Acetic, Lactic, and Hydrochloric Acid Effects on Staphylococcus aureus 196E Growth Based on a Predictive Model

Mathematical models were developed with a modified Gompertz function to predict Staphylococcus aureus 196E growth, where pH was altered with either acetic, lactic or hydrochloric acid. S. aureus 196E was inoculated into broth formulated with 0.5, 4.5 or 8.5% sodium chloride, adjusted to pH 5.0, 6.0 or 7.0, and incubated aerobically at 12, 20 or 28°C. Each model adequately predicted log growth, and some interactive relationships between independent variables upon population growth were significant (p<0.05). Predictions of growth showed that acetic was generally more inhibitory than lactic or hydrochloric acids.     

分离自腊鱼的乳酸菌生长及产酸特性

采用Gompertz模型拟合从腊鱼中分离的5株乳酸菌的生长和产酸曲线,分析其生长和产酸特性。结果表明：Gompertz模型对乳酸菌的生长和产酸曲线的拟合精度很高;在生长模型和产酸模型中,5株乳酸菌生长的早期适应性相似,其中乳酸片球菌和食品乳杆菌的生长速率(0.32h-1)和产酸速率(0.32h-1)高于其他菌株;在生长模型中两者平衡菌数最高(分别为2.48和2.49);在产酸模型中两者平衡pH值最低(都为3.76);乳酸菌培养液的pH值与总菌数OD600nm值显著线性负相关。     

Effect of lactobacilli inoculation on cassava (Manihot esculenta) silage: Fermentation pattern and kinetic analysis

The major effect of Lactobacillus inoculation on laboratory cassava (Manihot esculenta Crantz) silage was a change from a heterofermentative pattern observed in natural silage to a homofermentation. Small amounts of starter culture (1% v/w) were required to produce a high level of lactic acid (> 28 g kg^?1 DM) and to reach a pH of at least 4. The Gompertz model was used to evaluate the effect of inoculation level on the lactic formation based on kinetic criteria. Also an empirical pH lactic acid correlation was proposed to monitor the progress of ensiling, based solely on pH measurements. The simulation model may be used to improve guidelines for silo safety and to evaluate the effect of lactobacilli inoculants.     

Modelling of Microbial Growth in Potato Homogenate

The use of linear and non-linear models (Gompertz and logistic equations) to fit changes in microbial counts in a model system of potato homogenate at various concentrations of chemical preservatives (citric and ascorbic acids) was evaluated. The effect of undissociated acid concentrations (UAC) on μ (specific growth rate), lag phase duration and inactivation rate of Enterobacteriaceae, Lactobacillus sp, Pseudomonas sp and psychrotrophic microorganisms was determined. Citric acid had a strong inhibitory action on growth rate at low concentrations (0.065 mM UAC, pH=5). Pseudomonas sp were the microorganisms most inhibited by citric acid. Ascorbic acid, at low UAC concentrations (0.302 mM UAC) was more inhibitory to Enterobacteriaceae than to the other microorganisms. For UAC concentration lower than 3 mM , μ values of all the microorganisms tested were higher with ascorbic acid than with citric acid; however at higher concentrations (>10 mM ) both acids had similar effects on μ. © 1997 SCI.     

Effects of Acids on Potassium Sorbate Inhibition of Food-Related Microorganisms in Culture Media

Effects of potassium sorbate in combination with citric, lactic, phosphoric, and hydrochloric acids on the growth of six food-related microorganisms were studied. Trypticase soy broth with 0.1 or 0.2% sorbate adjusted to pH 5.5 with any of the acids was bacteriostatic to Yersinia enterocolitica 0:17. These combinations at pH 5.5 were also bacteriostatic to Salmonello group D, and extended the lag phase of Pseudomonas fluorescens for 24 hr. Combinations of either organic acid with 0.2% sorbate at pH 5.5, reduced the growth rate of Lactobacillus plantarum and an unidentified lactobacillus isolated from frankfurters. Pseudomonas aeruginosa was unaffected by any sorbate-acid combination. Organic acids, specifically citric and lactic, potentiate the antimicrobial action of potassium sorbate.     

