Professor Wang Mingfu of the University of Hong Kong and Associate Professor Zhao Moon of Shanghai Ocean University, among others, published a research paper online at
Journal of Agricultural and Food Chemistry
(IF-4.192, Division I of the Chinese Academy of Sciences). The study explores chemical changes and changes in antioxidant activity in the process of inhibiting oxidation of fish oil. The first author is Liu Shaojun, a master's student at Shanghai Ocean University, and the correspondents are Professor Wang Mingfu and Associate Professor Zhao Moon.
is rich in omega-3 polyunsaturated fatty acids such as 20 carbon quyrenic acid (EPA) and 22 carbon hetoleic acid (DHA). Epidemiological studies have shown that omega-3 polyunsaturated fatty acids have functional activities such as improving vision, promoting brain and neurodevelopment in infants and young children, preventing and reducing heart disease, anti-inflammatory and anti-allergy. However, fish oil in the processing and storage process, under the influence of oxygen, light, high temperature and metal ions are very easy to oxidize, the production of aldehyde, ketones and other active carboxyl compounds (RCS), affecting food quality, endangering human health. Adding antioxidants, especially natural phenolic antioxidants, is considered one of the effective ways to prevent and delay oil oxidation. However, polyphenols inhibit oil oxidation while also participating in different stages of lipid oxidation reactions, resulting in the loss of polyphenols, chemical structure changes and changes in antioxidant activity. In this paper, the polyphenols, which are widely found in ingredients, are studied, and their antioxidant effect on fish oil, as well as its inhibition of oil oxidation at the same time its own chemical changes and antioxidant activity changes. The results provide theoretical basis for the use of dietary polyphenols to control oil oxidation and provide technical support for the protection of oil and fat food safety.
Results and Discussion
1. The antioxidant activity of quercetin in the process of accelerated oxidation of fish oil
First, the effect of quercetin on RCS formation and fatty acid composition in fish oil under accelerated oxidation conditions was studied. The accelerated oxidation system of fish oil is as follows: the control group is fish oil, the treatment group is fish oil and quercetin (200mg/kg fish oil), the heating temperature is 60 oC, the heating time is 0-5d. Using SPME-GC/MS, GC-FID analysis of changes in RCS content and fatty acid composition in fish oil, it was found that quercetin significantly inhibited the formation of RCS in fish oil, but with the extension of heating time, the inhibition rate decreased from 46.73% to 33.29% (Table 1). In addition, quercetin significantly inhibits oxidation and degradation of fatty acids in fish oil, but inhibition is also reduced with the extension of heating time (Table 2). This suggests that quercetin may have been converted into a less antioxidant-active quercetin derivative.
2. Chemical changes of quercetin during accelerated oxidation of fish oil
HPLC analysis found that during the accelerated oxidation process, the content of quercetin in fish oil decreased (Figure 1), while the decrease in quercetin was accompanied by the formation of two major new substances (Figure 2A). The two new substances were purified by semi-preparation HPLC separation, and ESI-MS analysis showed that the molecular weights of the two new substances were 586 and 612 (Figures 2B, 2C, respectively), which may be hydroxyl of quercetin C-rings reacting with EPA and DHA and losing a molecule of water. To further confirm the structure of these quercetin derivatives and clarify the formation mechanism of these derivatives, we chemically synthesized the two new substances and used MS and NMR to personalize the structure, which are quercetin-3-O-Twenty carbon quercetones and quercetin-3-O-twenty-two carbon heptonates, the HPLC retention time and MS map of these synthetic compounds are the same as the compounds we isolated from the fish oil that added quercetin. Based on the chemical structure of these two new substances, we deduced that quercetin reacted with EPA and DHA to convert into a less antioxidant-active quercetin fatty acid ester derivative (Figure 3), so that the antioxidant activity of quercetin decreased gradually as the heating time increased. Other newly generated substances may be the addition of quercetin and RCS, and due to their small content, we do not separate purification and structural features.
3. The formation law of quercetin derivatives during the accelerated oxidation process of fish oil
In addition, upLC-MS was used to determine the formation law of two quercetin derivatives in fish oil, and it was found that quercetin-3-O-20 carbon-fiveene was found within five days of heat treatment. The gradual increase in acid and quercetin-3-O-22 carbon heptonate content (Figure 4) indicates that quercetin is sustainable in the capture capacity of EPA and DHA in fish oil, and further indicates that quercetin inhibits chemical structure changes in the process of fish oil oxidation. This may be the reason for its gradual weakening of antioxidant activity.
