Rapid and specific method for screening ergosterol as an index of fungal contamination in cereal grains

Investigating Useful Properties of Four Streptomyces Strains Active against Fusarium graminearum Growth and Deoxynivalenol Production on Wheat Grains by qPCR

Streptomyces spp. can be exploited as biocontrol agents (BCAs) against plant pathogens such as Fusarium graminearum, the main causal agent of Fusarium head blight (FHB) and against the contamination of grains with deoxynivalenol (DON). In the present research, four Streptomyces strains active against F. graminearum in dual plate assays were characterized for their ability to colonize detached wheat grains in the presence of F. graminearum and to limit DON production. The pathogen and BCA abundance were assessed by a quantitative real-time PCR, while DON production was assessed by HPLC quantification and compared to ergosterol to correlate the toxin production to the amount of fungal mycelium. Fungal growth and mycotoxin production were assessed with both co-inoculation and late inoculation of the BCAs in vitro (three days post-Fusarium inoculation) to test the interaction between the fungus and the bacteria. The level of inhibition of the pathogen and the toxin production were strain-specific. Overall, a higher level of DON inhibition (up to 99%) and a strong reduction in fungal biomass (up to 71%) were achieved when streptomycetes were co-inoculated with the fungus. This research enabled studying the antifungal efficacy of the four Streptomyces strains and monitoring their development in DON-inducing conditions.

Three-Dimensional Study of F. graminearum Colonisation of Stored Wheat: Post-Harvest Growth Patterns, Dry Matter Losses and Mycotoxin Contamination

Fusarium causes significant post-harvest quality losses and mycotoxin contamination in stored wheat but the colonisation dynamics of the grain and how this may be affected by the initial inoculum position in the grain mass is poorly understood. This study examined the 3D growth kinetics and mycotoxin production (deoxynivalenol and zearalenone) by F. graminearum during hyphal colonisation from different initial inoculum positions in wheat microcosms (top-centre, bottom-centre, and bottom-side) maintained at two water activities (a_w; 0.95 and 0.97). Clear jars were used to visually follow the colonisation dynamics. Fungal respiration and associated dry matter loss (DML) and ergosterol were also quantified. Colonisation dynamics was shown to be affected by the inoculation position. At the end of the colonisation process, fungal respiration and DML were driven by the inoculation position, and the latter also by the prevailing a_w. Fungal biomass (ergosterol) was mainly affected by the a_w. The initial inoculum position did not affect the relative mycotoxin production. There was a positive correlation between respiration and ergosterol, and between mycotoxin production and colonisation indicators. We suggest that spatially explicit predictive models can be used to better understand the colonisation patterns and mycotoxin contamination of stored cereal commodities and to aid more effective post-harvest management.

Grading of fermented and dried cocoa beans using fungal contamination, ergosterol index and ochratoxin a production

Sixty four samples of cocoa beans replicated in quadruplicates were collected from five warehouses from southwest Nigeria and examined for fungal loads, ergosterol and ochratoxin A The levels of all the variables obtained were further used as indices for cocoa grading into food quality, FoQ (erg < 5 mg/kg; OTA < 1 µg/kg), feed quality, FeQ (erg = 5~10 mg/kg; OTA in the range of 1.1~3.11 µg/kg), Screen for mycotoxin, SFM (erg = 10~20 mg/kg; OTA from 3.12 µg/kg and above) with fuel quality, FuQ having erg > 20 mg/kg and OTA > 6.12 µg/kg. Using these ergosterol indices, 18.75% of the cocoa beans examined was classified with the FoQ, 18.75% with the FuQ while 31.25% was classified with both the FeQ and the SFM, respectively. In conclusion, ergosterol can be used as a rapid index to grade fermented, dried cocoa beans meant for export.

Relationship of mould count, ergosterol and ochratoxin A production

The relationship between viable mould count, ergosterol content and ochratoxin A (OA) formation was studied at different inoculum concentrations of Aspergillus ochraceus NRRL 3174 and Penicillium verrucosum NRRL 3260 grown on sterile long-grain enriched white rice as the substrate. Ergosterol was determined by extraction, saponification and quantification using high performance thin layer chromatography (HPTLC) with UV detection. Ergosterol and ochratoxin A were detected after 3 days of incubation and reached their maximum at 7-10 days of incubation. After that, a decline in the concentrations in both ergosterol and ochratoxin was observed. Ergosterol measurement by HPTLC appeared to be a useful method to detect fungal activity, which corresponded to ochratoxin production. Thus, the ergosterol assay may have a use as an early indicator of potential mycotoxin production.

Anti-aflatoxigenic activity of Lactobacillus casei pseudoplantarum

Lactobacillus casei pseudoplantarum 371 isolated from a silage inoculant was found to inhibit aflatoxins B1 and G1 biosynthesis by Aspergillus flavus subsp. parasiticus NRRI. 2999, in liquid medium. The inhibitory activity in the Lactobacillus cell-free supernatant was found to be sensitive to proteolytic enzymes such as trypsin and alpha-chymotrypsin, but resistant to pepsin. Lab-Lemco tryptone broth (LTB), supplemented with 20% of dialyzed protein concentrate of the supernatant, totally inhibited the production of aflatoxins B1 and G1. When the protein concentrate was digested with trypsin, the production of aflatoxins B1 and G1 was restored. The inhibitory activity of the supernatant was inactivated within 10 min at 100 degrees C. A. flavus grown in the Lactobacillus cell-free supernatant did not produce a mutagenic response in the Salmonella mutagenicity test. However, Lactobacillus casei pseudo plantarum 371 did not have an effect on aflatoxin production and mold growth as measured by ergosterol and plate count, when the organisms were inoculated together on sterile steamed rice.