Effect of essential oil of Myrtus communis L. and Rosmarinus officinalis L. on growth control of Listeria monocytogenes in fresh cheese
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2017-09-13
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O principal objetivo deste trabalho consistiu na avaliação do efeito antimicrobiano de óleos essenciais de plantas aromáticas em queijo fresco de ovelha inoculado com L. monocytogenes. Nas amostras controlo foram analisados microrganismos mesófilos totais, Bactérias do Ácido Lático (BAL), Enterobacteriaceae e Fungos e foi efetuada também a medição de pH e aw.
Os óleos essenciais foram obtidos a partir de plantas colhidas em diferentes momentos e em diferentes locais. O seu efeito antimicrobiano relativamente a diferentes bactérias foi testado in vitro.
Recolheram-se folhas e bagas frescas na região de Trás-os-Montes durante Setembro, Outubro, Novembro e Dezembro de 2015 e Janeiro de 2016 de Myrtus communis L.. Recolheram-se folhas e flores frescas na região de Trás-os-Montes durante Outubro, Novembro e Dezembro de 2015 de Rosmarinus officinalis L. As folhas e bagas secas foram submetidas a hidrodestilação com o aparelho de Clevenger.
A composição química dos EOs foi determinada por cromatografia gasosa e espectrometria de massa (GC-MS) e os espetros de absorção foram medidos na região de infravermelho através de FTIR.
No local A, para a 1ª colheita de EO de folhas de Myrtus determinou-se 44 compostos e na 2ª colheita determinou-se 62 compostos. Para a 1ª colheita de EO de bagas de Myrtus determinou-se 43 compostos, enquanto na 2ª colheita determinou-se 53 compostos. No local B, a principal diferença foi obtida para EO de Myrtus na 2ª colheita com um total de 49 e 50 compostos identificados para folhas e bagas respetivamente.
No EO de flor de alecrim na 1ª colheita determinou-se 25 compostos que correspondem a 95,10% dos compostos totais, enquanto na 2ª colheita determinou-se 24 composto que correspondem a 97,55% dos compostos totais.
O óleo essencial de flor de alecrim apresenta uma percentagem inferior de compostos antimicrobianos em relação ao óleo essencial de alecrim, tendo um menor efeito inibitório face a microrganismos deteriorativos e patogénicos.
Listeria monocytogenes apresentou valores de MIC para as folhas de EO de Myrtus communis L. para a 1ª e 2ª colheita de 6.25 e 3.125 μL/mL, respectivamente. Em relação ao OE de Rosmarinus officinalis L., Listeria monocytogenes obteve-se um valor mais elevado de 18.75 μL/mL comparativamente com o OE de murta. O OE de Murta apresentou valores MIC de 25 μL/mL para E. coli O157:H7 e Salmonella, exceto Pseudomonas spp. que foi de 50 μL/mL.
Para as amostras com OE de murta e alecrim, as analises microbiológicas para mesófilos apresentaram uma carga microbiana de 7.96 log ufc/g e 9.47 log ufc/g, respetivamente, às 672 horas.
Relativamente às BAL, as amostras com OE de murta e alecrim apresentaram uma carga microbiana às 672 horas de 8.07 ufc/g e 8.95 ufc/g, respetivamente. Pode-se concluir que o OE de murta apresenta maior inibição microbiana.
Para Enterobacteriaceae, nas amostras com OE de murta e alecrim não foram detetadas contagens desta população até às 672 horas, verificando-se uma carga microbiana de 7.14 e 8.19 log ufc/g, respetivamente, nesse tempo.
As contagens de Fungos às 672 horas foram de 6.87 e 7.21 log ufc/g para as amostras com EO de murta e alecrim, respetivamente.
O EO de murta e alecrim levaram a uma multiplicação ligeira de Listeria monocytogenes a partir das 72 horas às 336 horas, seguindo-se uma diminuição até as 672 horas com uma carga microbiana de 4.72 para 4.54 log ufc/g e 5.30 para 5.05 log ufc/g, respetivamente.
O óleo essencial pode ser utilizado como estratégia de controlo para evitar a proliferação de L. monocytogenes, especialmente numa matriz alimentar como o queijo fresco, que pode levar à multiplicação deste microrganismo patogénico.
