Inhibitory Effect Of Acid Research Articles

Unstructured model for free and immobilized cell culture without pH control of Bifidobacterium animalis subsp. lactis Bb 12—Inhibitory effect of the undissociated organic acids

A model was developed to describe growth and organic acids production of Bifidobacterium animalis growing without pH control in free and immobilized cell culture. The Verlhust model was considered for growth, and to account for the inhibition observed at acidic pH, the Luedeking–Piret production model was modified by introducing an additional term involving the undissociated form of the organic acids, acetic and lactic acids, the main inhibitory species. To describe the relationship between pH and both the dissociated and the undissociated forms of organic acids, the Henderson–Hasselbach equation was considered. The model was found to satisfactory describe experimental growth and production data recorded during free and immobilized cell cultures. The part of each acid produced can be deduced from the calculated production data, since a constant lactic to acetic acid mass ratio was found, 1.29 and 1.66 during free and immobilized cell cultures. Owing to the acidic pH values recorded, 4.43 at lowest, higher amounts of undissociated acetic acid were produced, leading to a higher inhibitory effect of this acid if compared to lactic acid.

Microbial-growth inhibition during composting of food waste: Effects of organic acids

Factorial designs were employed to analyze the inhibitory effects of acetic, butyric, lactic, and propionic acids on composting microorganisms. Compost samples were withdrawn on different days of composting and treated with acids alone and in combination (at 0 and 0.5mmol/g). Microorganisms were enumerated to determine degree of growth inhibition. Generally, inhibition was more severe on the day when pH decreased rather than on the day when pH started to increase. Butyric or lactic acid alone, and the combination of butyric, lactic, and propionic acids, significantly inhibited thermophilic bacteria. Only 51.0–65.0% of the thermophilic bacteria exist if 0.5mmol/g of these acids were present in compost. Temperature, microbial populations, and microbial growth phase might cause variation in the inhibitory effects of acids. These findings are useful not only in the study of microorganisms in acidic microenvironments, but also in preventing microbial-growth inhibition by predicting population via a regression model.

Production of organic acids by Lactobacillus strains in three different media

Ten strains of Lactobacillus (Lb). casei, Lb. rhamnosus, Lb. plantarum, Lb. paracasei and Lb. curvatus species were chosen to determine the production of organic acids after cultivation in skimmed milk, MRS broth and Jerusalem artichoke (JA) medium. The highest acidity was obtained in MRS broth and the weakest acidification was found in skimmed milk. Lb. casei Shirota produced the highest amount and Lb. rhamnosus VT1 the lowest amount of substances being estimated as titratable acidity. All strains produced lactic acid in the investigated broth and most of the strains produced acetic acid in MRS broth except Lb. curvatus 2768 and Lb. casei Shirota, in JA broth except Lb. paracasei SF1 and in skimmed milk except Lb. casei 2750, Lb.curvatus 2768, Lb. curvatus 2775 and Lb. casei Shirota. All strains, except Lb. plantarum 01, produced butyric acid in MRS broth. Beside the lactic and acetic acids, formic, citric, succinic and glutamic acids were also produced in MRS broth; formic and succinic acids were produced in skimmed milk and succinic acid in JA broth. Some strains showed change in their fermentation profile from homofermentative to mix-acid fermentation in milk. The antifungal efficiency of the lactic and acetic acid in the amount produced by lactobacilli was investigated. None of the investigated aspergilli were inhibited. The inhibitory effect of acids against Fusarium increased unequivocally with the increasing concentration. The study pointed at the dissimilarity of organic acid production of Lactobacillus strains, which was considerably influenced by the media.

Roles of aconitase in growth, metabolism, and morphological differentiation of Streptomyces coelicolor.

The studies of aconitase presented here, along with those of citrate synthase (P. H. Viollier, W. Minas, G. E. Dale, M. Folcher, and C. J. Thompson, J. Bacteriol. 183:3184-3192, 2001), were undertaken to investigate the role of the tricarboxylic acid (TCA) cycle in Streptomyces coelicolor development. A single aconitase activity (AcoA) was detected in protein extracts of cultures during column purification. The deduced amino acid sequence of the cloned acoA gene constituted the N-terminal sequence of semipurified AcoA and was homologous to bacterial A-type aconitases and bifunctional eukaryotic aconitases (iron regulatory proteins). The fact that an acoA disruption mutant (BZ4) did not grow on minimal glucose media in the absence of glutamate confirmed that this gene encoded the primary vegetative aconitase catalyzing flux through the TCA cycle. On glucose-based complete medium, BZ4 had defects in growth, antibiotic biosynthesis, and aerial hypha formation, partially due to medium acidification and accumulation of citrate. The inhibitory effects of acids and citrate on BZ4 were partly suppressed by buffer or by introducing a citrate synthase mutation. However, the fact that growth of an acoA citA mutant remained impaired, even on a nonacidogenic carbon source, suggested alternative functions of AcoA. Immunoblots revealed that AcoA was present primarily during substrate mycelial growth on solid medium. Transcription of acoA was limited to the early growth phase in liquid cultures from a start site mapped in vitro and in vivo.

