Vitamin Stability

Vitamin Stability

Vitamins are a group of chemically diverse compounds that vary considerably in their stability and susceptibility to destruction by physical and chemical agents. The stability of individual vitamins in premixes and finished feeds varies according to a number of factors. Therefore, the ideal approach to ensuring vitamin activity in feed production is to monitor vitamin activity in samples of finished products. In the absence of such data, generalized stability data, such as that presented in this section, can be used as a guideline for product formulation and expiration dates.

Significant research by major vitamin manufacturers has led to the development of a number of specialized vitamin product forms, such as the cross-linked beadlet formulation of vitamin A, to provide increased stability at reasonable cost (Frye, 1994). While no product form can assure complete and unlimited stability of a vitamin, the more advanced product forms now available to commercial feed and premix manufacturers provide stability far superior to the raw vitamin product, thus enhancing the value to the feed manufacturer, livestock producer and pet owner.

Besides stability, the primary factors considered in the development of vitamin product forms are bioavailability, uniform vitamin activity within the product form, and optimal handling and mixing characteristics such as: high flowability, low dusting, low hygroscopicity and caking, and minimal segregation and carryover effects (Frye, 1994). These characteristics are especially important with vitamins because these essential nutrients are normally added in small amounts to livestock diets, where their presence or absence in individual rations can markedly affect animal performance and health. Figure 3 illustrates the concept of balance among the three major components of vitamin product form quality: bioavailability, stability and mixability.

A. Factors Affecting Vitamin Stability

A number of common physical and chemical factors affect the stability of vitamins in premixes and finished feeds (Figure 4) (Gadient, 1986; Frye, 1994; Reddy and Love, 1999). Exposure to multiple stresses generally multiplies the effect on vitamin stability. For example, exposure to moisture through high relative humidity during storage significantly increases the rate at which vitamins are degraded by chemical reactions, such as oxidation. A similar statement could be made about exposure of vitamins to elevated temperature or strong light during storage.

The individual vitamins vary in their susceptibility to degradation by chemical and physical factors (Table 15). Shursonet al. (1996) created a relative stability ranking for the vitamins based on results of a research study (Table 16). The rankings may vary depending on product form and conditions of manufacturing and storage; however, the overall relationship among vitamins is consistent with previous studies (Frye, 1994).

Premix composition affects vitamin stability (Table 17), especially with regard to the presence or absence of choline and inorganic trace minerals (Frye, 1994). These compounds are reactive with vitamins and reduce their stability. Similarly, the processes used in feed conditioning and manufacturing affect vitamin activity (Table 18 and Table 19) (Gadient, 1986; Reddy and Love, 1999). Both pelleting and extrusion both reduce vitamin activity in proportion to the amount of heat and pressure applied to the feed during processing. Thus, the tables and figures shown here should serve only as guidelines for vitamin stability in livestock feed and not absolute values.

Often, the net stability of vitamins in feeds or premixes is affected by two or more major factors, including the time of storage. The stability of vitamin A (one of the least stable vitamins) is strongly affected by both product form and storage conditions (Figure 5). Likewise, the product form of vitamin E has a significant effect on its stability in an “aggressive” premix, which normally means a premix with high levels of trace minerals relative to carrier, as well as high pH (Figure 6).

B. Product Forms

Strategies for improving vitamin stability through product formulation have been developed since the beginning of commercial vitamin synthesis in the 1950s, using specific criteria (Table 20). One of the first innovations was the production of esterified forms of vitamins A and E to improve their stability while maintaining bioavailability (Frye, 1994). More recently, several major vitamin manufacturers developed and refined the spray-dried and beadlet product forms. The spray-dry process and a cross-sectional view of the final product are shown in Figure 7 and Figure 8. Beadlet manufacturing and structure are depicted in Figure 9 and Figure 10. The latest innovation in beadlet technology is the use of cross-beadlet (Figure 11). These products provide consistent levels of vitamin activity under commercial feed manufacturing conditions. A general comparison of the spray-dried and beadlet product form is shown in Table 21.

The bioavailability of new product forms must be verified through research. For example, the bioavailability of vitamin C stabilized through phosphorylation is equivalent to that of crystalline vitamin C (Figure 12 and Figure 13). The effects of particle size and uniformity of vitamin activity within product forms of vitamin D3 are shown in Table 22.

