Добірка наукової літератури з теми "Spoilage microorganisms"

Thesis (MScAgric (Viticulture and Oenology))--Stellenbosch University, 2008.
The production of good quality wine is essential to ensure competitiveness on an international level. Wine quality is usually evaluated for the visual, olfactory and taste characteristics of that specific wine. The winemaking process starts with the grapes in the vineyard followed by oenological practises in the winery until the final wine is bottled. Factors that could influence wine quality include the grape quality from which the wine is made and different techniques used during wine production. Other factors include the presence as well as the interaction between microorganisms found in the grape juice and wine, and the biochemical effect these microorganisms have on certain chemical compounds in the wine. The different microorganisms found in grape juice and wine can either have a negative or positive contribution to the final quality of the wine. During certain stages of the winemaking process the growth and metabolic activity of certain microorganisms is a necessity to produce good wine. During other stages the presence of certain microorganisms can lead to the development of compounds that is regarded as off-flavours and therefore lead to unpalatable wines of low quality. Yeast strains that naturally present on the grapes and in the winery can also contribute to the final quality of the wine. Brettanomyces yeasts are part of the natural flora of winemaking and can drastically influence the aroma characters of a wine through the production of volatile phenols. The general aroma descriptions of volatile phenols include "smoky", "spicy", "barnyard", "animal" and "medicinal". Although some wine drinkers believe that these characters can add to the complexity of a wine, high levels of volatile phenols is mostly regarded as off-flavours and mask the natural fruity flavours of a wine. With this study we wanted to generate a better understanding of the effect of different winemaking practises on the production of volatile phenols by B. bruxellensis. We evaluated the difference in volatile phenol production when B. bruxellensis was introduced before or after alcoholic fermentation. We have shown that B. bruxellensis could grow and produce volatile phenols during alcoholic fermentation. Results obtained also showed that commercial wine yeast strains could produce the vinyl derivatives that serve as precursors for Brettanomyces yeast to produce the ethyl derivatives. The commercial yeast strains differed in their ability to produce vinyl derivatives. Different malolactic fermentation scenarios were evaluated, namely spontaneous versus inoculated, and with or without yeast lees. Results showed that spontaneous malolactic fermentation had higher volatile phenol levels in the wine than inoculated malolactic fermentation. The treatment with lees reduced the level of volatile phenols, probably due to absorption by yeast cells. The presence of the phenyl acrylic decarboxylase (PAD1) gene and the production of volatile phenols by S. cerevisiae commercial yeast strains were evaluated in Shiraz grape juice and in synthetic grape juice. The results indicated that the yeast strains differ in their ability to produce 4-vinylphenol and 4-vinylguaiacol. All the yeast strains tested had the PAD1 gene. We also evaluated the presence of the phenolic acid decarboxylase (padA) gene and the ability of different lactic acid bacteria strains to produce volatile phenols in synthetic wine media. Although some of these strains tested positive for the phenolic acid decarboxylase gene most of them only produced very low levels of volatile phenols. This study made a valuable contribution on the knowledge about the effect of Brettanomyces yeast on the volatile phenol content of red wines during different stages of the winemaking process and when applying different winemaking practices. It also showed the effect between Brettanomyces yeast and other wine microorganisms and the possible influence it could have on the final quality of wine. Research such as this can therefore aid the winemaker in making certain decisions when trying to manage Brettanomyces yeast spoilage of wines.

La present tesi doctoral es centra en l'aplicació dels bacteris de l'àcid lactic (BAL) com a agents bioprotectors davant microorganismes patògens i deteriorants.Es van aïllar i seleccionar BAL de fruites i hortalisses fresques i es van assajar in vitro davant 5 microorganismes fitopatògens i 5 patògens humans.Es van realitzar assajos d'eficàcia en pomes Golden Delicious amb tots els aïllats enfront les infeccions causades pel fong Penicillium expansum. La soca més eficaç era Weissella cibaria TM128, que reduïa el diàmetre de les infeccions en un 50%.Les soques seleccionades es van assajar enfront els patògens Salmonella typhimurium, Escherichia coli i Listeria monocytogenes en enciams Iceberg i pomes Golden Delicious.Els BAL interferien eficientment amb el creixemet de S. typhimurium, and L. monocytogenes, però van mostrar poc efecte enfront E. coli.Finalment, es van realitzar assajos dosi-resposta amb les soques Leuconostoc mesenteroides CM135, CM160 and PM249 enfront L. monocytogenes. De totes les soques assajades, la soca CM160 va ser la més efectiva.
The present thesis focuses on the use of lactic acid bacteria as bioprotective cultures to inhibit pathogenic and spoilage microorganisms.
Lactic acid bacteria were isolated and selected from fresh fruit and vegetables and tested in vitro against five plant pathogens and five human pathogen test bacteria.Efficacy trials with all the isolates were performed in Golden Delicious apples against the blue mould rot infections, caused by Penicillium expansum. The highest effectivity found in this assay was of about 50%, with strain Weissella cibaria TM128.Selected lactic acid bacteria were tested against Salmonella typhimurium, Escherichia coli and Listeria monocytogenes in Iceberg lettuce and Golden Delicious apples. Lactic acid bacteria interfered efficiently with the growth of S. typhimurium, and L. monocytogenes, but showed little effectivity over E. coli.Finally, dose-response assays were done with Leuconostoc mesenteroides strains CM135, CM160 and PM249 against L. monocytogenes.Among the three strains tested, strain CM160 showed the highest effectivity.

