Succinylation of sodium caseinate and its effect on physicochemical and functional properties of protein B.G. Shilpashree, Sumit Arora * , Prince Chawla, Ravikumar Vakkalagadda, Apurva Sharma Dairy Chemistry Division, National Dairy Research Institute, Karnal, Haryana, 132001, India article info Article history: Received 13 April 2015 Received in revised form 2 July 2015 Accepted 7 July 2015 Available online 17 July 2015 Keywords: Sodium caseinate Succinylation Functional properties Microstructure Hydrophobicity abstract Succinylation is one of the most widely studied modification processes and well known to alter func- tionality of food proteins. Sodium caseinate (NaCas) is widely applicable protein ingredient among different varieties of caseinates. But hardly we find reports on effect of succinylation on physicochemical and functional properties of NaCas. Therefore, the present work was attempted to investigate the effect of succinylation on the functionality of NaCas. Ninhydrin method was adopted for the quantification of succinylation. Highest degree of succinylation was achieved at the level of 4 mol of succinic anhydride/ mol of lysine in NaCas. Findings from surface hydrophobicity stated that NaCas undergoes structural modification upon succinylation. Further, the effects of succinylation on different functional properties of NaCas were evaluated. The solubility of NaCas improved significantly (P < 0.05) up on succinylation at higher pH values (6). Other properties like water- and oil-binding capacity, viscosity and emulsifying properties of native NaCas increased significantly (P < 0.05) with no change in foam capacity and sig- nificant reduction in foam stability than native NaCas. Succinylation led to structural modification of protein and improved some functional properties of NaCas. The modified form of NaCas could be incorporated in food systems where fat management plays a critical role. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Succinylation is one of the frequently used modification method, which enhances solubility, emulsification, foaming char- acteristics and other functional properties of protein (Gruener & Ismond, 1997; Kohara, Kanei, & Nakajima, 2001; Mirmoghtadaie, Kadivar, & Shahedi, 2009; Yang, Zhang, Wen, Zhang, & Liang, 2014). Succinylation involves chemical derivatization of 3 -amino group of lysine in proteins with succinic anhydride. Application of succinylation to probe the structure of food proteins as well as to improve their functional properties has become an area of expanding interest of protein chemists. Modification in physico- chemical and functional properties of succinylated proteins de- pends mainly upon degree of modification (Schwenke, 1997). The native conformation of protein also drastically affected by the introduction of excess negative charge on proteins (Howell, 1996). Many workers also reported that succinylation of proteins posi- tively enhances some functional properties especially the protein solubility of wide range of proteins such as rape seed protein, flax protein isolate, oat protein isolate and soy protein isolate (Dua, Mahajan, & Mahajan, 1996; Franzen & Kinsella, 1976; Mirmoghatadaie et al., 2009; Wanasundara & Shahidi, 1997). On the other hand, succinylation also showed to enhance the foam capacity of a variety of proteins (Dua et al., 1996; Franzen & Kinsella, 1976; Mirmoghatadaie et al., 2009) but reduced foam expansion capacity or stability (Wanasundara & Shahidi, 1997). It was also reported that the techniques such as intrinsic tryptophan fluores- cence and circular dichroism showed changes in the secondary and tertiary structures of soy protein hydrolysate upon succinylation (Achouri & Zhang, 2001). Milk proteins especially casein can able to possess better functional properties particularly surface properties (De Jongh & Broersen, 2012) and suitable for many food applica- tions. Generally, casein is not consumed as food on its own, but casein in the form of caseinates could be incorporated into food products to improve nutritional and functional properties (Crowley et al., 2002). Among different varieties of caseinates sodium caseinate (a soluble form of casein) has been widely applied in food system especially due its improved emulsifying capacity (Modler, * Corresponding author. E-mail addresses: shilpashreebg14@gmail.com (B.G. Shilpashree), sumitak123@ gmail.com (S. Arora), princefoodtech@gmail.com (P. Chawla), ravikumar. vakkalagadda@gmail.com (R. Vakkalagadda), apu.sharma2312@gmail.com (A. Sharma). Contents lists available at ScienceDirect LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt http://dx.doi.org/10.1016/j.lwt.2015.07.008 0023-6438/© 2015 Elsevier Ltd. All rights reserved. LWT - Food Science and Technology 64 (2015) 1270e1277