Combined Effect Of pH Research Articles

Relationship between the apparent heat resistance of Bacillus cereus spores and the pH and NaCl concentration of the recovery medium

Conventional heat resistance data, D values, were previously established by other workers at optimal condition for spores outgrowth. However, in canned food conditions of outgrowth are generally suboptimal in term of pH, salt concentration, water activity. The combined effects of pH and NaCl level of the recovery medium for the D value and z pH value were studied. Spores of Bacillus cereus were heated at 95°C in phosphate–citrate buffer media at pH 7. Cells were recovered at 25°C in Nutrient Agar with pH ranging from 5 to 7 and 1% to 4% (w/w) NaCl concentration. For each condition D′ values (decimal reduction time associated with the recovery media characteristics) were determined. The results show a major influence of the recovery pH on the D′ values. This effect is characterised by the z′ pH values, distance of recovery medium pH from optimum recovery pH* medium (6.7) which leads to a tenfold reduction time of D value. The increase of the salt concentration leads to a slight decrease of D′ value. However z′ pH values are not significantly affected by the salt concentration. A simple three parameter model describing the effects of pH and NaCl concentration of the recovery medium upon the heat resistance of spores is proposed. The interaction between pH and salt concentration is sufficiently low to be neglected by the model.

The combined effects of pH and temperature on penicillin G decomposition and its stability modeling

The stability of penicillin G was analyzed as a function of temperature, pH, and the combined effects of pH and temperature were investigated by proposing a second-order polynomial model for penicillin G decomposition reaction rate constant. The modeling results obtained for the first-order decomposition reaction of penicillin G are in good agreement with the experimental data obtained at the pH range of 1.8–10.0 and temperature range of 0–52°C. The stability analysis shows that penicillin G is more stable at the pH range of 5.0–8.0 than out of it and lower temperatures for subsequent isolation. The maximum stability of penicillin G is at about pH 6.0 and its instability its much higher at acidic than basic pH values. The stability of penicillin G decreases by increase in temperature for all pH values. The stability results as well as the proposed second-order model for penicillin G decomposition reaction rate constant can be used for investigating penicillin G losses during its isolation process.

Microorganisms as metal sorbents: comparison with other soil constituents in multi-compartment systems

A multi-compartment experimental system (PIGS) was used to study the importance of microorganisms for metal distribution in simulated soil systems. The influence of pH, solute composition (NaCl and CaCl 2) and presence of fulvic acid on the distribution of zinc, cadmium and mercury among different phases in the multi-compartment system was studied, i.e., among bacteria, fungi and five other solid soil components and a solution phase. Using the multi-compartment system combined with a factorial design made it possible to study several soil factors as well as solid soil components simultaneously as well as to estimate interaction effects between soil factors. The microorganisms accumulated a considerable part (up to 38%) of the metal, despite the fact that they constituted only a minor fraction (0.4 or 1.7%) of the total solid mass. In contrast, quartz and feldspar, which together constituted 80% of the solid mass, accumulated less than 10%. The fraction associated with peat was generally large (11–57%) and the other solid components accumulated intermediate amounts of metal. Solution pH was the single factor that had the largest effect on the metal distribution. The effect of pH was less pronounced on fungi than on most other solid components, which indicates that the relative importance of fungi as metal sorbents increases as pH decreases. Changing solution composition from NaCl to CaCl 2 decreased metal sorption to most sorbents except for the microorganisms where an increased accumulation was observed. The combined effects of pH and fulvic acid were considerable in some cases. This study stresses that the microbial sorbents can respond to changes in the soil solution chemistry in other ways than other solid soil components do. Thus, the microorganism fraction of the solid phase should not be neglected in metal distribution studies of soil.

Thermal and pH-induced conformational changes of a beta-sheet protein monitored by infrared spectroscopy.

