Spotlight Food & Beverage Analysis


Mykotoxins are natural metabolism products of moulds which have a toxic effect on humans and animals. Just like micro- organisms which generate antibiotics, moulds which generate mycotoxins have spread all over the world. Aflatoxins are the most toxic form of mycotoxins. Some types of food show an increased risk of aflatoxin release due to fungal infestation: dried fruit, spices, nuts (peanuts, hazelnuts, pistachios) and grain (wheat, corn).


Detection of Mycotoxins in Nuts


Mycotoxins need certain conditions of temperature and humidity to form as well as sufficient nutrients. These conditions often occur with food when it is stored too long and in an unsuitable way. The result can be a complete family of chemical compounds instead of only one substance. As mycotoxins are temperature-resistant they are usually not destroyed when the food is processed.


PRELIMINARY AND FINE SIZE


“Often entire ship loads of nuts or similar products cannot be released before the aflatoxin content is determined exactly. The method described here provides representative results in a very short time thus giving the


supplier as well as the consumer optimum protection.”


Author Details:


Dr. Andreas Theisen Retsch GmbH


42781 Haan, Germany Phone: +49 2129/5561-0 Fax: +49 2129/87 02 E-Mail: info@retsch.com


Hazelnuts before grinding The result of preliminary size reduction


REDUCTION For a sufficient extraction of the mycotoxins from the initial product, the sample must be reduced in size and homogenized. As the maximum permissible mycotoxin values range between 0.025 and 15 µg/kg and fungal infestation usually occurs in nests, a random sample taken from the bulk must be sufficiently large to allow for the detection of contaminants. The first step is the preliminary size reduction of a representative amount of 1 - 2kg per ton of nuts with the Retsch Cutting Mill SM 100 to a particle size of 1 - 3mm. This mill is suitable for the rapid and gentle size reduction of dry materials down to a fineness of 0.25mm. The sample is then divided into representative sub-samples with the help of the rotary tube divider PT 100 which provides a very high division accuracy.


The subsequent fine size reduction is ideally carried out with Retsch's Ultra Centrifugal Mill ZM 200. This powerful rotor mill is easy and safe to operate and very versatile due to a wide selection of accessories. For the processing of hazelnuts, the use of distance sieves is recommendable which have been specially developed for grinding temperature-sensitive brittle materials. As mycotoxins are lipophilic, the grinding process should be as gentle as possible to avoid the release of fat from the sample. A fineness of 300 µm is sufficient for the subsequent extraction of the mycotoxins from the sample.


EXTRACTION


For the extraction 25g of the homogenised sample are shaken in 200ml water/acetonitrile (16+84 v/v) for 60 minutes and are then filtrated. 100ml of the filtrate are extracted with 100ml petroleum ether. The petroleum ether phase can be disposed. An aliquot of the remaining phase is mixed with activated carbon / Al2


O3


SM 100


The solution is introduced to an immuno-affinity column, washed with water and eluted with methanol. The eluate can then be analysed by HPLC.


HIGH PERFORMANCE LIQUID / Celite (7:5:3 - w/w/w)


for 10 minutes and then centrifuged. The supernatant is evaporated and resolved in water.


CHROMATOGRAPHY High Performance Liquid Chromatography (HPLC) is an analysis method which has various advantages such as high selectivity and reproducibility and very low detection levels.


For sample preparation, immuno-affinity columns are available for solid phase extraction (SPE). Retaining the


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