Multi-solvent extraction, quantification and characterisation of tannin from Neltuma juliflora bark: a pathway to sustainable utilisation

This research investigates the extraction, quantification and characterisation of tannin from the bark of Neltuma juliflora (Sw.) Raf. (N. juliflora, formerly known as Prosopis juliflora (Sw.) DC.), an invasive species that is widely available but underutilised. Various solvent extraction techniques, including single-phase, combined and sequential extractions, were evaluated. The highest tannin yield (85%) was obtained with 4% NaOH in single-phase extraction, while combined extraction resulted in the highest tannin purity (85.91%). Sequential extraction demonstrated solvent selectivity, with methanol producing the highest extract (93.6%) and acetone yielding a highly purified fraction (83.14%). The presence of essential tannin functional groups was validated by Fourier Transform Infra-red (FTIR) spectroscopy. The analysis of band gap energy indicated values between 4.00 and 5.09 eV, varying with the extraction method. These findings underscore N. juliflora as a promising sustainable tannin source, which offers an eco-friendly alternative to conventional sources and supports invasive species control efforts.