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Abstract(s)
O queijo Serra da Estrelaé um queijo tradicional produzido a partir de leite de ovelha cru, altamente reconhecido e referenciado, com um período de maturação de 45 dias, sendo posteriormente comercializado sob refrigeração. Sendo um queijo de leite cru, alterações nos parâmetros microbiológicos podem dificultar o armazenamento prolongado. O principal objetivo desta tese de doutoramento foi avaliar a possível contribuição que o processamento de alta pressão (AP), como uma tecnologia de pasteurização a frio, pode ter para melhorar asegurança microbiológica, mantendo a qualidade físico-química e sensorial (45 dias de maturação) durante armazenamento prolongado a 4 ºC. Uma vez estabelecidas a complexidade das relações entre os parâmetros de AP e o queijo, um segundo objetivo foi testar se a aplicação de AP para pré-tratar o leite de ovelha cru, isoladamente ou em combinação com o tratamento com AP dos queijos maturados resultantes poderia melhorar ainda mais a segurança microbiológica sem comprometer os seus atributos únicos de texturae sabor. Para tal, queijos com 45 dias de maturação foram submetidos a AP a 600 MPa/6 min (P1), 450 MPa/6 min (P2) e 450 MPa/9 min (P3). A contagem de células viáveis de lactococos, lactobacilos, enterococos e microrganismos mesófilos totais foram reduzidas em cerca de 4 log ufc/g nos queijos P1 e em 2 log ufc/g nos queijos P2 e P3, comparativamente aos queijos controlo (não processados, ChC). As contagens deEnterobacteriaceaee Pseudomonas spp. mostraram reduções >5 e >4 ciclos logarítmicos, respetivamente, para números abaixo do limite de quantificação durante o armazenamento. De uma forma geral, os índices proteolíticos foram mais baixos nos queijos AP do que nos ChC. Os queijos submetidos à AP nas condições P1 mantiveram o índice de extensão de maturação ao longo dos 15 meses de armazenamento (27-30%) próximo do valor quantificado para o ChCaos 45 dias de maturação (29%), mantendo a textura característica, mas foram considerados mais duros que o ChCdo ponto de vista sensorial. O tratamento AP não causou grandes alterações nem no perfil lipídico do queijo Serra da Estrela(conteúdo total de triglicerídeos (65-66 TG/100 g) e de ácidos gordos) nem nas propriedades nutricionais (índices de aterogenicidade e trombogenicidade similares; ~2,3 e ~2,6, respetivamente). Um estudo complementar foi realizado para análise comparativa de dois sistemas de embalamentono embranquecimento da crosta do queijo: embrulhado em papel sem vácuo (P) e embalado a vácuo em plástico (V), na qualidade de queijos Serra da Estrelapreviamente pasteurizados por AP a 525 MPa/6 min. Queijos controle (ChC) e queijos AP (ChP) foram embalados nesses dois sistemas (ChC+V; ChC+P; ChP+V e ChP+P) e foram conservados sob refrigeração durante 10 meses. Os queijos ChP+V e ResumoIVChP+P continham um número de células viáveis de lactococos, lactobacilos, enterococos e mesófilos totais mais baixo do que os queijos ChC+V e ChC+P, i.e. entre 4 e 6 log ufc/gvs aprox. 6 log ufc/g, respetivamente. Osbolores e leveduras (>5 log ufc/g) proliferaram nos queijos embrulhados em papel. Os queijos ChP+V revelaram um índice de extensão de maturação constante ao longo dos 10 meses de conservação, com valores próximos aos quantificados para queijos ChC+V aos 0meses. Sistema de embalamento em papel pode ser adequado para curtos períodos de conservação, enquanto o sistema a vácuo é preferível para longos períodos. A aplicação de AP ao leite de ovelha cru como pré-tratamento antes da produção de queijo pode levara um aumento no rendimento do queijo e incremento da qualidade. Inicialmente, foi realizado um amplo desenho experimental (200–400 MPa; 5–30 min; 1–48 h de tempo de espera antes da AP; 1–24 h após AP), e os resultados alcançados permitiram identificar quea intensidade da pressão, o tempo sob pressão e o tempo de espera após AP foram os fatores mais importantes. A aplicação do modelo de superfície de resposta (100-300 MPa; 5-30 minutos, 24 horas antes e após AP), visando uma redução tão pequena quanto possível do número de células viáveis de lactococos, lactobacilos e enterococos, permitiu identificar como condições ideais de AP o tratamento