J Sci Food Agric 1997, 75, 472È480

Influence of Texture of Suwari Gels onKamaboko Gels Made from Sardine

pilchardus) Surimi(Sardina

Cristina Alvarez and Margarita Tejada*

Instituto del Fri� o (CSIC), Ciudad Universitaria, 28040 Madrid, Spain

(Received 13 September 1996 ; revised version received 24 February 1997 ; accepted 28 April 1997)

Abstract : The textural characteristics and water holding capacity of suwari (set)and kamaboko (set and cooked) sardine surimi gels were examined in order toclarify the inÑuence of the initial network formed in setting conditions (25, 35and 40¡C for 30 and 60 min) on the texture of the kamaboko gels. Although thetexture of suwari gels set at 35¡C improved with longer setting, both setting timesensured kamaboko gels with the highest gel strength. Suwari gels set at 25¡C alsoimproved with longer setting but the gel strength of both suwari and kamabokogels was lower than at 35¡C. For gels set at 40¡C prolonged setting weakened thesuwari networks formed, leading to kamaboko gels with poorer textural charac-teristics.

J Sci Food Agric 75, 472È480 (1997)No. of Figures : 5. No. of Tables : 1. No. of References : 44

Key words : suwari, kamaboko, sardine, gels, texture, water holding capacity

INTRODUCTION

Heating to form thermally irreversible surimi gels isnormally carried out in two steps : Ðrst, salt-solubilisedmyoÐbrillar proteins (sol) are set at O50¡C to producetranslucent gels (suwari type) ; the second step consistsof heating at P80¡C to produce opaque, highly elasticgels (kamaboko type) (Alvarez et al 1995 ; Careche et al1995). This procedure is commonly known as the two-step heating process (Matsumoto and Noguchi 1992).

The Ðnal texture of these gels is determined by theformation of a protein network held together by electro-static and hydrophobic interactions, hydrogen bondsand disulphide and non-disulphide covalent bonds(Niwa 1992 ; Careche et al 1995). It is generally esti-mated that most of the bonds forming at setting tem-peratures are secondary interactions which lay downthe gel matrix, although disulphide bonds and alsocovalent bonds resulting from transglutaminase actionhave been reported (Seki et al 1990). At cooking tem-

* To whom correspondence should be addressed.

peratures ( º 80¡C), on the other hand, mainly intermo-lecular disulphide bonds and more extensiveintermolecular hydrophobic interactions are formed(Niwa 1992).

It was previously thought that prolongation of settingwould result in a more orderly structure, giving kama-boko gels of good textural characteristics (Niwa 1992).However, in a previous work using sardine surimi(Alvarez et al 1995) we found that the textural charac-teristics of kamaboko gels were determined by thenetwork that forms in di†erent combinations of settingand cooking time and temperature, there being anoptimum cooking time for each settingÈcooking com-bination. In some combinations, gel strength decreasedif setting or cooking was prolonged beyond a certainpoint. We have also found that solubility of suwari andkamaboko networks made with sardine surimi di†eredwhen these were treated with a succession of solutionsto achieve selective rupture of the bonds involved innetwork formation ; the majority proteins among thosesolubilised di†ered according to the temperature atwhich the gel was made (Careche et al 1995). All these

4721997 SCI. J Sci Food Agric 0022-5142/97/$17.50. Printed in Great Britain(

T exture of suwari on kamaboko gels 473

results would indicate that in sardine surimi, the charac-teristics of suwari and kamaboko networks will di†eraccording to processing time and temperature.

The aim of the present work was to determinewhether in sardine surimi gels the rheological character-istics of the suwari networks determine the texture ofkamaboko gels. To this end, the two networks obtainedwith various combinations of setting time and tem-perature were examined separately.

