58. Food Hydrocolloids as Additives to Improve the Mechanical and Functional Properties of Fish Products - A Review

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Food hydrocolloids as additives to improve the mechanical and functionalproperties of fish products: A review

José A. Ramírez a, Rocio M. Uresti a, Gonzalo Velazquez a,b, Manuel Vázquez c,*

aDepartamento de Tecnología de Alimentos, Cuerpo Académico de Alimentos, UAM, Reynosa-Aztlán, Universidad Autónoma de Tamaulipas, Apdo. Postal 1015, Reynosa,Tamaulipas 88700, MexicobCICATA Querétaro, Cerro Blanco No. 141, Col. Colinas del Cimatario, Querétaro 76090, MexicocDepartment of Analytical Chemistry, Faculty of Veterinary Science, University of Santiago de Compostela, Campus Lugo, 27002 Lugo, Spain

a r t i c l e i n f o

Article history:Received 27 October 2010Accepted 24 May 2011

Keywords:SurimiRestructured productsStarchLow saltCaseinateTransglutaminaseHydrocolloidsAdditives

a b s t r a c t

The restructuring process offers to fish processors the opportunity to obtain new products, takingadvantage of both low-value fish species and remains from filleting and other processing operations.However, mechanical and functional properties of restructured products depend on the biochemical andphysicochemical properties of muscle proteins, mainly myosin and actomyosin. In this regard, thebiochemistry of fish muscle is different from that of mammals and birds. Therefore, fish products must beprocessed in a different way from red meat or poultry. The main fish products are surimi and restruc-tured products. Fish products can be improved or modified by using hydrocolloids (carbohydrates andprotein) as additives. In this review, the modern technology to obtain these products, the applications ofhydrocolloids in fish products, and the implications of the increasing demand for healthy, low-salt fishproducts are discussed.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

The increasing demand for fish and fish products by consumersis affecting the fishery resources worldwide, drastically reducingthe stocks of many fish species such as flounder, cod, hake, andother fishes. At the same time, there are several underutilised fishspecies due to their size, flavour, odour, colour, or texture. Inaddition, some filleting by-products could be transformed intohigh-value products through restructuring technology. Both low-value species and filleting remains could be transformed intohigh-value products by surimi technology and restructuring tech-nology. These technologies are used to obtain novel products usingan array of additives to improve the mechanical and functionalproperties. However, several biochemical and physicochemicalconsiderations regarding muscle proteins must be taken intoaccount to obtain high-quality products.

The restructuring process allows the acquisition of productswith high commercial value. This process implies the milling of fishmuscle, solubilisation of fish proteins with salt, formatting of fishpaste and induction of the gelling phenomenon, usually by heat.

Several restructured fish products have been developed, includingthe following: vacuum-tumbling processing of trimmed salmonidfish with posterior canning and retorting; and tumbling of channelcatfish using egg white as binder (Borderías & Pérez-Mateos, 1996;Yetim & Ockerman, 1995a, 1995b; Zimmerman, Bissel, & McIntosh,1998).

The restructuring process allows for the commercialisation ofsome low-value fish species with higher profits: non-commercialfish species, smaller fishes than commercial size (such as caughtas shrimp by-catch), and trimmings from filleting of commercialfish species (Noriega-Rodríguez et al., 2009; Pacheco-Aguilar et al.,2010).

1.1. Biochemical considerations

The biochemistry of fish muscle is different from that ofmammals and birds. Consequently, fish products must be processedin a different way than red meat or poultry. The introduction of thesurimi technology in occidental countries has allowed a betterunderstanding of the biochemistry of fish muscles and the physi-cochemical behaviour of proteinaceous matrix when forming gels.Particular phenomena in fish products are modori and suwari.

Modori is a deteriorative phenomenon affecting the gel struc-ture (weakening) and takes place at temperatures near 60 �C. It has

* Corresponding author. Tel.: þ34 982822420; fax: þ34 982254592.E-mail address: [email protected] (M. Vázquez).

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Food Hydrocolloids 25 (2011) 1842e1852


been associatedwith the activity of endogenous serine and cysteineproteases in the muscle. To minimise this negative effect, surimiproducts must be heated as quickly as possible, being careful thatthe fish paste remains in the 50e70 �C range. Usually, fish gels areobtained by water immersion (90 �C for 20e30 min) of formattedfish paste (An, Peters, & Seymour, 1996; Ramírez, García-Carreño,Morales, & Sánchez, 2002; Ramos-Martínez, Morales-González,Ramírez, García-Carreño, & Montejano-Gaitán, 1999; Sánchez,Ramírez, Morales, & Montejano, 1998).

Suwari, or “setting”, is the gelling of muscle protein at temper-atures in the 0e40 �C range. This phenomenon is consideredbeneficial because it improves the mechanical and functionalproperties of fish gels and is usually induced before heating the fishpaste at 90 �C for 30 min. Setting results from the activity ofa calcium-dependent endogenous transglutaminase (TGase). Thisenzyme catalyses the formation of covalent bonds between adja-cent proteins, improving gel structure. Transglutaminase catalysesan acyl-transfer reaction between g-carboxyamide groups ofglutaminyl residues in proteins. When the primary amine is the3-amino group of lysine and lysyl residues, 3-(g-glutamyl) lysinecross-linking takes place (Kumazawa, Seguro, Takamura, & Motoki,1993). Adding calcium to restructured products improves theirmechanical properties because calcium is a cofactor of endogenoustransglutaminase. For example, adding 10e100 mM calcium chlo-ride (CaCl2) induced the aggregation of actomyosin from Oreo-chromis niloticus incubated at 4 and 40 �C. It was associated withthe activity of endogenous transglutaminase, determined by thepresence of protein aggregates (Yongsawatdigul & Sinsuwan, 2007).In addition, calcium improves proteinecalciumeprotein bonds inthermal-induced gels, increasing the mechanical properties ofsurimi gels. However, it is important to consider that the presenceof proteinecalciumeprotein interactions has been reported asdetrimental for protein stability during the frozen storage of surimi.Thus, calcium must be added during the solubilisation of fishpastes, just before inducing the setting (Lee & Park, 1998; Morales,Ramírez, Vivanco, & Vázquez, 2001).

