Method for removing fishy smell substances of freshwater fish by enzyme degreasing

Abstract

The invention discloses a method for removing fishy smell substances of freshwater fish by enzyme degreasing. The method comprises the following steps: pretreating materials, adding enzyme liquid, adjusting pH, carrying out water bath enzymolysis, cleaning fish blocks, and draining. The method can effectively remove fishy smell substances, including hexaldehyde, 1-octylene-3-alcohol, octanal, nonanal and the like, of the freshwater fish, and has the advantages that the equipment investment cost is low; the degreasing rate is high, and the protein loss rate is relatively low and is only 0.71%; the method has the advantages of high specificity, high safety, no secondary pollution and the like, and is more suitable for freshwater fish processing.

Description

Technical Field

[0001] The invention relates to a method for removing freshwater fish odor substances by using enzyme degreasing, belonging to the technical field of aquatic product processing. Background Art

[0002] Freshwater fish is rich in high protein and various amino acids that are easily digested and absorbed, and is loved by consumers. However, with the improvement of people's living standards, the quality requirements for aquatic products are getting higher and higher, and the unique fishy smell of pre-prepared freshwater fish fillets limits consumers' acceptance and also affects the economic benefits of its processing industry. Aquatic products are an indispensable part of our daily diet, and pre-prepared fish fillets have gradually become the choice of more and more consumers. Therefore, it is of great significance to take necessary measures to inhibit and remove the fishy smell. There are three main sources of fishy smell: one is environmental sources, such as geosmin and dimethylisoborneol (2-Methylisoborneol, MIB); the second is fat oxidation; and the third is amines such as trimethylamine.

[0003] In recent years, there has been a lot of research on the removal of fishy smell from aquatic products. It is relatively easy to remove the fishy smell of marine fish in aquatic consumption, usually by rinsing it several times with clean water or dilute salt water. However, the fishy smell of freshwater fish is strong and complex, and the removal process is more difficult. The current defatting and deodorizing treatment methods are relatively immature.

[0004] Existing deodorization technologies mainly include physical, chemical and biological methods. Physical deodorization methods include adsorption method, embedding method and steam deodorization method. There are phenomena of incomplete deodorization, loss of nutrients and production of other irritating tastes. Chemical deodorization methods include acid, alkali and salt deodorization methods and ozone deodorization methods, but there are problems such as wastewater generation, residual organic matter and environmental damage. Biological deodorization methods include microbial fermentation method and microbial fermentation deodorization method. The disadvantage is that the protein is destroyed, the scope of application is limited, and large-scale application cannot be achieved.

[0005] Patents CN101095531A and CN102132898A disclose that the early freshwater fish deodorization technology is mainly salt and acid pickling, but may cause problems such as excessive sodium content and protein loss. In recent years, there are also some novel deodorization technologies, such as patent CN109259049A discloses a grapefruit peel deodorizer and its preparation method and its use method on freshwater fish, but may be difficult to maintain the original freshwater fish flavor. Enzymatic deodorization effect is relatively significant, mainly utilizing biological enzymes, such as patent CN102771827A discloses a method for utilizing biological enzymes to remove the fishy smell of tilapia, and Wang Xuan adopts alkaline lipase to defat freshwater fish, and the fishy smell component related index decreases, but alkaline environment can cause the loss of protein in fish fillet (Wang Xuan, the impact of enzymatic degreasing on catfish quality and drying characteristics). And then the loss of protein is still a problem to be solved in the enzymatic deodorization.

[0006] Therefore, it is necessary to develop a technology for removing the fishy smell of freshwater fish fillets and effectively reduce the loss of protein in fish meat. Summary of the invention

[0007] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for removing freshwater fish odor substances by enzyme defatting, aiming to solve the technical problem of the lack of a method for removing the odor of freshwater fish fillets and effectively reducing the loss of protein in fish meat.

[0008] The first technical aspect provided by the present invention is a method for removing freshwater fish odor substances by enzyme defatting, wherein the method comprises treating fish fillets with neutral lipase in a glycine (Gly)-sodium hydroxide (NaOH) buffer solution, wherein the addition amount of the neutral lipase in the treatment system is 80 to 300 U / ml.