The control of microbial contamination in the food industry is critical, as contamination of food produce, surfaces and equipment can lead to acquisition of foodborne infections. Microbial contamination can also result in food spoilage, which can cause both product and financial loss. Consequently novel decontamination technologies are being sought to help reduce contamination. Initial investigations examined the efficacy of 405 nm light for inactivation of a range of common foodborne microorganisms, both in suspension and on agar surfaces. All exposed populations were significantly reduced following 405 nm light exposure. The hypothesised inactivation mechanism involves photoexcitation of endogenous porphyrin molecules within the microorganisms, resulting in production of reactive oxygen species, oxidative cell damage and microbial inactivation. This theory was investigated by exposing fungi to 405 nm light under both aerobic and anaerobic conditions. Results displayed significant reduction in inactivation rates under oxygen depleted conditions, highlighting the critical role of oxygen during 405 nm light inactivation. This study also demonstrated inactivation of bacterial contamination and biofilms on a range of surfaces, demonstrating potential environmental decontamination applications. Further work highlighted the enhanced bacterial inactivation efficacy of 405 nm light when bacteria were exposed under sub-lethal environmental conditions, typical of those present in the food processing industry. Further studies also demonstrated the synergistic effect of TiO2 with 405 nm light, thereby enabling significantly enhanced bacterial inactivation rates. Studies also investigated potential applications for food decontamination and preservation, with preliminary results highlighting successful prevention of spoilage on a range of food products and significant decontamination of E. coli on fresh fruit. This study has confirmed the microbicidal efficacy of 405 nm light, whilst demonstrating a range of potential applications for use within the food industry for improved environmental decontamination. In conclusion 405 nm light has potential to be used safely and effectively as an additional decontamination technology in the food industry.

Thesis (MTech (Food Technology))--Cape Peninsula University of Technology, 2015.
Rooibos iced tea (RIT), as one of the products of Rooibos is fast becoming very popular as a beverage in society due to the benefits of the phenolic compounds that are associated with this herbal tea. Some of the commercially available products have been found to contain, if any, lower contents of the major phenolic compounds, namely aspalathin and its oxidation products, iso-orientin and orientin. Their presence is considered as indicators of a good quality product. The purpose of this study was to investigate the effect of ultraviolet-C (UV-C) light as an alternative treatment to heat treatment on the shelf life, pH, phenolic composition, colour and microorganisms associated with Rooibos. Two formulations of RIT were used in order to determine the efficacy of the UV-C on the shelf life whilst three formulations were used for the physicochemical analysis. Only one formulation was used for inoculation with three spoilage bacteria, yeast and mould spoilage microorganisms namely; Escherichia coli K12, Staphylococcus aureus, Salmonella sp., Saccharomyces cerevisiae and Cladosporium sp. The UV-C dosages of 0, 918, 1 836, 2 754 and 3 672 J.l -1 were used to treat the RIT using a pilot-scale UV-C system with a turbulent flow at a constant flow rate of 4000 l.hr-1 . A log count of 4 log10 was considered the limit for the spoilage growth since it is the average log10 afternormal pasteurisation. The use of UV-C treatment was found to have significantly (p1) effect on the overall colour difference of the RIT in formulations A, B, and C. All the spoilage microorganisms were significantly reduced by UV-C dosage to less than 4 log10 except the Cladosporium sp. The S. cerevisiae was the most sensitive microorganism whilst Cladosporium sp. was the most resistant. The effect of UV-C on the spoilage microorganism followed the sequence: S. cerevisiae>Salmonella sp.>S. aureus>E. coli K12>Cladosporium sp. This study indicated that microbiological reduction was achieved as a function of increasing UV-C dosage. In order to achieve the highest log10 reduction, the highest UV-C dosage of 3 672 J.l-1 may be used. However, the dosage may need to be increased in order to achieve the desired results in the treatment of Cladosporium sp. It can thus be concluded from the above investigations that UV-C dosage treatment of 3 672 J.l-1 is optimum in the non-thermal treatment of RIT
South African Association for Food Science & Technology Cape Peninsula University of Technology Bursary

