This study aims to optimize sequential ultrasound-microwave assisted extraction (UMAE) on pomelo
peel using citric acid. The effects of pH, sonication time, microwave power and irradiation time on the
yield and the degree of esterification (DE) of pectin were investigated. Under optimized conditions of pH
1.80, 27.52 min sonication followed by 6.40 min microwave irradiation at 643.44W, the yield and the DE
value of pectin obtained was respectively at 38.00% and 56.88%. Based upon optimized UMAE condition,
the pectin from microwave-ultrasound assisted extraction (MUAE), ultrasound assisted extraction (UAE)
and microwave assisted extraction (MAE) were studied. The yield of pectin adopting the UMAE was
higher than all other techniques in the order of UMAE > MUAE > MAE > UAE. The pectin’s galacturonic acid
content obtained from combined extraction technique is higher than that obtained from sole extraction
technique and the pectin gel produced from various techniques exhibited a pseudoplastic behaviour.
The morphological structures of pectin extracted from MUAE and MAE closely resemble each other. The
extracted pectin from UMAE with smaller and more regular surface differs greatly from that of UAE. This
has substantiated the highest pectin yield of 36.33% from UMAE and further signified their compatibility
and potentiality in pectin extraction.