Interaction of selected phenolics with key food chemical reactions to affect their original bioactivities and the formation of advanced glycation endproducts

Abstract

Phenolic compounds, abundant in various of foods, are a class of natural antioxidants with multiple biological activities. As active components, phenolics may participate in food chemical reactions during food storage and processing, thereby influence the constitute of reaction products and food quality. Maillard reaction and lipid oxidation are two key food reactions in food thermal processing. Both of them produce color, flavor compounds and harmful substances to foods, such as advanced glycation endproducts (AGEs), which contribute to the development of diabetes. Phenolics in foods can inhibit toxicants’ formation and reduce the risk of chronic diseases, while their efficacy is finally dependent on the experienced processing processes. During processing, especially thermal conditions, phenolics may develop into new compounds by degradation or interaction with food components, resulting in enhanced or weakened biological activities. However, little is known about the bioactivity changes of phenolics in thermal or real food systems. The present study tested four phenolics (rosmarinic acid, carnosic acid, resveratrol, and epicatechin) tightly associated with food processing in different models, aiming to evaluate their original protective effects against AGEs and diabetes, bioactivity changes in thermal conditions, and health benefits to cookies. Rosmarinic acid (RA) and carnosic acid (CA) are major components of rosemary, a herb commonly used in cooking. Both of them exhibited inhibition capacity on fluorescent AGEs, carboxymethyl-lysine (CML) and carboxyethyl-lysine (CEL) in the models of bovine serum albumin (BSA)/glucose or BSA/dicarbonyl in a dose dependent manner. They also decreased the concentration of dicarbonyls, protein carbonylation and fluorescence intensity of protein oxidation products, suggesting that RA and CA could inhibit AGEs formation through limiting dicarbonyl levels and antioxidative effects. Subsequently, they were analysed in diabetic rats and showed antioxidative and anti-glycative effect by decreasing the levels of MDA and AGEs. Besides, they mitigated the diabetic symptoms of rats by protection against tissue damage and inflammation in the abdominal aorta. Another phenolic compound, resveratrol, is a famous cancer chemopreventive agent with confirmed anti-glycative effect. When added into lipid thermal-oxidation model with unsaturated fatty acids, it demonstrated acrolein-trapping effect by forming conjugation adducts. Compared to resveratrol, the acrolein-conjugated resveratrol showed no cytotoxicity in colon normal cells but enhanced anti-proliferative effect in colon cancer cells (HCT 116). It significantly induced cell cycle G1 phase arrest and apoptosis, which was consistent with the mechanism of resveratrol. Finally, these three phenolics together with epicatechin were incorporated in a cookie model. Temperature was a significant determinant affecting their stability and accordingly influenced cookies’ antioxidant capacity. Total fluorescent AGEs in cookies were inhibited by all of the phenolics while rosmarinic acid couldn’t reduce the level of glyoxal and methyglyoxal. Nevertheless, cytotoxicity of rosmarinic acid against cancer cells was enhanced in thermal processing. In conclusion, this research contributed to the knowledge that certain phenolics could inhibit AGEs formation in vitro and in vivo, obtain enhanced biological activities in food chemical reactions, and increase beneficial effects of cookies, suggesting that they are functional additives for improving antioxidant intake and reducing harmful substances of food matrix.