The presence of off-flavor compounds in fish represents one of the significant economic problems encountered in aquaculture. These off-flavor compounds are due to the absorption of substances produced by microorganisms. Currently, a number of strategies have been employed to prevent or limit the growth of these microorganisms in recirculating aquaculture system. Therefore, it is important to evaluate the effectiveness of these strategies by monitoring the concentrations of off-flavor compounds in fish. In-vivo solid phase microextraction (SPME), a rapid and simple sample preparation method, allows the monitoring of concentrations of off-flavor compounds in live fish. In this research, geosmin and 2-methylisoborneol (2-MIB), which are produced by cyanobacteria and actinomycetes being the major sources for “earthy” and “muddy” flavors in fish, were selected as representatives. In order to accurately quantify these compounds in fish muscle, two kinetic calibration methods, on-fibre standardization and measurement using pre-determined extraction rate, were used. Results obtained were validated by traditional methods. The detection limit of in-vivo SPME in fish muscle was 0.12 ng/g for geosmin and 0.21 ng/g for 2-MIB, both below the human sensory threshold. Additionally, the binding effect of geosmin and 2-MIB in fish muscle was investigated in details. Facilitated by the agarose gel model, it was proven that binding did not impact the extraction rate under the pre-determined sampling time. Furthermore, an optional sampling position was undertaken by inserting the fibre into the fat tissue found under the fish belly, the results indicating that this method could decrease extraction time by up to two-thirds of its usual time.

The presence of off-flavor compounds in fish represents one of the significant economic problems encountered in aquaculture. These off-flavor compounds are due to the absorption of substances produced by microorganisms. Currently, a number of strategies have been employed to prevent or limit the growth of these microorganisms in recirculating aquaculture system. Therefore, it is important to evaluate the effectiveness of these strategies by monitoring the concentrations of off-flavor compounds in fish. In-vivo solid phase microextraction (SPME), a rapid and simple sample preparation method, allows the monitoring of concentrations of off-flavor compounds in live fish. In this research, geosmin and 2-methylisoborneol (2-MIB), which are produced by cyanobacteria and actinomycetes being the major sources for “earthy” and “muddy” flavors in fish, were selected as representatives. In order to accurately quantify these compounds in fish muscle, two kinetic calibration methods, on-fibre standardization and measurement using pre-determined extraction rate, were used. Results obtained were validated by traditional methods. The detection limit of in-vivo SPME in fish muscle was 0.12 ng/g for geosmin and 0.21 ng/g for 2-MIB, both below the human sensory threshold. Additionally, the binding effect of geosmin and 2-MIB in fish muscle was investigated in details. Facilitated by the agarose gel model, it was proven that binding did not impact the extraction rate under the pre-determined sampling time. Furthermore, an optional sampling position was undertaken by inserting the fibre into the fat tissue found under the fish belly, the results indicating that this method could decrease extraction time by up to two-thirds of its usual time.

No description available.

京都大学 / 新制・課程博士 / 博士(農学) / 甲第24110号 / 農博第2515号 / 新制||農||1093(附属図書館) / 学位論文||R4||N5401(農学部図書室) / 京都大学大学院農学研究科食品生物科学専攻 / (主査)教授 井上 和生, 教授 谷 史人, 准教授 後藤 剛 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

No description available.

The use of slower acid-producing starter bacteria for the production of lower fat Cheddar cheese has lead to milder flavor Cheddar cheeses that lack intense Cheddar notes. The metabolism of methionine leads to the production of methanethiol, which is one of the desirable Cheddar cheese flavor compounds. The influence of NaCl and reduced pH was determined for aminopeptidase, lipase/ esterase, and methanethiol-producing capability in selected lactic acid bacteria and brevibacteria in simulated cheese-like conditions. The activity of each enzyme decreased with NaCl addition and pH reduction to approximate a Cheddar cheese environment (5% NaCl and pH 5.2). The mechanism for methanethiol production by the starter and adjunct bacteria was also investigated. Different enzyme systems were found to be responsible for methanethiol production in starter lactococci, lactobacilli, and brevibacteria. In the lactococci, enzymes that acted primarily on cystathionine were responsible for methanethiol production from methionine. Lactobacilli also contained cystathionine-degrading enzymes, but these enzymes have properties different from the lactococcal enzymes. Brevibacterium linensBL2 lacked cystathionine-degrading enzymes, but was capable of the direct conversion of methionine to methanethiol. L-Methionine γ-lyase from B. linens BL2 was purified to homogeneity, and was found to catalyze the α, γ elimination of methionine resulting in the production of methanethiol, α-ketobutyrate, and ammonia. Characterization of the pure enzyme demonstrated that it is pyridoxal phosphate dependent, which is active at salt and pH conditions existing in ripening Cheddar cheese. The addition of either B. linens BL2 or L-methionine γ-lyase to aseptic cheese curd slurries increased methanethiol and total volatile sulfur compound production. In an attempt to increase methanethiol production and Cheddar cheese flavor in reduced-fat Cheddar cheese, B. linens BL2 was added as a starter adjunct to 60% reduced-fat cheese. Sensory evaluation of the cheese indicated that B. linens BL2 improved the flavor of 60% reduced-fat Cheddar cheese. This suggests that the addition of B. linens BL2 is an alternative to the addition of lactic acid bacteria to improve Cheddar cheese flavor via the metabolism of methionine.