Survival and Growth of Probiotic Lactic Acid Bacteria in Refrigerated Pickle Products

We examined 10 lactic acid bacteria that have been previously characterized for commercial use as probiotic cultures, mostly for dairy products, including 1 Pediococcus and 9 Lactobacilli. Our objectives were to develop a rapid procedure for determining the long‐term survivability of these cultures in acidified vegetable products and to identify suitable cultures for probiotic brined vegetable products. We therefore developed assays to measure acid resistance of these cultures to lactic and acetic acids, which are present in pickled vegetable products. We used relatively high acid concentrations (compared to commercial products) of 360 mM lactic acid and 420 mM acetic acid to determine acid resistance with a 1 h treatment. Growth rates were measured in a cucumber juice medium at pH 5.3, 4.2, and 3.8, at 30 °C and 0% to 2% NaCl. Significant differences in acid resistance and growth rates were found among the 10 cultures. In general, the acid resistant strains had slower growth rates than the acid sensitive strains. Based on the acid resistance data, selected cultures were tested for long‐term survival in a simulated acidified refrigerated cucumber product. We found that one of the most acid resistant strains (Lactobacillus casei) could survive for up to 63 d at 4 °C without significant loss of viability at 10⁸ CFU/mL. These data may aid in the development of commercial probiotic refrigerated pickle products.     

Growth kinetics and predictive model of Aeromonas hydrophila in a broth-based system

This study developed a predictive model of Aermonas hydrophila in tryptic soy broth for any combination of temperatures (5 to 40°C), pH (6 to 8), and NaCl (0 to 5%) using a response surface model. A. hydrophila tended to grow within a pH range of 6.0 to 8.0 and could not tolerate NaCl up to 5.0%. The interaction of pH and NaCl did not affect the specific growth rates (SGR). The primary model to obtain the SGR showed a good fit (R²≥0.980). A secondary model was obtained by non-linear regression analysis and calculated as: SGR= 0.4577+0.0529X₁−0.1641X₂−0.1493X₃−0.0016X₁X₂−0.0001X₁X₃+0.0115X₂X₃0.0006X₁ ²+0.0114X₂ ²+0.0150X₃ ² (X₁=temperature, X₂=pH, X₃=NaCl). The appropriateness of the polynomial model was verified by the mean square error (0.0023), bias factor (0.922), accuracy factor (1.343), and coefficient of determination (0.937). The newly secondary model of SGR for A. hydrophila could be incorporated into the tertiary model to predict the growth of A. hydrophila.     

Evaluation of A Modified Gradient Feed Culturing System for Growth of Lactobacillus plantarum Sausage Starter Organism

An internally controlled gradient feed culturing technique, where a nutrient gradient was initiated and subsequently controlled by the lactic acid synthesis, was compared to conventional batch culturing for growth of a sausage starter organism, Lactobacillus plantarum. Significantly higher cell densities (p < 0.01) were observed with twice the culturing time for gradient feed culturing compared to batch culturing. Cell yields within batch or gradient feed culturing system were not affected by pH control at 5.8 or 6.0. Significantly higher (p < 0.05) cell yields, however, were obtained for gradient feed cultures (pH 6.0) with NH₄OH addition at 50% theoretical lactic acid (TLA) level than were obtained at 10% TLA or without NH₄OH addition.     

Behaviour ofYersinia enterocolitica andAeromonas hydrophila in skim milk during fermentation by various lactobacilli

In this study, behaviour ofYersinia enterocolitica andAeromonas hydrophila in skim milk during fermentation by various_{lactobacillus} sp. were determined. pH values of the skim milk samples were also examined during fermentation. The amount of produced lactic acid and diacetyl/acetoin productions of theLactobacillus sp. were estimated. Antimicrobial effects of the lactobacilli onY. enterocolitica andA. hydrophila were also determined by an agar diffusion method. WhileY. enterocolitica was not inhibited and grew during fermentation,A. hydrophila was inhibited, in part, and the growth was retarded. Results were supported by the agar diffusion method forY. enterocolitica, whereas inhibition activity was not found forA. hydrophila. The highest lactic acid productions were estimated inL. bulgaricus (7.50 mg/ml) andL. acidophilus (5.63 mg/ml) and four out of sixLactobacillus sp. were found to be diacetyl/acetoin producers.     

