Preparing Foodstuff Samples for QC Testing

Consumers are constantly confronted with scandals in the foodstuff sector. The latest scandal is the Fipronil egg scandal in the laying hen farming in the Netherlands and in Lower Saxony (Germany). What do foodstuff producers and marketers actually do to avoid such scandals? A lot, if you believe the rising costs in the area of advanced foodstuff analysis.

During the last decades, newer and more refined processes have been developed with the most sensitive detection thresholds (PCR, ELISA, or the mycotoxin analysis) for quality control, so as to lower the number or even eliminate such scandals and the probable danger for consumers.

So now, in the context of these repeated analytical processes, techniques for sample preparation of the most diverse matrixes were created. Since foodstuffs and the raw materials, respectively, convenience products are mostly composed clearly more heterogeneous like all other substance groups. Especially in relation to comminution, there are frequently limits like the rheological properties of a material, the ingredients or the volatile components which can only be prepared without regulating factors (sieves). That is why knife mills are frequently utilized. FRITSCH currently offers such a knife mill in industry quality: the Knife Mill PULVERISETTE 11. In the following article, there are examples of the comminution of foodstuffs and their backgrounds.

Hopfen und Malz Gott erhalts

The above traditional German saying seeks God’s blessing for hops and malt. Known and used as a base material for beer production, hops show much more diverse pharmacological-effective aspects. So a number of secondary plant substances like caryophyllene, humulene, as well as a few plant dyes contribute to the anti-inflammatory or soothing effects of hops. They possibly contain species-related mechanism of action to the body’s own sleep hormone melatonin. In order to analyze this in detail and to ensure an improved extraction of these ingredients, fresh female hop cones were comminuted and homogenized in the PULVERISETTE 11 at 4,000 rpm for 15 seconds.

Hop cones before and after the comminution

Figure 1. Hop cones before and after the comminution.

Hops milled at 4,000 rpm

Figure 2. Hops milled at 4,000 rpm, grinding time 15 seconds.

Mandatory Labeling of Sweets

With the purpose of identifying vitamins or other ingredients of fruit-flavored hard candy according to the mandatory product labeling, typically the candy must be mechanically processed. The frequently utilized HPLC requires only weighted samples of a few milligrams though, in which a realistic random distribution of characteristic features of the sampling appears hard. During the sample preparation, often the high content of sugars and the vitamin content are problematic. An embrittlement with liquid nitrogen seems thus inevitable, so as to change the breaking behavior of the hard candy and to ensure the temperature stability of the vitamins.

All this can also be performed using the Knife Mill PULVERISETTE 11. A previously conducted embrittlement in the stainless steel vessel along with a brief comminution of 20 seconds at 5,000 rpm, created a finely distributed powder without using too much energy.

Hard candy with liquid center, embrittled in nitrogen.

Figure 3. Hard candy with liquid center, embrittled in nitrogen.

Comminuted hard candy after 20 seconds.

Figure 4. Comminuted hard candy after 20 seconds.

On the Trail of Mycotoxins

Mycotoxins as metabolites of mildew, like aspergillus niger or aspergillus flavus, pose a health risk to the consumer. Furthermore, there are enormous economic losses due to unidentified infestation and the associated spoilage of the quality because of mildew.

Particularly important are the so called aflatoxins, as they are carcinogenic in the slightest quantities. Owing to this reason, the detection limits are in the range of a few µg/kg. Spices or nuts of any kind are particularly prone to such “mildew nests”. Based on the formation of nests in such material samples, the representative sample preparation for a laboratory sample requires a moderately large sample size. Hence, for the tests with the Knife Mill PULVERISETTE 11, approximately 800 g hazelnuts were processed.

Approximately 800 g hazelnuts.

Figure 5. Approximately 800 g hazelnuts.

At first, the interval mode of 3 x 5 seconds with 4,500 rpm was utilized, and then the whole sample was homogenized again for 15 seconds at 6,500 rpm.

Hazelnuts after 30 seconds grinding

Figure 6. Hazelnuts after 30 seconds grinding in the grinding vessel made of stainless steel.

Homogenous sample of hazelnuts.

Figure 7. Homogenous sample of hazelnuts.

This information has been sourced, reviewed and adapted from materials provided by FRITSCH GMBH - Milling and Sizing.

For more information on this source, please visit FRITSCH GMBH - Milling and Sizing.

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