analysis of plants represented MP1 and MP15 mapping populations confirmed that the QTL located on 7R chromosome in both mapping populations is responsible for Al tolerance.

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Comparison of effects of dietary coconut oil and animal fat blend on lactational performance of Holstein cows fed a high-starch diet.

Hollmann, M. & Beede, D. K. (2012). Journal of Dairy Science, 95(3), 1484-1499.

Dietary medium-chain fatty acids (C8:0 through C12:0) are researched for their potential to reduce enteric methane emissions and to increase N utilization efficiency in ruminants. We aimed to 1) compare coconut oil (CNO; ∼60% medium-chain fatty acids) with a source of long-chain fatty acids (animal fat blend; AFB) on lactational responses in a high-starch diet and 2) determine the effect of different dietary concentrations of CNO on dry matter intake (DMI). In experiment 1, the control diet (CTRL) contained (dry basis) 40% forage (71% corn silage, and alfalfa hay and haylage), 26% NDF, and 35% starch. Isonitrogenous treatment diets contained 5.0% of AFB (5%-AFB), CNO (5%-CNO), or a 1-to-1 mixture of AFB and CNO (5%-AFB-CNO) and 0.8% corn gluten meal in place of corn grain. Thirty-two multiparous dairy cows (201 ± 46 d postpartum; 42.0 ± 5.5 kg/d 3.5% fat-corrected milk yield) were adapted to CTRL, blocked by milk yield, and randomly assigned to 1 of 4 treatment diets for 21 d with samples and data collected from d 15 through 21. Treatment 5%-CNO decreased DMI markedly and precipitously and was discontinued after d 5. In wk 3, 5%-AFB and especially 5%-AFB-CNO lowered total-tract NDF digested vs. CTRL (2.6 vs. 1.8 vs. 3.1 kg/d, respectively), likely because fat treatments reduced DMI and 5%-AFB-CNO impaired total-tract NDF digestibility. Milk fat concentrations were 3.10% (CTRL), 2.51% (5%-AFB), and 1.97% (5%-AFB-CNO) and correlated negatively to concentrations of C18:2 trans-10,cis-12 in milk fat. Additionally, 5%-AFB and 5%-AFB-CNO tended to lower milk yield and decreased yields of solids-corrected milk and milk protein compared with CTRL. Fat treatments decreased milk lactose concentration, but increased milk citrate concentration. Moreover, cows fed 5%-AFB-CNO produced less solids-corrected milk than did cows fed 5%-AFB. In experiment 2, diets similar to CTRL contained 2.0, 3.0, or 4.0% CNO. Fifteen multiparous cows (219 ± 42 d postpartum; 42.1 ± 7.0 kg milk yield; mean ± SD) were blocked by DMI and randomly assigned to 1 of 3 treatment diets for an 8-d evaluation. Dietary concentration of CNO affected DMI, with the greatest depression at 4.0% CNO. Overall, dietary CNO depressed DMI and NDF digestibility of a high-starch diet compared with AFB. Feeding CNO to lactating cows equal to or greater than 2.5% decreased lactational performance or DMI.

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Taxonomic characterization and potential biotechnological applications of Yarrowia lipolytica isolated from meat and meat products.

Mirbagheri, M., Nahvi, I., Emtiazi, G., Mafakher, L. & Darvishi, F. (2012). Jundishapur Journal of Microbiology, 5(1), 346-351.

Background: Some species of yeast such as Yarrowia lipolytica produce citric acid, lipases, single-cell oil, etc. Y. lipolytica can degrade renewable, low-cost substrates to produce organic acids like citric acid, more efficiently than Aspergillus niger, and result in higher product yield and lesser waste production and toxicity. Objectives: The aim of this study was to isolate yeast strains with potential for use in biotechnological applications such as production of citric acid and lipase. Materials and Methods: For yeast strain screening, we isolated 179 yeast strains from meat and meat products that were prepared at the RAK and Pegah factories in Isfahan, Iran. Different media were used for screening of yeast colonies and for analyses of citric acid and lipase production; the production of these metabolites was assayed over time. Results: One of the yeast strains isolated from poultry produced 55.5 g/L of citric acid and 12.3 U/mL of lipase. Biochemical and molecular tests showed that this strain belonged to the species Y. lipolytica. Molecular identification was confirmed by DNA sequencing, and the strain was named Y. lipolytica M7 (GenBank accession number, HM011048). Conclusions: The results of this study suggest that meat and its products, especially poultry products, are suitable sources for isolation of yeast strains that produce two biotechnologically valuable products-citric acid and lipase. The yeast strain Y. lipolytica M7 can be used for citric acid production in bioreactor.

