A Review of Walnut Allergy: Allergens Characteristic, the Impact of Processing on Allergenicity and Future Perspectives

(1) Background: As one of the world’s four major nuts, walnuts are rich in nutritional value; however, concerns regarding their allergenicity are becoming increasingly prominent. (2) Scope and Approach: This article provides a systematic review of the nutritional value and allergenicity of walnuts, the composition of major allergenic proteins, and their detection techniques. A particular focus is placed on elucidating the mechanisms by which different processing methods—including heat treatment, ultra-high pressure, ultrasound, low-temperature plasma, enzymatic treatment, and polyphenol modification—affect the structure and allergenicity of walnut allergenic proteins. (3) Key Findings and Conclusions: Current evidence suggests that processing techniques can alter the secondary and tertiary structures of walnut proteins, change the accessibility of linear or conformational epitopes, and reduce their Immunoglobulin E/Immunoglobulin G (IgE/IgG) binding capacity under certain in vitro conditions. Among these, high-temperature and high-pressure treatment, enzymatic hydrolysis, polyphenol modification, and combined processing strategies demonstrate promising potential for reducing walnut protein immunoreactivity. However, structural modifications, reduced antibody-binding capacity, or increased digestibility should not be directly interpreted as definitive evidence of reduced clinical sensitization. This paper summarizes the current status of the development and application of hypoallergenic foods, analyzes the technical challenges and future development directions, and aims to provide a theoretical basis and technical reference for the development of allergenicity-reduced walnut products.