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The microbial stability of refrigerated intermediate moisture foodsLi, Ken-yuon 05 August 1988 (has links)
The lag phase, the specific growth rate, the minimum a [subscript w]
required for growth and the temperature characteristic of
Fsendomonas fluorescens, Brochothrix thermosphacta, Salmonella
typhlmurium, Streptococcus faecalis and, Staphylococcus aureus
have been studied in liquid model media under controlled temperature
and a [subscript w] conditions. The results show that the lag phase increases
and the specific growth rates decreases when the temperature is
lowered or the a [subscript w] is reduced. The minimum a [subscript w] required for growth
increases when the incubation temperature is lowered. At
refrigeration temperature the minimum a [subscript w] for growth of mesophiles
is higher than that of psychrotrophs. The temperature characteristic (representing the activation energy for growth) of psychrotrophs is lower than that of mesophiles, and therefore mesophiles are more
sensitive to temperature changes. All of these growth parameters
depend on the a [subscript w] controlling solute. The solute effect can be
traced to the ability of the solute to penetrate into the cell and
can be explained by the osmoregulatory mechanism. In general, it was
found that the effect of the solute on these parameters had the order
glycerol<NaCl<sucrose.
A comparison of three models for the effect of temperature on
growth rate (linear, square-root, and Arrhenius) showed that the
linear model had both the advantage of simplicity and accuracy. In
general, the Arrhenius model showed the poorest fit to experimental
data.
A predictive method was developed to assess the microbial
stability of liquid model systems exposed to fluctuating
temperatures. The strategy was to predict lag time and growth rate
by different regression equations, and to estimate microbial growth
using an integral function of the accumulated time. A lag time
predictive model was developed using a linear relationship between
lag time and reciprocal growth rate. A linear equation was used to
predict growth rate as a function of temperature. The model was used
to predict the growth of B. thermosphacta in liquid model media
with low a [subscript w] and exposed to fluctuating temperatures. The
predictions were acceptable at a 95% confidence level. This method
will be used in future studies to predict the microbial stability of
refrigerated foods exposed to temperature abuse. / Graduation date: 1989
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The stability and oxygen consumption of retinol at low water activityGuevara-Lequay, L. V. January 1985 (has links)
No description available.
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Estudo dos métodos para a medida da atividade de água.Ditchfield, Cynthia 01 September 2000 (has links)
A atividade de água é um dos parâmetros mais mportantes para a indústria de alimentos. Existem muitos métodos para a medida da atividade de água e cada um tem suas limitações. Foram analisados os diversos métodos existentes para a medida da atividade de água, considerando-se seu princípio de funcionamento, o manuseio do equipamento, o tempo para realização da medida, a faixa de medida, a calibração do equipamento, a repetibilidade e reprodutibilidade e o custo do equipamento. Foram comparados dados da atividade de água de soluções saturadas e insaturadas de sais e de soluções de ácido sulfúrico de várias referências. O objetivo foi uniformizar os padrões adotados nos diversos métodos de medida da atividade de água. Não apenas, são apresentados os modelos matemáticos de Brunauer, Emmett e Teller e o de Guggenheim, Anderson e De Boer, para aproximar isotermas de sorção, mas também, são analisadas as aplicações das medidas da atividade de água e isotermas de sorção de água em alimentos. Os melhores métodos existentes atualmente são o higrômetro eletrônico e o higrômetro de ponto de orvalho. A principal desvantagem desses métodos é seu custo elevado, o que os torna inacessíveis a uma parcela significativa da indústria de alimentos brasileira. Um novo método foi proposto para ser usado na indústria e deve reunir as características de rapidez suficiente e baixo custo. / Water activity is one of the most important parameters for the food industry. There are many methods to measure water activity and each one of them has its handicaps. Several of the available methods to measure water activity were studied considering their technical details, handling of the equipment, measurement speed, measurement range, calibration of the equipment, repeatability and reproducibility and cost. Water activity data of saturated and unsaturated salt solutions and sulphuric acid solutions from various sources are compared. The purpose is to provide standards to be adopted by the different methods to measure water activity. The mathematical models of Brunauer, Emmett and Teller and Guggenheim, Anderson and De Boer for estimating sorption isotherms are presented. The many uses of water activity and sorption isotherms are also discussed. The best methods to measure water activity that exist nowadays are the electric hygrometers and the dew point hygrometer. The main disadvantage of these methods is that their cost is far too high for a significant part of the Brazilian food industry. A new method to measure water activity is proposed that should combine the speed required by the food industry and a low cost.
