| Hairtail(Trichiurus haumela) is one of the most important marine economical species in China with rich nutritions, high moisture content, but with low glass transition temperature (Tg). Because of its high perishable leading to bad quality on hairtail products, it faces great difficult in storage.This study aims to analyize the effect of different freezing methods on the quality of hairtail harvested in Zhoushan coast near the East China Sea. Based on the results, the hairtail samples treated by the best freezing methods were selected to make hairtail products. The effects of macromolecular materials on the Tg of hairtail surimi products were studied and storage experiments were conducted as well. In the last, hurdle technology was applied in hairtail products. The main results of this paper were as follow:1. Effects of different pretreatment by liquid nitrogen frozen, plate frozen and ordinary refrigerator frozen on the quality of hairtail fresh fish were studied. The basic content of fresh hairtail which captured in May in Zhoushan coast near East China Sea showed to be water of77.6%, crude protein of15.2%, fat of4.7%, ash of1.3%and others of1.2%.Different freezing method had obvious effects on the quality of the hairtail.The fresh hairtail dealed with liquid nitrogen frozen had the best over all quality than that of plate frozen and ordinary refrigerator frozen.The TVB-N, TBA values of samples frozen by ordinary refrigerator increased the fastest, while the samples pretreated by liquid nitrogen increased rather slowly. The soluble protein, water holding capacity, sensory quality and whiteness value of hairtail pretreated by three frozen methods all declined while the Ca2+-ATPase enzyme activity and the total sulphur content increased first, followed by declining later with the storage time. As the extension of strorage time, the pH values of samples treated by theses three frozen methods decreased first and then increased. Comprehensive sensory quality and whiteness values of hairtail treated by liquid nitrogen frozen and plate frozen were similar, but both were better than that of the ordinary refrigerator frozen. Texture results of hairtail showed that, elasticity values of samples treated by liquid nitrogen were generally higher than the samples treated by the plate frozen and ordinary refrigerator frozen. Changes of coherence and the toughness were similar to the change of elasticity. In general, hairtail treated by liquid nitrogen had the best texture values. Microscopic scanning electron microscopy profiles revealed that myofibril of hairtail slightly damaged by the liquid nitrogen, compared to the other frozen methods.2. Macromolecular substances had great effects on the glass transition in hairtail products. Single factor results showed that trehalose, maltodextrin, and xanthan gum could significantly increase the Tg values of hairtail products. Samples adding with4%trehalose had the highest Tg value (25.1±0.23℃),23.4℃increased than the control which with the Tg of48.5±0.32℃, and39.7癈increased than the fresh fish meat with the Tg of64.8±0.25℃.Based on the results of single factor, trehalose (X1), maltodextrin(X2) and xanthan gum (X3) were chosen as three factors, Tg (Y1) was used as response value. The response surface experiment simulation equation model was obtained as the following eqution ofY1=-16.62+0.25X1+2.16X2+0.59X3-4.64X12+0.34X22-3.72X32+0.23X1X2+0.025X1X3-0.05X2X3. And the model R2=0.9640, RAdj=0.9176, its fitting is very high. Variance analysis showed that between the trehalose and maltodextrin, maltodextrin and xanthan gum had significant interactions with each other, but had indistinctively interactions between the trehalose and xanthan gum.The sequence of various factors influence on Tg values of hairtail products was X1X2>X2X3>X1X3. Response surface experiments for simulation of ideal optimal combination were trehalose of4.1%, maltodextrin of5.0%, and xanthan gum of0.41%. The simulative value of Tg was calculated as-14.1℃. Verified experiments showed the practical optimal combination of macromolecular materials were4.0%trehalose,5.0%maltodextrin and0.4%xanthan gum, and the actual Tg value was-14.3℃. Scanning electron microscopy (SEM) showed that the best combination of macromolecular substances (4.0%trehalose,5.0%maltodextrin, and0.4%xanthan gum) had certain effects on the protein products, making the protein network structure more closely.3. Storage experiments of hairtail products showed that the storage temperature and macromolecular substances had important effects on its quality. When the hairtail surimi products were stored in-8℃,-14℃,-18℃, its Ca2+-ATPase, salt soluble protein content, gel strength, whiteness value, the sensory evaluation and water holding capacity all decreased as the storage time prolonged, and the lower the storage temperature, the slower of its decline. Total number of bacterial colony and TVB-N, and TBA values all increased with the extension of storage periods, the lower the temperature, and the slower of its increased. Total number of colonies of the hairtail surimi products(control group and composite group)in-14℃(Tg) and-18℃(<Tg), were below the samples storage in-8℃(>Tg). The gel strength values of samples stored in-14℃(Tg) and-18℃(<Tg) significantly higher than that of stored at-8℃(>Tg), suggesting that the quality of hairtail surimi products stored in-14℃(Tg) and18℃(<Tg) were better than that stored at-8℃(>Tg). Possibly, low temperature, especially under Tg, could inhibit the oxidation of protein and fat, keeping the quality and the original of products.The falling speeds of various indexes of hairtail surimi products adding with macromolecular substances (4.0%trehalose+5.0%maltodextrin+0.4%xanthan gum-composite group) were lower than the control group, suggesting that the macromolecular substances could inhibit protein denaturation and maintaining the original function of protein structure.4. The results of application of hurdle technology in the processing and preservation of hairtail surimi products showed that the barrier factors which had significant impact were salt (A), citric acid (B) and sterilization temperature (C).Using response surface analysis to optimize barrier factors in processing of hairtail surimi products with the total number of colonies (Y2) and comprehensive sensory scores (Y3) as response values, quadratic regression equation were established as the follows:Y2=410+212.5A-50.0B-150.0C+12.5AB+12.50BC+112.50AC+1.25 A2+26.25B2+1.25C2(p<0.0045=0.05, R2=0.9187);Y3=4.66+0.14A+0.037B+0.12C+0.075AB+0.30AC+0.050BC+0.62A2-0.22B2-0.29C2(p=0.0091<0.05, R2=0.8994);Y2and Y3model were highly significant with optimal hurdle combination factors to be salt of2.5%, citric acid of0.15%and sterilization temperature of80℃. The products used the optimal combination of hurdle factors (2.5%salt+0.15%citric acid+80℃sterilization temperature;0.03%Nisin and0.9MPa vacuum packing) processed could be stored at4℃for one months, which extend hairtail surimi products keeping fresh about20days than the control. |
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