Although the setting depends on the optimal activity of theendogenous TGase, it is critical to consider the physicochemicalproperties of myosin and actomyosin, which are the substrates forthe enzyme. Obtaining the optimal activity of TGase requires themuscle proteins to be denatured to expose the residual groups,allowing the covalent cross-linking of adjacent proteins. However,muscle proteins tend to aggregate quickly and show a short rangeof temperatures between the onset of denaturation and thebeginning of aggregation. Additionally, muscle proteins from cold-water fishes denature at lower temperatures than muscle proteinsfrom warm-water fishes. These differences should be considered toobtain restructured products. Fishes from cold water, e.g., AlaskaPollock, form stronger gels when solubilised pastes are incubated at0 �C for 12e24 h or at 25 �C for 2 h before being heated to 90 �C for30 min. Conversely,fish species from tropicalwater, e.g., tilapia, formstronger gels when setting is induced at 40 �C for 30 min. In thisregard, gels from lizardfish (Saurida undosquamis), a warm-waterfish species, showed better mechanical properties when incubatedat 40 �C for 30 min compared to 25 �C for 2 h prior to heating at90 �C for 20 min. Gels from O. niloticus formed at 40 �C for 30 minshowed better mechanical properties than gels formed at 4 �C for2 h. The setting was induced by formation of higher molecularweight protein (HMP), which occursmore frequently at 40 �C than at4 �C. This was induced by higher protein denaturation, measured bychanges in surface hydrophobicity and loss of the alpha-helicalstructure. The low mechanical properties of gels induced bysetting at 4 �Cwas associatedwith a partial covalent cross-linking ofadjacent proteins by the endogenous transglutaminase because thelow temperature did not induce denaturation of native actomyosin,

and reacting residual groups were not exposed (Yongsawatdigul &Sinsuwan, 2007).

Even species from habitats with similar temperatures (cold orwarm waters) show different onset temperatures for the denatur-ation of muscle proteins. Muscle proteins from warm-waterspecies, e.g., walleye pollock, white croaker, and threadfin bream,showed species-specific properties, which resulted in differentrheological properties. Optimum temperatures for shaping fishmeat pastes were different depending on the temperature requiredto initiate protein denaturation (Fukushima, Okazaki, Fukuda, &Watabe, 2007). It has been reported that natural actomyosin frompacific whiting and threadfin bream showed different properties onthermal transitions, measured by circular dichroism (CD) anddifferential scanning calorimetry (DSC). Pacific whiting actomyosinrequired a lower temperature to initiate its thermal transitions andshowed higher unfolding of its tertiary structure, measured bysurface hydrophobicity, alpha-helical content, and solubilityinduced by incubation at 25 �C for 4 h and 40 �C for 2 h. The higherdegree of unfolding of the protein structure exposed more residualgroups, allowing more covalent cross-linking of adjacent proteinsby transglutaminase activity. Transglutaminase catalysed morecross-linking of pacific whiting myosin heavy chain than threadfinbream myosin heavy chain (Hemung, Li-Chan, & Yongsawatdigul,2008).

Finally, the freshness of fish muscle is important. In similarprocess conditions, the mechanical properties of gels from liz-ardfish decreased with the freshness of fish muscle kept in iceover ten days (Benjakul, Phatcharat, Tammatinna, Visessanguan, &Kishimura, 2008).

1.2. Microbial transglutaminase

Initially, the setting was considered a technological problem forsurimi processing because the solubilised fish paste tended to gelduring refrigerated storage. Once the beneficial effect of inducingthe setting was shown to improve the mechanical properties ofgels, several studies were carried out to understand its origin.Finally, its enzymatic origin was understood, and several groupsworked to find how to produce transglutaminase by biotechnologytechniques. Currently, a commercial calcium-independent micro-bial transglutaminase (MTG) is used to improve themechanical andtextural properties of several protein foods, including surimi andrestructured fish products. This enzyme can be obtained fromStreptoverticillium ladakanum or Streptoverticillium mobaraense(Jiang, Leu, & Tsai, 1998) and has been applied to increase thetextural properties of surimi from the cold-water fish Alaskapollock, and several warm-water species, such as Southern bluewhiting and white croaker (Asagami, Ogiwara, Wakameda, &Noguchi, 1995), striped mullet (Ramírez, Rodríguez-Sosa, Morales,& Vázquez, 2000) or silver carp (Ramírez, Santos, Morales,Morrisey, & Vázquez, 2000).

MTG catalyses the same reaction as endogenous trans-glutaminase, but MTG shows lower deamidation affinity than theendogenous transglutaminase of fish or pig (Ohtsuka, Umezawa,Nio, & Kubota, 2001). Several studies have reported the optimalconditions for using MTG in surimi gels (Lee, Lanier, Hamann, &Knopp, 1997; Ramírez, Rodríguez-Sosa, et al., 2000; Ramírez,Santos, et al., 2000) and restructured fish products (Téllez-Luis,Uresti, Ramírez, & Vázquez, 2002; Uresti, López-Arias, González-Cabriales, Ramírez, & Vázquez, 2003). Recent studies have repor-ted that MTG induced more extensive cross-linking of myosinheavy chain proteins than endogenous fish transglutaminase,allowing the formation of gels with better mechanical propertiesthan from Pacific whiting actomyosin (Hemung et al., 2008).Although better mechanical properties are obtained by increasing

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the amount of MTG, the optimal activity of the enzyme is reachedwhen setting is obtained at temperature conditions that induce thedenaturation of fish actomyosin.

Although commercial applications for protein cross-linking arebased on MTG, there is an interest to explore the use of severaloxidative enzymes, including tyrosinases, laccases, and sulfhydryloxidases as alternatives. However, the reaction mechanisms ofthese cross-linking enzymes differ, resulting in different techno-logical properties. Therefore, the use of novel enzymes requiresextensive knowledge of the complex structure of proteins to giveeach enzyme access to reactive groups and to avoid processconditions that affect the extent of cross-linking. This considerationis required to tailor proteins towards better functionality, such asimproved gelling, emulsifying property or others (Buchert et al.,2010).

2. Surimi

Surimi technology offers a great opportunity to transformdifferent fish species into high commercial value products. Thus,the demand for surimi and kamaboko is increasing worldwide.However, surimi technology has several negative environmentalimpacts, which are necessary to minimise. One such impact is theover-exploitation of white fish stocks, which has compromised thesupply of these species. Strategies for using alternative species andfisheries by-catch, together with the maximum utilisation of fish,are being proposed (Jafarpour & Gorczyca, 2008; Martin-Sanchez,Navarro, Perez-Alvarez, & Kuri, 2009).