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Estudo dos métodos para a medida da atividade de água.Cynthia Ditchfield 01 September 2000 (has links)
A atividade de água é um dos parâmetros mais mportantes para a indústria de alimentos. Existem muitos métodos para a medida da atividade de água e cada um tem suas limitações. Foram analisados os diversos métodos existentes para a medida da atividade de água, considerando-se seu princípio de funcionamento, o manuseio do equipamento, o tempo para realização da medida, a faixa de medida, a calibração do equipamento, a repetibilidade e reprodutibilidade e o custo do equipamento. Foram comparados dados da atividade de água de soluções saturadas e insaturadas de sais e de soluções de ácido sulfúrico de várias referências. O objetivo foi uniformizar os padrões adotados nos diversos métodos de medida da atividade de água. Não apenas, são apresentados os modelos matemáticos de Brunauer, Emmett e Teller e o de Guggenheim, Anderson e De Boer, para aproximar isotermas de sorção, mas também, são analisadas as aplicações das medidas da atividade de água e isotermas de sorção de água em alimentos. Os melhores métodos existentes atualmente são o higrômetro eletrônico e o higrômetro de ponto de orvalho. A principal desvantagem desses métodos é seu custo elevado, o que os torna inacessíveis a uma parcela significativa da indústria de alimentos brasileira. Um novo método foi proposto para ser usado na indústria e deve reunir as características de rapidez suficiente e baixo custo. / Water activity is one of the most important parameters for the food industry. There are many methods to measure water activity and each one of them has its handicaps. Several of the available methods to measure water activity were studied considering their technical details, handling of the equipment, measurement speed, measurement range, calibration of the equipment, repeatability and reproducibility and cost. Water activity data of saturated and unsaturated salt solutions and sulphuric acid solutions from various sources are compared. The purpose is to provide standards to be adopted by the different methods to measure water activity. The mathematical models of Brunauer, Emmett and Teller and Guggenheim, Anderson and De Boer for estimating sorption isotherms are presented. The many uses of water activity and sorption isotherms are also discussed. The best methods to measure water activity that exist nowadays are the electric hygrometers and the dew point hygrometer. The main disadvantage of these methods is that their cost is far too high for a significant part of the Brazilian food industry. A new method to measure water activity is proposed that should combine the speed required by the food industry and a low cost.
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Characterisation of Stachybotrys chartarum from water damaged buildingsFrazer, Schale January 2011 (has links)
Fungal contaminated buildings and related adverse human health implications have long been a topical issue throughout the world and concern is mounting with regards to the presence of more toxigenic fungi found in buildings and the associated health risks. These risks are compounded when homes are affected by water damage as a result of water intrusion problems, in particular flooding. With the ever changing climate and unpredictable weather conditions the frequency of flash flooding has increased in recent years and is set to increase and subsequently more homes will inevitably be effected by mould contamination. The present study initially aimed to determine the types of fungi commonly detected in buildings in the United Kingdom with varied levels of water intrusion problems via a small survey using various sampling techniques and particularly aimed to determine the conditions by which growth of the toxigenic fungi Stachybotrys chartarum could occur. Penicillium, Cladosporium and Aspergillus species were the most commonly detected fungi in buildings with relatively moderate levels of water intrusion problems; Stacybotrys chartarum was only detected in building with more severe water intrusion problems. Cont/d.
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Crystallization of pseudopolymorphic forms of sodium naproxen in mixed solvent systemsChavez, Krystle J. 22 June 2009 (has links)
Several pseudopolymorphic forms of sodium naproxen were crystallized from methanol-water and ethanol-water solutions, including hydrated and alcohol-solvated forms. Results showed that the transitions of the pseudopolymorphic forms occur at temperatures that depend upon the solvent concentration. Results also revealed that water activity is a controlling factor for the transitions because regardless of which alcohol solvent mixture was used. The heats of solution for each pseudopolymorph were estimated by fitting the solubility data with the van't Hoff equation. The stability of hydrated forms over solvated forms at higher temperatures was proven for enantiotropic systems from a thermodynamic cycle.
A 1:1 methanol-solvated form of sodium naproxen was discovered and fully characterized using a variety of analytical techniques. For further analysis, a single crystal was performed and revealed a two to three ratio solvate of sodium naproxen to methanol. The 1.5 solvate was shown to not be representative of the entire sample, but still provided insight into the bonding of the methanol solvent in sodium naproxen. Additionally, the ability of sodium naproxen to solvate with other alcohol solvents was explored, specifically looking at comparisons between pure ethanol, 1-propanol, 2-propanol, 1-butanol, and isobutanol solvents. It was shown that as the size of the alcohol increases and/or branching increases the ability to solvate decreases in relation to the molar amount of the alcohol present in the crystal structure. Additionally larger, branched alcohols required more energy to desolvate.
