Lactic Acid Bacteria In Milk Research Articles

Modelling and Predicting the Growth of Escherichia coli and Staphylococcus aureus in Co-Culture with Geotrichum candidum and Lactic Acid Bacteria in Milk

The growth of two pairs of co-cultures (Escherichia coli/Geotrichum candidum and Staphylococcus aureus/Geotrichum candidum) with a starter culture of lactic acid bacteria was studied in milk at temperatures ranging from 15 °C to 21 °C, related to the ripening of artisanal cheese. For an inoculum of approximately 106 CFU/mL, LAB not only induced an early stationary phase of E. coli (two isolates BR and PS2) and S. aureus (isolates 2064 and 14733) but also affected their death phase. In co-cultures with LAB and G. candidum, the numbers of E. coli and S. aureus increased in 2 logs and 1 log, respectively, reaching maximum population densities (MPDs) of less than 5 and 4 logs, respectively. After that, the populations of both bacteria represented with two isolates decreased in more than 2 logs and 3 logs within 2 days compared to their MPDs, respectively. G. candidum was found to be the subject of interactions with LAB within a given temperature range only partially. To develop a tertiary model for the growth curves of the populations, a one-step approach was used, combining the Huang-Gimenez and Dalgaard primary model with secondary square-root models for growth rate and lag time. Furthermore, the reparametrized Gompertz-inspired function with the Bigelow secondary model was used to describe the death phase of the E. coli and S. aureus isolates. The prediction ability of the growth of the H-GD tertiary model for co-cultures was cross-validated within the isolates and datasets in milk and milk medium with 1% NaCl. The study can be used as knowledge support for the hygiene guidelines of short-ripened raw milk cheeses, as was our case in Slovakia.

One- and Two-Step Kinetic Data Analysis Applied for Single and Co-Culture Growth of Staphylococcus aureus, Escherichia coli, and Lactic Acid Bacteria in Milk

The objective of this study was to compare one- and two-step kinetic data analysis approaches to describe the growth of Staphylococcus aureus, Escherichia coli, and lactic acid bacteria Fresco 1010 starter culture in milk under isothermal conditions between 10 and 37 °C. The primary Huang model (HM) and secondary square root model were applied to lag times and growth rates of each of the population. The one-step approach for single cultures data enabled the direct construction of a tertiary model combining primary and secondary models to determine parameters from all growth data, thus minimizing the transfer of errors from one model to another. The statistical indices showed a significant improvement in the prediction capability provided by this approach. Then, a one-step approach combining the primary Huang, Giménez, and Dalgaard model (H-GD) with the secondary square root model was used to simultaneously model the growth of the populations mentioned above in co-culture under the same conditions. Independent isothermal data sets were chosen for validation of the growth description of single cultures (HM) and co-culture (H-GD) using validation factors, including the bias (Bf) and accuracy (Af). For example, the values of Af for the one-step approach range from 1.17 to 1.20 and 1.04 to 1.08 for single cultures and co-culture, respectively, demonstrating high accuracy. Thus, this approach may be used for co-culture growth description in general or specifically, e.g., in various types of lactic acid fermentation, including artisanal cheese-making technology.

Monitoring Commercial Starter Culture Development in Presence of Red Grape Pomace Powder to Produce Polyphenol-Enriched Fresh Ovine Cheeses at Industrial Scale Level

Red grape Nero d’Avola cultivar grape pomace powder (GPP) was applied during fresh ovine cheese production in order to increase polyphenol content. Before cheeses were produced, the bacteria of a freeze-dried commercial starter culture were isolated and tested in vitro against GPP. Two dominant strains, both resistant to GPP, were identified. Thestarter culture was inoculated in pasteurized ewe’s milk and the curd was divided into two bulks, one added with 1% (w/w) GPP and another one GPP-free. GPP did not influence the starter culture development, since lactic acid bacteria (LAB) counts were 109 CFU/g in both cheeses at 30 d. To exclude the interference of indigenous LAB, the pasteurized milk was analyzed, and several colonies of presumptive LAB were isolated, purified and typed. Four strains were allotted into Enterococcus and Lacticaseibacillus genera. The direct comparison of the polymorphic profiles of cheese bacteria evidenced the dominance of the starter culture over milk LAB. The addition of GPP increased cheese total phenolic compounds by 0.42 g GAE/kg. Sensory evaluation indicated that GPP-enriched cheese was well appreciated by the judges, providing evidence that GPP is a suitable substrate to increase the availability of total phenolic content in fresh ovine cheese.

