Effects of different processing methods on digestibility of Scylla paramamosain allergen (tropomyosin)

Abstract

Crustacean allergy is a significant health problem around the world, and tropomyosin (TM) represents the major allergen of crustaceans. The aim of this study was to evaluate three processing methods (boiling, CUB, HPS) and identify the one method that is most effective in the degradation of TM and reduction of its IgE-binding reactivity, and make it easier to be decomposed during gastrointestinal digestion. SDS–PAGE analysis indicated that boiling had little impact on the digestive stability of TM. In contrast, combined ultrasound and boiling (CUB), and high pressure steaming (HPS) both could accelerate the digestion of TM. Similarly, western blotting and inhibition ELISA also demonstrated that the reactivity of IgG/IgE-binding of TM that was extracted from processed crab was partially decreased after treating with CUB or HPS. Among the three processing methods, HPS was the most effective method to accelerate the digestion of TM in gastrointestinal digestion, and reduce the reactivity of IgG/IgE-binding of TM. These results suggest that proper processing of crab could promote the degradation of TM in simulated gastrointestinal digestion, reduce the reactivity of IgG/IgE-binding of TM, and decrease the incidence of crab hypersensitivity in humans.

Introduction

There is growing concern about food allergy because it can lead to autoimmune diseases. Food allergy is representative of type I allergies that are mediated by IgE antibodies. The main food allergens are mostly proteins or glycoproteins with molecular masses of 10–60 kDa (Shainti et al., 1993). A report of the Centers for Disease Control and Prevention has indicated an 18% increase in childhood food allergy from 1997 to 2007, with an estimated 3.9% of children currently affected (Branum and Lukacs, 2008). In addition, according to an epidemiological survey, adverse immune responses to foods affect approximately 5% of young children and 3–4% of adults in westernized countries, and appear to have increased in prevalence (Scott et al., 2010).

Among a number of allergenic foods, crustaceans are considered to be one of the most common causes of food allergy due to their widespread consumption, especially in coastal countries (Lehrer et al., 2003, Wild and Lehrer, 2005). Crustaceans are one of the eight major sources of food allergens proposed by the Food and Agriculture Organization (FAO) of the United Nations and World Health Organization (WHO) (FAO/WHO, 2001), and they are favored by people because of their delicacy and nutritious value. Recently, with the development of processed crab products, researchers around the world have paid much more attention to the study of crab allergens. It has been demonstrated that the major allergen of crab is tropomyosin (TM), a myofibrillar protein that is composed of two identical subunits with molecular masses of 35–38 kDa and an isoelectric point of 4.5. In contrast with other proteins, TM is stable and can tolerate heat, grinding and the normal processing methods (Leung et al., 1998, Motoyama et al., 2006, Motoyama et al., 2007).

According to the research of Lee and Park (2004), digestibility of common whelk allergens that were digested by simulated gastrointestinal fluid remained unchanged after thermal treatment, thus demonstrating that the main allergen of crustaceans is heat stable. Moreover, compare to the numerous food processing methods, ultrasound is an effective processing and preservation technology, on account of its good directivity and strong penetrability (Villamie and Jong, 2000). Currently, there have been few studies about the impact of ultrasound on food allergens. Li et al. (2006) have adopted ultrasonic treatment of shrimp protein extract and muscle. They have indicated that high-intensity ultrasound can clearly reduce the allergic properties of shrimp allergens, and this will be beneficial to allergic individuals. In addition, the effect of high pressure treatment (300 MPa) on the hydrolysis of dairy whey proteins in simulated gastrointestinal digestion has been analyzed. After treatment with high pressure, dairy whey proteins and β-lactoglobulin were hydrolyzed easily by protease, and the IgE-binding was much lower (Izquierdo et al., 2005, Peñas et al., 2006). Therefore, it is meaningful to study the effect of different processing methods on crab allergens, and to establish proper processing methods to reduce or remove the stability and reactivity of crab TM.

In the present study, in order to identify the method that is most effective in the degradation of TM and reduction of its IgE-binding reactivity, in vitro simulated gastrointestinal digestion was adopted to investigate the digestive stability of TM extracted from crab treated by boiling, combined ultrasound and boiling (CUB), and high pressure steaming (HPS). Meanwhile, western blotting and inhibition ELISA were used to analyze the IgG/IgE-binding of TM from the digested crab crude extract (CCE) from processed crabs.