Ecophysiology of Penicillium expansum and patulin production in synthetic and olive-based media
Artigo de ConferênciaTeses
Visão geral
Pesquisas
Ver Todos
Visão geral
resumo
In the Mediterranean basin, a large number of olive varieties are cultivated. In Tunisia, oliviculture represents one of the most significant agricultural products that are produced annually. Storage under inadequate conditions poses serious problems concerning fungal contamination, with consequent defects and potential mycotoxin production in olives and olive oils. Penicillium expansum represents one of the most significant postharvest pathogens in several fruits, including olives. Not only it causes blue mold but also is the most relevant patulin (PAT) producing species of the genus Penicillium.
In this study, the first aim was to identify and characterize a selected group of fungi previously isolated from olives from Tunisian groves. For this purpose, 28 fungi were selected for identification by a polyphasic approach consisting of: i) morphological identification on Malt Extract Agar (MEA) and Czapek Yeast Autolysate (CYA); and ii) molecular identification by sequencing of the ITS region of the rRNA gene. Mycotoxigenic ability of fungi was screened on Coconut Agar Medium (CAM). Methanolic extracts of those fungi showing fluorescence on CAM were obtained from CYA cultures and analysed by HPLC. The second aim of this research was to evaluate the ecophysiological conditions governing growth and PAT production by P. expansum strains previously isolated from Tunisian olives. For this purpose, four P. expansum isolates (three from olives and one reference strain) were tested in a synthetic medium (CYA) and in olive-based medium (OM) for their ability to grow and produce PAT under different temperatures (4 ºC, 15 ºC and 25 ºC) for 10 and 20 days. Growth was measured through the colonies’ diameter, and PAT mycotoxin was analyzed by HPLC-UV.
After morphological and molecular identification, eight species belonging to the genera Alternaria, Aspergillus, Fusarium, Penicillium, Pleospora and Trichothecium were identified. The dominant genus was Penicillium (82% of the isolates), and the species identified were P. expansum, P. crustosum and P. polonicum. Based on HPLC analysis three of the four P. expansum isolates were able to produce PAT.
In the ecophysiology study, all isolates were able to grow on tested media at different temperatures, with maximum growth at 25 ºC. Different PAT production profiles were
ii
found. Maximum PAT production occurred at 15 ºC on CYA after 10 days of incubation, but a significant increase was observed on OM between 10 and 20 days of incubation. At 4 ºC, PAT was produced only on CYA after prolonged incubation.
In conclusion, contamination of olives with PAT must be considered in the safety and quality plans of production. The olive-based matrix does not seem to be highly adequate for growth and PAT production by P. expansum only if adequate temperatures throughout storage (refrigeration) are guaranteed. However, if there is an abuse on storage temperature and longevity, PAT becomes a real risk.
The olive and its derivatives, in particular olive oil, represent one of the most significant agricultural products in the Mediterranean basin. Storage under inadequate conditions poses serious problems concerning fungal contamination, with consequent defects and potential mycotoxin production in olives and olive oils. Penicillium expansum represents one of the most significant postharvest pathogens in several fruits, including olives. Not only it causes blue mold but also is one of the most relevant patulin (PAT) producing species of the genus Penicillium.
The aim of this research was to evaluate the ecophysiological conditions governing growth and PAT production by P. expansum strains previously isolated from Tunisian olives. For this purpose, four P. expansum isolates were tested in a synthetic medium (Czapek Yeast Autolysate, CYA) and in olive-based medium (OM) for their ability to grow and produce PAT under different temperatures (4 ºC, 15°ºC and 25°ºC) for 10 and 20 days. The mycotoxin was analysed by HPLC-UV.
Results showed that all isolates were able to grow on tested media at different temperatures. Different PAT production profiles were found, showing that at 25 ºC P. expansum isolates were able to produce PAT on CYA and OM medium. At 15 ºC the production of PAT was only detected on CYA medium, while no PAT production was detected at 4 ºC for the two media.
