Role of stationary phase and eluent composition on the determination of log P values of N-hydroxyethylamide of aryloxyalkylen and pyridine carboxylic acids by reversed-phase high-performance liquid chromatography

The partition coefficients, P, between n-octanol and water of a number of growth stimulating substances, N-hydroxyethylamide of aryloxyalkylen- and pyridine carboxylic acids were obtained from Pomona College (C log P), and Rekker's (log P_Rekker) revised fragmental constant system was used to calculate log P data sets. Both of these data sets were correlated with two different substance lipophilicity parameters, log k_w and ₀. Log k_w was obtained by extrapolation of log retention factor (k) to 0% organic modifier measured in reversed-phase liquid chromatography (RPLC) systems. ₀ values were obtained from the slopes and intercepts of these relationships. The RPLC experiments were performed on four commercially available reversed-phase columns. Binary mixtures of methanol–water, methanol–phosphate buffer (pH 7.0), methanol–tricine buffer (pH 7.0) and acetonitrile–water were used as mobile phases for the determination of log k_w values. For the methanolic eluents linear regression provided satisfactory correlations (r>0.99) for the relationships log k vs. organic modifier content in the eluent, while for the acetonitrile-containing eluents a second-degree polynominal regression was necessary. For all four RPLC columns, by linear regression satisfactory correlations (r>0.99) were obtained between log k_w and log P data using methanolic eluents. In such eluents ₀ values were shown to be the second-best lipophilicity parameters. For acetonitrile-containing eluents the use of second-degree polynominal regression was necessary and, in contrast to methanol, significant influence of the applied column on regression results was observed. For acetonitrile-containing eluents the ₀-index does not provide satisfactory results for our substances. No difference in regression results between the use of buffered and non-buffered eluents was observed.     

The effect of p-aminosalicyclic acid on iron transport and assimilation in mycobacteria

p-Aminosalicylic acid inhibits growth of Mycobacterium bovis BCG and Mycobacterium smegmatis more effectively if cells are growing with a sufficiency of iron (> 1 μg Fe/ml) in the medium than if cells are deficient in iron (<0.1 μg Fe/ml). In iron-deficient cultures formation of mycobactin, an ionophore for iron transport, is strongly inhibited by p-aminosalicylic acid. Uptake of iron into cell suspensions is also inhibited and the activity of several iron-containing enzymes declines in cells exposed to p-aminosalicylic acid during their growth. p-Aminosalicylic acid is about 50 times more effective towards a mutant of M. smegmatis which required mycobactin under iron-deficient growth conditions than towards the wild-type parent. p-Aminosalicylate is taken up into cells by an active process independent of the salicylate uptake system, possibly by the route used for assimilation of p-aminobenzoate. (This could account for why p-aminobenzoic acid, but not salicylic acid, antagonizes the action of p-aminosalicylic acid.) With iron-deficient cells, salicylate assimilation is about 50 times greater than either p-aminosalicylate or p-aminobenzoate but with iron-sufficient cells and with the mycobactin mutant salicylate uptake is negligible whereas p-aminobenzoate and p-aminosalicylate uptakes are unaffected. p-Aminosalicylic acid at 3.3 mM (500 μg/ml) partially inhibits the uptake of both p-aminobenzoate and, if it is occuring, that of salicylate as well. As p-aminosalicylic acid is always more effective when the intracellular concentration of salicylic acid is low, it probably acts as an anti-metabolite of salicylic acid, not, however, by inhibiting the conversion of salicylic acid to mycobactic, but probably somewhere along the metabolic pathway of iron uptake.     

