Phytochemical Profile and Antioxidant Capacity of Coffee Plant Organs Compared to Green and Roasted Coffee Beans

Abstract

The current study investigates the phytochemical composition of coffee plant organs and their corresponding antioxidant capacities compared to green and roasted coffee beans. HPLC analysis indicated that the investigated compounds were present in all organs except mangiferin, which was absent in roots, stems and seeds, and caffeine, which was absent in stems and roots. Total phytochemicals were highest in the green beans (GB) at 9.70 mg g−1 dry weight (DW), while roasting caused a 66% decline in the roasted beans (RB). This decline resulted more from 5–CQA and sucrose decomposition by 68% and 97%, respectively, while caffeine and trigonelline were not significantly thermally affected. Roasting increased the total phenolic content (TPC) by 20.8% which was associated with an increase of 68.8%, 47.5% and 13.4% in the antioxidant capacity (TEAC) determined by 2,2–diphenyl–1–picryl hydrazyl radical (DPPH), 2,2–azino bis (3–ethyl benzothiazoline–6–sulphonic acid) radical (ABTS) and Ferric ion reducing antioxidant power (FRAP) assays, respectively. Amongst the leaves, the youngest (L1) contained the highest content at 8.23 mg g−1 DW, which gradually reduced with leaf age to 5.57 mg g−1 DW in the oldest (L6). Leaves also contained the highest TPC (over 60 mg g−1 GAE) and exhibited high TEAC, the latter being highest in L1 at 328.0, 345.7 and 1097.4, and least in L6 at 304.6, 294.5 and 755.1 µmol Trolox g−1 sample for the respective assays. Phytochemical accumulation, TPC and TEAC were least in woody stem (WS) at 1.42 mg g−1 DW; 8.7 mg g−1 GAE; 21.9, 24.9 and 110.0 µmol Trolox g−1 sample; while herbaceous stem (HS) contained up to 4.37 mg g−1 DW; 27.8 mg g−1 GAE; 110.9, 124.8 and 469.7 µmol Trolox g−1 sample, respectively. Roots contained up to 1.85 mg g−1 DW, 15.8 mg−1 GAE and TEAC of 36.8, 41.5 and 156.7 µmol Trolox g−1 sample. Amongst the organs, therefore, coffee leaves possessed higher values than roasted beans on the basis of phytochemicals, TPC and TEAC. Leaves also contain carotenoids and chlorophylls pigments with potent health benefits. With appropriate processing methods, a beverage prepared from leaves (coffee leaf tea) could be a rich source of phytochemicals and antioxidants with therapeutic and pharmacological values for human health.

Exogenous Kinetin Promotes the Nonenzymatic Antioxidant System and Photosynthetic Activity of Coffee (Coffea arabica L.) Plants Under Cold Stress Conditions

“…This increase was more ostensibly indicated by the FRAP assay, whereas DPPH and ABTS, despite showing increment tendencies with kinetin treatment, were not affected significantly amongst the treatments. Although the assays employ different principles in the determination of radical scavenging values, they normally report consistent values [22,23,66], as was observed in the current study.…”

“…HPLC quantification of the selected antioxidant compounds was done according to Acidri et al [22]. Two (2) alkaloids (caffeine and trigonelline) and two phenolic compounds (5-caffeoylquinic acid and mangiferin) were extracted and thereafter analyzed simultaneously from the freeze-dried powder samples in 50 mL Falcon tubes, using 80% methanol.…”

“…Sample extraction and TPC determination was done as described by Acidri et al [22]. 50 mg of freeze-dried leaf samples were infused in 25 mL boiling water in 50 mL falcon tubes for 8 minutes, and thereafter cooled under room temperature.…”

“…Total radical scavenging capacities of the coffee leaves was assayed as described by Acidri et al [22] using 5 mg of the freeze-dried, powdered sample obtained from the previous subsection. The samples were dissolved in 8 mL of ultrapure water and followed thereafter by methanol (100%) in 25 mL flasks.…”

“…The accumulation of these compounds, in particular polyphenols, is associated with increased ROS scavenging capacity, which is normally assessed as vitamin E equivalent and expressed as trolox (tocopherol analogue) equivalent antioxidant capacity [22,23].…”