Effects of Bundle Type and Substitution with Spent Laying Hen Surimi on Quality Characteristics of Imitation Crabsticks

AP surimi was obtained from Hansung Food Co. Ltd. (Korea), and SH surimi was prepared using the pH method described by Hur et al. (2011) with modification. In brief, SH breast (pectorals major m.) was purchased from a commercial slaughter house and its external fat and skin were removed from the muscle. SH muscles were ground through a 3-mm-diameter orifice using a grinder (M-12S, Hankook Fujee, Korea) and homogenized with a Polytron homogenizer (IKA Labortechnik T25-B, Germany) with six volume of water at 8,000 rpm for 30 s. The homogenates were filtered through a 1-mm-mesh metal screen to remove connective tissue and then adjusted to pH 11.0 using 1 N NaOH. The slurry was centrifuged at 10,000 g for 25 min, and the top and bottom layers were discarded. The middle layer was taken, adjusted to pH 5.0 using 1 N HCl, and centrifuged at 10,000 g for 25 min. The sediment was obtained and its pH and water content were adjusted to 7.0 and 80%, respectively. The SH surimi was mixed with 5% sorbitol and 0.3% phosphate, packed in a polyethylene bag, frozen at −70°C, and stored at −20°C for two wk.

Imitation crabsticks were prepared using the manufacturing process shown in Fig. 1. Four batches (two for AP and two for SH per each batch) were prepared. SH treatments were carried out by substituting 20% AP surimi with SH surimi, as presented in Table 1. After slitting the baked sample sheet, the sample fiber was processed as either SB or DB type (the latter was done by treating with additional processes such as diagonal cutting, turning, and secondary bundling at 60 degree angle). Imitation crabsticks were vacuum-packed in plastic bags and stored at 0°C for 6 wk. Each of the four batches was collected on three different days (12 batches total) for analyses.

Fig. 1. Manufacturing process of crabsticks.

Download Original Figure

The pH values were measured in 5.0 g of sample homogenates in 45 mL of distilled water using a pH meter (Model 420A, Orion, USA)

Color values (CIE L* [lightness], a* [redness], and b* [yellowness]) were measured using a Minolta colorimeter (CR-400, Minolta Co., Japan), which was standardized with a white plate (Y = 93.5, x = 0.3132, and y = 0.3198). Whiteness was determined using the following: L* − 3b*, as described by Park (1994).

Gel characteristics were determined according to the method described by Phatcharat et al. (2006). In brief, samples were equilibrated at room temperature for 20 min, and five cylindrical pieces (3.5 cm wide and 3.0 cm thick) were prepared. Thereafter, the breaking force, deformation, gel strength, and jelly strength were measured using a texture analyzer (EZ-test, Shimadzu, Japan) equipped with a cylindrical plunger (5 mm diameter and 66 mm/min depression speed). Samples for shear force were prepared by using a 1.0-cm-diameter core, and shear force was determined using an Instron Universal Testing Machine (Model 3343, Instron Corp., USA) equipped with a Warner-Bratzler shearing device (100 mm/min crosshead speed).

Lipids from the samples were extracted using a chloroform-methanol (2:1 by volume) solution, as described by Folch et al. (1957). Fatty acid methyl esters were prepared from the lipid extracts by saponification with 1.0 N-methanolic NaOH followed by methylation with 14% boron trifluoride in methanol. The separation of fatty acid methyl esters was performed using a gas chromatography machine (6890N, Agilent Technologies Inc., USA) equipped with an SP-2560 column (100 m × 0.25 mm × 0.20 μm, Supelco, USA). Oven temperature was maintained at 140°C and then increased to a final temperature of 240°C at a rate of 4°C/min. The temperatures of the injector and detector were set at 240°C and 250°C, respectively. The flow rate for N₂ carrier gas was 50 mL/min. Each fatty acid was identified by comparing the retention time with the mixture of fatty acid methyl ester standards (FAME Mix CRM47885, Sigma-Aldrich Co., USA). Saturated fatty acid (SFA) was presented as the sum of C10:0, C12:0, C14:0, C16:0, C17:0, C18:0, and C20:0. Monounsaturated fatty acid (MUFA) was calculated as the sum of the compositions of C16:1n-7, C17:1, C18:1n-9, and C20:1n-9, whereas polyunsaturated fatty acid (PUFA) was calculated as the sum of the compositions of C18:2n-6, C18:3n-3, C20:3n-3, C20:4n-6, and C22:6n-3. Total unsaturated fatty acid (UFA) was calculated as the sum of MUFA and PUFA.

