The consumption of seafood in the United States has increased rapidly in recent years due to high quality protein and health benefits of seafood. Seafood can be a carrier for bacteria normally distributed in the marine environment and, in some cases, can be contaminated by human pathogens. Therefore, there is a potential health risk if seafood is consumed raw or undercooked. However, information regarding prevalence of foodborne pathogens in retail seafood products and the ability of pathogens to survive in the products during refrigerated and frozen storage is limited. The objective of this study was to generate such information for a better understanding of distribution of foodborne pathogens in seafood products and provide data which might be used for risk assessment of foodborne infection associated with seafood consumption. A total of 45 seafood products were collected from local retail stores and analyzed for aerobic plate counts (APC) and psychrotrophic bacterial counts (PBC) as well as presence of foodborne pathogens, including Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, Staphylococcus aureus, Vibrio parahaemolyticus, and Vibrio vulnificus according to procedures described in the U.S. Food and Drug and Administration Bacteriological Analytical Manual (BAM). Presumptive isolates for each foodborne pathogen were further characterized by biochemical reactions using commercial identification kits and confirmed with polymerase chain reaction (PCR) assay. The samples had bacterial populations ranging from 1.90 to 6.11 CFU/g for APC and from 2.00 to 6.78 CFU/g for PBC. According to the microbiological criteria of International Commission on Microbiological Specifications for Foods (ICMSF), all 45 samples were considered acceptable quality (APC < 10⁷ CFU/g, E. coli < 3 MPN/g) with most samples (93.3%) being good quality (APC < 5 × 10⁵ CFU/g, E. coli < 3 MPN/g). No E. coli O157:H7, Salmonella, S. aureus, V. parahaemolyticus, and V. vulnificus was detected in any samples. Two previously frozen shrimp products (4.4%) were confirmed to carry L. monocytogenes. Studies of growth and survival of L. monocytogenes (3 strains), S. aureus (2 strains), and Salmonella (2 serovars) in raw yellowfin tuna meat stored at 5 - 7 °C for 14 days revealed that L. monocytogenes had the ability to multiply in the tuna meat during refrigerated storage while populations of S. aureus and Salmonella were reduced by 1 to 2 log CFU/g after 14 days at 5 - 7 °C. Studies of holding raw yellowfin tuna meat contaminated with L. monocytogenes, S. aureus, and Salmonella at -18 ± 2 °C for 12 weeks observed that all three pathogens, except Salmonella Newport, in tuna samples survived the frozen storage with less than 2- log of reductions in the populations over 12 weeks of storage. No viable cell of Salmonella Newport was detected in samples after 42 days storage at -18 °C. Raw seafood can be a carrier of foodborne pathogens, particularly L. monocytogenes, and many foodborne pathogens can survive in frozen products for several months. Consumption of raw or undercooked seafood products may lead to human infection if the products are contaminated with pathogens. Therefore, sanitation standard operating procedure (SSOP), good manufacturing practice (GMP) and hazards analysis and critical control points (HACCPs) programs shall all be implemented in the seafood industry to prevent seafood products from being contaminated with foodborne pathogens during handling and processing. Moreover, proper storage of raw seafood products and avoiding cross-contamination during handling at the retail levels also helps to minimize risk of human infection associated with ready-to-eat products. / Graduation date: 2013

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 4 uppsatser.

No description available.