Electrostatic effects on polynucleotide transitions. II. Behavior of titrated systems

The theory developed in the previous paper to discuss changes in electrostatic free energies in polynucleotide order–disorder transitions is extended to cases where one or more of the participating species is titrated to some degree α. It is shown that, for any class of transition, the melting temperature T_m at constant pH is a linear function of the logarithm of the monovalent counterion concentration M, that at high salt the logarithm of the depression of the melting temperature by pH titration is proportional to the pH change, and that the stability of the ordered form as measured by its melting temperature at neutral pH, is a monotonic function of the quantity pH_m – pK, where pH_m and pK are the pH of melting and the monomer base pK, both measured under similar conditions of temperature and ionic strength. For the transition from double helix to coil, the dependences of T_m and dT_m/d log M on pH are determined experimentally and compared with the qualitative predictions of the theory. It is found that dT_m/dlog M, a measure of – ΔF?^el (the negative of the electrostatic free energy change in the transition), decreases with increasing pH. In acid solution, where the coil is more extensively prolonated than the helix, the change in electrostatic free energy in the transition is larger than at neutral pH. Conversely, in alkali the electrostatic five energy change is smaller than at neutral pH. Hence (dT_m/d log M)_acid > (dT_m/d log M _neutral) > (dT_m/d log M)_alkali. At Suffeciently high pH, dT_m/d log M is observed to become negative, indicating that the electrostatic free energy change is positive in the transition of this region. Date from the literature on the ionic strength dependence of the melting temperature for the acid helices of poly rA, poly rC, and poly dC are also considered from the standpoint of the theory.     

In vitro studies of the effect of Environmental Conditions on the anthacnose pathogen of bananas, Colletotrichum musae

In vitro studies were undertaken to determine the effect of pH, temperature, water availability and carbon dioxide (CO₂) concentration on germination and growth of Colletotrichum musae, the causal pathogen of anthracnose of bananas. The optimum pH for germination and growth varied between 4·0 and 5·0 depending on temperature. At low pH (< 3·0) and 15°C, both germination and growth were significantly reduced, with a marked increase in the lag time, in days, prior to growth. C. musae germinated and grew over a wide range of water activities (a_w; 0·995−0·94 and 0·995−0·92, respectively) at 20, 25 and 30°C. In all cases where germination occurred appresoria were subsequently produced. Optimum growth occurred at 30°C and 0·995 a_w, although this changed to 0·98 a_w at 35°C. Increasing CO₂ concentration to 15% or reducing oxygen concentration to 1% resulted in a significant (P < 0·05) reduction in growth, but did not inhibit growth completely.     

Transdermal Delivery of an Anti-Cancer Drug via W/O Emulsions Based on Alkyl Polyglycosides and Lecithin: Design,Characterization, and <Emphasis Type="Italic">In Vivo</Emphasis> Evaluation of the Possible Irritation Potential in Rats

The purpose of this work was to develop w/o emulsions that could be safely used to promote transdermal delivery of 5-fluorouracil (5-FU). Two pseudo-ternary phase diagrams comprising oleoyl-macrogol glycerides, water, and a surfactant/co-surfactant (S/CoS) mixture of lecithin, ethanol, and either coco glucoside or decyl glucoside were investigated for their potential to develop promising 5-FU emulsions. Six systems were selected and subjected to thermodynamic stability tests; heat–cool cycles, centrifugation, and finally freeze–thaw cycles. All systems passed the challenges and were characterized for transmission electron microscopy, droplet size, rheological behavior, pH, and transdermal permeation through newly born mice skin in Franz diffusion cells. The systems had spherical droplets ranging in diameter from 1.81 to 2.97 μm, pH values ranging from 7.50 to 8.49 and possessed Newtonian flow. A significant (P < 0.05) increase in 5-FU permeability parameters as steady-state flux, permeability coefficient was achieved with formula B5 comprising water (5% w/w), S/CoS mixture of lecithin/ethanol/decyl glucoside (14.67:12.15:18.18% w/w, respectively) and oleoyl-macrogol glycerides (50% w/w). When applied to shaved rat skin, this system was well tolerated with only moderate skin irritation that was recovered within 12 h. Indeed, minor histopathologic changes were observed after 5-day treatment. Further studies should be carried out, in the future, to investigate the potentiality of this promising system to promote transdermal delivery of 5-FU through human skin.     

