Postharvest management

Grain at harvest and entering initial storage contains numerous microbes that could spoil the grain or produce toxins (Magan et al., 2003a). The microbial population present depends largely on the field conditions and harvesting process, and may change during storage. Sometimes grain is kept for a short period of time on the farm in buffer storage before drying. During this time conditions conducive to Fusarium growth may occur and the mycotoxin contamination level increase. Thus, poor postharvest management can result in rapid loss of quality and increased mycotoxin contamination. These problems are exacerbated in wet harvest years.

At harvest, moisture management is the dominant control measure for preventing further mycotoxin production. Moisture management requires prompt accurate measurement of moisture content and procedures to efficiently dry the grain, if needed. Another equally important control measure at this stage is an effective assessment of the crop for the presence of diseases such as Fusarium head blight. If diseased kernels are present, then an efficient method for separating diseased material from healthy grain also is needed.

In general, if efficiently dried to the correct moisture content, i.e., < 0.70 aw (< 14.5% moisture by weight), then there will be no additional fungal spoilage or mycotoxin production. However grain often is harvested at moisture levels far in excess of this level and may even be traded on a wet weight basis. The bulk drying and storage of grain presents technological challenges in addition to those that result from poor practice or negligence. Thus, mycotoxin production is a hazard associated with both preharvest grain production and with postharvest grain handling and storage.

Overall, the most important control measures relevant to storage stages are:

• Regular and accurate moisture determination.

• Prompt, efficient drying of wet grain. This process includes consideration of holding time/temperature prior to drying as well as the actual drying conditions.

• Infrastructure for quick response, including provisions for segregation of contaminated grain and appropriate transportation conditions.

• Appropriate storage conditions at all stages in terms of moisture and temperature control, and general maintenance of facilities to prevent pest and water ingress.

• Ability to efficiently identify and reject material below specified standards in terms of fungal disease and mycotoxin level, especially when passing material to a third party.

• Operation of approved supplier systems, i.e., setting the specifications for acceptance/ rejection.

Although complex, postharvest stages of the wheat commodity chain, including drying, storage, transportation, milling and baking are far more conducive to a "classic" type HACCP analysis than are the preharvest stages. Unlike the preharvest stages, in the postharvest stages it is possible to apply definitive control measures, to set critical limits, and to initiate monitoring procedures. In particular, flour milling and baking can be viewed as straightforward food processing procedures that are immediately amenable to the HACCP approach.

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