Understanding the Sensitivity and Stability of Vitamins

understanding the sensitivity and stability of vitaminS

By Amir Attar, Alireza Abbasipour, Samira Hassanpour New Millennium Feed Processing Co. (www.nmfeed.com), Mashhad, Iran

introduCtion

Feed technology has progressed in the past two decades. However, NRC (1994) vitamin requirements for monogastric animals have not altered to any great extent due to limited research in this field. Vitamins are important for livestock nutrition and performance. They are intentionally added to animal feed in order to achieve the improvement of health and growth of animals and the characteristics of products of animal origin. Additionally, if lacking from the diet, vitamins can cause a specific deficiency disease because they are essential for normal metabolism. Vitamins, as biologically active biochemicals, are generally quite delicate to their physical and chemical environment. Feed processes tend to improve the distribution of nutrients (premixing) and the digestibility of carbohydrates (pelleting, extrusion). However, these processes are harmful to labile nutrients, such as vitamins, that can be easily oxidized.

Vitamin formulations vary significantly in complexity and cost. Cost is a very important factor because the vitamin manufacturing costs are passed on to the consumer. Manufacturing processes should not only be evaluated based on physio-chemical properties of the vitamin, but also the need to further process the vitamin to improve handling properties and stability through feed processing.

vitamin Stability

The stability of vitamins in a premix is critical in maintaining vitamin potency. Susceptibility to degradation varies depending on individual vitamins and on a number of factors that affect vitamin stability. Safety margins for vitamin premix formulation are usually based upon vitamin cost, presence or absence of trace minerals and choline in the premix, feed processing characteristics, environmental conditions, anticipated storage time, and expected rates of vitamin potency losses.

Not all vitamins are equal in stability. Commercial vitamins for feeds and foods are formulated to counter anticipated stresses, and these formulations act as a buffer between the vitamin and the

aggressor. Differences exist in the stability of vitamins in their natural form. The ability of vitamins to withstand the rigors of storage in mineral premixes or in the presence of choline chloride is not good. The stability characteristics differ across a variety of conditions for the full collective of important vitamins. It is the unique chemical structure and other characteristics of each vitamin that directs

the type of stabilization or formulation. For example, heat can be especially destructive to vitamin A, folic acid, or vitamin B but has little consequence on niacin or riboflavin. Therefore, the focus on some vitamins is their weaknesses to heat, knowing that most feed processing methods utilize heat.

FaCtorS aFFeCting vitamin Stability

Vitamin stability in premixes is affected by exposure to light, heat, moisture, oxygen, and pH, and contact with other compounds. These factors subject vitamins to degradation primarily through oxidation. The long-term or multiple exposures to these factors generally magnify the negative impact on vitamin stability. The individual vitamins vary in their susceptibility to degradation (Table 1).

pelleting

Conditioning/pelleting temperature is the most obvious contributor to vitamin losses for poultry feed. According to Van’t Hoff’s Rule, an increase in temperature by 10°C will increase the rate of chemical reactions by 2- to 3-fold. Thus, the integrity of the vitamin is threatened with exposure to oxygen and trace minerals, during conditioning of feeds.

Conditioning time affects vitamin degradation, with a longer conditioning time posing the greater threat. The goal of conditioning feed is to uniformly penetrate each feed particle with moisture and heat. Under pressure and with rigorous mixing in the feed conditioner, this creates an environment especially harsh to vitamins and other feed additives. Often, moisture is increased to 17-18%, and provides a solvent for destructive agents since moisture is often essential for harmful chemical reactions.

The type of feed, mineral and fat content must be considered. Each brings characteristics that can influence the degree of friction as the feed passes through the die. At least theoretically, we expect lower vitamin degradation in finisher type diets (i.e. higher fat, lower mineral content).