卤制鸭腿中乳酸菌生长预测模型研究

测定了卤制鸭腿中的乳酸菌在5、10、15、20、25℃条件下的生长情况,并利用Gompertz模型拟合了测定温度下的乳酸菌生长一级模型和乳酸菌生长状况。结果表明:模型拟合的R2都大于0.99,利用平方根模型描述温度与最大比生长速率和延滞期的关系,建立了乳酸菌在鸭腿基质上的生长预测二级模型,方差分析表明二级模型拟合显著。模型可用于预测5～25℃范围内乳酸菌在鸭腿上的生长变化情况,为卤制鸭腿中腐败微生物的预测研究提供参考。     

Fermentation of Cucumbers Brined with Calcium Chloride Instead of Sodium Chloride

ABSTRACT: Waste water containing high levels of NaCl from cucumber fermentation tank yards is a continuing problem for the pickled vegetable industry. A major reduction in waste salt could be achieved if NaCl were eliminated from the cucumber fermentation process. The objectives of this project were to ferment cucumbers in brine containing CaCl₂ as the only salt, to determine the course of fermentation metabolism in the absence of NaCl, and to compare firmness retention of cucumbers fermented in CaCl₂ brine during subsequent storage compared to cucumbers fermented in brines containing both NaCl and CaCl₂ at concentrations typically used in commercial fermentations. The major metabolite changes during fermentation without NaCl were conversion of sugars in the fresh cucumbers primarily to lactic acid which caused pH to decrease to less than 3.5. This is the same pattern that occurs when cucumbers are fermented with NaCl as the major brining salt. Lactic acid concentration and pH were stable during storage and there was no detectable production of propionic acid or butyric acid that would indicate growth of spoilage bacteria. Firmness retention in cucumbers fermented with 100 to 300 mM CaCl₂ during storage at a high temperature (45 °C) was not significantly different from that obtained in fermented cucumbers with 1.03 M NaCl and 40 mM CaCl₂. In closed jars, cucumber fermentations with and without NaCl in the fermentation brine were similar both in the chemical changes caused by the fermentative microorganisms and in the retention of firmness in the fermented cucumbers.     

Predicting microbial growth: growth responses of salmonellae in a laboratory medium as affected by pH, sodium chloride and storage temperature

The growth responses of salmonellae (mixed inoculum of Salmonella thompson, S. stanley and S. infantis) as affected by NaCl concentration, pH level and storage temperature were studied in laboratory medium. Growth curves were obtained at 5 concentrations of NaCl (0.5-4.5%, w/v), 5 pH levels (5.6-6.8) and 5 storage temperatures (10-30 degrees C). Sigmoid curves (Gompertz form) were fitted to the data and the curve parameters used to produce a polynomial model from which predicted growth curves could be generated for any combination of NaCl, pH and storage temperature within the limits studied. From those growth curves values for growth rate, generation time, lag time and other values such as time to a 1000-fold increase in numbers were derived. Such a model offers a cost-effective approach to understanding the microbial growth response in foods, and forms a data-base against which other controlling factors could be evaluated. Some problems of fitting curves to microbial growth data and of modelling such data are discussed.     

Microbiological and physicochemical changes of naturally black olives fermented at different temperatures and NaCl levels in the brines

The effect of different temperatures (25°C, 18°C and ambient temperature) and NaCl levels in brines (4%, 6% and 8%) on the microbiological and physicochemical characteristics of naturally black olives of Conservolea variety was studied for up to 190 days. Fermentation was carried out according to the traditional anaerobic method. The initial microflora consisted of Gram-negative bacteria, lactic acid bacteria and yeasts. Inhibition of Gram-negative bacteria was evident in all fermentations. The prevailing micro-organisms were lactic acid bacteria and yeasts, the association of which was dependent on the conditions of fermentation. At 25°C and 18°C in brines containing 4% and 6% NaCl, the growth of lactic acid bacteria was favoured resulting in a lactic acid fermentation, as indicated by the high free acidity levels and low pH values in the brines. On the contrary, 8% NaCl concentration affected the growth of lactic acid bacteria and enhanced the activity of fermentative yeasts, producing a final product with lower free acidity and higher pH value. At ambient temperature, the counts of lactic acid bacteria followed the fluctuation of temperature regardless of salt concentration, while yeasts did not seem to be affected. The lactic acid bacteria identified belonged to the species Lactobacillus mesenteroides, Lactobacillus brevis, Lactobacillus plantarum and Lactobacillus pentosus. The best conditions for fermentation were at 25°C and 6% NaCl, developing free acidity of 142 mM (1·28% w/v) lactic acid and pH value of 3·8. After 5 months of brining, olives fermented at 25°C were judged by panelists as being debittered and ready to eat. No off-odour development was detected in any case due to anomalous fermentation. The HPLC analysis revealed that citric, malic, tartaric, succinic, lactic and acetic were among the end products of fermentation.     

