Changes in whiteness values
All the UM, CWS and CWS gels exhibited a significant difference between lightness (L*), redness (a*), yellowness (b*) values. The whiteness value exhibited a significant difference between UM, CWS and CWS gel (p<0.05) and the highest whiteness value found for gels prepared from CWS. UM showing lightness value of 39.08 which indicates the presence of myoglobin and other pigments. On the other hand CWS which was washed 3 times showing improved lightness value of 61.07 and redness value of -1.37. Priyadarshini et al., (2017)
reported that the lightness value of surimi from tilapia sausage after cooking was 72.4 and the results obtained in the present investigation also showed the similar trend (Table 1). The whiteness index value of CWS was 61.45 which shows the potential of using as an alternative raw material for threadfin bream surimi which has whiteness value of 70.05 (Santana et al., 2015).
Changes in gel strength values
Table 1: Whiteness value of UM, CWS and CWS gel.
For estimating the textural property of any surimi related products breaking force is one of the important parameter effectively analyze the quality of sausage. The breaking force and distance to rupture values of UM and CWS gels were about 69.94±4.31 and 191.06±6.26 g.cm (p<0.05) respectively (Table 2). The gel strength of UM was lesser than that of CWS gel which could be explained by the fact that sarcoplasmic protein in UM will coagulate by the addition of salt during the heat setting and does not take a part in the configuration of network structure whereas for CWS gel, the formation of sol takes place with addition of salt at 2.5% and ample amount of water leading to solubilisation of myofibrillar protein, which subsequently turns into an elastic gel by heating process (Lee, 1992)
Changes in texture profile values (TPA)
Table 2: Determination of gel strength of UM and CWS gel.
Texture profile analysis of CWS gel shown in Table 3. Hardness value of CWS gel shows maximum compression and deformations values (46.48 N) and was within the range (14,520-44,180 g mm, respectively) as previously reported for Malaysian commercial fish sausage (Huda et al., 2012).
Chewiness value of CWS gel was higher which indicates more the elasticity of the product. The cohesiveness value of CWS gel samples were 0.76 N and low cohesiveness value reported might due to the addition of water and ice during sausage preparation which makes internal arrangements softer and less fragile (Dincer et al., 2017).
Springiness value of 0.90 mm was found for CWS gels and represents how the sausage recovered during compression tests by TPA analyzer, mainly due to the myosin contributing to the elasticity of the sausage which is the important factor in the development of kamaboko gel network (Chan et al., 1995).
Analyzing the protein pattern of UM, CWS and CWS gel
Table 3: Texture profile analysis (TPA).
Protein distribution patterns of UM, CWS and CWS gels are shown in Fig 1. CWS showing clear myosin heavy chains because of augmentation of myofibrillar proteins by multiple washing methods exhibited. The visibility of sarcoplasmic proteins in gel matrix is less, indicating the successful removal of sarcoplasmic proteins during washing cycles. Heavy chain myosin bands concentration decreased in heat induced CWS gels, compared to that observed in the UM and CWS due to polymerization of protein takes place during setting signifying a strong gel matrix. However, minimal changes in actin were observed in UM, CWS and CWS gel because it could not be polymerized during gelation efficiently and it overcomes proteolysis effect (Balange and Benjakul, 2009)
Changes in the fourier transform infrared spectra of UM, CWS and CWS gel
Fig 1: Fourier transform infrared (FTIR) spectroscopy of UM, CWS and CWS gel. UM-Unwashed mince, CWS-Conventional washed surimi.
FTIR analytical technique extensively used for figuring the protein secondary structure. Fig 2 shows a distinctive FTIR spectrum obtained from UM, CWS and their respective CWS gel ranging from 4000 to 400 cm-1. The distinctive central band for CWS at 1665.34 cm-1 determined for β-turn structures, which indicating a more packed structure and central bands for UM at 1688.07 cm-1 indicates more β-turn structures followed by CWS gel prepared from surimi possess central bands at 1653.20 cm-1. The disappearance β-helix structure desired the formation of more β-sheet and β-turn as an ordered network due to heating of protein structures which is unfolded. Partial unfolding of a secondary structure for UM during solubilisation process leads to high band intensity having more random/loop arrangements (Zhou et al., 2014).
The β-sheet in CWS gels prepared from CWS, exhibit proper gelation after setting which coincides with the ideal gel strength (Table 2).
Microstructure of UM, CWS and CWS gel
Fig 2: Protein pattern of UM, CWS and CWS gel. UM- Unwashed mince, CWS- Conventional washed surimi.
The SEM micrographs of the surface layers of the thermal gels at 10000 x magnification are shown in Fig 3. The UM shows slack and grainy surface with various size intervals and imprecise network structure. Pores of various sizes in UM might due to the lower pH formed which leads the myosin to form a coarse and disordered gel network (Liu et al., 2010).
The firmness and devoid of gaps in CWS might be attributed due to hydrophobic interactions which forms a three dimensional network structure with the reactive group of solubilized surimi protein (Weng and Zheng, 2015)
. In case of CWS gel, more particulate structure was observed and this might be due salt present in the gel sample which is beneficial to soften and swell the myofibrillar proteins, fostering protein–protein cross-linking leads to uniform and denser network (Kang et al., 2015).
Fig 3: Microstructure of UM, CWS and CWS gel UM- Unwashed mince, CWS- Conventional washed surimi.