The use of these formulas is based on the premise that predigested protein provides protein in a less antigenic form.

Hydrolysate formulas are processed using three main techniques: heat denaturation which eliminates conformational antigenic determinants; enzymic hydrolysis, which alters sequential determinants; or a combination of both techniques.

There are two broad categories of protein hydrolysates comprising of partially and extensively hydrolysed proteins.

Partially Hydrolysed Formulas (pHF)

Partial hydrolysates are characterised by a larger proportion of long peptides. They are considered more palatable than extensively hydrolysed formulas. However, they are intended for prophylactic use and are not considered suitable for treatment of cow milk allergy/intolerance. There have been many reports of adverse reactions to these products.

Extensively Hydrolysed Formulas (eHF)

The extensively hydrolysed proteins comprise predominantly of free amino acids and short peptides. A major problem with these products is palatability. Also, these formulas are not always tolerated.

Casein hydrolysates have been in use for over 50 years, whey hydrolysates for rather less time and hydrolysates of pork/soya have more recently been introduced. Casein and whey from cow's milk are the most commonly used sources of protein for hydrolysates because of their high nutritional quality and their amino acid composition. This choice is somewhat surprising given that casein and whey are the major allergens in cow's milk.
Therefore other formulas utilising hydrolysates of other protein sources have been developed to try and eliminate the risk of reaction. Vegetable proteins such as soya, rice and chickpea have all been used successfully in the preparation of hypoallergenic protein hydrolysates, however due to the low biological value these protein hydrolysates require supplementation with essential amino acids.