Effect of Temperature, Solute and pH on the Tolerance of Clostridium perfringens to Reduced Water Activities

Two strains of C. perfringens type A (FDI and S45) were grown in Thioglycolate medium adjusted to a_ws of 0.995, 0.975, or 0.965 by the addition of NaCl, KCL or LiCl. Combinations of controlled and uncontrolled pHs (7.0, 6.5 and 6.0) and incubation temperatures of 45°C, 37°C, or 30°C were observed at each a_w. Maximal numbers of cells and shortest lag times occurred at a_w of 0.995, 45°C and pH 7.0. No growth occurred at a_w of 0.965. At 0.985, growth did not occur when KCl was used as the solute and the temperature and pH were 30°C and 6.0, respectively. NaCl was less inhibiting than KCl. LiCl inhibited growth completely.     

Development of twoListeria monocytogenesgrowth models in a meat broth and their application to beef meat

Growth variation ofListeriastrains was taken into account by building two growth models with strains previously characterized, respectively, by their slow (L. monocytogenes CLIP 19532) and fast (L. monocytogenes 14) growth in different conditions of pH, a_wand temperature. Strains of intermediate growth were studied in a meat broth and strains used for the models were grown on the surface of beef meat. Ten growth repetitions at 14°C– a_w0.98–pH 6.2 showed that generation times were similar [ratio value (R=standard deviation/average): 3.2%] but that range of lag times was wide (R=27.4%). In broth, calculated lag and generation times were not significantly different between strains from 30 to 14°C, but variations became larger as temperatures came close to 4°C. Model values corresponded well to experimental generation times and to a lesser extent to lag times. On meat at 4°C and 14°C both strains had experimental lag times three-fold longer than predicted lag times. Experimental generation times were shorter than predicted values at 14°C and longer at 4°C: differences between growth in broth and on meat could be due to the characteristics of the meat, the experimental conditions of growth, the mode of inoculation and the way of adjustment of a_w. Growth variations were found between available predictive models.     

MODEL OF MICROBIAL GROWTH ON FRESH-CUT LETTUCE TREATED WITH CHLORINATED WATER DURING STORAGE UNDER DIFFERENT TEMPERATURES

Various Gompertz models of the growth of bacteria on fresh‐cut lettuce were established in order to predict the shelf life of fresh‐cut lettuce untreated and treated with chlorinated water in storage under different temperatures. The sensory quality of fresh‐cut lettuce treated with water containing 75 µg/L of available chlorine was also examined during storage at 0, 4 and 25C, respectively. Bacteria growth on fresh‐cut lettuce in storage was analyzed to evaluate the effect of temperature, and the established model of predictive bacteria growth on fresh‐cut lettuce fitted the Gompertz modified model best. The lag time λ, the asymptote A and maximum specific growth rate μ_m of the bacteria were calculated, according to Gompertz models. The value of μ_m and A at 0C were lower than that at 4 and 25C, and the lag time was longer at a low temperature than at a higher temperature, indicating that the lower the storage temperature, the slower the growth of bacteria on lettuce, and the smaller the maximum bacteria number reached on the lettuce. The efficacy of preservation of fresh‐cut lettuce treated with chlorinated water was significantly better than that of nontreated lettuce under the same storage temperature. It was found that the final bacteria number predicted (S) on lettuce treated with chlorinated water was lower than that on nontreated lettuce, and that the higher the storage temperature, the higher the final bacteria number predicted (S). The established growth models at different temperature were able to predict the shelf life of fresh‐cut lettuce.     

