Research ArticleImprovement of the Quality of Surimi Products withOverdrying Potato Starches

Tangfei Li,1 Jianxin Zhao,1,2,3 Jie Huang,1 Wenhai Zhang,4 Jianlian Huang,4

Daming Fan,1,2,3 and Hao Zhang1,3

1State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi 214122, China2National Engineering Research Center for Functional Food, Jiangnan University, Wuxi 214122, China3Collaborative Innovation Center of Food Safety and Quality Control in Jiangsu Province, Wuxi 214122, China4Fujian Anjoy Food Co. Ltd., Xiamen 361022, China

Correspondence should be addressed to Jianxin Zhao; jxzhao@jiangnan.edu.cn

Received 2 June 2017; Revised 17 September 2017; Accepted 1 October 2017; Published 29 October 2017

Academic Editor: Susana Fiszman

Copyright © 2017 Tangfei Li et al.This is an open access article distributed under theCreativeCommonsAttributionLicense, whichpermits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This study investigated the effect of overdrying potato starches on surimi products. The chemical composition of protein andchemical interactions, gel solubility, and protein conformation of the mixture of surimi gel protein, respectively, with 8% nativepotato starch and with 8% overdrying potato starch were investigated. The results show that the starch increased the insolubleprotein content. In terms of the chemical interactions, the overdrying potato starch increased the amount of hydrogen bond andnondisulfide covalent bond and decreased the amount of ionic bond, which might stabilize the network structure of protein gel.The analysis of Raman Spectroscopy shows that more 𝛼-helices turn into random coin structure after the starch was added, whichis conducive to higher strength and a better water retention ability of the surimi product.

1. Introduction

Starch is an important ingredient in surimi seafood productssince it would affect textural and physical characteristics ofsurimi fish protein gels. For instance, it can improve surimigel strength, modify texture, reduce cost [1], and improvefreeze-thaw stability [2]. The starch could replace a portionof the fish protein while maintaining desired gel propertiesdue to its water-holding ability [3].

For the mechanism of improving the quality of surimigel with the addition of starch, there are three theory modelswhich have been widely recognized: the cavity model raisedby Couso et al. [4] at 1998; the filling extrusion model raisedby Yang and Park [5]; and the pack and bundle effect modelraised by Kong et al. [6]. In general, these three models werefrom the physical point of view, explaining the relationshipbetween the starch and gel properties of surimi. However, theinfluence of starch on surimi gel protein function from thechemical perspective has not been reported yet.

In this study, compared with pure minced surimi gel, theeffects of starch on surimi gel protein were investigated under

the addition of 8% native and overdrying potato starch, inorder to provide a theoretical basis for the mechanism ofinteraction between starch and protein in surimi.

2. Materials and Methods

2.1. Materials. Native and overdrying potato starches wereobtained from France ROQUETTE. AA grade of silver carpsurimi was purchased from Hong hu Hong ye AquaticFood Co., Ltd. Polyvinyl chloride (PVC) plastic casing werepurchased from Longhai Ri sheng plastic color printingpackaging Co. Ltd.

2.2. Samples Preparation. Frozen surimi was thawed at 4∘Covernight and then diced and chopped for 3min. 3% salt wasadded to the surimi and it was cut for 2min until the surimipaste was fully decentralized. Then 8% potato starches wereadded and the mixture was mixed at a low speed for 3minuntil the slurrywas uniform (adjust the finalmoisture contentto 78%). The final intestinal samples were made according to

HindawiJournal of Food QualityVolume 2017, Article ID 1417856, 5 pageshttps://doi.org/10.1155/2017/1417856

2 Journal of Food Quality

simulated industrial formula. 8% fat, 5% ice egg white, 4%soy protein, 0.6% sugar, and 0.6% of the MSG were added tothe slurry, and then the mixture was mixed for 2min. Thisfish paste was chopped and mixed through the exhaust intoa diameter of 30mm plastic casing, made of approximately20 cm in length of intestine. The intestines were placed at40∘C water bath for 30min, the gelation; then at 90∘C for30min; then in ice water to cool the samples rapidly. Thesamples were stored at 4∘C overnight.

2.3. Determination of Protein Composition. According toParker’s method [7], the composition of protein was deter-mined as follows.

Determination of water soluble protein content: 100mLlow phosphate buffer (0.05mol/L KCl-0.01mol/L NaH

2PO4-

0.03mol/L Na2HPO4) was added to 10 g of chopped surimi

gel samples. The mixture was mixed and homogenized for2min and then stirred for 3 h and centrifuged at 4∘C,5000 r/min for 10min. Protein content in the supernatant wasmeasured by BCA method.