EXPERIMENTAL PROCEDURE

Material used

Frozen sardine (Sardina pilchardus) surimi, prepared inone batch for this study by SCOMA (Lorient, France),was air-freighted with solid to the laboratory, cutCO2into blocks, vacuum-packed in Cryovac BB-1 bags(10É66 kPa pressure) and stored at [20¡C(^1) for 1month. Cryoprotectants added to the surimi were40 g kg~1 sucrose, 40 g kg~1 sorbitol and 3 g kg~1 Natripolyphosphate. Crude protein was measured by Kjel-dahl method (AOAC 1984), crude fat by Bligh and Dyer(1959) method as modiÐed by Knudsen et al (1985) andmoisture and ash by AOAC (1984). The proximate com-position of the surimi was : crude protein : 131É3 g kg~1 ;crude fat : 30É5 g kg~1 ; moisture : 758É2 g kg~1 ; ash :6É3 g kg~1. The pH was 6É6.

Gel preparation

Surimi was tempered for about 2 h at 20¡C(^2) until itreached [5¡C(^1), then ground for 1 min (StephanUM12 refrigerated vacuum cutter mixing machine(Stephan u So� hne GmbH & Co, Hameln, Germany)10 kPa, coolant temperature [2¡C). The surimi waschopped for 1 min at high speed (setting 1). Salt (NaCl30 g kg~1 of surimi, equivalent to 24É4 g kg~1 in theÐnal gel) and ice Ñakes (as necessary to adjust moisturecontent to 780 g kg~1) were added, and the mixturewas beaten slowly (setting 2) for 5 min. Temperature ofthe surimi sol was kept below 10¡C at all times. The solsobtained were heated in stainless-steel cylinders (30 mminner diameter and 30 mm height) with screw-on topsand bottoms with TeÑon rings to seal, taking specialcare to ensure that sols were well packed and free of airbubbles. Suwari (S) and kamaboko (K) gels wereobtained by heat-setting at 25, 35 and 40¡C for 30 and60 min in a water bath (Julabo F10, LabortechnikGmbH, Seelbach, Germany). Kamaboko gels werecooked at 90¡C for 30 min using a saturated steam oven(Rational Combi-Master CM6, Grobku� chentechnikGmbH, Landsberg Lech, Germany). After treatment,the gels were cooled with iced water and stored at4¡C(^1) for 24 h before analysis.

Rheological analysis

A penetration test was performed on samples (30 mmheight by 30 mm diameter, 20¡C(^1)) using a cylin-drical stainless-steel spherical probe (dia 5 mm)attached to a 100 N load cell connected to an InstronUniversal Testing Machine Model 4501 (Instron Engin-eering Corporation, Canton, MA, USA). A Hewlett-Packard Vectra ES/12 computer was used toprogramme the cross-head movement to 10 mm min~1and to develop and analyse forceÈdeformation curves.Gel strength (GS) (N mm) was determined as theproduct of yield strength (YS) (N) and yield deformation(YD) (mm) measured at the point of gel breakage(Roussel 1988 ; Hamann and MacDonald 1992).

Folding test

Folding test (FT) was determined at 20¡C by themethod of Tanikawa et al (1985) on gel slices 3 mmhigh. The maximum score (FT\ 5) was obtained if nocracks were observed when the slice was folded twicewithout breaking. The minimum score (FT\ 1) wasobtained if the slice broke into fragments when foldedin half.

Texture proÐle analysis (TPA)

TPA was performed as described by Bourne (1978). Thesamples (30 mm height by 30 mm diameter, 20¡C(^1))were axially compressed by a cylindrical plunger(diameter 36 mm) to 30% (suwari gels) or 50%(kamaboko gels) of original height (Instron Model 4501).The di†erent compression percentages are derived frompreliminary work done to establish the rupture force.ForceÈtime deformation curves were plotted with a5 kN load cell applied at a crosshead speed of50 mm min~1. Hardness (N), springiness (mm),cohesiveness (dimensionless), gumminess (N) and adhe-siveness (g cm) were calculated according to Bourne(1978) and Montejano et al (1985).

