Phytochemical profile and antioxidant potential of coffee leaves influenced by green extraction techniques and in vitro bio-accessibility of its functional compounds

The present study aims to assess the nutritional composition and the impact of diverse green extraction techniques like conventional (CE), microwave-assisted (MAE), ultra-sound assisted (UAE), and brewing (BR) on the phytochemicals, antioxidant activities, and bio-accessibility of functional compounds by in vitro simulated gastrointestinal digestion from Coffea arabica and Coffea robusta leaves. The nutritional composition unveiled that the leaves enclose high fibre (17.3 +/- 2.2%), ash (8.2 +/- 1.4%), calcium (636 +/- 3 mg/100 g), and potassium (152 +/- 0.69 mg/100 g). C. robusta prevailed C. arabica leaves in total phenolics (TP) while the UAE, MAE, and BR (68.05 +/- 1.5, 56.1 +/- 1.2, 55.52 +/- 1.8 mg of CGAE (chlorogenic acid equivalent)/g respectively), recaptured higher TP as compared to the CE (27.26 +/- 1.1 mg of CGAE/g). Chlorogenic acid (8-36 mg/g) followed by quercetin (1-3 mg/g), caffeine (4-12 mg/g), trigonelline (2-8 mg/g) and theophylline (0.05-0.3 mg/g) represent the major phytochemicals. The antioxidant activities (ABTS and FRAP) were in accordance with the total phenolics present in the extracts. Higher bio-accessibility was exhibited for alkaloids (60-70%) than chlorogenic acid (40-50%) while quercetin was the least bio-accessible. Principle component analysis revealed 59.3% and 28.9% of the total variance between extractions, phytochemicals, and antioxidant activities. The utilization of coffee leaves could be a promising raw material for food and pharma sector besides providing sustainability and waste valorisation for the coffee industry. [GRAPHICS] .