Surimi is not a final product; it is a wet concentrate of high-quality myofibrillar proteins, obtained by washing the minced fishmeat with cold water several times. The washing operationremoves the water-soluble sarcoplasmic proteins responsible fororganoleptic properties and concentrates the water-insolublemyofibrillar proteins, such as, myosin, actin, and the actomyosincomplex (Ramírez, Martín-Polo, & Bandman, 2000).

Although it is technically feasible to obtain surimi from any fishspecies, the functional properties are highly dependent on fishspecies, and surimi from many species shows low gelling capacityproperties. Gelling and other functional properties of surimidepend on the overall effect of all proteins in the food system.Gelling is a functional property that involves three main steps inmuscle protein systems: 1) solubilisationwith 2e3% salt at pH closeto 7 (pH of muscle in post-riguormortem); 2) thermal denaturationof proteins (50e90 �C), and 3) a consequent protein aggregation.These conditions allow the acquisition of an irreversible and opa-que gel with different levels of rigidity and deformability,depending on the thermal treatment, fish species, and otherparameters.

The surimi industry in Japan usually evaluates the quality ofsurimi gels using the folding test where a small sample (less than0.5 cm) is folded twice. In this simple test, high-quality surimi doesnot show any fracture. A torsion test has been proposed as anobjective method to measure the mechanical properties of surimigels, which could be applied to other gelling foods. This methodallows the determination of shear stress and the shearing strain atfailure (Fig. 1). Shear stress measures gel strength and correlateswell with sensory hardness, TPA hardness, and TPA fracturability.This parameter can be improved by different processing conditionsand additives. Shear strain measures the gel deformability andcorrelates well with cohesiveness and springiness (TPA). Thisparameter highly depends on the fish species and freshness;generally, it is not improved by process or additives. A surimi gelwith a shear strain value higher than 2.2 is considered high qualityand can be used for producing crab or shrimp analogues. Surimi

gels with strain values lower than 1.8 are considered low quality(Hamman & Lanier, 1987; Kim, Hamman, Lanier, & Wu, 1986).

Most fish species from warm-water produce surimi gels withlow to medium shear stress and low shear strain values. These gelsare perceived as ‘mushy’ (low stiffness and low cohesiveness) andhave low commercial value (Luo, Kuwahara, Kaneniwa, Murata, &Yokoyama, 2001; Ramírez, García-Carreño, et al., 2002; Ramírez,Santos, et al., 2000). Fig. 1 shows the relationship between shearstress and shear strain and sensory textural perception.

Several studies have been carried out to improve themechanicaland functional properties of surimi gels. The use of calciumimproved the shear stress of surimi gels from several fish species,but had no effect on the shear strain. This behaviour is associatedwith the activity of residual endogenous transglutaminase after thewashing cycles that are necessary to obtain surimi (Lee & Park,1998; Morales et al., 2001). Several additives, including MTG andhydrocolloids, have been used to improve the mechanical proper-ties of surimi gels (Ramírez, Rodríguez-Sosa, et al., 2000; Ramírez,Santos, et al., 2000). Recently, it has been reported that centrifu-gation, rather than decanting and filtering, improves the mechan-ical properties by more efficiently removing the sarcoplasmicproteins. Other techniques explored whether various alterationsimproved the mechanical properties of surimi products, includingmodification of the pH and the use of alkaline treatments duringwashing (Jafarpour & Gorczyca, 2008).

Surimi is also considered an ingredient in the establishment ofmany products. Recently, the use of surimi as a protein-basedcarrier in developing high omega-3 fatty acid-containing seafoodproducts has been proposed because it allows for uniform disper-sion and oxidative stability of omega-3 fatty acid oil in the highlycohesive gel system without the use of antioxidants (Tolasa, Lee, &Cakli, 2010).

3. Restructured products

Although several methods of restructuring have been devel-oped, the most common process includes cutting, tumbling, andmassaging (with or without vacuum). This process uses salt tosolubilise and extract myofibrillar proteins, which form a stickyexudate responsible for binding all the products (Boyer, Joandel,Ouali, & Culioli, 1996; Ramírez, Martín-Polo, et al., 2000).

Myofibrillar proteins (particularly myosin) are responsible forthe heat-induced aggregation involved in gelling and bindingmechanisms (Boyer, Joandel, Roussilhes, Culioli, & Ouali, 1996). The

Fig. 1. Effect of shear stress and shear strain on the appearance of surimi andrestructured product.

J.A. Ramírez et al. / Food Hydrocolloids 25 (2011) 1842e18521844


level of salt used during massaging is important, as it determinesthe amount of exuded protein, which acts as a binding agent,leading to the protein aggregation. A different mechanism oftemperature-induced aggregation has been reported for myosin, asinfluenced by the ionic strength. At low ionic strength, myosinaggregation could be induced by side-to-side interactions, while athigh ionic strength, the aggregation could be induced by head-to-head interactions, which implies a more structured system(Boyer, Joandel, Ouali, et al., 1996; Ramírez, Rodríguez-Sosa, et al.,2000).

Restructured products can be obtained by combining abundantand low commercial value fish species. Striped mullet (Mugilcephalus), an abundant fish species caught in the north of the Gulfof Mexico with very low commercial value because of its darkmeat and strong flavour, was combined with Mexican flounder(Cyclopsetta chittendenni), an abundant fish species highly appre-ciated for its white flesh and good taste, but with a small size andlow commercial value when caught as shrimp by-catch in thenorth of the Gulf of Mexico. Although gels from both fish speciesalone showed good mechanical properties, gels obtained from themixture had lower mechanical properties. When microbial trans-glutaminase was used as binder at 3 g/kg, the mechanical prop-erties of the mixture (1:1) of striped mullet:Mexican flounderwere improved, allowing for restructured products withmechanical, functional and sensorial properties appropriate forcommercialisation (Ramírez, Del Ángel, Uresti, Velázquez, &Vázquez, 2007).