This work was aimed at studying lipid stability of silver catfish (Rhamdia quelen) fillets. The influence of the inclusion (5%) of soybean or rice oil in silver catfish diet and vacuum packaging on lipid and color stability of raw silver catfish fillets was evaluated during frozen storage (18 months). Besides, the influence of seven cooking methods (boiling, conventional baking, microwave baking, grilling, deep frying in soybean oil, canola oil, or partially hydrogenated vegetable oil) on the oxidation, proximate, and fatty acid composition of fillets was also evaluated. The different diets had no effect on the proximate composition of the fish fillets. The content of thiobarbituric acid reactive substances (TBARS, lipid oxidation index) of fillets from both diets increased after 12 months of storage with or without vacuum, but this increase was higher in fish fed with soybean oil. Color parameters were not affected by the vacuum storage or diet, but most parameters (a*, b*, chroma, and Hue values) were affected by the time of storage. Hue value showed that raw fillets tended to yellowness and after 18 months of frozen storage became greener. The content of various fatty acids in fillets was influenced by the type of vegetable oil used in the diet, but n-3/n-6 polyunsaturated fatty acids ratio and unsaturated/saturated ratio did not differ between diets. All cooking methods evaluated reduced moisture and increased protein content. Fat content was higher in the fried fillets. The free fatty acid content of fillets was significantly reduced by the different cooking methods, while conjugated dienes and peroxide values decreased for all fried samples, but remained constant in the samples submitted to the other cooking methods. Boiling and baking increased TBARS, while grilling and frying did not change TBARS. Boiling, baking, and grilling did not affect the silver catfish fillets fatty acid composition. Frying in canola oil increased n-3/n-6 ratio, in soybean oil increased general polyunsaturated fatty acid content, and in hydrogenated vegetable oil incorporated trans fatty acids in the fillets. Results indicated that fillets from silver catfish fed diets with soybean or rice oil have different lipid profile and lipid stability during frozen storage. Frying silver catfish fillets in canola oil could increase the low n-3/n-6 polyunsaturated fatty acids ratio of raw silver catfish fillets. / O presente trabalho teve por objetivo estudar a estabilidade lipídica de filés de jundiá (Rhamdia quelen). Foi avaliada a influência da inclusão (5%) de óleo de soja ou arroz na dieta do jundiá, e a embalagem a vácuo, sobre a estabilidade lipídica e a cor de filés crus congelados (18 meses). Avaliou-se também a influência de sete métodos de cocção (cozido em água, assado em forno convencional ou microondas, grelhado, ou frito em óleo de soja, arroz ou gordura vegetal hidrogenada) sobre a oxidação, a composição centesimal e de ácidos graxos de filés de jundiá. Não houve diferença na composição centesimal dos filés entre as dietas. O conteúdo de substâncias reativas ao ácido tiobarbitúrico (TBARS, índice de lipoperoxidação) aumentou nos filés dos peixes de ambas as dietas, após 12 meses de armazenamento congelado, tanto nos filés embalados com ou sem vácuo. Esse aumento foi mais acentuado nos filés dos peixes alimentados com dietas contendo óleo de soja. Os parâmetros de cor não foram afetados pela embalagem a vácuo ou pela dieta, mas a maioria dos parâmetros (a*, b*, croma e ângulo de matiz), foi afetada pelo tempo de estocagem. O valor de ângulo de matiz mostrou que os filés crus tendiam ao amarelo, e após 18 meses de armazenamento congelado tenderam ao verde. O conteúdo de vários ácidos graxos nos filés foi influenciado pelo tipo de óleo vegetal utilizado na dieta, porém a razão dos ácidos graxos poliinsaturados n-3/n-6 e insaturados/saturados não diferiu entre as dietas. Todos os métodos de processamento térmico avaliados reduziram a umidade e aumentaram o conteúdo de proteína dos filés. O teor de gorduras foi maior nos filés fritos. O conteúdo de ácidos graxos livres dos filés foi significativamente reduzido pelos diferentes métodos de processamento térmico, enquanto os teores de dienos conjugados e peróxidos diminuíram em todas as amostras submetidas à fritura, mas permaneceram constantes nas amostras submetidas aos demais métodos de processamento térmico. Nos filés cozidos e assados observou-se aumento dos teores de TBARS, enquanto os grelhados e fritos não sofreram alteração neste parâmetro. A composição de ácidos graxos dos filés de jundiá cozidos, assados e grelhados não foi alterada pelo tratamento térmico. A fritura em óleo de canola aumentou a razão n-3/n-6, enquanto que a fritura em óleo de soja aumentou o conteúdo total de ácidos graxos poliinsaturados, e a fritura em gordura vegetal hidrogenada incorporou ácidos graxos trans aos filés. Os resultados indicam que os filés de jundiá alimentados com dietas contendo óleo de soja ou de arroz tiveram perfil lipídico e estabilidade lipídica diferente durante o armazenamento congelado. A fritura dos filés de jundiá em óleo de canola poderia aumentar a razão de ácidos graxos poliinsaturados n-3/n-6, que é baixa nos filés de jundiá crus.

