Optimization of pectin extraction from watermelon rind and characterization of the extracted pectin

Watermelon rind, comprising approximately 30% of the fruit weight, is commercially discarded as waste. This study explored the extraction of pectin from watermelon rind using citric acid, examining the effects of acid concentration, pH, and extraction temperature on yield using a Central Composite Design approach. The optimized conditions comprising of 3% citric acid, pH 1.28, 90°C extraction temperature, and a solid-to-extractant ratio of 1:25 for 1 hour, yielded a maximum pectin of 20.09%, closely matching the experimental yield of 19.02%, with an R²; value of 99.8%. Vacuum drying at 40°C and 550 mmhg^-1 was determined to be ideal for drying the precipitated pectin. The extracted pectin exhibited high purity with a moisture content of 7.90%, methoxyl content of 6.86%, anhydrouronic acid content of 71.25%, ash content of 2.05%, and a degree of esterification (DE) of 55.24%, categorizing it as moderately high methoxyl pectin. The pectin could successfully be stored in low-density polyethylene (LDPE) pouches and borosilicate glass containers under ambient and refrigerated conditions for up to six months without significant quality degradation. The process outlined in this study provides a sustainable method for valorizing watermelon rind, demonstrating its potential as a raw material for high-quality pectin production.