| Name: | Description: | Size: | Format: | |
|---|---|---|---|---|
| 1.11 MB | Adobe PDF |
Authors
Abstract(s)
A Listeria spp. é um contaminante em queijos curados produzidos com leite cru. Os ácidos orgânicos e os seus sais são conservantes comummente utilizados na indústria alimentar. Neste trabalho foi testada a actividade de ácido láctico; ácido acético; sorbato de potássio e acetato de sódio, sobre o microrganismo indicador Listeria innocua por não ser patogénico. Foi estudado o efeito da concentração dos conservantes (0,5-5% v/v) e pH do meio de cultura no intervalo 4 a 8, através da metodologia CCD (Central Composite Design). O crescimento bacteriano foi monitorizado por turbidimetria. Verificou-se que acima de 1% (v/v) de ácido láctico e ácido acético ocorreu uma inibição do crescimento da Listeria innocua superior a 90%. Para determinar se os conservantes apresentavam actividade bactericida, foram repetidos os ensaios em placa com meio OCLA (Oxoid Chromogenic Listeria Agar) a 37ºC. Confirmou-se que o ácido acético tem propriedades bactericidas contra a Listeria innocua a partir de 1% (v/v) com uma redução de 5,0log UFC/ml2 enquanto que o ácido láctico inibe a partir de 2% (v/v) com uma redução de 3,5log UFC/ml2. Quanto aos sais os resultados obtidos não foram favoráveis. Após este estudo foi seleccionado o ácido acético para testar a sua eficácia na redução da Listeria innocua e bolores nos queijos, comparativamente ao conservante Delvocoat usado na fábrica. Concluiu-se que a aplicação de 5% de ácido acético na superfície dos queijos permite reduzir a contaminação por Listeria innocua mas não por bolores.
Listeria spp. is a contaminant in cheeses made with raw milk. Organic acids and their salts are preservatives commonly used in food industry. In this study we tested the activity of lactic acid, acetic acid, potassium sorbate and sodium acetate on the non-pathogenic Listeria innocua. The effect of preservatives concentration (0.5-5% v /v) and the pH of culture medium in the range 4-8 were studied using CCD (Central Composite Design). Bacterial growth was monitored by turbidimetry. It was found that above 1% (v / v) of lactic acid and acetic acid there was a growth inhibition of Listeria innocua above 90%. To determine whether the preservative showed bactericidal activity, the tests were repeated in an OCLA medium (Oxoid Chromogenic Listeria Agar) at 37 ° C. It was confirmed that acetic acid has antibacterial properties against Listeria innocua from 1% (v / v) with a reduction of 5.0 log UFC/ml2 while lactic acid inhibits from 2% (v/v) with a reduction of 3.5 log UFC/ml2 . As for the salts the results were not favorable. After this study acetic acid was selected to test its effectiveness in reducing Listeria innocua and molds in cheeses, compared with a preservative Delvocoat used in the factory. It was concluded that the application of 5% acetic acid on the surface of the cheese can reduce the contamination by Listeria innocua but not mold.
Listeria spp. is a contaminant in cheeses made with raw milk. Organic acids and their salts are preservatives commonly used in food industry. In this study we tested the activity of lactic acid, acetic acid, potassium sorbate and sodium acetate on the non-pathogenic Listeria innocua. The effect of preservatives concentration (0.5-5% v /v) and the pH of culture medium in the range 4-8 were studied using CCD (Central Composite Design). Bacterial growth was monitored by turbidimetry. It was found that above 1% (v / v) of lactic acid and acetic acid there was a growth inhibition of Listeria innocua above 90%. To determine whether the preservative showed bactericidal activity, the tests were repeated in an OCLA medium (Oxoid Chromogenic Listeria Agar) at 37 ° C. It was confirmed that acetic acid has antibacterial properties against Listeria innocua from 1% (v / v) with a reduction of 5.0 log UFC/ml2 while lactic acid inhibits from 2% (v/v) with a reduction of 3.5 log UFC/ml2 . As for the salts the results were not favorable. After this study acetic acid was selected to test its effectiveness in reducing Listeria innocua and molds in cheeses, compared with a preservative Delvocoat used in the factory. It was concluded that the application of 5% acetic acid on the surface of the cheese can reduce the contamination by Listeria innocua but not mold.
Description
Keywords
Ácido acético Ácido láctico Fabrico de queijo Listeria monocytogenes