The stability of a lentil lectin, an all-beta protein, has been perturbed by changes in pH and temperature. In the pH interval 5.0 --> 10.0, the overall secondary structure does not undergo significant changes. However, if the individual components of the infrared amide I band are considered, changes in band components attributed to variations in beta-sheet and beta-turns cross-interactions are detected. The combined effects of pH and temperature reveal that the protein is more compact at pH 7.5 with lower denaturation temperatures at pH 5.0 or 10.0, indicating a less stable protein under those conditions. According to our results, the structural stability of the beta-sheet would depend not only on the intermolecular interactions among the strands but also on the conformation of the segments connecting these strands. The protein infrared band assignment has also been examined since the three-dimensional structure of the lentil lectin protein is known from X-ray diffraction studies. Two of the bands observed are attributed to beta-sheet. The one at 1620 cm-1, not affected if the medium is deuterated, is assigned to hairpins composed by two strands connected by a rigid turn whereas that located at 1633 cm-1 corresponds to strands associated by more flexible segments. The band appearing at 1645 cm-1 in H2O corresponds to the open, flexible loops that are connecting the beta-strands. The simplest assumption of the various secondary structure components having identical IR extinction coefficients is enough to provide IR-derived data that are in good agreement with the structure solved by X-ray diffraction.

Voluminosity of some food proteins in aqueous dispersions at various pH and ionic strengths

Commercial casein and whey protein and laboratory preparation of soybean protein of various pH were dispersed in distilled water at the initial concentration of 4.0% w/v and then diluted with NaCl solutions of known ionic strengths (μ). Viscosity was measured and voluminosity (Ve=ml/g) was calculated using Lee’s equation relating volume fraction (φv) to relative viscosity: η/ηo=1+2.5φv+7.031φ2v+37.371φ3v. The combined effects of pH and μ on Ve were determined from regression analysis. Ve was inversely related to μ between 0.005 and 0.07M and increased with pH between 6 and 8 and decreased at higher pH. The results are discussed in terms of the relationship between the protein electrostatic charges and structure. It is concluded that in associative proteins Ve is controlled by the number of electrostatic charges and their strength.

PH and thermal stability studies of carboxymethyl cellulase from intergeneric fusants of Trichoderma reesei/Saccharomyces cerevisiae

The combined effect of pH and temperature on carboxymethyl cellulase from two intergeneric fusants (M 14 and M 62) of Trichoderma reesei QM 9414/Saccharomyces cerevisiae NCIM 3288 was studied using response surface methodology. A central composite design for two variables was employed for the optimization studies. This study was compared with similar studies carried out with Trichoderma reesei QM 9414. The optimal pH and temperature for the enzymes derived from these organisms were: for the fusant M 14—pH 5.7 and 41.7°C, for the fusant M 62—pH 5.3 and 43°C, and for Trichoderma reesei QM 9414—pH 4.31 and 38.3°C.

Acidity and calcium interaction affecting cell envelope stability inRhizobium

Calcium improves the ability of many rhizobia to survive and persist in acid soils, but the mechanism responsible for this phenomenon has not been studied in detail. Here, we present data examining the combined effects of pH and calcium on the cell envelope of Rhizobium strains that differ in pH tolerance. The effect of pH and calcium on solute uptake was demonstrated by a change in the resistance to selected antimicrobial agents. When grown at pH 5.0, all strains exhibited fatty acid methyl ester profiles that were significantly different from those obtained using cells grown at pH 7.0. These differences included changes in the C16:C18 ratio and the percentage of 19:0 cyclopropane in the membrane. Both pH and calcium level had marked effects on Rhizobium etli UMR1632 lipopolysaccharide-banding patterns, but there was little evidence of a change in lipopolysaccharides with pH and calcium in Rhizobium tropici UMR1899. Both pH and calcium influenced expression of outer membrane proteins in all strains.Key words: Rhizobium, acidity, calcium, lipopolysaccharide, cell envelope, outer membrane protein.

Physiological Characterization of Common Fungi Associated with Cheese.

ABSTRACTA multivariate statistical method (PLS) was used for a physiological characterization of fungi associated with the cheese environment. The combined effects of pH, salt content, oxygen and carbon dioxide levels on growth and sporulation were studied. Significant factors affecting growth were salt content, level of carbon dioxide and temperature. Interactions between those factors were illustrated and showed that some fungi were especially sensitive to carbon dioxide levels and salt content, at low temperature. Sensitivity to the factors often was more pronounced in the early growth phase. Results may aid in eliminating unwanted fungal growth during cheese production.

Vanillin and pH Synergistic Effects on Mold Growth

ABSTRACTThe combined effects of pH (3.0–4.0) and vanillin concentration (500–1,000 ppm) on the growth of Aspergillus flavus, A. niger, A. ochraceus and A. parasiticus were evaluated in potato‐dextrose agar adjusted to a water activity 0.98. Mold germination time and radial growth rates (RGR) were significantly affected by the variables (p<0.05). For equal concentration of the antimicrobial the reduction in pH had important effects lowering the RGR. The lag time increased as vanillin concentration increased and pH decreased. The inverse lag times of each mold could be described by second order polynomials.

