Pretreatment method of pre-baked pseudosciaena crocea fillets

Abstract

The invention relates to a pre-treatment method of pre-baked pseudosciaena crocea fillets, which is characterized by comprising the following steps: before pre-baking the pseudosciaena crocea fillets, pickling the pseudosciaena crocea fillets, and then air-drying the pseudosciaena crocea fillets, so that the water content of the pseudosciaena crocea fillets is reduced to 60-70%. By reducing the initial water content of the pseudosciaena crocea fillets and then performing baking, the texture, sensory quality and appearance of the baked fillets can be obviously improved, and the degradation of proteins and lipids is delayed, so that the prebaked pseudosciaena crocea fillets have good quality characteristics, and a reference is provided for optimizing the baking process of the pseudosciaena crocea fillets.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aquatic product processing, and in particular to a pre-roasting large yellow croaker fillet pretreatment method. BACKGROUND

[0002] Large yellow croaker, belonging to Perciformes, Sciaenidae and Pseudosciaena, is an important marine economic fish. It is widely welcomed by consumers because of its tender meat and delicious taste. With the continuous progress of aquaculture technology, its yield has increased significantly. At present, large yellow croaker has become the largest scale of marine aquaculture fish in China. According to statistics, the yield of large yellow croaker in China reached 281,000 tons in 2023. However, the degree of deep processing of large yellow croaker is not high at present, mainly concentrated in traditional ways such as freezing, cold storage, pickling and drying. Freezing and cold storage can effectively prolong the shelf life of large yellow croaker, but to some extent, it will affect its taste and flavor. Pickled large yellow croaker imparts unique flavor by adding salt, sugar, spices and other seasonings, but if not properly controlled during pickling, it may lead to excessive salt, affecting health. Dried large yellow croaker can be stored for a long time, making it convenient for transportation and sale, but some nutrients are lost during the drying process, and the taste is relatively hard.

[0003] In addition to traditional processing methods, in recent years, with the increasing demand of consumers for food quality and taste, some new processing methods have gradually emerged. Among them, roasting is a processing method that has attracted much attention. Roasting can form a golden and crispy crust on the surface of large yellow croaker fillets, while keeping the inside fresh and juicy, and also imparting a unique smoked flavor. However, different processing conditions have a significant impact on the quality characteristics of roasted large yellow croaker fillets. At present, different manufacturers are trying step by step based on their own experience, and the quality of the products is uneven, without scientific guidance. SUMMARY

[0004] The purpose of the present application is to provide a pre-roasting large yellow croaker fillet pretreatment method, which can ensure that the subsequent pre-roasted large yellow croaker fillets have good quality characteristics, and is beneficial to the promotion of deep processing products of large yellow croaker.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows: A pre-roasting large yellow croaker fillet pretreatment method, which is to marinate large yellow croaker fillets before pre-roasting, and then air dry, so that the water content of large yellow croaker fillets is reduced to 60-70%.

[0006] Preferably, the water content of large yellow croaker fillets is reduced to 65% before pre-roasting.

[0007] Preferably, the marinating process for the large yellow croaker fillets involves soaking and marinating the fillets in a 2-5% salt solution for 2-5 hours.

[0008] Preferably, the large yellow croaker fillets are soaked and marinated in a 3% salt solution for 3 hours.

[0009] Preferably, the marinated yellow croaker fillets are air-dried at 40-60℃.

[0010] Preferably, the marinated yellow croaker fillets are air-dried at 45°C. Low-temperature air-drying helps to preserve the texture and flavor of the yellow croaker fillets.

[0011] Preferably, the air-drying time should not exceed 3 hours. This is to prevent the large yellow croaker fillets from being exposed to air for too long, which would affect the quality of the final product.

[0012] Preferably, the large yellow croaker fillets are obtained by slicing the dorsal muscle of the large yellow croaker. This ensures that the texture of the large yellow croaker fillets is more consistent.

[0013] The present invention has the following beneficial effects: By reducing the initial moisture content of large yellow croaker fillets before baking, the texture, sensory quality, and appearance of the baked fillets can be significantly improved. At the same time, the degradation of proteins and lipids is slowed down, thus ensuring that the pre-baked large yellow croaker fillets have good quality characteristics, providing a reference for optimizing the baking process of large yellow croaker fillets. Attached Figure Description Figure 1 To investigate the effect of different moisture contents on the textural properties of roasted large yellow croaker fillets.

