Insoluble and soluble roasted walnut proteins retain antibody reactivity

Abstract

Thermal processing techniques commonly used during food production have the potential to impact food allergens by inducing physical and/or chemical changes to the proteins. English walnuts (Juglans regia) are among the most commonly allergenic tree nuts, but little information is available regarding how walnut allergens respond to thermal processing. This study evaluated the effects of dry roasting (132 or 180°C for 5, 10, or 20min) on the solubility and immunoreactivity of walnut proteins. A dramatic decrease in walnut protein solubility was observed following dry roasting at 180°C for 20min. However, both the soluble and insoluble protein fractions from roasted walnuts maintained substantial amounts of IgG immunoreactivity (using anti-raw and anti-roasted walnut antisera), with similar patterns of reactivity observed for human IgE from walnut-allergic individuals. Thus, walnut proteins are relatively stable under certain thermal processing conditions, and IgE reactivity remains present even when insoluble aggregates are formed.

Effects of the Varietal Diversity and the Thermal Treatment on the Protein Profile of Peanuts and Hazelnuts

“…In this regard, numerous methods to detect allergens contamination and/or to assess in vitro the allergenicity of specific ingredients rely on protein extraction systems. It was clearly demonstrated that the use of inappropriate extraction conditions can have a dramatic impact on protein extraction yield, decreasing the recovery of proteins which constrains the analysis sensitivity or, in the worst case, impairing the reliability of the immunoassay tests for allergenicity assessment [22]. Moreover, the proteins solubility is important not only in the determination of the allergen content or allergenicity assessment, but also in a variety of other applications such as clinical research studies and immunotherapy, as well as, evaluation of the quality and nutritional value of different foods.…”

Shrimp tropomyosin retains antibody reactivity after exposure to acidic condition

“…This has the tendency to reduce the pH of the extraction solution, its buffering capacity and its ability to solubilize myofibrillar proteins. Effective solubilization of allergenic protein is essential for the accurate immunochemical detection of allergenic proteins . Therefore reduced soluble protein recovery may be the main challenge in the immunochemical analysis of acid‐marinated foods or high acid foods.…”

“…In general, the authors identified differences in the solubility of the allergens in the two fractions as one of the factors responsible for the difference in antigenicity . Similarly, the IgE binding of walnut allergens heated at 120 or 180 °C for up to 20 min was more enhanced in the insoluble pellet compared with the soluble fraction . From this study, it was also reported that the allergenic proteins in the insoluble pellet still retained their conformational epitopes, as shown by the decrease in IgE binding of this pellet fraction under reducing condition .…”

“…Similarly, the IgE binding of walnut allergens heated at 120 or 180 °C for up to 20 min was more enhanced in the insoluble pellet compared with the soluble fraction . From this study, it was also reported that the allergenic proteins in the insoluble pellet still retained their conformational epitopes, as shown by the decrease in IgE binding of this pellet fraction under reducing condition . Allergenic proteins may become denatured during food processing, which subsequently reduces their solubility in most extraction buffers used for immunochemical detection of allergens .…”

“…More so, pH-induced denaturation of allergenic proteins can reduce their solubility in extraction solution, therefore their detection and accurate quantification via immunochemical methods may be affected. 19 Moreover, the antigenic properties of proteins in the insoluble pellet obtained after the recovery of supernatant are often overlooked by investigators.…”