The occurrence and detection of moulds, mycotoxins and actinomycetes in UK grain

ABSTRACT
Mould growth in grain is undesirable since it leads to respiratory hazards for those handling the grain, loss of nutritional value and possible formation of poisonous substances (mycotoxins).

A number of techniques are available for assessing the microbiological quality of grain. Traditional cultural techniques are widely accepted and well understood although further research is needed to optimize and standardize the procedures. However. since cultural methods are slow attention has been directed recently to a number of rapid methods, the most promising of which are analysis of metabolic products and immunoassay. All of these require further investigation.

There is only limited information to indicate the numbers and types of moulds which occur on home-grown cereals before or after harvesting. Most of this has been gathered by ADAS in the course of advisory work. Wheat at harvest is subject to contamination with ergot as well as Fusarium, Alternaria and Cladosporium species but a change takes place in grain mycoflora during storage with these field moulds dying out in favour of Penicillium and Aspergillus species. More work is required to understand the changes in the mould population as a result of harvesting, drying and handling the grain on the farm before it is put into store.

The most insidious consequence of mould spoilage is the production of mycotoxins and over the past 25 years many such substances have been discovered and their role in human and animal disease recognized. Methods of analysis for mycotoxins are required for surveillance, quality control and public health enforcement programmes since a number of countries have enacted legislation to control mycotoxin levels in food and feed. Cytotoxicity tests are valuable for preliminary screening of samples for biological activity to identify those for which chemical analysis is warranted. They have particular value in detecting the presence of a toxin even when its chemical identity cannot be established. There is a very large amount of literature relating to chemical methods of analysis, such as TLC, HPLC and GLC, and many different methods are available for some mycotoxins. Nevertheless, new techniques such as immunoassay are emerging which could have a considerable impact on the speed and ease of mycotoxin analysis. However, the difficulties involved in mycotoxin analysis of naturally contaminated samples become apparent when methods are evaluated by a number of laboratories analyzing the same samples.

Different mould genera produce distinct groups of mycotoxins, therefore the possible range of contamination is dictated by the mycoflora, although widespread contamination of cereals with moulds, as in the case of the 1982 harvest. does not necessarily result in widespread mycotoxin contamination. Surveys have shown, however, that Fusarium toxins such as deoxynivalenol, nivalenol and zearalenone occur at low levels in home-grown wheat and barley at harvest (afthough there are few data relating to zearalenone). Unlike the moulds themselves, mycotoxins arising from field contamination remain together with those produced during storage. The latter are predominantly mycotoxinssuch as ochratoxin A and citrinin produced by Penicillium species. although aflatoxin B1 (produced by Aspergillus flavus) occurs spasmodically. The mycotoxins referred to so far are probably only the tip of the iceberg; current studies are revealing the presence of other hitherto unsuspected mycotoxins such as naphthoquinones, and it is clear that more research is needed into the co-occurrence of these and other toxins in home-grown cereals.

Although food processing operations such as milling, baking and brewing result in some losses of the mycotoxins found in cereals, a significant proportion may find its way into the human food chain. Few studies have been carried out to establish the identity and toxicity of the degradation products formed.

This review, completed in December 1988, has 93 pages in the full article.