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Natural variation for Fe-efficiency is associated with upregulation of Strategy I mechanisms and enhanced citrate and ethylene synthesis in Pisum sativum L.

Kabir, A. H., Paltridge, N. G., Able, A. J., Paull, J. G. & Stangoulis, J. C. R. (2012). Planta, 235(6), 1409-1419.

Iron (Fe)-deficiency is a common abiotic stress in Pisum sativum L. grown in many parts of the world. The aim of the study was to investigate variation in tolerance to Fe deficiency in two pea genotypes, Santi (Fe-efficient) and Parafield (Fe-inefficient). Fe deficiency caused greater declines in chlorophyll score, leaf Fe concentration and root–shoot development in Parafield compared to Santi, suggesting greater Fe-efficiency in Santi. Fe chelate reductase activity and ethylene production were increased in the roots of Santi and to a lesser extent in Parafield under Fe deficiency, while proton extrusion was only occurred in Santi. Moreover, expression of the Fe chelate reductase gene, FRO1, and Fe transporter, RIT1 were upregulated in Fe-deficient roots of Santi. Expression of HA1 (proton extrusion) was also significantly higher in Santi when compared to Parafield grown in Fe-deficient conditions. Furthermore, the application of the ethylene biosynthesis inhibitor, 1-aminoisobutyric acid reduced the Fe chelate reductase activity, supporting a direct role for ethylene in its induction. A significant increase in root citrate was only observed in Santi under Fe deficiency indicating a role for citrate in the Fe-efficiency mechanism. Taken together, our physiological and molecular data indicate that genotypic variation in tolerance to Fe deficiency in Santi and Parafield plants is a result of variation in a number of Strategy I mechanisms and also suggest a direct role for ethylene in Fe reductase activity. The pea cultivar, Santi provides a new source of Fe-efficiency that can be exploited to breed more Fe-efficient peas.

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Enhanced production of citric acid in Yarrowia lipolytica by Triton X-100.

Mirbagheri, M., Nahvi, I., Emtiazi, G. & Darvishi, F. (2011). Applied Biochemistry and Biotechnology, 165(3), 1068-1074.

Various chemical surfactants could affect permeability of yeast cells. In this study, effects of the surfactant addition upon yeast cells permeability and citric acid (CA) production by Yarrowia lipolytica strains DSM 3286 and M7 were investigated. The addition of Triton X-100 increased 1.4–1.8-fold of the maximum CA quantity achieved for both strains, with final CA concentrations ranging between 75–85 g/l that correspond to CA conversion yields per unit of glucose consumed of ~0.80–0.84 g/g. Scanning electron micrographs of yeast cells showed that the cells treated with Triton X-100 had altered cell structure and were smaller and narrower compared with the non-treated ones. The results showed that Triton X-100 could be used in order to increase the efficiency of CA production by Y. lipolytica strains.

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Influence of starter cultures on the antioxidant activity of kombucha beverage.

Malbaša, R. V., Lončar, E. S., Vitas, J. S. & Čanadanović-Brunet, J. M. (2011). Food Chemistry, 127(4), 1727-1731.

This paper investigates the influence of starter cultures, obtained from kombucha isolates, on the antioxidant activity of kombucha beverages. Three starter cultures were used as follows: (1) mixed culture of acetic bacteria and Zygosaccharomyces sp. (SC1); (2) mixed culture of acetic bacteria and Saccharomyces cerevisiae (SC2); as well as (3) native local kombucha. The starter cultures were added to black and green tea sweetened with 7% of sucrose. Fermentation was carried out at 28°C for 10 days. Antioxidant activity to hydroxyl and DPPH radicals was monitored. Kombucha beverage on black tea has shown the highest antioxidant activity to both types of radicals with starter SC1, while the green tea beverage has shown the highest activity with native kombucha. The main reason for the different antioxidant activities, beside tea composition, was ascribed to differing production of both vitamin C and total organic acids in the investigated systems.

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Isolation of lipase and citric acid producing yeasts from agro-industrial wastewater.

Mafakher, L., Mirbagheri, M., Darvishi, F., Nahvi, I., Zarkesh-Esfahani, H. & Emtiazi, G. (2010). New Biotechnology, 27(4), 337-340.

