International Journal of Nutrition and Food Sciences
Volume 5, Issue 3, May 2016, Pages: 179-184

Antimicrobial Substances Production at Refrigeration Temperatures by Lactobacillus delbrueckii MH10: A Candidate for Food Biopreservation

Hrachya Hovhannisyan*, Alireza Goodarzi, Andranik Barseghyan

SPC "Armbiotechnology" NAS, Yerevan, Armenia

Email address:

(H. Hovhannisyan)

*Corresponding author

To cite this article:

Hrachya Hovhannisyan, Alireza Goodarzi, Andranik Barseghyan. Antimicrobial Substances Production at Refrigeration Temperatures by Lactobacillus delbrueckii MH10: A Candidate for Food Biopreservation. International Journal of Nutrition and Food Sciences. Vol. 5, No. 3, 2016, pp. 179-184. doi: 10.11648/j.ijnfs.20160503.15

Received: April 2, 2016; Accepted: April 11, 2016; Published: April 26, 2016


Abstract: The objective of this study was to determine formation of antibacterial substances in supernatants of L. delbrueckii during cold storage and evaluate whether the application of this bacteria to raw ground beef would result in significant reductions of E. coli O157:H7 during refrigerated storage. Antibacterial activity of a newly isolated Lactobacillus delbrueckii MH 10 at refrigeration temperatures against food-borne pathogen Escherichia coli O157: H7 was studied. The size of inhibition zone depends on concentration of LAB cells. The cells (~109 CFU/ml) of L. delbrueckii produced significant amount of antibacterial substances mainly hydrogen peroxide ~ 35 μg/ml in sodium phosphate buffer (0.2 M, pH 6.5) and ~ 40 μg/ml in beef broth at 5°C during submerged cultivation without of growth. Submerged cocultivation of E. coli O157: H7 with lactobacilli in NB broth at 5°C reducing the total number of the pathogen more than 3 log for 5 days. The cell suspension intendent for treatment must contain 108-9 CFU/ ml of LAB. L. delbrueckii reduced initial amount 2x105 of E. coli O157: H7 in ground beef cocultivation up to 3 log for 3 days and become undetectable after 7 days. The application of L. delbrueckii bacteria does not cause any changes in sensory characteristics of ground beef by itself; moreover promote expanding of shelf-life due to inhibition of psychrophilic spoilage microorganisms.

Keywords: Biopreservation, Lactobacillus delbrueckii, Refrigerated Temperatures, Hydrogen Peroxide, E. coli O157: H7


1. Introduction

For ground meat shelf life prolongation, synthetic chemicals have been traditionally used to inhibit resident pathogenic and spoilage microorganisms in refrigerated products. The increasing consumer concerns of potential health risks associated with some of synthetic preservatives has led researchers to evaluate the opportunity of using natural bio-preservatives such as Lactic Acid Bacteria (LAB) selected for their inhibitory activity towards undesirable microorganism [1,2]. For these applications lactic acid bacteria are usually chosen as they have the GRAS (Generally Recognized As Safe) status and produce a wide range of inhibitory compounds such as organic acids, hydrogen peroxide, diacetyl and bacteriocins and thus, expanding shelf life and increasing food safety [3-7]. The inhibitory actions of LAB toward food-borne pathogens and spoilage organisms in non-processed foods occur during entire storage period by continuous production of inhibitory compounds instead of a one-time reduction, as occurs with antimicrobial substances interventions. It has been shown that for bio-preservation the most effective are LABs able to produce hydrogen peroxide at refrigerated temperatures in absence of growth [8-10].

The species Lactobacillus delbrueckii subsp. lactis more of all used in food preservation, but hydrogen peroxide production is variable amongst strains [11,12]. The use of limited number of LAB strains may cause decreasing of treatment efficacy due to accumulation of deleterious mutations and/or adapting of pathogens to antibacterial substances which are produced [2]. In order to enhance biopreservation efficacy new LABs producing hydrogen peroxide should be selected and methods developed for their cultivation and application to food [13-15]. Because hydrogen peroxide production plays the mayor role in elimination of the pathogens at refrigerator storage, it levels should be assessed for newly selected strains.

