The present study evaluated the effect of thermal (temperature) and thermochemical (temperature+oregano essential oil (EO)) inactivation of Bacillus coagulans spores in Nutrient Broth (NB) adjusted ...at 4°Brix and pH of 4.2. Thermal treatments included temperatures between 95 and 103°C. For thermochemical treatment, first temperature was fixed at 100°C and EO concentration varied between 250 and 1000μg/g. Thermochemical treatment significantly reduced the time needed to reduce a 6log level of spores compared to thermal treatment, for example around 1.4min with 400μg/g of EO. Then, EO concentration was fixed at 400μg/g and temperature varied between 90 and 100°C. Although the first results showed a faster spore reduction with 500μg/g, the fixed EO concentration was 400μg/g, since it represents a lower organoleptic impact and also a significant reduction in the spores’ resistance. For instance, at 97°C and 400μg/g, about 4.3min was needed to reduce the spores in 6log, without the EO this time was 5.0min. These findings indicate that oregano EO may be used to render B. coagulans spores more susceptible to the lethal effect of heat.
► Oregano essential oil as an antimicrobial agent against spores of Bacillus coagulans. ► Nutrient broth adjusted to 4°Brix and pH 4.2, added with oregano essential oil and inoculated with the spores. ► Oregano essential oil decreased the time to reach 6 decimal reductions of B. coagulans during thermal treatment.
This study innovatively produced polymeric active antibacterial films by incorporating zinc oxide nanoparticles (ZnO-NP) into linear low-density polyethylene grafted with maleic anhydride (LLDPE-MA) ...and low-density polyethylene (LDPE) using polymer melting and coating of ZnO-NP. It was evaluated the physical properties and antibacterial effects against foodborne pathogens (
Staphylococcus aureus
,
Salmonella
Typhimurium, and
Pseudomonas aeruginosa
) by liquid and disk-diffusion in agar tests. The active films presented 1.0, 2.5, and 5.5% of ZnO-NP. The two with higher ZnO-NP content presented similar antibacterial activity, demonstrating that the ZnO-NP availability on the film surface is more important than their total amount. Disk-diffusion in agar showed an inhibition halo for
P. aeruginosa
in both films with more than 5.0% in ZnO-NP, whereas for
S. aureus
and
S.
Typhimurium, the inhibition zones were not detected after 48 h. In liquid tests,
P. aeruginosa
was the least sensitive microorganism: from 5 log CFU/mL, it reached 9 log CFU/mL in LLDPE-MA films without ZnO-NPs and 7 log CFU/mL in films with 5.5% of ZnO-NPs after 5 days.
S
. Typhimurium was the most sensitive in the liquid test, with 9 log CFU/mL growth in 5 days for films without ZnO-NPs and 3 log CFU/mL for 5.5% of ZnO-NPs, in 5 days. In conclusion, ZnO-NP incorporated on LLDPE-MA and LDPE films is a promising packaging technology to increase food shelf-life and safety.
•Structuring of relevant terms in microbiological risk assessment modelling domain.•Definition of metadata and controlled vocabularies for annotation of QMRA models.•Harmonized model annotation will ...support knowledge exchange between software tools.•Establishment of curated food safety knowledge repository is proposed.•Need of rules for knowledge annotation essential for knowledge reusability.
In the last decades the microbial food safety community has developed a variety of valuable knowledge (e.g., mathematical models and data) and resources (e.g., databases and software tools) in the areas of quantitative microbial risk assessment (QMRA) and predictive microbiology. However, the reusability of this knowledge and the exchange of information between resources are currently difficult and time consuming. This problem has increased over time due to the lack of harmonized data format and rules for knowledge annotation. It includes the lack of a common understanding of basic terms and concepts and of a harmonized information exchange format to describe and annotate knowledge. The existence of ambiguities and inconsistencies in the use of terms and concepts in the QMRA and predictive microbial (PM) modelling necessitates a consensus on their refinement, which will allow a harmonized exchange of information within these areas. Therefore, this work aims to harmonize terms and concepts used in QMRA and PM modelling spanning from high level concepts as defined by Codex Alimentarius, Food and Agriculture Organization (FAO) and World Health Organization (WHO), up to terms generally used in statistics or data and software science. As a result, a harmonized schema for metadata that allows consistent annotation of data and models from these two domains is proposed. This metadata schema is also a key component of the Food Safety Knowledge Markup Language (FSK-ML), a harmonized format for information exchange between resources in the QMRA and PM modelling domain. This work is carried out within a research project that aims to establish a new community resource called Risk Assessment Modelling and Knowledge Integration Platform (RAKIP). This platform will facilitate the sharing and execution of curated QMRA and PM models using the foundation of the proposed harmonized metadata schema and information exchange format. Furthermore, it will also provide access to related open source software libraries, converter tools and software-specific import and export functions that promote the adoption of FSK-ML by the microbial food safety community. In the future, these resources will hopefully promote both the knowledge reusability and the high-quality information exchange between stakeholders within the areas of QMRA and PM modelling worldwide.
