COMPOSITIONAL CHARACTERIZATION OF GUARANA SEEDS (Paullinia cupana): CARBOHYDRATES, TOTAL METHYLXANTHINES AND PROCYANIDINS QUANTIFICATIONS

Guarana (Paullinia cupana Kunth) seeds have a starch-rich composition, containing 60% starch, 2–6% caffeine, 15% protein, 0.2% lipids, and 14% polyphenols, including 5.7% procyanidins [1]. However, carbohydrate hydrolysis profiles and the distribution of procyanidins between solvent-extractable and insoluble-bound fractions remain poorly understood. This study characterized the guarana seed matrix and quantified carbohydrates, total methylxanthines, and extractable and insoluble-bound procyanidins. Compositional analysis followed an NREL-based two-step acid hydrolysis, with monosaccharides quantified by HPLC [2]. X-ray diffraction (XRD) was performed using Cu Kα radiation over 2θ = 4–45°. Total methylxanthines were determined in powdered guarana seeds according to the Brazilian Pharmacopoeia by acidic extraction and UV spectrophotometry at 272 nm, expressed as caffeine [3]. Procyanidins were quantified using the HCl-butanol-acetone-iron (HBAI) assay with a guarana-derived enriched fraction as analytical standard [4]. For sequential analysis, seeds were extracted with acetone (7:3, v/v) under ultrasound for 45 min, and extract and residual solid were analyzed separately. Seeds contained 26.97 ± 1.90% extractives, 43.47 ± 0.34% cellulose, 6.25 ± 0.06% hemicellulose, 17.61 ± 0.07% apparent acid-insoluble lignin, and 1.85 ± 0.30% total ash, with 96.15% mass recovery. The hydrolysate contained glucose (46.09 ± 0.28%), xylose (2.56 ± 0.09%), galactose (2.14 ± 0.00%), arabinose (1.87 ± 0.10%), and mannose (0.88 ± 0.02%). Together, quantified monosaccharides represented 53.54% of seed mass, with glucose accounting for 86.1% of this fraction, highlighting the predominance of glucose-based carbohydrates. XRD showed peaks at 2θ = 15.16°, 17.20°, 17.99°, 19.83°, and 23.06°, consistent with the crystalline pattern generally associated with A-type starch. Total methylxanthines reached 5.11 ± 0.14% (RSD 2.83%), meeting the pharmacopoeial minimum of 5.0%. Direct HBAI analysis yielded 8.77 ± 0.16% procyanidins, whereas sequential analysis recovered 10.36%, comprising 9.32 ± 0.55% in the solvent extract and 1.04 ± 0.07% in the residual solid, exceeding the 5.7% previously reported [1]. Together, total methylxanthines and extractable procyanidins represented 53.5% of total extractives, indicating that these bioactive classes constitute a major proportion of the extractable fraction. Although oligomeric procyanidins have previously been characterized in guarana extracts [5], our results demonstrate that a measurable fraction remains associated with the residue after extraction. Exhaustive extraction reduced residual procyanidins to 1.19 ± 0.06% after six cycles, while α-amylase treatment decreased the residual content from 1.04% to 0.44%, suggesting that part of this fraction is associated with the starch-rich matrix. Sephadex LH-20 purification and chemical characterization are ongoing to clarify its structural features. Overall, these findings provide a broader view of guarana composition, reveal a procyanidin fraction not fully recovered by a single extraction step, and suggest that starch contributes to its retention, supporting further investigation of insoluble-bound procyanidins and improving understanding of the chemical organization within the seed matrix.

Acknowledgment: FAPESP grants 2026/02454-9 and 2024/14698-4.