The effects of local anesthetics on lipid multilayers. A spin probe study

The effects of a series of local anesthetics on multilayers formed from ox brain white matter lipids were investigated using an intercalated spin-labeled analog of cholestane as a monitor of molecular organization. Local anesthetics could disorder or disrupt these films at pH values approaching or above the pK of the anesthetic. At a constant concentration of a local anesthetic this effect increased with increasing pH. In films formed from lipids with a reduced cholesterol content, local anesthetics promoted the formation of ordered multilamellar arrays and increased their thermal stability. This effect required a lower concentration of local anesthetic than did the disordering effect, and each local anesthetic exhibited an optimal pH range. Depending upon the lipid, the concentration of anesthetic, and the pH of the bathing solution, local anesthetics can either stabilize or disrupt lipid bilayers.     

Tendency for oxidation of annelid hemoglobin at alkaline pH and dissociated states probed by redox titration

The redox titration of extracellular hemoglobin of Glossoscolex paulistus (Annelidea) was investigated in different pH conditions and after dissociation induced by pressure. Oxidation increased with increasing pH, as shown by the reduced amount of ferricyanide necessary for the oxidation of hemoglobin. This behavior was the opposite of that of vertebrate hemoglobins. The potential of half oxidation (E_{1 / 2}) changed from − 65.3 to + 146.8 mV when the pH increased from 4.50 to 8.75. The functional properties indicated a reduction in the log P₅₀ from 1.28 to 0.28 in this pH range. The dissociation at alkaline pH or induced by high pressure, confirmed by HPLC gel filtration, suggested that disassembly of the hemoglobin could be involved in the increased potential for oxidation. These results suggest that the high stability and prolonged lifetime common to invertebrate hemoglobins is related to their low tendency to oxidize at acidic pH, in contrast to vertebrate hemoglobins.     

Production of a novel indole ester from 2-aminobenzoate by Rhodobacter sphaeroides OU5

Culture supernatants of Rhodobacter sphaeroides OU5 grown in the presence of 2-aminobenzoate gave an orange-red color-reaction with Salpers reagent, suggesting the presence of an indole derivative. This production was light-dependent and inducible only with 2-aminobenzoate. Replacement of 2-aminobenzoate with other 2-substituted benzoates did not result in the formation of indole. Fumarate appeared to be the conjugating molecule with 2-aminobenzoate, resulting in the formation of an indole derivative. The purified indole derivative was orange-brown in color, with a yields 0.34 mM from 1 mM 2-aminobenzoate. Infrared analysis suggested an indole ester and ¹H NMR analysis indicated an indole carboxylate, esterified with a terpenoid alcohol. The indole ester has a mass of 441 with the molecular formula C₂₇H₃₉NO₄. The IUPAC name of the compound is (3 E,5 E)-14-hydroxy-3,7,11-trimethyl-3,5-tetradecadienyl 2-(hydroxymethyl)-1 H-indole-3-carboxylate; and the common name given to this compound is sphestrin.     

Anaerobic aniline degradation via reductive deamination of 4-aminobenzoyl-CoA in Desulfobacterium anilini

