RESUMEN
Lactococcus lactis subsp lactis BSA (L. lactis BSA) was isolated from a commercial fermented product (BSA Food Ingredients, Montreal, Canada) containing mixed bacteria that are used as starter for food fermentation. In order to increase the bacteriocin production by L. lactis BSA, different fermentation conditions were conducted. They included different volumetric combinations of two culture media (the Man, Rogosa and Sharpe (MRS) broth and skim milk), agitation level (0 and 100 rpm) and concentration of commercial nisin (0, 0.15, and 0.30 µg/ml) added into culture media as stimulant agent for nisin production. During fermentation, samples were collected and used for antibacterial evaluation against Lactobacillus sakei using agar diffusion assay. Results showed that medium containing 50 % MRS broth and 50 % skim milk gave better antibacterial activity as compared to other medium formulations. Agitation (100 rpm) did not improve nisin production by L. lactis BSA. Adding 0.15 µg/ml of nisin into the medium-containing 50 % MRS broth and 50 % skim milk caused the highest nisin activity of 18,820 AU/ml as compared to other medium formulations. This activity was 4 and ~3 times higher than medium containing 100 % MRS broth without added nisin (~4700 AU/ml) and 100 % MRS broth with 0.15 µg/ml of added nisin (~6650 AU/ml), respectively.
Asunto(s)
Microbiología Industrial/métodos , Lactococcus lactis/metabolismo , Nisina/biosíntesis , Canadá , FermentaciónRESUMEN
The aim of this study was to evaluate the effect of combining marinating and γ-irradiation at doses of 1, 1.5 and 3kGy on Escherichia coli O157:H7, Salmonella typhimurium and Clostridium sporogenes in raw meat packed under vacuum and stored at 4°C and to estimate its safety and shelf-life. Further, the effect of combined treatments on sensorial, nutritional values (lipid oxidation, concentration of thiamin and riboflavin) and color was evaluated. The study demonstrated that the use of marinade in combination with a low dose of γ-irradiation (1.5kGy) could act in synergy to reduce to undetectable level of pathogenic bacteria and increase the shelf-life of ready-to-cook meat loin without affecting its sensorial and nutritional quality.
Asunto(s)
Manipulación de Alimentos , Irradiación de Alimentos , Rayos gamma , Carne/microbiología , Carne/efectos de la radiación , Valor Nutritivo , Animales , Fenómenos Químicos , Clostridium/efectos de la radiación , Color , Comportamiento del Consumidor , Seguridad de Productos para el Consumidor , Grasas de la Dieta/análisis , Relación Dosis-Respuesta en la Radiación , Escherichia coli O157/efectos de la radiación , Contaminación de Alimentos/prevención & control , Microbiología de Alimentos , Inocuidad de los Alimentos , Almacenamiento de Alimentos , Humanos , Huésped Inmunocomprometido , Oxidación-Reducción/efectos de la radiación , Riboflavina/análisis , Salmonella typhimurium/efectos de la radiación , Porcinos , Gusto , Tiamina/análisis , VacioRESUMEN
The marine environment is a proven source of structurally complex and biologically active compounds. In this study, the antimicrobial effects of a small collection of marine-derived extracts and isolates, were evaluated against 5 foodborne pathogens using a broth dilution assay. Results demonstrated that algal extracts from Padina and Ulva species and cyanobacterial compounds antillatoxin B, laxaphycins A, B and B3, isomalyngamide A, and malyngamides C, I and J showed antimicrobial activity against Gram positive foodborne pathogens (Listeria monocytogenes, Bacillus cereus and Staphylococcus aureus) at low concentrations (⩽ 500 µg/ml). None of the algal extracts or cyanobacterial isolates had antibacterial activity against Gram negative bacteria (Escherichia coli and Salmonella enterica serovar Typhimurium).
Asunto(s)
Antibacterianos/farmacología , Cianobacterias/química , Microbiología de Alimentos , Phaeophyceae , Ulva , Bacillus cereus/efectos de los fármacos , Listeria monocytogenes/efectos de los fármacos , Pruebas de Sensibilidad Microbiana , Salmonella typhimurium/efectos de los fármacos , Staphylococcus aureus/efectos de los fármacosRESUMEN
The objective of this study was to evaluate the impact of seven independent factors consisting of sodium nitrite, pH, sodium chloride, sodium acetate, sodium lactate syrup, calcium propionate and a blend of nisin and hop alpha acids on the growth rate of Listeria monocytogenes in ham as a model of ready-to-eat (RTE) meat products. A central composite consisted of seven factors mentioned above was designed and the response surface methodology was applied for creating a mathematic model to predict the growth rate of L. monocytogenes in RTE meat products. Six parameters showed a significant (P ≤ 0.1) influence on the growth rate of L. monocytogenes. Only the blend of nisin and hop alpha acids did not show any significant effect (P > 0.1) in the concentrations used in this study. Increasing concentration of sodium chloride, sodium nitrite, sodium acetate, potassium lactate and calcium propionate in meat reduced bacterial growth rate while increasing pH in meat increased the growth rate of L. monocytogenes. The current mathematical equation will be an important tool in order to reduce the required number of challenge studies performed in order to ensure a safe food product.