Aflatoxin M1 binding by lactic acid bacteria in milk

This research focused on biocontrol solution to increase food safety through studying lactic acid bacteria (LAB) which can bind aflatoxins in milk. Aflatoxins are toxic contaminants found in feeds and foods. In milk aflatoxin is found in metabolised form, aflatoxin M1 (AFM1). Three indigenous LAB Lactobacillus strains and one Lactococcus strain isolated from Kenyan spontaneously fermented foods were tested for their AFM1 binding abilities in different conditions and after different treatments along with two reference Lactobacillus strains. Binding of AFM1 in different concentrations was examined with unconcentrated, concentrated, heat treated and concentrated heat-treated LAB cultures. Observed binding of AFM1 by LAB varied between 11 to 100%, being approximately at the level of 40% throughout the analysis sets. The results of this study suggest that the aflatoxin binding ability by LAB strain is not strongly strain specific and depends on many external and condition variables. Also, the methods used in determination of aflatoxin binding warrant critical evaluation.

Impedance microbiology to speed up the screening of lactic acid bacteria exopolysaccharide production

Bacterial production of exopolysaccharides (EPS) is of increasing interest near food manufacturers, biotechnology industries and nutritionists because of their different roles. Several analytical methods are available for recovery, quantification and characterization of EPS from lactic acid bacteria (LAB) in food. However, direct screening method for production of EPS is still based on the visual observation of filamentous texture of the colonies developed on supplemented solid growth media. To overcome weaknesses of many currently used screening methods, we propose adopting impedance microbiology to evaluate the EPS production from LAB in milk. In this work we have proven that the peculiar shape of capacitance curve of Lactobacillus delbrueckii subsp. bulgaricus 2214, measured in milk by means of a BacTrac 4300® system, is due to production of EPS. Besides the pH measurement, the amounts of EPS evaluated after 0, 8, 13 and 55 h of incubation in milk, were in agreement with the evaluation of gene expression and confirmed by the observations by confocal laser scanning microscopy and by transmission electron microscopy.With the aim to verify the applicability of the proposed method, the drop entity of the capacitance curve (ΔE%) of 22 EPS-producing (EPS+) LAB strains and one negative (EPS-) control was evaluated both in broth medium and in milk. The positive ΔE% value found for all of the strains cultivated in the clear broth medium allowed to confirm the EPS production, simply observing a strain-dependent amount of EPS on surface of the measurement electrodes of the device. When the same EPS+ strains were cultivated in milk, the obtained ΔE% values showed that only a few of them were able to produce EPS in this environment, supporting their diversified ability to utilize lactose for this purpose.Results obtained by this multidisciplinary study demonstrate that impedance microbiology represents a suitable method to overcome the limits of the most commonly used methods to screen LAB for EPS production in milk. Moreover, these results also open a door to the application to other food and beverages, in which the EPS produced in situ could be of great interest for food industry.

Growth prediction of two bacterial populations in co-culture with lactic acid bacteria.

The co-culture growth of Staphylococcus aureus, Escherichia coli and lactic acid bacteria starter culture in milk was quantitatively evaluated and modelled with a set of coupled differential equations originally proposed by Baranyi and Roberts and by Gimenez and Dalgaard (BR-GD model). The lactic acid bacteria starter culture showed the ability to induce an early stationary phase of both E. coli and S. aureus populations at different combination of temperature (ranging from 12 to 37 ℃) and lactic acid bacteria inocula (from approx. 103 to 106 CFU/ml). First, the prediction ability was performed only with parameters estimated from individual growth curves of E. coli, S. aureus and the lactic acid bacteria in milk (Dataset 1, 21 experiments). Subsequently, the model was extended with the average competition coefficients (E-BR-GD model) that represented quantitative relations among the populations. The prediction ability of this model was validated with the second dataset consisting of seven experiments. Results and also their statistical indices (accuracy and bias factors) showed that the E-BR-GD model improved growth prediction of all involved populations. Thus, the total root mean square error decreased from 0.457, 0.840 and 0.322 log CFU/ml (BR-GD model) to 0.290, 0.245 and 0.333 log CFU/ml (E-BR-GD) for S. aureus, E. coli and lactic acid bacteria, respectively. This approach in growth prediction of multiple competing microbial populations can be used in assessment of S. aureus and E. coli exposure from raw milk cheeses consumption and contribute to decision making in prevention of staphylococcal enterotoxin production.

