Hydrolysed Protein in Kibble: Is It Really Hypoallergenic?

Hydrolysed proteins are a frequent member of the ingredient lists of some pet food products, above all of extruded dry foods such as kibble.

What are proteins? What is hydrolysis? Does it have anything to do with food allergies in dogs? Let's look in detail at the whole process and the uses of hydrolysed proteins in canine nutrition.

The Structure of Proteins

A protein is a molecule formed by the joining together of thousands of monomers called amino acids. The linear joining of these is known as the primary structure. This line of amino acids, by means of electromagnetic charges, gradually deforms because the amino acids interact with one another.

Alpha helices or beta sheets can form depending on the interaction. This is known as the secondary structure. In turn, these secondary structures interact with each other to give the protein its characteristic shape in what's known as the tertiary structure.

Hydrolysis is precisely the opposite process: it consists of taking the amino acid chain and splitting it into small pieces called peptides, or even into individual amino acids.

How Is a Protein Hydrolysed in Dog Food?

The methods for hydrolysing proteins can be based on applying heat treatment, altering the protein's pH (or acidity) and using enzymes known as proteases.

The method spreading fastest because of its low cost is the use of proteases. These are obtained either from bacterial cultures or from animal samples. They act like a pair of scissors, cutting the protein at the ends or at intermediate fragments. The longer they act, the smaller the molecules they leave behind.

Why Are the Proteins in Kibble Hydrolysed?

The reasons for hydrolysing a protein are varied. In the first place, it makes it possible to use proteins that in their normal tertiary structure aren't very digestible, since their shape prevents the pancreas's proteases from attacking them.

The digestibility of hydrolysed proteins is subtly greater than that of whole proteins, but cases have been seen in some species other than the dog and cat where they turned out to be highly digestible.

Then there's their relationship with allergic reactions, not only in dogs and cats but in people. These reactions are based on the response of immunoglobulin E to the proteins in the food.

These recognise certain characteristic regions, or antigens, of the proteins. They're normally parts of the larger protein structures, such as the secondary or the tertiary, so the smaller those structures become, the less likely they are to trigger allergic reactions.

In fact, a point of hydrolysis can be reached at which the peptides are so small that they can't occupy the binding sites with the immunoglobulin.

The Limits of Hydrolysing the Proteins in Dog Food

Despite all the good applications hydrolysing proteins has, there's a problem. While proteins in their whole form give food very characteristic, rich flavours, smaller peptides have a very different taste: they're bitter.

Whether in their natural state or through hydrolysis, the smaller an amino acid sequence is, the more bitter it is. This is a limiting factor when it comes to producing foods with this ingredient, since a food the dog won't eat is of no use at all.

This in turn has meant that products with small-sized hydrolysed proteins, usually prescription ones, have to be high in lipids to offset that bitter taste and be palatable to dogs.

Hydrolysed Proteins on the Market and Hypoallergenic Products for Dogs

As already mentioned, these are recurring ingredients that we'll be able to see on the ingredient lists of the products we trust. Many times they can even be the main source of protein. From a nutritional point of view that isn't a problem: as we've already seen, digestibility increases and it can even turn ingredients that weren't digestible and nutritious into ingredients that are, which is very interesting from an environmental standpoint.

The problem arises when products using this ingredient claim that it's hypoallergenic. This happens because of a point we've already discussed: the relationship of hydrolysis with proteins. The fact that a food contains hydrolysed proteins doesn't mean it's hypoallergenic, for several reasons:

1. The food normally has other ingredients (tubers, fruit, cereals) which also have their own proteins that aren't hydrolysed.
2. The fact that they're hydrolysed doesn't mean they're small enough to avoid allergic responses.

Bibliography 1. Protein Structure. Lerman. 2. Protein hydrolysates: processes and applications. Benítez et all. 3. Hydrolyzed Protein Dietsfor Dogs and Cats. Cave et all. 4. Effect of replacing marine protein with hydrolyzed feather meal on growth, apparent digestibility and body composition of juvenile tilapias; Oreochromis mossambicus. Awao et all. 5. El problema del sabor amargo en los hidrolizados enzimáticos de proteína de pescado. Pastoriza et all. 6. Control of the proteolytic reaction and of the level of bitterness in protein hydrolysis processes. Jens Adler-Nissen