Proteomic study of walnut oleosome and first evidence on oleosin sensitization in allergic patients

Walnut is considered the healthiest of all nuts, mainly because of its polyunsaturated fatty acid content. As far as its protein component is concerned, a rather interesting class of oil-body (OB) associated proteins, which, together with lipids, generates the "oleosome”, still needs to be explored in detail. This study aimed to characterize the walnut oleosome proteins by a double off-gel and in-gel approach, with a focus on the effect of processing on protein profile and oleosin immune recognition. The off-gel approach (label free quantification, LFQ) allowed the identification of all the three oleosome specific associated class of proteins: oleosins, caleosins, and steroleosins. The in-gel separation coupled with immunoblotting experiments proved that walnut oleosins were immune recognized by walnut allergic patients’ IgEs, providing first evidence of their potential role in walnut allergenicity. Oleosin immune recognition seemed to be increased by boiling procedure compared to raw and roasted walnut, probably due to the increased solubility of oleosome associated proteins in this condition.