Chemical Changes in Vacuum Packed Meat

South American beef is imported to the Europe in vacuum shrunk plastic bags and in this status underwent the phase of ripening. The time of ripening is prolonged by the low storage temperature which is kept under +2°C since the slaughtering until the arrival to the final consumer. Usually such an import takes from 6 to 8 weeks until the meat reaches the Czech Republic (M. Brodina, XO FOODS, Czech Republic, personal communication). Post-mortem period (in which the native enzymes work actively) is known as autolysis of meat. In principle, the autolysis of meat is divided into three basis phases: post  mortem stiffening (rigor mortis), ripening and deep autolysis (Ingr, 2003). Meat achieves optimal quality for culinary and technological use in various times post-mortem, depending on the type of meat and the temperature. In the basic model situation where the slaughter animal carcass is properly processed, quickly and properly refrigerated in cold storage (0 to +2°C), beef cut in quarters optimally ripens in 10 to 14 days or even more depending on the cattle breed, age and sex. In the Czech Republic the meat is stored under 0 to + 1°C in the cold storage which has the most negative influence on ripening and beef quality especially when the expedition usually takes place after two days (R. Sovják, Municipal Veterinary Administration in Prague, Czech Republic, personal communication). Insufficiently ripened meat from cattle is too rigid and hard, lacking the expected tenderness, juiciness and softness, which, together with the relatively high price are the main causes of reduced interest of the beef in the Czech Republic. According to Ingr (2003), the BSE incidence in this country was not so serious reason to impact the trade. Usually, after culling beef ripens at 10 – 15°C for 2- 3 days, at 1 – 2°C for 8 – 14 days and at about 1°C for 21 days. During ripening, the pH decreases due to glycolysis creating the accumulation of lactic acid. Lactic acid is produced in meat just after slaughter and changes its value during the autolysis (Matyáš et al., 1965). Microbial growth in meat is characterized by a specific growth cycle consisting of these phases: log-phase, logarithmic phase of growth, stationary phase and final stage, that is death of microbes. All the phases play a negative role in the course of meat storage. Changes in chemical parameters of meat are influenced by psychrotrophic bacteria e.g. Pseudomonas, Aeromonas, Acinetobacter, which have very strong proteolitic activities (Steinhauser et al., 1995). Besides the factors the change in temperature leading to dew point creation presents a great influence on the meat shelf life as the surface of meat became wetter (which may create increase in microbe growth) (Sovják and Reisnerová, 2001). Acid environment decreases microbial growth in meat and thus has a good effect on the meat shelf life. Therefore sometimes the lactic acid spraying is used to prolong the shelf life of vacuum packed meat though in the Czech Republic this technique was not allowed until 2013 (EC Regulation No 101/2013).

In the course of meat treatment by lactic acid pH on the meat surface decreases up to 3.5%. This status lasts up to 72 h after treatment (Borutová, 2006). Experiments with the use of lactic and peracetic acids already took place in Veterinary Military Research Institute in Prague in 1965 – 1967. Besides pH, water activity (aw) plays a great role on a log phase of microbes in the meat (Sovják, 1967). Water activity is a physical quantity expressing the degree of ability of the water to take part in chemical, biochemical and microbial processes (Troller and Christian, 1978). According to ČSN ISO 21807 (2006), the values of the water activity of most foods range from 0.992 for untreated raw meat to 0.800 for salted and dried products. Fresh meat has the highest water activity (aw > 0.99), on the other side the aw of dried meat products, such as dry sausage or raw ham has correspondingly lower values between 0.92 and 0.80 or less due to higher salt content. It is an important factor for the growth of microorganisms in food, as it is the water that is not chemically bound in cells and the microorganisms can use it for their growth. Growth of most of the pathogenic microorganisms is inhibited when aw is less than 0.9 (Troller and Christian, 1978). Different types of microorganisms tolerate water activity only within a certain range.

Water activity can therefore be used to predict the growth of certain microorganisms in the food or raw material (ČSN ISO 21807, 2006). The water activity also has an important role in the chemical reactions in food (Troller and Christian, 1978). In the course of ripening the water-binding capacity of muscle increases and thus the muscle becomes softer and with tenderer texture (Ingr, 2003). Water-binding capacity is the ability to retain inherent moisture. Binding capacity greatly varies depending on the post-mortem changes – first decreases due to an acidification and a solid structure formation – rigor mortis, and then again increases during ripening (Felício, 1997). Act 326/2001 Coll. of Ministry of Agriculture of the Czech Republic, says that preparation of meat (cutting and packaging) and manipulation with meat must be done during the technologically necessary time and ambient temperature must not be higher than +12°C. Also according to Czech legislation (Ministry of Agriculture of the Czech Republic, 2013) meat cutting must be carried out at a temperature up to 4°C. Maca et al. (1997) studied vacuum packaged ground beef patties containing sodium lactate, sodium propionate, sodium acetate and sodium citrate at various levels and combinations. They were stored up to 28 days at +4°C. Addition of sodium lactate, alone or in combination with sodium propionate, increased shelf life of the patties by decreasing microbiological growth and decreasing negative flavour notes associated with lipid oxidation.

