Evaluation of allergenicity of the alternative food protein sources microalga Spirulina and rapeseed cake – A study in Brown Norway rats

New food sources and unexplored by-products from current food production are necessary to meet the need for more sustainable food proteins. Nevertheless, allergenicity assessment should be performed before introducing them to the market. In this study, we characterised the protein profile and evaluated the inherent immunogenicity and sensitising capacity of protein extracts from the microalga Spirulina and the rapeseed cake in comparison to the known low-allergenic spinach and high-allergenic peanut in a Brown Norway rat model of food allergy. Moreover, the impact of digestion and heat treatment on the allergenicity was assessed. Further, the cross-reactivity between rapeseed proteins and the known allergic food mustard was explored. Mass spectrometry and in silico analyses of the protein extracts identified the potential allergen c-phycocyanin in Spirulina, whereas rapeseed cake contained 2S albumin and 11S globulin proteins with high sequence identity to mustard allergens. Both Spirulina and rapeseed proteins were immunogenic and induced sensitisation in rats to a higher degree than spinach. Whereas Spirulina showed a significantly lower immunogenicity and sensitising capacity than peanut, rapeseed demonstrated comparable sensitising capacity to peanut. Digestion and heat treatment affected the binding of specific IgG1 and IgE to both Spirulina and rapeseed, implying an effect of digestion and heating on their allergenicity, though the effect was highest for rapeseed. Furthermore, great cross-reactivity between mustard and rapeseed proteins was demonstrated. This study suggested that rapeseed cake proteins exhibit a high de novo sensitising capacity and significant cross-reactivity to mustard proteins, though this should be confirmed in human studies.