Most raw foods are contaminated with pathogenic and spoilage microorganisms. Ground beef products are common sources of E. coli O157:H7 and its reduction is an important concern in the beef industry. Although many intervention technologies are applied to beef carcasses, ground beef processors currently do not have effective intervention steps for ground beef safe storage. There are only a few studies of LAB inhibition of E. coli O157:H7 in ground beef products and their impact on the sensory properties of these products [6, 16, 17].

The aim of this research was to determine formation of antibacterial substances supernatants of L. delbrueckii during cold storage and evaluate whether the application of this bacteria to raw ground beef would result in significant reductions of E. coli O157:H7 during refrigerated storage.

2. Materials and Methods

2.1. The Bacterial Cultures

The Lactobacillus delbrueckii MH 10 from human origin was isolated and identified in our laboratory by Hovhannisyan and Pashayan (2010) and deposited in Armenian National Microbial Depository Center (MDC) under code MDC 9617. Food born pathogen Escherichia coli O157: H7 MDC 5003 used in this study was from the MDC.

2.2. Media

LAPTg: yeast extract – 10 g, peptone -15 g, tryptone – 10 g, glucose – 10 g, Tween -1ml, for solid medium, 1.5% Bacto-agar was included. Nutrient broth (NB) [Serva, Germany], Tryptose agar (T-agar) [Merck, Germany]. beef broth: Beef extract powder (Sigma Aldrich) – 30 g to 1000 ml of distilled water, pH 6.0 - 7.0. Fresh ground beef were purchased from butchers in Armenia and transported to the laboratory using a refrigerated box. Sodium phosphate buffer (pH 6.5). Physiological saline - 0.9% NaCl. Merckoquant Peroxide Test strips [Merck, Germany].

2.3. Bacteriological Analysis

Bacterial counts in liquid media were made using standard methods. For enumeration of E. coli and lactobacilli in ground beef 1 g treated meat sample was inoculated in 9 ml of sterile physiological, homogenized, made serial ten-fold dilutions and plated on Tryptose and MRS agars for determination of E. coli and LAB counts, respectively.

2.4. Hydrogen Peroxide Assay

Hydrogen peroxide concentration measured by Merckoquant Peroxide Test strips with measuring ranges 0.5 – 2 – 5 –10 – 25 and 1 – 3 – 10 – 30 – 100, according to the manufacturer instruction.

2.5. Potentiometric and Titratable Acidity

The pH was measured at room temperature, using a digital pH meter. Titratable acidity expressed as a percentage of lactic acid was measured by titrating 9 mL of the sample (where added 3 spots of phenolphthalein) with 0.1 N NaOH, until a pink color appeared.

2.6. Agar Disk Diffusion Method

Agar disk diffusion method was used to evaluate the antimicrobial effect of LAB suspensions. E. coli O157: H7 culture grown in NB broth for 18 h at 37°C diluted to concentration of 107 cells/ml and spread onto Tryptose agar. The paper discs (diameter, 5 mm) were soaked with LAB culture liquids and placed on the test culture lawn. After 2h exposition in cold the plates were incubated at 37°C for 18 h and examined for size of clear inhibitory zones.

2.7. Quantification of Antimicrobial Activity of LAB in Cold Cultivation

Lactobacilli were grown in LAPTg broth for 18 h at 37°C divided in four 10 ml aliquots, centrifuged at 12,000 × g for 10 min and each pellet resuspended in 10 ml of cold medium; sodium phosphate buffer (with or without glucose), LAPTg broth or physiological saline and incubated at 5°C. Every two days for 7 days and then each week antimicrobial activity, hydrogen peroxide amount, OD600 and pH of the cell cultures were determined.

2.8. Submerged Cocultivation of LAB Along E. Coli in Nutrient Broth (NB)

For evaluating the antagonistic activity of L. delbrueckii MH 10 against of E. coli O157:H7 overnight culture was diluted in 200 ml of fresh NB to obtain cell concentration of approximately 105 CFU/ml. Divided in two equal portions and supplied L. delbrueckii MH 10 in ratios 1: 100 and 1: 10. Both samples stored at 5°C and subjected to microbial analysis on days 0, 1, 3, 5, and 7.

