Influência do ph final e tipo de embalagem na conservação de carne de bovino da raça maronesa: Parâmetros microbiológicos, físico-químicos, sensoriais e fracção volátil
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Data
2008
Autores
Saraiva, Cristina Maria Teixeira
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Resumo
A carne de bovino é uma das que tem maior valor comercial no panorama das espécies pecuárias. Para além do valor intrínseco da carne de bovino, a sua origem associada a uma raça autóctone e a um sistema de produção ecologicamente sustentável, como é o caso da raça bovina Maronesa DOP, aumenta o seu valor comercial e a sua aceitabilidade. Porém, para poder explorar todo o potencial desse produto, é necessário assegurar que chega ao consumidor nas melhores condições, e encontrar formas de apresentação que tornem mais fácil e segura a sua distribuição por unidades comerciais que frequentemente não têm serviço de corte de carnes. Assim, a comercialização desta carne previamente embalada, num sistema que prolongue ao máximo a sua vida útil, preservando o seu aspecto natural, principal factor que determina a decisão de compra pelo consumidor pode ser vantajosa. Por outro lado, é conhecida a ocorrência de carnes de condição DFD no sistema de produção desta carne, cuja capacidade de conservação é previsivelmente inferior.
O presente trabalho teve como objectivo determinar quais as melhores condições de embalagem de carne de bovino Maronês DOP, de diferentes condições post mortem - Normal, DFD moderado e DFD.
Desenhou-se um ensaio em que se embalou a carne destas condições post mortem em cinco tipos de embalagem diferente (aerobiose, vácuo, e 3 atmosferas modificadas, com uma proporção de O2:CO2 de 70:20, 50:40 e 30:60) e armazenadas a 4ºC. As amostras foram analisadas às 24 h post mortem, imediatamente após a sua preparação, e ao fim de 3, 7, 10, 14, 21, 28 e 35 dias de armazenamento (os tempos mais avançados só incluíram as embalagens sob vácuo e AM30/60). O ensaio foi conduzido com 6 repetições, correspondentes a 6 animais em cada unidade experimental.
Em cada tempo de análise determinou-se o teor em microrganismos potencialmente associados à deterioração da carne: Bactérias do ácido láctico, Brochothrix thermosphacta, Enterobacteriaceae, Pseudomonas spp., Fungos e totais mesófilos e psicrotróficos. Determinou-se o teor em azoto básico volátil total (ABVT) e as coordenadas de cor L*a*b*. Um painel de provadores analisou a carne imediatamente após a abertura das embalagens quanto à sua cor (em 4 escalas possíveis: vermelho-vivo, vermelho-escuro, púrpura e castanho), superfície de descoloração e apreciação global de frescura. Após 60 minutos de avermelhamento, as mesmas amostras voltaram a ser analisadas pelo painel, para as características supra-mencionadas e cheiro a deteriorado. Os provadores indicaram ainda qual a nota aromática específica que detectaram. Num subgrupo de amostras (t10 e t21; embalagens sob vácuo e AM70/20; pHf normal e DFD) determinou-se a composição da fracção volátil por HS-SPME-GC-MS, e detectou-se a nota aromática de alguns desses compostos por acoplamento de uma porta de olfactometria à técnica mencionada.
Verificou-se que a maioria da microflora foi influenciada pelos efeitos em estudo, não se verificando nenhuma interacção entre esses. Confirma-se a importância do pHf da carne no comportamento de alguns microrganismos, determinando contagens superiores nas carnes com pHf mais elevado – ainda que, em termos absolutos, essas diferenças se situem entre 1 e 2 log (ufc/g). O teor em CO2 mostrou ser importante na inibição da maioria dos microrganismos.
A cor da carne foi muito influenciada pelo tipo de embalagem, pelo pHf e pela interacção entre ambos, destacando-se a elevada ocorrência de colorações acastanhadas nas amostras de carne normal embalada em AM, ao contrário do observado em carnes com pHf mais elevado, e, uma melhor recuperação da cor vermelha após abertura da embalagem sob vácuo nas carnes normais.
