Reta Reta 1,*, Andi Lutfiah Husna2, Zaimar Zaimar 1, Muhammad Fitri 1 and Sri Udayana Tartar 1
1Agroindustry Study Program, Department of Agricultural Technology, Pangkep State Polytechnic of Agriculture, Pangkajene Kepulauan, South Sulawesi, Indonesia; 2Undergraduate student of Agroindustry Study Program, Department of Agricultural Technology, Pangkep State Polytechnic of Agriculture, Pangkajene Kepulauan, South Sulawesi, Indonesia
*Corresponding author: retariskinapolitani@gmail.com
Liberica coffee husk is an underutilized agro-industrial by-product with potential as a source of pectic material. This study investigated how ammonium oxalate concentration and extraction temperature affect gravimetric recovery and the physicochemical properties of pectic material extracted from Liberica coffee husk. A two-factor rotatable circumscribed central composite design (CCD) was employed within the framework of response surface methodology (RSM). We evaluated gravimetric recovery, moisture content, ash content, galacturonic acid (GalA) content, and instrumental total color difference (ΔEab) and subjected them to multi-response optimization using a desirability function. Gravimetric recovery ranged from 10.0 to 37.3%, while GalA content ranged from 52.31 to 79.32%, indicating differences in pectic enrichment rather than directly establishing product purity. Ammonium oxalate concentration was the most influential factor affecting both responses. Multi-response optimization identified 3% (w/v) ammonium oxalate at 80°C as the model-predicted preferred extraction condition, with a composite desirability of 0.858. Under these conditions, the models predicted a gravimetric recovery of 33.16%, moisture content of 13.20%, ash content of 1.44%, GalA content of 75.70%, and ΔEab of 19.64. The corresponding experimental run included in the original CCD yielded a gravimetric recovery of 37.30%, moisture content of 13.90%, ash content of 1.57%, GalA content of 78.45%, and ΔE*ab of 20.36. However, because this run was used to develop the predictive models, it cannot be considered an independent validation experiment. Therefore, the selected extraction condition should be regarded as a model-predicted preferred condition rather than an experimentally validated optimum. These findings demonstrate the potential of Liberica coffee husk as a source of pectic material and provide a basis for further process development. Independent experimental validation, along with structural characterization, functional evaluation, safety assessment, and scale-up studies, is needed to establish the recovered material's suitability for practical applications.