PH and thermal stability studies of chitinase from Trichoderma harzianum: A thermodynamic consideration

The combined effect of pH and temperature on chitinase was investigated using response surface methodology. A central composite design for two variables was employed. The optimal pH and temperature for the least degree of deactivation were found out to be 5.4 and 24°C respectively. The deactivation rate constants and the half life of chitinase were estimated at different pH and temperature combinations. At the optimal pH of 5.4, the rate of the deactivation was found to be the least. Thermodynamic parameters, viz., ΔH*, ΔS*, ΔG* and activation energy of thermal deactivation of chitinase were calculated in the temperature range from 50°C to 60°C.

Combined Effects of pH and Temperature on Listeriolysin O Production by Listeria monocytogenes SLCC 5764

Listeria monocytogenes SLCC 5764 was propagated at 4, 25, or 37°C in tryptic soy broth (TSB) acidified with either acetic acid at pH 5.2, 5.7, or 7.0, or hydrochloric acid at pH 5.0, 5.7, or 7.0; or made alkaline with sodium hydroxide at pH 7.5, 8.5, or 9.5. These studies were undertaken to determine the combined effects of temperature and pH on the production of listeriolysin O (LLO). The LLO activity was greatest after the cells were propagated in TSB acidified by either acid to pH 7.0 at 37°C. Very little LLO activity was detected for cells propagated at 4° under acidic conditions. There were no significant differences found between the LLO produced in media acidified with either acid. The LLO activity was highest after the cells were propagated in media at pH 7.5 at 37°C.

Measurement of electrokinetic and size characteristics of estuarine colloids by dynamic light scattering spectroscopy

The combined use of flow-through (0.4 μm) and cross-flow (~1 nm) filtration techniques allowed the transfer of estuarine colloids into electrolyte solutions suitable for their characterization by dynamic light scattering (DLS) measurement techniques. Acid-base titrations monitored by laser doppler electrophoresis revealed the existence of two classes of acid groups having pK a values of 2.6–2.7 and 8.8–9.1 respectively. Similar centres of pK a distributions as well as similar dependencies of pK a on ionic strength were observed on humic acids isolated from the same estuary. This suggests that the (de)protonation behaviour of the natural colloidal material from the Beaulieu estuary is determined by that of humic substances. Measurements of their effective mean size by photon correlation spectroscopy revealed that individual humic molecules were held together in units of 2–300 nm in size, the precise value increasing with time and decreasing with increasing pH or ionic strength. On the other hand, the same measurements on the raw colloidal material gave a completely different picture: only at very low ionic strength ( I = 0.006) was there an unambiguous dependence of size on pH; at higher ionic strength ( I = 0.06) the combined effect of pH and time was complex. These results suggest that the humic molecules which so profoundly influence the surface properties of Beaulieu estuary colloids are either strongly bound to or irreversibly incorporated into their colloidal carrier.

Predictive model of the effect of temperature, pH and sodium chloride on growth from spores of non-proteolytic Clostridium botulinum

Non-proteolytic strains of Clostridium botulinum are capable of growth at chill temperatures and thus pose a potential hazard in minimally-processed chilled foods. The combined effect of pH (5.0–7.3), NaCl concentration (0.1–5.0%) and temperature (4–30 °C) on growth of non-proteolytic C. botulinum in laboratory media was studied. Growth curves at various combinations of pH, NaCl concentration and temperature were fitted by the Gompertz and Baranyi models, and parameters derived from the curve-fit were modelled. Predictions of growth from the models were compared with data in the literature and this showed them to be suitable for use with fish, meat and poultry products. This model should contribute to ensuring the safety of minimally-processed foods with respect to non-proteolytic C. botulinum.

Metallothionein isoform analysis by liquid chromatography-electrospray ionisation mass spectrometry.

