Abstract
Ochratoxin A (OTA) is a mycotoxin which is a common contaminant in grains during storage. Aspergillus ochraceus is the most common producer of OTA. Essential oils play a crucial role as a biocontrol in the reduction of fungal contamination. Essential oils namely natural cinnamaldehyde, cinnamon oil, synthetic cinnamaldehyde, Litsea citrate oil, citral, eugenol, peppermint, eucalyptus, anise and camphor oils, were tested for their efficacy against A. ochraceus growth and OTA production by fumigation and contact assays. Natural cinnamaldehyde proved to be the most effective against A. ochraceus when compared to other oils. Complete fungal growth inhibition was obtained at 150–250 µL/L with fumigation and 250–500 µL/L with contact assays for cinnamon oil, natural and synthetic cinnamaldehyde, L. citrate oil and citral. Essential oils had an impact on the ergosterol biosynthesis and OTA production. Complete inhibition of ergosterol biosynthesis was observed at ≥100 µg/mL of natural cinnamaldehyde and at 200 µg/mL of citral, but total inhibition was not observed at 200 µg/mL of eugenol. But, citral and eugenol could inhibit the OTA production at ≥75 µg/mL and ≥150 µg/mL respectively, while natural cinnamaldehyde couldn’t fully inhibit OTA production at ≤200 µg/mL. The inhibition of OTA by natural cinnamaldehyde is mainly due to the reduction in fungal biomass. However, citral and eugenol could significant inhibit the OTA biosynthetic pathway. Also, we observed that cinnamaldehyde was converted to cinnamic alcohol by A. ochraceus, suggesting that the antimicrobial activity of cinnamaldehyde was mainly attributed to its carbonyl aldehyde group. The study concludes that natural cinnamaldehyde, citral and eugenol could be potential biocontrol agents against OTA contamination in storage grains.
Highlights
Aspergillus species are frequent contaminants of low-moisture foods
Natural cinnamaldehyde, synthetic cinnamaldehyde, L. citrate oil and citral significantly inhibited the growth of A. ochraceus at 502250 mL per liter malt extract agar (MEA) medium (P,0.01)
After 20 days incubation, the plates showing no growth were incubated for a further 7 days after removal of Essential oils (EOs), and no visible growth of A. ochraceus mycelia was observed. These results suggested a fungistatic effect of natural cinnamaldehyde, cinnamon oil, synthetic cinnamaldehyde and citral at lower concentrations and a fungicidal effect at higher concentrations
Summary
Aspergillus species are frequent contaminants of low-moisture foods (water activity ,0.75). Increase in metabolic activity of Aspergillus species causes the food to spoil leading to enormous economic loss. Some Aspergillus species can produce toxic secondary metabolites: like aflatoxins, ochratoxins and they affect the food safety. Ochratoxin is common contaminant in food products such as cereals, coffee, wine, beer, and spices. Ochratoxin A (OTA) is the commonly produced analogue and highly toxic [4]. OTA is mainly produced by Aspergillus ochraceus, Aspergillus carbonarius, Aspergillus westerdijkiae, Aspergillus niger, Penicillium nordicum and Penicillium verrucosum [5]. A. ochraceus is responsible for OTA contamination in rice, wheat, oats, coffee, and beverage. A. carbonarius and A. niger are responsible for OTA in grapes, raisins, and wine [6,7]
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