Determination of salt soluble protein content: 100mLhigh phosphate buffer solution (0.5mol/L KCl-0.01mol/LNaH2PO4-0.03mol/L Na

2HPO4) was added to 10 g chopped

surimi gel samples.Themixture wasmixed and homogenizedfor 2min and then stirred for 3 h and centrifuged at 4∘C,5000 r/min for 10min. Protein content in the supernatant wasmeasured by BCA method.

Determination of insoluble protein content: themeasuredtotal protein in surimi gel (crude protein) was subtracted bythe content of water soluble and salt soluble protein content.

2.4. Determination of Chemical Forces. 4 g minced fishsausage sample was, respectively, added to 20mL of0.05mol/L NaCl (S1), 0.6mol/L NaCl (S2), 0.6mol/LNaCl + 1.5mol/L urea (S3), 0.6mol/L NaCl + 8mol/Lurea (S4), and 0.6mol/L NaCl + 8mol/L urea + 0.5mol/Lbeta mercaptoethanol (S5). The mixture was mixed andhomogenized for 2min. The homogeneous liquid wascentrifuged 20000𝑔 for 15min [8]. The protein in thesupernatant was determined by Lowry method. Thedifferences in protein dissolved in S2 and S1 solutions saidthe contribution of ionic bond, the differences in S3 andS2 solutions indicated a hydrogen bond contribution, thedifferences dissolved in S4 and S3 solutions indicated thecontribution of hydrophobic interactions, and the differenceof protein content dissolved in S4 and S5 solutions indicateddisulfide bond contribution [9]. All results were expressedas the percentage of protein content accounting for the totalamount of protein.

2.5. Determination of Solubility of Gel. 20mL 20mmol/L wasadded to 1 g chopped surimi gel sample, pH 8.0 in Tris-HClbuffer solution, and mixed and homogenized for 2min. Thebuffer contains 1% (w/v) SDS, 8mol/Lurea and 2% (v/v) 𝛽-mercaptoethanol. The mixed solution was heated at 100∘Cfor 2min and centrifuged at 10,000𝑔 for 30min after stirringat room temperature for 4 h. After centrifugation, 50% (m/v)trichloroacetic acid (TCA) was added in 10mL supernatant

and the protein was precipitated. Mixing liquid was storedat 4∘C for 18 h and then centrifuged at 10,000𝑔 for 30min.Precipitation dissolved in 30mol/L NaOH 0.5mL after wash-ing with 10% (m/v) concentration of TCA. Lowry methodwas used to determine protein content. The dissolution ratewas expressed as the percentage of total protein content ofthe protein in the solvent [10]. Total protein content wasmeasured by the amount of protein dissolved in 0.5mol/LNaOH of surimi gel.

2.6. FT-Raman Spectroscopic Analysis. The sliced gel sampleswere stick to a layer of foil glass slide and placed on theobject loading table of Raman Spectroscopy. The scanningrange was from 300 to 3800 cm−1 [11]. Income spectrum forbaseline correction with a benzene ring in 1003 ± 1 cm−1 ringvibration (due to the little microenvironmental impact) is thenormalized spectra within standard [12]. Peak Fit softwarewas used for original spectrum curve fitting of amide I band,and the overlap in different bands was completely resolved.The percent of the protein secondary structure was calculatedby the integral area.

2.7. Statistical Analysis. All measurements were conducted atleast three times. The least significant difference (LSD) at 5%was applied to define the significant difference. All analyseswere performed using SPSS software v 19.0.

3. Results and Discussion

3.1. Protein Composition. Due to the presence of starch in thestarch-surimi system, the total protein (TP) contents wouldbe different among samples of CON (control, i.e., pure surimigel), NPS (surimi gel with native potato starch), and LMPS(surimi gel with overdrying potato starch). Therefore, thetotal protein contents of surimi gel samples were first deter-mined. The water soluble protein (WSP), salt soluble protein(SSP), and insoluble protein content (ISP) are expressedas the fraction accounting for the total amount of protein(Table 1). It showed that potato starch had a significant effecton surimi gel protein composition (𝑃 < 0.05). Solubleand salt soluble protein contents of LMPS were significantlylower than those of CON and NPS, while the insolubleprotein content of LMPS was significantly higher. It is ofnote that the surimi gel formation is essentially a process ofsalt soluble protein crosslink and then gradually convertedinto the insoluble protein [11]. Therefore, we proposed thatthe presence of overdrying potato starch could promote thecrosslink formation of salt soluble protein in the surimi gel,thus enhancing the quality of the gel.