Other binding agents that have been reported include fibrin-ogen, thrombin, phosphate, isolated soy protein, sodium caseinate,waxy modified corn starch, carrageenan, oat flour, modified foodstarch, kappa-carrageenan, and soy protein. The suggested mech-anisms for these additives can be acting as fillers or by interactionswith the solubilised myosin as shown in Fig. 2 (Motzer, Carpenter,Reynolds, & Lyon, 1998; Shao, Avens, Schmidt, & Maga, 1999; Tsai,Unklesbay, Unklesbay, & Clarke, 1998).

3.1. Low-salt restructured products

The growing concern over the elevated consumption of sodiumfrom processed products opens an opportunity for the foodindustry to offer low-salt products. Reduction of salt intake couldprevent and control adverse blood pressure levels, and consumersare interested in alternative products with lower levels of salt(Narhinen et al., 1998). However, adding salt is necessary forobtaining restructured products with the appropriate mechanicaland functional properties.

As discussed previously, the techniques used to obtain restruc-tured products require solubilisation and extraction of myofibrillarproteins with salt to obtain sticky exudates, which are used to bindmeat pieces. Decreasing the salt levels induces a reduction in theamount of solubilised and extracted protein, which affects thebinding capacity. The use of transglutaminase as a binding agent inrestructured products, containing low concentration or no salt, aswell as raw products (uncooked), has been suggested becauseproteins extracted during massaging are also a good substrate forcross-linking reactions by MTG (Kuraishi et al., 1997). However,restructured products obtained by thermal-induced aggregationrequire at least 1% NaCl to promote cross-linking reactions, whichimprove themechanical properties of restructured fish products. Atthis salt concentration, there were no differences in the mechanicalproperties of products obtained with 3 or 6 g/kg of the enzyme.MTGwas able to induce protein cross-linking even in the absence ofsalt. However, protein aggregation was not enough to improve theoverall functional and textural properties (Ramírez, Uresti, Téllez-Luis, & Vázquez, 2002).

3.2. Cold binding

The heat-induced setting depends widely on the denaturationtemperature of myosin, which induces the exposure of the buriedg-carboxyamide groups of glutamyl residues and 3-amino group of

Solubilized fish paste

Non treated Cooking

Cooking

Good gel

Better gel

Protein structure showing intramolecular interactions

Food hydrocolloids added as additives induce crosslinking and protein interactions

Thermal induced denatured protein

Food hydrocolloidsas additives

Fig. 2. Suggested mechanism for induced changes in proteins due to hydrocolloids.



lysine residues during MTG-induced cross-linking (Cofrades, Ayo,Serrano, Carballo, & Jiménez, 2006). However, MTG shows activityeven in cold temperatures (under 4 �C). This property is importantwhen binding raw meat under refrigeration to produce restruc-tured products. This practice is called cold binding and implies theaggregation of myofibrillar proteins without the denaturation/aggregation induced by heat. In cold binding, aggregation is duemostly to the MTG activity (Castro-Briones et al., 2009; Hemunget al., 2008). Cold binding using MTG alone or combined withothers binders, such as carbohydrates or proteins, allows the use offish fillet trimmings and minced muscle to prepare restructuredproducts that could be commercialised as raw material to producesushi, cold smoked fish fillets, carpaccios or marinated products.Furthermore, restructured raw products could be cooked as freshfish fillet or pieces of fillet in several dishes (Moreno, Carballo, &Borderias, 2010).

Uncooked restructured products were obtained with MTGunder refrigeration or freezing conditions. The binding of 2-cmcubes of lean pork meat for 16 h of frozen-induced aggregationat �40 �C required at least 30 g/kg NaCl and 1 g/kg MTG to obtaingood mechanical properties. Products obtained with 10 g/kg NaCland 1 g/kg MTG showed inappropriate mechanical properties(Kuraishi et al., 1997). Minimally processed raw restructured fishproducts with appropriated mechanical and functional propertieswere obtained from pieces or homogenised hake muscle aftersolubilisationwith 15 g/kg sodium chloride,10 g/kgMTG, and 7.5 g/kg sodium caseinate. The soluble pastes were incubated for 24 h at5 �C to allow protein cross-linking (Moreno, Carballo, & Borderias,2009).

The cold binding technique allows the production of low-saltproducts (5e15 g/kg salt) by using MTG (5e10 g/kg) and storing thesolubilised pastes at 5 �C for 48 h at different pHs (Moreno et al.,2010).

AlthoughMTG improves the mechanical properties related withthe gel strength, it has a minimal effect on shear strain. A minimalor negative effect on the water-holding capacity (WHC) has alsobeen reported (Téllez-Luis, Ramírez, & Vázquez, 2004). Thus, theuse of hydrocolloids to improve the WHC might be needed whenrestructured products are obtained using MTG. The compatibilityamong MTG and the hydrocolloids must be considered becausesometimes the combined use leads to unstructured weaker prod-ucts as is explained below. Other side to consider when using thisenzyme is its high cost. Frequently, the fish products can requirea minimal improvement in the mechanical properties which couldbe obtained just by adding some hydrocolloids instead of MTG.

4. Hydrocolloids as additives

Polysaccharides and proteins are food hydrocolloids with animportant role in the structure, stability and functional propertiesof several processed foods. Proteinecarbohydrate interactionsdetermine the functional properties in foods where proteins are themajor ingredients, such as meat and fish processed products.Different hydrocolloids have been proposed to improve themechanical and functional properties of surimi and restructuredfish gels (Gomez-Guillén, Borderias, & Montero, 1997; Lee, Wu, &Okada, 1992; Park, 2000; Ramírez, Barrera, Morales, & Vázquez,2002).

Fish proteins solubilised by salt and water form a continuousmatrix. Some additives can be entrapped within this matrix, fillingthe gel and exerting their functional effects in the restructuredproducts by a) influencing the formation of the continuous surimigel matrix during thermal-inducing gelation; b) modifying theviscosity, mobility and other properties of the liquid phase; c)influencing texture and appearance of the gel, i.e., particle size,

distribution, rheological (textural) properties, and relative volumefraction of the gel (Lee et al., 1992).

