To the couch potato, the word “plasma” likely conjures up thoughts of a new television; to Trekkies, it’s the high-energy gaseous field the USS Enterprise has to traverse periodically. In other words, the term by itself doesn’t necessarily conjure up a yuck factor. However, some take exception to the use of plasma, specifically animal plasma, in their pets’ food.
Okay, maybe the idea is a little yucky—but maybe we’ve become a bit too squeamish. Plasma is the vital fluid component of blood; it is found throughout the body and the medical community even considers it a tissue. In an analogy to milk, plasma is equivalent to whey, which seems to be in all sorts of foods and no one takes issue.
To feed our carnivore friends food containing plasma should seem quite natural. After all, those are the very first parts our household predators relish after the kill (or when you open the can). Plasma is a high-quality, natural component that should be considered a valuable part of a dog or cat diet. So, how is it that animal plasma, as an ingredient, gets into a pet’s diet and what role might it play?
As a function of our livestock agriculture and meat production systems around the world, proper slaughter practices dictate that the animal be exsanguinated (to make bloodless). This blood is collected immediately under sanitary conditions in slaughter facilities under regulatory inspection. In the US, this would be under the purview of a licensed veterinarian employed by the Department of Agriculture.
Beyond the slaughter facility, there is a sophisticated infrastructure to process the blood, lest it putrefy and become a public health concern. Upon collection, the blood is maintained in a liquid state through the addition of anticoagulants such as sodium citrate or sodium phosphate. It is kept under refrigeration until the red blood cells can be separated from the fluid plasma by centrifugation, whereupon some of the moisture is removed to concentrate the plasma (by reverse osmosis or evaporation under vacuum). It is then spray-dried, resulting in a fine tan to cream-colored powder.
Since liquid animal plasma is a highly perishable and bioactive fluid, precautions regarding handling and stabilization are an everyday concern. Conversely, in a dry state, plasma is relatively stable, though slightly hygroscopic, so it must be stored in a cool, dry place.
Spray-dried animal plasma is usually sold at around 7-8% moisture and has a high protein content of nearly 80%. It contains very little fat or fiber (trace amounts), and minerals (ash) are low at less than 10% of the total. The protein fraction is rich in lysine and cysteine, contributes a meaningful amount of tryptophan and taurine but is short on methionine. The mineral fraction contains negligible calcium, potassium and magnesium but a fair amount of sodium (>2%) and phosphorus (>1%). Plasma is also known to contain albumin proteins (about 50%) with bioactive peptides and immunoglobulin G (IgG) that reputedly keep the immune system from over-reacting.
In the US, the Association of American Feed Control Officials defines animal plasma as “the product obtained by spray drying plasma which has been separated away from the cellular matter (red and white blood cells) of fresh whole blood by chemical and mechanical processing. The protein portion of this product is primarily albumin, globulin and fibrinogen type proteins. The minimum percent crude protein and the maximum percent ash must be guaranteed on the label. If it bears a name descriptive of its kind, composition or origin, it must correspond thereto.” Alternatively, one could also make the argument that plasma would fall under the definition of meat by-product.
There were concerns when bovine spongiform encephalopathy was first detected that the infective agent could be transmitted via blood and other fluids. However, after extensive testing, no infectivity has been detected in bovine plasma or serum proteins, according to the World Organization for Animal Health and the US Food and Drug Administration. To paraphrase the regulations as they stand currently, there is no prohibition of blood or blood product use in animal feeds (21CFR 589.2001). Further, there is no explicit restriction for bovine plasma use in petfoods. Despite this, today virtually all plasma used in petfoods is derived solely from pigs.
While the protein content is high and the ash content low in plasma, making it a great ingredient for use in formulating cat diets and high-protein diets in which minerals are being controlled, it is often too expensive for this purpose alone. Rather, plasma is primarily used in petfoods for its functional food properties—namely, its ability to form a resilient, irreversible, thermoplastic gel in restructured meat products (e.g., the meat pieces in a chunks and gravy wet food).
In this capacity, it binds water, acts as an emulsifier, has anti-foaming properties and forms a stable gel. It works for both chunk formation and in loaf applications at levels from 0.5-5%, with 1.5-2% being most common (Polo et al., 2005; Polo et al., 2007; Polo et al., 2009). It also helps level inconsistency in meats from supply-to-supply (Polo, 2011).
Animal plasma function is “activated” with increasing temperatures up to 120º C (Polo et al., 2005). This just so happens to correspond with the temperature at which wet foods are sterilized in the retort. It does this without co-factors or restrictions on pH, and it’s easy to use, mixing easily with a meat batter. It has a favorable cost benefit when compared to other binders, such as wheat gluten or egg white/albumin, commonly used for this purpose.
In petfood, animal plasma is very well liked by both dogs and cats—it has a favorable palatability profile and a neutral to beneficial effect on stool consistency. It has been shown to increase dry matter digestibility in dogs (Quigley et al., 2004) and has been reported to reduce the overstimulation of immune response in pigs and rats. However, this latter function is likely only effective if the plasma has not been subjected to denaturation by thermal processes.
If one looks for animal plasma in petfoods, it will quickly become obvious that this ingredient is a staple in restructured meat (i.e., chunks and gravy) products for its function as a binder. While plasma provides beneficial effects for the visual and nutritional components of these products, there have been fewer opportunities to capitalize on the bioactive aspects in conventional food formats, such as extruded or baked products. However, research is under way to capture these features in dry petfoods. When this happens, animal plasma will become more prevalent in petfood as an element to promote health.