The main aim of this study was to evaluate the antimicrobial effect of essential oils (EO) of aromatic herbs in fresh sheep cheese inoculated with L. monocytogenes. In the control samples, total mesophilic microorganisms, lactic acid bacteria (LAB), Enterobacteriaceae and Fungi were analyzed, and pH and aw were also measured. The essential oils were obtained from plants harvested at different times and in different locations. Their antimicrobial effect against different bacteria was tested in vitro. Fresh leaves and berries of Myrtus communis L. were collected at Trás-os-Montes, in September, October, November and December of 2015 and January of 2016. Fresh leaves and flowers of Rosmarinus officinallis L. were collected at Trás-os-Montes, in October, November and December of 2015. Dried leaves, flowers and berries were separately submitted to hydrodistillation using a Clevenger-type apparatus. The chemical composition of EOs was determined by gas chromatography mass spectrometry (GC-MS) analysis and the spectra in the infrared region was measured by (Fourier Transform Infrared Spectroscopy) FTIR. In local A, the myrtle leaves EO in 1st harvest presented 44 volatile compounds and in 2nd harvest a total 62 compounds were identified. The myrtle berries EO in 1st harvest presented 43 compounds and in 2nd harvest samples a total 53 compounds were identified. In local B, the main difference in myrtle EO was obtained in 2nd harvest with of total compounds identified, 49 and 50 respectively for leaves and berries. A total of 25 volatile compounds were identified by GC-MS accounting for 95.10% of the rosemary EO of the 1st harvest, while for the 2nd harvest were determined 24 compounds, corresponding to 97.55% of the total compounds. The MIC values for the essential oil leaves of Myrtus communis L. were 6.25 and 3.125 μL/mL, respectively 1st and 2nd harvest, against Listeria monocytogenes. Regarding the EO of Rosmarinus officinalis L., a value of 18.75 μL/mL was obtained against Listeria monocytogenes, showing a lower antimicrobial effect than myrtle EO. The myrtle EO showed MIC of 25 μL/mL for E. coli O157: H7 and Salmonella sp., except Pseudomonas spp. for which it presented a MIC of 50 μL/mL. For total mesophilic, samples with myrtle EO and rosemary EO had a microbial load at 672 hours of 7.96 log cfu/g and 9.47 log cfu/g, respectively. The myrtle EO has a greater effect on the inhibitory of microorganisms compared to rosemary EO. For LAB, samples with myrtle EO and rosemary EO had a microbial load at 672 hours of 8.07 log cfu/g and 8.95 log cfu/g, respectively. It can be concluded that myrtle EO is more effective in microbial reduction of LAB. For Enterobacteriaceae, samples with myrtle EO and rosemary EO have not showed microbial load until 672 hours with a microbial load of 7.14 and 8.19 log cfu/g, respectively at this time. Fungi had a microbial load at 672 hours of 6.87 log cfu/g and 7.21 log cfu/g, for samples with myrtle EO and rosemary EO, respectively. Myrtle EO and rosemary EO samples showed a slight growth of Listeria monocytogenes from 72 hours to 336 hours, followed by a decrease from 336 hours to 672 hours with a microbial load of 4.72 log cfu/g to 4.54 log cfu/g and 5,30 log cfu/g for 5.05 log cfu/g, respectively. EO can be used as control strategies to avoid L. monocytogenes proliferation, specially in food matrix that can support them patogen growth such as fresh cheese.
The main aim of this study was to evaluate the antimicrobial effect of essential oils (EO) of aromatic herbs in fresh sheep cheese inoculated with L. monocytogenes. In the control samples, total mesophilic microorganisms, lactic acid bacteria (LAB), Enterobacteriaceae and Fungi were analyzed, and pH and aw were also measured. The essential oils were obtained from plants harvested at different times and in different locations. Their antimicrobial effect against different bacteria was tested in vitro. Fresh leaves and berries of Myrtus communis L. were collected at Trás-os-Montes, in September, October, November and December of 2015 and January of 2016. Fresh leaves and flowers of Rosmarinus officinallis L. were collected at Trás-os-Montes, in October, November and December of 2015. Dried leaves, flowers and berries were separately submitted to hydrodistillation using a Clevenger-type apparatus. The chemical composition of EOs was determined by gas chromatography mass spectrometry (GC-MS) analysis and the spectra in the infrared region was measured by (Fourier Transform Infrared Spectroscopy) FTIR. In local A, the myrtle leaves EO in 1st harvest presented 44 volatile compounds and in 2nd harvest a total 62 compounds were identified. The myrtle berries EO in 1st harvest presented 43 compounds and in 2nd harvest samples a total 53 compounds were identified. In local B, the main difference in myrtle EO was obtained in 2nd harvest with of total compounds identified, 49 and 50 respectively for leaves and berries. A total of 25 volatile compounds were identified by GC-MS accounting for 95.10% of the rosemary EO of the 1st harvest, while for the 2nd harvest were determined 24 compounds, corresponding to 97.55% of the total compounds. The MIC values for the essential oil leaves of Myrtus communis L. were 6.25 and 3.125 μL/mL, respectively 1st and 2nd harvest, against Listeria monocytogenes. Regarding the EO of Rosmarinus officinalis L., a value of 18.75 μL/mL was obtained against Listeria monocytogenes, showing a lower antimicrobial effect than myrtle EO. The myrtle EO showed MIC of 25 μL/mL for E. coli O157: H7 and Salmonella sp., except Pseudomonas spp. for which it presented a MIC of 50 μL/mL. For total mesophilic, samples with myrtle EO and rosemary EO had a microbial load at 672 hours of 7.96 log cfu/g and 9.47 log cfu/g, respectively. The myrtle EO has a greater effect on the inhibitory of microorganisms compared to rosemary EO. For LAB, samples with myrtle EO and rosemary EO had a microbial load at 672 hours of 8.07 log cfu/g and 8.95 log cfu/g, respectively. It can be concluded that myrtle EO is more effective in microbial reduction of LAB. For Enterobacteriaceae, samples with myrtle EO and rosemary EO have not showed microbial load until 672 hours with a microbial load of 7.14 and 8.19 log cfu/g, respectively at this time. Fungi had a microbial load at 672 hours of 6.87 log cfu/g and 7.21 log cfu/g, for samples with myrtle EO and rosemary EO, respectively. Myrtle EO and rosemary EO samples showed a slight growth of Listeria monocytogenes from 72 hours to 336 hours, followed by a decrease from 336 hours to 672 hours with a microbial load of 4.72 log cfu/g to 4.54 log cfu/g and 5,30 log cfu/g for 5.05 log cfu/g, respectively. EO can be used as control strategies to avoid L. monocytogenes proliferation, specially in food matrix that can support them patogen growth such as fresh cheese.
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Dissertação de Mestrado em Segurança Alimentar
Palavras-chave
Segurança alimentar , Óleos essenciais , Listeria monocytogenes , Queijo , Rosmarinus officinalis , Myrtus communis