Suppression of ochratoxin biosynthesis by naturally occurring alkaloids.

The effects of four alkaloids on the biosynthesis of ochratoxin A (OTA), ochratoxin B (OTB) and citrinin were examined on four OTA-producing aspergilli: Aspergillus auricomus, A. sclerotiorum and two isolates of A. alliaceus. Piperine and piperlongumine, natural alkaloids of Piper longum, significantly inhibited OTA production at 0.001% (w/v) for all aspergilli examined. Piperine and piperlongumine affected the polyketide synthesis step of OTA production and inhibited production of citrinin. Curcumin, a constituent of tumeric, completely inhibited mycelial growth of A. alliaceus isolate 791 at 0.1% (w/v) and decreased OTA production by approximately 70% at 0.01% (w/v). Sesamin, a constituent of sesame oil, inhibited OTA and OTB production by 60 and 45%, respectively, at 0.1% (w/v), showing its effect was on chloroperoxidase and polyketide synthase activity. The potential advantage of these natural products to reduce ochratoxin contamination of agricultural commodities is discussed.

Integration of enzyme-linked immunosorbent assay with conventional chromatographic procedures for quantitation of aflatoxin in individual cotton bolls, seeds, and seed sections.

Integration of an enzyme-linked immunosorbent assay (ELISA) with conventional chromatographic methods proved the versatility of ELISA as a research tool and allowed for rapid assessment of aflaxtoxin in individual cottonseeds, parts of cottonseed, and composite samples of seeds taken from individual cotton bolls. Aqueous acetone was substituted for methanol in the extraction procedure prescribed by ELISA. The substitution allowed the use of a common extract for all analytical methods. An aliquot of the extract was used to screen samples by ELISA. Negative samples were identified, and toxin levels between 1 and 70 ng/g were quantitated by ELISA. Samples with toxin levels beyond the upper limit of detection by ELISA were then subjected to more time-consuming conventional cleanup prior to quantitation by liquid chromatography (LC) or thin-layer chromatography (TLC). Toxin levels detected by LC or TLC ranged from 100 to 845,000 ng/g sample. The screen by ELISA detected large numbers of toxin-negative cotton bolls or individual seeds in minimum analysis time. The combination of techniques verified the presence of seed with no toxin adjacent to toxin-containing seed in the same lock. Toxin-negative portions of individual seed with high toxin in another portion were identified for the first time. Integration of techniques provided needed information on distribution patterns of aflatoxin in cotton so that preventive measures can be developed.