Biogenic amine formation in turkey meat under modified atmosphere packaging with extended shelf life: Index of freshness

ABSTRACT

The aim of this study was to evaluate the effect of modified atmosphere packaging (MAP) on biogenic amine production in turkey meat according to its shelf life period, determining an index of freshness. Sliced meat samples of different meat quality categories (according to color and pH₂₄) were individually packaged under aerobiosis (aerobic package) and in 6 different modified atmospheres containing different gas mixtures: MAP1, 50% N₂/50% CO₂; MAP2, 0.5% CO/50% CO₂/49.5% N₂; MAP3, 50% Ar/50% N₂; MAP4, 0.5% CO/80% CO₂/19.5% N₂; MAP5, 100% N₂; and MAP6, 50% Ar/50% CO₂. All samples were stored at 0 ± 1°C in the dark for between 12 and 25 d. Meat samples packaged in aerobic packaging were analyzed for their microbial and physicochemical characteristics on d 0, 5, and 12 of storage, and then extended to 19 and 25 d when samples were under MAP. The production of biogenic amines analyzed in turkey meat increased over time. The values of putrescine, cadaverine, and tyramine increased significantly (P < 0.05) during storage time in samples packaged under aerobiosis, MAP3, and MAP5. Histamine was not detected in turkey meat packaged under study conditions, or when present, the levels were below the limit of quantification (1.03 mg/kg). Tyramine in turkey meat under MAP was not the best amine indicator of meat deterioration, with cadaverine being suggested instead, or the sum of the amines putrescine, cadaverine, and tyramine, to characterize and quantify meat freshness. After 25 d of storage, the meat packaged under MAP with a mixture containing a higher concentration of CO₂ and with CO was the one with a lower index value (11.36 mg/kg), although not significantly different from the indices provided by the meat packaged with MAP1, 2, and 6.

INTRODUCTION

In the last few years, poultry meat presentation has undergone modification through the use of modified atmosphere packaging (MAP) with cold storage, giving rise to an extension of meat shelf life. Poultry meat and products are highly susceptible to microbial spoilage, and in the case of aerobic storage, Pseudomonas are the main microorganisms prevailing, whereas under MAP storage, Brochotrix thermosphacta and lactic acid bacteria (LAB) usually predominate (Fraqueza et al., 2008).

The usual gas mixture used for retail sliced poultry meat under MAP is 20% CO₂, 70% O₂, and 10% N₂, giving a shelf life of approximately 8 d. However, other gas mixtures can lead to an extension of shelf life of 1 to 3 wk, variable according to poultry meat quality, color, and temperature (Fraqueza et al., 2008; Fraqueza and Barreto, 2009, 2011). Poultry meat quality and freshness is frequently evaluated only by microbial indicators or by sensorial evaluation. However, chemical indicators could be useful to assess those attributes including volatile bases, nucleotide breakdown, volatile acidity, and the levels of biogenic amines (BA; Halász et al., 1994; Dainty, 1996; Balamatsia et al., 2006; Fraqueza et al., 2008). The quantification of biogenic amines in meat and meat products is important not only as an indicator of freshness but also from a toxicological point of view.

Biogenic amines are mainly formed by bacterial enzymatic decarboxylation activity of free amino acids with the exception of physiological polyamines. The inhibition of this decarboxylase activity or prevention of bacterial growth is of great importance to its control. There are several factors that affect decarboxylase activity or bacterial growth, and consequently, the formation of biogenic amines. The production of biogenic amines is mainly influenced by temperature, availability of oxygen, redox potential, and pH (Halász et al., 1994; Masson et al., 1996). The presence of carbohydrates, such as glucose, also promotes the growth of bacteria and their decarboxylase activity (Silla Santos, 1996).

The amount and type of biogenic amines formed in food depends on the nature of the substrate and type of microorganisms. Many Enterobacteriaceae and certain Lactobacilli (Lactobacillus buchneri), Pediococci, and Enterococci are particularly active in the formation of one or more biogenic amines (Latorre-Moratalla et al., 2010). Decarboxylation of histidine is mainly attributed to the genera Escherichia, Salmonella, Clostridium, Bacillus, and Lactobacillus (Voigt et al., 1977, quoted by Halász et al., 1994) and gives rise to histamine, a mediator of severe anaphylactic manifestations. Pseudomonas spp., which is the dominant microorganism of fresh meat spoilage, produces mainly putrescine, whereas Enterobacteriaceae preferably form cadaverine (Halász et al., 1994; Bover-Cid et al., 2003).