[0009] In certain embodiments, the material-liquid ratio of the buffer solution to the fish fillet is 1:0.8 to 1:3.

[0010] In certain embodiments, the neutral lipase is used to treat the fish fillet for 25 to 90 minutes.

[0011] In certain embodiments, the temperature of the neutral lipase-treated fish fillet is 25-50°C.

[0012] In certain embodiments, the pH of the fish fillet treated with neutral lipase is 6.5-9.

[0013] In certain embodiments, the method comprises treating fish fillets with a neutral lipase in a glycine-sodium hydroxide buffer solution;

[0014] The neutral lipase is added in an amount of 80 to 120 U / ml in the treatment system;

[0015] The material-liquid ratio of the buffer solution to the fish fillet is 1:0.8 to 1:1.2;

[0016] The neutral lipase treatment time of the fish fillet is 25 to 35 minutes;

[0017] The temperature of the fish fillet treated with neutral lipase is 25-35°C;

[0018] The pH of the fish fillet treated with the neutral lipase is 6.5-7.5.

[0019] In certain embodiments, the fish fillets are treated with neutral lipase and then washed with distilled water to remove the surface enzyme solution and then drained.

[0020] In certain embodiments, the method for preparing the fish fillet is as follows: after removing the head, tail and internal organs of the fresh fish, wash, peel, debone and cut the fish body into fish fillets about 1.5 cm thick with a mass of about 60 g, wash and drain.

[0021] The second technical solution provided by the present invention is a method for reducing the content of hexanal, 1-octen-3-ol, octanal and / or nonanal in fish fillets. The method comprises treating the fish fillets with a neutral lipase in a glycine (Gly)-sodium hydroxide (NaOH) buffer solution at 25 to 50° C. and a pH of 6.5 to 9, wherein the amount of the neutral lipase added to the treatment system is 80 to 300 U / ml.

[0022] In certain embodiments, the material-liquid ratio of the buffer solution to the fish fillet is 1:0.8 to 1:3.

[0023] In certain embodiments, the neutral lipase is used to treat the fish fillet for 25 to 90 minutes.

[0024] In certain embodiments, the fish fillets are treated with neutral lipase and then washed with distilled water to remove the surface enzyme solution and then drained.

[0025] The third technology provided by the present invention is the application of the method described in the first technical solution or the method described in the second technical solution in processing fish fillet products.

[0026] The technical effects of the present invention are as follows:

[0027] 1. The present invention uses common freshwater fish on the market, catfish, as the experimental object, and conducts defatting and deodorization research on it to reduce the fat of freshwater fish, reduce the fishy smell of fish body, and simultaneously reduce other fishy smell substances (hexaldehyde, 1-octen-3-ol, octanal and nonanal) in fish fillets, thereby improving the meat texture and quality of freshwater fish. Compared with the traditional chemical method, the enzymatic deodorization method is more gentle, will not affect other ingredients in food, and maintains the original flavor of food.

[0028] 2. The present invention adopts the technology of enzymatic deodorization, which has the following three advantages: 1. protein is the main nutrient of freshwater fish and determines the level of the nutritional value of fish. However, in the fish processing process, due to the influence of the external environment, such as rinsing, soaking, pickling, heating, etc., it is easy to cause the loss of protein, so the water rinsing method is not adopted; 2. the ethanol extraction method needs to remove and recycle the absolute ethanol, which increases the equipment investment cost and also has safety problems such as flammable and explosive; 3. the enzymatic degreasing has a high degreasing rate and a relatively low protein loss rate of only 0.71%. The enzymatic degreasing has the advantages of strong specificity, high safety, and no secondary pollution, and is more suitable for freshwater fish processing.