4.1. Carbohydrates

Gel-forming capability is important to obtain fish products, suchas restructured products (from whole-minced pastes) or surimi-based products (water-washed pastes). Carbohydrates, such asgums and starches, promote the formation of the continuousmatrix by interacting with water and proteins in the fish paste.Some additives interact with proteins to form a more structuredsystem, while others act as fillers, binding water and modifying theviscosity of the system (Lee et al., 1992). It is also important toconsider that adding carbohydrates into a formulation couldmodify the capacity of salt to solubilise myofibrillar proteins, whichwould affect the mechanical and functional properties of gels.Furthermore, some carbohydrates are not compatible with themuscle proteins and have a disruptive effect in the gelling property.

Several hydrocolloids, such as starch, carrageenan, and konjac,are typically used to improve the mechanical properties of surimigels (Gomez-Guillén et al., 1997; Park, 2000).

4.1.1. StarchStarch is the most common ingredient used as filler in products

based on surimi or fish. It increases firmness and gel strength (Lee,1984; Lee et al., 1992; Susuki, 1981; Wu, Hamman, & Lanier, 1985;Wu, Lanier, & Hamman, 1985). Starch is used in the production ofsurimi products at 40e120 g/kg to control wetness, stickiness, and/or thermal stability during storage and serving temperatures.Another important attribute of native andmodified starches is theircapacity to partially replace fish proteins while maintaining desiredgel characteristics at a lower cost (Hunt, Getty, & Park, 2009).

There is an increasing interest in identifying novel applicationsfor both native and modified starches to improve the mechanicaland functional properties of restructured and surimi products.Native wheat starch modified the rheological properties of kama-boko gels from sardine surimi without affecting the thermal tran-sitions, as determined by DSC (Karayannakidis, Zotos, Petridis, &Taylor, 2008). Potato starch slightly improved the strength ofsurimi seafood gels treated with ohmic heating, but it had a detri-mental effect on whiteness, as compared to wheat starch (Chai &Park, 2007). Adding pre-gelatinised starches to SA-grade surimichanged the mechanical properties by enhancing the stiffness ofthe gel while decreasing yield and breaking force (Yamamoto,Murakami, Nakachi, Nishino, & Nishikawa, 2007). Adding acety-lated rice starch at 40e80 g/kg improved the freeze-thaw stabilityof surimi pastes, but reduced the gel strength and expressiblemoisture content of surimi gels. The effect of acetylated starch onrheological properties of surimi sols and gels seems to be related tothe swelling capability of starch granules in the presence of limitedwater (Jung, Kim, & Yoo, 2007). Frozen storage affects themechanical, functional and sensorial properties of fish meals, andthe effect is higher when food is subjected to several freeze-thawcycles during storage and commercialisation. A rubbery texture isgenerally associated with a loss inWHC and usually results in loweracceptability. Modified tapioca starch (hydroxypropylated distarchphosphate), added at 10 g/kg to bigeye snapper (Priacanthus taye-nus) mince paste, reduced the negative changes caused by fivefreeze-thaw cycles, improving the mechanical, functional, andoverall properties of restructured products, as compared to prod-ucts with no starch. Restructured products containing 10 g/kgmodified starch showed a finer matrix with smaller strands at allfreeze-thaw cycles used, observed by scanning electronmicroscopy(SEM), as compared with the control minced gel (Tuankriangkrai &Benjakul, 2010).



Most frequently, starch is the first choice for producing tradi-tional fish burgers or sausages. However, there is a growing interestto obtain new products with different textures and sensorialattributes to offer meals that satisfy the expectations of meals thatcustomers will enjoy eating. Using small amounts of proteins andnon-starch hydrocolloids in the formulation could improve thequality of minced fish products, taking advantage of their multi-faceted functionality as texture modifiers. These formulationschange the upper and lower bounds for the attributes of instru-mental texture, increasing sensory acceptability (Kasapis, 2009).

4.1.2. GumsGums are considered a good alternative for improving the

mechanical properties of restructured products. They are readilyavailable and they are not expensive. Most of them are compatiblewith fish muscle proteins, improve the yield without negativeeffect on texture. Usually, they do not affect significantly the colour.The main effect is improving the WHC. Other important factor toconsider when using gums is that although gums are carbohydratesthey do not add calories and have the beneficial effects of the fibreon diet. Many consumers, especially those looking for healthyfoods, could appreciate this effect. Carrageenan and konjac arehighly compatible with fish muscle meals, but others gums havea negative effect on texture and some especial considerations mustbe taken into account. On this regard, locust bean and xanthan gumat a 0.25/0.75 ratio has been proposed to improve the mechanicalproperties of surimi gels from silver carp (Ramírez, Barrera, et al.,2002).

Alginates weaken surimi gels when incorporated (Lee et al.,1992). However, alginates are commonly used for obtaining rawrestructured fish products by the cold binding technique underchilling or freezing conditions. The effectiveness of sodium alginateas cold binder can be improved by adding a low concentration (1 g/kg) of CaCl2, whereas a higher concentration (10 g/kg) reduces thebinding capability of the alginate (Moreno et al., 2009, 2010).

Konjac glucomannan (KGM) has been proposed to be an efficientcryoprotective agent for fish myofibrillar proteins. This gum wasable to decrease the muscle protein denaturation/aggregation fromgrass carp (Ctenopharyngodon idella) during storage at �18 �C,improving the amount of salt-extractable protein and reducing theCa2þ-ATPase activity, total sulphydryl groups, and active sulphydrylcontents. Adding KGM at 10 g/kg showed the same cryoprotectiveeffect as a conventional cryoprotectant (100 g/kg sucroseesorbitol,1:1). Adding 15e20 g/kg KGM allowed an increase inwater-holdingcapacity, breaking force, and deformation of surimi gels, althoughthe whiteness decreased and the colour became darker (Xionget al., 2009).

4.1.3. PectinsPectins are classified as high methoxyl (HM) or low methoxyl

(LM) pectins. Both types of pectins have been reported to notimprove the mechanical and functional properties of surimi.Moreover, both pectins induced a disruptive effect during gelling.However, amidated LM (ALM) pectin is compatible with surimi gelsand improves gelling properties. Results suggest that electrostaticproteinepectin interactions induced a disruptive effect when HMand LM pectinwere added. Amidation could improve the polarity ofLM pectin. Thus, hydrogen bonds between amidated LM pectin andprotein could form a more compatible proteinecarbohydratesystem (Barrera, Ramírez, González-Cabriales, & Vázquez, 2002).

