Keeping camel meat fresher for longer

Wednesday, 06 April, 2005

Extending the shelf life of fresh minced camel meat at ambient temperature by using Lactobacillus delbrueckii subsp. Delbrueckii.

Highly perishable foods such as meat provide excellent conditions for the growth of hazardous microorganisms. Microbial contamination can lower the quality of fresh minced camel meat, shorten its shelf life and result in economic loss and probably health hazards.

Several researchers have investigated biopreservatives such as lactic acid bacteria (LAB) and their metabolites and considerable research has been done on the ability of LAB to inhibit growth of pathogenic microorganisms. However, the capability of these bacteria to control growth of spoilage microorganisms has not been investigated to the same extent.

To be successful in biopreservation, a bacteriocinogenic LAB culture must compete with the relatively high indigenous microbial loads of raw meat, to actively inhibit pathogenic and spoilage bacteria.

Traditionally several methods have been used to preserve meat including cooking, fermenting, salting, smoking and drying. Fermentation is an inexpensive method for preservation of meat and meat products. Acid formation (low pH), H2O2 and bacteriocins produced by starter cultures are responsible for preventing the growth of food poisoning and spoilage bacteria in meat. It has been speculated that the shelf life of meat could be extended by low temperatures combined with a treatment with LAB strain.

Moroccan researchers, Ichraq Kalalou¹, Mohamed Faid² and Ahmed Touhami Ahami³ have investigated the possibility of extending the shelf life of fresh minced camel by fermentation using mixed lactic acid bacteria cultures isolated from natural fermented foodstuffs and selected for their antimicrobial activity against some hazardous microorganisms.

LAB strains isolated from camel meat were selected on the basis of their inhibitory activities on various Gram negative and Gram positive bacteria to select the most efficient strain to be used in meat preservation.

The antimicrobial activity of a range of isolated strains on Escherichia coli (4 strains), Pseudomonas aeruginosa (4 strains), Klebsiella pneumoniae (4 strains), Staphylococcus aureus (4 strains), Citrobacter freundii (2 strains), Bacillus subtilis (1 strain), Bacillus megaterium (1 strain), Bacillus cereus (3 strains) were determined by the well diffusion assay. The antimicrobial activity was determined by measuring the clear zone around the colonies.

L.delbrueckii subsp. delbrueckii was identified as the most efficient strain. A culture was grown on MRS for 24 hours at 30°C and from this culture, dilutions up to 10-6 were plated on MRS to determine the cell concentration. The amount used to inoculate meat was around 107 cfu/g.

Glucose (5% w/w) was mixed with the minced meat. The inoculated meat was introduced in sterile plastic bags and stored at 22°C. The control (minced meat without addition of glucose and lactic culture) was stored under the same conditions.

Results from the in vivo assay showed a pH drop in the minced camel meat from 5.5 to 4.0-4.2. This was achieved in three days' incubation at ambient temperature (Figure 1). In the non-inoculated assay (control) the pH was around 7.2 after the same period. This may lead to a severe deterioration of meat leading to an off odour, poor appearance and many other changes in the meat.

The pH decrease in the inoculated assay is due to the lactic acid formation by LAB. The pH decrease to 4-4.2 is related to the formation of the lactic acid in the medium. The microbial profiles including SPC, coliforms, staphylococci, enterococci and LAB for the inoculated assay and the control are shown in Figure 2. The standard plate counts (SPC) were decreased by approximately two log units during the first 24 hours in the inoculated assay. The initial SPC of the mixture was around 1.4 x 106 cfu/g, which decreased to 1.2 x 104 cfu/g after 24 hours and 8 x 102 cfu/g after 7 days of incubation at the ambient temperature (22°C).

The same decrease pattern was also observed for the coliforms. Coliforms were reduced from 8 x 102 cfu/g to 102 cfu/g after 24 hours and to less than 1 cfu/g after 7 days' storage. It is interesting to note that the level of coliforms was reduced from the start of inoculation and development of an off odour was prevented during storage of the meat.

Not only coliforms induce changes in meat as many other groups of microorganisms, such as staphylococci, enterococci and others, may cause deteriorations in fresh meat. A net decrease of the counts compared to the control was observed and populations reached low levels being less than 1 cfu/g in the assay but they reached 105 cfu/g in the control.

The prevention of staphylococci in meat is very beneficial for the quality of fresh meat since these microorganisms may induce lipolysis and proteolysis reactions in the product leading to an off flavour.

Enterococci are also ubiquitous microorganisms, which can grow in meat at high temperature. The same pattern as coliforms was observed. Enterococci numbers decreased in the inoculated samples from 4 x 103 cfu/g to 40 cfu/g after 24 hrs and to less than 1cfu/g after 7 days, while the control showed a high level (105 cfu/g). LAB counts in the sample from the initial mixture (to) tell about the level of the inoculation (107 cfu/g) in the sample. Counts in the inoculated assay were higher than the control, indicating a difference in physico-chemical changes in meat and consequently in the undesirable microbial load.

Fresh meat and fresh meat products are susceptible to biochemical changes due to the microbial growth at ambient temperatures, which are high in some countries (20 to 30°C in Morocco). Minced meat is widely consumed in Morocco as a popular product called Kefta. This is exhibited at ambient temperature in retail stores and restaurants. Deterioration may occur quickly because of the high contamination levels, contamination during mincing and the high ambient temperature. Most processes used to extend the shelf life of fresh meat are based on low temperatures (refrigerating or freezing) but this may not be possible for fresh meat products exhibited in retail environments in some countries. Here biological processes, such as the use of LAB, may be used to delay or to stop the spoilage microorganisms proliferating making the meat safer for consumers.

Several authors have reported the use of LAB as biopreservatives at refrigeration temperatures and subtropical temperatures. In these studies, after the fermentation was started at 20°C, samples were stored under refrigeration and the growth of spoilage microorganisms and pathogens was prevented. In the case of subtropical climates or conditions of temperature abuse, temperatures above 20°C are expected. The pH reduction due to acid production reduced the growth rate of undesirable strains. The desired pH (4.0-4.2) was reached after 24 hours in minced meat stored at 37°C and in 30 hours in minced meat incubated at 30°C. In the Moroccan study the desired pH (4.1) was achieved after 3 days.

The use of a mixture of LAB could be used to extend the shelf life of minced meat at high temperature and inhibit the growth of pathogenic microorganisms and the desirable low pH (4.0-4.2) can be achieved faster using a LAB culture. The extended shelf life at ambient temperature may be especially useful in hot countries like Morocco where refrigeration facilities are not available or are inadequate enabling camel meat or meat from other species to be preserved for a longer time. This procedure for preservation could also be used to improve sanitation conditions in rural butcheries or restaurants where minced meat is exposed to ambient temperature.

  1. Department of Biology College of Sciences Ibn Toufail University
  2. Department of Food Engineering and Technology Hassan II Institute of Agronomy and Veterinary Medicine Department of Biology
  3. College of Sciences Ibn Toufail University
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