Selection of lactic acid bacteria for acidification of brown juice (grass juice), with the aim of making a durable substrate for L‐lysine fermentation

BACKGROUND: Brown juice is a waste product from the green crop‐drying industry. Heating and pressing of green crops prior to drying produces a juice rich in nutrients, which can be converted to a stable universal fermentation medium by lowering its pH to 4.0–4.5 via lactic acid fermentation. The aim of this study was to select a strain of lactic acid bacteria for industrial acidification of brown juice. RESULTS: Several strains were tested in fermentation experiments and Lactobacillus salivarius ssp. salivarius DSM 20555 was found to be the best choice. It showed high growth rates at temperatures ranging from 40 to 48 °C, with an optimum temperature of 46 °C (µ_max = 2.2 h^?1), and maintained a high productivity at pH 4.0 in continuous fermentation. The highest productivity of 7.23 g L^?1 h^?1 was found at a dilution rate of 1.0 h^?1. CONCLUSION: With today's increased focus on utilisation of residues from food and agro‐industry, coupled with restrictions on their use as fertiliser for farmlands, lactic acid fermentation could play a significant role in conservation of these nutrient‐rich liquids. This study shows that Lb. salivarius ssp. salivarius DSM 20555 is a very promising micro‐organism for use in such a process. Copyright © 2008 Society of Chemical Industry     

Growth of Listeria monocytogenes as a function of dynamic environment at 10°C and accuracy of growth predictions with available models

A combination of a factorial design and two central composite designs was used to assess quantitatively the effects and interactions of water activity (1–0·95) and pH (5·6–9·5) variations on the growth of Listeria monocytogenes in a meat broth at 10°C. At inoculation or at the beginning of the exponential phase, the cells were exposed to the addition of NaCl and acetic acid or NaCl and NaOH. The effects of abrupt fluctuating conditions on the generation and lag times were analysed using turbidity measurements. The data indicated that the cells exposed to osmotic and acid or alkaline variable conditions from the time of inoculation were less affected than cells exposed at the beginning of the exponential phase. In this last case, a lag phase could be induced and the growth recovery was different from those expected in the new environment. Generation time values were estimated by three available predictive models which describe the effects of temperature, salt concentration and pH on L. monocytogenes growth to highlight the potential problems of variable conditions.     

Fermentation profiles of Manzanilla-Aloreña cracked green table olives in different chloride salt mixtures

NaCl plays an important role in table olive processing affecting the flavour and microbiological stability of the final product. However, consumers demand foods low in sodium, which makes necessary to decrease levels of this mineral in fruits. In this work, the effects of diverse mixtures of NaCl, CaCl₂ and KCl on the fermentation profiles of cracked directly brined Manzanilla-Aloreña olives, were studied by means of response surface methodology based in a simplex lattice mixture design with constrains. All salt combinations led to lactic acid processes. The growth of Enterobacteriaceae populations was always limited and partially inhibited by the presence of CaCl₂. Only time to reach half maximum populations and decline rates of yeasts, which were higher as concentrations of NaCl or KCl increased, were affected, and correspondingly modelled, as a function of salt mixtures. However, lactic acid bacteria growth parameters could not be related to initial environmental conditions. They had a longer lag phase, slower growth and higher population levels than yeasts. Overall, the presence of CaCl₂ led to a slower Enterobacteriaceae and lactic acid bacteria growth than the traditional NaCl brine but to higher yeast activity. The presence of CaCl₂ in the fermentation brines also led to higher water activity, lower pH and combined acidity as well as a faster acidification while NaCl and KCl had fairly similar behaviours. Apparently, NaCl may be substituted in diverse proportions with KCl or CaCl₂ without substantially disturbing water activity or the usual fermentation profiles while producing olives with lower salt content.     

Growth of Escherichia coli O157:H7 and Listeria monocytogenes with prior resistance to intense pulsed light and lactic acid

Previous study showed that repetitive mild decontamination treatments with intense light pulses (ILP) and lactic acid (LA) can induce increased resistance in surviving pathogenic cells. Research has evaluated the potential of increased resistance to enhance the persistence of resistant variants of Listeria monocytogenes and Escherichia coli O157:H7 under suboptimal growth conditions. Growth of resistant variants and parental strains was determined by optical density (OD) measurements in nutrient broths with different pH values and NaCl concentration, at low temperature. The real lag phase was calculated, and results indicated that intense light pulses (ILP) resistant variants needed longer time to initiate growth compared to their parental strains, for both L. monocytogenes and E. coli O157:H7 when incubated at 7 °C and 10 °C, respectively. These selected variants were of the similar resistance towards heat and low pH (no cross-tolerance). Nevertheless, lactic acid (LA) resistant variant of L. monocytogenes was cross-protected when exposed to low pH, but not when treated with heat.