Pectins are a complex family of polysaccharides characterised bytheir degree of esterification (DE), which varies with the age,location inside the plant tissue, extraction method, and neutralsugar content. Commercial HM pectins have a typical DE of55e80%; HM pectins usually gel in the presence of sugar at low pH

conditions (Morris, 1998). The gels are formed by associations ofchains by stacking the esterified homogalacturonic acid zones,resulting in a three-fold helical configuration governed byhydrogen bonding and hydrophobic interactions. In contrast, LMpectins may form gels in the presence of calcium over a wide rangeof pHs with or without sugar (Fu & Rao, 2001). Gels are normallyformed at concentrations of 1 g/kg. Two types of LM pectins areproduced commercially: (a) ordinary LM pectins, prepared by acidtreatment in ethanol or isopropanol, and (b) amidated pectins,prepared with ammonia in alcoholic suspensions of pectin (Morris,1998). The formation of proteinepolysaccharide complexes couldimprove the functional properties of proteins.

Pectins are anionic hydrocolloids with different degrees ofmethoxylation. Therefore, pectins have a wide range of ioniccharges. HM pectins interact with proteins above the isoelectricpoint, for instance, with lysozyme (Yang, Chen, & Chang, 2001) andbovine serum albumin (Ledward, 1994). HM pectins improved thegelling capacity and thermal stability of whey protein concentratein the pH range of 4.6e8.5 when the protein concentrate was above80 g/kg. Proteinepectin interactions improved solubility, emulsifi-cation, gelation, and foaming behaviour of whey protein concen-trates (Mishra, Mann, & Joshi, 2001). Pectins have been used ascryoprotectants in surimi (Sych, Lacroix, Adambounou, & Castaigne,1990; Ueng & Chu, 1996).

The use of HM pectins decreases the shear stress and shearstrain of surimi gels when added without calcium. This behaviourcould be associated with the anionic property of both types ofhydrocolloids, and consequently, the repulsive driving force resultsin a less structured system. In a system containing HM pectins,adding calcium chloride improved the shear stress of gels, reachingequal or higher values than control gels without calcium chloride.Shear strain was improved in all gels containing HM pectins andcalcium, as compared to gels containing only HM pectins. However,neither gel showed a shear strain value equal to or higher thancontrol gels. These results suggest that endogenous trans-glutaminase present in surimi induced the formation of strongergels by covalent bonds andwere not affected by the presence of HMpectin. Another possibility could be that this behaviour is indicativeof a proteinecalciumepectin interaction because, as previouslydiscussed, transglutaminase did not improve the shear strain ofsurimi gels. Despite this type of interaction, surimi gels containingHM pectins showed less mechanical properties than surimi controlgels.

LM pectin improved the hardness of surimi gels and decreasedthe shear strain and cohesiveness, but had no significant effect onshear stress, springiness, or water-holding capacity. The mechan-ical properties of surimi gels containing LM pectin were notaffected by adding calcium. This could be due to covalent bondedsurimi gels masking or inhibiting the proteinecalciumepectininteractions, or because these interactions do not have a beneficialeffect on the mechanical properties of surimi gels.

ALM pectin showed a beneficial effect on the mechanicalproperties of surimi and restructured fish products, as compared toLM pectins (Barrera et al., 2002; Uresti et al., 2003). This behaviourcould be associated with a different structure of ALM. The amida-tion of the LM pectin confers different physicochemical and func-tional properties, i.e., LM amidated pectins require less calciumthan LM non-amidated pectins to form a gel. ALM pectins arereported towork better under acidic conditions (pH 3.2e3.6), whilenon-amidated LM pectin works in the pH range of 2.8e6.5.

Hydrogen bonds between ALM pectin and myofibrillar proteinscould result in an improvement in the mechanical properties,specifically hardness and breaking force, of fish gels when ALMpectins are added at 10 g/kg. The detrimental effect on mechanicalproperties associated with higher concentrations of ALM pectin



(20e50 g/kg) could be caused by swelling of the hydrocolloid orchanges in the native structure of muscle proteins by pectinepro-tein interactions, with the presence of both hydrogen bonds andelectrostatic interactions. The swelling of pectin could promotea disruptive effect by competing for water molecules (a salting-outeffect) or simply by interfering in gel formation.

A different mechanism seems to take place in fish pastes andgels containing ALM pectins. Fish pastes with 10 or 20 g/kg ofamidated LM pectin showed lower values for firmness andconsistency compared to control pastes, but did not improve theWHC. This behaviour suggests the presence of proteinepectininteractions, decreasing the proteinewater and pectinewaterinteractions. Alternatively, the significantly higher levels of firm-ness and consistency and WHC reported for solubilised fish pastesusing 30 or 50 g/kg of ALM pectin may be associated with higherentrapment of water by amidated LM pectin (Fig. 3). Adding 10 g/kgALM pectin improved the mechanical properties of restructuredfish gels. However, higher levels of ALM pectin showed a disruptiveeffect on the system. These results suggest that during the gelling ofthe fish system containing ALM pectin, the proteinepectin inter-actions in fish pastes could be substituted by proteineproteininteractions, increasing pectinewater interactions (Uresti et al.,2003).

4.1.4. FibreModern human diet has evolved from diets high in fruits,

vegetables, lean meats, and seafood to processed foods high insodium and hydrogenated fats and low in fibre. These diet changeshave affected dietary parameters related to health, resulting in anincrease in obesity and chronic disease, including cardiovasculardisease (CVD), diabetes, and cancer (Jew, AbuMweis, & Jones, 2009).Dietary fibre obtained from plants is considered a functionalingredient because it provides several health benefits beyondbowel regularity. These benefits may include digestive health,weight management, cardiovascular health, and general wellness.These facts have increased the interest of researchers and the foodindustry to offer healthy food products while preserving theirsensorial acceptance (Viuda-Martos et al., 2010).

Adding 10e30 g/kg of rice bran to frankfurter sausage did notaffect its shelf life. Total viable cells, anaerobic, and psychrotrophicbacteria showed a low growth rate and longer lag time (Heo, Kim,Choi, Kim, & Paik, 2009).