[0014] Figure 2 The effect of different moisture contents on the TBARS of roasted large yellow croaker fillets.

[0015] Figure 3 The effect of different moisture contents on TVB-N in roasted large yellow croaker fillets.

[0016] Figure 4 T2 inversion spectra of large yellow croaker fillets with different moisture contents after baking at 220℃ for 20 min.

[0017] Figure 5 The peak area ratio of large yellow croaker fillets with different moisture contents after baking at 220℃ for 20 min.

[0018] Figure 6 False-color images of large yellow croaker fillets with different moisture contents after baking at 220℃ for 20 minutes.

[0019] Figure 7 Radar images of large yellow croaker fillets with different moisture contents after baking at 220℃ for 20 minutes.

[0020] Figure 8 PCA plot of P. major fillets with different moisture contents after roasting at 220℃ for 20 min (electronic nose).

[0021] Figure 9 Histogram of P. major fillets with different moisture contents after roasting at 220℃ for 20 min.

[0022] Figure 10 PCA plot of P. major fillets with different moisture contents after roasting at 220℃ for 20 min (electronic tongue).

[0023] Figure 11 Relative concentration of volatile flavor components of P. major fillets with different moisture contents after roasting at 220℃ for 20 min.

[0024] Figure 12 Number type of volatile flavor components of P. major fillets with different moisture contents after roasting at 220℃ for 20 min.

[0025] Figure 13 Heat map of volatile flavor components of P. major fillets with different moisture contents after roasting at 220℃ for 20 min.

[0026] Figure 14 Scatter plot of volatile components of P. major fillets with different moisture contents after roasting at 220℃ for 20 min.

[0027] Figure 15 VIP plot of volatile components of P. major fillets with different moisture contents after roasting at 220℃ for 20 min.

[0028] Figure 16 Effect of different moisture contents on the protein composition of P. major roasted fillets.

[0029] Figure 17 Correlation analysis of quality characteristics of P. major roasted fillets with different moisture contents.

[0030] Figure 18 Changes in the microstructure of P. major fillets after roasting in terms of cross-sectional and longitudinal sections. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions, and advantages of the present application clearer, the present application will be further described in detail below with reference to examples.

[0032] The application discloses a pre-roasting large yellow croaker fillet pretreatment method. The large yellow croaker fillet is obtained by slicing the back muscle of the large yellow croaker. Before pre-roasting the large yellow croaker fillet, the large yellow croaker fillet is subjected to pickling treatment. The pickling method is soaking the large yellow croaker fillet in 2-5% salt water for 2-5 hours, preferably 3% salt water for 3 hours. The salt water can well retain the taste of the large yellow croaker and help remove the moisture in the fillet. After pickling, the large yellow croaker fillet is subjected to air drying at 40-60 DEG C, preferably 45 DEG C. The air drying time is preferably less than 3 hours, and the moisture content of the air-dried large yellow croaker fillet is 60-70%.

[0033] The method is verified through specific tests.

[0034] 1. Test method Fresh large yellow croakers are slaughtered, and the heads, scales and internal organs are removed. The back muscle is taken out and cut into 2 cm*2 cm*1.5 cm fillets. The fillets are pickled with 3% salt for 3 hours. The pickled fillets are placed in a hot air dryer at 45 DEG C for 1.3 hours, 1.6 hours, 2.08 hours, 2.48 hours and 3.08 hours respectively to obtain fillets with different moisture contents. The fillets are placed in a preheated oven and pre-roasted at 220 DEG C for 20 minutes to obtain BMC-77, BMC-70, BMC-65, BMC-60 and BMC-55 (xx in BMC-xx represents the moisture content). After pre-roasting, the fillets are cooled to room temperature, and the color, texture, TBARS, TVB-N, moisture distribution, flavor substances, myofibrillar protein and sensory evaluation and other related indexes are tested.