Modeling the inhibitory effects of organic acids on bacteria

The inhibitory effect of acids on microbial growth has long been used to preserve foods from spoilage. While much of the effect can be accounted for by pH, it is well known that different organic acids vary considerably in their inhibitory effects. Because organic acids are not members of a homologous series, but vary in the numbers of carboxy groups, hydroxy groups and carbon–carbon double bonds in the molecule, it has typically not been possible to predict the magnitude, or in some cases even the direction, of the change in inhibitory effect upon substituting one acid for another or to predict the net result in food systems containing more than one acid. The objective of this investigation was to attempt to construct a mathematical model that would enable such prediction as a function of the physical and chemical properties of organic acids. Principal Components Analysis (PCA) was applied to 11 properties for each of 17 acids commonly found in food systems; this resulted in four significant principal components (PCs), presumably representing fundamental properties of the acids and indicating each acid’s location along each of these four scales. These properties correspond to polar groups, the number of double bonds, molecular size, and solubility in non-polar solvents. Minimum inhibitory concentrations (MICs) for each of eight acids for six test microorganisms were determined at pH 5.25. The MICs for each organism were modeled as a function of the four PCs using partial least squares (PLS) regression. This produced models with high correlations for five of the bacteria ( R 2=0.856, 0.941, 0.968, 0.968 and 0.970) and one with a slightly lower value ( R 2=0.785). Acid susceptible organisms ( Bacillus cereus, Bacillus subtilis, and Alicyclobacillus) exhibited a similar response pattern. There appeared to be two separate response patterns for acid resistant organisms; one was exhibited by the two lactobacilli studied and the other by E. coli. Predicting the inhibitory effects of the organic acids as a function of their chemical and physical properties is clearly possible.

Inhibition of palmito ( Acanthophoenix rubra) polyphenol oxidase by carboxylic acids

The inhibition of palmito ( Acanthophoenix rubra) polyphenol oxidase (PPO) is reported. Recently, two forms of palmito PPO were partially purified by hydrophobic chromatography. Inhibitory effects of various carboxylic acids on these two forms have been studied. Both forms showed identical behaviour towards the inhibitors studied. Cinnamic acid was found to have the greatest inhibitory effect ( K i = 0·06 mM). When the inhibitory effects of acids from the benzoic acid family and from the cinnamic acid family were compared, it was found that acids which possess a double bond between the benzene ring and the carboxylic function showed the highest inhibitory effect. This inhibitory effect was decreased by substitutions on the benzene ring. The influence of pH on the inhibitory effect of carboxylic acids on palmito PPO has also been investigated. K i decreased with a decrease in pH. This effect is due to the fact that it is only the undissociated form (AH) of carboxylic acids that is responsible for inhibition of PPO. Inhibition constants ( K i for the AH form have been recalculated and were found to remain constant in the pH range studied (for benzoic acid K i = 0·14 mM, for cinnamic acid K i = 0·019 mM, for sorbic acid K i = 0·15 mM).

Growth and survival kinetics of Yersinia enterocolitica IP 383 0:9 as affected by equimolar concentrations of undissociated short-chain organic acids.

The influence of different organic acids (lactic, acetic, formic and propionic acids) at equimolar concentrations of undissociated acid with pH range of 3.9, 5.8, on the aerobic and anaerobic growth and survival kinetics of the virulent strain of Y. enterocolitica IP 383 0:9, was determined in tryptone soy broth at 4 degrees C. Growth and survival data were analyzed and fitted by a modification of the Whiting and Cygnarowicz-Provost model, using the Minpack software library. Initial generation times, initial specific growth rates, lag time and dead rate were subsequently calculated from the model parameters. The results demonstrate that the inhibitory effects of the acids were divided into two categories dependent upon pH. At high pH (5.8) the order of inhibition was formic acid > acetic acid > propionic acid > lactic acid, whereas at lower pH it became formic acid > lactic acid > acetic acid > propionic acid. The inhibitory effect of lactic acid is enhanced under anaerobic condition. Nevertheless, when the organism was cultured anaerobically, it was shown to be more tolerant to formic and acetic acids. Moreover, these variables (type of organic acid, pH and atmosphere) did not lead to the loss of the virulence plasmid in growing and surviving cells. The mechanism of inhibitory effect for each of the acids are also discussed.