•Update on microbiological food safety databases, software and mathematical models.•Harmonized data formats supported by software will benefit knowledge exchange.•Rules for knowledge annotation are ...essential for knowledge reusability.•Establishment of a microbiological food safety knowledge repository is proposed.
Predictive microbial modelling and quantitative microbiological risk assessment, two important and complementary areas within the food safety community, are generating a variety of scientific knowledge (experimental data and mathematical models) and resources (databases and software tools) for the exploitation of this knowledge. However, the application and reusability of this knowledge is still hampered as the access to this knowledge and the exchange of information between databases and software tools are currently difficult and time consuming. To facilitate transparent and consistent knowledge access and exchange new tools and community resources are needed. These resources will promote the creation of a public microbiological food safety knowledge repository encompassing available data and models. However, essential components are currently missing, such as open data formats supported by different software tools and consistent rules for knowledge annotation. The knowledge repository would be a user friendly tool to benefit different users within the microbiological food safety community, especially users like risk assessors and managers, model developers and research scientists working in the private sector (e.g. food industries, consultancy companies), research institutes or food authorities.
Given the importance of pH reduction and thermal treatment in food processing and food preservation strategies, the cross-protection between acid adaptation and subsequent thermal inactivation for 48 ...Escherichia coli strains was investigated. Those strains were selected among 188 E. coli strains according to their odds of growth under low pH conditions as determined by Haberbeck et al. (2015) Haberbeck, L.U., Oliveira, R.C., Vivijs, B., Wenseleers, T., Aertsen, A., Michiels, C., Geeraerd, A.H., 2015. Variability in growth/no growth boundaries of 188 different Escherichia coli strains reveals that approximately 75% have a higher growth probability under low pH conditions than E. coli O157:H7 strain ATCC 43888. Food Microbiol. 45, 222–230. E. coli cells were acid and nonacid-adapted during overnight growth in controlled acidic pH (5.5) and neutral pH (7.0), respectively, in buffered Lysogenic Broth (LB). Then, they were heat inactivated at 58°C in non-buffered LB adjusted to pH6.2 and 7.0. Thus, four conditions were tested in total by combining the different pH values during growth/thermal inactivation: 5.5/6.2, 5.5/7.0, 7.0/6.2 and 7.0/7.0. Acid adaptation in buffered LB at pH5.5 increased the heat resistance of E. coli strains in comparison with nonacid-adaptation at pH7.0. For instance, the median D58-value of strains inactivated at pH7.0 was approximately 6 and 4min for acid-adapted and nonacid-adapted strains, respectively. For the nonacid-adapted strains, the thermal inactivation at pH6.2 and 7.0 was not significantly (p=0.06) different, while for the acid-adapted strains, the thermal treatment at pH6.2 showed a higher heat resistance than at pH7.0. The correlation between the odds of growth under low pH previously determined and the heat resistance was significant (p<0.05). Remarkably, a great variability in heat resistance among the strains was observed for all pH combinations, with D58-values varying between 1.0 and 69.0min. In addition, highly heat resistant strains were detected. Those strains exhibited D58-values between 17.6 and 69.0min, while E. coli O157:H7 (ATCC 43888) showed D58-values between 1.2 and 3.1min. In summary, results clearly showed that adaptation of E. coli cells to constant acidic pH results in cross-protection against thermal inactivation.
•E. coli acid adaption at pH5.5 provides cross-protection against thermal inactivation.•Acid-adapted cells were more heat resistant in slightly acidic inactivation media.•Large variability in the D-values of 48 strains was observed (from 1 to 69min at 58°C).•Correlation was observed between the heat resistance and odds of growth under low pH.
