Food & Beverage Analysis
Tough? Fatty? Fibrous? Quick and reproducible homogenisation of complex food samples
Dr Tanja Butt, Retsch GmbH,
www.retsch.com
Food comes in different shapes and textures and is not uniform. However, for analyses such as fi nding out the nutritional value or identifying harmful substances, samples that are homogeneous and representative are needed to ensure reliable and consistent results. Therefore, the samples need to be made uniform and smaller in size. This crucial step in the analytical process can be facilitated by using various kinds of laboratory mills as provided by Retsch. For most analyses, only a small amount of sample is required which needs to refl ect the whole original sample. Depending on the part of the original sample from which the analysis sample was taken, results can vary substantially which affects reproducibility. The sample preparation process in general needs to suit the sample properties and the requirements of the chosen analysis method to avoid false results. The selection of grinding parameters and accessories should not change the sample properties that are to be analysed. The type of sample preparation and the required particle size are determined by the analysis method. For most digestion and extraction processes a particle size of 0.5 mm is ideal. As food differs greatly in terms of hardness, moisture or fat content, Retsch offers a range of appropriate mills and grinders for the specifi c requirements of the different analysis methods.
is much better suited for cutting through the tough meat than a conventional knife. By using the volume reduction lid, the sample is continuously forced against the knife blades, thus ensuring complete homogenisation.
Granular samples like grain, rice, or corn
Granular food that is medium-hard and has small grains is best ground into fine particles with a mix of forceful impact and shearing. The impact effect makes the grain burst and the shearing effect further reduces the samples to smaller pieces. For this purpose, the ZM 300 is very suitable, a high-speed rotor mill that can reach a maximum speed of 23,000 min-1 and grinds samples by impact and shearing between rotor and fixed ring sieve. The sample stays in the grinding chamber of the ZM 300 for a very short time so that the properties that need to be analysed are not altered in any way.
Application example: 200 g corn are fully homogenised at a speed of 18,000 min-1 in less than 30 seconds without blocking the rotor. When using a 0.5 mm ring sieve, the whole sample is ground to a fi neness below 0.5 mm.
Figure 1: Knife Mill GRINDOMIX GM 200. Food with a high water, oil or fat content
In food laboratories all over the world, Retsch’s Knife Mill GRINDOMIX GM 200 (Figure 1) is the standard mill for the preparation of food samples. The cutting effect of the steel blades ensures thorough homogenisation of samples with a high water, oil, sugar or fat content. The GM 200, which accommodates up to 700 ml sample material, covers a wide application range from granular materials like rape seed, rice or soybeans to fi brous or tough samples like plants, meat, fi sh, candy, or cheese. Example: Thanks to the powerful 1000 W drive with increased traction, the GM 200 is able to homogenise diffi cult samples like very fatty bacon within 30 seconds without blockages (Figure 2). For this kind of sample, a special serrated knife is used which
Figure 3: corn before and after homogenisation in a rotor mill.
To prevent clogging of the sieve when homogenising fatty or temperature-sensitive samples, a distance sieve should be used which creates a small gap between sieve and rotor.
Preliminary grinding of large sample pieces Figure 2: bacon before and after homogenisation in a knife mill
Cutting mills are used for preliminary size reduction of soft, medium-hard or fibrous samples such as roots, nut shells or bones. The speed is either fixed or can be set from 100 to 3000 min-1, depending on the model. The final grind size is determined by the aperture size of the exchangeable bottom sieve, which ranges from 0.25 mm to 20 mm, and by the sample properties. Three rotor types ensure optimum cutting of different types of material. By using a cyclone the sample is discharged more quickly from the grinding chamber, and the sample and grinding tools are cooled by the air stream.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68