Effect of First Part of Duodenum on Gastric Emptying in Dogs: Response to Acid, Fat, Glucose, and Neural Blockade

Five dogs were prepared, each with a gastric and duodenal fistula (5 cm distal to the pylorus), to study the inhibitory role of the first 5 cm of the duodenum on gastric emptying. The basic design of the experiments was to instill the test meal (300 ml at 37 degrees C, containing phenol red 40 mg 1(-1)) into the stomach and collect it at 1- or 2-min intervals for 10 or 20 min from the duodenal fistula. As the test meal emptied from the stomach it bathed the first 5 cm of duodenum and thus stimulated the appropriate receptor. A Foley catheter with an inflated balloon prevented passage into the second part of the duodenum. Test meals of hypertonic glucose (15%, 865 milliosmoles kg-1) or 20 and 80 mM of sodium oleate emptied at the same rate as water when allowed to bathe the first 5 cm of duodenum, whereas test meals of 100 mM of HCl were slowed. In further studies using neural blocking agents, the emptying of water meals was slowed with subcutaneous atropine sulfate (0.03 and 0.15 mg kg-1), intravenous hexamethonium chloride (10 mg kg-1), and norepinephrine bitartrate (0.04 mg kg-1). The emptying of 100 to 120 mM HCl meals was slowed by subcutaneous atropine sulfate (0.03 and 0.15 mg kg-1), intravenous norepinephrine bitartrate (0.04 mg kg-1), and the intravenous alpha-receptor blocking agents phenoxybenzamine HCl (2 mg kg-1) and phentolamine (2 mg kg-1), was unaffected by intravenous hexamethonium chloide (10 mg kg-1), and was unchanged (1.0 mg kg-1) or slightly slowed (2.0 mg kg-1) by the beta-receptor blocker propranolol. In contrast, acid test meals were emptied at the same rate as water when treated with intravenous guanethidine monosulfate (2 mg kg-1) or intramuscular reserpine (1 mg kg-1), indicating that the acid inhibition was mediated by an adrenergic mechanism. The emptying of water meals was unchanged by these two drugs. The authors suggest that the first 5 cm of duodenum contain receptors for inhibition of emptying of acid but not for fat or hypertonic glucose. Furthermore, the neural blocking studies indicate that the inhibitory effect of acid in the first part of the duodenum is an adrenergic mechanism which appears to be neither alpha nor beta-receptor-mediated.

Inhibitory effect of acid in the intestine on rumen motility in sheep.

Inhibitory effect of acid in the intestine on rumen motility in sheep.

Changes in Lower Esophageal Sphincter Pressure During Insulin-Induced Hypoglycemia

Lower esophageal sphincter (LES) pressure has recently been shown to increase following injection of submaximal doses of pentagastrin or after maneuvers designed to cause endogenous gastrin release. These observations suggested that changes in LES pressure might provide a means to evaluate endogenous gastrin activity in vivo. This study was undertaken to observe possible changes in LES pressure during vagal stimulation of acid secretion following hypoglycemia induced by intravenous injection of 0.2 U per kg of regular insulin. In a group of normal subjects a rapid decrease in LES pressure was consistently noted at the time of occurrence of hypoglycemic symptoms and resulting increased gastric acidity. In each subject the study was repeated on a subsequent day, but with constant neutralization of the stomach by instillation of 0.1 n NaHC03. Under these conditions, consistent increases in LES pressure occurred during the hypoglycemic reaction. Further studies in patients having previous vagotomy and pyloroplasty revealed increased LES pressure during hypoglycemia despite the absence of gastric acid production. No increase in LES pressure was seen during hypoglycemia in patients having vagotomy and subtotal gastrectomy. These results would seem to confirm in man the effect of hypoglycemia on gastrin which has previously been shown in dog preparations. During hypoglycemia gastrin is released from the antrum, but this effect is inhibited by the simultaneous acid secretion. Neutralization of gastric contents or absence of acid secretion during hypoglycemia prevents the inhibitory effect of acid on the antral mucosa. The results of these studies suggest that gastrin release during hypoglycemia in man is not dependent on the vagus nerve.

A telemetering capsule for gastrointestinal pH measurement.

THE QUANTITATIVE determination of the gastric acidity is important to the clinician because of the relationship between acid-pepsin, peptic ulcer, and gastric carcinoma. The clinical investigator also is interested in such determinations since he needs valid, quantitative data on the physiological responses of the gastrointestinal tract to food, sleep, and mental and physical stress. There is no indisputably physiological method available that yields such data. Gastric acidity is usually studied by inserting a tube into the empty stomach via the nose or mouth. This method has yielded much valuable information 1 but has the following objections: (1) The secretory response of only the empty stomach can be measured since food would clog the tube. (2) Aspiration of the acid gastric juice may cause an artificially high rate of secretion since the inhibitory effect of acid in the stomach is removed. (3) The presence of the tube in the nose or

A quantitative study of the inhibitory effect of acid in the intestine on gastric secretion

Acid introduced into the smal intestine of Pavlovpouch dogs inhibits gastric secretion in response to a meal, providing an adequate degree of intestinal acidity is attained. Marked inhibition of secretion occurs if the pH of the intestinal contents is about 2.5 and almost complete depression when the pH is 2.0 or lower. This regulatory effect of intestinal acidity on gastric secretion is not present when the secretion is provoked by histamine. The role of this regulatory mechanism during the secretory period following a meal and the various factors which may be involved are discussed.