The initial reactions involved in anaerobic aniline degradation by the sulfate-reducing Desulfobacterium anilini were studied. Experiments for substrate induction indicated the presence of a common pathway for aniline and 4-aminobenzoate, different from that for degradation of 2-aminobenzoate, 2-hydroxybenzoate, 4-hydroxybenzoate, or phenol. Degradation of aniline by dense cell suspensions depended on CO₂ whereas 4-aminobenzoate degradation did not. If acetyl-CoA oxidation was inhibited by cyanide, benzoate accumulated during degradation of aniline or 4-aminobenzoate, indicating an initial carboxylation of aniline to 4-aminobenzoate, and further degradation via benzoate of both substrates. Extracts of alinine or 4-aminobenzoategrown cells activated 4-aminobenzoate to 4-aminobenzoyl-CoA in the presence of CoA, ATP and Mg²⁺. 4-Aminobenzoyl-CoA-synthetase showed a K _m for 4-aminobenzoate lower than 10 M and an activity of 15.8 nmol · min^-1 · mg^-1. 4-Aminobenzoyl-CoA was reductively deaminated to benzoyl-CoA by cell extracts in the presence of low-potential electron donors such as titanium citrate or cobalt sepulchrate (2.1 nmol · min^-1 · mg^-1). Lower activities for the reductive deamination were measured with NADH or NADPH. Reductive deamination was also indicated by benzoate accumulation during 4-aminobenzoate degradation in cell suspensions under sulfate limitation. The results provide evidence that aniline is degraded via carboxylation to 4-aminobenzoate, which is activated to 4-aminobenzoyl-CoA and further metabolized by reductive deamination to benzoyl-CoA.     

The effects of endogenous or exogenous catecholamines on blood respiratory status during acute hypoxia in rainbow trout (Oncorhynchus mykiss)

Summary An extracorporeal circulation of rainbow trout (Oncorhynchus mykiss) was utilized to continuously monitor the rapid and progressive effects of endogenous or exogenous catecholamines on blood respiratory/acid-base status, and to provide in vivo evidence for adrenergic retention of carbon dioxide (CO₂) in fish blood (cf. Wood and Perry 1985). Exposure of fish to severe aquatic hypoxia (final P _wO₂=40–60 torr; reached within 10–20 min) elicited an initial respiratory alkalosis resulting from hypoxia-induced hyperventilation. However, at a critical arterial oxygen tension (P _aO₂) between 15 and 25 torr, fish became agitated for approximately 5 s and a marked (0.2–0.4 pH unit) but transient arterial blood acidosis ensued. This response is characteristic of abrupt catecholamine mobilization into the circulation and subsequent adrenergic activation of red blood cell (RBC) Na⁺/H⁺ exchange (Fievet et al. 1987). Within approximately 1–2 min after the activation of RBC Na⁺/H⁺ exchange by endogenous catecholamines, there was a significant rise in arterial PCO₂ (P _aCO₂) whereas arterial PO₂ was unaltered; the elevation of P _aCO₂ could not be explained by changes in gill ventilation. Pre-treatment of fish with the -adrenoceptor antagonist phentolamine did not prevent the apparent catecholamine-mediated increase of P _aCO₂. Conversely, pre-treatment with the -adrenoceptor antagonist sotalol abolished both the activation of the RBC Na⁺/H⁺ antiporter and the associated rise in P _aCO₂, suggesting a causal relationship between the stimulation of RBC Na⁺/H⁺ exchange and the elevation of P _aCO₂. To more clearly establish that elevation of plasma catecholamine levels during severe hypoxia was indeed responsible for causing the elevation of P _aCO₂, fish were exposed to moderate hypoxia (final P _wO₂=60–80 torr) and then injected intraarterially with a bolus of adrenaline to elicit an estimated circulating level of 400 nmol·l^-1 immediately after the injection. This protocol activated RBC Na⁺/H⁺ exchange as indicated by abrupt changes in arterial pH (pHa). In all fish examined, P _aCO₂ increased after injection of exogenous adrenaline. The effects on P _aO₂ were inconsistent, although a reduction in this variable was the most frequent response. Gill ventilation frequency and amplitude were unaffected by exogenous adrenaline. Therefore, it is unlikely that ventilatory changes contributed to the consistently observed rise in P _aCO₂. Pretreatment of fish with sotalol did not alter the ventilatory response to adrenaline injection but did prevent the stimulation of RBC Na⁺/H⁺ exchange and the accompanying increases and decreases in P _aCO₂ and P _aO₂, respectively. These results suggest that adrenergic elevation of P _aCO₂, in addition to the frequently observed reduction of P _aO₂ are linked to activation of RBC Na⁺/H⁺ exchange. The physiological significance and the potential mechanisms underlying the changes in blood respiratory status after addition of endogenous or exogenous catecholamines to the circulation of hypoxic rainbow trout are discussed.Abbreviations P _aCO₂ arterial carbon dioxide tension - P _aO₂ arterial oxygen tension - P _da dorsal aortic pressure - pHa arterial pH - P _wO₂ water oxygen tension - RBC red blood cell - V _f breathing frequency     