Lean colour also was improved by addition of sodium lactate alone or in combination with sodium propionate. Fresh rib eye steaks were examined for microbiological, lipid oxidation, pH, colour and weight changes after immersion in water or in aqueous solutions of a phosphate blend and of a mixture of potassium sorbate, phosphates, sodium chloride and sodium acetate and subsequent vacuum packaging. Keeping characteristics of steaks were monitored during 12 weeks storage at +2 to +4°C. Mesophilic, psychrotrophic, anaerobic and facultative anaerobic bacteria and lactobacilli were strongly inhibited (P<0.05) in steaks treated with the composition that contained potassium sorbate, whereas growth of Enterobacteriaceae was suppressed (P<0.01). Compared with controls, compositions containing phosphates with or without potassium sorbate protected lipids, increased solution uptake and decreased purge in steaks without affecting meat colour (Unda et al., 1990). During decontamination procedures of carcases of cattle and pigs, Houška (2003) demonstrated that the combined effect of decontamination by spraying with a jet pressure steam and subsequent fogging of aqueous solution of lactic acid ensured an immediate reduction of the amount of surface microflora 100 times.

During cooling and maturation of meat in the cooling box, the number of microorganisms on the surface of the treated halves increased very slowly, on untreated halves the number of microbes increased quickly or at best comparatively quickly. The aim of this study was to identify changes in chemical parameters of vacuum packed meat imported from Argentina in the period of 4 months recommended storage. Meat examinations continued for another month (5th one) in order to find out which changes would appear. Comparison with the shelf life of vacuum packed Czech meat should reveal changes in non treated meat. In our opinion, the Argentinean beef was treated by lactic acid before packing.

Four packages of boneless chilled heart of rump (“corazon de quadril“ in Spanish, “cheio de alcatra“ in Portuguese and “hovězí zadní“ in Czech) of young bulls from one of the EU approved abattoir by DG SANCO in Argentina was imported to Europe and purchased from XO FOODS s.r.o. in the Czech Republic. All these samples were of Argentinean origin, slaughtered and cut in Argentina and imported to the Czech Republic 6 weeks after manufacturing under these conditions: vacuum packaged, kept in

temperature between -1 and + 2°C, labelled with a note: “Once the packaging is opened, consume within the next 4 days.” The best time recommended for consumption was 4 months after manufacture. Packaging was made 2 days after slaughter. Also three packages of Czech boneless chilled vacuum packed rump steak of young bulls (“quadril“ in Spanish, “alcatra“ in Portuguese and “hovězí zadní – ořech v celku“ in Czech), slaughtered, cut and purchased in the Czech Republic were used. They were stored in vacuum packaging in temperature between +1 and +7°C as recommended by the producer on the label which corresponds also to the Regulation (EC) No 178/2002. The best time recommended for consumption was 16 days after manufacturing. Packaging was made 2 days after slaughter. This meat was not treated by any lactic acid containing product and thus was used just as control for comparison and demonstration of evidence of lactic acid content in imported packages during chemical analysis. Chemical examinations were carried out in the laboratories of the Institute for Food Examination in Prague in the Czech Republic. Before opening, all the packs of meat were kept in recommended conditions (from -1 to +2°C the beef from Argentina and from +1 to +7°C the beef from the CR), vacuum packed in “CRYOVAC” vacuum shrunk bags. The packages were removed out from the cooling box just before examination.

All the values of each package were measured five times. All the measured characteristics of the imported beef from Argentina were monitored once in a month since the meat entered the Czech Republic, therefore the first measurement was done 2 months after packaging of the meat, second one 3 months after, the third one 4 months after and the last – the fourth measurement – was done 5 months after the packaging when the meat was already one month after the shelf life date. Czech beef parameters were monitored once in a week since the packaging. The Czech beef shelf life was 16 days since the packaging and 18 days since the slaughtering. The first measurement was done 1 week after the packaging, second one 2 weeks after and the third and the last one 3 weeks after packaging when the meat was already a week after the best time recommended for consumption. Five samples of meat inner part, surface and juice in each package were examined. These chemical analyses were performed in meat: the content of ammonia (NH3), fats, water (respectively dry matter), ash, proteins, water activity, and histamine. Content of lactic acid was measured in meat and meat juice of imported beef as well as in the Czech samples of beef was examined just for this purpose. All these chemical parameters were analyzed in accordance to Czech Technical Standards (ČSN) or Standard Operating Procedures (SOP) of the laboratory (Table 1).

The average values of chemical examinations of South American beef are stated in Tables 2 and 3, the results of the chemical tests of the Czech beef are shown in Tables 4 and 5. The values of ash, protein, fat; H2O and histamine content were not counted in average as they do not play an informative role in the course of ripening. Examination of selected meat parameters in South American beef during the course of 4th and 5 th month’s storage revealed no basic differences even after 5 months storage. This result corresponds with bacteriological examination (Vidová et al., 2012) which was the main reason of Czech meat spoilage.

