Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem Enhancing tilapia fsh myosin solubility using proline in low ionic strength solution Yige Zhou a,b , Hongshun Yang a,b,⁎ a Department of Food Science & Technology, National University of Singapore, Singapore 117542, Singapore b National University of Singapore (Suzhou) Research Institute, 377 Lin Quan Street, Suzhou Industrial Park, Suzhou, Jiangsu 215123, PR China ARTICLEINFO Keywords: Myosin Solubilisation Amino acid Aggregation Protein Secondary structure Aquatic food Molecular interaction ABSTRACT The efects of using proline to solubilise fsh myosin under low ionic strength conditions were studied. After solubilising myosin in 0.1 M NaCl containing 5, 10, 15, and 20 mM proline, respectively, it was observed that more than 80% of the myosin was efectively solubilised using 10 mM proline. The addition of 10 mM proline lowered the surface hydrophobicity of myosin from 18.25 to 8.22 mg/g, increased the amount of β-sheet structure from 33.87% to 46.88%, both of which facilitated solubilisation. As revealed by transfer free energy measurements, the interactions between proline and tyrosine and tryptophan residues were more favourable. Furthermore, the ability of proline to shield hydrophobic sites of myosin and to partially break disulphide bonds helped to form myosin oligomer aggregates. Transmission electron microscopy images verifed the efects of proline on myosin proteins. A solubilisation mechanism based mainly on chemical interactions between myosin and proline was proposed. 1. Introduction Fish is a popular food worldwide, not only because of its low lipid content and delicious taste, but also the high digestibility of fsh protein provides humans with premium protein. In addition to fresh fsh fllets, processed fsh meat has become more prevalent; for example, fsh balls, fsh cakes, and fsh sticks are major fshery products. To assure good product texture, fsh proteins are the main concern. Myosin is the major muscle protein in fsh, and NaCl at a concentration of 2–3% (0.47–0.68 M) is required to facilitate adequate myosin solubilisation (Hayakawa et al., 2012): better solubilisation leads to a better fnal product (Chen, Zou et al., 2016). However, the excessive intake of salt canresultinnumeroushealthproblems,thusthereisanemergingtrend to seek ways to improve myosin solubilisation under low salt condi- tions. What’s more, for the sake of people with mastication and swal- lowing difculties, which is usually the elderlies and infants, it would be of great help for them if meat with fbrous hard texture can be readily solubilised in low salt condition and has very soft and tender texture (Nieuwenhuizen, Weenen, Rigby, & Hetherington, 2010; Tokifuji, Matsushima, Hachisuka, & Yoshioka, 2013). Methods including high pressure processing (Chen, Xu et al., 2016), thepHshiftmethod(Park,Yongsawatdigul,Choi,&Park,2008;Zhou& Yang, 2019), substituents of Na + (Tahergorabi & Jaczynski, 2012), and the addition of small amounts of amino acids (Arakawa et al., 2007; Chen, Zou et al., 2016; Hayakawa, Ito, Wakamatsu, Nishimura, & Hattori, 2010) have been developed and confrmed to efectively in- crease the solubility of myosin. The utilisation of amino acids, as universally popular and generally safefoodadditives,couldbeexpanded. Chen,Zouetal.(2016) reported that the imidazole moiety in histidine could impede the assembly process of flaments and increase the solubility myosin. In addition, transmission electron microscopy (TEM) revealed that histidine could elongate light meromyosin, which inhibited flaments formation (Hayakawa et al., 2010). Furthermore, the interaction with hydro- phobic amino acid residues also played an important role (Li, Zheng, Xu,Zhu,&Zhou,2018). Takai, Yoshizawa, Ejima, Arakawa, and Shiraki (2013) reported that L-lysine induced no structural changes in porcine myosin; however, the activation energy of the self-association of monomeric myosin increased. Myosin is a pH sensitive protein (Liu et al., 2010); therefore, Zhou, Li, and Tan (2014) proposed that the pH changes caused by lysine and arginine were related to the increased solubility of myosin. However, according to Schifman and Dackis (1975), although the above studied amino acids showed excellent ability in solubilising myosin, histidine was “defnitely not foodlike”; arginine had a repulsive and complex taste, and even made people feel like they were being poisoned; and people described lysine to be both salty and bitter. These taste attributes could be detrimental in food processing, even though they were proved to efciently increase https://doi.org/10.1016/j.foodchem.2020.126665 Received 25 October 2019; Received in revised form 19 March 2020; Accepted 20 March 2020 ⁎ Corresponding author at: Department of Food Science & Technology, National University of Singapore, Science Drive 2, Singapore 117542, Singapore. E-mail address: fstynghs@nus.edu.sg (H. Yang). Food Chemistry 320 (2020) 126665 Available online 21 March 2020 0308-8146/ © 2020 Elsevier Ltd. All rights reserved. T