ANTIFUNGAL AND ANTIBACTERIAL ACTIVITY OF SOME LACTOBACILLI ISOLATED FROM CAMEL’S MILK BIOTOPE IN THE SOUTH OF ALGERIA

Antifungal activity has been the subject of numerous recent works to fight the development of molds in food products and to reduce alteration. The objective of this study is the detection of new indigenous lactic acid bacteria (LAB) strains isolated from Algerian camel’s milk which have an antifungal activity. A number of 264 LAB were isolated from fermented camel’s milk where 80 rods isolates were identified by phenotypical, physiological and biochemical tests. All retained isolates belong to the genus Lactobacillus (Lb.). The antifungal activity was determined by using confrontation and overlay techniques. The screening of antifungal activity against Aspergillus niger, Aspergillus fumigatus and Penicillium sp. showed that 14 strains have an antifungal activity. These later isolates were identified as Lb. plantrarum, Lb. paracasei subsp. paracasei, Lb. brevis, Lb. rhamnosus and Lb. pentosus. These strains have shown an effect on mycelial growth and spore germination. Penicillium sp. is the most inhibited followed by Aspergillus ssp. No inhibitory activity could be detected against fungi with the supernatant. However, supernatant have an inhibitory activity against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Listeria ivanovii. P. aeruginosa is the only specie who has been affected by the neutralized supernatant. The redissolved dry supernatant of Lb. brevis revealed an inhibition of both fungal and bacterial indicator strains. Results suggest that camel’s milk LAB’s strains could be selected for application to control spoilage, fungal growth and pathogenic bacteria. The use of LAB producing antifungal metabolites represents a technological advantage for the food industry.

Application of competitive models in predicting the simultaneous growth of Staphylococcus aureus and lactic acid bacteria in milk

The simultaneous growth of Staphylococcus aureus and lactic acid bacteria (LAB) starter culture was studied in milk at different temperatures and LAB inoculums (ranging from 12 °C to 30 °C and 103–107 CFU ml−1, respectively). The modelling and predictive ability of three competition models were evaluated. Competition coefficients representing mutual population influence were incorporated into two of the models. This enabled the use of model parameters from individual S. aureus and LAB growth curves as well as those from co-culture growth in milk. Both the results and their statistical indices showed that incorporation of averaged competition coefficients resulting from individual co-culture trials improved the prediction of S. aureus behaviour in co-culture with LAB.

Growth of Lactic Acid Bacteria in Milk for the Preparation of Functional Frozen Misti Dahi (Sweet Curd)

Growth of Lactic Acid Bacteria in Milk for the Preparation of Functional Frozen Misti Dahi (Sweet Curd)

Application of Impedance Microbiology for Evaluating Potential Acidifying Performances of Starter Lactic Acid Bacteria to Employ in Milk Transformation.

Impedance microbiology is a method that enables tracing microbial growth by measuring the change in the electrical conductivity. Different systems, able to perform this measurement, are available in commerce and are commonly used for food control analysis by mean of measuring a point of the impedance curve, defined “time of detection.” With this work we wanted to find an objective way to interpret the metabolic significance of impedance curves and propose it as a valid approach to evaluate the potential acidifying performances of starter lactic acid bacteria to be employed in milk transformation. To do this it was firstly investigated the possibility to use the Gompertz equation to describe the data coming from the impedance curve obtained by mean of BacTrac 4300®. Lag time (λ), maximum specific M% rate (μmax), and maximum value of M% (Yend) have been calculated and, given the similarity of the impedance fitted curve to the bacterial growth curve, their meaning has been interpreted. Potential acidifying performances of eighty strains belonging to Lactobacillus helveticus, Lactobacillus delbrueckii subsp. bulgaricus, Lactococcus lactis, and Streptococcus thermophilus species have been evaluated by using the kinetics parameters, obtained from Excel add-in DMFit version 2.1. The novelty and importance of our findings, obtained by means of BacTrac 4300®, is that they can also be applied to data obtained from other devices. Moreover, the meaning of λ, μmax, and Yend that we have extrapolated from Modified Gompertz equation and discussed for lactic acid bacteria in milk, can be exploited also to other food environment or other bacteria, assuming that they can give a curve and that curve is properly fitted with Gompertz equation.