2.9. LAB Antimicrobial Activity Determination in Ground Meat

200 g of freshly prepared commercial ground beef was obtaining from local grocery. 150 g of this ground beef was inoculated with E. coli O157 to obtain a pathogen concentration of approximately 105 CFU/g and divided into three equal portions. L. delbrueckii MH 10 was prepared as described previously and added individually in two of ground beef samples inoculated with E. coli O157:H7 at final concentrations of 107 and 108 CFU/g respectively. The control portions of the ground meat with and without E. coli O157:H7 were processed in the same manner. All samples were mixed, packaged in vacuum polyethylene packets, kept at 5°C and sub­jected for microbiological analysis on days 0, 1, 3, 5, 7 and 10.

2.10. Sensory Evaluation

Sensory evaluation of the con­trol and the samples inoculated with the LAB strains was conducted in the open laboratory. Odor, color and appearance of slime on the external surface of ground meat were assessed.

2.11. Statistical Analysis

Statistical analysis was performed using SPSS program (Version 16). Standard deviation of mean was used to describe data. Fisher’s range test was used to determine differences between tested groups. P value < 0.05 and 0.001 were considered as significant and highly significant, respectively.

3. Results and Discussion

3.1. Antibacterial Substances Production by Washed L. Delbrueckii Cells at 5°C

Laboratory experiments revealed that hydrogen peroxide producing ability of LAB at non permissive temperature is strongly dependent on nutrition media composition used for their prior propagation as well as media for sub cultivation at refrigeration temperatures. The largest amount of hydrogen peroxide at 5°C formed when LAB cells priory propagated in rich medium and then transferred in sodium phosphate buffer [1,18]. In this study along with phosphate buffer we used beef broth in order to ensure the lack of substances inhibitory to antimicrobials formation e. g. hydrogen peroxide.

Antimicrobial compounds production by 2 fold dilutions of washed cells L. delbrueckii MH 10 in beef broth and phosphate buffer were studied during storage at 5°C by disk diffusion method (Figures 1, 2).

The growth inhibition zones of E. coli O157:H7 around the disks, impregnated in the both media, gradually increased for 5 days period in cold storage.

Figure 1. Zones of E. coli O157: H7 growth inhibition caused by supernatants of different concentrations L. delbrueckii washed cells inoculated in meat extract at 5°C. Cell concentration CFU/ml (♦) 2 x 108, (■) 6 x 10 7, (▲) 3 x 107.

Figure 2. Zones of E. coli O157: H7 growth inhibition caused by supernatants of different concentrations L. delbrueckii washed cells inoculated in Phosphate buffer at 5°C. Cell concentration CFU/ml (♦) 2 x 108, (■) 6 x 10 7, (▲) 3 x 107.

Inhibitory compounds formation in beef broth by L. delbrueckii at refrigerating temperatures was shown for the first time. The inhibitory zones caused by cells inoculated in beef broth were remarkably larger than in phosphate buffer. The inhibitory zones size required high concentration of cells.

3.2. Hydrogen Peroxide Production by L. delbrueckii During Storage at 5°C

The dominant inhibitory factor produced by lactobacilli at refrigerating temperatures was identified as hydrogen peroxide [11,19,21]. In this study production of hydrogen peroxide by L. delbrueckii at 5°C storage were obtained. The hydrogen peroxide accumulation by lactobacilli in both media phosphate buffer and beef broth gradually increased and riche maximum after five days of cold storage. Cell suspensions in beef broth showed higher accumulation of H2O2 in comparison to phosphate buffer. The overall H2O2 amount in phosphate buffer and beef broth were approximately 35 and 40μg/ml, respectively (Fig. 3, 4). Thus, the strain MH 10 by hydrogen peroxide production was not inferior to known strains L. delbrueckii [20, 22].

Figure 3. Kinetic of hydrogen peroxide production by L. delbrueckii MDC 9617 at 5°C in beef broth. Cell concentration CFU/ml (♦) 2 x 108, (■) 6 x 10 7, (▲) 3 x 107.