O cheiro a deteriorado foi determinado por notas a pútrido e a acídico/fermentado em carnes embaladas em aerobiose e sob vácuo, e a ranço nas carnes normais embaladas em AM. Observou-se existir nessas amostras uma associação entre o cheiro a ranço e a ocorrência de colorações castanhas. Essas notas aromáticas vieram a ser confirmadas pelos resultados da composição da fracção volátil, onde foram identificados vários compostos com origem provável na oxidação lipídica.
Demonstrou-se que o grupo de pHf e o tipo de embalagem da carne de bovino de raça Maronesa tiveram uma marcada influência em diversos parâmetros associados à sua frescura. As soluções de embalagem que se mostraram mais eficazes foram o vácuo, para o tipo de carnes, e as atmosferas modificadas apenas para as carnes com pHf elevado.
Beef has the highest commercial value among types of meat. Besides the intrinsic value of beef, when it origins can be traced to an autochthonous breed and to a environmentally sustainable production system, as observed in the case of Maronesa beef (Protected Designation Of Origin – PDO), its commercial value and acceptability are both increased. However, in order to exploit this product’s full potential it is vital to ensure that it reaches the consumer in the best possible condition. Also, display strategies must be found that ensure the product’s practical and safe distribution to commercial outlets, which frequently do not have meat-cutting facilities. Thus, the commercialization of this meat in a pre-packaged form, using a system that extends its shelf-life and preserves its appearance for longer -one of the main factors influencing consumers’ choice-, might well be advantageous. Additionally,in the production system of this meat is known the occurrence of DFD (Dark, Firm and Dry) condition, with a predictable reduction in the product’s shelf-life. The objectives of this current study were to determine the best packaging strategies for Maronesa meat PDO, at different post mortem conditions: Normal, Moderate DFD and DFD. An experiment was designed which involved packaging meats from each post mortem condition category in 5 different types of packaging (aerobic, vacuum, and 3 modified atmospheres (MA) with a proportion of O2:CO2 of 70:20, 50:40 and 30:60) and stored at 4ºC. Samples were analysed at 24 hours post mortem, immediately after preparation, and after 3, 7, 10, 14, 21, 28 and 35 days of storage (latter sampling times only included vacuum and MA30/60 packaging). Experiments were performed using 6 repetitions, corresponding to 6 animals in each experimental unit. At each sampling point, the number of microorganisms potentially associated with meat spoilage was counted. These were: Lactic acid bacteria, Brochothrix thermosphacta, Enterobacteriaceae, Pseudomonas spp., Fungi and total mesophilic and psicrothrophic microflora. The level of total volatile basic nitrogen was evaluated as well as the colour coordinates L*a*b*. Sensory panellists evaluated the meat’s colour immediately after opening the packaging (using 4 possible scales: cherry-red, dark-red, purple and brown); surface discolouration and a general freshness evaluation. After 60 minutes of blooming, the same samples were evaluated again for the same characteristics and for spoiled aroma. Panellists also indicated the specific aromatic note detected. In a sub-group of samples (t10 and t21, vacuum and MA70/20 packages; pHf normal and DFD), the composition of the volatile fraction was determined by SPME-GC-MS, and the aroma of some of these compounds were detected using a sniffer coupled with the aforementioned technique. It was observed that the majority of the microflora enumerated was influenced by both of the effects studied, but not by the interaction between the two. The importance of ultimate pH levels was confirmed in the behaviour of certain microorganisms; higher pH meats were associated with higher counts, representing absolute differences between 1 to 2 log (ufc/g). CO2 concentration was an inhibitory factor for the majority of microflora studied. The colour of the meat was highly influenced by the packaging, the pH and the interaction between both. Brownish colours were observed in normal meat packaged under MA, in contrast to the red colour that high pH meat maintained; normal pH meat exhibited better blooming after vacuum packing was opened. Spoilage smell was composed of putrid and sour aromatic notes in aerobic-packaged meat, and by rancidity in normal pH meat packaged under MA. In those samples, an association between brownish colours and rancid aromas was observed, which was subsequently confirmed by the composition of the volatile fraction that revealed several compounds with probable origins associated with lipid oxidation. It was proven that the ultimate pH and packaging type of Maronesa beef meat influenced the various parameters that are associated with its freshness. The packaging that was revealed to be most efficient for all types of meat was vacuum packaging, and MA packaging for high pH meats.
