Effect of ionic strength of different salts on the binding of volatile compounds to porcine soluble protein extracts in model systems Marı ´a Pe ´rez-Juan, Mo ´ nica Flores * , Fidel Toldra ´ Instituto de Agroquı ´mica y Tecnologı ´a de Alimentos (CSIC), P.O. Box 73, 46100 Burjassot, Valencia, Spain Received 10 July 2006; accepted 25 November 2006 Abstract The effect of different salts on the binding ability of porcine soluble protein extracts was studied using solid-phase microextraction (SPME) and GC/MS analysis. Previously, the effect of the different salts (NaCl, KCl, MgCl 2 and CaCl 2 ) on the volatile compound head- space concentration in water solution was determined. KCl produced a similar salting out effect as NaCl increasing the volatile com- pound headspace concentration up to 5–10 times. However, MgCl 2 and CaCl 2 did not produce a salting out effect on the volatile compounds studied. Finally, NaCl and KCl produced a significant reduction on the binding ability of sarcoplasmic protein extracts to branched aldehydes, hexanal and methional while no effect was produced on octanal and 2-pentanone. On the other hand, the effect of MgCl 2 and CaCl 2 was much lower even at high ionic strength, except for the branched aldehydes where the presence of MgCl 2 at 1.0 ionic strength produced the complete liberation of the volatile compound bound. Consequently, the partial NaCl substitution in meat products by other salts must be considered not only due to their salting out effect but also due to their effect on protein binding ability. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Aroma; Dry-cured products; Curing agents; Salt; Meat protein; Headspace; SPME 1. Introduction Sodium chloride is an essential ingredient in dry-cured products which has three major functions: it acts as a pre- servative, contributes directly to flavour and is a source of dietary sodium (Ruusunen & Puolanne, 2005). Firstly, salt is essential in the elaboration of dry-cured meat products due to the reduction of a w and its contribution to texture and flavour development. During the ripening stage of the dry-curing process many biochemical reactions, prote- olysis and lipolysis, take place and produce the precursors of flavour compounds (Toldra ´ & Flores, 1998). Moreover, salt and other ingredients used during the dry-curing pro- cess affect the product quality due to their own effect on taste (Pearson & Tauber, 1984) and to the control of the muscle enzyme system (Toldra ´ & Flores, 1998). In this sense, several authors have studied the effect of salt on the proteolysis (Flores, Aristoy, & Toldra ´, 1997a; Rosell & Toldra ´, 1996) and lipolysis (Andre ´s, Ventanas, Ventanas, Cava, & Ruiz, 2005; Coutron-Gambotti, Gandemer, Rousset, Maestrini, & Casabianca, 1999; Motilva & Toldra ´, 1993; Zanardi, Ghidini, Battaglia, & Chizzolini, 2004) occurred during the dry-curing process by inhibiting many of the proteolytic and lipolytic enzymes. On the other hand, sodium chloride mainly provided by processed foods (Ruusunen & Puolanne, 2005) is the main source of sodium in diet which is important for regulation of blood pressure, water transport into and out of cells, tis- sue osmolality, and transmission of nerve cell impulses (Guinee, 2004). However, sodium intake exceeds the nutri- tional recommendations (5–6 g/day) in many industrialized countries (Ruusunen & Puolanne, 2005). Moreover, this excessive intake have undesirable physiological effects like an increased calcium excretion, which may lead to osteopo- rosis and hypertension linked to risk of stroke and car- diovascular diseases (Guinee, 2004; Muguerza, Gimeno, 0963-9969/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2006.11.013 * Corresponding author. Tel.: +34 96 3900022; fax: +34 96 3636301. E-mail address: mflores@iata.csic.es (M. Flores). www.elsevier.com/locate/foodres Food Research International 40 (2007) 687–693