Effect of different types of roasting on hazelnut immunoreactivity

Introduction: It is known that thermal processing, commonly used during food production, may affect food allergenicity by inducing physical and/or chemical changes in macronutrients. However, due to the lack of detailed information on processing procedures, available evidences on this topic are presently contradictory. This study aims to evaluate the effects of different types of roasting on hazelnut protein solubility and immune reactivity. Methods: We investigated the IgE-binding capacities of both soluble and insoluble hazelnut protein fractions from C. avellana (Cv. Tonda Gentile delle Langhe), before and after roasting using two different roasting techniques: hot air (HA) as a ''traditional method," and infrared (IR), as an ''innovative method". Two combinations of time and temperature for each oven were considered: 140°C for 25min (LT) and 170°C for 17 min (HT) in HA; 140°C for 12 min (LT) and 170°C for 10 min (HT) in IR. Total protein and oil body associated protein extracts were used for immunoblotting experiments with allergic patient sera. Results: A decrease in hazelnut protein solubility was detectable following LT-IR roasting and it became more evident after HT processing, for both roasting types. Concerning allergenicity, the raw hazelnut proteins extract was the most immune reactive, followed by LT-HA and LT-IR processed hazelnut that showed a very similar immune reactive pattern. The HA-HT treatment resulted in a low, although detectable, immune reactivity, while the IR-HT processing caused a quite complete disappearance of immune reactivity of hazelnut proteins. The different hazelnut allergens (Cor a 8, 9, 11, 12, 13, 14, 15) were differently affected by thermal treatments, in accordance with their thermal stability, as already reported by literature. Discussion: HA oven is the most conservative processing, especially at low temperatures, both considering protein solubility and immune-reactivity. Both the HT treatments demonstrated to reduce immune-recognition of hazelnut proteins by allergic patient sera.