[0029] 3. The present invention reduces the secondary products converted from fat oxidation substances, introduces a corresponding enzymatic hydrolysis method, and conducts experiments with different reagent ratios based on considerations of health, taste, efficiency, cost, etc., to explore the most suitable technical solution for reducing the freshwater fish odor. This method can not only achieve large-scale industrial production in the future and play a significant role in reducing the freshwater fish odor, but also be expanded and applied in multiple fields such as catering companies, snack processing plants, and household use, and has a very high practical application value for the transformation of basic research results. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a diagram showing the changes in fishy odor substances after enzyme treatment in Example 1 of the present invention.

[0031] Figure 2 The data of degreasing rate, acid value, POV, and TBA at different enzyme addition amounts in Example 1 of the present invention and a graph showing the changing trend with increasing freeze-thaw times.

[0032] Figure 3 This is a radar chart of the sensory experiment under different enzyme addition amounts in Example 1 of the present invention.

[0033] Figure 4 The data of degreasing rate, acid value, POV and TBA at different soaking times in Example 2 of the present invention and the changing trend chart with the increase of freeze-thaw times are shown.

[0034] Figure 5 This is a radar chart of the sensory experiment at different soaking times in Example 2 of the present invention.

[0035] Figure 6 The data of fat removal rate, acid value, POV, TBA at different fish liquid ratios in Example 3 of the present invention and a trend chart of changes with increasing freeze-thaw times are shown.

[0036] Figure 7 This is a radar chart of the sensory experiment under different fish liquid ratios in Example 3 of the present invention.

[0037] Figure 8 The data of degreasing rate, acid value, POV, TBA at different pH values ​​in Example 4 of the present invention and a graph showing the changing trend with increasing freeze-thaw times are shown.

[0038] Fig. 9 It is a radar chart of the sensory experiment at different pH values ​​in Example 4 of the present invention.

[0039] Fig.10 The data of degreasing rate, acid value, POV and TBA at different temperatures in Example 5 of the present invention and the changing trend chart with the increase of freeze-thaw times are shown.

[0040] Fig.11 It is a radar chart of the sensory experiment at different temperatures in Example 5 of the present invention.

[0041] Fig.12 The data of degreasing rate, acid value, POV, TBA in Example 6 of the present invention and the changing trend chart with the increase of freeze-thaw times are shown.

[0042] Fig.13 This is a graph showing protein loss after enzyme treatment in Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0043] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explaining the present invention and are not used to limit the present invention.

[0044] The analytical test method used in the embodiment of the present invention is:

[0045] Grind the fish chunks into minced fish: Use a meat grinder to grind the enzymatically hydrolyzed fish chunks for 5 seconds at a time, repeat 10 times, and grind into minced fish for later use.

[0046] Determination of fat content and degreasing rate: Weigh 3g of surimi and place it on tin foil, weigh the tin foil and the mass after adding surimi respectively and record them. Place the whole part in a hot air drying oven and bake at 60℃ for more than 20h. After the water is completely removed and the mass is constant, take it out and weigh it again, and record the data. Put the dried surimi into a mortar and grind it into powder, put it into the filter paper tube on the upper part of the extraction bottle, weigh it again, and record the data. Add an appropriate amount of petroleum ether to the extraction bottle, do not cover the lower part, install the device, set the temperature to 55℃, and the time is more than eight hours. After the time is up, recover the petroleum ether, take out the filter paper tube and weigh it, record the data and then calculate. Make 3 sets of parallel measurements;

[0047] Determination of acid value: Take 5g sample in a beaker, add 50ml neutral buffer, homogenize and put in a water bath, take out after 10 minutes in a 50℃ water bath, and warm it to dissolve. Then put it in a conical flask, cool to room temperature, add 2 to 3 drops of phenolphthalein indicator solution, and titrate with potassium hydroxide standard titration solution (0.050mol / L) until a slight red color appears and it does not fade within 30s. Substitute into the formula Calculate. Perform 3 sets of parallel measurements;