Two fermentation types exist in the Enterobacteriaceae family. Mixed-acid fermenters produce substantial amounts of lactate, formate, acetate, and succinate, resulting in lethal medium acidification. ...On the other hand, 2,3-butanediol fermenters switch to the production of the neutral compounds acetoin and 2,3-butanediol and even deacidify the environment after an initial acidification phase, thereby avoiding cell death. We equipped three mixed-acid fermenters (Salmonella Typhimurium, S. Enteritidis and Shigella flexneri) with the acetoin pathway from Serratia plymuthica to investigate the mechanisms of deacidification. Acetoin production caused attenuated acidification during exponential growth in all three bacteria, but stationary-phase deacidification was only observed in Escherichia coli and Salmonella, suggesting that it was not due to the consumption of protons accompanying acetoin production. To identify the mechanism, 34 transposon mutants of acetoin-producing E. coli that no longer deacidified the culture medium were isolated. The mutations mapped to 16 genes, all involved in formate metabolism. Formate is an end product of mixed-acid fermentation that can be converted to H2 and CO2 by the formate hydrogen lyase (FHL) complex, a reaction that consumes protons and thus can explain medium deacidification. When hycE, encoding the large subunit of hydrogenase 3 that is part of the FHL complex, was deleted in acetoin-producing E. coli, deacidification capacity was lost. Metabolite analysis in E. coli showed that introduction of the acetoin pathway reduced lactate and acetate production, but increased glucose consumption and formate and ethanol production. Analysis of a hycE mutant in S. plymuthica confirmed that medium deacidification in this organism is also mediated by FHL. These findings improve our understanding of the physiology and function of fermentation pathways in Enterobacteriaceae.
ABSTRACT
The aim of this work was to validate the prediction of the nonisothermal thermochemical inactivation of Bacillus coagulans spores in nutrient broth, adjusted to 4 °Brix and pH 4.2, with 400 ...ppm of oregano essential oil (EO), using the Weibull dynamic model proposed by Peleg. First, the spores were heat treated at four constant temperatures. Afterwards, empirical secondary models were employed to describe the influence of temperature on the primary parameters. Finally, primary and secondary models were used to simulate microorganism inactivation under two nonisothermal temperatures, ranging from 90 to 95C every 1 min; and from 90 to 95C for 5 min at each temperature. Even if a limited experimental data was employed for the nonisothermal analysis, it appears that the proposed model can be used to estimate the nonisothermal inactivation of B. coagulans spores in nutrient broth with 400 ppm of oregano EO.
PRATICAL APLICATIONS
Oregano essential oil (EO) demonstrates an important antibacterial action against food spoilage microorganisms, as Bacillus coagulans spores. This EO is capable of decreasing the time of the spores' inactivation and, then, the food thermal processing time can be reduced. The industrial heat treatment of foods includes nonisothermal temperatures, as temperature fluctuations during the process, and it is important to understand the behavior of spoilage microorganism all through this temperatures oscillations.
Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia de Alimentos, Florianópolis, 2011
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Aumentar a vida útil dos produtos, sem afetar sua qualidade, funcionalidade e propriedades físico-químicas, modificando e desenvolvendo novos tipos de processos para a preservação microbiológica dos alimentos, é um desafio constante para a indústria. A aplicação de conservantes naturais, como óleos essenciais de plantas e especiarias, é percebida como uma nova tendência na preservação dos alimentos nos últimos anos. A bactéria Bacillus coagulans é um micro-organismos relevante no processamento de alimentos devido à sua capacidade deteriorante e à sua termorresistência. Além disso, B. coagulans causa o fenômeno flat-sour caracterizado pela acidificação do alimento sem a produção de gás. O tratamento térmico necessário para garantir a inativação deste microrganismo pode levar à perda de nutrientes e/ou à alterações organolépticas nos alimentos processados. Assim sendo, o objetivo geral deste trabalho foi estudar o efeito da ação conjunta do óleo essencial (OE) de orégano e do calor sobre a resistência dos esporos de B. coagulans, em caldo nutriente ajustado em condições que simulam um produto ácido como, por exemplo, a polpa de tomate (4 °Brix e pH 4,2). O OE de orégano estudado apresentou como principais moléculas constituintes carvacrol (58%), seguido de seu precursor ?-cimeno, ?-terpineno, linalool, timol, entre outras. Essas moléculas têm sua atividade microbiana estudada e comprovada pela literatura, sendo o carvacrol e o timol, apontadas como umas das mais eficazes na inibição de micro-organismos. O teste inicial para a determinação da concentração mínima inibitória (CMI) do OE resultou na concentração de 300 ppm, que foi capaz de inibir o crescimento visual do B. coagulans por 7 dias. Em seguida, na avaliação da resistência termoquímica, a ação conjunta do calor e do óleo essencial de orégano sobre os esporos foi iniciada com a CMI de 300 ppm e posteriormente, as concentrações de 0, 250, 400, 500 e 1000 ppm foram testadas, todas à temperatura de 100 °C. Entre as diferentes concentrações de OE, a de 400 ppm foi a menor concentração onde o tempo necessário para se obter 6 reduções decimais foi significativamente (P < 0,01) diferente da resistência térmica sem o óleo essencial de orégano. Assim, a segunda etapa do estudo da resistência termo química foi realizada fixando-se a concentração de OE em 400 ppm e variando a temperatura entre 90 e 100 °C. Para todas as curvas experimentais de inativação termoquímica de B. coagulans, o modelo primário de Weibull teve um bom ajuste aos dados. Após o ajuste primário, modelos secundários empíricos, como as equações
