Heat treatment and enzymatic hydrolysis induce distinct physicochemical modifications of cow’s and camel milk proteins, affecting their allergenicity in different ways

Background: Heat treatment (HT) and enzymatic hydrolysis (EH) are techniques used to reduce milk protein allergenicity. HT contributes to modification and/or masking of epitopes by denaturation and aggregation, whereas EH leads to destruction of epitopes by cleavage of the primary structure. These processes are widely used in manufacturing of hypoallergenic infant formulas for cow’s milk allergic patients. Recent studies have shown that some cow’s milk allergic patients tolerate camel milk due to differences in protein profile and relatively low sequence homology between camel and cow’s milk
proteins, though some experience cross- reactivity. Yet, the knowledge on how HT and EH influence camel milk protein structure and their usefulness in camel milk- based infant formulas are scarce. Method: The aim of this study was to evaluate how HT and EH influence cow’s and camel milk protein physicochemical properties and consequential allergenicity. Unmodified intact, heat treated or enzymatically hydrolysed cow’s and camel milk were characterised by different chromatography and mass spectrometry methods for protein and peptide profile, degree of hydrolysis, protein denaturation, protein aggregation and Maillard reaction markers. Antibodies raised against intact unmodified cow’s and camel milk proteins in the high- IgE responder Brown Norway rats were used to evaluate allergenicity by various ELISAs. Results: Results showed that even though cow’s and camel milk have comparable fat, carbohydrate and protein contents, they were affected differently under the same conditions of HT and EH. For example, HT of cow’s milk generated more amino acid cross- linking and consequently protein aggregation compared to camel milk, whereas EH caused more breakdown of camel milk proteins compared to cow’s milk proteins. The latter correlates well with the literature stating β- lactoglobulin as one of the most proteolytically resistant proteins found in cow’s milk, but is absent in camel milk. Only EH reduced allergenicity of cow’s milk, in contrast to HT. Both HT and EH reduced the allergenicity of camel milk and this to a higher degree than for the cow’s milk. Further, the cross- reactivity between cow’s and camel milk was reduced after HT and EH of camel milk. Conclusion: Processing of intact cow’s and camel milk proteins influenced their allergenicity in different ways, reflecting their differences in structure and composition. This knowledge may contribute to the development of camel milk- based infant formulas.