MICROBIOLOGICAL STATUS OF MINCED MEAT DIRECTLY POST PRODUCTION IS INFLUENCED BY ITS INTERNAL TEMPERATURE AND PH VALUE

Adam Malicki¹, Szymon Brużewicz^2
1 Department of Food Hygiene and Consumer Safety, Agricultural University of Wrocław, Poland
² Institute of Social Problems of Health and Education, Warsaw School of Social Psychology, Poland

ABSTRACT

The microbiological quality of industrially-produced minced meat is still unsatisfactory. The purpose of present study was to determinate the microbiological status of minced meat directly post production. Moreover, we tried to establish if its microbiological quality depends on pH value, water activity and the rate of chilling at that stage of production. One hundred twenty samples of mixed (pork and beef) minced meat were subjected the studies. Within 2 hours post production, their water activities, pH values and internal temperatures were measured and they underwent microbiological analysis (total plate count, the numbers of Escherichia coli, coliforms, coagulase-positive staphylococci, yeasts and moulds and the presence of salmonellae). Mean, median, minimum, maximum and standard deviation were calculated for each continuous variable in course of statistical analysis. The Pearson´s coefficients of correlation between microbiological and intrinsic parameters of minced meat were determined. The influence of water activity, pH value and internal temperature of minced meat on its microbiological parameters was tested by means of variance analysis. Escherichia coli was determined in 43/120 (35.8%), coliforms - in 113/120 (94.2%), coagulase-positive staphylococci - in 1/120 (0.8%), whereas yeasts and moulds - in 66/120 (55%) samples. Salmonellae were not determined in any of the sample analyzed. Internal temperature and pH value were proved to affect the microbiological parameters (total plate count, Escherichia coli number) of minced meat on multivariate analysis.

Key words: minced meat, microbiology, water activity, pH, internal temperature.

INTRODUCTION

Despite of increasing sanitary requirements, the quality of industrially-produced minced meat is still unsatisfactory. Thirty six of 81 (40.4%) portions of minced meat designed for retail sale, examined between 2000 and 2001, did not meet the requirements of Polish Standards, mainly because the number of Escherichia coli exceeded the reference values [2]. Also coagulase-positive staphylococci, including the doxycycline-, oxacillin and methicillin-resistant strains, were isolated from the frozen samples of minced meat available on Polish market [9].

The excessive contamination of minced meat with Escherichia coli was also determined in other EU countries, and the fraction of enteropathogenic strains isolated was particularly alarming [4-5, 8, 23, 25]. The incidence of Salmonella was described in minced meat as well. The bacteria were detected in 93 of 1485 (6.3%) samples of mixed minced meat produced in a European Union-approved slaughtering and cutting plant in Germany. Serotyping revealed S. typhimurium in nearly 70% of the strains isolated [24]. The consumption of minced beef contaminated with Salmonella was confirmed as the reason for 3 salmonellosis outbreaks which occurred in France between 1998 and 2000 [7].

The microbiological contamination of minced meat might be of primary or secondary origin. Microorganisms present in animal tissues before slaughter constitute primary contaminations, whereas the secondary ones occur in course of product manufacturing, storage or distribution. The initial level of postproductive contamination as well as the numerous intrinsic and extrinsic parameters of product determine its microbiological stability and consequently affect the safety of consumer.

Our previous studies on the stability of the different products of animal origin revealed that water activity and pH belong to the main factors affecting the microbiological quality [10-12].

In the aforementioned papers, however, the dynamics of food microflora was evaluated after the different periods of storage. In turn, the purpose of present study was to determinate the microbiological status of minced meat directly post production. Moreover, we tried to establish if its microbiological quality depends on pH value, water activity and the rate of chilling at that stage of production.

MATERIALS AND METHODS

One hundred twenty samples of mixed, pork and beef (60%:40%), minced meat, originating from 2 Lower-Silesian plants with implemented HACCP system, were subjected the studies. The samples, each of ca 300 g, were obtained by veterinary inspector and brought to laboratory within 2 hours post production. Subsequently, their water activity, pH and internal temperature were measured and the samples underwent microbiological analysis.

The water activity of the samples was determined using Thermoconstanter Novasina RTD 33 TH-1 avumeter. The pH was measured with an aid of V 628, type N 517 pH-meter. The internal temperature of minced meat was monitored using type DT1 electronic thermometer with theromocouple.