The modulus of rigidity

The modulus of rigidity (G) during the solÈgel heatingprocess was determined by thermal scanning rigiditymonitor (TSRM) on the basis of the model proposed byHamann (1987). The TSRM evaluations were per-formed in the water-jacket cup (with no bottom) sup-plied for small samples by BrookÐeld EngineeringLaboratories Inc (Stoughton, MA, USA) with its stan-dard rotary viscometers. The cup was mounted on anInstron Model 4501. The rod (grooved to prevent itfrom sliding through the samples during testing) wasÐtted to a 100 N cell connected to the crosshead of the

474 C Alvarez, M T ejada

machine. The sols obtained as previously were loadedinto the cup, which was connected to a bath (JulaboF10) Ðtted with a Julabo PRG1 temperature pro-grammer. Special care was taken to ensure that the solswere well packed and bubble-free. The sols constituteda paste capable of supporting itself in the annular gapbetween the rod and the cup. The sample surface wassprinkled with a few drops of oil to prevent dehydrationand skin formation (Montejano et al 1984). The samplewas heated from 12¡C to 80¡C at a rate of 1¡C min~1.The internal temperature (T) was measured with a ther-mocouple probe connected to a model 3087 tem-perature recorder (Yokogawa Hokushin Electric YEW,Tokyo, Japan). A Hewlett-Packard Vectra ES/12 com-puter was used to programme the cross-head movementto 0É2 mm at speed of 0É5 mm min~1, at intervals of2 min. The modulus of rigidity (G) (kPa) of the sampleswas determined by means of the equation :

G\ [F ln(R2/R1)]/(2nDL )

where F is the cyclic axial force amplitude ; D is the rodtravel ; L is the length of the rod in contact with thesample ; is the rod radius and is the inner radiusR1 R2of the outer cylinder (Hamann 1987).

Water holding capacity (WHC)

WHC was determined on gels following the methoddescribed by Roussel and Cheftel (1990) and modiÐedby Alvarez et al (1992a). Two grams of sample (cut intocubes of about 3 mm) was spun (Sorvall RT6000B DuPont Co, Wilmington, DE, USA) for 15 min at1000 ] g and the exudate collected with Whatman Ðlterpaper. WHC was expressed as the percentage of waterretained with respect to the water present in the gelprior to centrifuging.

All determinations were performed at least Ðve times,except for modulus of rigidity which was performed induplicate.

Statistical analysis

Two-way analyses of variance were performed using theprogramme Statgraphics STSC Inc (Rockville, MD,USA). The di†erences of means between pairs wereresolved by a LSD test to obtain the conÐdence inter-vals. Level of signiÐcance was set for P\ 0É05.

RESULTS AND DISCUSSION

Rheological analyses

Penetration and folding testIn suwari gels set for 30 min, gel strength (Fig 1)increased signiÐcantly when setting temperature was

Fig 1. Gel strength (N mm) of sardine suwari (S) and kama-boko (K) gels prepared at di†erent setting temperatures (25, 35and 40¡C) and times (30 or 60 min). Folding test scores lowerthan 5 are indicated as a number on the bars. Vertical lines

indicate standard deviation.

increased, whereas in gels set for 60 min, values peakedat 35¡C, falling when the temperature was increased to40¡C. The decrease observed at 40¡C was due partly tovariations in yield deformation (Fig 2) but mainly tovariations in yield strength (Fig 3). All suwari gelsscored maximum in the folding test except those set at25¡C for 30 min (FT\ 4) and at 40¡C for 60 min(FT\ 3) (Fig 1). With setting at 25¡C, more time wasneeded for suwari gels to attain maximum FT scores.This would appear to indicate that with setting at 25¡Cfor 30 min, orientation of the proteins to form the gelnetwork was only beginning, so the gel did not reachoptimum texture at this temperature in the given time.Beas (1989) reported very low rigidity values for thesetemperatures in hake actomyosin gels, which she inter-preted as unfolding of the myosinÏs a-helix structures inthe early stages of gel formation. At 40¡C longer settingaltered the network formed in the Ðrst 30 min, resultingin more brittle suwari gels. The increase of GS atO35¡C is time dependent and in pollack has beenassociated with the cross-linking which occurs amongmyosin heavy chains (MHC) at P40¡C, GS increaseswith respect to lower temperatures, however it decreaseswith time ; it has been suggested that this is connectedwith the predominance of protein-protein bondingthrough non-covalent bonds (Arai et al 1995).