Asunto(s)
Comida Rápida/microbiología , Conservantes de Alimentos/farmacología , Listeria monocytogenes/efectos de los fármacos , Listeria monocytogenes/crecimiento & desarrollo , Productos de la Carne/microbiología , Animales , Recuento de Colonia Microbiana , Contaminación de Alimentos/análisis , Conservación de Alimentos , Modelos Biológicos , PorcinosRESUMEN
The purpose of this research was to evaluate the application of commercially available essential oils (EOs) and oleoresins to control bacterial pathogens for ready to eat food. In this study, sixty seven commercial EOs, oleoresins (ORs) and pure compounds were used to evaluate in vitro their antimicrobial activity against six food pathogens. These products were first screened for their antimicrobial activity using disk diffusion assay. Forty one products were then chosen for further analysis to determine their minimum inhibitory concentration against 6 different bacteria. There were 5 different products (allyl isothiocyanate, cinnamon Chinese cassia, cinnamon OR, oregano and red thyme) that showed high antimicrobial activity against all tested bacteria. Further analysis examined the effect of four selected EOs on controlling the growth rate of mixed cultures of Listeria monocytogenes in ham. A reduction of the growth rate by 19 and 10% was observed when oregano and cinnamon cassia EOs were respectively added in ham at a concentration of 500 ppm.
Asunto(s)
Antiinfecciosos/farmacología , Contaminación de Alimentos/prevención & control , Productos de la Carne/microbiología , Aceites Volátiles/farmacología , Extractos Vegetales/farmacología , Animales , Cinnamomum zeylanicum/química , Estudios de Evaluación como Asunto , Microbiología de Alimentos , Conservación de Alimentos , Conservantes de Alimentos , Listeria monocytogenes/efectos de los fármacos , Listeria monocytogenes/crecimiento & desarrollo , Pruebas de Sensibilidad Microbiana , Origanum/química , Porcinos , Thymus (Planta)/químicaRESUMEN
The present study evaluated the response of Bacillus cereus LSPQ 2872 vegetative cells, following exposure to single and repetitive sublethal γ-radiation treatment at 1 kGy alone or in combination with nisin at its maximum tolerated concentration, in BHI broth supplemented with 0.5% glucose. Results showed that B. cereus has the capability to develop increased resistance to subsequent cycles of gamma irradiation and a significant increase (p ≤ 0.05) of the relative radiation resistance (D(10)) value was noticed after the fourth irradiation at 1 kGy. The sequence and the repetitive sublethal treatment of γ-radiation with nisin affected significantly (p ≤ 0.05) B. cereus radio-tolerance since lower D(10) values were recorded. Our results showed that the response of B. cereus to repetitive mild bactericidal treatment was accompanied by relevant modifications in the cell properties leading to the increased resistance. Transmission electron microscopy revealed that resistance might be related to changes in the cell wall. Multiparameter flow cytometry revealed effectively diverse physiological changes that B. cereus underwent during development of radio-resistance. The development of increased resistance to gamma irradiation was accompanied by an increase of the percentage of injured and viable cells at the expense of dead cells. Nisin treated cells developed also increased radio-resistance if repetitively processed with γ-radiation at sublethal doses which was not demonstrated by plate counting.
Asunto(s)
Antibacterianos/farmacología , Bacillus cereus/efectos de los fármacos , Bacillus cereus/efectos de la radiación , Nisina/farmacología , Bacillus cereus/crecimiento & desarrollo , Rayos gamma , Viabilidad Microbiana/efectos de los fármacos , Viabilidad Microbiana/efectos de la radiación , Tolerancia a RadiaciónRESUMEN
Methylcellulose (MC)-based films were prepared by solution casting from its 1% aqueous suspension containing 0.25% glycerol. Trimethylolpropane trimethacrylate (TMPTMA) monomer (0.1-2% by wt) along with the glycerol was added to the MC suspension. The films were cast and irradiated from a radiation dose varied from 0.1 to 10 kGy. Then the mechanical properties such as tensile strength (TS), tensile modulus (TM), and elongation at break (Eb) and barrier properties of the films were evaluated. The highest TS (47.88 PMa) and TM (1791.50 MPa) of the films were found by using 0.1% monomer at 5 kGy dose. The lowest water vapor permeability (WVP) of the films was found to be 5.57 g·mm/m(2)·day·kPa (at 0.1% monomer and 5 kGy dose), which is 12.14% lower than control MC-based films. Molecular interactions due to incorporation of TMPTMA were supported by FTIR spectroscopy. A band at 1720 cm(-1) was observed due to the addition of TMPTMA in MC-based films, which indicated the typical (CâO) carbonyl stretching. For the further improvement of the mechanical and barrier properties of the film, 0.025-1% nanocrystalline cellulose (NCC) was added to the MC-based suspension containing 1% TMPTMA. Addition of NCC led to a significant improvement in the mechanical and barrier properties. The novelty of this investigation was to graft insoluble monomer using γ radiation with MC-based films and use of biodegradable NCC as the reinforcing agent.