[0035] 2. Test conclusion 2.1. Effect of different moisture contents on the color of large yellow croaker fillets after roasting Color is one of the important indicators reflecting product quality. Changes in the color of fish fillets during processing may be related to moisture evaporation, browning reaction, caramelization, and the formation of a hardened outer shell. Table 1 shows the color of roasted large yellow croaker fillets with different moisture contents. In Table 1, L* values ​​represent brightness, with 0~100 indicating samples ranging from black to white; a* values ​​represent the saturation of color on the red-green axis, with a larger a* value indicating a redder color; b* values ​​represent the saturation of color on the yellow-blue axis, with a larger b* value indicating a yellower color. As the moisture content decreased, the L* value of the roasted fish fillets decreased significantly (P<0.05), from 69.43 to 63.24. This may be due to two reasons: firstly, it is related to the Maillard reaction, which produces brown pigments that darken the color of the fish fillets; secondly, the decrease in moisture content during processing may reduce light reflection. The whiteness value also decreased with decreasing moisture content. The a* and b* values ​​showed a significant upward trend with decreasing water content (P<0.05). This may be due to the oxidation of methemoglobin in the fish fillets during processing, leading to an increase in the a* value, while the increasing degree of lipid oxidation in the fish fillets resulted in a significant increase in the b* value. Considering both sensory evaluation and the color of the fish fillets, BMC-60 showed no significant difference from BMC-65 (P>0.05), indicating better color.

[0036] Table 1. Effects of different moisture contents on the color of roasted yellow croaker fillets

[0037] 2.2 Effect of different moisture contents on the texture of roasted large yellow croaker fillets The results are as follows Figure 1 As shown, from Figure 1 It can be seen that the hardness and shear force of the large yellow croaker fillets significantly increased with decreasing water content (P<0.05). When the water content decreased to 65%, the hardness and shear force of BMC-65 were 246.24 g and 1383.23 g / sec, respectively, which were 2.19 times and 2.79 times higher than BMC-77, and also significantly higher than BMC-70 (P<0.05). However, with further reduction of water content, the change in shear force was no longer significant (P>0.05), indicating that certain pickling and hot air drying processes can reduce the water content of the fillets and cause significant changes in their texture. This is because after the fish fillets are marinated and dried by hot air, the myofibrils become shorter and the sarcomeres become shorter, causing the fish fillets to dry out and shrink. At the same time, the rate of evaporation of surface moisture from the fish fillets is greater than the rate of evaporation of moisture that diffuses from the inside to the surface. As the surface of the fish fillets loses moisture, it shrinks and dries rapidly, forming a dense and firm hard shell. As the baking continues, the formation of the hard shell on the surface increases, resulting in a harder texture and increased shear force on the fish fillets.

[0038] 3.3 Effect of different moisture contents on the TBARS of roasted large yellow croaker fillets The degree of fat oxidation is closely related to the sensory quality and flavor quality of the product. Large yellow croaker fillets contain a high level of fat. During storage, heat and O2 can accelerate the hydrolysis and oxidation of fish fillet fat, leading to lipid peroxidation and the production of malondialdehyde and other lipid peroxidation products. The malondialdehyde produced can combine with thiobarbituric acid to form a stable complex in a high-temperature environment, which has a maximum absorption at 532 nm. The TBARS of large yellow croaker fillets with different water contents after roasting was determined, and the results are shown in Figure 2 The lower the water content of large yellow croaker fillets, the higher the TBARS value of the fillets after roasting, increasing from 0.52 mg / 100 g to 0.66 mg / 100 g. This indicates that marinating and hot-air drying can have some effect on the oxidation of fish fillet fat. The TBARS values of BMC-65 and BMC-60 were not significantly different (P>0.05), but were significantly lower than that of BMC-55 (P<0.05).