High levels of putrescine, histamine, tyramine, and cadaverine occurred during meat storage, while spermidine concentration remained constant and that of spermine slightly decreased (ten Brink et al., 1990; Hernández-Jover et al., 1997). Spermidine and spermine are naturally present in relatively constant concentrations in pork and beef and in meat products, and their formation is not attributed to meat spoilage or fermentation processes (Zee et al., 1983; Hernández-Jover et al., 1997; Alfaia et al., 2004).

In pork and beef stored at 4°C for 35 d, it was found that concentrations of putrescine and cadaverine increased, followed by those of tyramine and histamine; however, the amount of these biogenic amines did not exceed 150 mg/kg. In putrid meat samples, concentrations above 1.000 mg/kg were found (Bauer et al., 1994). The spermidine content in pork was 1 to 16 mg/kg during the storage period, whereas spermine showed values of 20 to 50 mg/kg and did not change its content over time (Bauer, 1995).

Biogenic amines do not represent a hazard to the health of consumers unless large amounts are consumed or the natural mechanism for their catabolism is impaired by the ingestion of substances that inhibit monoamine oxidase (MAO; drugs and alcohol), gastrointestinal disease, or genetic deficiency (Stratton et al., 1991; Pinho et al., 2000). Typical symptoms of intoxication can be observed in some individuals, manifested by nausea, rashes, headaches, and hypotension or hypertension. The intoxication-type reactions frequently caused by biogenic amines are related to histamine (much associated with consumption of scombroid fish, such as tuna, herring, and mackerel) and tyramine (related to the ingestion of cheese) (Tarján and Jánossy, 1978; Smith, 1981; Stratton et al., 1991; Mariné et al., 1995). However, determination of the toxicity threshold of biogenic amines in individuals is extremely difficult because the toxic dose is very dependent on the efficiency of the detoxification mechanisms (Halász et al., 1994). The toxic dose depends on the sensitivity of individuals, and levels above 100 mg/kg of histamine, 100 to 800 mg/kg for tyramine, and 30 mg/kg of phenylethylamine in foods can cause poisoning (ten Brink et al., 1990).

The aim of this study was to evaluate the effect of MAP on biogenic amine production in turkey meat stored at 0°C according to its shelf life period and to establish a relationship between BA production and the level of specific microorganism indicators.

MATERIALS AND METHODS

Collection of Samples and Packaging Procedure

Turkey breasts were selected according to luminance (L*) and pH₂₄: L* > 51 and pH < 5.8 for light color, 43 < L* < 51 for intermediate color, L* < 43 and pH > 5.8 for dark color (Fraqueza et al., 2006).

Sliced meat samples were individually packaged under aerobiosis (aerobic package, AP), using polypropylene trays (Tecknopack plastics, S/L, Barcelona, Spain) and polyvinyl chloride film, and they were put in 6 different modified atmospheres containing different gas mixtures: MAP1, 50% N₂/50% CO₂; MAP2, 0.5% CO/50% CO₂/49.5% N₂; MAP3, 50% Ar/50% N₂; MAP4, 0.5% CO/80% CO₂/19.5% N₂; MAP5, 100% N₂; and MAP6, 50% Ar/50% CO₂. For modified atmosphere packaging, polypropylene trays (Tecknopack plastics) were used and polylaminated plastic bags HBX-070 (R. Bayer, Veitsbronh, Germany) with high impermeability to O₂ and CO₂ (permeability: O₂ = 7.5 cm³/m².d.bar, 75% RH, 23°C; CO₂ = 32 cm³/m².d.bar, 75% RH, 23°C; N₂ = 3 cm³/m².d.bar, 75% RH, 23°C; and water steam = 0.77 g/m².d) due to a high barrier layer of ethylene vinyl alcohol. Packages were sealed in an EVT-7-CD machine (Tecnoprip, Barcelona, Spain) after a vacuum of 97% and an introduction of gas mixture of 60%. All meat samples were stored in refrigeration (0 ± 1°C) in the dark for between 12 and 25 d.