Asunto(s)
Embalaje de Alimentos/métodos , Metacrilatos/química , Metilcelulosa/química , Nanopartículas/química , Celulosa/química , Relación Dosis-Respuesta en la Radiación , Rayos gamma , Fenómenos Mecánicos , Metilcelulosa/efectos de la radiación , Permeabilidad , Espectroscopía Infrarroja por Transformada de Fourier , Vapor , Resistencia a la TracciónRESUMEN
Methylcellulose (MC)-based films were prepared by casting from its 1% aqueous solution containing 0.5% vegetable oil, 0.25% glycerol, and 0.025% Tween 80. Puncture strength (PS), puncture deformation (PD), viscoelasticity coefficient, and water vapor permeability (WVP) were found to be 147 N/mm, 3.46 mm, 41%, and 6.34 g.mm/m(2).day.kPa, respectively. Aqueous nanocellulose (NC) solution (0.1-1%) was incorporated into the MC-based formulation, and it was found that PS was improved (117%) and WVP was decreased (26%) significantly. Films containing 0.25% NC were found to be the optimum. Then films were exposed to gamma radiation (0.5-50 kGy), and it was revealed that mechanical properties of the films were slightly decreased after irradiation, whereas barrier properties were further improved with a decrease of WVP to 28.8% at 50 kGy. Molecular interactions due to incorporation of NC were supported by FTIR spectroscopy. Thermal properties of the NC-containing films were improved, confirmed by TGA and DSC. Crystalline peaks appeared due to NC addition, found by XRD. Micrographs of films containing NC were investigated by SEM.
Asunto(s)
Embalaje de Alimentos/instrumentación , Metilcelulosa/química , Elasticidad , Calor , Metilcelulosa/síntesis química , PermeabilidadRESUMEN
Carvacrol and mild heat treatment were tested for their efficiency to increase the radiosensitivity of Bacillus cereus in broth. The bacterium was treated with gamma-irradiation alone or in combination with carvacrol at its minimal inhibitory concentration or mild heat treatment for 10 min at 45 degrees C. The effects of this combination of treatments were studied on various parameters: the bacterial viability, the modifications of the cell morphology with scanning electron microscopy (SEM), the cellular fatty acids composition of the membrane quantified by gas chromatography, the intracellular and extracellular adenosine 5'-triphosphate (ATP) concentrations, and the DNA degradation. Combined treatments resulted in additive or synergistic effects as compared to gamma-irradiation alone. A significant modification (P < or = 0.05) of the fatty acid composition and unsaturation ratios was observed. Pretreatment with mild heat or carvacrol before irradiation disturbed the membrane integrity of B. cereus and induced a significant decrease (P < or = 0.05) of the intracellular ATP concentration. SEM observations revealed that the cell membrane was more severely affected with combined treatment than irradiation alone. The electrophoresis analysis showed that DNA degradation by combined treatments was greater than the gamma-irradiation alone.
Asunto(s)
Bacillus cereus/efectos de los fármacos , Bacillus cereus/efectos de la radiación , Monoterpenos/farmacología , Adenosina Trifosfato/metabolismo , Bacillus cereus/genética , Bacillus cereus/metabolismo , Cimenos , Daño del ADN/efectos de los fármacos , Daño del ADN/efectos de la radiación , ADN Bacteriano/genética , ADN Bacteriano/metabolismo , Rayos gamma , Calor , Viabilidad Microbiana/efectos de los fármacos , Viabilidad Microbiana/efectos de la radiaciónRESUMEN
This present study was carried out to evaluate the effects of gamma irradiation on the fatty acids (FA) and mureins composition of two different radiotolerant bacteria. Bacillus cereus LSPQ 2872 and Salmonella Typhi ATCC 19430 were used for this study. The bacterial strains were treated with a sublethal radiation dose of 1kGy to cause a cellular damage. Gas chromatography (GC) and high performance liquid chromatography (HPLC) analysis were performed to demonstrate respectively the modification of the FA composition and the changes in muropeptide profile. Results obtained show, for both bacteria, that this treatment had a significant effect (P< or =0.05) on the FA content with an increase of unsaturated FA percentage. Substantial changes were also noticed for the relative percentage and the number of the muropeptides. This study represents one of the few to demonstrate the modifications on bacterial membrane as a cellular response to survive the ionising radiation stress.