Fibers in general
Chemical or synthetic fibers are produced synthetically, often on the basis of crude oil. The best-known synthetic fibers include polyester, elastane and polyacrylic. Natural fibers, on the other hand, come from plants, animals or minerals and are therefore of natural origin. Plant fibers play an important role among natural fibers. They are made from plant fibers and are part of the plant cell wall. Plant fibers are found in leaves and stems as well as in roots and fruits.
Plant fibers consist mainly of cellulose, a polysaccharide made up of simple glucose molecules. The cellulose fibrils in turn are located in a matrix of pectin, hemicellulose and proteins. In many cases, perennial plants also contain the biopolymer lignin. Lignin ensures the lignification of cells.
Many feedstuffs are based on plant fibers. This applies not only to green feed such as grasses and herbs, but also to dry feed, which is often fed in the form of pellets. Therefore, in addition to crude protein and crude fat, crude fibers are also an essential component of feed.
Crude fibers are difficult or impossible to digest and therefore do not provide the animal with any additional energy. Nevertheless, they are beneficial to health in certain quantities. This is because crude fibers increase intestinal activity and thus stimulate digestion, acting in a similar way to dietary fibers in food. When producing animal feed, it is therefore important to ensure a good balance between crude fibers that promote digestion and a high level of digestibility. Fiber analysis provides a remedy for an optimal composition.
Historical development of Weender feed analysis
The analysis of fibers poses a particular challenge. This is because fiber components are firmly bound in a sample. They must therefore be released from the bond and non-fiber components such as proteins and pectins must be removed. The Weender method meets this challenge.
The Weender analysis is easily reproducible, so that large amounts of data can be obtained quickly for all feed components. Nevertheless, the analysis also has weaknesses: for example, it is not possible to segment the carbohydrates within a sample more specifically. This means that no precise information can be provided on the content of specific nutrients such as lignin, hemicellulose or cellulose. Weender analysis alone is therefore not enough to fully assess the usability of nutrients in animal feed.
Advantages and disadvantages of the Weender analysis
| Advantages | Disadvantages |
| Reproducibility | No analysis of specific nutrients |
| Consistency of content over a long period of time | No exact assessment of the nutrient composition possible |
| Large amounts of data within a short period of time | No exact segmentation of carbohydrates |
As the classic Weender analysis is relatively unspecific, it is now supplemented by the detergent method for analyzing animal feed according to van Soest. This was developed in the 1960s by Peter van Soest at the United States Department of Agriculture.
The van Soest determination is based on the concept of detergent fibre analysis. It first divides the plant cell into cell walls and cell components. The cell walls consist of the less soluble components hemicellulose, cellulose and lignin. The largely soluble cell components are raw protein, raw fat, pectins, starch and sugar.
The Weender method considers the crude protein and crude fat components separately. However, pectins, starch and sugars are considered by Weender to be nitrogen-free extractives and are therefore not considered separately. Van Soest first divides them into two groups, the cell walls and cell components. The components of the cell wall are then analysed further to determine the following detergent fibres:
- Neutral Detergent Fibers (NDF): Also called "Neutral Detergent Fibre", these are the fiber components that are insoluble in a neutral detergent solution.
- Acid detergent fibers (ADF): Also "Acid Detergent Fibre", the fiber components that are insoluble in a slightly acidic detergent solution.
- Acid detergent lignin (ADL): Also "acid detergent lignin", i.e. the lignin portion of the sample that is insoluble even in concentrated sulphuric acid.
Analytical process for fiber determination
In the Weender analysis, the crude ash, crude protein, crude fat and crude fiber content of a feed sample is determined. The nitrogen-free extract is then calculated from this. Of these five components, the crude fiber content is the decisive parameter for fiber analysis.
When determining the crude fiber content, the first analysis step is to dry the feed sample. This means that the water is first removed from the sample at 103-105°C, leaving behind the dry matter. This is made up of inorganic and organic substances. The latter are crude protein, crude fat, crude fiber and nitrogen-free extracts.
The second step is to degrease the sample. To do this, the fat is extracted with a solvent. In the third step, the starch, sugar and crude protein components are gradually washed out through a boiling process with alkalis and acids. In the fourth step, the remaining sample is first dried again and then incinerated at 500°C in a muffle furnace. Only the inorganic substances then remain in the form of ash. In the fifth step, the crude fiber content is quantitatively determined by differential weighing.
