Spatio-temporal analysis of post-harvest moulds genera distribution on stored durum wheat cultivated in Tunisia

Wheat represents a principal ingredient in traditional Tunisian diet including couscous, bread, pasta and biscuits. Northen Tunisia is an important growing area of wheat which after harvest is stored in silos and on farm. The cereal grains can become contaminated by post-harvest moulds during storage in silos under unfavorable conditions leading to a decrease in quality, packing and marketing of wheat. In this study, a mycological survey was undertaken to determine the biodiversity of post-harvest moulds on durum wheat stored in silos localized in five regions of Northern Tunisia and to investigate changes during the storage period. A total of 127 samples were obtained from Oued Mliz, Jendouba, Ksar Mezouar, Mateur and Ghezala silos during 2010-2011 and 2011-2012 wheat seasons. After sampling, seeds were placed on Potato Dextrose Agar medium (PDA) for 7 days of incubation at 28 degrees C. A total of 6035 strains of filamentous fungi were isolated. The quantitative and qualitative changes on wheat mycoflora during storage were statistically explored by multivariate methods including correspondence and hierarchical cluster analysis. The most predominant post-harvest moulds genera isolated were Alternaria (28%), Fusarium (19%), Penicillium (19%), Aspergillus (14%), Mucor (8%) and Rhizopus (7%). Various genera of fungi imperfecti, including Ulocladium, Geotrichum, Chaetomium, Trichothecium, Paecilomyces, Aureobasidium and Chrysonilia (anamorphic Neurospora), and the Mucorales genera Lichtheiia and Syncephalastrum accounted for the remainder of about 6% of the total. Statistical data analysis revealed six mycological patterns corresponding to six distinct communities as characterized by the prevalence of different moulds. Such patterns clearly showed different spatio-temporal variability indicating that distribution and evolution of moulds during storage was sensitive to geographic location, year of sampling and short or long-term storage

Lactic acid bacteria against post-harvest moulds and ochratoxin A isolated from stored wheat

A total of 54 lactic acid bacteria (LAB) were isolated from stored wheat samples sourced from grain silos in North Tunisia. Fifteen representative isolates were identified by 16S rDNA sequencing as Pediococcus pentosaceus, Lactobacillus plantarum, Lactobacillus graminis, Lactobacillus coryniformis and Weissella cibaria. These isolates were screened for antifungal activity in dual culture agar plate assay against eight post-harvest moulds (Penicillium expansum, Penicillium chrysogenum, Penicillium glabrum, Aspergillus flavus, Aspergillus niger, Aspergillus carbonarius, Fusarium graminearum and Alternaria alternata). All LAB showed inhibitory activity against moulds, especially strains of L. plantarum which exhibited a large antifungal spectrum. Moreover, LAB species such as L plantarum LabN10, L. graminis LabN11 and P. pentosaceus LabN12 showed high inhibitory effects against the ochratoxigenic strain A. carbonarius ANC89. These LAB were also investigated for their ability to reduce A. carbonarius ANC89 biomass and its ochratoxin A (OTA) production on liquid medium at 28 and 37 degrees C and varied pH conditions. The results indicated that factors such as temperature, pH and bacterial biomass on mixed cultures, has a significant effect on fungal inhibition and OTA production. High percentage of OTA reduction was obtained by L. plantarum and L. graminis (>97%) followed by P. pentosaceus (>81.5%). These findings suggest that in addition to L. plantarum, L graminis and P. pentosaceus strains may be exploited as a potential OTA detoxifying agent to protect humans and animals health against this toxic metabolite