[0048] Determination of POV: Weigh 80g of surimi into a beaker, add 2-3 times the volume of petroleum ether into the beaker, extract for 12 hours, filter the extract in a funnel filled with anhydrous sodium sulfate, take the filtrate and distill the petroleum ether in a rotary evaporator, and extract the remaining liquid in the distillation flask. Weigh the mass of the extracted liquid as m, place it in a dry and clean 250ml iodine volumetric flask, add 30ml of chloroform-glacial acetic acid mixture, and shake immediately to completely dissolve the sample. Then use a pipette to add 1.00ml of saturated potassium iodide solution, add a stopper, shake gently for 0.5min, place in a dark place for 3min, take it out, add 100ml of distilled water and 1ml of starch indicator, shake well, and titrate with 0.01mol / L sodium thiosulfate solution until the blue disappears. Record the volume of liquid V0 and V1 in the burette before and after titration. Substitute the formula POV = (V1-V0) * 0.01 * 0.1269 * 100 / m, calculate POV and find the average value. Perform 3 sets of parallel measurements;

[0049] Determination of TBA: Weigh 2g of sample into a centrifuge tube, add 15mL of 7.5% (w / v) trichloroacetic acid solution (containing 0.1% (w / v) disodium ethylenediaminetetraacetate), homogenize and centrifuge at 8000rpm for 20min at 4℃, then take 4mL of supernatant into a 25mL stoppered colorimetric tube and mix with 4mL of 0.02mol / L 2-thiobarbituric acid solution, and the fixed volume V=8mL. The mixed solution is placed in a 90℃ water bath for 30min, cooled to room temperature and the absorbance is measured at a wavelength of 532nm. The absorbance value is substituted into the 1,1,3,3-tetraethoxypropane standard curve (Y=0.2396X-0.0025) for calculation to obtain the malondialdehyde concentration (μg / mL), and then substituted into the formula x(TBA)=(Y*V*1000) / (m*1000), and the final result is expressed in mg malondialdehyde / g sample. Three sets of parallel measurements were performed.

[0050] Sensory evaluation experiment: The sensory evaluators recruited were students majoring in food science and had good professional quality in food science. According to GB / T 16291.1-2012

[94] , the observation and odor recognition abilities of the sensory candidates were trained, and finally 12 sensory assessors were determined, with a male-female ratio of 1:1. The samples were randomly numbered with 3 digits. The odor of the surimi gel was descriptively scored. According to GB / T 10211-2012

[95] and GB / T 37062-2018

[96] , the sensory evaluation guide for aquatic products sets the following descriptors for the odor of the surimi gel: earthy smell, inherent smell of fish meat, fishy smell, and sour smell. 1 point means that the odor is very light, and 5 points means that the odor is very strong. The results are summarized and plotted on a radar chart. (Hexanal: fishy, ​​grassy; 1-octen-3-ol: mushroom, earthy; (E,E)-2,4-heptadienal: fishy; (E)-2-octenal: fishy, ​​fat, grassy.) Determination of hexanal, 1-octen-3-ol, octanal, and nonanal: Solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS)

[0051] Solid phase microextraction (SPME) conditions

[0052] Accurately weigh 3.000 ± 0.006 g of sample and place it in a 20 mL brown headspace bottle. Add 7.0 mL of saturated NaCl solution and 10 μL of internal standard TMP (100 mg kg -1 ), put it into the magnetic rotor to mix evenly, quickly cover it with a silicone cap, and ensure that the constant temperature water bath is balanced. Insert the aged fiber extraction head (65μm, PDMS / DVB) into the headspace of the sample bottle, adsorb at 60℃ for 30min, and desorb at the injection port at 250℃ for 3min. All samples were measured three times in parallel.

[0053] Gas chromatography-mass spectrometry (GC-MS) conditions

[0054] Chromatographic (GC) conditions were as follows: gas phase model Trace 1310, using TG-5 capillary column (60m×0.25mm×0.25μm); carrier gas was He, constant flow rate 1.0mL / min. Temperature program: initial temperature 40℃; initial time 3min; injection port temperature: 280℃; column temperature 40℃, maintained for 2min, column flow rate increased to 280℃ at 5℃ / min, maintained for 5min; injection in splitless mode.