The determination according to van Soest specifies the fiber analysis by determining the NDF, ADF and ADL content of a sample in addition to the crude fiber content.
The analytical procedure is similar to the determination of the crude fiber content, but differs in the composition of the detergent solutions and their pH value.
For the NDF determination, after sample preparation, drying and degreasing, the sample is first treated with a neutral detergent solution (NDS) for approx. 60 minutes and washed with a heat-stable amylase. As the name suggests, this is a neutral detergent solution. This dissolves sugar, starch and pectins and the proportion of NDF can be determined. The remaining residues then consist only of the indigestible or poorly digestible cell wall components hemicellulose, cellulose and lignin.
In the ADF determination, the sample is also treated with a detergent solution for approx. 60 minutes after sample preparation, drying and degreasing. In this analysis, however, an acid detergent solution (ADS) is used. This dissolves the hemicellulose and only lignin and cellulose remain. The proportion of acid-detergent fibers can then be determined.
In ADL determination, the sample is first treated like an ADF sample. This means that after sample preparation, drying and degreasing, the sample is first treated with an acid-detergent solution (ADS) for approx. 60 minutes. The cellulose and lignin residue is then treated with concentrated sulphuric acid in a final step. This dissolves the cellulose and leaves behind lignin. The acid-detergent lignin (ADL) content is then determined.
Automation of analytics
The analytical processes according to Weender and van Soest consist of many manual steps. Accordingly, the processes are very time-consuming for laboratory staff. However, they can be simplified and automated through the use of certain technologies and analysis systems so that valuable working time can be saved.
C. Gerhardt offers various options for process optimization in fibre analysis.
The sample preparation can be simplified by using a degreasing module, for example. Degreasing the sample before analysis is important as it prevents the sample from foaming during the boiling process and prevents the filter from clogging. The module can be used to degrease six samples simultaneously. A handy insert is used for this purpose, which enables the samples to be evenly wetted with solvent. In contrast to the classic glass frit method, where solvent has to be added again and again, the degreasing module saves solvent.
C. Gerhardt has also developed the so-called FibreBag: This is a special filter bag in which the sample is weighed. This technology considerably simplifies the dissolving and filtering of the sample components, as it
- standardizes the filtration through a defined mesh size,
- offers a large surface area for effective passage of detergents,
- can be incinerated without residue in the muffle furnace and
- has an adapted pore size for ADF/NDF determination.
The points mentioned above ensure better and more reliable analysis results compared to the classic filter method using frits and filter beds. This is because glass filters offer the advantage of reusability. However, they have to be burned out, packed with Celite and prepared in advance. In addition, the service life of a standard frit is severely limited due to the harsh conditions of the process with acids, alkalis and temperatures of up to 550°C. For this reason, the pore size has usually already changed so much after 10-20 applications that the frit has to be replaced.
With FibreBag technology, the pre- and post-processing steps are completely eliminated. In addition, filtration is standardized as the pore size is the same for every analysis. This means that FibreBag technology achieves results comparable to those of the classic glass filter method according to Weender and van Soest. By standardizing the filtration conditions, even a better standard deviation can be achieved.
Fiber analysis with FIBRETHERM
For the analytical process itself, C. Gerhardt offers the fully automated FIBRETHERM analysis system. FIBRETHERM performs the complex boiling, washing, filtration and rinsing processes for extracting the fiber components in a closed system for 12 samples simultaneously. The analytical method can be programmed in advance and then selected so that it is adapted to the various sample parameters: crude fiber, NDF and ADF.
For ADL analysis, FIBRETHERM can be used to prepare the sample, as ADF analysis can be performed. However, the treatment of the sample with concentrated sulphuric acid must be carried out manually. The degreasing module can be used for this. This is because it is a degreasing module and the manual FibreBag system in one. This can also be used for the other fiber analysis parameters. For example, for laboratories with a smaller sample volume. Even if the washing and cooking processes are then carried out manually, the degreasing module and FibreBag technology still optimize the process.
Corresponding application documents for both the manual FibreBag system and FIBRETHERM are available to the user for initial orientation.
