Effect Of Malondialdehyde Modification On Allergenicity Of Shrimp Tropomyosin

Shrimp is favored by people for the nutritional value and delicious taste. However, it is one of eight categories allergenic food, and there are 2% of adults are allergic with shellfish. As the major allergen of shrimp, researches have been focus placed on tropomyosin that investigate change occur during food processing and storage period. However, their effects are not consistent. Recent studies indicate that there are various chemical reactions that occur during food processing, and oxidation is the great impact one. Especially for shrimp that is rich in unsaturated fatty acids; it easily undergoes lipid peroxidation and then produces small molecular reactive compounds, such as malondialdehyde. The reactive aldehyde is accounting for strong change of immunogenicity. The present study investigates the effect of malondialdehyde on protein structure, effector cells and simulated digestion in vitro of tropomyosin, with the aim of providing insight into the mechanisms that underlie the changes that occurred during shrimp processing and preservation. In addition, it can promote development of hypoallergenic food. The main results are as followed:1. The study is to investigate effect of malondialdehyde modification on allergenicity and structure of shrimp tropomyosin.Following treatment with malondialdehyde, tropomyosin cross-linking was observed, and then the aggregates were recognized by IgG/IgE in immunoblot analysis. Meanwhile, TM allergenicity had found reduced significantly by 56.31%, 63.40%,61.92% and 50.79% measured by ELISA. Secondary structure of tropomyosin became more disordered from tight structure. Moreover, surface hydrophobicity was found risen 93-fold. Carbonyl content was found enhanced 14-fold. Free amine group and available lysine were found decreased 14% and 46.77% respectively. The results suggest that malondialdehyde promotes crossing-linking of tropomyosin, and the conformational changes in tropomyosin leading to significantly impair on the antigenicity, which in turn reduce allergenicity of tropomyosin.2. The study is to investigate effect of malondialdehyde modification on potential allergenicity of tropomyosin.Mediators such as β-hexosaminidase, histamine, tryptase, cysteinyl leukotrienes, and prostaglandin D2 clearly reduced in a concentration-dependent manner following malondialdehyde treatment. As for cytokines, the levels of IL-4 and IL-13 drastically decreased in the sera of three patients, while the other patient did not show significant changes. The results indicated that malondialdehyde could strongly modulate degranulation of RBL-2H3 cell lines and significantly reduce the release of mediators and cytokines from mast cells stimulated by malondialdehyde-treated tropomyosin, thus decrease allergenicity of tropomyosin. The study is demonstrated that malondialdehyde could change allergenic potency in cell level based on alteration of structure.3. The study is to investigate effect of malondialdehyde modification on digestion stability in vitro of tropomyosin.Tropomyosin resisted pepsin digestion relatively after modified by malondialdehyde. It indicated that as enhancement of oxidation, surface hydrophobicity increased, and therefore, comformational structure of cross-linking was altered with the certain amino acids packed into protein. The immunogenicity had almost no obvious change. Or maybe malondialdehyde-treated tropomyosin tended to stabilize in acid situation and restrained pepsin digestion ratio; while tropomyosin was easily susceptible to trpsin. As protein was unfolding, more digestible sites were exposed, and structure of cross-linking was changed after degradation, which resulted in decline in allergenicity. The study is demonstrated that malondialdehyde could change digest stability based on alteration of structure.In sum, the study is to investigate major allergen of shrimp-tropomyosin alteration of structure and allergenicity after oxidized by malondialdehyde produced from lipid peroxidation during food processing. It initially indicates effect of oxidation on allergen and underlies research insights for changing of allergenicity in food processing and preservation.