TBARS as a lipid oxidation were analyzed using the method described by Salih et al. (1987) with some modification. In brief, 5 g of sample was weighed in a 50-mL test tube and homogenized with 15 mL of distilled water. Thereafter, 2 mL of homogenate were transferred into another test tube and mixed with 100 μL of butylated hydroxyanisole (10% in ethanol) and 4 mL of 0.2 M thiobarbituric acid in 10% trichloroacetic acid. The mixture was incubated in boiling water for 15 min and then cooled in cold water for 10 min. After centrifugation at 2,000 g, the absorbance of supernatants was determined at 531 nm against a blank. A standard curve was prepared using a 1,1,3,3-tetraethoxypropane solution, and the TBARS value was presented as milligrams of malondialdehyde per kilogram of sample.

VBN analysis was conducted as a protein degradation value using the Pearson (1976) method with modification. In brief, 10 g of ground sample was taken into a beaker and homogenized with 90 mL distilled water. The homogenate was filtered through a Whatman No.1 paper and its volume was adjusted to 100 mL with distilled water. Thereafter, 10 mL of the filtrate and two drips of phenolphthalein indicator were placed in a flask, to which 3.5 mL of 20% NaOH was added. Steam distillate was collected in a flask containing 20 mL of 4% boric acid and two drips of indicator (methyl red/methylene blue, 2:1); this procedure was continued until 250 mL of distillate was collected. Titration was performed using 0.01 N HCl, and the VBN contents were presented in milligrams per 100 g of sample.

Sensory evaluation was performed using 9-point scale by six panelists from Gyeongnam National University of Science and Technology, Republic of Korea. The panelists were selected based on their frequency of consuming surimi-based products and experience in sensory evaluation of various meat products. One slice (1 cm thick and 5 cm in diameter) was cut into six pie-shaped wedges and presented to each of the panelists, who sat separately in their individual booth and were provided with distilled water and unsalted crackers to cleanse the palate between the samples. The panelists evaluated whiteness, flavor, tenderness, and overall acceptability using a nine point scale, in which 0 represented the least intense for each parameter and 9 represented the most intense for each parameter. Data for sensory evaluation were collected five times for each batch at 0, 2, 4, and 6 wk of cold storage.

The data for each measurement were collected from three plastic bags of each treatment and batch at 0, 2, 4 and 6 storage wk. The effects of SH surimi substitution and BT on quality of imitation crabsticks were analyzed using the SAS program (SAS, 2002). Two-way ANOVA (analysis of variance) was adopted to analyze the effects of SH surimi substitution and BT, separately and combined, on pH, color, gel characteristics, sensory evaluation, fatty acid compositions, and TBARS during the 6 wk of cold storage. The storage effect was also examined by ANOVA and t-test (fatty acid composition). Duncan’s multiple range tests were used to determine the statistical significance among the means at a 95% significant level.

The pH values of imitation crabsticks were not affected by SH substitution and BT at storage wk 0 (p<0.05), although BT effects were observed at other storage time points (p<0.01; Table 2). The pH at storage wk 0 was significantly lowest regardless of treatment (p<0.05). However, SH substitution did not affect pH during cold storage (p>0.05). The SH surimi was adjusted to pH 7.0, and 20% of AP surimi was substituted with SH surimi for making imitation crabsticks. The pH of SH substitution level did not affect the initial pH of imitation crabsticks. Moreover, phosphate among the additives played a main role in pH adjustment in the imitation crabsticks, as phosphate increases the pH value in the various processed products by binding its negative charges with positively charged groups of myofibrillar proteins (Athaillah and Park, 2016; Offer and Knight, 1988).

All color traits except for redness (CIE a*) were influenced by SH substitution throughout the cold storage (p<0.01), whereas BT effect and combined effect of SH and BT were found at 4 or 6 wk of storage (p<0.05; Table 3). Redness was slightly increased during storage regardless of treatment (p<0.05), whereas whiteness values of all samples were greatly increased (p<0.0001) with decreases in yellowness (CIE b*) (p<0.05) by 4 wk of storage. Chicken breast muscle has a relatively whiter color when compared with other chicken muscle and muscles from other animal species; this is because chicken breast muscle consists of white muscle fibers (type IIB) that contain low myoglobin content (Kim et al., 2008; Ordway and Garry, 2004). In our previous study, the myoglobin content was not different between AP imitation crabsticks and the SH-incorporated ones (Hur et al., 2011). Whiteness is one of the important quality traits in surimi-based products, including imitation crabsticks (Chen, 2002; Ochiai et al., 2001). Although redness did not differ between AP and SH crabsticks (p>0.05), low lightness (CIE L*) and high yellowness resulted in lower whiteness in SH than in AP crabsticks (p<0.01). Whiteness was not affected by BT at 2 wk of storage (p>0.05); however, DB treatment had offered lower whiteness than SB treatment at 4 (p<0.0001) and 6 (p<0.01) wk of storage. It seems that additional processes, including diagonal cutting, turning, and bundling at 60 degree angle influenced color changes in imitation crabsticks later in the storage period.

