Browsing by Author "Abid, Salwa"
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- Efeito de uma cultura starter e de leveduras nativas na produção de Ocratoxina A por Penicillium nordicum em produtos cárneosPublication . Meftah, Sana; Abid, Salwa; Dias, Teresa; Rodrigues, PaulaOcratoxina A (OTA) é uma das mais relevantes micotoxinas da cadeia alimentar animal e humana. Em produtos cárneos fermentados, Penicillium nordicum é considerado o principal produtor de OTA. Diversas estratégias têm sido desenvolvidas de forma a reduzir a acumulação de OTA em produtos alimentares. O presente trabalho teve como objetivo avaliar o papel de leveduras e de uma cultura starter comercial no crescimento de P. nordicum e na produção de OTA em produtos cárneos. Os mecanismos subjacentes aos efeitos observados foram também estudados. A cultura starter e duas leveduras (Candida zeylanoides e Rhodotorula mucilaginosa) isoladas de chouriços de carne de porco foram co-inoculadas com P. nordicum em três meios de cultura preparados com carne – presunto, chouriço tradicional e chouriço industrial. O crescimento do fungo foi determinado por medição do diametro da colónia e a OTA foi quantificada por HPLC-FL. Verificou-se que apenas nos meios de cultura à base de presunto ocorreu a produção de OTA por P. nordicum e que ambas as leveduras reduziram significativamente a produção de OTA, sendo a C. zeylenoides a mais eficaz. Por sua vez, a cultura starter estimulou significativamente a produção de OTA. O contato direto e o crescimento simultâneo dos organismos estudados foram os mecanismos mais significativos nas respostas fúngicas Este trabalho evidencia que P. nordicum não reage a todos os microrganismos da mesma forma. O uso de agentes de biocontrolo com o objetivo de reduzir o crescimento fúngico e a produção de micotoxinas pode provocar efeitos contraditórios, conduzindo a problemas de segurança inesperados.
- Efeito de uma cultura starter e de leveduras nativas na produção de Ocratoxina A por Penicillium nordicum em produtos cárneosPublication . Meftah, Sana; Abid, Salwa; Dias, Teresa; Rodrigues, PaulaOchratoxin A (OTA) is a secondary metabolite produced by Penicillium and Aspergillus genera and is considered one of the most important mycotoxins occurring in animal and human food chains. Oxidative stress, inhibition of protein synthesis, disruption of calcium homeostasis, inhibition of mitochondrial respiration and DNA damage are some of OTA´s mechanisms of action causing teratogenicity, immunotoxicity, neurotoxicity and mostly nephrotoxicity. In dry-cured and fermented meat products, OTA is strongly associated with Penicillium nordicum. Fungal growth and OTA production in meat products can be influenced by environmental conditions, physico-chemical characteristics of the matrix, and its endogenous flora. OTA is highly stable, so its destruction during normal food processing is very difficult to achieve. Bacteria and fungi have been tested as biocontrol agents against fungal development and OTA production, with variable results.