Ces travaux portent sur l’étude du transfert de l’arôme viennoiserie encapsulé dans une matrice constituée du mélange gomme acacia – maltodextrines et incorporé dans une génoise emballée (plastiques et papier), dans des conditions contrôlées de stockage (humidité relative et température). Le procédé d’encapsulation utilisé dans cette étude est la lyophilisation. Les propriétés physicochimiques des molécules volatiles influencent leur rétention. Ainsi, les molécules hydrophobes à haut poids moléculaire sont mieux conservées dans ce système. L’incorporation de capsules d’arômes dans les génoises influence leurs propriétés physiques (la couleur et la texture) et favorise la formation d’une croûte pouvant jouer un rôle barrière sur les transferts d’arômes. Au cours du stockage des génoises emballées, l’apport positif de l’encapsulation sur la rétention des arômes a été révélé. Le type d’emballage peut influencer la perte en composés d’arôme dans l’espace de tête génoise – emballage. Ainsi, les emballages plastiques offrent une meilleure conservation des molécules volatiles par rapport aux papiers traités / This study deals with transfer of viennoiserie aroma encapsulated in a acacia gum - maltodextrines matrix and incorporated in a packaged sponge cake (plastic and treated-paper), under controlled storage conditions (temperature and relative humidity). The process of encapsulation used in this work is freeze-drying. The physicochemical properties of the volatiles molecules influence their retention in the matrix. Thus, the hydrophobic molecules with high molecular weight are more retained. The incorporation of capsules in the sponge cake matrix influences the physical properties of food matrix (color and texture) and supports the formation of a crust which acts as a barrier in the flavour transfer. It was noted that encapsulation contributed in retaining flavour compounds during the storage of packaged sponge cake. Also, the type of packaging can influence the loss of flavour in the headspace between sponge cake and packaging. Indeed, plastic packaging offers a better conservation of volatiles molecules compared to treated-papers

The relationships between volatile flavor compounds, sensory descriptors and consumer acceptability were determined for eight commercial American dry-cured hams using external preference and flavor mapping. The majority of consumers preferred (p<0.05) hams that had more intense caramelized, smoky, savory and molasses aromas as well as more intense sweet and savory flavors. Sixteen aroma impact compounds were identified from the headspace volatiles of dry-cured hams. The consumers with the highest acceptability scores preferred (p<0.05) hams that were characterized by 4-methyl-2-methoxyphenol (sweet ham), 4-ethyl-2-methoxyphenol (sweet ham), 2-methoxyphenol (smoky, cocoa), 2,6-dimethoxyphenol (smoky ham, savory) and 2uranmethanol (burnt meat, vitamin). Fourteen percent of consumers preferred (p<0.05) two hams that were characterized by methional (baked potato). Consumer acceptability scores were lower for hams either characterized by methanethiol (sulfur), carbon disulfide (sulfur), 2-butanone (sweet), 3-methylbutanal (malty, fermented), 2-heptanone (burnt meat, vitamin), hexanal (cut grass), benzeneacetaldehyde (floral), 1-octen-3-ol (mushroom) or characterized by benzaldehyde (burnt meat, cooked meat) and limonene (citrus).

No description available.