The vitamin D3 metabolite 25-hydroxy vitamin D3 (25-(OH)D3) is being used successfully to replace all or part of the vitamin D3 requirement of some species. Most of the research has been with poultry and now 25-(OH)D3 (commercial name is Hy-D®) is used routinely in commercial poultry programs (McDowell and Ward, 2008).

In a study with broiler chicks to compare the absorption of 25-(OH)D3 and vitamin D3, the former was found to be more efficient (Ward, 2004; Chung, 2006). Note: I don’t know about this protein. Could ask Nelson? This protein has an affinity for 25-(OH)D3 that is at least 1,000 times greater than for other D3 metabolites (Teegarden et al., 2000). Also, studies find that the intestinal uptake of 25-(OH)D3 occurs irrespective of bile acid secretion and micelle formation/fat absorption. The newly hatched bird struggles to coordinate an infantile digestive system with a rapidly developing skeleton. The 25-(OH)D3 could offer pronounced advantages to the bird under typical production challenges, not only early in the bird’s life, but also when some disease organisms are most prone to express themselves (Ward, 2004).

C. An Approach to Assuring Vitamin Activity in Feeds and Premixes

Assurance of nutrient concentrations in feeds and premixes is a vital component of quality assurance programs. In the case of vitamins, this becomes a complex problem due to the variety of chemical structures and multiple interactions that may occur among vitamins and between other compounds. Data such as that presented in this section provide a benchmark for assessing vitamin stability and for developing a plan for monitoring vitamin activity in finished products. Clearly, certain vitamins such as vitamins A and K are most subject to losses during manufacturing and storage. Therefore, these vitamins would be candidates for larger safety margins in formulation and might be chosen as monitors of overall vitamin stability in feeds.

Some of the important factors worthy of consideration by the feed manufacturer in designing a quality assurance program for vitamin activity in feeds or premixes include:

  1. Conditions and use rate (storage time) of vitamin or vitamin-mineral premixes prior to basic feed manufacturing. Combination vitamin-mineral premixes are less stable than premixes without trace minerals and choline
  2. Feed manufacturing conditions, including conditioning and pelleting temperatures, use of higher temperature and pressure methods such as gap expansion or extrusion.
  3. Formulation of specialized feed vitamin-mineral mixes with extremes of pH, and/or high concentrations of trace minerals. Examples would include high magnesium products (high pH), intake-limiting products such as acidified liquid feeds, and dry products containing high levels of urea or other strongly hygroscopic ingredients.
  4. General condition and accuracy of the weighing, mixing and conveying equipment in the feed mill or premix plant.
  5. Length and condition of storage of finished feeds and premixes prior to consumption by livestock.

Typically, the use of good manufacturing procedures (GMP) and other quality assurance and regulatory guidelines require periodic mixer studies, including nutrient or medicinal assays. A plan can be devised whereby selected vitamin assays on specified products are included in a predetermined number of these evaluations per year. Likewise, a defined number of samples of finished products can be obtained from warehouses and retail locations during the year for vitamin analysis. These assay data provide a valuable benchmark for determining vitamin activity in feed products and can be used effectively to monitor manufacturing and storage conditions.

Because feed products are complex and multiple interactions can occur between formulation, manufacturing, storage conditions and time, feed manufacturers should ideally develop their own databases of vitamin activities. The data will provide the most solid and reliable evidence if customers or other parties call into question the vitamin activity of manufactured products. A final consideration is the inherent variation within a particular vitamin assay and laboratory (Table 23). Choice of laboratory and use of adequate sampling and assay replication can overcome this problem.

The vitamin manufacturing industry has developed products of high purity and quality, with improved stability, high bioavailability and optimum handling and mixing properties. Today’s vitamin product forms have marked advantages over the raw vitamin forms when used in feed or food manufacturing.

However, when dealing with complex and reactive compounds such as the vitamins, no product form can offer complete and unlimited protection against destructive conditions, excessive periods of storage or severe manufacturing processes. The individual feed manufacturer must take responsibility for assuring customers that vitamins have been stored, handled and added to feeds in an optimum manner and that vitamin levels are routinely monitored for quality assurance.

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