Table 4 presents the gel characteristics of the imitation crabsticks. SH substitution decreased breaking force and gel strength, resulting in a decrease in shear force throughout the storage period (p<0.05). Shear force was lower in DB than SB regardless of SH substitution (p<0.01). BT effects were mainly observed in deformation and jelly strength in addition to shear force. Furthermore, the SH and BT combination also affected these three characteristics. There was a similar trend for deformation and jelly strength: the highest values seen in SB treatment with SH substitution at initial storage (p<0.01), whereas the lowest values seen in DB treatment with SH substitution at 2 and 4 wk storage (p<0.01) among the treatments. However, the shear force was lowest in DB type imitation crabsticks substituted with SH, as expected, because of the different content and type of myofibrillar proteins, especially the myosin heavy chain between AP and SH. The myosin heavy chain is the main protein for the formation of surimi gel during heating along with a three-phase process of denaturation, unfolding, and polymerization (Chen et al., 1992; Kamath et al., 1992; Ogawa et al., 1993). Therefore, SH was found to deteriorate gel properties of imitation crabsticks. The BT effects on gel characteristics was different than the SH effects. Deformation and jelly strength were higher in SB than in DB at initial storage (p<0.01) regardless of SH. For SB treatment, jelly strength increased at mid storage period and decreased later during the storage (p<0.05). On the contrary, for DB treatment, this characteristics increased with the storage period (p<0.05). During the 6 wk of cold storage, most traits of gel characteristics increased regardless of treatment. However, shear force decreased in SB type with SH substitution with increase in the storage time (p<0.01). As mentioned above, high deformation and jelly strength at initial storage decreased due to the combination of SH and BT and, consequently, resulted in a shear force decreasing with storage time.

For lipid oxidation during cold storage, TBARS and fatty acid composition were investigated and the results are shown in Fig. 2 and Table 5, respectively. For lipid oxidation SH effects were noted at all storage wk (p<0.0001), whereas BT effects were observed only at 6 wk of storage (p<0.0001). The TBARS values of imitation crabsticks increased during the 6 wk of cold storage (p<0.05). AP, when compared with SH, had higher PUFA content at initial storage (p<0.01). The PUFA composition of AP (68.40% and 69.50%) decreased to 60.67% and 58.93% (p<0.01) and that of SH also decreased like AP, although the initial composition was lower than that of AP. However, the TBARS values were lower in SH than in AP throughout the cold storage. Our previous report (Jin et al., 2009) supports these results, and Ahn et al. (1993) also reported that lipid oxidation could be influenced by the differences in fat content and fatty acid composition. Moreover, PUFA is more susceptible to oxidation than MUFA and SFA. Like TBARS at 6 wk of storage, the BT effect on PUFA was observed at 6 wk of storage (p<0.01). DB treatment had significantly higher TBARS values (p<0.0001) and lower PUFA compositions (p<0.01) than SB treatment, although there were no differences at initial storage (p>0.05). These results indicate that more storage time-dependent lipid oxidation could occur in DB type imitation crabsticks than the SB type ones.

Fig. 2. Changes of TBARS of imitation crabsticks during 6 wk of cold storage.

Download Original Figure

VBN results showed a different trend than lipid oxidation (Table 6). SH and BT effects were observed at all storage weeks (p<0.05) and VBN increased with increase in storage time regardless of treatments (p<0.05). At storage week 0, combined effect of SH and BT was found (p<0.05); SB type imitation crabsticks with SH substitution had the highest VBN value, among all the treatments. These results did not agree with our previous study (Hur et al., 2011) where we observed no significant differences between imitation crabsticks made from AP and those from AP with SH substitution, regardless of SH preparation methods. Although the VBN value is an important reference index to evaluate freshness of meat as well as meat product (Castro et al., 2006; Rodtong et al., 2005) and protein degradation can be compared among the treatments with VBN values, the shelf-life of imitation crabsticks in the present study should be considered in light of lipid oxidation. The interesting finding of the opposite trends between lipid oxidation and protein degradation indicates that more specific studies are needed on their relationship and on the effects of BT and SH on shelf-life of imitation crabsticks.

SH substitution had effects only on sensory characteristics of color, tenderness, and overall acceptability at storage wk 0 (Table 7). At initial storage, the panels evaluated that imitation crabsticks with SH substitution were darker (high color value) and tougher than AP imitation crabsticks regardless of BT (p<0.05). Consequently, overall acceptability was significantly lower in SH than in AP crabsticks (p<0.0001). As presented in Tables 3 and 4, SH had poor color (low whiteness) and gel characteristics (low breaking force and gel strength) than AP. However, there were no significant effects of BT and combined SH and BT. Again, although color and gel characteristics of imitation crabsticks changed during cold storage, the storage did not affect sensory evaluation findings. Thus, 20% SH substitution and DB did not largely affect sensory characteristics of imitation crabsticks.