exponencial e linear, foram ajustados aos parâmetros do modelo de Weibull para descrever a influência da temperatura sobre os parâmetros primários ?(T), ?(T) e b(T). Com base no modelo primário e secundário, foi realizada a resistência termoquímica não isotérmica dos esporos de B. coagulans. Nesta etapa, o modelo não isotérmico proposto por Peleg (2006) foi utilizado para a predição dos dados não isotérmicos. Assim, o modelo proposto foi validado com dados experimentais de B. coagulans em caldo nutriente adicionado de 400 ppm de óleo essencial de orégano sob dois perfis de temperatura diferentes. O efeito antibacteriano do óleo essencial de orégano foi comprovado através de diferentes tipos de análises, mostrando que este conservante natural pode ser utilizado na indústria de alimentos. Deste modo, o OE de orégano pode reduzir o tratamento térmico de produtos, resultando em menor gasto de energia e diminuindo o impacto do calor nas propriedades organolépticas e/ou nutricionais do produto. Além disto, no caso de produtos como polpa e molhos de tomate, o orégano pode ser adicionado como uma alternativa de adição de sabor ao alimento.
Increasing shelf-life of products, without affecting their quality, physicochemical properties and functionality, by modifying and developing new preservations steps, is a constant challenge for the food industry. Application of natural preservatives, as essential oils (EO) from plants and herbs, has been increasingly noticed as a new trend in biological preservation of foods in recent years. Bacteria resistant to heat stress, such as Bacillus coagulans, are relevant microorganisms in food processing because of its deteriorating ability after surviving the heat treatment. Besides that, B. coagulans, causes the flat-sour phenomenon characterized by the acidification of food without gas production. The heat treatment necessary to ensure the inactivation of this microorganism can lead to loss of nutrients and/or organoleptic changes in the processed foods. Thus, the general objective of this work was to study the synergistic effect of oregano essential oil (EO) and heat on the resistance of Bacillus coagulans spore in nutrient broth adjusted to conditions simulating an acid product, for instance, tomato pulp (4 ° Brix and pH 4.2). The oregano EO studied showed carvacrol (58%) as main constituent molecules, followed by its precursor ?-cymene, ?-terpinene, linalool, thymol, among others. These molecules have their antimicrobial activity confirmed by the literature, and carvacrol and thymol are one of the most effective molecules in inhibiting microorganisms. The initial test for determining the minimum inhibitory concentration (MIC) of the OE resulted in a concentration of 300 ppm, which was capable of inhibiting the visual growth of B. coagulans for 7 days. Then, the themochemical resistance, the joint action of heat and essential oil of oregano on the spores was initiated with the MIC of 300 ppm and subsequently the concentrations of 0, 250, 400, 500 and 1000 ppm, at 100 ° C were tested. Among the different concentrations of the EO, 400 ppm was the lowest concentration where the time needed to obtain 6 decimal reduction was significantly (P < 0.01) different from the thermal resistance without the essential oil of oregano. The second stage of the study termochemical resistance was performed by fixing the concentration of EO at 400 ppm and varying the temperature between 90 and 100 °C. For all experimental termochemical inactivation curves of B. coagulans, the primary model of Weibull presented a good fit to the data. After adjusting the primary model, the secondary empirical models, such as exponential and linear equations, were fitted to the Weibull parameters to describe the influence of temperature on the primary parameters ? (T), ? (T) and b (T). Based on the model primary and secondary models, it was realized the non-isothermal thermochemical resistance of B. coagulans spores. In this step, the non-isothermal model proposed by Peleg (2006) was used to predict non-isothermal data. Thus, the proposed model was validated with experimental data of B. coagulans in nutrient broth supplemented with 400 ppm of oregano EO in two different temperature profiles. The antibacterial effects of oregano EO was proved through different types of analysis, showing that this natural preservative can be used in food industry. Thus, the EO of oregano may reduce the thermal treatment of products, resulting in less energy consumption and reducing the impact of heat on organoleptic and/or nutrition properties. Besides that, in the case of products such as pulp and tomato sauce oregano can be added as an alternative to adding flavor to food.
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