Polyphenol Compounds and Biological Activity of Caper (Capparis spinosa L.) Flowers Buds

The aim of the study was to analyze potential health-promoting components of caper flower buds (Capparis spinosa L.) at six stages of development in two cultivars. Polyphenol compounds (flavonols, hydroxycinnamic acids, flavan-3-ols) were identified by Liquid Chromatography– quadrupole Time–of–Flight –Mass Spectrofotometer/Mass Spectrofotometer (LC-qTOF-MS/MS) and quantified by Ultra Performance Liquid Chromatography–Photodiode Array-Fluorescence Detector (UPLC-PDA-FL). Moreover, antioxidant properties (ABTS+•, FRAP, and ORAC), anti-diabetic potential (α-amylase and α-glucosidase), and anti-aging activity (acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE)) of the buds were examined. Total phenolic compounds in the investigated caper varied from 10,720 to 3256 mg/100 g dry weight (DW), and depended on a genotype and growing stage of caper flowers. Among six different growing stages, the one named ‘nonpareilles’ was characterized by significantly higher content of polyphenols than the remaining five stages. The flavonols in caper flowers represented a mixture of different glycosylated quercetin, kaempferol, myricetin, and isorhamnetin derivatives, accounting for 38%–67%, 15%–36%, 4%–7%, and 0.8%–3%, respectively, of total flavonols,. Their contents strongly depended on the growth stage. ‘Nonpareilles’ and ‘surfines’ were richer in flavonols than ‘fines’ and ‘gruesas’. Of the six investigated growth stages, ‘nonpareilles’ accumulated the greatest amounts of bioactive compounds that correlated with antioxidant and anti-diabetic properties, and were more potent BuChE than AChE inhibitors.