4. The antioxidant capacity of quercetin derivatives
Finally, the antioxidant capacity of quercetin and its derivatives in chemical models, grease models, biological models and cells was measured. It was found that quercetin derivatives significantly reduced the antioxidant capacity of fish oil due to the reaction of a hydroxyl, compared with quercetin DPPH and ABTS
free radical removal capacity (Figure 5A, 5B) on fish oil also significantly reduced (Figure 5C, 5D), which is also the reason for the gradual decrease in the oxidation activity of quercetin anti-fish oil. In biological systems and cell models, the antioxidant activity of quercetin derivatives is higher than that of quercetin, which may be due to the introduction of fat chains in quercetin to enhance the pro-lipid properties of quercetin derivatives, which better pass through the phospholipid double molecular layer of the cell membrane into the cell to play its antioxidant activity.
paper systematically studies the antioxidant effects and chemical changes of quercetin in fish oil. The results showed that quercetin could significantly inhibit the oxidation of fish oil, but the inhibition decreased gradually with the extension of heating time. In the process of inhibiting the oxidation of fish oil, quercetin is converted into quercetin fatty acid esters. Compared with quercetin, the DPPH and ABTS
removal capabilities of their conversion products, as well as the antioxidant effect of fish oil, were significantly reduced. However, in biological systems and cell models, the antioxidant activity of quercetin derivatives is higher than that of quercetin. Therefore, quercetin can be used to inhibit oil oxidation, compared with quercetin, the newly formed quercetin derivatives may have better biological activity in the human body, which needs further study.
study was supported by projects such as the National Natural Science Foundation of China (31901807, 31871901), the Shanghai Sailing Talent Program (19YF1419600), and the Shanghai Young Oriental Scholars.
, Ph.D., Professor of Food and Nutrition, University of Hong Kong. He received his Ph.D. in Food Science from Rutgers University in 2000, joined the University of Hong Kong in 2005 and received a tenured teaching position in 2011. He is also an adjunct professor at Shanghai Ocean University and a visiting professor at Jilin University. Research focuses on the discovery and optimization of functional dietary plant compounds, which in turn enable plant compounds to regulate chemical reactions in food, inhibit the formation of mutagenic and carcinogens, regulate the formation pathways of diabetes and colon cancer, etc., with a view to promoting food safety and human health. In addition, with the support of the Hong Kong Government Innovation and Technology Fund, Dr. Wang's laboratory has successfully developed a number of natural skin care products with independent intellectual property rights, the results of which have been transformed into technology, and the corresponding start-ups have received angel round investment. Dr. Wang has published more than 200 SCI papers in internationally renowned journals (Google Academic Citations: 10573, H-index:58), published 2 monographs in English, participated in the preparation of more than 10 monographs, and applied for/granted more than 10 patents. Currently, Dr. Wang is also the editor/editor of several international journals in the field of food science and technology, including Journal of Functional Foods. He has received a number of research awards, including the Distinguished Young Scholars Award of the University of Hong Kong (2013) and the AGFD Fellow Award (2018) of the American Chemical Society. Dr. Wang has trained more than 20 doctoral students, including a number of national/provincial-level talent program winners in the field of food.
Zhao Moon, male, Ph.D., University of Hong Kong (2017), admitted to the Shanghai Ocean University School of Food in 2018, served as an associate professor, Shuo, in 2019 was selected as the Shanghai "Young Oriental Scholars" and "Flying Talent Program", the research direction involves (1) food thermal processing in the prevention and control of hazards theoretical technology; Dr. Zhao currently presides over 4 projects such as the National Natural Science Foundation of China Youth Project, publishes 18 SCI papers with the first/communication author, and co-authors the English-language book Hand Book of Food Chemistry. Guest editors of SCI Journals Oxidative Medicine and Cellular Longevity (IF:5.076) and Molecules (IF:3.267) and reviewers of more than 10 SCI journals, including Food Chemistry.
about the author
Shaojun, a 2018 master's student at Shanghai Ocean University, studied food safety and nutritional health.