Meat samples in AP were analyzed for their microbial and physicochemical characteristics on d 0, 5, and 12 of storage. This evaluation was extended to 19 and 25 d when samples were under modified atmosphere packaging.

For each meat quality color class and packaging condition, 4 replications (n = 4) were made on different storage days.

Microbial Analysis

The preparation of meat samples for microbial analysis was performed in accordance with ISO (1999, 6887–1). Microbial determinations were carried out for total mesophilic aerobic counts (Plate Count Agar, Sharlau, Sentmenat, Spain) after incubation at 30°C for 2 d in accordance with ISO (2003, 4833); total psychrotrophic aerobic counts (Plate Count Agar, Sharlau) at 7°C for 10 d (ISO, 2005, DIS 6730); anaerobic count at 7°C for 10 d (Brewer Anaerobic Agar, Merck, Darmstadt, Germany); Enterobacteriaceae counts in Violet Red Bile agar (VRB agar, Merck) at 37°C for 2 d (ISO, 2004, 21528–2); for Pseudomonas spp. counts [cephaloridene, fucidin and cetrimide (CFC) agar base; Oxoid, Cambridge, UK] incubation was carried out at 30°C for 2 d (ISO, 1995, 13720), LAB counts in Man Rogosa Sharpe Agar (Oxoid) incubated at 30°C for 3 d (ISO, 1998, 15214), and Brochothrix thermosphacta count in streptomycin, actidione, thallous acetate agar (STAA, Oxoid) incubated for 2 d at 30°C (ISO, 1996, 13722; Santé et al., 1994). Counts were expressed as log cfu/g.

Physical-Chemical Analysis

The pH was measured directly on sliced turkey meat with a portable pH meter (HI9023, Hanna Instruments, Padova, Italy) equipped with a pH electrode (FC 230B, Hanna Instruments). Each value is an average of 3 determinations on the sliced meat.

Biogenic Amines Determination

The extraction, derivatization, and quantification of 6 biogenic amines (cadaverine, spermidine, spermine, histamine, tyramine, and putrescine) were performed according to the technique described by Eerola et al. (1993) and Alfaia et al. (2004). Biogenic amines were separated and quantified by a high-performance liquid chromatographic method described by Eerola et al. (1993). The amines were extracted with perchloric acid and derivatized with dansyl chloride. The chromatographic separations were performed on a reversed-phase column (Supelcosil RP-18, 5 μm, 250 × 4.6 mm, Supelco, Bellefonte, PA), with UV detection at 254 nm. 1,7-Diaminoheptane was used as an internal standard. The Biogenic Amine Index (BAI) or index of freshness was calculated from the addition of putrescine, cadaverine, and tyramine.

Statistical Analysis

For biogenic amine variables, the comparison between color quality meat classes was performed for each packaging condition and each day by a simple one-way ANOVA performed using SPSS 17.0 for Windows (SPSS Inc., Chicago, IL). As no significant differences between color quality meat classes were observed, the subsequent data analyses were conducted without considering this factor. The analysis of effects for different packaging conditions was carried out independently for each day by a simple one-way ANOVA (Pestana and Gageiro, 2003). If the F-test from ANOVA was significant, a least significant mean difference of a post hoc multiple comparisons test was performed.

The comparison between days was performed independently for each packaging using the MIXED procedure (SAS Institute Inc., 2009), considering the breasts as random block and the days as repeated measures. Least squares means were presented and compared using the LSMEANS/PDIFF option when interaction effect was significant (P < 0.05).

The relationship between the various microbiological variables, pH, and biogenic amine concentration quantities and the BA index were analyzed by the Pearson correlation coefficients.

RESULTS AND DISCUSSION

Aminogenesis in Turkey Meat Under MAP

The microbial shelf life period extension of sliced turkey meat under MAP compared with aerobic packaging (5 d shelf life) was 1 wk more for MAP3 and MAP5 mixtures, 2 wk (19 d) for MAP1 and MAP2, and 3 wk (25 d) for MAP4 and MAP6 (Fraqueza et al., 2008; Fraqueza and Barreto, 2009, 2011).

