Negative effect of combining microbial transglutaminase with low methoxyl pectins on the mechanical properties and colour attributes of fish gels R.M. Uresti a, ,J.A.Ramı ´ rez a, *,N.Lo´pez-Arias a ,M.Va´zquez b 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, Col. Aztla ´n. Reynosa, Tamaulipas 88740, Mexico b A ´ rea de Tecnologı´a de los Alimentos, Departamento de Quı´mica Analı´tica, Escuela Polite ´cnica Superior, Universidad de Santiago de Compostela (Campus Lugo), 27002 Lugo, Spain Received 22 March 2002; received in revised form 2 July 2002; accepted 2 July 2002 Abstract The objective of this work was to determine the effect of combining different concentrations of microbial transglutaminase (MTGase) and types of low methoxyl (LM) pectin on the mechanical properties (textural profile analysis, puncture test) and the colour attributes of fish restructured products. A disruptive effect was observed when LM pectin and MTGase were added to fish gels.Adding1%MTGasewithLM32pectinsignificantlydecreasedthehardness(3.85kg),springiness(0.631)andchewiness(0.434 kg). When LM32 pectin and 0.1% MTGase were added together, significant decreases of the three puncture test parameters were observed.Thechromaoffishgelsdecreasedsignificantlywhen0.3%MTGasewasadded.FishgelscontainingtheLM35pectinhad higherchromavaluesthanallotherfishgelswiththesamelevelofMTGase.Huevaluewasincreasedinallfishgelsafterincreasing the MTGase level. The results obtained showed that LM pectin is not suitable for use in products containing MTGase. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Surimi; Transglutaminase; Pectin; Fish 1. Introduction The shrimp by-catch is an abundant resource that is widelymisusedinmanycountries.Manyfisharecaught during the catching of shrimp. In the Gulf of Mexico, 75,000 tons of shrimp are caught annually by Mexican fishing boats. An average of 83% in volume of shrimp catching is by-catch. Thus at least 355,000 tons of by- catch are being wasted. It is estimated that 80% of this resource is fish (Southeastern Fisheries Association, 2001).Severalfactorsinfluencethewastingofthisnatural resource: small size, diversity of species, presence of non-commercial or non-edible species, and the absence of processing alternatives. Mexicanflounder(Cyclopsetta chittendenni),Northern kingfish (Menticirrhus saxatilis), Atlantic croaker (Micropogon undulatus), and Barred grunt (Conodon nobilis) are some of the most abundant fish species caught as shrimp by-catch in the Tamaulipas coast, Mexico. The biochemical and mechanical properties of such species have been previously reported (Morales, Ramı´rez, Vivanco, & Va´zquez, 2000; Ramos-Martı´nez, Morales-Gonza´lez, Ramı´rez, Garcı´a-Carren˜o, & Mon- tejano-Gaita´n,1999).Mostofthemshowtoopoorgelling properties for processing as surimi products. Therefore, analternativeprocessingtechniquecouldberestructuring fish products using microbial transglutaminase (Ramı´rez, Uresti, Te´llez, & Va´zquez, 2002; Te´llez-Luis, Uresti, Ramı´rez, & Va´zquez, 2002). The biochemistry of fish muscle is distinct from that of mammals and birds, and so fish products must be processedinadifferentwayfromredmeatandpoultry. Particular phenomena in fish products are Modori and Suwari (setting). Modori is a deteriorative phenomenon that takes place at temperatures near 60  C.Ithasbeen associated with the presence and activity of endogenous serine and cysteine muscle proteases (An, Peters, & Seymour, 1996; Ramı´rez, Garcı´a-Carren˜o, Morales, & 0308-8146/03/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0308-8146(02)00343-6 Food Chemistry 80 (2003) 551–556 www.elsevier.com/locate/foodchem * Corresponding author. E-mail address: ramirez@qui-rey.uat.mx (J.A. Ramirez).