Figure 4. Kinetic of hydrogen peroxide production by L. delbrueckii MDC 9617 at 5°C in phosphate buffer. Cell concentration CFU/ml (♦) 2 x 108, (■) 6 x 10 7, (▲) 3 x 107.

It was revealed that the character of hydrogen peroxide accumulation was similar to antibacterial activity growth in LAB suspension (see figures 1, 2) which indicates on main role of hydrogen peroxide in inhibitory action lactobacilli against E. coli O157: H7 at refrigerator storage.

3.3. Cells Viability and Acidity Changes During Cold Storage

During the entire period of storage at 5°C live cells count and culture pH and titrable acidity were monitored (Table 1).

Table 1. Cells viability and acidity in the media during storage at 5°C.

  Day zero After 7 days
Medium pH Viable cells, CFU/ml pH Viable cells, CFU/ml
Beef broth 6.7±0.2 6.3±0.3 x 108 6.5±0.2 5.8±0.4 x 108
PBS 6.8±0.05 6.3±0.2 x 108 6.8±0.05 5.6±0.2 x 108

Footnote: Titrable acidity i.e. lactic acid in samples was not detected.

No significant differences were found in the population levels of LAB cultures during entire storage period at 5°C indicating that LAB reproduction was not necessary for the inhibition of pathogens. These findings come in accordance with the observations of other authors who also suggested that the production of inhibitory metabolites can occur by LAB during storage in the absence of growth [1,18]. Any significant changes of pH and titrable acidity in all of media weren’t detected which indicated that the organic acids are not formed.

3.4. Antagonistic Action of L. delbrueckii on E. coli O157:H7 in NB at 5°C

L. delbrueckii was added to NB along with E. coli O157:H7 in order to determine its antagonistic activity against the pathogen at 5°C. Two ratios of E. coli O157:H7 to L. delbrueckii 1: 100 and 1: 10 were tested. The total number of E. coli O157:H7 cells in both treatments were determined on days 0, 1, 3, 5 and 7 by plating appropriate dilutions on Tryptose agar and incubation at 37°C for 24 hours.

Figure 5. Kinetic of inactivation of E coli O157:H7 by L. delbrueckii in NB submerged cocultivation and in at 5°C.

(■) – E. coli O157:H7, (♦) E coli O157:H7 + L. delbrueckii MH 10 ratio (1:10), () E coli O157:H7 + L. delbrueckii MH 10 ratio (1:100).

On day zero there were no significant differences among the initial populations of E. coli O157:H7 for all treatments (Figure. 5). After 3 days of storage, there were significant decline in numbers of E. coli O157:H7 for treatments containing 1.1 x 108 of L. delbrueckii. There was an additional significant decline (3 log) in the numbers of viable cells of E. coli after 5 days of storage. There was only 1 log decline in the treatment containing 1.4 x 107 CFU/ml of lactobacilli. It suggesting that, there sufficient numbers of LAB must be present to have an antagonistic effect on pathogens. The number of viable cells of E. coli O157:H7 in control was not significantly changed in non-permissive temperature. These results are similar with date obtained by Brashears et al [23].

3.5. LAB Inhibitory Effect on E. coli O157:H7 in Ground Meet at 5°C

Cell suspension of L. delbrueckii was tested in packaged ground meat stored for their ability to reduce the viability of Escherichia coli O157:H7 during storage temperature at 5°C. Fresh ground meat was inoculated with 105 CFU/g of E. coli. The trial samples were treated with L. delbrueckii, at a level of 107 and 108 CFU/g and stored at 5°C for 7 days in plastic vacuum bags. Samples were analyzed for E. coli O157:H7 survivors and lactic acid bacteria on days 1 to 7.

Figure 6. Kinetic of E. coli O157:H7 inactivation by L. delbrueckii MH 10 in ground meat at 5°C. (■) – E. coli O157:H7, (♦) E coli O157:H7 + 107 L. delbrueckii MH 10, (▲) – E coli O157:H7 + 108 L. delbrueckii MH 10.