Czech vacuum packed beef after 3 weeks storage was found to be not eatable due to great sensory changes, although the chemical parameters were not significantly changed. Water activity was in a normal level of vacuum packed beef during the whole shelf life period as well as one month after. Content of NH3 of Argentinean beef was constantly increasing. The amount of NH3 in Czech beef did not change a lot within the studied period, because 3 week’s period is too short time for this process under stated conditions (temperature and vacuum packing). There was a visibly huge difference in content of lactic acid in both types of beef (Tables 2 and 4); the Argentinean meat showed almost double amount of lactic acid than the Czech meat, also the amount of lactic acid in juice was visibly higher (Tables 3 and 5). Our hypothesis concerning the use of lactic acid treatment in case of Argentinean meat was confirmed.

Based on the measured differences in the content of lactic acid in both types of meat from South America and the Czech Republic we can say that South American meat was treated with lactic acid before packing in order to maintain a longer shelf life. This procedure, even though it was not allowed until 2013 in the Czech Republic (EC Regulation No 101/2013) it was obviously already in practice before in Argentina but not stated on the label. This statement except that of our findings corresponds to experiments done in 2002 by Food Research Institute Prague (Houška, 2003). According to Matyáš et al. (1965) the Czech nonvacuum packed beef ripens at 10 – 15°C for 2-3 days, at 1 – 2°C for 8 – 14 days and at about 1°C for 21 days. According to our study, the Czech vacuum packed beef stored at a temperature of +1 to +7°C should be consumed up to 16 days which might be not properly ripened yet. The pH of the meat from Czech Republic stayed at almost same level during the whole shelf life, the pH of the juice slightly decreased and lactic acid in the juice slightly increased which confirms the previous studies of Matyáš et al. (1965).

The lactic acid amount in the meat from Czech Republic was decreasing with time due to further decomposition. During ripening, the pH rises due to glycolysis as stated by Matyáš et al. (1965). On the other hand in our study with Argentinean beef meat, the pH level was growing or stagnating in the course of the whole shelf life while the lactic acid was reducing its value, the pH of the juice was decreasing with the growing lactic acid. We cannot compare the results of pH measurement with Borutová (2006) because our measurements were done later than 72 h after treatment. Generally we can state that the Argentinean beef was treated by lactic acid or some product containing it before packing, it is very visible on the start amount of this acid in comparison with the Czech beef (Tables 2 and 3 in contrast with Tables 4 and 5). At the time of purchase the lactic acid treatment was not allowed in the Czech Republic yet, it was only allowed in 2013 as already stated earlier. We got similar results of extending the shelf life using the lactic acid in Argentinean beef as Maca et al. (1997) in his study using various types of chemicals for extending the shelf life of ground beef patties. Changes of chemical properties of South American meat in time revealed the slow progress of ripening of meat due to constantly reduced temperature and vacuum packing. There were no signs of meat deterioration or other changes incompatible with wholesomeness after 4 months of storage.

Even after 5 months of storage, chemical or microbiological changes measured in previous research (Vidová et al., 2012) did not indicate any signs of decay that would cause removal of the meat from the market. We recommend a further exploration of the topic and the possible extension of the shelf life for another one month. Regarding Czech vacuum packaged meat, in which producers has shelf life not longer than 3 weeks, is probably due to lack of addition of lactic acid or other product used to extend the shelf life, or due to storage temperature, which the producer states from +1 to +7°C, unlike South American meat that have an information about recommended storage from 0 to +2°C. According to the Czech legislation (MZe CR, 2013) meat cutting must be carried out at a temperature that is up to 4°C, but that is often ignored. Another point leading to the rapid meat deterioration are surfaces of cutting tables and cutting tools which are significantly contaminated after a certain time and if a critical point related to their disinfection is not introduced in the HACCP system, the machines and tools become an important source of microbial recontamination speeding up the process of decay. Another reason which can lead to reduction of the shelf life of the Czech beef in comparison to the Argentinean beef may be the chemical composition of the meat itself affected by external factors such as breed, the method of breeding, age, sex, feeding, movement of the animal etc. All of these factors may affect the future quality and shelf life of vacuum packed meat and its sensory properties. Czech vacuum packed meat storage did not last more than 3 weeks from a microbiological point of view. It is therefore appropriate to continue in a further research in the application of antimicrobial agents in the preservation of the meat. In accordance with ČSN ISO 21807 (2006) the water activity of South American beef meat ranged within specified values for raw untreated meat. Content of NH3 of Argentinean beef was constantly increasing due to advancing degradation of meat as described by Ingr (2003).

The comparison of lactic acid content in the Czech and South American beef indicates the use of the acids in South American meat. Even after 5 months of storage, chemical and microbiological changes measured in previous research did not indicate any changes that would cause removal of the meat from the market. Nontreated Czech vacuum packed beef showed signs of decay after 3 weeks of storage. It means that its shelf life of 16 days after packing without treatment is according to our findings the maximum limit for the storage depending on the extent of recontamination.