Dissertação(mestrado) - Universidade Federal do Rio Grande, Programa de Pós-Graduação em Engenharia e Ciência de Alimentos, Escola de Química e Alimentos, 2008.
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Durante a produção, armazenamento, transporte e embalagem de produtos alimentícios, a presença de microrganismos é inevitável. A carne de frango, especialmente, é um alimento altamente perecível e, juntamente com outros tipos de carnes provenientes de ave, apresenta grande variedade de bactérias patogênicas e deteriorantes quando comparada com outros alimentos. Assim, a avaliação do crescimento microbiano e o controle da temperatura de armazenamento são importantes para garantir a segurança e vida útil dos alimentos. O trabalho objetivou caracterizar microbianamente três peitos de frango (cru, temperado com NaCl e cozido), produzidos no Brasil e exportados para a Europa, bem como, estimar a vida útil de tais produtos após o descongelamento, quando armazenados em diferentes condições de temperatura. Foi simulada a cadeia de abastecimento dos peitos de frango congelados, durante 20 dias a -18 ± 0,5 C para simulação do transporte destes produtos por navio até a Europa, desde sua expedição no Brasil e, após descongelamento, durante 21 dias a 4 ± 0,5 C para simulação da vida útil em gôndola de supermercado. Os produtos foram analisados quanto a Pseudomonas spp., Salmonella spp., Listeria monocytogenes, Staphylococcus spp. e microrganismos viáveis totais (mesófilos e psicrotróficos). Em termos de contagens de número de colônias viáveis totais, durante os primeiros 20 dias (a -18°C), a presença de microrganismos se manteve estável em baixos níveis de detecção. Após o descongelamento foram observadas as curvas de crescimento dos microrganismos, onde as fases lag ocorreram durante os primeiros 6 dias. A máxima concentração microbiana foi atingida após 15-18 dias, dependendo do produto. Em nenhuma das amostras foi detectada a presença de Salmonella spp. e Listeria monocytogenes. Após este estudo inicial foi avaliado o tempo de vida útil dos três produtos em diferentes condições de temperatura de armazenamento (2, 4, 7, 10, 15 e 20ºC). O estudo foi baseado na determinação de microrganismos aeróbios psicrotróficos, Pseudomonas spp., aeróbios mesófilos e Staphylococcus spp. O aumento da temperatura fez reduzir a vida útil dos três produtos estudados, em relação a todos os microrganismos. De modo geral, os produtos apresentaram faixas de vida útil de 10 até mais de 26 dias, a 2ºC; de 9 até mais de 21 dias, a 4ºC; de 6 até 12 dias, a 7ºC; de 4 até 8 dias, a 10ºC; de 2 até 4 dias, a 15ºC; e de 1 a 2 dias, a 20ºC. Quando armazenadas em temperaturas de refrigeração (2, 4 e 7°C), as amostras apresentaram pouca variação no tempo de vida útil, especialmente a 2 e 4°C. Já quando armazenadas à temperatura ambiente (temperaturas iguais ou superiores a 10ºC), a cada 5ºC de elevação na temperatura de armazenamento, a vida útil reduziu-se à metade do tempo.
During production, storage, transport and packaging of food products, the presence of microorganisms is unavoidable. The chicken meat, especially, is a highly perishable food and, together with other types from poultry meat presents great variety of pathogenic bacteria and spoilage when compared with other foods. Like this, the evaluation of the microbial growth and the control of the storage temperature are important to guarantee the safety and shelf life of the foods. The work aimed to characterize microbially, three chicken breast (raw, tempered with NaCl and cooked), produced in Brazil and exported to Europe, as well as, to estimate the shelf life of such products after thawing, when stored in different temperature conditions. The supply chain of frozen chicken breast was simulated for 20 days at -18±0,5oC for simulation of the transport of these products by ship to Europe, from its expedition in Brazil and, after thawed, during 21 days at 4 ± 0,5oC for simulation of the supermarket shelf life. Pseudomonas spp., Salmonella spp., Listeria monocytogenes, Staphylococcus spp. and total viable microorganisms (mesophilic and psicrotrophic) were analyzed in the products. In terms of accountings of total viable colonies number, during the first 20 days (-18°C), the presence of microorganisms was stable at low levels of detection. After thawing the microorganism growth curves showed that the lag phases happened during the first 6 days. The highest microbial concentration was reached after 15-18 days, according to the product. In none of the samples the presence of Salmonella spp. and Listeria monocytogenes were detected. After this initial study it was evaluated the shelf life time of the three products in different conditions of storage temperature (2, 4, 7, 10, 15 and 20ºC). The study was based on the determination of aerobic psicrotrophic, Pseudomonas spp., aerobics mesophilic and Staphylococcus spp. The increase of temperature reduce the shelf life of the three studied products, in relation to all of the microorganisms. In general, the products presented shelf life ranges from 10 to more than 26 days, at 2ºC; from 9 to more than 21 days, at 4ºC; from 6 to 12 days, at 7ºC; from 4 to 8 days, at 10ºC; of 2 to 4 days, at 15ºC; and, from 1 to 2 days at 20ºC. When stored in refrigerating temperature (2, 4 and 7°C), the samples presented a few variation in the shelf life time, especially at 2 and 4°C. But when stored to room temperature (at 10ºC or higher temperature), to each 5ºC of elevation in the storage temperature, the shelf life was reduced to half time.