**4. Analysis**

Phenolic compounds can be analyzed using various techniques. Mass spectrometry (MS), high performance liquid chromatography (HPLC), gas chromatography (GC), GC–MS, calorimetry, ultraviolet (UV), ultraviolet–visible (UV/VIS) spectrophotometry, and other spectrophotometric techniques represent examples of such techniques [15–18]. Total phenolic content (TPC) of phenolic compounds in plants is commonly measured using spectrophotometry techniques such as Folin-Denis and Folin–Ciocalteu methods [19]. The latter method which is based on electron-transfer, was found to be more preferable and thus more common [15, 16]. GC has been used to analyze phenolic acids, condensed tannins, flavones, and falvonoids. HPLC has been used to analyze anthocyanins, hydrolysable tannins, phenolic acids, cinnamic acids and favonoids [18]. Anthocyanins have been analyzed using UV absorption at a wavelength range of 489–550 nm [18]. Hydrolysable tannins have been also analyzed at a wavelength of 500–550 nm [18]. Based on their ability to bind proteins, tannins have been analyzed using protein-binding methods [20, 21]. Calrimetric methods have been used to determine the TPC in flavonoids and tannins. Other techniques for analysis of phenolic compounds include capillary electrophoresis (CE) and micellar electro-kinetic chromatography [22].

Recent methods of analysis include ultra-high performance liquid chromatography (UHPLC) [23], ultra-high performance liquid chromatography-quadrupole-orbitrap (UHPLC-Q-Orbitrap) [24], high performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) [25], liquid chromatography coupled with electrospray- ionization triple quadrupole time- of- flight mass spectrometry (LC- ESI- QTOF- MS) and high- performance liquid chromatography- photo diode array (HPLC- PDA) [26], ESI-Ms/MS [27].
