RESEARCH ARTICLE Physicochemical, rheological, and molecular characterization of colloidal gelatin produced from Common carp by-products using microwave and ultrasound-assisted extraction Armin Mirzapour-Kouhdasht 1,2 | Forouzan Sabzipour 3 | Mohammad Sadegh Taghizadeh 4 | Marzieh Moosavi-Nasab 1,2 1 Department of Food Science and Technology, School of Agriculture, Shiraz University, Shiraz, Iran 2 Seafood Processing Research Group, School of Agriculture, Shiraz University, Shiraz, Iran 3 MSC of Fish Products Processing, School of Agriculture, Shiraz University, Shiraz, Iran 4 Institute of Biotechnology, School of Agriculture, Shiraz University, Shiraz, Iran Correspondence Armin Mirzapour-Kouhdasht, Department of Food Science and Technology, School of Agriculture, Shiraz University, Shiraz, Iran. Email: armin.mirzapour@shirazu.ac.ir Abstract The effects of ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) methods on molecular and physicochemical characteristics of the resultant gelatin were examined. Before extraction procedure, we investigated the optimum pH for swell- ing of Common carp by-products, which is an important pretreatment for gelatin produc- tion. The highest swelling yield was achieved at pH 13 among pH 1–14 with unit intervals. Results indicated that the UAE gelatin has a higher gel strength, viscosity, melt- ing point, and gelling point. The power and time of sonication showed a reverse relation with these characteristics. In addition, as the time of microwave heating was raised, the gel strength, viscosity, melting point, and gelling point were decreased. The FT-IR spectra showed similar peaks but the Amide B in UAE gelatin slightly vanished. The electropho- retic pattern also revealed the higher gel strength and viscosity of UAE gelatin due to the higher intensity of α and β chains compared to MAE gelatin. It can be concluded from all of the results of this study that the produced gelatin using these procedures can be a good source of gelatin in food and drug industries. KEYWORDS fish by-products, gelatin, microwave- and ultrasound-assisted extraction, molecular characterization 1 | INTRODUCTION Collagen is a fibrous protein, which is found mainly in the skin, tendon, and cartilage. This protein can be extracted using appropriate heat treat- ments. All 28 types of collagen which have been identified and described are composed of three polypeptides, called α-chains (Karim & Bhat, 2009), that is formed as a right-handed triple helix, stabilized by the hydrogen bonds (Kinsman, Kotula, & Breidenstein, 1994). Gelatin is obtained from collagen, the most important protein component of the skin, bones, and connective tissue of animals, treatment by acid, alkaline, or collagenolytic enzymes (Ahmad & Benjakul, 2011; Arnesen & Gildberg, 2006; Jang, Lim, & Kim, 2002). It has been extensively utilized in the food and pharmaceutical industries due to its superb functional properties. Recently, the annual growth rate of gelatin production has been reported to be significant (Gómez-Guillén et al., 2009). The ultrasound-assisted extraction (UAE) method is an efficient technique of extraction in the food and pharmaceutical industry (Li, Pordesimo, & Weiss, 2004; Nascentes, Korn, & Arruda, 2001; Rodrigues & Pinto, 2007; Rostagno, Palma, & Barroso, 2003; Zhang et al., 2008; Zhu, Sun, & Zhou, 2009). Ultrasound waves can enhance the extraction yield due to the disruption of the cell walls leading enhancement of mass transfer of the cell content (Zhang et al., 2008). Microwave-assisted extraction (MAE) technique has been suggested as one of the most efficient methods to improve the molecular and phys- icochemical characteristics, including gel strength, viscosity, melting This article was published on AA publication on: 13 May 2019 Received: 7 March 2019 Revised and accepted: 6 May 2019 DOI: 10.1111/jtxs.12408 J Texture Stud. 2019;1–10. wileyonlinelibrary.com/journal/jtxs © 2019 Wiley Periodicals, Inc. 1