Isolation and characterization of pectin from onion and garlic wastes

In this master thesis, pectin was extracted from large amounts of onion and garlic waste generated in our country using hot acid, microwave, and ultrasonic-assisted extraction methods as extractants, as well as 0.1 N citric (CA), acetic (AA), hydrochloric (HCl), and sulfuric (H2SO4) acid solutions, and dual acid mixtures of these acids (CA-HCl, CA-H2SO4, CA-AA, AA-H2SO4, AA-HCl, and HCl-H2SO4). The yield and physicochemical properties (degree of esterification, methoxyl content, galacturonic acid value, equivalent weight, FTIR spectrum) of the extracted pectins were determined, and the quality and proximity of the extracted pectins to commercial pectin properties were assessed. The optimum extraction conditions were determined for the preliminary studies conducted. For the hot acid extraction method (HAE), the optimum extraction conditions were 90 ℃ extraction temperature, 90 min extraction duration, 1/30 (w/v) solid-liquid ratio, for the microwave-assisted extraction method (MWE), 600 W microwave power, 4 min extraction duration, 1/30 (w/v) solid-liquid ratio, for the ultrasonic-assisted extraction method (UAE), 50% amplitude, 15 min extraction duration, pulse (10 s-5 s on-off), 1/30 (w/v) solid-liquid ratio. From garlic wastes 6.33-22.40% with HAE, 6.70-24.62% with MWE, and 6.35-13.98% with UAE were obtained; from onion wastes, pectin yields ranging from 3.57-16.22% with HAE and 4.52-24.93% with MWE were obtained. The highest pectin yields were obtained using the microwave-assisted extraction method for both raw materials. The use of organic and inorganic acid mixtures as extractant during the extraction process resulted in obtaining pectins with desired physicochemical properties. The extracted pectin samples generally consisted of high methoxyl pectins, and their methoxyl content were observed to be close to those of commercial pectin. The FTIR spectrum results of the extracted samples from onion and garlic waste confirmed the structure of pectin when compared with the FTIR spectrum of commercial pectin.