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Studies on drying of sugar solutions and stabilization of dried foods by sugars / 糖溶液の乾燥と糖による乾燥食品の安定化に関する研究Fujii, Sachie 23 July 2014 (has links)
京都大学 / 0048 / 新制・論文博士 / 博士(農学) / 乙第12849号 / 論農博第2801号 / 新制||農||1027(附属図書館) / 学位論文||H26||N4866(農学部図書室) / 31432 / (主査)教授 安達 修二, 教授 保川 清, 教授 谷 史人 / 学位規則第4条第2項該当 / Doctor of Agricultural Science / Kyoto University / DFAM
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Influence of water activity on processing resistance of Salmonella serovars and implications on sanitization of pistachios by heat and ozonePena-Melendez, Marilia 19 December 2011 (has links)
No description available.
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Recovery of Salmonella from Steam and Ethylene Oxide-Treated Spices Using Supplemented Agar with OverlayCaver, Christopher Branden 06 July 2016 (has links)
Salmonella enterica has been associated with several outbreaks due to consumption of low water activity foods including spices. Consequently, to improve microbiological quality, spices are commonly treated before ultimately reaching consumers. These processes may result in sub-lethal injury to cells, which can lead to an underestimation of microbial populations when plating on selective media. Sub-lethally injured cells are difficult to enumerate due to reduced ability to grow on selective microbiological media. Poor recovery of sub-lethally-injured cells may obscure process validation results and lead to overestimation of process effect. Therefore, this work was performed to determine the influence of agar overlay and media supplementation methods on the recovery of Salmonella from steam and ethylene oxide treated peppercorns and cumin seeds. Traditional agar overlay allowed recovery of significantly more Salmonella (p < 0.05) from inoculated peppercorns treated with steam (65.5C, 15 sec.) than selective media (XLT4) or solid agar overlay. Additional supplementation of the TSA base to contain 3,3'-thiodipropionic acid further improved Salmonella recovery from steam treated peppercorns (p < 0.05). For peppercorns and cumin seeds subjected to ethylene oxide, neither sodium pyruvate + yeast extract, 3,3'-thiodipropionic acid, glycerophosphate, ATP, nor magnesium enhanced recovery compared to overlay alone but both methods recovered significantly higher numbers than XLT-4 alone (p < 0.05) for both cumin seeds and peppercorns. / Master of Science in Life Sciences
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Impacts of inoculation strategy on survival of Salmonella enterica and Enterococcus faecium at low water activity on dry peppercorn and cumin seedsBowman, Lauren Stewart 05 November 2015 (has links)
Salmonella contamination of spices and other low water activity foods is a growing concern for the food industry due to increased frequency of salmonellosis outbreaks and detection-based product recalls. The impact of inoculation preparation on the survival of a Salmonella enterica and its proposed surrogate, Enterococcus faecium NRRL B-2385, on the whole black peppercorns and cumin seeds was examined. Three liquid inoculation methods (biofilm-inclusion, agar-grown, broth-grown) for Salmonella enterica and surrogate Enterococcus faecium and one dry transfer method for Salmonella enterica were developed then applied to whole peppercorn and cumin seeds. Spices were returned to original water activity (aw 0.3) and stored for 28 days with periodic sampling (0, 1, 7, 14, 21, 28 days) and surviving bacteria enumerated. Average log reductions (LR) over time were statistically analyzed to determine differences in stability during storage. Inoculation preparation was associated with significant differences in recovered Salmonella and Enterococcus from both peppercorn and cumin over the storage period. At 28 days, the most stable inoculations of Salmonella resulted from the biofilm-inclusion (-0.04 CFU/g LR) and agar grown (-0.75 CFU/g LR) methods on peppercorn and the biofilm inclusion method (-0.28 CFU/g LR) on cumin. Log reductions of Enterococcus faecium (-0.02 CFU/g LR biofilm-inclusion-peppercorn, -0.19 CFU/g LR agar-grown-peppercorn, -0.61 CFU/g LR biofilm-inclusion-cumin) were comparable to Salmonella after 28d desiccated storage. These results will guide the inoculation strategies for validating inactivation processes for reducing Salmonella on whole spices, and for comparisons of inactivation of Salmonella and its proposed surrogate Enterococcus faecium. / Master of Science in Life Sciences
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