This study investigated the effect of overdrying potato starches on surimi products. The chemical composition of protein and chemical interactions, gel solubility, and protein conformation of the mixture of surimi gel protein, respectively, with 8% native potato starch and with 8% overdrying potato starch were investigated. The results show that the starch increased the insoluble protein content. In terms of the chemical interactions, the overdrying potato starch increased the amount of hydrogen bond and nondisulfide 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
Starch is an important ingredient in surimi seafood products since it would affect textural and physical characteristics of surimi fish protein gels. For instance, it can improve surimi gel strength, modify texture, reduce cost [
For the mechanism of improving the quality of surimi gel with the addition of starch, there are three theory models which have been widely recognized: the cavity model raised by Couso et al. [
In this study, compared with pure minced surimi gel, the effects of starch on surimi gel protein were investigated under the addition of 8% native and overdrying potato starch, in order to provide a theoretical basis for the mechanism of interaction between starch and protein in surimi.
Native and overdrying potato starches were obtained from France ROQUETTE. AA grade of silver carp surimi was purchased from Hong hu Hong ye Aquatic Food Co., Ltd. Polyvinyl chloride (PVC) plastic casing were purchased from Longhai Ri sheng plastic color printing packaging Co. Ltd.
Frozen surimi was thawed at 4°C overnight and then diced and chopped for 3 min. 3% salt was added to the surimi and it was cut for 2 min until the surimi paste was fully decentralized. Then 8% potato starches were added and the mixture was mixed at a low speed for 3 min until the slurry was uniform (adjust the final moisture content to 78%). The final intestinal samples were made according to simulated industrial formula. 8% fat, 5% ice egg white, 4% soy protein, 0.6% sugar, and 0.6% of the MSG were added to the slurry, and then the mixture was mixed for 2 min. This fish paste was chopped and mixed through the exhaust into a diameter of 30 mm plastic casing, made of approximately 20 cm in length of intestine. The intestines were placed at 40°C water bath for 30 min, the gelation; then at 90°C for 30 min; then in ice water to cool the samples rapidly. The samples were stored at 4°C overnight.
According to Parker’s method [
Determination of water soluble protein content: 100 mL low phosphate buffer (0.05 mol/L KCl-0.01 mol/L NaH2PO4-0.03 mol/L Na2HPO4) was added to 10 g of chopped surimi gel samples. The mixture was mixed and homogenized for 2 min and then stirred for 3 h and centrifuged at 4°C, 5000 r/min for 10 min. Protein content in the supernatant was measured by BCA method.
Determination of salt soluble protein content: 100 mL high phosphate buffer solution (0.5 mol/L KCl-0.01 mol/L NaH2PO4-0.03 mol/L Na2HPO4) was added to 10 g chopped surimi gel samples. The mixture was mixed and homogenized for 2 min and then stirred for 3 h and centrifuged at 4°C, 5000 r/min for 10 min. Protein content in the supernatant was measured by BCA method.
Determination of insoluble protein content: the measured total protein in surimi gel (crude protein) was subtracted by the content of water soluble and salt soluble protein content.
4 g minced fish sausage sample was, respectively, added to 20 mL of 0.05 mol/L NaCl (S1), 0.6 mol/L NaCl (S2), 0.6 mol/L NaCl + 1.5 mol/L urea (S3), 0.6 mol/L NaCl + 8 mol/L urea (S4), and 0.6 mol/L NaCl + 8 mol/L urea + 0.5 mol/L beta mercaptoethanol (S5). The mixture was mixed and homogenized for 2 min. The homogeneous liquid was centrifuged
20 mL 20 mmol/L was added to 1 g chopped surimi gel sample, pH 8.0 in Tris-HCl buffer solution, and mixed and homogenized for 2 min. The buffer contains 1% (w/v) SDS, 8 mol/Lurea and 2% (v/v)
The sliced gel samples were stick to a layer of foil glass slide and placed on the object loading table of Raman Spectroscopy. The scanning range was from 300 to 3800 cm−1 [
All measurements were conducted at least three times. The least significant difference (LSD) at 5% was applied to define the significant difference. All analyses were performed using SPSS software v 19.0.
Due to the presence of starch in the starch-surimi system, the total protein (TP) contents would be different among samples of CON (control, i.e., pure surimi gel), NPS (surimi gel with native potato starch), and LMPS (surimi gel with overdrying potato starch). Therefore, the total protein contents of surimi gel samples were first determined. The water soluble protein (WSP), salt soluble protein (SSP), and insoluble protein content (ISP) are expressed as the fraction accounting for the total amount of protein (Table
Protein composition of surimi gel samples.
