Flavonoid Metabolites and Detection Methods

Classification of Flavonoids

Flavonoid active ingredients are one of the important classes of plant secondary metabolites that are widely found in many medicinal plants and also in almost all vegetables and fruits. Flavonoids have outstanding biological activities, such as strong antioxidant, anti-inflammatory, anti-cancer and cardio-protective effects, which have greater benefits for human health. Flavonoids have a phenylpropyl-γ-pyrone parent nucleus. According to the chemical structure, they can be divided into major types such as flavonoids, isoflavonoids, flavonols, flavanones, flavanols and anthocyanins.

Flavonoid Metabolic Pathway

In plants, flavonoid metabolites belong to a relatively important class of plant secondary metabolites. Their synthesis is catalyzed by chalcone synthase with malonyl-CoA and 4-coumaroyl coenzyme A. The basic carbon shelf structure is then provided to trichothecene, anthocyanin 3-O-glucoside, isoquercitrin, kaempferol 3-O-rutinoside, wild lacoside, xanthohumol, etc. Flavonoid metabolites are commonly found in plant diets, especially in the Rosaceae (apple, pear), Rutaceae (orange, grapefruit, tangerine, orange), and Gramineae (wheat, rice, corn, sorghum), etc. They have attracted great attention for their antioxidant and free radical scavenging functions, which are important for human health.

In the organism, the metabolic pathways of flavonoid active ingredients are similar, however, the metabolism of different flavonoid compounds shows some individual variability. This individual variability may affect the biological activity of flavonoid active ingredients by affecting the intestinal flora and thus the biological activity of flavonoids. Flavonoids and flavonoid metabolites may shape the intestinal flora by inhibiting the growth of various pathogens and increasing beneficial bacteria such as bifidobacteria and lactobacilli. At the same time, the intestinal flora maintains intestinal immune homeostasis and improves intestinal health by reducing the production of endotoxins, which in turn promotes the absorption of flavonoid compounds.

Flavonoid Metabolite Detection Method

Extraction methods of flavonoid metabolites

The extraction preparation of flavonoid substances mainly includes solvent extraction, solid phase extraction, supercritical extraction, microwave extraction, enzyme extraction, ultrasonic extraction and other methods. Among them, solvent extraction method is one of the most widely used extraction methods of flavonoids, mainly used for the extraction of soluble flavonoids. Organic solvent extraction method is based on the solubility of flavonoid compounds in different solvents and extract different kinds of flavonoid substances. Commonly used organic solvents are methanol, ethanol, acetone, ethyl acetate, etc. This method can not only improve the extraction rate, but also greatly shorten the reaction time.

Analytical methods of flavonoid metabolites

Flavonoid detection methods mainly include high performance liquid chromatography (HPLC), chromatography-mass spectrometry, chromatography-nuclear magnetic coupling, spectroscopy, thin-layer scanning, capillary electrophoresis and so on. HPLC and liquid chromatography-mass spectrometry (LC-MS) are the most commonly used methods.

The extraction of phytochemicals, screening using chemical reagents, UV–Vis and FTIR analyses, total phenolic and flavonoid and their antioxidant activities (Patle et al., 2020).

Reference

1. Patle, T. K., Shrivas, K., et al. (2020). Phytochemical screening and determination of phenolics and flavonoids in Dillenia pentagyna using UV–vis and FTIR spectroscopy. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 242, 118717.