White and red grape dietary fibre concentrate (GDF) is obtainedfrom wine industry residues and is considered a potential func-tional ingredient for the enrichment of foods because of its highconcentration of dietary fibre with a high-soluble/insoluble dietaryfibre ratio and associated bioactive compounds. Adding 20e40 g/kg

GDF to minced fish muscle from horse mackerel (Trachurus tra-churus) improved water and oil retention, lipid stabilisation, andcooking yield during frozen storage at �20 �C for six months.Although GDF showed a good dispersion in the protein matrixaccording to scanning electronic microscopy (SEM), the matrix wasmore discontinuous compared to control samples and was associ-ated with an increase in aggregation of myofibrillar proteins duringfrozen storage. Samples containing 20 g/kg GDF scored highest inoverall acceptance compared to control samples (Sanchez-Alonso &Borderias, 2008; Sanchez-Alonso, Solas, & Borderias, 2007).

The use of wheat fibre in surimi as a healthy ingredient at 30 and60 g/kg with different particle sizes decreased the strength, cohe-siveness, and water binding capacity of surimi gels and was asso-ciated with the formation of a non-homogeneous protein netobserved by SEM. The concentration and particle sizes of fibre didnot change the appearance but affected the texture of the gel. Fibrewith large particle sizes protected surimi from the loss of gelstrength and hardness during freezing (Sanchez-Alonso, Haji-Maleki, & Borderias, 2006). Adding fibre into minced hake (Mer-luccius merluccius) and horse mackerel (T. trachurus) muscleincreased the WHC when water was not added to maintain themoisture constant, but even in these conditions, rigidity andcohesiveness were lower for products containing fibre than controlsamples (Sanchez-Alonso, Haji-Maleki, & Borderias, 2007).

Chicory root inulin, a soluble fibre, has been used as an additivein restructured fish products with a detriment to mechanicalproperties, specifically hardness. This negative effect can be avoi-ded by adding 20 g/kg carrageenan, but it was not compatible withMTG (Cardoso, Mendes, & Nunes, 2007a, 2007b, 2008; Cardoso,Mendes, Pedro, & Nunes, 2008; Cardoso, Mendes, Vaz-Pires, &Nunes, 2009).

Pea fibre can be added tominced fish and surimi up to 40 g/kg toobtain restructured products without modifying the textural andfunctional properties. It was compatible with up to 20 g/kg carra-geenan, allowing increased hardness of restructured hake products.Pea fibre was compatible with MTG at 1 g/kg or above, and itimproved the textural properties of surimi gels from Atlanticmackerel (Scomber scombrus) and chub mackerel (Scomber japoni-cus) (Cardoso et al., 2007a, 2007b, 2009; Cardoso, Mendes, & Nunes,2008).

4.1.5. OthersAdding 10 g/kg chitosan to kamaboko gels from grass carp

(Ctenopharyngodon idella) allowed an increase in hardness,springiness, cohesiveness, chewiness, adhesiveness, whiteness,WHC, and TBA while decreasing peroxide value and bacterialgrowth. The preservative function was related to the molecularweight of chitosan. Relatively low molecular weight chitosanshowed a higher antioxidant capacity than high molecular weightchitosan. However, a mixture of 300 and 10 kDa chitosan exhibitedthe highest antibacterial activity (Mao & Wu, 2007; Wu & Mao,2009).

4.2. Proteins

4.2.1. Effect of proteins on restructured productsWhey protein concentrate (WPC) at 10e30 g/kg inhibited the

autolytic modori phenomenon, associated with the activity ofendogenous proteases activated at 60 and 65 �C in surimi frombigeye snapper (P. tayenus), goatfish (Mulloidichthys vanicolensis),threadfin bream (Nemipterus bleekeri), and lizardfish (Sauridatumbil). Adding WPC decreased the amount of hydrolysed protein,as demonstrated by the decrease in trichloroacetic acid-solublepeptide content, the higher level of myosin heavy chain and thebetter mechanical and functional properties of the surimi gels.

Fig. 3. Effect of the ALM pectin concentration on the firmness (close circles) andconsistency (open circles) of solubilised fish pastes. Bars show standard deviation.Adapted from Uresti et al. (2003).



However, WPC at 30 g/kg affected the colour attributes, decreasingthe whiteness of gels (Rawdkuen & Benjakul, 2008). AddingWPC incombination with calcium chloride (50 mmol/kg) improved themechanical and functional properties of surimi gels from goatfish(M. vanicolensis) obtained by incubating surimi paste at 40 �Cbefore cooking (Benjakul, Yarnpakdee, Visessanguan, & Phatcharat,2010).

Beef plasma protein (BPP) added at 10e30 g/kg improved themechanical properties of red tilapia surimi gels obtained by settingat 40 �C for 90 min followed by heating at 90 �C for 30 min.However, the whiteness of gels decreased when the concentrationof BPP was increased (Duangmal & Taluengphol, 2010). Similarresults were obtained by adding BPP to surimi gels from arabesquegreenling (Pleurogrammus azonus) and walleye pollock (Theragrachalcogramma). The mechanical properties of these surimi gelsincreased when 10e30 g/kg BPP was added to solubilised pastesand incubated at 25 �C for up to 15 h before cooking at 90 �C for30 min (Kato et al., 2010).

Soy protein isolate (SPI) modified the textural properties ofsurimi gels from silver carp (Hypophthalmichthys molitrix) and grasscarp (C. idella). SPI negatively affected the mechanical properties ofsurimi gels obtained by setting fish pastes at 30 and 40 �C for60 min before heating at 85 �C for 30 min. The mechanical prop-erties decreased when the protein concentration increased(100e400 g/kg). However, adding 100 g/kg SPI improved themechanical properties of surimi gels obtained by incubating fishpastes at 50 �C for 60 min before heating at 85 �C for 30 min (Luo,Shen, & Pan, 2006; Luo, Shen, Pan, & Bu, 2008).

Egg white (EW) added at 10e30 g/kg improved the mechanicalproperties of red tilapia surimi gels obtained by setting at 40 �C for90 min followed by heating at 90 �C for 30 min, as well as for surimigels from arabesque greenling (P. azonus) and walleye pollock (T.chalcogramma), incubated at 25 �C for up to 15 h before cooking at90 �C for 30 min (Duangmal & Taluengphol, 2010; Kato et al., 2010).Special dried egg white showed a larger effect on the mechanicalproperties of surimi gels from Pacific whiting (Merluccius pro-ductus) and Alaska pollock (T. chalcogramma), as compared toregular dried egg white and liquid egg white. Adding egg whitewith cryoprotectants before freezing for 12 months was less effi-cient at improving the mechanical properties of surimi gels thanadding 20e30 g/kg egg white during chopping of solubilised pastes(Hunt, Park, & Handa, 2009).