Microbiological analyses considered the determinations of total plate count, the numbers of Escherichia coli, coliforms, coagulase-positive staphylococci, yeasts and moulds and the presence of salmonellae. All the determinations were performed following the compulsory Polish Standards [14-19].

Statistical analysis of intrinsic (water activity, pH and internal temperature) and microbiological parameters of minced meat was carried out using Statistica 5, Version 97 software. The bacterial counts were transformed into logarithms. Mean, median, minimum, maximum and standard deviation were calculated for each continuous variable. The Pearson´s coefficients of correlation (r) between microbiological and intrinsic parameters of minced meat were determined. In course of variance analysis the intrinsic parameters were assumed as categorizing variables (Table 1). The differences of mean microbiological counts between the groups were tested by means of univariate analysis (ANOVA). The intrinsic parameters significant on univariate analysis were subjected multivariate analysis (MANOVA).

RESULTS

The statistical characteristics of the microbiological parameters of minced meat are given in Table 2. Escherichia coli was determined in 43/120 (35.8%), coliforms - in 113/120 (94.2%), coagulase-positive staphylococci - in 1/120 (0.8%), whereas yeasts and moulds - in 66/120 (55%) samples. Salmonellae were not determined in any of the sample analyzed. The distribution of total plate count in the material studied is presented in Figure 1.

The statistical characteristics of the intrinsic parameters of minced meat are given in Figures 2-4 and in Table 3.

The Pearson´s (r) coefficients between microbiological and intrinsic parameters of minced meat are given in Table 4. Significant correlations were determined between the total plate count and pH or internal temperature and between Escherichia coli number and internal temperature (p<0.05).

The univariate analysis of variance revealed that the following intrinsic factors had significant effect on the microbial counts of minced meat (p<0.05):

• water activity (p=0.044), pH (p=0.041) and internal temperature (p=0.001) - on total plate count;

• pH (p=0.0003) and internal temperature (p=0.003) - on Escherichia coli number;

• pH (p=0.011) - on the number of coliforms.

The following of intrinsic factors significant on univariate analysis were proved to affect the microbiological parameters of minced meat on multivariate analysis (p<0.05):

• internal temperature (p=0.013) - on total plate count;

• pH (p=0.004) and internal temperature (p=0.043) - on Escherichia coli number.

DISCUSSION

With the exception of Escherichia coli and coliform counts, the level of microbiological contamination of material studied met the compulsory standards [20].

There is an evidence that Escherichia coli might be present in minced meat produced in Poland and other European Union countries [2, 4-5, 8, 23, 25]. The particular health risk of consumer is related to the contamination of food with the enteropathogenic strains of that organism. Since the serotyping of Escherichia coli is no performed on routine sanitary examination, each case of the isolation of those bacteria should be considered as a substantial threat.

Escherichia coli present in minced meat might originate from farm animal tissues or contaminate the raw material during slaughter and related treatment or cutting. Since the aforementioned literature data indicate that the contamination of minced meat with Escherichia coli occurs even in EU-approved plants, there is a need to maintain the intrinsic parameters of the product the least favorable for microbial growth.

Multivariate analysis revealed that lower pH reflected in the increased contamination of minced meat with Escherichia coli. Comparing to other microorganisms, Escherichia coli is relatively more resistant to pH decrease [1, 3, 21-22]. Conceivably, the lower pH of meat caused the death of other microorganisms, and consequently vacated ecological niche was colonized by Escherichia coli. The range of pH of material studied (5.23-6.00) was however too narrow for more advanced conclusions.

The temperature of storage, and consequently the internal temperature of product, undoubtedly determinates its microbiological status [6, 13], which was proved in present study as well. Multivariate analysis revealed that the internal temperature of minced meat is independent factor affecting total plate count and the number of Escherichia coli. The wide range of the temperature of samples examined allows to hypothesize that the sufficient rate of meat chilling either before, during, or post cutting might be crucial for its further microbiological status.

The results of statistical analysis indicated that water activity has not influenced the microbiological status of material studied. The latter conclusion however, might reflect the relatively low variability of that parameter, which remained at non-limiting level in most of the samples.

CONCLUSION

The values of pH and internal temperature might determine the microbiological status of minced meat directly post production, particularly referring to Escherichia coli.

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