Metallothionein (MT) is a class of small metal-binding proteins [ l ] whose mass can vary from under 6OOO to over 7000 daltons depending on a) variation in non-conserved amino acid regions b) the degree of metal saturation and c) the species of metal bound. Many mammalian species have several functioning genes of MT and accurate mass values of the corresponding protein isoforms can be deduced from published gene sequences. However, the translated product of each gene has yet to be confirmed in purified MT protein samples because the isoforms can be difficult to separate by conventional chromatography or electrophoresis. In the case of sheep which have at least 4 functioning MT genes [2], the deduced N-terminally acetylated apoprotein masses are 5993 (MT-la), 6023 (MT-lb), 6027 (MT-lc) and 6070 (MT-2). The objective of this work was to study the proteins by high accuracy, high resolution electrospray mass spectrometry and to confirm their predicted mass values. Metallothionein was purified from the liver of a gray-faced sheep which had been injected with Zn. For LC-MS studies, an LDC 4100 MS gradient HPLC system with 2 x 125 mm C,, column and UV detector was coupled to a MAT 900 mass spectrometer fitted with a PATRIC detector and using an electrospray ionisation source (Finnigan Mat GmbH). Separations were performed using a 2-step linear gradient of 030% acetonimle with 0.1% TFA over 5 min. followed by 30-40% acetonitrile with 0.1% TFA during the remaining 40 min. Flow rate was 300 pl/min. and sample injection was 20 p1 at a concentration of 1 pg/pL. Separated components were detected by UV monitoring at 214 nm prior to electrospray at 3 kV (1 pA) with a capillary temperature of 270'C. Mass spectra were collected over the range lo00 2300 amu using a resolution of 1400 at 5 sec/decade. For flow injection, the same MS parameters were used and samples were dissolved in either water/acetonitrile (1/1) or water/acetonitrile (4/6) + 0.1% TFA. They were then analysed using a 5 FL loop injection with a flow rate of 30 pUmin. Analysis of sheep MT-I proteins by on-line HPLCESI-MS revealed components with distinct mass profiles whose chromatograms can be seen in Fig. 1. Mass spectra and derived deconvoluted spectra of the components resolved by chromatography confirmed the presence of proteins whose masses were within a fraction of predicted values for MT-la, -1b and -1c (Fig. 1, inset table). Indeed, the relative abundance of these isoforms was similar to that reported for the corresponding MT mRNA in sheep liver [3] and the translation of all 3 MT-1 proteins is consistent with the evidence for isoform heterogeneity obtained using capillary electrophoresis techniques [4]. A further minor isoform of mass 5951 was detected in MT-1 (Fig. 1). which is consistent with the presence of a form of deacetylated MT la. This may have physiological relevance since the rate of protein degradation may be influenced by the degree of deacetylation. The study of MT-1 by flow injection ESI-MS at acid and neutral pH gave rise to complex spectra (Fig. 2). A repetitive pattern with a repeat interval of 63-64 amu can be seen, with components at neutral pH being of higher mass than those at low pH. This pattern was caused by a varying degree of Zn or Cu dissociation from MT isoforms depending on the combined effect of pH and electrospray conditions.

Direct conversion of cellulosic material to ethanol by the intergeneric fusant Trichoderma reesei QM 9414/ Saccharomyces cerevisiae NCIM 3288

Single-stage direct bioconversion of cellulosic materials to ethanol, under almost the same fermentation conditions applied to the Saccharomyces cerevisiae-ethanol process, was attempted using intergeneric fusants of Trichoderma reesei QM 9414/ S. cerevisiae NCIM 3288. Optimization of medium constituents was made using the Box-Behnken design method. The combined effect of pH and temperature on the fermentation was analyzed by the central composite design method. Under optimal conditions the fusant produced 0.17 g l −1 ethanol in 30 h.

A response surface study on the role of some environmental factors affecting the growth of Saccharomyces cerevisiae

The combined effect of pH, ethanol and fructose on the growth of Saccharomyces cerevisiae at 25 °C was studied by the standard Response Surface Methodology. Canonical analysis of the obtained response surface led to the conclusion that the effects of ethanol and fructose can be described by a single factor, the value of water activity, which can be calculated from the other two. Therefore the number of explanatory variables can be reduced. The computational usefulness of the transformation b w = √(1 − a w) is demonstrated.

Rennet coagulation of buffalo milk as affected by some factors

AbstractThrombelastograph was used to measure the rennet coagulation properties of buffalo milk. The combined effect of pH with temperature fat and protein contents, addition of whey protein concentrat (WPC) and sodium chloride on rennet coagulation (r) and clot forming (K20) times were evaluated. The fat content had little effect on r or K20 compared to pH. Increasing temperature from 30 to 40 °C or the protein content of UF milk retentate from 3 to 12% decreased K20 and K20 of buffalo milk. The K20 was greatly affected by the replacement of casein with 10, 20, 30 and 40% WPC while r was less affected. Addition of sodium chloride (2–10%) increased and K20 and the effect was more pronounced at low pH. The relations between the studied factors and r and K20 of buffalo milk were calculated and discussed.

