Acid and Deep Eutectic Solvent (DES) extraction of pectin from pomelo (Citrus grandis (L.) Osbeck) peels

Pectin was extracted from pomelo peel using citric acid. A Box-Behnken design was employed to optimize the yield and the Degree of Esterification (DE) of pectin. The effects of pH, temperature, extraction time and liquid-solid ratio on the yield were investigated. It was found that under optimized conditions at pH 1.80, extraction time of 141 min, temperature of 88 °C and a liquid-solid ratio of 29:1 mL/g, a pectin yield of 39.72% and a DE value of 57.56% were obtained. The results indicate that the pectin extracted from pomelo peel is a slow set high methoxyl type of pectin. pH was found to have the greatest influence on pectin yield and DE. Varying pH at a narrow range between 1 and 2 interestingly showed the formation of diverse pectin functional groups with different structural modifications. The findings suggest that extraction conditions could influence pectin extraction performance, chemical structure, as well as morphological and gelling properties. This study also explored various acid based Deep Eutectic Solvents (DESs) in pectin extraction. The lactic acid-glucose-water DES with a ratio of 6:1:6 gave the highest pectin yield of 23.04%. Citric acid was found to have a better yield performance and more energy saving as compared to DES in pectin extraction.