Extraction of phenolic compounds with antioxidant potential from coconut (Cocos nucifera L.) testa and identification of phenolic acids and flavonoids using UPLC coupled with TQD-MS/MS

Coconut testa, a brown skin covering of a coconut endosperm, is a rich source of phenolics. It is one of the by-products obtained in the coconut processing industries and currently underutilized despite being rich in phenolic compounds. A study was conducted to identify the suitable solvent system for maximum extractability of total phenolic content (TPC) and total flavonoid content (TFC) with antioxidant potential from the testa. Individual phenolic acids and flavonoids of different solvent extracts were also determined using UPLC-H class coupled with TQD-MS/MS. The TPC and TFC ranged from 4.9 to 167 mg GAE/g and 8.84-115 mg QE/g defatted testa, respectively; significant differences were observed for various solvent systems studied. Acidification of solvents significantly increased the extractability of TPC and reduced the extractability of TFC. A total of 28 phenolics comprising 16 phenolic acids and 12 flavonoids were identified. Protocatechuic acid, p-coumaric acid and ferulic acid are the major phenolic acids identified whereas, catechin, apigenin and kaempferol are the major flavonoids identified. In summary, this study proved that coconut testa is a natural source of multiple phenolics acids and flavonoids with potent antioxidant capacity, and it can be used as a natural source of antioxidants.