- Effect of commercial starter cultures and native yeasts on Ochratoxin A production in meat productsPublication . Meftah, Sana; Abid, Salwa; Dias, Teresa; Rodrigues, PaulaOchratoxin A (OTA) is one of the most important mycotoxins in animal and human food chains, and its distribution is universal. Increased oxidative stress, inhibition of protein synthesis, and DNA damage are some of OTA’s mechanisms of action. It is nephrotoxic, teratogenic, immunotoxigenic and carcinogenic. OTA is produced by several strains of Penicillium and Aspergillus species. In dry-cured and fermented meat products, it is strongly associated with Penicillium nordicum, but Aspergillus westerdijkiae, a strong OTA producer usually associated with contamination of coffee beans, has also been found to be responsible for high OTA levels in cured meat products. Because of its harmful effects, many efforts have been put on the development of strategies able to reduce the accumulation of OTA in food products, either by inhibition of fungal growth, inhibition of OTA production or OTA degradation. This work aimed to evaluate the role of yeasts, previously isolated from meat products, and of a commercial starter culture, on the growth of OTA-producing fungi as well as on OTA production, by using meat-based culture media as model systems. A commercial starter culture and 2 yeasts (Candida zeylanoides and Rhodotorula mucilaginosa) isolated from pork sausage were co-inoculated with P. nordicum and A. westerdijkiae separately in three meat-based culture media - ham, traditional sausage and industrial sausage - at different conditions: 15 °C and 20 °C; water activity 0.99, 0.98 and 0.96, for 15 days. Fungal growth was determined by measuring colony diameter and OTA was quantified by HPLC-FLD after extraction with methanol. Results showed that P. nordicum was only able to produce OTA in ham-based medium, with significant reduction of OTA production caused by all co-cultures, being C. zeylenoides the most effective. On the other hand, all co-cultures of A. westerdijkiae lead to a significant stimulation of OTA production, when compared with the control (A. westerdijkiae only). This is the first study evaluating the effects of either native or commercial starter cultures on the OTA-producing fungus A. westerdijkiae in meat products, and it highlights the need to account for all mycotoxigenic fungi potentially present in food products. Studies are currently being developed to try to understand the mechanism behind these unexpected results.
- Effect of dry-sausage starter culture and endogenous yeasts on Aspergillus westerdijkiae and Penicillium nordicum growth and OTA productionPublication . Meftah, Sana; Abid, Salwa; Dias, Teresa; Rodrigues, PaulaProcessed meat products frequently suffer from fungal and mycotoxin contamination, mostly ochratoxin A (OTA). Penicillium nordicum is considered responsible for this contamination, but Aspergillus westerdijkiae has recently been associated with high levels of OTA in meat products. Several biocontrol agents have been tested against P. nordicum growth and OTA production in meat products, but A. westerdijkiae has not been considered. The aim of this work was to evaluate in vitro the effect of a commercial starter culture used in sausage fermentation and of sausage-native yeasts on OTA production by A. westerdijkiae, as compared with the highly studied P. nordicum, in meat-based culture media. Four representative yeasts isolated from dry-cured sausage and a commercial starter culture were co-inoculated with both fungi in different meat-based media, under varying conditions. Fungal growth was determined by measuring colony diameter, and OTA production was quantified by HPLC-FLD. A. westerdijkiae was significantly stimulated to produce OTA under all tested conditions, and, in ham, OTA production by P. nordicum was stimulated by co-culture with the starter culture. In conclusion, endogenous or added microorganisms enrolled in fermentation or in biocontrol in meat products seem to exert varying responses on different ochratoxigenic fungi, thus leading to unforeseen safety problems.
- Mechanisms underlying the effect of commercial starter cultures and a native yeast on ochratoxin A production in meat productsPublication . Meftah, Sana; Abid, Salwa; Dias, Teresa; Rodrigues, PaulaProcessed meat products are of worldwide importance, but they are highly prone to fungal and ochratoxin A (OTA) contamination. In previous studies, several Lactic Acid Bacteria (LAB) and yeasts have been tested as biocontrol agents against P. nordicum growth and OTA production in meat products, with promising results. However, A. westerdijkiae has been poorly studied for this matrix. The aim of this work was to evaluate in vitro the mechanisms underlying the effects of a commercial starter culture and of a meat-native Candida zeylanoides strain on the growth and OTA production of P. nordicum and A. westerdijkiae, by co-culture in ham and sausage-based media under different conditions. In ham medium, C. zeylanoides live cells, cell broth and diffused compounds significantly inhibited OTA production by P. nordicum, but live cells of the starter culture significantly increased it. For A. westerdijkiae strong and significant stimulation was observed by direct contact in both media. In conclusion, ochratoxigenic fungi do not all respond to antagonistic microorganisms in the same way. This study sheds some light on the mechanisms behind the different effects of microorganisms.