[0039] 3.4. Changes in TVB-N of large yellow croaker fillets with different water contents after roasting The results are shown in Figure 3 . As can be seen from Figure 3 , through a certain degree of marinating and drying, the TVB-N value of the fillets significantly increased (P<0.05) as the water content decreased, and was less than 30 mg / 100 g. The TVB-N value of the roasted fillets was higher than that of the treated samples, possibly because the Maillard reaction and lipid oxidation during roasting caused further decomposition of proteins in the fillets to produce amine substances. During storage, the growth and reproduction of bacteria and the oxidative decomposition of enzymes in large yellow croaker fillets caused the decomposition of proteins to produce ammonia and amine substances, leading to spoilage and deterioration of the fillets. As can be seen from Figure 3 , after marinating and drying, the water content of large yellow croaker fillets gradually decreased, but the TVB-N value of the fillets significantly increased (P<0.05). After roasting, the TVB-N value of the fish further increased, possibly because the high temperature caused further decomposition of proteins in the fillets to produce amine substances. When the water content decreased to 65%, the TVB-N content of BMC-65 was not significantly different from that of BMC-60. When the water content continued to decrease, the TVB-N content of BMC-55 increased sharply, close to 30 mg / 100 g.

[0040] 3.5. Effect of different water contents on the water migration pattern of large yellow croaker fillets after roasting Low-field nuclear magnetic resonance (LF-NMR) can effectively clarify the state and distribution of water in large yellow croaker fillets. The main parameters include transverse relaxation time (T2) and signal amplitude. T2 relaxation time can reflect the degree of water and substrate combination. The smaller the T2 value, the tighter the combination, and the lower the water freedom. In the T2 spectrum, the peak position is more biased to the left. According to its state, it can be divided into T21 (0-10 ms) bound water; T22 (10-100 ms) not easily flowing water in myofibrillar structure; T23 (100-1000 ms) free water in myofibrillar structure.

[0041] The results are shown in Figures 4-6 Figure 4 T2 inversion spectrum of large yellow croaker fillets with different water contents baked at 220℃ for 20 min. It can be seen from Figure 4 that compared with BMC-77, the T21, T22 and T23 of BMC-65 were significantly reduced (P<0.05). With the decrease of water content, compared with BMC-65, the T22 of BMC-60, BMC-60 and BMC-55 was significantly reduced (P<0.05). Combined Figure 5 it can be found that the results are consistent with the results presented by T2 inversion spectrum. Among them, the P22 of BMC-70 fillet is the highest, and the P21 and P23 are the lowest. Compared with BMC-70, the P22 of BMC-65 fillet decreased by 45.72%, and the P21 and P23 increased by 38.04% and 7.68% respectively, indicating that with the decrease of water content, the not easily flowing water of the fillet was converted to free water after baking. The possible reason is that the myofibril of the fillet shrinks during processing, preventing the loss of not easily flowing water, so that it is converted to free water. At the same time, the content of not easily flowing water in the fillet decreases during baking, so that the percentage of combined water increases significantly.

[0042] MRI provides a visual two-dimensional image of the internal morphology of the fillet. Color shading represents signal intensity levels, and brighter colors mean more protons. From Figure 6 it can be observed that the lower the water content of the fillet, the less and less uniform the water distribution after baking, showing a state of more water in the center and less water on the periphery. This may be due to the fact that the pre-treatment of curing and drying has caused a certain damage to the protein organization of the fillet, making the water and macromolecular compounds more tightly combined. During the baking process, the outside is heated first, and then the heat is conducted to the inside, resulting in the loss of water on the outside first, and less water loss on the inside.

[0043] 2.6, the results of electronic nose analysis of large yellow croaker fillets with different water contents after baking ​Electronic nose is a common tool for identifying and analyzing the aroma of samples. Principal component analysis (PCA) is a mathematical dimension reduction technique used to visualize the differences between the sample information obtained by analysis. The radar chart of the aroma of large yellow croaker fillets with different water contents after detection by 10 odor sensors is shown in Figure 7 The results show that W1W (sensitive to sulfides), W2W (aromatic components, sensitive to organic sulfides) and W5S (high sensitivity, sensitive to nitrogen oxides and ) sensors have the strongest response to the volatile compounds of large yellow croaker fillets with different water contents after roasting. It is worth noting that in the sample of BMC-65, the odor values of W5S, W6S, W1W and W2W are significantly higher than those of other groups of large yellow croaker fillets, reaching 1.51, 1.04, 3.37 and 2.70, respectively.

