| Surimi is a kind of delicious fish product from fish meat after mincing and rinsing process. Traditional rinsing process always needs lots of water,and there is plenty of soluble protein in effluents,on one hand,it is very wasteful;on the other hand,it leads to serious environment problems.Therefore,to develop new water saving rinsing approaches is urgent to sustainable development of surimi industry. A new rinsing strategy was set up through combination using of soluble carboxymethyl chitosan(CBC),ozone solution,and ultrasound wave to rinse silver carp surimi. Its effects and mechanism were investigated in this paper. Main results were as follows:Na Cl condensation influnced surimi gel strenghth and surimi protein ingrients. Surimi gel strenghth increased with Na Cl condensation rising.Crude protein, water-soluble protein and salt-soluble protein showed first rising and then dropping of change. 0.5%Na Cl got higher salt-soluble protein of 10.13%, water-soluble protein of 4.31%. Surimi gel hardness also showed alike change,0.50%Na Cl had highest value of 1682 g(p<0.05).CBC(0.5%,1.0%,1.5%,2.0%,w/w) was used to rinse silver carp mince, Surimi gel strength increased with CBC condensation rising. 1.5%CBC got biggest chewiness value 1273 g,and adhesiveness value 1166 g. However, chewiness value and adhesiveness value decreased at 2.0%CBC.Ozone solution(0.5ppm,1.0ppm,1.5ppm,2.0ppm) was used to rinse silver carp mince, Surimi gel strength increased with ozone condensation rising. 2.0% ozone got biggest value 1698 g,and high adhesiveness value 1160 g was got at 1.5 ppm condenation(p<0.05).50W,100 W,150W and 200 W of ultrasound wave was used to treat silver carp mince,surimi yield reached biggest value 73.16%,and protein loss was lowest 11.83%.Surimi gel hardness increased with ultrasound wave power. chewiness value and adhesiveness value reached biggest 1283 g,1186 g,respectively.Then, a new water-saving rinsing process method of surimi was established using CBC/ozone/ultrasound combination treatment through orthogonal design.This new combination rinsing method included 2 times of washing,the first step adopted 1.5% CBC+1.5ppm ozone+150W ultrosond,rinsing period was 8 min(silver crap mince and rinsing liquor 1:5,w/w),the second step used 0.5% Na Cl to rinsing 8 min(1:5,w/w). The surimi product had almost equivalent gel strength to that from the traditional 3 times rinsing process,and surimi yield increased by 25%,whiteness was improved,water-consumption decreased by 33%.For investigating the action mechanisms of this new water-saving rinsing strategy, serine protease M-SP and S-SP were isolated and purified from myosin-bound protein and sarcoplasm from silver crap. Heat-stability,optimum temperature and p H of cathepsin B,L,M-SP and S-SP were investigated.and these cathepsins’ inactivation by ozone and ultrasound treatment was researched. The results showed that ozone and ultrasound wave exihibited outstanding inactivation effect on cathepsins.The changes of cathepsin B,L,M-SP,S-SP in silver carp mince during rinsing with Na Cl,CBC,ozone solution or ultrasound treatment were investigated. As 1.5% CBC was used to rinse fish mince,cathepsin B and L were 0.52u/mg and 1.03u/mg,respectively, S-SP was 3.96 u/mg. They increased by 8.33%,7.29% and 6.16%,respectively,with comparision to control group. CBC could prompt flocculation and raise surimi yield,while cathepsin increased. Cathepsin B,L and S-SP showed regular decline while ozone was used rinsing reagent,cathepsin B,L and S-SP were 0.47±0.01 u/g,1.08±0.06u/g and 3.79±0.01u/mg,respectively,being 13.0%,9.2% and 15%(p<0.01) lower than the blank group.These results were almost equivalent to those of the control group. 1.5% ozone had significant inhibitory effects on cathepsins. As 150 W ultrasonic wave was utilized to rinse silver carp mince for 8 min, cathepsin B,L and S-SP were 0.46 u/mg,1.02u/mg,and 3.89u/mg,respectively,which were close to those of the control group. Cathepsin dropped with ultrasonic power rising. Ultrasonic wave also played an important role in dropping cathepsin.For elucidating the action mechanisms of the new water-saving rinsing strategy,the differences of effects of ozone,ultrasonic wave and squeezing treatment on molecule surface characteristics and secondary structure of silver carp protein and cathepsin.Cathepsin L was taken as the respresentative and Fourier transform infrared spectroscopy(FTIR) was used to research the influences of ozone(concentration, treatment period),ultrasonic wave(power,treatment period), and squeezing dehydration(pressure,treatment period) on surface characteristics and secondary structure.Ozone had significant effects on the surface hydrophobicity of cathepsin L,as its concentration was 2.0ppm,the surface hydrophobicity were 4.21(silver carp protein) and 5.53(cathepsin L),that was 1.36 and 1.84 times of control group. Ozone had no significant effects on surface exposed –SH content of silver carp protein and cathepsin L.As 1.5ppm ozone was used to treat silver carp protein, α-helix of silver carp protein was 26.12%(dropping by 19.26%,in comparison with control p<0.01),β-sheet 42.13%,β-turn 27.07%,and random coil 4.68%(rinsing by 210.0%,p<0.01). α-helix contents dropped and random coil contents rised with treatment period prolonging within 3~12min,but both had no more changes in 15 min.As 1.5ppm ozone was utilized to treat cathepsin L, α-helix was 23.53%,dropping by 28.68% in comparision to control,and random coil was 7.04%,rising by 331.90%(p<0.01).Both of them had more changes with ozone treatment period prolonging, but no more changes were observed in 12~15min. comparing the differences of effects of ozone on silver carp protein and cathepsin L, we found that denaturation of cathepsin L was much more serious than silver carp protein.The surface hydrophobicity of silver carp protein and cathepsin L treatment with 150 W ultrasonic wave for 8 min were 5.64, 6.17, respectively,they were 1.84 and 2.04 times of control group. Ultrasonic wave had outstanding impacts on the secondary structure of silver carp protein and cathepsin L, α-helix contents dropping and random coil contents rising were main changes.Silver carp protein was treated with ultrasonic wave for 8min, α-helix content was 21.22%(dropping by 34.87%,in comparison with control,p<0.01), β-sheet and β-turn were 41.71% and 28.05%,respectively,random coil was 9.02%(rising by 53.77%.p<0.01). Cathepsin L was treated with similar ultrasonic wave condition, α-helix content was17.02%(dropping by 48.41%,p<0.01),random coil was 13.43%(rising by 723.93%,p<0.01). The ultrasonic wave had much more impacts on cathepsin L,no significant influences were found on surface hydrophobicity,surface exposed,-SH content,and secondary structure composition, while silver carp protein or cathepsin L was squeezed under 0~2.0MPa pressure.This study showed that the CBC/ozone/ultrasonic wave rinsing trategy could effectively increase surimi yield, decrease water consumption and reduce largely the amount of effluent and protein loss. Surimi product had desirable whiteness and gel strength. Its action mechanisms could be explained as follows:water-soluble CBC prompted fish protein’s flocculation,and improved gel strength of surimi because of its cohesive effects. Ozone improved color of surimi by decomposing pingments,ozone and ultrasonic wave remarkablely changed the surface hydrophobicity and secondary structure composition of cathepsin,including significant decreasing of α-helix and sharp increasing of random coil,and ultimately, resulting in cathepsin denaturation, assuring desirable surimi quality. |
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