Respiratory characteristics of the blood pigments of three worms from an intertidal mudflat

Abstract

Three worms living in an intertidal mudflat near Auckland have respiratory pigments with different oxygen-binding properties. The burrowing sipunculid Xenosiphon mundanus has hemerythrin contained within coelomic cells. Oxygen is co-operatively bound to the hemerythrin (Hill's coefficient, n, = 1.8), resulting in a sigmoidal oxygen-binding curve of high oxygen affinity (halfsaturation tension, P₅₀, = 7.0 mm Hg at pH 7.5 and 20°C). Oxygen release is regulated by pH, and the Bohr effect is quantified by Ф = Δ log P₅₀ / ΔpH = - 0.30. The errant polychaete Glycera sp. has hemoglobin-charged coelomocytes with low oxygen affinity (P₅₀ = 13.5 mm Hg at pH 7.3 and 20°C)? and the oxygen-binding curve is essentially hyperbolic and insensitive to pH. The burrowing polychaete Abarenicola affinis has a vascular (circulating) erythrocruorin which binds and releases much oxygen for small changes in PO₂ (Hill's n = 3.8) and is insensitive to pH (Ф = -0.09). The physiological properties of these pigments cannot be related to the availability of oxygen in the near-environment, or to the habits of the animals, but appear to be dictated by the level of body organisation, particularly with regard to the gas exchange surfaces.     

A stochastic model for the synthesis and degradation of natural organic matter part II: molecular property distributions

A stochastic biogeochemical model has been developed to simulate the transformation and degradation of natural organic matter (NOM) using an agent-based algorithm which treats each molecule as a separate and potentially unique entity. Molecules react when a pseudo-random number is lower than the calculated reaction probability in a given time step; repeated time steps simulate the transformation of precursor molecules into a complex NOM assemblage. The data for each molecule—elemental and functional group composition—can be used to calculate many properties directly and exactly for each molecule in the assemblage, e.g., molecular weight (MW), fraction of aromatic C (Ar), and charge at pH 7 (Z). Empirical quantitative structure activity relationships (QSARs) are developed which permit the estimation of thermodynamic quantities K _ow (the octanol–water partition coefficient) and pK _a (acidity) for each molecule. Root mean square errors for these QSARs are 0.39 log units for log K _ow and 0.45 log units for pK _a. Distributions of both exactly calculated (MW, Ar, Z) and estimated thermodynamic (K _ow, pK _a) properties are examined and compared with published experimental data. Molecular weight distributions from size exclusion HPLC experiments on aquatic NOM are quantitatively similar to simulation results. pH titrations and polarity distributions from reversed-phase HPLC are qualitatively similar to simulation results. This agreement suggests that the agent-based model can be used to explore hypotheses regarding both compositional and thermodynamic properties of NOM. Robert Wetzel—deceased.     

Proteins as potential bacterial growth inhibitors in foods: Suppression of the activity of water by proteins as determined by NMR relaxation methods