Regarding different meat quality color groups, significant differences were not found between the 6 biogenic amines (putrescine, cadaverine, tyramine, histamine, spermidine, and spermine) analyzed in turkey meat packaged under aerobic and MAP conditions.

Figure 1 shows the evolution of the biogenic amines putrescine, cadaverine, tyramine, spermidine, and spermine levels in turkey meat, packaged under aerobiosis and MAP, throughout the storage time.

Figure 1

Evolution of biogenic amines: putrescine (A), cadaverine (B), tyramine (C), spermidine (D), and spermine (E) in sliced turkey meat packaged under aerobiosis and modified atmosphere packaging (MAP) with mixtures MAP1 to MAP6 (see Materials and Methods) during storage time at 0°C (n = 4). ^a–cValues on the same day of storage not sharing a common letter are significantly different, P < 0.05.

The values of putrescine, cadaverine, and tyramine increased significantly (P < 0.05) during storage time in samples packaged under aerobiosis, MAP3, and MAP5. At 12 d of storage, the meat under aerobic conditions showed significantly higher levels of putrescine (15.30 mg/kg; P < 0.001), cadaverine (32.50 mg/kg; P < 0.001), and spermidine (8.76 mg/kg; P < 0.01) than the one packaged under MAP. However, the meat packaged under MAP3 and MAP5 had quite high values of cadaverine (19.41 and 18.14 mg/kg, respectively; Figure 1A) which differed significantly (P < 0.001) from those registered in meat packaged with mixtures containing CO₂ (MAP1, 2, 4, and 6). The concentration of cadaverine in meat under MAP3 was not significantly different from that found in meat under aerobic conditions.

The levels of tyramine (Figure 1C) in turkey meat packaged with MAP3 (24.42 mg/kg) and MAP5 (12.62 mg/kg) were the highest and were significantly different (P < 0.001) from those found in meat packaged under the other study conditions. The concentrations of putrescine, cadaverine, and tyramine in meat under MAP3 and MAP5, at both 19 d and 25 d of storage, were significantly higher (P < 0.001) than those observed in meat packaged with other mixtures. The biogenic amine cadaverine reached high concentrations in turkey meat packaged during storage time. Vinci and Antonelli (2002) also observed higher concentrations of cadaverine in beef and chicken meat stored at 4°C for 36 d, compared with the other amines. In fact, these meats are very rich in lysine, the precursor of this biogenic amine (cadaverine). Moreover, in chicken meat, the content of lysine is higher and so the cadaverine was detected earlier, showing a more rapid increase than in beef. According to these authors, the tyramine content in chicken is low, not exceeding average values of 40 mg/kg, after 30 d of storage at 4°C.

Histamine was not detected on turkey meat packaged under study conditions or, when present, showed concentration values below the limit of quantification (1.03 mg/kg). Rokka et al. (2004) did not detect histamine in fresh chicken parts either. The spermidine and spermine concentrations were not significantly different between the meat samples packaged under MAP, even after 25 d of storage. These amines were present in relatively constant values on meat under different conditions of packaging and during storage time, which agrees with statements reported by Bauer et al. (1994) and Rokka et al. (2004). The turkey meat samples analyzed showed an average of 4.27 mg/kg for spermidine and 46.82 mg/kg for spermine. The values of spermidine and spermine found in chicken meat by Rokka and colleagues (2004) were 9.8 to 14 mg/kg and 75 to 82 mg/kg, respectively.

The evolution of the index of freshness (BAI) for turkey meat packaged aerobically and under MAP is represented in Figure 2. Analyzing the rate of freshness, meat packaged under MAP3 and MAP5, after 12 d of storage, showed amine concentration values and reporting protein and amino acid degradation that were not different from those found in meat packaged under aerobic conditions. After 25 d of storage, only the meat packaged under MAP with a mixture containing a higher concentration of CO₂ and with CO showed a lower index value (11.36 mg/kg), although this was not significantly different from the indices provided by the meat packaged with MAP1, 2, and 6.