Au cours des dernières années, les autorités sanitaires ont recommandé une réduction de la teneur en sel et en gras dans la consommation alimentaire quotidienne. Cependant, les aliments à teneur réduite en sel et en gras sont souvent peu appréciés par les consommateurs, ce qui a amené au développement des recherches sur les stratégies possibles pour maintenir l’acceptabilité des aliments tout en réduisant les teneurs en ces ingrédients. Dans cette thèse, l’intégration multi-sensorielle et les cinétiques de libération du sel et des arômes mesurées in vitro ont été étudiés pour évaluer leur potentialité à compenser une réduction en sel et matière grasse d’un fromage modèle de composition variable et d’un fromage réel (type trappiste).Dans une première étape, une approche sensorielle a permis d’étudier les interactions multi-sensorielles arômes-saveurs-texture pour les formages modèles et réels. La structure et la perception sensorielle de vingt-quatre modèles fromagers variant en composition (2 niveaux de gras, 2 de sel, 2 de pH à l’emprésurage) et aromatisés avec un arôme de sardine (associé au sel), d'un arôme de beurre (associé au gras) ou non aromatisés (témoin) ont été caractérisés par des mesures rhéologiques (compression uniaxiale) et des mesures sensorielles (profil descriptif). Les résultats ont montré une influence de la composition sur la structure et la texture perçue des produits. Par ailleurs, l’arôme sardine a conduit à une perception plus salé ; l’arôme de beurre a permis de renforcer la perception du caractère gras. Toutefois cette influence des arômes sur les autres dimensions sensorielles est fonction de la texture des produits donc de leur composition et de leur structure. Ces résultats ont été étendus à des fromages réels avec toutefois des spécificités. Si l’arôme sardine renforce la perception du sel, seul l’arôme de beurre associé à l’arôme de sardine permet de renforcer le caractère gras.Dans une deuxième étape, une approche physico-chimique a été développée pour explorer les cinétiques de libération des stimuli odorants et sapides dans des conditions simulant la mastication in vitro à l’aide d’un simulateur de mastication. L’objectif était d’utiliser les données ainsi obtenues pour expliquer l’influence de la structure des produits et de leur déstructuration lors de la mastication sur les effets sensoriels observés dans la première étape. Les modèles fromagers et les fromages réels ont été ainsi étudiés. La libération des composés volatils a été évaluée en connectant le simulateur de mastication à un spectromètre de masse à pression atmosphérique (PTR-MS) ; la libération du sodium a été suivie grâce à une sonde de conductivité. Les résultats ont montré une influence des trois paramètres de composition (teneur en matière grasse, en sel et pH à l’emprésurage) sur les cinétiques de la libération des arômes. Cette variation dépend néanmoins de la nature de l’arôme suivi ; les arômes plus hydrophobes étant moins sensibles aux variations de la teneur en matière grasse et plus sensibles aux variations de pH et donc à la structure du produit. La cinétique de libération du sel lors de la mastication in vitro est aussi largement influencée par la composition et la structure des produits. Outre la teneur en sel qui conditionne les quantités libérées, la teneur en matière grasse et le pH à l’emprésurage module la cinétique de libération du sel. Au final, ces travaux montrent une importante contribution de la cinétique de libération et donc probablement de la temporalité des sensations dans perception globale du sel et de la matière grasse lors de la consommation d’un aliment complexe. / In recent years, health authorities worldwide advise for a reduction of salt and fat in daily food consumption. However, foods with reduced salt and fat content are often not appreciated by consumers, Therefore, the formulation of low-salt-fat foods that maintain acceptability is a major concern in food research. In this thesis, the multi-sensory integration and release kinetics of flavor compounds were explored as strategies to compensate for salt and fat reduction in cheese products (model cheeses and real cheeses). The objective was to better understand the mechanisms leading to aroma and salt release during mastication and to evaluate how the matrix composition and structure influence salt and aroma release profile.Multisensory integration approach to compensate for salt and fat reduction was studied in a first step. The structure and sensory perception of 24 cheese models varying in composition (2 levels of fat, 2 salt, 2 pH at renneting) and flavored with either a sardine aroma (associated to salt), a butter aroma (associated to fat) or not flavoured (control) were characterised by rheological measurements (uniaxial compression) and sensory evaluation (descriptive analysis). The results demonstrated an influence of the composition on the products structure and perceived texture. Furthermore, a significant saltiness enhancement was induced by sardine aroma while significant fat perception enhancement was induced by butter aroma. However, this influence of the aroma on other sensory dimensions depends on the texture of the products thus on their composition and structure. These results have been extended to real cheeses but with specificities. If the sardine flavor enhanced the perception of salt, only butter-sardine-flavor enhanced the perception of fat.In a second step, a physico-chemical approach was developed to explore the release kinetic of flavor compounds during in vitro breakdown using a chewing simulator. The aim was to use these data to explain the influence of the structure of model cheeses and real cheeses and their breakdown during chewing on sensory effects observed in the first step. Volatile compounds release was monitored by connecting the chewing simulator to a proton transfer reaction-mass spectrometry (PTR-MS), while salt release was monitored using a conductivity probe. Results showed that product composition and structure (fat, salt and pH at renneting) influenced aroma release, which however depends on the nature of the aroma: the more hydrophobic compounds are less sensitive to variations in fat content and more sensitive to variations in pH and therefore to the products structure. The salt release kinetic during in vitro chewing was also influenced by the composition and structure of the products. Indeed, beyond salt content which determined the amount of salt released, fat content and the pH at renneting modulated the release kinetic. In conclusion, this work showed a significant impact of the flavor compounds release kinetic and probably of temporality of sensations on the overall perception of salt and fat when consuming a complex food.