[0044] Based on the response of the electronic nose sensor, the results of PCA analysis of large yellow croaker fillets with different water contents are shown in Figure 8 Among them, the first principal component (PC1) and the second principal component (PC2) contribute 54.1% and 28.1%, respectively, and the cumulative variance contribution rate is 82.2%, indicating that these two principal components can reflect the overall aroma characteristics of each group of large yellow croaker fillets. The odor response distribution area of fresh fish fillets and salted samples has some overlap, indicating that there is no significant difference in the odor of the samples. At the same time, the odor response distribution area of the two is quite different from that of other samples, indicating that there is a significant difference in the odor effect of samples treated by drying and not treated by drying.

[0045] 2.7, the influence of different water contents on the electronic tongue of large yellow croaker fillets after roasting Electronic tongue is an intelligent taste bionic system that simulates the taste buds on the human tongue and converts electric potential value into taste value, which can distinguish and quantify the basic taste sensory indicators of fish fillets such as sour, sweet, bitter, fresh, salty, etc. Therefore, the electronic tongue was used to determine the taste differences of large yellow croaker fillets with different water contents after roasting, and the taste profile of large yellow croaker fillets was constructed by the response intensity of each sensor. The results are shown in Figure 9It can be seen that the moisture content of fish fillets is different, and the bitterness, astringency, astringency aftertaste, richness, saltiness and umami of the roasted fish fillets have significant influence (P<0.05) and are not the same. The fish fillets of BMC-77 and BMC-65 groups have significant differences (P<0.05) in umami, richness and saltiness, but the fish fillets of BMC-65 and BMC-60, MC-55 groups have no significant difference (P>0.05). When the moisture content of fish fillets is 65%, that is, the fish fillets of BMC-65 group after roasting, its umami value can reach 5.12, which is 1.29 times of BMC-77 group, and its richness is increased by 11.45 than BMC-77 group; similarly, in terms of saltiness, BMC-65 group is 1.33 times of BMC-77 group; but its astringency value is significantly reduced, which is reduced by 18.15% than BMC-77 group. The above results show that the curing and drying process changes the moisture content of fish fillets, and then affects the taste components of the roasted fish fillets.

[0046] Principal component analysis (PCA) is an analysis tool that can highlight and distinguish the differences between samples. It is a multivariate statistical method that can reduce the dimensionality of the data and extract the main information of the data. Figure 10 It can be seen that PC1 (76.6%) and PC2 (16.0%) account for 92.6% of the total variance, indicating that the model can cover all the information of the samples. Compared with BMC-77 group, the projection (VIP) of the sample moves to the positive axis of PC1 with the decrease of moisture content, indicating that the curing and drying process significantly changes the taste characteristics of large yellow croaker fillets. The projection of BMC-65 group overlaps with that of BMC-60 group and BMC-55 group, indicating that the taste characteristics of BMC-65 group are similar to those of BMC-60 group and BMC-55 group. The results show that the taste of large yellow croaker roasted fish fillets changes with the decrease of moisture content, and the fish fillets of BMC-77 group and BMC-70 group have significant difference (P<0.05) with BMC-65 group, and BMC-65 group has no significant difference (P>0.05) with BMC-60 group and BMC-55 group.

[0047] 2.8, Effect of different moisture contents on volatile components of large yellow croaker fillets after roasting Generally, high temperature can cause lipid oxidation in fish fillet tissue, producing a variety of aldehyde and ketone substances, among which aldehyde has a relatively high content and a low threshold, which contributes greatly to the odor of fish fillets. Therefore, the volatile components of fish fillets with five different moisture contents after roasting were analyzed by GC-MS, and 70 kinds of volatile components were identified, mainly including aldehydes, alcohols, acids, hydrocarbons, esters and aromatic compounds and other compounds. BMC-77, BMC-70, BMC-65, BMC-60 and BMC-55 identified 35, 30, 38, 39 and 40 kinds of volatile compounds respectively.