Figure 2

Evolution of freshness index in sliced turkey meat packaged under aerobiosis and modified atmosphere packaging (MAP) with mixtures MAP1 to MAP6 (see Materials and Methods) during storage time at 0°C (n = 4). ^a–cValues on the same day of storage not sharing a common letter are significantly different, P < 0.001.

Relationship Between Microbiological Parameters and the Biogenic Amines in Turkey Meat under MAP

Biogenic amines are formed from the catalytic decarboxylation of the respective amino acids as a result of the endogenous activity of decarboxylases, or by the action of decarboxylase-positive microorganisms (Crahay and Noirfalise, 1996). For this reason, the Pearson correlation values between the microbiological parameters of meat samples under study conditions (396 observations) and the levels of the different biogenic amines were calculated to find the best indicator of freshness, as can be seen in Table 1.

Pearson correlation coefficients established between biogenic amines and microbiological variables in turkey meat under the study conditions (n = 396)

Table 1

Pearson correlation coefficients established between biogenic amines and microbiological variables in turkey meat under the study conditions (n = 396)

Item	Putrescine	Cadaverine	Histamine	Tiramine	Spermidine	Spermine	Biogenic Amine Index
Mesophilic aerobic counts	0.509**	0.613**	0.113*	0.495**	0.305**	0.140**	0.630**
Anaerobic count	0.480**	0.614**	0.038	0.529**	0.180**	0.047	0.632**
Psychrotrophic aerobic counts	0.490**	0.597**	0.118*	0.495**	0.317**	0.150**	0.615**
Enterobacteriaceae	0.455**	0.602**	0.066	0.423**	0.179**	0.094	0.594**
Pseudomonas spp.	0.400**	0.533**	0.053	0.325**	0.279**	0.103*	0.505**
Lactic acid bacteria	0.367**	0.461**	−0.105*	0.393**	−0.051	−0.108*	0.475**
Brochothrix thermosphacta	0.389**	0.422**	0.050	0.390**	0.291**	0.156**	0.457**
pH	0.269**	0.212**	−0.220**	0.086	0.072	−0.141**	0.214**

**Pearson correlation is significant at 0.01.

*Pearson correlation is significant at 0.05.

Significant high correlation coefficients (P < 0.01) were observed between putrescine, cadaverine, and tyramine with mesophilic and anaerobic counts. Thus, there is a preference for the sum of these amines only for the freshness indicator (BAI), which is in agreement with Slemr and Beyermann (1984), Hernández-Jover et al. (1997), and Rokka et al. (2004). The BAI presented the highest correlation values (0.630 and 0.632) with the microbial parameters. Cadaverine alone was also a good indicator of spoilage, with these results being in agreement with Vinci and Antonelli (2002).

According to the correlation coefficients obtained in this study, the Enterobacteriaceae and Pseudomonadaceae families seem to be more involved in the formation of these amines in turkey meat.

Enterobacteriaceae showed a correlation of 0.602 with cadaverine, which was also indicated by Nogueras et al. (2003). Many species of this family are producers of cadaverine. However, despite the association of these species to the formation of histamine in fish, no association was established for turkey meat, indicating that only certain uncommon species may be histidine decarboxylase-positive or because their production does not exist at temperatures below 5°C (Halász et al., 1994; Bover-Cid et al., 2003).

Pseudomonadaceae has also been referred to as aminogenic, with moderate decarboxylase activity for the production of putrescine (Silla Santos, 1996). The correlation values found between these parameters in turkey meat were also significant (0.400).

Slemr et al. (1985, cited by Halász et al., 1994) demonstrated that Enterobacteriaceae and Pseudomonadaceae produced a significant amount of putrescine and cadaverine in beef and pork stored at refrigeration temperatures. Nassar and Emam (2002) also related the occurrence of biogenic amines in processed products from chicken meat with an increase of Enterobacteriaceae, coliforms, Pseudomonas aeruginosa, and Lactobacilaceae counts.

Krizek et al. (1995) observed that LAB are implicated in the production of biogenic amines, such as tyramine, but in our conditions, the correlation was lower (0.393), whereas the correlation value obtained between Enterobacteriaceae and tyramine was higher. However, it should be noted that in this study, the correlation analysis was performed for turkey meat under different conditions of aerobic and MAP packaging, without O₂ in the gas mixtures. Consequently, the dominant flora in meat packaged under aerobic conditions was different from the dominant flora in meat under anaerobic MAP. Furthermore, when flora growth inhibition was observed, no formation of biogenic amines was reported.

