Stability of the Product in its Natural State, Premixes and Feeds

The stability of a vitamin product is its capacity to retain its initial physicochemical state over time.

Vitamins are complex organic molecules. Structural modifications may lead to considerable loss in their activity.

Redox reactions are the main causes of degradation of vitamins in animal feed (Table 8).
These reactions are made possible, in premixes and feeds, by the simultaneous presence of free water from raw materials and redox compounds (organic acids, reducing sugars, trace minerals, oxidized fats).

These reactions are exacerbated, during the manufacture of premixes and feeds, by mixture with air during pneumatic transfers, and by the addition of steam, heat and mechanical actions. They continue, during storage, in the finished products (premixes, feeds).

Sensitivity of vitamins to
oxidation and reduction

Major role of water
Water is the transfer medium for the ions involved in redox reactions.

The water originates from three sources:

• Air (by hygrometry).
  
  
• Raw materials (free water).
  
  
• Manufacturing process (steam, water added).
  

Certain hygroscopic ingredients (choline, betaine, calcium pantothenate, chlorides, etc.) contribute to water content increase (and resultant water activity) into the feed or premix.

These ingredients may playa dominant role in the stability of vitamins. Hygroscopicity is measured as water uptake by the product placed in a chamber of controlled humidity and temperature (RPAN 24 - VPC - 1.0).

Factors promoting redox reactions
Many factors promote redox reactions: pH, minerals, light, temperature, contact surface area and mechanical constraints.

pH
In premixes, the pH becomes a factor when the amount of free water is sufficient to allow the release of cations and anions from soluble components.

A resistance zone (stability) and a sensitivity zone (degradation) is defined for the stability of each vitamin.

Minerals and trace minerals
Minerals are often the catalysts for chemical reactions involving vitamins.
The most reactive mineral salts are the sulfates. The use of carbonates or oxides, which are less hygroscopic, makes it possible to limit the chemical reactions. The bioavailability of these products, however, may be less than the sulfate forms and may need to be verified and adjusted for.

Light
Ultraviolet rays promote redox reactions. Vitamins A, D₃, K₃ and B₂ are particularly sensitive to the action of light.

Temperature
Vitamins E (acetate). B₂, B₁₂ and Niacin have little sensitivity to heat. The other vitamins are reputed to be more labile.
Raising the temperature accelerates the kinetics of the redox reactions. It is commonly accepted that, above 25°C, a 5°C rise in temperature doubles the rate of activity loss of vitamins.

Surface Area
The larger the surface for contact of the vitamin with the ambient medium, the more this vitamin is exposed to attack. The surface area is a function of the size, shape and structure of the particles.

Mechanical influences
Mechanical influences (abrasion, crushing, shear) may increase the surface area by fragmentation and promote contact of the vitamin with the other reactive components of the mixture.

Practical Measurement of Stability
In practice, the stability of a vitamin product in a premix or a feed results from:

• The physical integrity of the vitamin product.
  
  
• The intrinsic resistance of the vitamin to physicochemical attack.
  

Physical integrity of the vitamin product
The stability of the vitamin product is verified by measuring its activity in the original packaging at the time of its use.

Results of the stability tests on Microvit™ A Supra 500

Premixes and feeds: resistance of the vitamin to physicochemical attack
The stability of a vitamin product is characterized by its ability to resist the physicochemical attack inherent in feed processing.

Premixes: in order to test the stability of a given vitamin in premixes, Adisseo has developed a standard procedure (RPAN 26 VPC - 1.0) representative of the premix industry. The stability is measured in :

• A vitamin complex (A, D₃, E and B).
  
  
• A "complete" premix including trace minerals and choline chloride.
  

In finished feeds, it is much more important to determine the stability of the product during manufacture, in particular with thermomechanical operations considered aggressive, in which the vitamins are subjected to the simultaneous effects of steam, pressure variations and increases in temperature. Pelleting, in particular, is an important process to monitor due to its widespread use and known effects on vitamin stability. The time life of feed is generally short, then a three months period is usually enough, except for the Petfood market.