Optimization and characterization of pectin extracted from sour orange peel by ultrasound assisted method Seyed Saeid Hosseini, Faramarz Khodaiyan ⁎, Milad Kazemi, Zahra Najari Bioprocessing and Biodetection Laboratory, Department of Food Science and Engineering, University of Tehran, Karaj 31587-77871, Iran abstract article info Article history: Received 11 September 2018 Received in revised form 1 December 2018 Accepted 9 December 2018 Available online 10 December 2018 In this work, a Box-Behnken design (BBD) with three variables (ultrasound power, irradiation time and pH) in three levels was applied for pectin extraction optimization. The optimization process showed that the maximum extraction yield was 28.07 ± 0.67% in ultrasound power of 150 W, irradiation time of 10 min and pH of 1.5 (as optimum conditions). In these conditions, ash, moisture and protein contents of SOPP were 1.89 ± 0.51, 8.81 ± 0.68 and 1.45 ± 0.23%, respectively. HPLC analysis indicated that 65.3% of the extracted pectin was galacturonic acid and approximately 72% of total neutral sugars was galactose. The optimized pectin had a total phenolic content of 39.95 ± 3.13 mg gallic acid equivalents/g pectin, the surface tension of 46.56 ± 0.23 and 42.14 ± 0.61 mN/m in concentrations of 0.1 and 0.5%w/v, water holding capacity and oil holding capacity of 3.10 ± 0.12 and 1.32 ± 0.21 g water or oil/g pectin with a suitable emulsifying and antioxidant properties. In addition, SOPP with degree of esterification of 6.77 ± 0.43% was classified as low methoxyl pectin, which con- firmed by FTIR and 1 H NMR analysis. © 2018 Elsevier B.V. All rights reserved. Keywords: Pectin Sour orange Ultrasound Optimization Monosaccharide composition 1. Introduction Pectin is a complex heteropolysaccharide including a backbone of α- 1,4-galacturonic acids which are partially esterified at the carboxylic acid groups [1]. Based on the esterified carboxylic acid groups, pectin di- vide to two categories with different applications: high methoxyl pectin (HMP, esterification degree higher than 50%) and low methoxyl pectin (LMP, esterification degree lower than 50%) [2]. The presence of the esterified groups and also neutral sugars, as the side chains, lead to create several parts covalently connected to each other, which homogalacturonan, rhamnogalacturonan I and II, and xylogalacturonan are the most important of them [3]. These polysaccharides, which are extensively distributed in cell wall of the plant tissues, have many appli- cations in food (as gelling agent, emulsifier and stabilizer) and drug (as anti-tumor, antioxidant, anti-diabetic and anti-cancer) industries [4,5]. Traditionally, pectin is obtained from citrus peel by acidified water, which leads to the destruction and the change of its structure and natu- ral properties, respectively. Therefore, the different non-conventional methods such as microwave-assisted extraction, supercritical fluid ex- traction and ultrasound-assisted extraction (UAE) were developed. Among these methods, UAE by the cavitional effect of ultrasound waves improves the destruction of plant cell wall and increases the rate of mass transferring which leads to the higher efficiency and quality of the recoverable pectin with a shorter extraction time. Also, this International Journal of Biological Macromolecules 125 (2019) 621–629 ⁎ Corresponding author. E-mail address: khodaiyan@ut.ac.ir (F. Khodaiyan). method is a green technique due to the lower consumption of solvents and energy. Thus, UAE can be a suitable alternative to conventional ap- proach [6]. Sour orange or bitter orange (Citrus aurantium L.) is a member of cit- rus family, which is used as sedative, hypnotic and appetizer in tradi- tional Iranian medicine. Sour orange peel, as a native product of Iran, is a rich source of pectin, which is unfortunately discarded as waste of fruit juice industry. In previous studies, we extracted sour orange peel pectin (SOPP) by aqueous and microwave-assisted extraction methods [7,8]. These papers focused more on the pectin extraction optimization from this byproduct and therefore, the structural and functional proper- ties of SOPP are still completely unclear. Therefore, the aim of this study is as follows: (1) UAE (as a new method) optimization of SOPP and in- vestigation of the effect of various extraction factors on the yield and properties of SOPP, (2) identification of the structure, monosaccharide and chemical compositions of the extracted pectin and its relationship with extraction method and also, (3) investigation of physicochemical and functional properties of SOPP. 2. Materials and methods 2.1. Raw material and chemicals The fresh sour orange (citrus aurantium L.) peels were obtained from a fruit store in Fasa, Fars, Iran. The peels were washed, finely cut to the small pieces and dried (50 °C) in an oven. The dried peels were blended in a blender and sieved using 40-mesh screen to remove non-powdered https://doi.org/10.1016/j.ijbiomac.2018.12.096 0141-8130/© 2018 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect International Journal of Biological Macromolecules journal homepage: http://www.elsevier.com/locate/ijbiomac