Survival and growth of Escherichia coli O157:H7 in ground, roasted beef as affected by pH, acidulants, and temperature

A study was undertaken to determine the fate of Escherichia coli O157:H7 in ground, roasted beef as influenced by the combined effects of pH, acidulants, temperature, and time. There was essentially no change in the viable population of E. coli O157:H7 when beef salads (pH 5.40 to 6.07) containing up to 40% mayonnaise were incubated at 5 degrees C for up to 72 h. At 21 and 30 degrees C, significant (P < or = 0.05) increases in populations of the organism occurred in salads containing 16 to 32% mayonnaise (pH 5.94 to 5.55) between 10 and 24 h of incubation. Death was more rapid as the pH of acidified beef slurries incubated at 5 degrees C was decreased from 5.98 to 4.70. E. coli O157:H7 grew in control slurries (pH 5.98) and in slurries containing citric and lactic acids (pHs 5.00 and 5.40) incubated at 21 degrees C for 24 h; decreases occurred in slurries acidified to pHs 4.70, 5.00, and 5.40 with acetic acid or pH 4.70 with citric or lactic acid. At 30 degrees C, populations decreased in slurries acidified to pHs 4.70 and 5.00 with acetic acid. Citric and lactic acids failed to prevent significant increases in populations in slurries at pH 4.70 to 5.40 between 10 and 24 h of incubation. The order of effectiveness of acidulants in inhibiting growth was acetic acid > lactic acid > or = citric acid. The same order was observed for inactivation of E. coli O157:H7 in acidified (pH 5.00) beef slurry heated at 54 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of pH, aluminium concentration and temperature on the embryonic development of the European common frog, Rana temporaria

The individual and combined effects of pH, aluminium concentration and temperature, on the development of common frog (Rana temporaria) embryos from an upland area of northern England, were investigated in a controlled laboratory study. There was strong evidence to suggest that embryonic survival was lower at pH 4.5 compared with pH 6.0. At pH 4.5, embryonic survival was reduced at the highest aluminium concentrations. There was no strong evidence for a reduction in embryonic survival at lower aluminium concentrations.Gastrulation and hatching appeared to be the most sensitive stages to both pH and aluminium concentration.There was strong evidence to suggest that temperature‐shocked embryos had reduced survival when compared with those kept at a constant temperature, particularly at pH 4.5.There was substantial variation in the survival of embryos from different clutches in the same pond with respect to low pH, aluminium concentration and temperatures. Thus R. temporaria has a wide genetic base from which to tolerate environmental changes. It is suggested, however, that the lethal and sublethal effects of low pH, high aluminium concentration and low temperature, could lead to a decrease in recruitment to the adult populations of R. temporaria in upland, northern England.

Combined effects of pH, cosolvent and penetration enhancers on the in vitro buccal absorption of propranolol through excised hamster cheek pouch

The combined effect of pH and vehicle composition on the buccal absorption of propranolol has been evaluated in vitro using hamster cheek pouch. Ethanol was used as cosolvent in various binary-water mixtures. Lauric acid, 1-menthol, sodium salicylate and phosphatidylcholine were evaluated as penetration enhancers. Isopropyl myristate was used as a model of the mucosal lipid phase in partitioning experiments. Permeation of propranolol increased in extent with increasing pH of the vehicle, as compared with the unionized lipophilic fraction of the drug. Permeation of propranolol was decreased at pH 9.4 and increased at pH 6.8 on the addition of ethanol. Ethanol increases the solubility of propranolol in the aqueous vehicle and reduces the oil/vehicle partitioning of the drug through a thermodynamic effect. In addition, at low concentration, ethanol is assumed to increase the permeability of the buccal mucosa to the polar ionized form of propranolol, while higher concentration is required to enhance the diffusivity of the nonpolar unionized form. Menthol and lauric acid were effective at promoting the buccal absorption of propranolol only when the drug was ionized. It was assumed that the mechanism of permeation enhancement was an interaction with the membrane components for 1-menthol, increasing the diffusibility of propranolol, whereas lauric acid may form a more partitionable complex with the drug without any action on membrane permeability.