Modelling and predicting the simultaneous growth of Escherichia coli and lactic acid bacteria in milk.

Modelling and predicting the simultaneous competitive growth of Escherichia coli and starter culture of lactic acid bacteria (Fresco 1010, Chr. Hansen, Hørsholm, Denmark) was studied in milk at different temperatures and Fresco inoculum concentrations. The lactic acid bacteria (LAB) were able to induce an early stationary state in E. coli The developed model described and tested the growth inhibition of E. coli (with initial inoculum concentration 10(3) CFU/mL) when LAB have reached maximum density in different conditions of temperature (ranging from 12 ℃ to 30 ℃) and for various inoculum sizes of LAB (ranging from approximately 10(3) to 10(7) CFU/mL). The prediction ability of the microbial competition model (the Baranyi and Roberts model coupled with the Gimenez and Dalgaard model) was first performed only with parameters estimated from individual growth of E. coli and the LAB and then with the introduced competition coefficients evaluated from co-culture growth of E. coli and LAB in milk. Both the results and their statistical indices showed that the model with incorporated average values of competition coefficients improved the prediction of E. coli behaviour in co-culture with LAB.

Capillary Isoelectric Focusing—Useful Tool for Detection and Quantification of Lactic Acid Bacteria in Milk

The lactic acid bacteria (LAB), including lactobacilli and enterococci, represent an important part of normal microflora in humans. Simultaneously, they are frequently used as probiotics and in food industry for production of fermented milk products. The rapid and sensitive detection of these microorganisms is crucial for the quality control. In this study, the capillary isoelectric focusing (CIEF) was successfully used for the separation and characterization of probiotic LAB, L. paracasei sp. paracasei; L. acidifarinae; L. fermentum; L. gasseri; L. helveticus; L. plantarum; L. delbrueckii; L. salivarius; E. durans; E. faecalis; and E. faecium, according to their isoelectric points (pI). All pIs of lactobacilli and enterococci were found in the acidic part of the pH range. Subsequently, the milk samples spiked with L. rhamnosus, and E. faecium were analyzed by CIEF. The optimal adjustment of the separation conditions allowed detection and quantification of the bacteria in the sample with sufficient sensitivity. Therefore, CIEF is an efficient approach to rapid detection and separation of LAB even directly in milk products in future.

Effect of Denak (Oliveria decumbens Vent) on Growth and Survival of Lactobacillus acidophilus and Bifidobacterium bifidum for Production of Probiotic Herbal Milk and Yoghurt

This study was undertaken to determine the suitability of different doses (0, 0.5, 1.0 and 1.5%) of Denak powder (Oliveria decumbens Vent) on viability of Lactobacillus acidophilus and Bifidobacterium bifidum in milk and yoghurt during 21 day refrigerated storage for production of probiotic herbal milk and yoghurt. In order to determine the effect of different doses of Denak powder on growth of probiotic bacteria in milk and yoghurt, first lyophilized bacteria Lactobacillus acidophilus was added to 1 liter of low fat sterilized milk and was considered as control. Denak powder at the concentrations of 0.5, 1 and 1.5% were added to the samples and incubated until acidity reached 40 degrees Dornic and then left in refrigerator. Similar procedure was applied to the bacteria Bifidobacterium bifidum. The results of this experiment indicate the positive correlation between increased bacterial growth and increased Denak concentration. The investigation showed that the yoghurt containing 1% Denak powder had the best for taste, color, and insolubility. The sample with 1.5% Denak powder in milk and yoghurt had greater viscosity than the other samples investigated. The shelf lives of products were determined to be 21 days during which the bacterial count decreased but not less than 10(9). All the results suggest that Denak (Oliveria decumbens Vent) promoted the metabolism of lactic acid bacteria in milk and yoghurt. According to these findings, addition of Denak powder to milk and yoghurt can be recommended to take advantage of their beneficial properties on human health attributed to antimicrobial activities.