Sarcoplasmic protein can be obtained from washing operationsduring surimi processing. This muscle fraction contains substantialtransglutaminase activity, which could be used for catalysing theprotein cross-linking of myofibrillar proteins, improving themechanical properties of surimi gels. MTG could be concentratedby ultrafiltration using a 30 kDa membrane, increasing the totalactivity without affecting the specific activity. Adding tilapia (O.niloticus) sarcoplasmic proteins increased the mechanical proper-ties of lizardfish surimi gels when produced by setting at 37 �C for1 h before cooking (Yongsawatdigul & Piyadhammaviboon, 2007).Adding common carp (Cyprinus carpio) sarcoplasmic proteins(Sp-P) improved the mechanical properties of gels from threadfinbream surimi at constant moisture and myofibrillar levels.Although adding Sp-P did not interfere with myofibrillar proteinsduring the solegel transition phase, this did enhance the texturalquality of kamaboko. However, the addition of Sp-P from the darkmuscle of the carp decreased thewhiteness of the surimi (Jafarpour& Gorczyca, 2009).

Soluble proteins from surimi wash water (SWW) can beinsolubilised by complexing with chitosanealginate, allowing itsrecovery and the reduction of suspended organic matter in waterdischarged from surimi processing plants. Adding 10e30 g/kg ofpacific whiting SWW recovered with chitosanealginate (chiealg

SWW) into Alaska pollock (T. chalcogramma) grade FA surimi pastesallowed for the improvement in the mechanical properties ofsurimi gels, but decreased the WHC and slightly increased theredness, an undesirable effect in the production of Alaska pollockgrade FA surimi (Velazquez et al., 2007). Pacific whiting SWWrecovered with chitosanealginate at 10 g/kg slightly improved themechanical properties of grade A Pacific whiting surimi gels witha minimal effect on colour. Higher concentrations resulted inquality deterioration, poor mechanical properties, and changes incolour.

Myoglobin, a sarcoplasmic protein, extracted from Pacificsardine decreased the mechanical properties of Pacific whitingsurimi gels when added at 2 g/kg. However, it showed a synergisticeffect when added at 10 g/kg together with 10 g/kg of beef plasmaprotein, increasing surimi gel strength (Park & Park, 2007).Myoglobin from tuna was able to bound tuna and sardine myosinproteins as a function of storage time at 4 �C for up to 24 h, inducinga higher oxidation of oxymyoglobin and loss in the Ca2þ-ATPaseactivity of myosin (Chaijan, Benjakul, Visessanguan, & Faustman,2007).

Fish gelatin is a commercially available food additive obtainedafter hydrolysis of collagen from fish. Fish gelatin had a disruptiveeffect on the mechanical properties of grade A or FA surimi gels(Alaska pollock) when added at 15 g/kg in solubilised surimi pastes,incubated at 40 �C for 30 min followed by cooking at 90 �C for15 min. However, fish gelatin had no effect on the mechanicalproperties when added at 5e10 g/kg. The same effect was observedin the expressible water (Fig. 4) when only 15 g/kg gave a statisticaldifference (Hernandez-Briones, Velazquez, Vazquez, & Ramirez,2009).

Insoluble proteins recovered by centrifugation from Pacificwhiting surimi wash water, consisting mainly of myofibrillarproteins, were added at 10e50 g/kg into Alaska pollock grade FAsurimi. The insoluble proteins increased the mechanical propertiesof surimi gels, but affected WHC and caused slight changes incolour attributes (Ramírez, Velazquez, Lopez-Echevarria, & Torres,2007; Velazquez et al., 2008).

4.2.2. Effects of proteins in low-salt restructured productsA decrease in salt concentration has a negative effect on protein

extractability and solubility, resulting in poor mechanical proper-ties. The protein solubilised and extracted during blending alsoserves as a substrate for cross-linking reactions by endogenous andmicrobial transglutaminase (Andrés-Bello, García-Segovia, Ramírez,& Martínez-Monzó, in press; Sun, 2009).

The effect of adding 10 g/kg of whey protein concentrate (WPC)and 10 g/kg of sodium caseinate (Na-caseinate) was studied in

Fig. 4. Effect of fish gelatin on expressible water content of surimi gels. Differentletters indicate significant differences between treatments (P� 0.05). Adapted fromHernandez-Briones et al. (2009).



restructured products from silver carp (H. molitrix) at three saltconcentrations (0, 10, and 20 g/kg). Dairy protein additives wereadded alone or in combination with MTgase at 3 g/kg. Themechanical properties and WHC of restructured productsdecreased when the salt concentration decreased. Sodiumcaseinate was more efficient than WPC in improving the mechan-ical properties of restructured products at each level of salt studied,as compared to control samples. The WHC was not improved byadding any of the dairy proteins. In the low-salt (10 g/kg NaCl)product, higher values of hardness were obtained by adding MTGand dairy proteins than by adding only MTG, suggesting a positiveinteraction between meat proteins, dairy proteins, and MTG. Thelast required the addition of salt to fish paste to improve themechanical properties. Unsalted and low-salt restructured prod-ucts supplemented with NA-caseinate or WPC and MTG showedbetter mechanical properties and WHC than control productsobtained only with MTG. In products containing 20 g/kg NaCl,samples containing only MTG showed equal or better mechanicalproperties than samples containingMTG and dairy proteins (Uresti,Téllez-Luis, Ramírez, & Vázquez, 2004). WPC added at 10 g/kgshowed a small effect in improving the mechanical properties ofregular and low-salt restructured products from Mexican flounder(C. chittendenni) (Ramírez, Del Ángel, Velázquez, & Vázquez, 2006).

5. Conclusions

The applications for food hydrocolloids in fish products offernew opportunities to develop novel products based on surimi orrestructured product technology. These products can include thenew low-salt requirements for healthy food.

Acknowledgements

The authors are grateful to Xunta de Galicia (Spain) for thefinancial support of this work (Project 10TAL402001PR) and theFEDER founds of the European Union.

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