[0048] From the results of the above experiments, it can be seen that the moisture content of fish fillets is different, and the bitterness, astringency, astringency aftertaste, richness, saltiness and umami of the roasted fish fillets have significant influence (P<0.05) and are not the same. The fish fillets of BMC-77 and BMC-65 groups have significant differences (P<0.05) in umami, richness and saltiness, but the fish fillets of BMC-65 and BMC-60, MC-55 groups have no significant difference (P>0.05). When the moisture content of fish fillets is 65%, that is, the fish fillets of BMC-65 group after roasting, its umami value can reach 5.12, which is 1.29 times of BMC-77 group, and its richness is increased by 11.45 than BMC-77 group; similarly, in terms of saltiness, BMC-65 group is 1.33 times of BMC-77 group; but its astringency value is significantly reduced, which is reduced by 18.15% than BMC-77 group. The above results show that the curing and drying process changes the moisture content of fish fillets, and then affects the taste components of the roasted fish fillets. Figure 11 andFigure 13 It can be seen that the relative content of aldehydes in BMC-65 was 25.03%, which was significantly lower than that in other groups (P<0.05); the relative content of aromatic and other types was the highest, reaching 37.74%, including 2-ethyl-5-methyl pyrazine, 2-ethane-3,5-dimethyl pyrazine, 2,6-dimethyl pyrazine, 2,4,6-trimethyl pyridine, 2,3-dimethyl-5-ethyl pyrazine, etc. Pyridine, pyrazine and other aromatic compounds were Maillard reaction-derived compounds, with nutty and roasted aroma. The possible reason was that the aldehydes in fish slices were affected by curing, drying and baking factors, accelerating the oxidative degradation of fatty acids, and part of the aldehydes were oxidized to alcohols, heterocyclic and other volatile substances. Some aromatic substances, such as pyrazine and pyridine, may be produced by Maillard reaction, promoting the formation and maintenance of flavor substances. From Figure 12 It can be seen that 7, 6, 9, 10 and 10 kinds of aldehydes were detected in 5 groups of samples, including heptanal, decanal, benzaldehyde and nonanal, etc. Among them, the BMC-70 group was cured and then baked, which accelerated the oxidation of fat, promoted the generation of aldehydes of the same kind (P<0.05), but the number of species was significantly lower than that of BMC-77; after curing and then drying and baking, the relative concentration of aldehydes increased instead of decreasing due to the decrease of water content. The thermal oxidative decomposition reaction of fat was intensified by hot air drying and baking, producing more aldehydes, so the number of aldehyde species also increased. Gao et al. also found that the number of aldehyde species in air-dried fish meat gradually increased, which was similar to the results of this study. Figure 11 The heat map showed that the relative concentration of nonanal in BMC-65 group decreased by 205.6 ng / 10 g compared with BMC-77 group; the flavor aldehydes such as heptanal and trans-2-octenal in the treated group increased compared with BMC-77. Some studies have reported that heptanal and trans-2-octenal are mainly derived from linoleic acid oxidation, which enriches the aroma of fish blocks. The relative content of ketones in the 5 groups of samples was 1.55%-3.21%, including (E, E)-3,5-octadien-2-one, 1,6-dioxacyclododecane-7,12-dione, 2-methylcyclopentanone, 2-piperazinone, 2-nonanone, 2-undecanone, 5-dodecyl dihydro 2 (3H) -furanone, alpha-pyrone, tetrahydro-2H-2-pyrone, among which, the number of ketone species in BMC-65 was the most. Ketones have special aroma, with fatty and burnt smell, which may be produced by fatty oxidation, playing an important role in the formation of fish baking aroma. Figure 13

[0049] ​To further determine how the variables of volatile organic compounds cause differences between samples, PLS-DA model analysis was performed. The goodness-of-fit parameter (R2X), model interpretability (R2Y), and predictability (Q2) were 0.942, 0.994, and 0.986, respectively, indicating that the model had good robustness and predictability. According to Figure 14 The five groups of samples can be divided into three categories, with BMC-77 concentrated in the fourth quadrant; BMC-70 concentrated in the first quadrant; BMC-65, BMC-60, and BMC-55 have no significant difference, and are all concentrated in the third quadrant. Then the projection (VIP) method was used to further distinguish the parameters of the five groups of fish fillet samples. The larger the VIP value of the variable, the more significant the distinction of the sample. From Figure 15 It can be seen that 23 compounds with VIP>1 were identified, including heptanal, decanal, diisobutyl phthalate, acetamide, dodecanal, dodecane, heptanal, trans-2,4-decadienal, trans-2-decenal, N-methyl-2-pyrrole carboxaldehyde, 2-ethyl-5-methyl pyrazine, 2-ethylhexyl acetate, 2-ethyl-3,5-dimethyl pyrazine, 3,4-dimethyl-1-hexene, 3,7-dimethyl-1,6-octadien-3-ol, 2-piperazinone, 2,6-dimethyl pyrazine, 2,4,6-trimethyl pyridine, 2,3-dimethyl-5-ethyl pyrazine, 2,3,5,8-tetramethyl decane, 1-octen-3-ol, (E,E)-3,5-octadien-2-one, dodecyl nonyl ether, which can be used as markers of aroma compounds of baked large yellow croaker fillets.