T exture of suwari on kamaboko gels 475

Fig 2. Yield deformation (mm) of sardine suwari (S) andkamaboko (K) gels. Conditions and abbreviations as in Fig 1.

Fig 3. Yield strength (N) of sardine suwari (S) and kamaboko(K) gels. Conditions and abbreviations as in Fig 1.

In kamaboko gels set for 30 min there were no signiÐ-cant di†erences in GS between those set at 35¡C or40¡C. Gel strength was higher than in those set at 25¡Cat both setting temperatures. However, in samples setfor 60 min, the same tendency for GS to peak at 35¡Cobserved in suwari gels was also found in kamabokogels. All kawaboko gels scored maximum (FT\ 5) in thefolding test. There was scarcely any di†erence in theyield deformation of kamaboko gels with respect toeither time or temperature (Fig 2). In the kamaboko gelsset for 30 min at 25¡C and 35¡C, YD was greater thanin the equivalent suwari gels, whereas in samples set at40¡C YD was signiÐcantly lower in the kamaboko gels.In all samples set for 60 min, YD was equal to orgreater than that of suwari gels. Gel deformation devel-oped largely during setting and di†ered among thesuwari gels but seldom among the kamaboko gels.

The yield strength of kamaboko gels (Fig 3) exhibitedthe same tendency as in suwari gels, although the di†er-ences between lots set at the same temperature for dif-ferent times were not signiÐcant. In all cases YS wasmuch higher in kamaboko gels than in the correspond-ing suwari gels. This would indicate that at cookingtemperature, protein-protein bonds were establishedwhich strengthened the network previously formed bysetting.

It is generally accepted that the reactions causingthermally induced myosin gels to be formed are proteinunfolding, aggregation and formation of a gel network,and the rates of denaturation and aggregation associ-ated with gel matrix properties (Liu et al 1996). Suwarigels set at di†erent temperatures exhibited networkswith di†erent characteristics, which altered in the tran-sition to kamaboko, improving the texture of thenetwork initially formed. Heating of suwari gels toproduce kamaboko gels causes further aggregation of astructure formed in the setting stage, due probably tolarge-scale formation of disulÐde bridges and hydropho-bic interactions at high temperatures (Sano 1988 ; Niwa1992 ; Careche et al 1995). However, Arai et al (1995)consider that in set gels, intermolecular bonding atcooking temperatures consists preferentially of non-covalent bonds between the myosin heavy chainsand/or other components. In sardine surimi we havefound that the microstructure of gels as observed byscanning electron microscopy changes from a mainlyÐbrous image to a globular one when temperature ortime is increased (Alvarez et al 1992b ; Couso et al 1992).

Texture proÐle analysis

The TPA values for suwari and kamaboko gels areshown in Table 1.