Production of conjugated linoleic acid by lactic acid bacteria in milk without any additional substrate

This study was undertaken to evaluate the production and isomeric distribution of conjugated linoleic acid (CLA) in milk fermented with lactic acid bacteria (LAB. A total of 155 cultures of LAB were analysed. Control milk samples had an average CLA content of 0.41 g/100 g of fatty acids (FA), while the lactic cultures produced CLA in the range of 0.43–1.12 g. No major changes in free fatty acids profiles were observed in milk samples fermented with CLA‐producing LAB. The present study demonstrated that LAB can increase levels of CLA in nonsupplemented milk fermented for a short period of 4 h.

Quantification of Geotrichum candidum growth in co-culture with lactic acid bacteria

The growth dynamics of filamentous fungus G. candidum was studied during the co-cultivation with the commercial lactic acid bacteria (LAB) culture Fresco. The experiments were carried out in milk and on the surface of a milk agar at the temperature ranging from 5 to 37°C. Ratkowsky model was used to describe the relationships of the fungal growth rate to the temperature during both, single and co-cultivation with LAB in milk. Simultaneous growth of LAB affected significantly the growth rate of the filamentous fungus. The growth of G. candidum was in average 39% slower in the co-culture than in the single cultivation. LAB pre-inoculated and growing in the solid medium did not show any significant inhibitory effect on the surface growth of G. candidum at all tested temperature. The precise data describing the growth of this cheese yeast-like fungus, G. candidum, may fill a gap in the field of quantitative food mycology and may be used for predicting its behavior in real conditions.

Antioxidant and cholesterol assimilation activities of selected lactobacilli and lactococci cultures

In present study, three strains of lactic acid bacteria (LAB) viz. Lactobacillus casei, Lactobacillus acidophilus and Lactococcus lactis and milk fermented with these strains have been studied for antioxidant and cholesterol assimilation activities in-vitro and in-vivo, in addition to the effect on total lactobacilli, lactococci and coliform counts into the gut of mice fed with diets supplemented by fermented milk. All three selected strains exhibited potent 2,2-diphenyl-1-picrylhydrazyl, malonaldialdehyde and hydrogen peroxide radical scavenging abilities as well as inhibition of linoleic acid peroxidation activity. These activities were highest in Lb. casei as followed by Lb. acidophilus and Lc. lactis. In addition, these bacterial cultures also exhibited good in-vitro cholesterol assimilation potential. Oral administration to mice of milk fermented with selected LAB strains, slightly decreased blood cholesterol, increased colonization of total lactobacilli and lactococci, and decreased coliforms in the intestinal tissues as well as faecal samples. These results indicate that, selected LAB strains have good antioxidant, hypocholesterolemic and coliform removal activities. It may suggest that, a novel functional food can be obtained by supplementation of selected LAB in milk, which may have various health beneficial properties such as antioxidant and hypocholesterolemic activities.

Des souches locales aux ferments lactiques spécifiques: démarche de recherche-action sur l'activation et la gestion d'une ressource biotechnique

This study presents a research-action program carried out in Corsica with a group of cheese makers to develop specific starters. Based on the direct participation of the cheese makers, this study consisted in designing starters with lactic acid bacterial strains isolated from milks and cheeses of this group of cheese makers. This process modified an individually and empirically used resource, local strains, into a shared and collectively managed resource, specific starters. Patrimonial features of these strains and the direct participation of the cheese makers were determining factors in the collective management of this resource. These starters are now used daily. They represent a concrete way of meeting the new conditions present in cheese dairies, characterised by low levels of lactic acid bacteria in milk.