[0050] 2.9, Effect of different water contents on myofibrillar protein of baked large yellow croaker fillets Myofibrillar protein (MP) is the most important type of protein in fish fillets, accounting for 55%-60% of the total protein content in fish fillets, and mainly includes myosin heavy chain (MHC, 200 kDa), actin (48 kDa), troponin I (23 KDa), and tropomyosin (35 kDa). In order to study the effect of different water contents on protein denaturation and degradation of baked large yellow croaker fillets, the relative molecular mass of MP and the number of subunits in the protein molecule were determined by SDS-PAGE method.

[0051] From Figure 16It can be seen that the protein bands of large yellow croaker fillets were not significantly different after different degrees of dehydration by marinating and drying pretreatment. After baking, MHC, myosin and Actin were degraded, indicating that high temperature reduced the thermal stability of myosin and actin, accelerating the degradation of proteins. The MHC band was clearly visible, and the Actin band remained basically unchanged. With the deepening of the drying degree, the myosin band of BMC-65, BMC-60 and BMC-55 and the troponin I band gradually deepened, indicating that heating treatment could cause the degradation of macromolecular proteins. The MHC band, myosin band and actin band of baked large yellow croaker fillets disappeared, indicating that high temperature baking could reduce the thermal stability of myosin and actin, accelerating the degradation of proteins.

[0052] 2.10 Effect of different water content on sensory evaluation of baked large yellow croaker fillets Sensory evaluation can intuitively analyze and describe the texture, color and morphology of fish fillets, and can reflect the acceptance and preference of the evaluator. The scoring criteria are shown in Table 2.

[0053] Table 2 Sensory evaluation table of pre-baked large yellow croaker baked fillets

[0054] The results are shown in Table 3. As shown in Table 3, with the decrease of water content, both the single score of morphology, odor and color and the total score increased first and then decreased. Among them, the fillets of BMC-60 group had the highest score of 6.75, and the total sensory score of BMC-65 group had no significant difference (P>0.05) with that of BMC-60 group, while the sensory score of BMC-77 group was the lowest, which was significantly lower than that of BMC-60 and BMC-65 groups by 40.15% and 37.94%, respectively. Combined with the results of electronic nose, electronic tongue, TBARS and TVB-N value, when BMC-65, the baked large yellow croaker fillets had the best quality in terms of texture, color, odor and morphology.

[0055] Table 3 Effect of different water content on sensory score of baked large yellow croaker

[0056] 2.11 Correlation analysis of quality indicators of baked large yellow croaker fillets with different water content In order to explore the relationship between the quality indicators of large yellow croaker fillets, the Pearson correlation analysis was carried out on the sensory evaluation (morphology, color, odor and taste), texture (hardness, shear force), color difference (L*, a* and b*), water distribution (P21, P22 and P23), TBARS and TVB-N of large yellow croaker fillets, and the results are shown in Table 4. Figure 17As shown in Fig. 4, the color difference (L*, a*, b*) was highly correlated with lipid oxidation and fish freshness. L* was significantly negatively correlated with TBARS, TVB-N and P21 (P<0.05, P<0.01), while a* and b* were significantly positively correlated with TBARS, TVB-N and P21 (P<0.05, P<0.01). With the decrease of moisture content, the volume of fish fillets shrank and water was lost. Meanwhile, protein was continuously degraded to generate more polypeptides and amino acids, which could participate in Maillard reaction. With the deepening of protein and lipid oxidation, the color of large yellow croaker fillets became dark and yellow. Meanwhile, the morphology of fish fillets was significantly positively correlated with the hardness and shear force of fish fillets (P<0.05, P<0.01). With the decrease of moisture content and the increase of drying degree, a hard shell was formed on the surface of fish fillets, and the texture and shear force of fish fillets were also increased.