Vitamin Abbreviation Temperature Humidity Light Oxygen Acid pH Alkaline pH

Vitamin A A Very sensitive Sensitive Very sensitive Very sensitive Sensitive Stable Vitamin D D Sensitive Sensitive Sensitive Very sensitive Sensitive Stable Vitamin E E Stable Stable Sensitive Sensitive Sensitive Very sensitive Vitamin K K Sensitive Very sensitive Stable Sensitive Very sensitive Stable Riboflavin B2 Stable Sensitive Sensitive Stable Stable Stable Niacin B3 Stable Stable Stable Stable Stable Stable Pantothenic acid B5 Sensitive Sensitive Stable Stable Stable Stable Vitamin B12 B12 Very sensitive Sensitive Sensitive Sensitive Stable Stable Pyridoxine B6 Very sensitive Sensitive Sensitive Stable Sensitive Stable Biotin H Sensitive Stable Sensitive Stable Stable Stable Folic acid Bc Very sensitive Sensitive Very sensitive Stable Very sensitive Stable

extrusion

The extrusion process can be severe with high heat and steam pressure over a longer time period than for pelleting. Thus, vitamins in extruded feeds generally have a lower retention or survivability, compared to pelleted feeds. Moisture can be as high as 35- 40%, or twice as high as conditioning during pelleting. As with pelleting, longer conditioning times, higher moisture and higher temperatures offer the greatest threat. In a nice review on extrusion and vitamin stability, Riaz et al., (2009) note that barrel temperature, screw rpm, moisture, and die diameter contribute to vitamin survival in the final feed. Generally, across a number of trials and conditions, vitamins A, E and C, along with folic acid and thiamin, were most sensitive to extrusion.

premix Stress

In vitamin/trace mineral premixes, the dominant effect exerted on vitamins is redox (reduction and oxidation reactions) reactions by trace minerals. Trace minerals also vary in redox potential. The type of trace mineral molecular structure, with copper, zinc and iron being the most reactive and manganese and selenium the least reactive, has a significant impact on vitamin stability. Free metal ion is the most reactive (metal filings) followed by sulfate, carbonate, oxide and the least reactive form is chelated. Chelated forms become incapable of initiating formation of free radicals. Friction is also an important factor because it erodes the coating that protects several vitamins and reduces vitamin crystals to a smaller particle size. In fat-soluble vitamins, esters are significantly more stable than alcohols. The hydroxy group of alcohols is extremely sensitive to oxidation. The five double bonds in retinyl acetate still make the compound sensitive to oxidations. Vitamin A is significantly more stable in vitamin premixes than in vitamin-trace mineral premixes because trace minerals catalyze oxidation of the five double bonds.

Physical form also affects stability. There are vitamins that are stable in crystalline form (thiamin, pyridoxine), but most vitamins benefit from some form of protection. For example, spray-dried and beadlets of vitamin A and D, fat-coated vitamin C, vitamin E and choline chloride adsorbed in silica carrier all possess far greater stability than their unprotected forms. Yet, some forms of vitamin protection may not be practical for feed manufacturing. Such examples include ethylcellulose coating and vitamin-starch spray-dried emulsions that decrease flowability due to increased adhesiveness.

vitamin and traCe mineral premixeS

In vitamin premixes and complete diets, vitamin stability is clearly affected by contact with certain trace minerals and choline chloride that cause friction and speed up oxidation. Copper, zinc and iron are very reactive, whereas selenium, iodine and manganese are almost inert. Free metal ions are most reactive, followed by sulfate, carbonate and oxide salts, with chelated minerals being virtually inert. Thus, blends of vitamins and trace minerals are expected to exhibit reduced vitamin retention, especially during prolonged storage and (or) elevated temperature/humidity conditions. For example, riboflavin in a straight vitamin premix retained 93 percent of its potency after six months of storage. But, when the premix also included trace minerals, retention dropped to 71 percent. Choline chloride also reduced riboflavin retention from 99 to 95 percent after six months.

Not all vitamins, however, are affected by trace minerals and choline chloride. For example, retention of folic acid after six months was 80 percent regardless of blending with trace minerals, and retention of retinol acetate remained constant with or without

chlorine chloride. In diets and premixes for young pigs that contain pharmacological concentrations of zinc oxide and copper sulfate, vitamin retention becomes problematic, and these salts should be kept separately from vitamins.

teChnologieS to improve vitamin Stability

Advances in research and technology have led to the development of specialized vitamin forms to provide superior vitamin stability. Many