Screening and enumeration of lactic acid bacteria in milk using three different culture media in Petrifilm™ Aerobic Count plates and conventional pour plate methodology

This study aimed to compare Petrifilm Aerobic Count (AC) plates and the conventional pour plate methodology using de Mann-Rogosa-Sharpe (MRS), Kang-Fung (KF) and Kang-Fung-Sol (KFS) culture media for screening and enumeration of lactic acid bacteria (LAB) in milk. Suspensions of 10 LAB species in reconstituted powder skim milk and 30 raw milk samples, without experimental inoculation, were tested. For selective enumeration, all samples were previously diluted in MRS, KF and KFS broths and then plated in Petrifilm AC and conventional pour plate methodology, using the same culture media with added agar. All plates were incubated at 37 degrees C for 48 h in anaerobic conditions. Differences in the counts were observed only for raw milk samples using KFS in conventional methodology, when compared with the counts obtained from MRS and KF (P0.05). The results showed excellent correlation indexes between both methodologies using the three culture media for LAB suspensions (r=0.97 for MRS, KF and KFS). For raw milk samples, the correlation indexes were excellent (r=0.97, for MRS) and good (r=0.84 for KF, and r=0.82 for KFS), showing some interference in Petrifilm AC when supplements were added, especially lactic acid. These results indicate the possibility of using Petrifilm AC plates for enumeration of LAB in milk, even with the use of selective supplements.

Article

Who determines the diversity of oligopeptide transport specificity in Lactococcus lactis? In this review our knowledge of oligopeptide transport by Opp in Lactococcus lactis is discussed. The specific oligopeptide transport system Opp is essential for growth of lactic acid bacteria in milk. This system belongs to the superfamily of ABC transporters containing a binding protein, generally described as the determinant of the specificity. The substrate specificity of this system, studied on one strain of lactococci, L. lactis MG1363, appears to be very different from that of other bacteria, especially Salmonella typhimurium. Relatively broad, this specificity is not fully representative of that of L. lactis species. In fact, each strain displays specific preferences for peptide transport. Despite binding protein OppA sequence varies to one strain to another, its variability cannot explain the observed diversity of substrate specificity. In L. lactis, OppA is essential for peptides transport but does not entirely determine the substrate specificity and its diversity among the species. Lactococcus lactis / oligopeptide transport / specificity / diversity

Detection and identification of lactic acid bacteria in milk and industrial starter culture with fluorescently labeled rRNA-targeted peptide nucleic acid probes

Detection et identification des bacteries lactiques dans le lait et les levains industriels par des sondes « peptide nucleic acids » fluorescentes ciblant l'ARNr. Une methode rapide et simple pour detecter et identifier les bacteries lactiques en croissance, au niveau cellulaire, dans le lait ou les levains industriels a ete developpee. Elle repose sur la technique d'hybridation de sondes fluorescentes a l'ARN ribosomique present dans les cellules entieres. Les « peptide nucleic acids » (PNA), analogues de l'ADN, ont ete utilises pour la synthese de certaines de ces sondes. La methode utilise aussi une technique de filtration des echantillons et la microscopie a epifluorescence. La detection et l'identification des cellules sont realisees en une heure et demie. Sept sondes oligonucleotidiques presentant des specificites differentes ont ete testees dans des experiences d'hybridation in situ pour detecter des souches industrielles et d'autres provenant de collections de micro-organismes. Les especes suivantes etaient representees: Lactobacillus delbrueckii, Lactobacillus helveticus, Lactobacillus pentosus, Lactobacillus plantarum, Lactococcus lactis, Leuconostoc sp. et Streptococcus thermophilus. Des limites dans l'utilisation de certaines sondes ont ete rencontrees a cause d'hybridations non specifiques observees. En fonction de la sonde utilisee, une detection specifique et simultanee des differentes especes en presence peut etre realisee. L'equipement utilise permet la detection d'un nombre de cellules compris entre 10 4 et 10 6 par mL de milieu. L'etat physiologique de levains thermophiles a pu aussi etre evalue par hybridation in situ. Ainsi, cette technique rapide est tout a fait adaptee pour le controle de la qualite des levains et des fermentations industrielles. Ce travail constitue une premiere description de l'utilisation de molecules de PNA pour la detection et l'identification des bacteries dans le lait et les milieux industriels.