Post-harvest control strategies: Minimizing mycotoxins in the food chain

Abstract

Contamination of cereal commodities by moulds and mycotoxins results in dry matter, quality, and nutritional losses and represents a significant hazard to the food chain. Most grain is harvested, dried and then stored on farm or in silos for medium/long term storage. Cereal quality is influenced by a range of interacting abiotic and biotic factors. In the so-called stored grain ecosystem, factors include grain and contaminant mould respiration, insect pests, rodents and the key environmental factors of temperature, water availability and intergranular gas composition, and preservatives which are added to conserve moist grain for animal feed. Thus knowledge of the key critical control points during harvesting, drying and storage stages in the cereal production chain are essential in developing effective prevention strategies post-harvest. Studies show that very small amounts of dry matter loss due to mould activity can be tolerated. With <0.5% dry matter loss visible moulding, mycotoxin contamination and downgrading of lots can occur. The key mycotoxigenic moulds in partially dried grain are Penicillium verrucosum (ochratoxin) in damp cool climates of Northern Europe, and Aspergillus flavus (aflatoxins), A. ochraceus (ochratoxin) and some Fusarium species (fumonisins, trichothecenes) on temperate and tropical cereals. Studies on the ecology of these species has resulted in modelling of germination, growth and mycotoxin minima and prediction of fungal contamination levels which may lead to mycotoxin contamination above the tolerable legislative limits (e.g. for ochratoxin). The effect of modified atmospheres and fumigation with sulphur dioxide and ammonia have been attempted to try and control mould spoilage in storage. Elevated CO2 of >75% are required to ensure that growth of mycotoxigenic moulds does not occur in partially dried grain. Sometimes, preservatives based on aliphatic acids have been used to prevent spoilage and mycotoxin contamination of stored commodities, especially feed. These are predominantly fungistats and attempts have been made to use alternatives such as essential oils and anti-oxidants to prevent growth and mycotoxin accumulation in partially dried grain. Interactions between spoilage and mycotoxigenic fungi and insect pests inevitably occurs in stored grain ecosystems and this can further influence contamination with mycotoxins. Effective post-harvest management of stored commodities requires clear monitoring criteria and effective implementation in relation to abiotic and biotic factors, hygiene and monitoring to ensure that mycotoxin contamination is minimised and that stored grain can proceed through the food chain for processing.

Postharvest Practices of Maize Farmers in Kaiti District, Kenya and the Impact of Hermetic Storage on Populations of Aspergillus Spp. and Aflatoxin Contamination

“…Other findings demonstrated that the ability of A. flavus to produce aflatoxin in groundnuts was substantially reduced with the increase in CO 2 and decrease in O 2 concentrations (Bartosik et al, 2008). Magan & Aldred (2007) observed that aflatoxin production decreased by 25% when CO 2 was elevated to 20% although it had no visible effect on growth and sporulation of fungi.…”

Ozone as fungicide in rice grains

“…Fungal activity, especially during storage, can lead to a rapid deterioration in the nutritional quality of grains and contamination with mycotoxins (Magan & Aldred, 2007). The fungal microbiota that most affects stored rice grains is of two genera: Penicillium and Aspergillus (Pitt, 2000).…”

Análise de trilha da contaminação por aflatoxinas em grãos de milho armazenados

“…A manutenção da qualidade ou a aceleração da degradação, durante esta etapa, é influenciada pela eficiência do processo de secagem, teor de umidade dos grãos, atmosfera e período de armazenagem, controle de pragas, temperatura e umidade relativa do ar, percentual de grãos danificados, presença de impurezas, matérias estranhas, microrganismos, insetos e ácaros (Magan & Aldred, 2007).…”