Analyzing the relationship between the microbiological parameters of turkey meat packaged under aerobiosis and the formation of biogenic amines (Table 1), higher correlations were found between increasing concentrations of cadaverine and the growth of Pseudomonas spp. (0.607), Enterobacteriaceae (0.577), and Brochothrix thermosphacta (0.565), whereas higher concentrations of putrescine were better correlated to the populations of Pseudomonas spp. (0.516) and Brochothrix thermosphacta (0.529). According to Nowak and Czyzowska (2011), Brochothrix thermosphacta can contribute to the activation of lysine decarboxylase in gram-negative bacteria of the genera Escherichia and Pseudomonas.

Increased concentrations of tyramine were associated to the growth of Enterobacteriaceae (0.472). Meat pH has no influence on biogenic amine production, being without significant correlation values (Tables 1–4).

Pearson correlation coefficients established between biogenic amines and microbiological variables in turkey meat under modified atmosphere packaging with gas mixture MAP5 (100% N₂; n = 60)

Table 4

Pearson correlation coefficients established between biogenic amines and microbiological variables in turkey meat under modified atmosphere packaging with gas mixture MAP5 (100% N₂; n = 60)

Item	Putrescine	Cadaverine	Histamine	Tiramine	Spermidine	Spermine	Biogenic Amine Index
Mesophilic aerobic counts	0.523**	0.674**	0.101	0.445**	−0.004	−0.089	0.675**
Anaerobic count	0.493**	0.678**	0.076	0.489**	−0.034	−0.069	0.686**
Psychrotrophic aerobic counts	0.561**	0.713**	0.091	0.515**	−0.030	−0.101	0.730**
Enterobacteriaceae	0.452**	0.630**	0.084	0.380**	−0.012	−0.070	0.612**
Pseudomonas spp.	0.482**	0.648**	0.016	0.352**	−0.056	−0.155	0.621**
Lactic acid bacteria	0.642**	0.761**	−0.048	0.557**	0.057	−0.086	0.787**
Brochothrix thermosphacta	0.291**	0.371**	0.086	0.436**	0.133	0.071	0.432**
pH	0.124	0.135	0.017	0.128	−0.069	−0.259*	0.151

**Pearson correlation is significant at 0.01.

*Pearson correlation is significant at 0.05.

The index of freshness (BAI) presented significant correlation coefficients (P < 0.01) with all groups of microorganisms tested, with the exception of LAB, indicating that this group contributes very little to the formation of biogenic amines in meat packaged aerobically (Table 2). However, these associations no longer occur when meat is packaged under atmospheres that cause great microbiological inhibition, such as MAP4 (Table 3).

Pearson correlation coefficients established between biogenic amines and microbiological variables in turkey meat under aerobic package (n = 96)

Table 2

Pearson correlation coefficients established between biogenic amines and microbiological variables in turkey meat under aerobic package (n = 96)

Item	Putrescine	Cadaverine	Histamine	Tiramine	Spermidine	Spermine	Biogenic Amine Index
Mesophilic aerobic counts	0.511**	0.602**	0.052	0.249*	0.543**	0.210*	0.626**
Anaerobic count	0.538**	0.633**	−0.075	0.371**	0.510**	0.070	0.668**
Psychrotrophic aerobic counts	0.513**	0.607**	0.049	0.458**	0.567**	0.224*	0.658**
Enterobacteriaceae	0.473**	0.577**	0.153	0.472**	0.598**	0.397**	0.626**
Pseudomonas spp.	0.516**	0.607**	0.037	0.450**	0.548**	0.206	0.657**
Lactic acid bacteria	0.349**	0.105	−0.208	−0.188	0.154	−0.062	0.134
Brochothrix thermosphacta	0.529**	0.565**	−0.033	0.246*	0.457**	0.115	0.606**
pH	0.386**	0.402**	−0.271*	−0.024	0.163	−0.172	0.383**

**Pearson correlation is significant at 0.01.

*Pearson correlation is significant at 0.05.

