Extraction of a low methoxylated pectin from coffee (Coffea arabica L.) pulp: Optimization process, chemical...

An optimization process for the acid extraction of pectin was performed using coffee (Coffea arabica L.) pulp as raw material, a major waste stream in coffee-producing regions. A central composite design (CCD) with 3 variables - pH, extraction time (Et) and liquid:solid ratio (LS) was used to assess their effect on the uronic acid (UA) and yield of pectins. The optimal condition was defined as pH = 1.58, Et = 220.9 min and LS = 35.1, with a predicted yield and UA content of 9.8 % and 70.9 %. The pectin obtained in the optimal conditions - Coffea arabica optimized pectin (CAOP), had a yield of 9.0 % and galacturonic acid (GalA) content of 72.6 %. Chemical and structural characterization showed that the pectin was low-methoxylated (LM), with a degree of methyl-esterification (DM) of 31.3 %, without the need of any further chemical treatment, commonly performed in the industrial process. CAOP had a high molar mass (M_w 4.072 × 10⁵ g/mol), low levels of protein, and phenolics. Frequency sweeps of CAOP in the presence of Ca²⁺ confirmed for the first time the gel formation for an LM pectin from coffee pulp.