3.2. Chemical Forces. The network structure in the surimigel system is mainly maintained through the interactionsamong and within protein molecules, such as chemicalbonds, ionic bonds, hydrogen bond, hydrophobic interaction,and covalent bonding [13] (Table 2). It can be seen fromTable 2 that the potato starch has a significant effect on theformation of chemical interactions in the surimi gel proteins(𝑃 < 0.05).

Journal of Food Quality 3

Table 1: Protein composition of surimi gel samples.

Sample CON 8% NPS 8% LMPSTP (%) 12.20 ± 0.03 10.92 ± 0.09 10.88 ± 0.05WSP (%) 5.09 ± 0.00 4.63 ± 0.04 4.03 ± 0.02SSP (%) 5.57 ± 0.03 4.75 ± 0.00 4.36 ± 0.01ISP (%) 89.34 ± 0.00 90.62 ± 0.02 91.61 ± 0.02CON (control, i.e., pure surimi gel), NPS (surimi gel with native potato starch), and LMPS (surimi gel with low-moisture potato starch).

Table 2: Chemical forces of surimi gel samples.

Sample CON 8% NPS 8% LMPSIonic bond (%) 1.14 ± 0.03 0.99 ± 0.02 0.91 ± 0.01Hydrogen bond (%) 1.79 ± 0.03 2.19 ± 0.02 2.93 ± 0.03Hydrophobic interaction (%) 47.84 ± 0.04 28.68 ± 0.00 28.51 ± 0.05Disulfide bond (%) 27.62 ± 0.07 12.27 ± 0.02 18.47 ± 0.06CON (control, i.e., pure surimi gel), NPS (surimi gel with native potato starch), and LMPS (surimi gel with low-moisture potato starch).

There is a large amount of ionic bonds in the frozensurimi, thus salt ions are generally needed to break the ionicbond in order to disperse the protein, and then the dispersedprotein could form the gel with elastic structure after heattreatment [14]. We found that the ionic bond was reducedin our starch-surimi gel systems, which may be becausethe presence of the starch blocks the formation of ionicbond between and within proteins. It could be concludedthat the potato starch is beneficial to the elasticity of thesurimi gel. Hydrogen bonds in surimi gel play an importantrole in the stability of the bound water and increase thestrength of surimi gel during the cooling process [13]. Table 2shows that the potato starch especially the overdrying starchsignificantly increased the amount of hydrogen bonds in thesurimi protein (𝑃 < 0.05).

Thehydrophobic sites in surimi proteinwould be exposedin the water environment after heat treatment. In orderto maintain the stability of the thermodynamic system,the hydrophobic interaction is enhanced, resulting in theaggregation of protein to forma gel network [13]. In this study,the hydrophobic interactions between proteins significantlydecreased (𝑃 < 0.05) after the adding of potato starch.The interaction between the starch and the surroundingwater may change the water status around the proteins, thusaffecting the hydrophobic interactions within the surimi gelsystems.

When the heating temperature is higher than 40∘C,disulfide bonds are thought to be the main covalent bondsthat can promote the formation of protein gel [15]. Comparedwith the pure surimi system, the amount of disulfide bondswas significantly reduced in native starch-surimi system (𝑃 <0.05). However, the amount of disulfide bonds after addingthe overdrying potato starch was higher than that in thenative starch-surimi system. It indicates that such negativeeffect on the formation of disulfide bonds induced by thepotato starch might be affected by the structure of starchgranules.

3.3. Solubility of Gel. The solvent containing SDS, urea, andbeta mercaptoethanol is usually used to dissolve nondisulfidecovalent bonds in protein [16]. Therefore, the solubility ofsurimi gel refers to the formation of nondisulfide covalentbond that is also involved in one of the main chemicalinteractions to form surimi gel network structure [11]. Asseen in Figure 1, the presence of starch especially overdryingpotato starch significantly reduced the surimi gel dissolu-tion rate (𝑃 < 0.05), indicating that overdrying starchsignificantly increased the amount of nondisulfide covalentbonds. Presumably, starch granules absorbed water in theheating process; therefore the contents of protein withinthe continuous phase and endogenous glutamine transferenzyme (TGase) were increased.

3.4. Protein Conformation. Raman Spectroscopy (Figure 2)can be used to investigate intermolecular interactions amongproteinmolecules: it could provide relative intensity informa-tion about amino acid side chains, peptides, and the vibrationfrequency of the polysaccharide backbone.

