Treatment of cashew extracts with Aspergillopepsin reduces IgE binding to cashew allergens

Abstract

Enzymes from Aspergillus fungal species are used in many industrial and pharmaceutical applications. Aspergillus niger and Aspergillus oryzae were cultured on media containing cashew nut flour to identify secreted proteins that may be useful as future food allergen processing enzymes. Mass-spectrometric analysis of secreted proteins and protein bands from SDS-PAGE gels indicated the presence of at least 63 proteins. The majority of these proteins were involved in carbohydrate metabolism, but there were also enzymes involved in lipid and protein metabolism. It is likely that some of these enzymes are specifically upregulated in response to cashew nut protein, and study of these enzymes could aid our understanding of cashew nut metabolism. Aspergillopepsin from A. niger was one of the proteolytic enzymes identified, and 6 distinct peptides were matched to this protein providing 22% coverage of the protein. Cashew extracts were incubated with a commercially available preparation of Aspergillopepsin (Acid Stable Protease, ASP) using simulated gastric fluid conditions to determine if ASP could degrade the protein and lower antibody binding to cashew allergens. Following treatment of cashew extract with ASP, a significant reduction was observed in cashew allergen binding to rabbit anti-cashew IgG using an immunoblot assay and serum IgE antibodies from cashew allergic individuals using competitive ELISA. These findings highlight the possible application of Aspergillopepsin/ASP from A. niger in food processing steps to attenuate cashew nut and other tree nut or peanut allergens.