Dressed maize kernels, prepared as seeds, are subject to testing in regards to possible contents of genetically modified organisms (GMO), according to Wieland Hopfe, application consultant at Fritsch.
Genetically modified maize was developed based on economic reasons: in order to gain a higher resistance against parasites such as, for example, the western corn rootworm or the European corn borer; stable and higher crop yields; and to obtain a quicker maturity.
Transgenic maize produces a toxic agent to repel these parasites.
In this context many questions remain unanswered - for example, the direct effect on humans; the impact on animals when used as animal feed and therefore the secondary effects on humans; implications on soils and therefore the following crops; the consequences for the entire animal kingdom, especially other insects; and the transfer of the modified gene to other crops.
Therefore, the cultivation and use of transgenic maize is not without controversy.
The necessity arises to test the seeds for possible properties of genetically modified contents.
From the to-be-examined type, 1,000 kernels are counted off and this amount is weighed.
Now, at least three samples with the same weight are drawn.
In the example, 1,000 kernels weighed 275g.
For the isolation of the DNA, 3g is weighed out.
The following theoretic deliberations clarify the necessity to grind the material as finely as possible.
On average a kernel weighs 0.275g.
Ten, or to be more exact, 11 kernels would correspond to a weight of 3g.
This means that without comminution, only each 100th kernel of the abovementioned sample would be analysed.
Forty kernels displace 10ml of water.
Consequently, an average volume of 0.25cm3 and a diameter (calculated as a sphere) of approximately 7.8mm can be determined for a kernel.
In order to consider in the weighted sample of 3g all kernels, at least each kernel has to be broken up in 1,000 pieces.
Then, in terms of figures, a 2.75g sample could contain of each maize kernel 10 pieces with a diameter of 0.75mm.
In order to absolutely ensure to have all 1,000 maize kernels represented in the 3g of weighted sample, an increase of the fineness by the power of 10 is desirable.
Are 10,000 equal parts generated from each maize kernel, so weighs each piece on the average 0.0275mg with a diameter of 0.36mm.
The 3g of the weighted sample for the analysis would then contain 109,000 pieces or approximately 100 pieces of each kernel.
Therefore, it is statistically ensured that during the analysis of the maize kernels for transgenic contents a representative sample is weighed.
Considering the following aspects - maize kernels as seeds; avoidance of all types of cross-contamination due to comminution; comminution down to at least 50 per cent smaller 0.5mm sieving; prevention of thermal damage affecting the analysis results; the variable-speed rotor mill Pulverisette 14 was chosen as the best instrument.
Of course, know-how with the comminution of maize kernels exists.
Often, up until now, food processors were mostly used due to financial reasons.
The obtained results were defined as minimum requirements.
It was monitored with a sieve cut of 0.5mm.
Utilised was the vibratory sieve shaker Analysette 3 Pro; maize comminuted with the variable-speed rotor mill Pulverisette 14 by means of a 1mm sieve already yielded a better result in comparison with the food processor: 52 per cent < 0.5mm was the requirement; 69 per cent < 0.5mm was achieved.
By using the 0.5mm sieve in the mill, the fineness was clearly additionally improved.
The sieve analysis showed that 89 per cent are < 0.5mm and therefore only 11 per cent are > 0.5mm.
This is because of the different shapes of the sieves and also inside the mill due to the high rotational speed the particles are accelerated and then are downright 'shot' through the sieve.
Also the maize kernels can still be comminuted when using a 2mm sieve.
Admittedly, the sample must be added significantly more slowly and it becomes rather warm.
According to general experience with the comminution via the variable-speed rotor mill Pulverisette 14, the material is 50 per cent smaller of half of the mesh width of the used sieve.
When using the 0.5mm sieve only half of the produced particles are smaller than 0.25mm.
When comparing this value with the in the theoretic contemplations included value, it becomes evident that the comminution with the variable-speed rotor mill Pulverisette 14 by using the 0.5mm sieve meets all required demands.