de leite a 121 MPa/30 min. O modelo foi validado e um estudo de aumento de escala foi realizado em queijaria, resultando num incremento do rendimento em 10,4% com o leite pré-tratado (MP) por AP em comparação com o queijo produzido com leite não tratado (MC). O leite pré-tratado por AP revelou insignificantes reduções da carga microbiológica no leite e coalhada. Aos 60 dias de maturação, metade dos queijos produzidos com MPe MCforam tratados com AP a 525 MPa/6 min (MP+ChP e MC+ChP, respetivamente) e a outra metade permaneceu como controlo (MP+ChCand MC+ChC, respetivamente). Todos os queijos foram conservados sob refrigeração por 5 meses. A aplicação de AP em queijos maturados causou similares reduções da carga microbiológica às obtidas nos estudos anteriores (1-3 reduções logarítmicas para bactérias ácido lácticas, e abaixo do limite de quantificação para bolores e leveduras, Enterobacteriaceaee Pseudomonassp.). O pré-tratamento com AP levou ao aumento do índice extensão de maturação, enquanto o tratamento AP no queijo manteve o mesmo. O pré-tratamento AP no leite parece melhorar as propriedades tecnológicas do queijo,enquanto a aplicação AP aos queijos maturados pode aumentar a segurança do queijo; o acoplamento de ambas manteve ascaracterísticas inalteradas e, poderá contribuir positivamente para a melhor promoção deste queijo juntodos produtores e consumidores.
Serra da EstrelaCheese is a highly recognized and referenced raw ewes’ milk cheese that is ripened for 45 days, being commercialized thereafter under refrigerated conditions. Being a raw milk cheese changes in microbiological quality may hamper desired prolonged storage. The major aim of this Ph.D thesis was to assess the contributionsthat high pressure processing (HPP), as a cold pasteurisation technology, could have on microbiological load and quality improvement while retaining optimum physicochemical, biochemical, texturaland sensorial quality of Serra da Estrelacheese during extended storage at 4 ºC. Once the complexity of relationships were established between HPP and cheese parameters and associated stability, a second major objective was to test whether the application of HPP to pre-treat the raw ewes milk,alone or in combination with HPP treatment of resulting ripened cheeses before storage, could further enhance microbial safety without compromising their unique texture and flavour attributes. For this,cheeses ripened for45 days underwent HPP at 600 MPa/6 min (P1), 450 MPa/6 min (P2) and 450 MPa/9 min (P3)in order to select the most favourable binomial pressure intensity/holding time. Lactococci, lactobacilli, enterococci and total mesophilic microorganisms were reduced ca. 4 log cfu/g in P1 cheeses and ca. 2 log cfu/g for P2 and P3 cheeses, comparatively to control cheeses (ChC). EnterobacteriaceaeandPseudomonasspp. counts showed > 5 and > 4 log cycle reductions, respectively, tonumbers below the quantificationlimit during storage. The proteolysis indiceswere, in general, lower in HPP cheeses in comparison to ChC. P1 cheeses kept the ripening extension index (27-30%) along the 15 months of storage closer to that reported for ChC(29%) at 45 days of ripening, retaining the characteristic texture, yet being considered harder than ChC from a sensorial point of view. HPP did not cause major changes in Serra da Estrelacheese lipid profilein terms of total triglycerides content (65-66g TG/100 g), esterified and non-esterified fatty acidsand similar atherogenicity and thrombogenicityindices(~2.3 and ~2.6, respectively)were obtained; a high total conjugated linoleic acidcontent (1.29-1.65 g FA/100g fat)wasquantified in all cheeses along storage.Given the whitening of cheesesurfacecolour as a consequence of its vacuum packaging, performed in order to apply HPP, a complimentary study was implemented to comparatively assess the impact of two packaging systems: paper wrapping package without vacuum (P) and packaging in plastic film under vacuum(V), on the quality of Serra da Estrelacheeses previously pasteurized by HPP at 525MPa/6 min. Control (ChC; untreated) and HPP treated (ChP) cheeses packed in either of the two systems (i.e. ChC+V; ChC+P; ChP+V and ChP+P) were stored for 10 months under refrigerated conditions. ChP+V and ChP+P cheeses carried lactococci, lactobacilli, enterococci and total viable bacteriaat lower viable cell numbers than ChC+V and ChC+Pcheesesi.e. between 4 and 6 log cfu/gvs approx. 