Sample | CON | 8% NPS | 8% LMPS |
---|---|---|---|
TP (%) | 12.20 ± 0.03 | 10.92 ± 0.09 | 10.88 ± 0.05 |
WSP (%) | 5.09 ± 0.00 | 4.63 ± 0.04 | 4.03 ± 0.02 |
SSP (%) | 5.57 ± 0.03 | 4.75 ± 0.00 | 4.36 ± 0.01 |
ISP (%) | 89.34 ± 0.00 | 90.62 ± 0.02 | 91.61 ± 0.02 |
CON (control, i.e., pure surimi gel), NPS (surimi gel with native potato starch), and LMPS (surimi gel with low-moisture potato starch).
The network structure in the surimi gel system is mainly maintained through the interactions among and within protein molecules, such as chemical bonds, ionic bonds, hydrogen bond, hydrophobic interaction, and covalent bonding [
Chemical forces of surimi gel samples.
Sample | CON | 8% NPS | 8% LMPS |
---|---|---|---|
Ionic bond (%) | 1.14 ± 0.03 | 0.99 ± 0.02 | 0.91 ± 0.01 |
Hydrogen bond (%) | 1.79 ± 0.03 | 2.19 ± 0.02 | 2.93 ± 0.03 |
Hydrophobic interaction (%) | 47.84 ± 0.04 | 28.68 ± 0.00 | 28.51 ± 0.05 |
Disulfide bond (%) | 27.62 ± 0.07 | 12.27 ± 0.02 | 18.47 ± 0.06 |
CON (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 frozen surimi, thus salt ions are generally needed to break the ionic bond in order to disperse the protein, and then the dispersed protein could form the gel with elastic structure after heat treatment [
The hydrophobic sites in surimi protein would be exposed in the water environment after heat treatment. In order to maintain the stability of the thermodynamic system, the hydrophobic interaction is enhanced, resulting in the aggregation of protein to form a gel network [
When the heating temperature is higher than 40°C, disulfide bonds are thought to be the main covalent bonds that can promote the formation of protein gel [
The solvent containing SDS, urea, and beta mercaptoethanol is usually used to dissolve nondisulfide covalent bonds in protein [
The solubility of surimi gel. CON (control, i.e., pure surimi gel), NPS (surimi gel with native potato starch), and LMPS (surimi gel with low-moisture potato starch).
Raman Spectroscopy (Figure
The Raman spectra of surimi gel. CON (control, i.e., pure surimi gel), NPS (surimi gel with native potato starch), and LMPS (surimi gel with low-moisture potato starch).
The Raman spectrum band within 1600~1700 cm−1 is called the amide I band, which gives information about the protein secondary structure. Specifically, the spectra of the bands of 1650~1660, 1665~1680, and 1660~1665 cm−1 ranges are, respectively, corresponding to
Secondary protein structure content of Amide I.
Sample | Content (%) | |||
---|---|---|---|---|
Alpha helix | Beta folding | Beta turn | Random coil | |
CON | 30.7 ± 0.6 |
34.4 ± 0.9 |
9.4 ± 0.3 |
25.5 ± 0.1 |
8% NPS | 28.4 ± 0.1 |
35.6 ± 0.5 |
8.5 ± 0.6 |
27.5 ± 0.4 |
8% LMPS | 25.4 ± 0.7 |
25.0 ± 1.1 |
7.9 ± 0.4 |
41.7 ± 0.8 |
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 different letters within a column indicate statistically significant differences (
In terms of the range of 3100~3500 cm−1, the Raman spectrum peak refers to the stretching movement of O-H, which is related to the intermolecular vibration of water molecules bonded with hydrogen bond [
The overdrying potato starch is proved to improve properties of surimi gel. It promoted the formation of insoluble protein, decreased the amount of ionic bonds, and increased that of nondisulfide covalent bonds and hydrophobic interaction, which would facilitate the formation of gel network structure. The data about protein conformation also confirms these positive effects of potato starch on the water binding and retention ability of surimi gel. Currently, because of the complex food system and pretreatment, it is difficult to use small interactions such as
The authors declare that they have no conflicts of interest.
This research was financially supported by the “Six Talent Peak” high-level talent project of Jiangsu Province (2015-NY-008), the Teaching and Researching Joint Innovation Funds of Jiangsu Province (Grant no. BY2015019-05), and the program of “Collaborative Innovation Center of Food Safety and Quality Control in Jiangsu Province.”