Milk and milk proteins have been around for eons. While likely not a large part of dog or cat diets beyond the weaning period, some milk constituents have periodically found their way into pet diets for years - likely as leftovers from the family's cereal bowls.
Most texts instruct us to avoid feeding milk products to cats and dogs past weaning as they lose the lactase enzyme activity necessary to utilize the lactose sugar found in milk. However, it is becoming increasingly common to find petfoods that contain whey, a milk protein, as a prominent ingredient on their labels.
Milk proteins, like whey, have been commercially available for many years. Likewise, research on milk production, composition and nutrition has been a mainstay for our agricultural universities for a hundred years or better. There are literally mountains of research on milk proteins like whey; but almost none of it pertains to this ingredient as part of a dog or cat diet. It would be nice if there were some published work directly related to petfood.
In the US, children grow up hearing a traditional poem about Miss Muffet eating her curds and whey. Just before being scared by a spider, Miss Muffet is eating curdled milk that has separated into its two main protein components, casein and whey. This separation is a result of adding acid or rennin (rennet) to whole milk, which causes the proteins to separate into casein (the insoluble curds) and whey (the soluble liquid).
The feed term in the AAFCO Official Publication (2007) identifies whey as the watery part of milk separated from the curd. While casein is primarily made by the mammary gland, the whey fraction represents the protein in milk that comes from both the mammary gland and the liver (serum proteins). The most abundant protein in whey is Beta-lactoglobulin. Whey also contains alpha-lactalbumin, blood serum albumin (liver derived), the iron-binding proteins transferrin and lactoferrin, immunoglobulins and numerous binding proteins.
As an ingredient, whey represents a quality, high protein component with nutritional and functional properties. - Greg AldrichCommercially, whey is the co-product stream resulting from the manufacture of cheese.
Commercially, whey is the co-product stream resulting from the manufacture of cheese. Most of the whey in the market comes from cows. In the cheese-making process, the casein is separated from the whey and then salted, pressed and allowed to age for several weeks. Depending on the processing facility and final product, some of the whey is used in the production of ricotta-type cheeses, and some is further refined and sold in the liquid form (e.g., sweet whey) often ending up in infant formula.
A large fraction of the whey is purified and dried, a form that is likely the most practical for petfood applications. The dried whey is produced by spray or drum drying with the net result being a dry, free-flowing, white to slightly tan powder. Several dried whey products are available: dried whey, whey protein concentrate and whey protein isolate. What really separates the whey products is the amount of protein and lactose they contain. For petfood applications, the whey protein concentrates (80% protein, 10% lactose) and whey protein isolates (80% protein, 0.5% lactose) have the greatest potential.
From a food functionality perspective, whey is used as a fat and protein binder, an emulsifying agent and a gelling agent. It has application as a browning agent and color development compound. It imparts a dairy (milk) flavor to foods, can aid expansion in extrusion and can influence product texture. Whey has also been demonstrated in meat and high oil products to improve shelf-life through physical and chemical antioxidant properties.
Whey mixes well for applications that require miscibility such as baking or canning. It has also been used as a complimentary protein source in palatability enhancers.
The amino acid composition of whey is quite favorable. It is high in essential amino acids, such as the sulfur-containing amino acids (methionine and cysteine), lysine, threonine and the branched chain amino acids (isoleucine, leucine and valine).
The protein quality of whey is quite good as well. The protein efficiency ratio (PER) of whey is approximately 83% of the PER of egg (the gold standard for protein quality). For comparison purposes, soybean protein is approximately 55% of the PER of egg. Whey is often found in protein supplements marketed to performance athletes and weight-lifters. One reason is because of its abundant supply of leucine, which has been identified as a key signal for the initiation of muscle protein synthesis.
The binding proteins in whey are known to aid in the transport of retinol and vitamin D, the immunoglobulins have been implicated in enhanced immune function and the binding proteins have been shown to reduce the impact of pathogenic bacteria. Whey is also a quality source of calcium, phosphorus, potassium and other trace minerals.
Commercially, whey is the co-product stream resulting from the manufacture of cheese.
In the literature no reports were found regarding negative effects of whey on cat or dog health. One can speculate that allergenic responses are possible, like that for any protein. As an ingredient, whey represents a quality, high protein component with nutritional and functional properties that some petfood manufacturers are using to enhance dog and cat diets. Whether consumers will understand what whey represents and consider it to be worthy of their pets may be another question altogether.