Towards the end of ground meat vacuum storage E. coli O157:H7 quantity, depending of L. delbrueckii ratio, was 2-3 log lower than those in the control. But the LAB count in treated and control samples after refrigeration storage didn't significantly change for 10 days. Growth of LAB in a fresh meat held at refrigeration temperature is not desirable because it would lead to premature spoilage of the product. Furthermore, the viable L. delbrueckii cells in ground beef, continuous protection by preventing secondary contamination during entire storage period.

It was revealed that the application of L. delbrueckii bacteria doesn’t causes any changes in sensory characteristics of ground beef entire 10 days storage, moreover promote expanding of shelf-life due to inhibition of psychrophilic spoilage microorganisms which is in agreement with other authors [6,24,27]. Thus, the LAB treated samples keep good quality for ten days whilst in the control sample at 7 day of storage appeared undesirable odor, greening and smooth on surface. Therefor the selected strain L. delbrueckii MH 10 is able to synthesize antimicrobial compounds in amounts sufficient to inhibit the growth of pathogens and spoilages.

The results of the experiments suggest that L. delbrueckii MH 10 has a potential to be used as a candidate culture in biopreservation method to improve the safety and extend the shelf life of meat products in cold storage.

4. Conclusion

The cells of L. delbrueckii MDC 9617 produced significant amount of antibacterial compounds mainly hydrogen peroxide in beef broth and sodium phosphate buffer at 5°C in absence of growth. This strain exerts inhibitory action against E. coli O157:H7 and dramatically (more than 95%) reduced number of pathogen bacteria in both submerged and solid-stat cocultivation trials at refrigeration temperatures. Thus, L. delbrueckii can be recommended as candidate bio-preservative for use in commercial applications.

Acknowledgment

The authors are thankful to SPC "Armbiotechnology" NAS, for facilitation and technical support on this work.