The Raman spectrum band within 1600∼1700 cm−1 iscalled the amide I band, which gives information about theprotein secondary structure. Specifically, the spectra of thebands of 1650∼1660, 1665∼1680, and 1660∼1665 cm−1 rangesare, respectively, corresponding to 𝛼-helix, 𝛽-sheet, andrandom coil of the protein.The band peaks of CON,NPS, andLMPS were located in 1653 cm−1 and 1667 cm−1, in 1654 cm−1and 1662 cm−1, and in 1656 cm−1 and 1664 cm−1. It can beseen that the addition of two kinds of starchmakes a blue shiftof the characteristic peaks of the helix structure, indicating adecrease of 𝛼-helix [17]. Liu et al. claimed the reason why theamount of 𝛼-helix in silver carp surimi decreased with theformation of the gel structure was the transition of 𝛼-helixinto random coil structure [11] (Table 3). Table 3 shows thequantitative analysis of the protein secondary structure in theamide I band, which reports that the overdrying potato starchhas a significant influence on the transition of 𝛼-helix intorandom coil structure: more 𝛼-helices were transformed intorandom coils, promoting the aggregation and interaction of

4 Journal of Food Quality

Table 3: Secondary protein structure content of Amide I.

Sample Content (%)Alpha helix Beta folding Beta turn Random coil

CON 30.7 ± 0.6a 34.4 ± 0.9a 9.4 ± 0.3a 25.5 ± 0.1c

8% NPS 28.4 ± 0.1b 35.6 ± 0.5a 8.5 ± 0.6b 27.5 ± 0.4b

8% LMPS 25.4 ± 0.7c 25.0 ± 1.1b 7.9 ± 0.4b 41.7 ± 0.8a

CON (control, i.e., pure surimi gel), NPS (surimi gel with native potato starch), and LMPS (surimi gel with low-moisture potato starch). Values with differentletters within a column indicate statistically significant differences (P > 0.05).

CON 8% NPS 8% LMPS

Solu

bilit

y (%

)

34

35

36

37

38

39

40

41

Figure 1: The solubility of surimi gel. CON (control, i.e., pure surimi gel), NPS (surimi gel with native potato starch), and LMPS (surimi gelwith low-moisture potato starch).

Rela

tive i

nten

sity

CON

8% NPS

8% LMPS

Rela

tive i

nten

sity

CON

8% NPS

8% LMPS

200018001600140012001000800600400 3800360034003200300028002600240022002000

Wave number (cＧ−1) Wave number (cＧ−1)

Figure 2:The Raman spectra of surimi gel. CON (control, i.e., pure surimi gel), NPS (surimi gel with native potato starch), and LMPS (surimigel with low-moisture potato starch).

protein molecules; therefore the starch seems to render thenetwork of surimi gel more stable.

In terms of the range of 3100∼3500 cm−1, the Ramanspectrum peak refers to the stretching movement of O-H,which is related to the intermolecular vibration of watermolecules bonded with hydrogen bond [18]. In this study, theO-H stretching band peaks of CON, NPS, and LMPS werelocated in 3280, 3277, and 3274 cm−1, and the correspondingstrength values were 0.76, 0.84, and 0.89, respectively. Thedecrease in thewave number of these peaks implies a strongerhydrogen bondwithwater, and a higher strength value revealsa larger amount of bound water molecules [12, 19]. Hence,potato starch could improve water binding and retentionability of the surimi gel, which is conducive to the formation

of the gel matrix during the heating process. The effect ofoverdrying potato starch seems more notable.

4. Conclusions

The overdrying potato starch is proved to improve propertiesof surimi gel. It promoted the formation of insoluble protein,decreased the amount of ionic bonds, and increased that ofnondisulfide covalent bonds and hydrophobic interaction,which would facilitate the formation of gel network structure.The data about protein conformation also confirms thesepositive effects of potato starch on the water binding andretention ability of surimi gel. Currently, because of thecomplex food system and pretreatment, it is difficult to

Journal of Food Quality 5

use small interactions such as 𝜋-𝜋 stack to explain theimprovement of the properties of surimi gel.

Additional Points

Practical Applications. The overdrying potato starch canimprove properties of surimi gel, as it promoted the for-mation of insoluble protein, decreased the amount of ionicbonds, and increased that of nondisulfide covalent bondsand hydrophobic interaction. Thus, potato starch, especiallyoverdrying potato starch, can be used to improve the qualityof surimi products.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Acknowledgments

This research was financially supported by the “Six TalentPeak” high-level talent project of Jiangsu Province (2015-NY-008), the Teaching and Researching Joint InnovationFunds of Jiangsu Province (Grant no. BY2015019-05), and theprogram of “Collaborative Innovation Center of Food Safetyand Quality Control in Jiangsu Province.”

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