Beef has the highest commercial value among types of meat. Besides the intrinsic value of beef, when it origins can be traced to an autochthonous breed and to a environmentally sustainable production system, as observed in the case of Maronesa beef (Protected Designation Of Origin – PDO), its commercial value and acceptability are both increased. However, in order to exploit this product’s full potential it is vital to ensure that it reaches the consumer in the best possible condition. Also, display strategies must be found that ensure the product’s practical and safe distribution to commercial outlets, which frequently do not have meat-cutting facilities. Thus, the commercialization of this meat in a pre-packaged form, using a system that extends its shelf-life and preserves its appearance for longer -one of the main factors influencing consumers’ choice-, might well be advantageous. Additionally,in the production system of this meat is known the occurrence of DFD (Dark, Firm and Dry) condition, with a predictable reduction in the product’s shelf-life. The objectives of this current study were to determine the best packaging strategies for Maronesa meat PDO, at different post mortem conditions: Normal, Moderate DFD and DFD. An experiment was designed which involved packaging meats from each post mortem condition category in 5 different types of packaging (aerobic, vacuum, and 3 modified atmospheres (MA) with a proportion of O2:CO2 of 70:20, 50:40 and 30:60) and stored at 4ºC. Samples were analysed at 24 hours post mortem, immediately after preparation, and after 3, 7, 10, 14, 21, 28 and 35 days of storage (latter sampling times only included vacuum and MA30/60 packaging). Experiments were performed using 6 repetitions, corresponding to 6 animals in each experimental unit. At each sampling point, the number of microorganisms potentially associated with meat spoilage was counted. These were: Lactic acid bacteria, Brochothrix thermosphacta, Enterobacteriaceae, Pseudomonas spp., Fungi and total mesophilic and psicrothrophic microflora. The level of total volatile basic nitrogen was evaluated as well as the colour coordinates L*a*b*. Sensory panellists evaluated the meat’s colour immediately after opening the packaging (using 4 possible scales: cherry-red, dark-red, purple and brown); surface discolouration and a general freshness evaluation. After 60 minutes of blooming, the same samples were evaluated again for the same characteristics and for spoiled aroma. Panellists also indicated the specific aromatic note detected. In a sub-group of samples (t10 and t21, vacuum and MA70/20 packages; pHf normal and DFD), the composition of the volatile fraction was determined by SPME-GC-MS, and the aroma of some of these compounds were detected using a sniffer coupled with the aforementioned technique. It was observed that the majority of the microflora enumerated was influenced by both of the effects studied, but not by the interaction between the two. The importance of ultimate pH levels was confirmed in the behaviour of certain microorganisms; higher pH meats were associated with higher counts, representing absolute differences between 1 to 2 log (ufc/g). CO2 concentration was an inhibitory factor for the majority of microflora studied. The colour of the meat was highly influenced by the packaging, the pH and the interaction between both. Brownish colours were observed in normal meat packaged under MA, in contrast to the red colour that high pH meat maintained; normal pH meat exhibited better blooming after vacuum packing was opened. Spoilage smell was composed of putrid and sour aromatic notes in aerobic-packaged meat, and by rancidity in normal pH meat packaged under MA. In those samples, an association between brownish colours and rancid aromas was observed, which was subsequently confirmed by the composition of the volatile fraction that revealed several compounds with probable origins associated with lipid oxidation. It was proven that the ultimate pH and packaging type of Maronesa beef meat influenced the various parameters that are associated with its freshness. The packaging that was revealed to be most efficient for all types of meat was vacuum packaging, and MA packaging for high pH meats.
Descrição
Tese de Doutoramento em Ciências Veterinárias
Palavras-chave
Carne de bovino , Embalagens , Qualidade alimentar , Deterioração