[0057] 2.12 Microstructure analysis of roasted large yellow croaker fillets with different moisture contents The results of microscopic observation are shown in Fig. 6. Figure 18 As shown in Fig. 6, the changes in muscle microstructure of fish meat can be observed from the cross-sections. Figure 18 It can be seen that the fiber structure of the BMC-77 sample was arranged in order, the structure was complete, and the tissue profile was clear. With the decrease of moisture content, the fiber became more compact. The fibers of the fish fillets treated with 3% salt were more compact. With the decrease of moisture content, the gap between the fibers became smaller. This result was consistent with the result of texture. With the decrease of moisture content, the microstructure of fish meat became more compact, and the hardness of fish meat was higher. From the longitudinal section, it can be observed that when the moisture content was reduced to 55%, the myofibrillar fibers of the sample were interlaced and disordered, and gaps gradually appeared between the fibers. The possible reason was that the moisture content in fish meat was low, and the myofibrillar protein was denatured and broken. This research result was similar to the research result of Cai Lu-yun et al. High temperature accelerated the evaporation of water, and the myofibrillar protein was severely denatured and broken at multiple sites.

[0058] In summary, fish fillets with higher initial moisture content had lower sensory scores after baking, mainly due to soft texture and insufficient flavor. Fish fillets with moderate initial moisture content (e.g. BMC-60 and BMC-65) showed the best sensory quality after baking, with better texture, flavor and overall acceptance. Fish fillets with lower initial moisture content showed a significant increase in b* value (yellowness) and a decrease in a* value (redness) after baking, indicating that lower moisture content helped to form a brighter appearance, which might be related to the enhanced surface Maillard reaction caused by water evaporation. With the decrease of initial moisture content, the proportion of ice water in fish fillets significantly decreased (P<0.05), while the proportion of strong bound water, free water and weakly bound water significantly increased (P<0.05). The hardness and shear force of fish fillets after baking significantly increased (P<0.05), indicating that appropriate reduction of initial moisture content in fish fillets helped to improve the texture properties and enhance the mouthfeel after baking. The five groups of large yellow croaker fillets with different moisture contents could be effectively distinguished by electronic tongue, electronic nose and GC-MS. Among them, the BMC-65 fillets were more outstanding in taste and flavor compared with BMC-77 and BMC-70, and there was no significant difference compared with other low-moisture groups. PLS-DA analysis of the volatile components of the five groups of samples showed significant differences.

[0059] The above merely illustrates the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A pre-roasting large yellow croaker fillet pretreatment method, characterized in that: Before pre-baking the large yellow croaker fillets, the large yellow croaker fillets are pickled and then air-dried to reduce the water content of the large yellow croaker fillets to 60-70%. ​ 2. The pre-roasting large yellow croaker fillet pretreatment method according to claim 1, characterized in that: Before pre-baking the large yellow croaker fillets, the water content of the large yellow croaker fillets is reduced to 65%.

3. The pre-cooking large yellow croaker fillet pretreatment method according to claim 1, characterized in that, The pickling of the large yellow croaker fillets is specifically: soaking the large yellow croaker fillets in 2-5% salt water for 2-5 hours.

4. The pre-cooking large yellow croaker fillet pretreatment method according to claim 3, characterized in that: The large yellow croaker fillets are soaked in 3% salt water for 3 hours.

5. The pre-baking large yellow croaker fillet pretreatment method according to claim 1, characterized in that: The pickled large yellow croaker fillets are air-dried at 40-60°C.

6. The pre-cooking large yellow croaker fillet pretreatment method according to claim 5, characterized in that: The pickled large yellow croaker fillets are air-dried at 45°C.

7. The pre-cooking large yellow croaker fillet pretreatment method according to claim 1, characterized in that: The air-drying time is no more than 3 hours.

8. The pre-cooking large yellow croaker fillet pretreatment method according to claim 1, characterized in that: The large yellow croaker fillets are obtained by slicing the dorsal muscle of a large yellow croaker.

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