Production of agro-industrial waste pollutants has become a major problem for many industries. However, agro-industrial wastes also can provide alternative substrates for industry and their utilization in this manner may help solve pollution problems. The aim of this study was to isolate yeasts from wastewater treatment plants that could be used to remove pollutants such as glycerol, paraffin and crude oil from the agro-industrial wastewater. In this study a total of 300 yeast isolates were obtained from samples of agro-industrial wastes, and two strains (M1 and M2) were investigated for their ability to produce valuable products such as lipase and citric acid. Identification tests showed that these isolates belonged to the species Yarrowia lipolytica. The Y. lipolytica M1 and M2 strains produced maximum levels of lipase (11 and 8.3 U/ml, respectively) on olive oil, and high levels of citric acid (27 and 8 g/l, respectively) on citric acid fermentation medium.

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Construction and characterization of three lactate dehydrogenase-negative Enterococcus faecalis V583 mutants.

Jönsson, M., Saleihan, Z., Nes, I. F. & Holo, H. (2009). Applied and Environmental Microbiology, 75(14), 4901-4903.

The roles of the two ldh genes of Enterococcus faecalis were studied using knockout mutants. Deletion of ldh-1 causes a metabolic shift from homolactic fermentation to ethanol, formate, and acetoin production, with a high level of formate production even under aerobic conditions. Ldh-2 plays only a minor role in lactate production.

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Apaf-1-deficient fog mouse cell apoptosis involves hypo-polarization of the mitochondrial inner membrane, ATP depletion and citrate accumulation.

Katoh, I., Sato, S., Fukunishi, N., Yoshida, H., Imai, T. & Kurata, S. I. (2008). Cell research, 18(12), 1210-1219.

To explore how the intrinsic apoptosis pathway is controlled in the spontaneous fog (forebrain overgrowth) mutant mice with an Apaf1 splicing deficiency, we examined spleen and bone marrow cells from Apaf1+/+ (+/+) and Apaf1fog/fog (fog/fog) mice for initiator caspase-9 activation by cellular stresses. When the mitochondrial inner membrane potential (Δψm) was disrupted by staurosporine, +/+ cells but not fog/fog cells activated caspase-9 to cause apoptosis, indicating the lack of apoptosome (apoptosis protease activating factor 1 (Apaf-1)/cytochrome c/(d)ATP/procaspase-9) function in fog/fog cells. However, when a marginal (~20%) decrease in Δψm was caused by hydrogen peroxide (0.1 mM), peroxynitritedonor 3-morpholinosydnonimine (0.1 mM) and UV-C irradiation (20 J/m2), both +/+ and fog/fog cells triggered procaspase-9 auto-processing and its downstream cascade activation. Supporting our previous results, procaspase-9 pre-existing in the mitochondria induced its auto-processing before the cytosolic caspase activation regardless of the genotypes. Cellular ATP concentration significantly decreased under the hypoactive Δψm condition. Furthermore, we detected accumulation of citrate, a kosmotrope known to facilitate procaspase-9 dimerization, probably due to a feedback control of the Krebs cycle by the electron transfer system. Thus, mitochondrial in situ caspase-9 activation may be caused by the major metabolic reactions in response to physiological stresses, which may represent a mode of Apaf-1-independent apoptosis hypothesized from recent genetic studies.

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Relationships between acceptance of sour taste and fruit intakes in 18-month-old infants.

Blossfeld, I., Collins, A., Boland, S., Baixauli, R., Kiely, M. & Delahunty, C. (2007). British Journal of Nutrition, 98(05), 1084-1091.

The present study examined whether infants show an acceptance for extreme sour tastes and whether acceptance of sour taste is related to infants' fruit intake. Fruit intake of fifty-three infants at 6, 12 and 18 months was assessed using 3 d food records. Sour acceptance of these infants was studied at 18•1 (sd1•5) months. Acceptance for four solutions differing in citric acid concentrations (0•00 m, 0•013 m, 0•029 m and 0•065 m) was measured by allowing infants ad libitum ingestion of each solution over brief time periods. The base solution to which citric acid was added was blackcurrant squash diluted in water. Infants' relative intake of each solution was used as a measure of sour acceptance. At 18 months, twelve infants readily accepted the two highest citric acid concentrations, whereas the remaining infants rejected these. Infants who accepted the most sour solutions had a significantly higher fruit intake (P = 0•025) and a higher fruit variety (P = 0•015) at 18 months than the infants who rejected the highly sour taste. Furthermore, infants who accepted the most sour solutions consumed fruits more frequently at 18 months (Χ2 5•1; P = 0•024). Infants who accepted the sourest solutions also had a higher fruit intake at 6 months, and a significantly higher increase in their fruit intake from 12 to 18 months. This is the first scientific study that demonstrates the acceptance of sour tastes in some infants at the age of 18 months. Furthermore, the present results suggest a relationship between acceptance of sour tastes and infants' fruit intakes.

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