HardnessThere were no signiÐcant di†erences in suwari gels set at25¡C or 35¡C for 30 min. Hardness decreased in gels set

476 C Alvarez, M T ejada

TABLE 1Texture proÐle analysis (TPA) of sardine suwari and kamaboko gels set at di†erent temperatures

(25, 35 and 40¡C) and times (30 or 60 min)a

T PA Setting temp Suwari gels Kamaboko gels(¡C)

30 min 60 min 30 min 60 min

Hardness (N) 25 10É571a 8É822a 43É821a 54É932a35 11É181a 9É631a 42É581a 51É972b40 7É581b 7É741b 46É181a 43É961c

Springiness (mm) 25 6É641a 7É051a 11É911a 12É912a35 7É851b 7É911b 12É321a 12É611a40 7É491b 7É241a 12É071a 11É212b

Cohesiveness 25 0É731a 0É752a 0É621a 0É682a35 0É841b 0É872b 0É681b 0É721a40 0É771c 0É722c 0É631a 0É621b

Gumminess (N) 25 7É731a 6É611a 27É061a 37É062a35 9É491b 8É381b 28É781a 37É172a40 5É861c 5É641c 28É801a 27É301b

Adhesiveness (g cm) 25 230É61a 171É12a 610É41a 645É91a35 149É91b 118É62b 498É71b 542É21b40 99É91c 102É91b 628É01a 558É71b

a Di†erent numbers in the same line, within each type of gel (suwari or kamaboko), indicate signiÐ-cant di†erences at di†erent setting times (30 or 60 min) (P\ 0É05). Di†erent letters in the samecolumn within each parameter, indicate signiÐcant di†erences at di†erent setting temperatures (25,35 or 40¡C) (P\ 0É05). Suwari gels : 30% compression ; kamaboko gels : 50% compression.

at 40¡C. The same tendency was found when setting for60 min, although hardness at 25¡C was lower withlonger setting. In kamaboko gels set for 30 min, hard-ness did not vary signiÐcantly with respect to settingtemperature. By prolonging setting to 60 min, harderkamaboko gels were obtained at 25¡C and 35¡C,although hardness of the corresponding suwari gels wasequal to or less than that of gels set for 30 min.

SpringinessSuwari gels set at the same temperature did not di†ersigniÐcantly with respect to setting time. Springinesswas signiÐcantly lower in gels set for 30 min at 25¡C,while with 60 min setting signiÐcant maximum valueswere attained at 35¡C. In kamaboko gels no di†erenceswere found among gels set for 30 min. Prolonging ofsetting to 60 min produced a signiÐcant increase ofspringiness in gels set at 25¡C and a decrease in thoseset at 40¡C. This di†erence was not found in the suwarigels.

CohesivenessThis parameter varied signiÐcantly in suwari gels withdi†erent setting times or temperature. Maximumcohesiveness was attained by setting at 35¡C for bothsetting times. With the longer time, cohesiveness

increased slightly in gels set at 25¡C and 35¡C anddecreased at 40¡C. In kamaboko gels, maximumcohesiveness was again attained by setting at 35¡C withboth times and increased at 25¡C with the longer settingtime. However, no di†erences were found in gels set at40¡C when setting time was prolonged.

GumminessSuwari gels set at the same temperature did not di†ersigniÐcantly with either setting time. Maximum valueswere attained at 35¡C and minimum at 40¡C. In kama-boko gels there were no signiÐcant di†erences amonggels set for 30 min ; values increased signiÐcantly at25¡C and 35¡C when setting was prolonged. Thisbehaviour was also observed in hardness. Temperature-dependent di†erences in gumminess of suwari gels werenulliÐed on heating at 90¡C to produce kamaboko gels.In the latter, gumminess increased when setting wasprolonged, except in the gel set at 40¡C, as occurredwith hardness.

AdhesivenessIn suwari gels, maximum adhesiveness was attained at25¡C with either setting time, adhesiveness decreasing assetting temperature increased. In gels set at 25¡C and

T exture of suwari on kamaboko gels 477

35¡C adhesiveness decreased when setting was prolong-ed, whereas at 40¡C it remained stable. In kamabokogels, no signiÐcant di†erences were found amonggels set at the same temperature when setting was pro-longed.

