Ensuring vitamin stability
Vitamins play an essential role in animal nutrition, but safeguarding their stability during processing is a must.
Vitamins play a central part in most metabolic functions of food production animals, including growth, maintenance and disease resistance. The way these additives are handled in feed manufacturing is often taken as routine. But should we take vitamin use for granted?
Just consider that:
- As feed conversion efficiency improves, less feed (hence vitamins at traditional levels) are used to bring animals to slaughter weight. Is routine vitamin supplementation still at the optimum level, given the advances in nutrition and genetics?
- There have been many advances made in feed processing as well. Techniques such as expansion and extrusion have become far more common and place greater stress on sensitive dietary components. Are all vitamins stable enough to perform well, given the changes made to feed processing?
- The demands placed on quality and traceability of the ingredients used in feed are now greater than ever. High purity of the vitamin, ingredients free of GMO-DNA, and products certified BSE-free are being requested in various parts of the world and have now become standards for high quality products. Further, the need to have full traceability of all components is a requirement not always easy to achieve.
In the following we will highlight some aspects about how vitamins can be formulated to ensure good stability, mixing and handling properties to meet today's requirements.
Stability and sensitivity
Vitamins are among the more labile additives used in feed. Depending on their chemical characteristics, the individual vitamin molecules are to a different degree sensitive to physical and chemical factors. Vitamin stability is influenced by several factors which occur during processing and storage in premixes and feeds. Heat, pressure, humidity, friction and redox reaction may vary dramatically among the different ways feed is processed.
Also, the conditions during storage have to be considered. Especially in warm climates, the stability of vitamins in feed or premixes may be heavily affected.
Design can ensure feed value
There is considerable difference in the design of vitamin forms and their resulting value in feed. Vitamin forms should be specifically designed to perform well in a feed industry environment. In addition, special care in the choice of the protective mechanisms should be placed in such a way as to not jeopardize the full bioavailability of vitamins to the animal.
To minimize losses in processed feed, differentiated vitamin manufacturers supply vitamins not as unprotected chemicals, but in a stabilized form. Depending on the vitamin molecule this could be done by two different technologies:
Chemical stabilization. For vitamins like vitamin A (retinol), vitamin E (a-tocopherol) or Vitamin C (ascorbic acid), the reactive hydroxyl groups of the molecule are esterified, and thus protected. Antioxidants may also be used in vitamin formulations to achieve further protection of vitamins which are sensitive to oxygen.
Physical protection by encapsulation. Building a physical barrier between oxygen and the sensitive molecules prevents oxidation processes or protects the molecules from exposure to moisture. Various formulation techniques are developed not only to protect the vitamin, but also to improve its handling and mixing abilities.
A good example where both technologies are combined is in the formulation of vitamin A. In addition to chemical stabilization, the molecule is protected in a cross-linked gelatin beadlet.' With this technique, vitamin A is embedded in particles which are formed by the three-dimensional protein structure of gelatin. Additionally, the particles contain other ingredients such as fructose and glycerin which permit a cross-linking of the particle, thus making it physically stable against treatment with steam, a feature especially important when the vitamin is exposed to aggressive hydrothermal treatment during pelleting or expansion. To ensure high bioavailability, a protein-based coating is selected which is easily hydrolyzed by proteolytic enzymes of the animal during digestion.
A high percentage of all compound feed is marketed as pellets. The pelleting technology is established, but it is increasingly run with more intensive conditioning and higher temperatures, especially for broiler and turkey feeds, to combat pathogens such as salmonella.
Expansion and extrusion
Even more energy-intensive hydrothermal processes are now more frequently installed, either to produce more hygienic compound feed, or to supply speciality feeds with, for example, higher digestibility, increased durability or specific shape. Long-time conditioning, expansion and extrusion are routinely used to make feeds for piglets, shrimp or pets. Common to these processes is an increased exposure of the feed to moisture, temperature and pressure; a combination of factors that can impact unprotected vitamins.
For this reason, the stability of vitamins used in the feed industry has gained significantly greater awareness. Their performance has been tested in controlled stability studies (Van der Poel, 1997; Gadient (unpublished), 2007) and guidelines are in place, which show the average stability performance of vitamin products in processed and stored feed.
Table 2 (DSM, 2006) shows that high quality vitamin products generally have a high stability performance in both expanded and extruded feed. The products can thus routinely be added via a dry premix to feed and processed. In case sizeable losses are expected, overages should be added to the premix.
Despite these changes to the feed product, good stability can still be found if properly formulated vitamin products are used.
Stability during storage
Now that an increasing percentage of feed is produced and stored in warm climates it is also important to observe the stability performance throughout the production chain of feed. As storage rooms are often not cooled, high temperature may also affect vitamins before they are processed into feed, i.e. at raw material storage and in premixes. A recent test conducted by DSM has shown that in the case of vitamin A, more vitamin losses might occur in the earlier stages, and considerable differences among the vitamin A formulations used over the course of the entire chain. Taking a six-month supply chain from additive receipt to the animal, differences between the three vitamin sources has amounted to over 30 percent.
Just as any other sensitive molecule, vitamin stability is influenced by today's feed processing technologies and composition of the recipe. Also, storage condition and duration have a significant influence on potential vitamin losses. Special formulation techniques for the various vitamins are developed to ensure good stability during all conditions of feed processing and storage. Although some formulation techniques may appear similar, differences in stability and bioavailability of the vitamins from the suppliers are observed. As well, quality aspects such as traceability of included components become more important.