Pectin is a family of complex heteropolysaccharides consisting of a backbone of a-(1?4) galacturonic acid residues which are partially esterified with methyl alcohol or acetic acid at the carboxylic acid. Pectin is widely used as a gelling, stabilizing and thickening agent in food systems such as jams and jellies, confectionery, and fruit juice. Citrus peels were usually discarded as by-products of juice and can production, causing severe environmental issues and economic wastes. However, the pectin content of dry citrus peel is as high as 25–30%, making it one of the primary pectin sources for commercial applications. In the commercial extraction process, pectin is conventionally extracted using hot water (60–100 C) under the pH range from
1.5 to 3.0 for hours. The process is time consuming and the yield of pectin is limited. Therefore, many innovative technologies, especially ultrasound, have been combined with heating extraction to improve extraction efficiency and pectin yield. However, the application of ultrasound-assisted heating extraction (UAHE) in pectin extraction is still at the stage
of laboratory research, and only few studies have been carried out in the last few decades, because there exists a big issue that ultrasound could break down polymers including pectin, leading to the modification of structural and physico-chemical properties, which is unfavorable to its gelling properties.