References

  1. Amézquita A,Brashears MM. (2002). Competitive inhibition of Listeria monocytogenes in ready-to-eat meat products by lactic acid bacteria. J Food Prot. Vol. 65(2), pp. 316–325.
  2. Gyawali R, Ibrahim SA. (2014). Natural products as antimicrobial agents. Food Control. Vol. 46, pp. 412429.
  3. Davidson PM, Harrison MA. (2002). Resistance and Adaptation to Food Antimicrobials, Sanitizers, and Other Process Controls. Scientific Status Summary, Food Technology. Vol. 56(11), pp. 69–78.
  4. Muhialdin BJ. Hassan Z. (2011). Screening of Lactic Acid Bacteria for Antifungal Activity against Aspergillus oryzae. American Journal of Applied Science. Vol. 8, pp. 447–451.
  5. Dalié DKD, Deschamps AM. Richard F. (2010). Lactic acid bacteria Potential for control of mould growth and mycotoxins. A review Food Control. vol. 21, pp. 370–380.
  6. Smith L, Mann JE, Harris K, Miller MF, Brashears MM. (2005). Reduction of Escherichia coli O157:H7 and Salmonella in ground beef using lactic acid bacteria and the impact on sensory properties.J Food Prot. Vol. 68(8), pp. 1587–92.
  7. Favaro L, Penna ALB, Todorov DD. (2015). Bacteriocinogenic LAB from cheeses -Application in Biopreservation. Trends in Food Science Technology. Vol. 41, pp. 37–48.
  8. Daly CW, Sandine E, Elliker PR. (1972). Interaction of food starter cultures and food-borne pathogens: Streptococcus diacetilactis versus food pathogens. J. Milk Food Technol. vol. 35, pp. 349–357.
  9. Daeschel MA. (1989). Antimicrobial substances from lactic acid bacteria for use as food preservatives. Food Technology. Vol. 1, pp. 164–167.
  10. Dahiya RS, Speck ML. (1968). Hydrogen peroxide formation by lactobacilli and its effect on Staphylococcus aureus. J. Dairy Sci. Vol. 51, pp. 1568–1572.
  11. Yap PS, Gilliland SE. (2000). Comparison of Newly Isolated Strains of Lactobacillus delbrueckii subsp. lactis for Hydrogen Peroxide Production at 5°C. J Dairy Sci. Vol. 83, pp. 628–632.
  12. Gilliland SE. (1980). Use of lactobacilli to preserve fresh meat. Proc Recip Meat Conf. Vol. 33, pp. 5458.
  13. Jones RJ, Hussein HM, Zagorec M, Brightwell G, Tagg JR. (2008). Isolation of lactic acid bacteria with inhibitory against pathogens and spoilage organisms asso­ciated with fresh meat. Food Microbiology. Vol. 25, pp. 228–234.
  14. Kostrzynska M, Bachand A. (2006). Use of microbial antagonism to reduce pathogen levels on produce and meat products: a review. Canadian Journal of Microbiol­ogy. Vol. 52, pp. 1017–1026.
  15. Maragkoudakis PE, Mountzouris KC, Psyrras D, Cremonese S, Fischer J, Cantor MD, Tsakalidou E. (2009). Functional properties of novel protective lactic acid bacteria and application in raw chicken meat against Listeria monocytogenes and Salmonella enteritidis. Inter­national Journal of Food Microbiology. Vol. 130, pp. 219–226.
  16. Holzapfel WH, Geisen R, Schillinger U. (1995). Biological preservation of foods with reference to protective cultures, bacteriocins and food-grade enzymes. Int J Food Microbiol. Vol. 24(3), pp. 343–62.
  17. SalemA M. (2012). Bio-Preservation Challenge for Shelf-Life and Safety Improvement of Minced Beef. Global Journal of Biotechnology and Biochemistry. Vol. 7 (2), pp. 50–60.
  18. Ruby JR, Ingham SC. (2009). Evaluation of potential for inhibition of growth of Escherichia coli O157:H7 and multidrug-resistant Salmonella serovars in raw beef by addition of a presumptive Lactobacillus sakei ground beef isolate. Journal of Food Protection. Vol. 72, pp. 251–259.
  19. Ammor S, Tauveron G, Dufour E. Chevallier I. (2006). Antibacterial activity of lactic acid bacteria against spoilage and pathogenic bacteria isolated from the same meat small-scale facility 1- Screening and characterization of the antimicrobial compounds. Food Control. Vol. 17, pp. 454–461.
  20. Villegas E, Gilliland SE. (1998). Hydrogen Peroxide Production by Lactobacillus delbrueckii subsp. lactis I at 5°C. Journal of food science. Vol. 63(6), pp. 1070–1074.
  21. Collins EB, Aramaki K. (1980). Production of hydrogen peroxide by Lactobacillus acidophilus. J. Dairy Sci. Vol. 63, pp. 353–357.
  22. Jaroni D, Brashears MM. (2000). Production of Hydrogen Peroxide by Lactobacillus delbrueckii subsp. lactis as Influenced by Media Used for Propagation of Cells. Journal of Food Science. Vol. 65(6), pp. 1033–1036.
  23. Brashears MM, Reilly SS, Gilliland SE. (1998). Antagonistic action of cells of Lactobacillus lactis toward Escherichia coli 0157:H7 on refrigerated raw chicken meat. J. Food Protect. Vol. 61, pp. 166–170.
  24. Gilliland SE, Speck ML, Morgan CG. (1975). Detection of L. acidophilus in feces of humans, pigs, and chickens. Appl. Microbiol. Vol. 30, pp. 541–545.
  25. Senne MM, Gilliland SE. (2003). Antagonism action of cells of Lactobacillus delbrueckii subsp. lactis against pathogenic and spoilage microorganisms in fresh meat systems. Journal of Food Protection. Vol. 66, pp. 418–425.
  26. Sakaridis I, Soultos N, Batzios Ch, Ambrosiadis I, Koidis P. (2014). Lactic Acid Bacteria Isolated from Chicken Carcasses with Inhibitory Activity against Salmonella spp and Listeria monocytogenes. Czech J. Food Sci. Vol. 32(1), pp. 61–68.
  27. Sparo MD, Confalonieri1 A, Urbizu L, Ceci1 M, Sánchez Bruni SF. (2013). Bio-preservation of ground beef meat by Enterococcus faecalis CECT7121. Brazilian Journal of Microbiology. Vol. 44(1), pp. 43–49.

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