Summary Food microbiologists have long known that suppression of the activity of water,a _w, can retard microbial growth in food systems. Traditionally,a _w, suppression has been achieved by addition of salts or humectants to foods. To limit the amount of preservatives added to food products, studies were initiated to assess the feasibility of using proteins to suppressa _w to a practical value for retarding bacterial growth and to determine the optimum environmental condition for maximizing this effect for milk proteins. New expressions were developed relating observed longitudinal and transverse NMR relaxation rates, in the absence of cross-relaxation, to protein hydration , to the protein activity coefficient, _p, and to the correlation time of the bound water, _c. From _p, the second virial coefficient of the protein,B _o, can be found. By use of andB _o,a _w could then be directly evaluated at any protein concentration. Resulting expressions were tested by²H-NMR relaxation measurements made as a function of protein concentration, for: -lactoglobulin A (the major whey protein) under nonassociating (pH 6.0) and associating (pH 4.65) conditions; and for casein (the major milk protein) in the micellar (with added Ca²⁺) and submicellar (without Ca²⁺) forms. Values ofa _w calculated from these²H-NMR data show that casein, at all the concentrations and temperatures examined, suppressesa _w more than does -lactoglobulin A because of a largerB _o. In turn, micellar casein suppressesa _w to a larger extent than does submicellar casein because of a larger . Extrapolation ofa _w at 4°C to a concentration ten times that in normal milk yields a value, ofa _w of less than 0.95, at whichSalmonella and some strains ofClostridium botulinum no longer grow. These results are in agreement with what is known about storageability of condensed milk. Generalizations regarding the types of proteins and cosolutes to be used for suppressinga _w will be discussed. Structural information on these proteins calculated from _c will also be presented.     

Plant self-thinning dynamics

Plant self-thinning of Hellianthus annuus is examined and it is shown that the mean leaf area ratio is equal to the mean plant density ratio to the power-4/3 independent of the mean plant dry weight and independent of the light intensity over the experimental range considered. The constant term of this basic self-thinning equation is identified, in terms of the mean leaf area and mean plant density values (L _c and p _c respectively) for the plant population in its earliest competing post germination stage and in terms of the derivatives (d log L/d log p)₁=(d log L/dt)₁/(d log p/dt)₁=-4/3 which is independent of light intensity, as L _c p_c ^-4/3.     

Chemical enthalpy-entropy compensation effect in the hydrolysis of p-nitrophenyl carboxylates catalyzed by alkaline mesentericopeptidase

The temperature dependence of the hydrolysis of p-nitrophenyl carboxylates with general formula H(CH₂)_nCOOC₆H₄NO₂ catalyzed by alkaline mesentericopeptidase has been studied (n varying from 1 to 7, temperature range 2–30°C, pH 8.80, 5 vol% dimethylsulfoxide). The activation parameters of the deacylation step depend on the length of the hydrophobic side chain of the substrate molecule ( , , and decrease by 2.0 kcal/mol, 4.9 kcal/mol, and 10 eu, respectively, as the length of the acyl carbon chain increases from n = 1 to n = 4). The following criteria were applied to establish a chemical enthalpy-entropy compensation effect: (a) Exner's plot of log vs : (b) Petersen's plot of log, k/T vs 1/T; (c) Exner's statistical treatment in coordinates log k vs 1/T; (d) according to Krug et al. (ΔH^≠ vs ΔG_Thm^≠). By use of all the above-mentioned criteria the existence of a chemical enthalpy-entropy compensation effect was proved with an isokinetic temperature β of about 470°K, which is significantly higher than the average experimental temperature.     

Population dynamics of a thistle-feeding lady beetle Epilachna niponica (Coccinellidae: Epilachninae) in Kanazawa, Japan. 1. Adult demographic traits and population stability