These results suggest that the suwari network formedat the lowest temperature (25¡C) requires more time inorder to ensure a gradual solÈgel transition process, sothat longer setting will improve the textural character-istics of the kamaboko network even although the di†er-ences between the suwari gels are smaller. Higher valuesof texture parameters in gels set for longer time at 25¡Chave been reported by Kim et al (1986) and Roussel andCheftel (1988). Although gels set at 25¡C had lower GSthan gels set at 35¡C, no di†erences were found in theTPA values for the two gels with the same setting time.The reason for this is probably that for the compressiontest the gel properties remain fairly constant until frac-ture, whereas breaking penetration values are lessdependent on sample deformation (Hamann and Mac-Donald 1992). The penetration (or puncture) test is thetest most commonly used by the surimi industry. Thecompression test measures the overall binding propertyof the gel material while the penetration test measuresthe degree of compactness or density, reÑecting di†erentgel properties (Lee and Chung 1989). The decrease inGS, YD, YS, FT springiness and cohesiveness observedin suwari gels upon prolonging setting at 40¡C may bedue to incipient destruction of the network, associatedwith the modori phenomenon. This was reÑected inlower GS and springiness of kamaboko gels as com-pared to gels set for 30 min and gels set for 60 min atlower temperatures. Modori has been related in sardineto heat coagulation of myoÐbrillar proteins (Sano 1988 ;Niwa 1992 ; Careche et al 1995). In sardine, such coagu-lation could also be connected with the sarcoplasmicproteins, which are more thermolabile than in demersalÐsh (Suzuki 1981) and are not completely removed withthe washing water in surimi production processes(Shimizu et al 1976). These proteins may a†ect networkformation if they precipitate when setting is performedat high temperature and longer time.

Modulus of rigidityPlot of the modulus of rigidity (G) vs internal tem-perature measured in sardine surimi sols prepared asdescribed, is shown in Fig 4. Rigidity data showed twoplateaux of high rigidity values (maxima between 20¡Cand 34¡C in the Ðrst and at temperatures over 66¡C inthe second), separated by a zone of minimum values(between 46¡C and 50¡C). In other batches of sardinesurimi, the curves have been found to change, exhibitingsharper peaks and displacement to a higher range oftemperature (Alvarez 1993).

The changes in the modulus of rigidity when tem-perature is increased have been associated with the tem-peratures at which the conformation of the myoÐbrillar

Fig 4. Modulus of rigidity (G)(kPa) of sardine surimi solduring heat processing (heating rate 1¡C min~1).

proteins (largely of myosin heavy chain) is altered whenthe gels are formed (Young et al 1992). They have alsobeen associated with the heat stability of each structuraldomain in the protein (Xiong 1994). Beas (1989) inter-preted the changes in rigidity values as unfolding of themyosinÏs a-helix, and this has been conÐrmed by Ishi-roshi et al (1979, 1983) and Yasui et al (1980) inmammal protein structures. The Ðrst plateau has beenassociated by Beas et al (1991) with myosin denatur-ation, while the changes occurring at higher tem-peratures have been related by these authors to actindenaturation. Lo et al (1991) reported di†erences inthermal transition of ordinary and dark muscle myosinsand related the changes in the low temperature zone tointeractions in the S-1 fragments and rod subfragments(ordinary muscle) and to rod subfragments (both muscletypes) in the high temperature zone. Sano (1988) report-ed that in carp natural actomyosin, at low temperaturesthe unfolding of the molecule and the formation ofaggregates proceeded gradually and occurred moreextensively when time or temperature was increased,resulting in more elastic gels. However, when the tem-perature was raised to 50¡C there was active disso-ciation of some myosin molecules from the actinÐlaments ; this led to a decrease in elasticity and anincrease in cross-linking in the partly broken gelmatrices. The stabilization of the structure formed bysetting when gels were heated to form kamaboko gelscaused an increase in storage modulus. Greater releaseof MHC in suwari and kamaboko gels set at 40¡C madefrom sardine surimi has been reported by Careche et al(1995).

