Preparation of surimi gels from striped mullet (Mugil cephalus) using an optimal level of calcium chloride J.A. Ramı ´ rez a, *, R. Rodrı ´ guez-Sosa a , O.G. Morales b , M. Va´zquez a,c a Department of Food Science and Technology, Unidad Acade ´mica Multidisciplinaria Reynosa Aztla ´n, Universidad Auto ´noma de Tamaulipas, Calle 16 y Lago de Chapala, 88740 Reynosa, Tamaulipas, Mexico b Instituto de Ecologı´a y Alimentos, Universidad Auto ´noma de Tamaulipas, Cd. Victoria, Tamaulipas, Mexico c Departamento de Quı´mica Analı´tica, A ´ rea de Tecnologı´a de los Alimentos, Escuela Polite ´cnica Superior, Universidad de Santiago de Compostela, 27002 Lugo, Spain Received 1 October 2002; received in revised form 2 December 2002; accepted 2 December 2002 Abstract Optimal conditions for the setting phenomenon in surimi, prepared from striped mullet (Mugil cephalus) by adding calcium chloride, were determined. Concentrations of calcium chloride (0–0.4%), temperature (25–45  C), and time (30–90 min) were opti- mised to improve the shear stress and shear strain properties of fish gels. After incubating under selected conditions for setting, all gels were cooked at 90  C for 15 min. Shear stress was mainly affected by the calcium concentration, while shear strain was moderately affected. Maximum shear stress (89.6 kPa) was obtained by employing a concentration of calcium of 0.4%, a tem- perature of 39.3  C and a time of 1 h. Under these conditions, a shear strain of 1.47 was obtained. The results suggest that the mechanical properties of surimi gels can be improved, simply, by adjusting the level of calcium to induce activity of the endogenous transglutaminase. # 2003 Elsevier Science Ltd. All rights reserved. Keywords: Surimi; Calcium; Shear stress; Shear strain; Mugil cephalus; Striped mullet 1. Introduction Mugil cephalus (striped mullet or sea mullet) is an extremely widespread fish species. This species is found in temperate and tropical waters throughout the world. Sea mullet is an object of both commercial fishery and game angling and it is not considered as a threatened or endangered fish species. The mullet caught on ocean beaches are mostly spawning run fish and their catches have increased as a result of a growing market for sea mullet roe, considered as a highly popular delicatessen fish product. Because of this, mullet is successfully cul- tivated in several countries. It is a popular food fish in the southeastern United States and Gulf coast, where they are sought after for both meat and roe. This fish feeds on floor silt and scales, scraping them off various underwater objects with its spade-like lower jaw. They feed by sucking in bottom sediments that contain decaying plant material, algae, and inorganic particles. They may also extract algae and microorganisms from scum that accumulates on the water surface or from the surface of submerged vegetation or other substrates (Collins, 1985; Murdy, Birdsong, & Musick, 1997). The mullet has tasty fat flesh which can absorb odor- ous compounds from its diet. For this reason, in many countries, such as Mexico, it is only caught to export its roe and meat is considered as a by-product. The increasing demand for striped mullet roe requires the development of technologies to process the meat, which has low commercial value. Several works dealing with the feasibility of using the mullet flesh in commercial process or products have been reported. Wootton and Chuah (1981) found that mullet fillets can be used to produce cold marinades of the roll-mop type with attri- butes similar to commercial products obtained from herring. Fish protein isolates and hydrolysates obtained from Mugil cephalus showed high protein level (90%), 0308-8146/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0308-8146(02)00594-0 Food Chemistry 82 (2003) 417–423 www.elsevier.com/locate/foodchem * Corresponding author. Tel.: +52-899-230622; fax: +52-899- 213340. E-mail addresses: vazquezm@lugo.usc.es (M. Va´zquez), ramirez@qui-rey.uat.mx (J.A. Rami ´ rez).