Les pâtes surgelées sont relativement stables et peuvent être fabriquées à l’échelle industrielle, distribuées et cuites à la demande au moment de la vente ou de la consommation (point chaud). La congélation des pâtes sucrées induit une baisse de volume et une augmentation du temps de fermentation, ces conséquences sont dues à deux facteurs : la baisse de la production de CO2 (viabilité des levures) et la faible capacité de rétention de gaz du réseau gluténique. La perte de la qualité des pâtes congelées est accélérée durant le stockage. Cette thèse porte sur l’étude de l’effet de la congélation et de la conservation sur les levures et les propriétés techno-fonctionnelles des pâtes sucrées type Kougelhopf. Ce travail vise à l’étude de l’impact de la vitesse de congélation sur les propriétés microbiologiques, rhéologiques, structurales et sensorielles de ces pâtes. Elles ont été congelées à différentes températures (-20 °C, -30 °C, -40 °C et une immersion dans l'azote liquide) puis conservées à -40 °C pendant 9 semaines. Les principaux résultats de cette étude ont permis de mettre en évidence le rôle de la vitesse de congélation et de la durée de conservation sur les propriétés intrinsèques des pâtes sucrées surgelées. Il en découle que l’activité fermentaire et l’intégrité du réseau du gluten sont tributaire de la vitesse de congélation. En effet, cette dernière contrôle la taille et la localisation des cristaux de glace d’où la recherche d’un compromis entre une vitesse de congélation ni trop rapide pour diminuer la viabilité des levures ni trop lente pour former de gros cristaux pouvant perforer le réseau de gluten de la pâte. Ce travail a démontré que le surdosage de levure reste valable uniquement pour les pâtes sucrées surgelées destinées à être conservées au-delà de 4 semaines. Ce surdosage améliore ainsi la qualité globale du Kougelhopf en compensant la perte de l'activité des levures pendant la congélation et le stockage / The frozen doughs are relatively stable and can be manufactured on an industrial scale, distributed and baked on demand at the point of sale or consumption (Bake-off). Freezing sweet dough induces a decrease in specific volume and an increase in fermentation time, these effects are due to two factors: lower production of CO2 (yeast viability) and losing capacity to retain gas (gluten network integrity). The loss of quality of frozen dough is accelerated during storage. This study focuses on the freezing and frozen storage effects on Kougelhopf sweet doughs. The aim of this work is to study the impact of freezing rate on microbiological, rheological, structural, and sensory properties of sweet doughs. The sweet doughs were frozen at different temperatures (-20°C, -30°C, -40°C and an immersion in liquid nitrogen) and stored at -40°C for 9 weeks. The main results obtained showed an impact of freezing rate and frozen storage duration on the frozen doughs intrinsic properties. This study shown the dependence of fermentation activity and integrity of the gluten network with freezing rate, which controls size and location of ice crystals resulting in research of a compromise between freezing rate nor too fast to reduce yeast viability, nor too slow to form large ice crystals that could perforate gluten network. Added the yeast amount is necessary only for frozen sweet doughs to be stored beyond 4 weeks, which improves the overall quality of Kougelhopf by compensating for yeast activity decrease during freezing and frozen storage