Denaturation transition temperatures vary accordingto species (Howell et al 1991 ; Carballo et al 1992 ; Mon-tejano et al 1993), gel moisture (Alvarez 1993) and dry

478 C Alvarez, M T ejada

matter content (Lanier 1986 ; Hamann 1990 ; Alvarez etal 1995) and decrease when salt is added (Park andLanier 1989). Di†erences in rigidity have also beenrelated to intrinsic di†erences in the myosin and facilityof myosin release from the thick Ðlament (Young et al1992). For these reasons maximum rigidity valuesassociated with the optimum setting temperature tendto change (Wu et al 1985 ; Kim et al 1986 ; Sano 1988 ;Carballo et al 1992 ; Montejano et al 1993). Thetemperature-dependent changes occurring in myosinwhich cause a reduction in G may also be connectedwith intrinsic myosin thermostability. In Ðsh speciesthey have been related to the environmental tem-perature, since the peak temperature of Ðrst myosintransition measured by di†erential scanning calorimetrywas lower where the temperature of the habitat waslower (Howell et al 1991).

Water holding capacity

In suwari gels, WHC was lower in samples set at 40¡C,irrespective of setting time, and in samples set at 25¡Cfor 60 min (Fig 5). In kamaboko gels signiÐcant di†er-ences were only found in the lot set at 25¡C for 30 min,where values were lower than in all other lots, probablybecause setting at 25¡C for 30 min is too short a timefor the gel network to form a stable enough structure tohold water in the given measurement conditions.

Fig 5. Water holding capacity (WHC) (% retained water/totalwater) of sardine suwari (S) and kamaboko (K) gels. Conditions

and abbreviations as in Fig 1.

Taking into account all the results it was found thatin kamaboko gels, the best gels as measured by penetrat-ion were obtained by setting at 35¡C. The di†erencesnoted in the suwari gels with respect to setting timewere scarcely apparent in the kamaboko gels set at thistemperature, so that heating of suwari gels to producekamaboko gels appears to eliminate these di†erences. At25¡C, the improvement in suwari gels with prolongedsetting was again not apparent in kamaboko gels, whichwere also very inferior to the gels set at 35¡C. TheseÐndings suggest that the di†erences found in gels set at25¡C and 35¡C when temperature was increased are dueto alterations in the characteristics of gel fracture, giventhat once the matrix has been formed, fracture proper-ties are determined by matrix structure and intermolec-ular interactions, rupture occurring after a Ðne numberof Ðlaments break. This would indicate a change instrand structure, with di†erent intermolecular forcesconnecting the strands or less homogeneity of thematrix (Foegeding et al 1995). This is not apparent incompression measurements, which remain fairly con-stant until fracture (Hamann and MacDonald 1992).However, according to these authors when setting isprolonged, the increase in compression parametervalues would indicate that the network is more deform-able at either of the two temperatures.

In the gels set at 40¡C, the decrease in gel strength insuwari gels with longer setting was also observed inkamaboko gels. This decrease was not appreciable bycompression test, which suggests that the parametersrelating to fracture were the ones that changed most.This behaviour may be connected with changes inprotein as detected in the modulus of rigidity, where avery sharp drop beyond 35¡C was observed.

CONCLUSIONS

In view of these results we believe that the textural char-acteristics of kamaboko gels made with sardine surimiare largely determined by the characteristics of the pre-cursor suwari gels. In sardine surimi, 35¡C has provento be the best setting temperature for stability to ensurekamaboko gels with good textural characteristics atsetting times of 30 or 60 min. At 25¡C, prolongedsetting is needed to improve the network, while at 40¡Cprolonged setting weakens the suwari network formedin the Ðrst 30 min, leading to kamaboko gels withpoorer texture. Studies on the microstructure of suwariand kamaboko sardine gels are now in progress.

ACKNOWLEDGEMENT

This work has been partly Ðnanced by the projects EUFEPI 43-1-216 and Spanish CICYT ALI94-0954-C02-01.

T exture of suwari on kamaboko gels 479

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