Optimized pressurized hot water extraction, HPLC/LC-MS characterization, and bioactivity of Tetrapleura tetraptera L. dry fruit polyphenols.

Despite the global preference for green extraction methods in the recovery of plant bioactives, Tetrapleura tetraptera fruit polyphenols (TTP) are yet to receive considerable attention. For the first time, pressurized hot water extraction (PHWE) of TTP was optimized for total phenol content (TPC) and antioxidant activity (AA) using the Box Behnken design of response surface methodology. Predictor variables were time, temperature, and liquid-to-solid ratio. An optimum solution with a desirability of 0.805 was selected and parameters were 43 min, 220°C, and 60 ml g -1 liquid-to-solid ratio, yielding TPC of 8.92 mg gallic acid equivalent per gram of sample on dry weight basis (GAE g -1  dw -1 ) and AA of 70.35%. Purified, optimized TTP were characterized and quantified using HPLC/LC-MS. PHWE mainly extracted rutin (379.04 µg g -1 ), cyanidin-3-O-glucoside (chloride) (299.55 µg g -1 ), naringenin 7-O-glucoside (240.11 µg g -1 ), p-coumaric acid (177.28 µg g -1 ), isorientin (150.43 µg g -1 ), and gallic acid (118.06 µg g -1 ) whereas cyanidin-3-O-glucoside (chloride) (83.27 µg g -1 ), protocatechuic acid (61.37 µg g -1 ), rutin (28.03 µg g -1 ), and gallic acid (22.62 µg g -1 ) were mainly extracted by hot water extraction, which was a control. PHWE-obtained TTP showed higher cellular antioxidant activity, cytotoxicity in human liver cancer cell lines (HepG2), and antimicrobial property against Escherichia coli, Staphylococcus aureus, and Bacillus subtilis than control. The potential mechanisms underlying the biological activities of some of the major polyphenols extracted were briefly discussed. Considering the wide use of the T. tetraptera (TT) fruit in Africa in foods and medicine, the use of more efficient green extraction methods such as PHWE is recommended. PRACTICAL APPLICATION: This study serves as a baseline for optimizing pressurized hot water extraction, purification, identification, and quantification of Tetrapleura tetraptera polyphenols (TTP) and their biological activities, being the first of its kind. The varied biological effects shown can be exploited further for applications of TTP as nutraceutical agents and preservatives in foods in different forms. Also, the high amounts of gallic acid and other phenolic acids and flavonoids confirmed in this study make TTP good candidates for the development of metal-phenol network nanoparticles to enhance adequate solubility and distribution in food systems in light of the above proposed applications.