 Population dynamics of a thistle-feeding univoltine lady beetle, Epilachna niponica Lewis (Coleoptera: Coccinellidae), was studied from 1996 to 1999 in Yuwaku, Kanazawa, Japan. The lady beetles often reached such a high density level that food was depleted. The Jolly–Seber method was used for adult marking, release, and recapture data to estimate population parameters of adult number, daily resident rate, longevity, reproductive rate (R, the number of new adults produced per overwintered adults), and survival rate of new adults to the reproductive seasons (S _w). These estimates were compared with those of the Asiu, Kutsuki (A and F), and Kyoto populations, which were previously studied with similar methods and have similar intensities. Asiu and Kutsuki F populations remained at a rather low density with a low R, while Kutsuki A and Kyoto populations reached a high density where food depletion occurred with a high R value. The Yuwaku population often reached a food-depleting level as in the Kutsuki A and Kyoto populations. It also shared the short life span of overwintered adults (13.5 days) of other high-density populations; however, it showed much shorter longevity of new adults (36.6 days), much lower R (1.0–2.5), and higher S _w (43%–53%). In some traits the Yuwaku population was similar to the Asiu population: low R, high S _w, and low population variability (SD of log densities; 0.103 and 0.115 for overwintered and new adults, respectively, which were lowest among the populations). Received: July 26, 2001 / Accepted: May 21, 2002     

Leaf morphology and leaf chemical composition in three Quercus (Fagaceae) species along a rainfall gradient in NE Spain

 Leaf features were examined in three Quercus species (Q. coccifera, Q. ilex and Q. faginea) along a steep rainfall gradient in NE Spain. The analyzed leaf traits were area, thickness, density, specific mass, leaf concentration of nitrogen, phosphorous, lignin, cellulose and hemicellulose, both on a dry weight basis (N_w, P_w, L_w, C_w, H_w) and on an area basis (N_a, P_a, L_a, C_a, H_a). These traits were regressed against annual precipitation and correlated with each other, revealing different response patterns in the three species. Q. faginea, a deciduous tree, did not show any significant correlation with rainfall. In Q. coccifera, an evergreen shrub, N_w, N_a, L_w, L_a and C_a increased with higher annual rainfall, while H_w decreased. In Q. ilex, an evergreen tree, leaf area, P_w and L_w increased with precipitation, whereas specific leaf mass, thickness and H_a showed the reverse response. Correlations between the leaf features revealed that specific mass variation in Q. faginea and Q. coccifera could be explained by changes in leaf density, while in Q. ilex specific leaf mass was correlated with thickness. Specific leaf mass in the three species appeared positively correlated with all the chemical components on a leaf area basis except with lignin in Q. ilex and with P in Q. ilex and Q. faginea. In these two tree species P_w showed a negative correlation with specific leaf mass. It is suggested that each species has a different mechanism to cope with water shortage which is to a great extent related to its structure as a whole, and to its habit. Received: 18 December 1995 / Accepted: 8 March 1996     

Potential of ochratoxin A production by Aspergillus carbonarius strains isolated from grapes at different ecological factors

Aspergillus carbonarius is known to colonize and produce ochratoxin A (OTA) on grapes and its derived products which is harmful to humans. We screened and tested A. carbonarius strains which isolated from grapes for production of OTA and selected three high OTA producing strains (ACSP1, ACSP2, ACSP3) for this study. These strains were further tested for their ability to produce OTA at different ecological factors [temperature 15, 25, 30, 35°C; water activity (a_w) 0.98, 0.95, 0.90, 0.88; and pH 4.0, 7.0, 9.0, 10.0]. Out of the three strains tested, A. carbonarius ACSP3 produced high levels of OTA than ACSP2 and ACSP1 in all the ecological factors. At 30°C A. carbonarius strains produced the highest OTA compared with other temperature regimes. With reference to water activity, a_w 0.98 favoured mycelial growth and accumulation of more OTA with all the three A. carbonarius strains. Further, pH 4.0 was encouraged the greatest production of OTA in all the strains. No growth was observed at a_w 0.88 and pH 10.0 in all the three strains except the strain ACSP3 at high pH. Our work demonstrated that temperature 30°C, a_w 0.98 and pH 4.0 is optimum for growth and production of OTA by A. carbonarius strains. Maximum amounts of OTA were found at earlier growth stages (7–9 days of incubation) in all the strains of A. carbonarius. The present study revealed that different ecological factors had great impact on OTA production by A. carbonarius which is useful for understanding OTA contamination and to develop proper management practices in future research programmes.