In¯uence of NaCl addition on the properties of emulsions formed with commercial calcium caseinate Aiqian Ye, Magesh Srinivasan 1 , Harjinder Singh* Institute of Food, Nutrition and Human Health, Massey University, Palmerston North, New Zealand Received 17 July 1999; received in revised form 16 September 1999; accepted 16 September 1999 Abstract Oil-in-water emulsions containing 30% soya oil, calcium caseinate and various NaCl concentrations were prepared in a two-stage homogeniser. The average volume-surface diameter (d 32 ) of emulsion droplets decreased with increasing NaCl from 0 to 20 mM, but remained constant beyond 20 mM. The surface protein concentration (mg/m 2 ) decreased with NaCl addition up to 50 mM, but increased with increasing NaCl concentration above 50 mM. a s -(a s1 -+a s2 -)Casein adsorbed at the droplet surface in preference to b-casein in emulsions made both with and without NaCl. In emulsions made with <2% calcium caseinate, the droplet size dis- tributions were broad and bimodal, but they became narrow when 50 or 150 mM NaCl was added prior to emulsion formation. The changes in creaming stability were consistent with the droplet sizes in emulsions. It appears that the aggregated protein in calcium caseinate dispersion was dissociated by NaCl, which consequently improved its emulsifying properties. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Adsorption; Calcium caseinate; Emulsion; NaCl 1. Introduction Large amounts of caseinates, especially sodium case- inate and calcium caseinate, are used as ingredients by the food industry. The properties of caseinates are in¯uenced by the method of manufacture, cation type, and the properties of the food system in which they are incorpo- rated (Morr, 1982). Caseinates provide fat emulsi®cation in coee creamers, whipped toppings, soups and meat emulsions and contribute to viscosity in various food products. Caseinate is a composite of four dierent pro- teins (a s1 -, a s2 -, b-, k-caseins, in weight proportions of approximately 4:1:4:1) which are coprecipitated at pH 4.6. Various caseins show dierent adsorption behaviour at oil±water interfaces because of their dierent chemical or physico-chemical properties. b-Casein adsorbs most rapidly at oil-water interfaces and is most eective in decreasing the interfacial tension (Dickinson, 1989). In oil-in-water emulsions made with sodium caseinate, all of the casein types are rapidly adsorbed at the droplet surface and decrease the interfacial tension (Hunt & Dalgleish, 1994; Robson & Dalgleish, 1987; Srinivasan, Singh & Munro, 1996). This provides stability to the resultant emulsion with respect to coalescence and ¯occulation. Most of the previous reports on the emulsifying properties and adsorption behaviour of caseinates at the oil/water interface have focused on sodium caseinate (Fang & Dalgleish, 1993; Galazka & Dickinson, 1995; Hunt & Dalgleish, 1994, 1996; Robson & Dalgleish, 1987; Srinivasan et al., 1996; Tornberg, 1978). Little information is available on the adsorption behaviour of calcium caseinate in oil-in-water emulsions (Mulvihill & Murphy, 1991). The eects of NaCl on the adsorption behaviour and stability of emulsions formed with cal- cium caseinate have not been reported. Calcium caseinate is a highly aggregated caseinate as indicated by its turbidity and high levels of sedimentable protein (Lee, Anema, Schrader & Buchheim, 1996; Srinivasan, Singh & Munro, 1999). The emulsifying capacity and adsorption behaviour of proteins at the oil/water interface are aected signi®cantly by the state of aggregation of protein (Mulvihill & Murphy, 1991; Oortwijn & Walstra, 1979; Singh, Fox & Cuddigan, 1993). Mulvihill and Murphy reported that the aggre- gated caseins/caseinates were less surface-active than the dispersed caseinates, and that the aggregated caseins/ caseinates have higher surface protein loads in emulsions. 0308-8146/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0308-8146(99)00253-8 Food Chemistry 69 (2000) 237±244 www.elsevier.com/locate/foodchem * Corresponding author. Tel.: +64-6-350-4401; fax: +64-6-350- 5655. 1 Current address: Dairy Product Technology Centre, California Polytechnic State University, San Luis ObisPo, CA 93407, USA. E-mail address: h.singh@massey.ac.nz (H. Singh).