8 log cfu/g, respectively. Yeasts and moulds proliferated (> 5 log cfu/g) inpaper wrapped cheeses. ChP+V cheeses maintaineda stable ripening extension index throughout storage, with values close to those reported for ChC+V cheeses at 0 months. The non-vacuum paper wrapping was shownadequate for short storage periods (< 3 months), but for long periods the vacuum-packaging in plastic film method is preferable.The application of HPP to raw ewes’ milk as a pre-treatment prior to cheesemaking could prompt an increment in cheese yieldand contribute to a better quality standardization. Hence, a broad screening experimental design was initially performed (200–400 MPa; 5–30 min; 1–48 h waiting time before HPP; 1–24 h after HPP), and results allowed to pinpoint that the pressure intensity, the holding time under pressure, and the time after HPP were the most important factors. The application of a response surface model (100–300 MPa; 5–30 min, 24 h before and after HPP), targeting a small as possible reduction of lactococci, lactobacilli, and enterococci viable cell numbers, identifiedas optimum HPP conditions the treatment of milk at 121 MPa/30 min. The model was validated and a scale-up experiment was performed. In such a real cheese production facility, cheese yield increased by 10.4% with HPP pre-treated milk (MP) in comparison to cheese manufactured from control untreated milk (MC). HPP milk pre-treatment led to small, insignificant reductionsin microbial viable cell numbers in milk and curd. At 60 days of ripening, half of the cheeses made from either MPor MCmilks were HPP treated at 525 MPa/6 min (MP+ChP and MC+ChP, respectively) and the other half remained as control (MP+ChCand MC+ChC, respectively). All cheeses were stored under refrigeration for 5 months. HPP of ripened cheeses was determinant upon reduction of the viable cell numbers of the different microbial groups (between 1 and 3 log cycle reductions for lactic acid bacteria, and to below the quantification limit for yeasts and moulds, Enterobacteriaceaeand Pseudomonassp.).The HPP milk pre-treatment led to an increase of the ripening extensionindex, while the pressure treatment on cheese kept it constant. The HPP milk pre-treatment improvescheese technological properties, while HPP application to ripened cheeses can increase cheese safety; the coupling of both revealed few quality characteristics being changed and undoubtedly could contribute positively to producers’ and consumers’ awareness of such an important cheese
Serra da EstrelaCheese is a highly recognized and referenced raw ewes’ milk cheese that is ripened for 45 days, being commercialized thereafter under refrigerated conditions. Being a raw milk cheese changes in microbiological quality may hamper desired prolonged storage. The major aim of this Ph.D thesis was to assess the contributionsthat high pressure processing (HPP), as a cold pasteurisation technology, could have on microbiological load and quality improvement while retaining optimum physicochemical, biochemical, texturaland sensorial quality of Serra da Estrelacheese during extended storage at 4 ºC. Once the complexity of relationships were established between HPP and cheese parameters and associated stability, a second major objective was to test whether the application of HPP to pre-treat the raw ewes milk,alone or in combination with HPP treatment of resulting ripened cheeses before storage, could further enhance microbial safety without compromising their unique texture and flavour attributes. For this,cheeses ripened for45 days underwent HPP at 600 MPa/6 min (P1), 450 MPa/6 min (P2) and 450 MPa/9 min (P3)in order to select the most favourable binomial pressure intensity/holding time. Lactococci, lactobacilli, enterococci and total mesophilic microorganisms were reduced ca. 4 log cfu/g in P1 cheeses and ca. 2 log cfu/g for P2 and P3 cheeses, comparatively to control cheeses (ChC). EnterobacteriaceaeandPseudomonasspp. counts showed > 5 and > 4 log cycle reductions, respectively, tonumbers below the