Many agricultural products are very susceptible to infection from moulds (fungi) that are widespread in the environment. These moulds can, under some circumstances, produce secondary metabolites known as mycotoxins.
Mycotoxins are toxic chemical contaminants which are harmful to human and animal health. In some cases they are known to be carcinogenic to humans at very low levels, and are therefore, of widespread concern as contaminants in the food chain.
Not all moulds produce mycotoxins, as the environmental conditions need to be favourable both for mould growth and to stimulate toxin production. Mould infection of vulnerable commodities such as red pepper spice (Capsicum annuum) may occur at any stage of production, from pre-harvest to drying and subsequent storage.
Mycotoxin formation is influenced by many factors such as the climate of the region, genotype of the crop planted and soil type. It is promoted by stress or damage to the crop due to drought, insect activity, heavy rains at and after harvest, and inadequate drying of the fruit before storage. As most mycotoxins are stable compounds and survive processing and storage, measures are taken by food safety authorities to control levels of contamination.
The critical conditions for mycotoxin production vary for different moulds, but moisture content (water activity) and temperature are important. Dried products are stable and safe from these fungal problems, but pre-harvest and during the drying process itself, the water activity will be within the critical range for mycotoxin production for a period of time. Generally, the sooner post-harvest drying can be undertaken and the quicker the drying process, the lower the risk of mycotoxin formation.
Red peppers are dried usually in greenhouse dryers or by spreading them on the ground in the open in most parts of the world. The colour retention of red pepper dried either under open atmosphere or greenhouse dryers can also be challenging since the necessary drying time is long in either case and browning reactions can occur in red pepper.
Unfortunately, during traditional sun-drying, infected fruit are also susceptible to mycotoxin formation. Even though not every fruit will be contaminated with mycotoxins, after grinding to a powder, the toxins will be distributed to an extent and detectable in the finished product.
Regulatory Controls & Enforcement
There are two different mycotoxins of concern with respect to contamination of spices. These are the co-occurring aflatoxins B1, B2, G1 and G2, which are formed both pre- and post-harvest and ochratoxin A which is formed only post-harvest during drying and storage.
In the EU, there are tough regulations concerning the levels of aflatoxins permitted in many commodities including spices. European Commission Regulation No 165/2010 covers Capsicum spp (dried fruits thereof, whole or ground, including chillies, chilli powder, cayenne and paprika), Piper spp (fruits thereof, including white and black pepper), Myristica fragrans (nutmeg), Zingiber officinale (ginger), Curcuma longa (turmeric) and mixtures of spices containing one or more of the above.
The regulations do not permit levels of aflatoxin B1 to exceed 5 µg/kg (ppb) nor total levels of aflatoxins to exceed 10 µg/kg in spices. These are exceeding low limits and are challenging to measure accurately. For ochratoxin A, at present time, the limits have not been extended to apply to spices although there are EU limits for some foodstuffs such as dried fruit.
Consignments of commodities which are exported to the EU may be detained at the border inspection post, and if deemed to be a high risk of mycotoxin contamination, will be subjected to sampling and analysis. EU Regulations stipulate how sampling should be undertaken in order to minimise uncertainty with respect to inhomogeneity of mycotoxin contamination which is a particularly acute problem.
For consignments of less than 15 tonnes, depending on the total weight, 5-100 incremental samples are taken, comprising a total sample size ranging from 0.5 to 10 kg. For consignments above 15 tonnes in total weight, 100 incremental samples are taken to give an analytical sample of 10 kg.
The regulations also specify how the sample should be divided, mixed and sub-sampled for analysis. This sampling may seem excessive but it is essential in order to ensure that the analytical sample is representative of the overall average level of contamination.
IN THE EU, THERE ARE TOUGHT REGULATIONS CONCERNING THE LEVELS OF AFLATOXINX PERMITTED IN MANY COMMODITIES, INCLUDING SPICES.
The EU Rapid Alert System for Food and Food (RASFF) shows there were 93 consignments of herbs and spices which were detained by authorities from January 2011 to October 2012 because of aflatoxin levels exceeding EU limits.
Of these products, 65 percent originated from India and were predominately chilli or nutmeg spices. On occasions, the levels found have been very high. For example, in August 2012, a consignment of chilli powder from India was found to have aflatoxin levels more than 20 times higher than the EU limits (aflatoxin B1 of 114 µg/kg with total aflatoxin levels of 120 µg/kg).
Even though ochratoxin A is not formally covered by existing EU regulations, there have nevertheless been consignments of spices detained as they were tested and found to have high levels of this mycotoxin, for example, dried chilli from Thailand found to contain 50.8 µg/kg of ochratoxin A.
Contaminated consignments of spices are invariably destroyed by the authorities, with consequent high financial costs to both the importer and producer in the country of origin. However, the producer not only suffers financial loss of the commodity itself, but will also have to cover the costs of production, transport, storage and will be required to pay the costs incurred by the authorities. As such, there are significant financial incentives to ensure that consignments of spices exported to the EU meet regulatory requirements with respect to levels of mycotoxin contamination.
There are some ‘Good Agricultural Practices (GAP)’ that can be undertaken during harvesting, processing and drying of spices to minimise fungal infection and reduce the risks of subsequent mycotoxin formation.
For example, thick layers of peppers should not be spread in direct contact with the soil during drying as this can be a significant infection route. Sheets of plastic or other suitable materials should be used as a barrier between the layer of fruit and the ground. Covering at night avoids condensation and provides protection in the event of a rain shower, which can re-wet the partially dried material and lead to fungal growth and mycotoxin formation.
Nevertheless, notwithstanding measures to minimise mycotoxin formation, it is still essential that all batches of spices in their final dried powdered state are fully tested to ensure that consignments for export meet regulatory requirements. Only testing following the same sampling regime as the EU authorities can fully guarantee that spices will meet statutory limits and allowed to enter the market.
There have been enormous advances in recent years in the available testing procedures for mycotoxins in spices, which enable reliable measurement at low levels for aflatoxin B1 and ochratoxin A. Testing methods nowadays employ antibodies incorporated into diagnostic test kits in various different ways, to isolate the mycotoxin of interest and provide a quantitative indication of whether a sample is compliant with regulations. Companies supply a range of products for testing aflatoxins and ochratoxin A in spices.
There are test kits available, such as test cards or lateral flow devices, are suitable for testing in the field without laboratory facilities. There are also products (such as immunaffinity columns) that are routinely used in analytical chemistry laboratories as a purification technique prior to analysis by an instrument known as HPLC.
The simplest of testing involves shaking a small sample of spice with solvent in a test tube, passing the extract through a column for purification before applying a few drops of the solution to a test card. Some simple steps are then taken, applying various reagents to the test card. Within a few minutes the results are obtained, with a negative result appearing as a coloured spot on the card, whereas a positive result (above the regulatory limit) does not give any colouration.
In the analytical laboratory the immunoaffinity columns for aflatoxin analysis, ochratoxin A and simultaneous analysis of both toxins have become accepted as the standard methods which are employed for official purposes both in the EU and elsewhere.
The CEN, the European Committee for Standardization has adopted many immunoaffinity based analytical methods as the standard by which official testing laboratories measure and control imports. Similar validated methods have also been adopted by AOAC International as official methods.
Spice producers in Asia should seek advice on appropriate testing which can be freely provided by mycotoxin test kit manufacturers, both from the perspective of factory testing or out-sourcing to an appropriate contract laboratory. Although inevitably costs are incurred through testing, these manageable costs are far preferable to risking the substantial financial losses of detention and destruction of exported consignments of spices.