Impact of thermal processing on dietary flavonoids.

Flavonoids are a class of polyphenols which are widely distributed in natural products and foods. They have diverse bioactivities, including anti-inflammatory, anti-aging, and antioxidant activities. Generally, the foods rich in flavonoids are usually consumed after thermal processing. However, thermal stability of flavonoids is usually low, and thermal processing could cause either positive or negative influences on their stability and bioactivities. In this review, the effects of thermal processing on thermal stability and bioactivity of dietary flavonoids from different food sources are summarized. Then, strategies to improve thermal stability of dietary flavonoids are discussed and the effect of some promising thermal technologies are also preliminary clarified. The promising thermal technologies may be alternative to conventional thermal processing technologies.

The stability and degradation products of polyhydroxy flavonols in boiling water.

Polyhydroxy flavonols readily degraded during thermal processing. In this study, the UPLC-Q-tof-MS/MS was applied to explore the stability of dietary polyhydroxy flavonols, myricetin, kaempferol, galangin, fisetin, myricitrin, quercitrin and rutin, in boiling water. The decomposition of flavonols was mainly caused by the heterocyclic ring C opening to form simpler aromatic compounds. The degradation products mainly included 1,3,5-benzenetriol, 3,4,5-trihydroxybenzoic acid, 2,4,6-trihydroxybenzoic acid and 2,4,6-trihydroxybenzaldehyde, etc. Compared with myricetin with a pyrogallol-type structure on the ring B, the glycoside in myricitrin slightly affects the stability. However, the glycosides in rutin and quercitrin dramatically improved the stability in water. During the boiling process, flavonols underwent a series of chemical reactions, such as hydroxylation, dehydroxylation, deglycosidation, deprotonation, and C-ring cleavage.

A designed self-microemulsion delivery system for dihydromyricetin and its dietary intervention effect on high-fat-diet fed mice.

The present study aims to design a self-microemulsion delivery system (d-α-tocopheryl polyethylene glycol 1000 succinate - quillaja saponin) to enhance the absorptivity of dihydromyricetin (DMY-S), and to investigate its dietary intervention effect on high-fat-diet (HFD) fed mice. We find DMY-S can inhibit the increase of body weight and fat mass, preventing non-alcoholic fatty liver disease. Compared to the model group, the abundance of mice intestinal flora is mainly changed in certain bacterial genera of Firmicutes and Bacteroides, including norank_f_Muribaculaceae and Blautia. The result of metabolism analysis indicated that the expression levels of cincassiol B, creatine, pantothenic acid and aminobutyric acid in the liver tissues of mice treated with DMY-S showed a down-regulation. The DMY-S prevented hyperlipidemia in HFD mice mainly by affecting different pathways including glycerophospholipid metabolism, sphingolipid metabolism and pantothenate and CoA biosynthesis.

Investigation of new products of quercetin formed in boiling water via UPLC-Q-TOF-MS-MS analysis.

Quercetin is one of most important flavonoids in foods with multi-benefits for human health. The thermal processing is the main food processing approach. Here, the stability of quercetin in boiling water (100 °C) was investigated by UPLC-Q-TOF-MS-MS. With the increasing boiling time, quercetin gradually degraded, and the initial degradation time is 17.57 min and the half-degradation time is 169.72 min. The degradation mechanisms included oxidation, hydroxylation and nucleophilic attack cleavage. Combining the retention time and characteristic fragment ion information of the corresponding standards, the degraded products of quercetin in boiling water were identified as 3,4-dihydroxyphenylglyoxylate, 1,3,5-trihydroxybenzene, 3,4,5-trihydroxybenzoic acid and 2,4,6-trihydroxybenzoic acid. Moreover, 2,3-dihydro-2,3',4',5,7-pentahydroxy-3-oxoflavone, quercetin dimers and quinones were also formed.