quantificationlimit during storage. The proteolysis indiceswere, in general, lower in HPP cheeses in comparison to ChC. P1 cheeses kept the ripening extension index (27-30%) along the 15 months of storage closer to that reported for ChC(29%) at 45 days of ripening, retaining the characteristic texture, yet being considered harder than ChC from a sensorial point of view. HPP did not cause major changes in Serra da Estrelacheese lipid profilein terms of total triglycerides content (65-66g TG/100 g), esterified and non-esterified fatty acidsand similar atherogenicity and thrombogenicityindices(~2.3 and ~2.6, respectively)were obtained; a high total conjugated linoleic acidcontent (1.29-1.65 g FA/100g fat)wasquantified in all cheeses along storage.Given the whitening of cheesesurfacecolour as a consequence of its vacuum packaging, performed in order to apply HPP, a complimentary study was implemented to comparatively assess the impact of two packaging systems: paper wrapping package without vacuum (P) and packaging in plastic film under vacuum(V), on the quality of Serra da Estrelacheeses previously pasteurized by HPP at 525MPa/6 min. Control (ChC; untreated) and HPP treated (ChP) cheeses packed in either of the two systems (i.e. ChC+V; ChC+P; ChP+V and ChP+P) were stored for 10 months under refrigerated conditions. ChP+V and ChP+P cheeses carried lactococci, lactobacilli, enterococci and total viable bacteriaat lower viable cell numbers than ChC+V and ChC+Pcheesesi.e. between 4 and 6 log cfu/gvs approx. 8 log cfu/g, respectively. Yeasts and moulds proliferated (> 5 log cfu/g) inpaper wrapped cheeses. ChP+V cheeses maintaineda stable ripening extension index throughout storage, with values close to those reported for ChC+V cheeses at 0 months. The non-vacuum paper wrapping was shownadequate for short storage periods (< 3 months), but for long periods the vacuum-packaging in plastic film method is preferable.The application of HPP to raw ewes’ milk as a pre-treatment prior to cheesemaking could prompt an increment in cheese yieldand contribute to a better quality standardization. Hence, a broad screening experimental design was initially performed (200–400 MPa; 5–30 min; 1–48 h waiting time before HPP; 1–24 h after HPP), and results allowed to pinpoint that the pressure intensity, the holding time under pressure, and the time after HPP were the most important factors. The application of a response surface model (100–300 MPa; 5–30 min, 24 h before and after HPP), targeting a small as possible reduction of lactococci, lactobacilli, and enterococci viable cell numbers, identifiedas optimum HPP conditions the treatment of milk at 121 MPa/30 min. The model was validated and a scale-up experiment was performed. In such a real cheese production facility, cheese yield increased by 10.4% with HPP pre-treated milk (MP) in comparison to cheese manufactured from control untreated milk (MC). HPP milk pre-treatment led to small, insignificant reductionsin microbial viable cell numbers in milk and curd. At 60 days of ripening, half of the cheeses made from either MPor MCmilks were HPP treated at 525 MPa/6 min (MP+ChP and MC+ChP, respectively) and the other half remained as control (MP+ChCand MC+ChC, respectively). All cheeses were stored under refrigeration for 5 months. HPP of ripened cheeses was determinant upon reduction of the viable cell numbers of the different microbial groups (between 1 and 3 log cycle reductions for lactic acid bacteria, and to below the quantification limit for yeasts and moulds, Enterobacteriaceaeand Pseudomonassp.).The HPP milk pre-treatment led to an increase of the ripening extensionindex, while the pressure treatment on cheese kept it constant. The HPP milk pre-treatment improvescheese technological properties, while HPP application to ripened cheeses can increase cheese safety; the coupling of both revealed few quality characteristics being changed and undoubtedly could contribute positively to producers’ and consumers’ awareness of such an important cheese
Description
Keywords
Queijo Serra da Estrela Processamento por alta-pressão Leite cru Segurança alimentar Qualidade do queijo Serra da Estrela cheese High pressure processing Raw milk Food safety Cheese quality