Pearson correlation coefficients established between biogenic amines and microbiological variables in turkey meat under modified atmosphere packaging with gas mixture MAP4 (0.5% CO/80% CO₂/19.5% N₂; n = 60)

Table 3

Pearson correlation coefficients established between biogenic amines and microbiological variables in turkey meat under modified atmosphere packaging with gas mixture MAP4 (0.5% CO/80% CO₂/19.5% N₂; n = 60)

Item	Putrescine	Cadaverine	Histamine	Tiramine	Spermidine	Spermine	Biogenic Amine Index
Mesophilic aerobic counts	−0.057	0.128	0.237	0.126	0.326*	0.315*	0.101
Anaerobic count	0.094	0.148	0.120	0.233	0.176	0.083	0.239
Psychrotrophic aerobic counts	0.052	0.188	0.294*	0.151	0.354**	0.318*	0.186
Enterobacteriaceae	−0.138	−0.027	0.152	0.046	0.118	0.213	−0.043
Pseudomonas spp.	−0.295*	0.283*	0.375**	0.144	0.300*	0.319*	0.068
Lactic acid bacteria	0.127	0.004	−0.016	0.172	0.017	−0.076	0.159
Brochothrix thermosphacta	0.014	0.162	0.271*	0.001	0.229	0.223	0.069
pH	−0.068	−0.349**	−0.504**	−0.264*	−0.409**	−0.459**	−0.329*

**Pearson correlation is significant at 0.01.

*Pearson correlation is significant at 0.05.

In turkey meat under MAP5 (Table 4), there was a modification of microbial dominance; LAB compared with the other microbial groups showed higher correlations with increasing concentrations of cadaverine, putrescine, and tyramine. The correlation value of the BAI with LAB was quite high, which is in accordance with the conclusions of several authors who refer to LAB as a producer of substantial amounts of tyramine when packaged under MAP and vacuum conditions (Krizek et al., 1995; Masson et al., 1996; Nogueras et al., 2003). In this MAP5 condition, the formation of biogenic amines continues to maintain a close association with Pseudomonas spp. and Enterobacteriaceae. Tyramine production in turkey meat packaged under aerobic conditions showed lower correlation values with the different microbial groups than spermidine, whereas the meat under MAP5 showed higher values. Spermidine and spermine did not show any relation with the different microbial groups. These 2 amines cannot be used as indicators of fresh chicken meat quality (Balamatsia et al., 2006).

It was demonstrated that cadaverine had the highest correlation values in both the 2 packaging conditions (aerobic and MAP5).

According to Yano et al. (1995), Bauer et al. (1994), and Krizek et al. (1995), tyramine is a good indicator of spoilage for beef packaged under vacuum. In turkey meat packaged with anaerobic gas mixtures and stored at 0°C, the concentrations of biogenic amines increased significantly during storage time in MAP3 and MAP5, reaching values of 45.82 mg/kg. However, these amounts are below the concentrations of cadaverine. Thus, tyramine showed lower correlation values with the various microbial groups than cadaverine did. In turkey meat under MAP, tyramine is not the best indicator for meat deterioration; it is suggested that freshness be characterized using cadaverine or the sum of the amines putrescine, cadaverine, and tyramine as an indicator of freshness.

The production of biogenic amines analyzed in turkey meat increased over time. Cadaverine had the highest concentration in packaged turkey meat during storage time. Histamine was not detected in turkey meat packaged under study conditions or, when present, the levels were below the limit of quantification (1.03 mg/kg). Tyramine in turkey meat packaged in MAP is not the best amine indicator of meat deterioration and, instead, cadaverine or the sum of the amines putrescine, cadaverine, and tyramine is suggested to characterize and quantify meat freshness.

ACKNOWLEDGMENTS

The authors thank the Centro de Investigação Interdisciplinar em Sanidade Animal (CIISA) for its financial support and the technicians Maria Helena Fernandes, Maria José Fernandes, and Maria Pedrosa (Faculdade de Medicina Veterinária, Departamento de Produção Animal e Segurança Alimentar, Universidade Técnica de Lisboa, Pólo Universitàrio, Lisboa, Portugal) for their excellent assistance.