[0055] The mass spectrometry (MS) conditions were as follows: mass spectrometer model TSQ 8000; using EI ion source; interface temperature 280°C; ion source temperature 300°C; emission current 25 μA; electron energy 70 eV; mass scan range set to 35 m / z to 350 m / z; detector voltage 1000 V.

[0056] Protein loss rate: According to GB / T5009.5-2010, Kjeldahl method was used.

[0057] The raw materials used in the examples are:

[0058] 1. Neutral lipase was purchased from Shandong Longkote Enzyme Preparation Co., Ltd. with production number SC20137132300142.

[0059] 2. Catfish was purchased from Xuelang Vegetable Market in Wuxi City, Jiangsu Province.

[0060] Example 1

[0061] After removing the head, tail and internal organs of the fresh fish, wash, peel, debone and cut the fish body into fish fillets about 1.5 cm thick with a mass of about 60 g, and drain after washing; add glycine (Gly)-sodium hydroxide (NaOH) buffer solution of equal mass to the fish fillets to a beaker, weigh a certain amount of enzyme in proportion using a weighing instrument, and change the enzyme addition amount to 100U / ml, 200U / ml, and 300U / ml after mixing; adjust the pH of the solution to 7; adjust the water bath temperature to 50°C, completely immerse the beaker, and soak for 90 minutes; after the enzymatic hydrolysis is completed, wash the enzymatically hydrolyzed fish fillets with distilled water, remove the surface enzyme solution and drain. Use a meat grinder to grind the enzymatically hydrolyzed fish pieces once every 5 seconds, repeat 10 times, beat into fish paste and measure relevant parameters, such as Figure 2 The sensory test results are shown in Figure 3 shown.

[0062] like Figure 1 As shown, in the untreated fish fillets, the contents of fishy substances were hexanal 13.21531ug / kg, 1-octen-3-ol 0.71685ug / kg, octanal 0.93946ug / kg, and nonanal 9.01548ug / kg. After treatment with 100U / ml neutral lipase, the contents of fishy substances were hexanal 4.21549ug / kg, 1-octen-3-ol 0.35449ug / kg, octanal 0.16584ug / kg, and nonanal 3.15497ug / kg, all of which were significantly decreased.

[0063] Depend on Figure 2It can be seen that adding different enzyme addition amounts will have a certain impact on the degreasing rate and related oxidation indicators, and the fishy smell is significantly reduced after adding enzymes (relative to 0U / ml). From the perspective of degreasing rate, the impact is 300U / ml>200U / ml>100U / ml. And the group with an enzyme addition of 300U / ml is higher than the other two groups. From the perspective of acid value, POV and TBA, 300U / ml is the highest after three freeze-thaw cycles, which is because the indexes are increased due to the influence of hydrolases. At 200U / ml, POV first increased and then decreased, which may be because a part of the primary oxidation products in the later stage of oxidation becomes secondary oxidation products.

[0064] From the sensory map ( Figure 3 ) It can be seen that with the increase in the amount of enzyme added, the fishy smell, grassy smell, earthy smell, and mushroom smell all increased, while the fat smell decreased. With the increase in the number of freeze-thaw cycles, the fishy smell became significantly heavier.

[0065] As the amount of enzyme added increases, the degreasing rate increases, but the acid value also increases. When the enzyme addition amount is 100U / ml, the acid value is relatively low and the fishy smell is also weak, so the optimal enzyme addition range is 80-120U / ml.

[0066] Example 2

[0067] After removing the head, tail and internal organs of the fresh fish, wash, peel, debone and cut the fish body into fish fillets about 1.5 cm thick with a mass of about 60 g, and drain after washing; add glycine (Gly)-sodium hydroxide (NaOH) buffer solution of equal mass to the fish fillets to a beaker, weigh a certain amount of enzyme in proportion using a weighing instrument, and after mixing, the enzyme addition amount is 300U / ml; adjust the pH of the solution to 7; adjust the temperature of the water bath to 50°C, immerse the beaker completely, and change the immersion time to 30min, 60min, and 90min respectively; after the enzymatic hydrolysis is completed, wash the enzymatically hydrolyzed fish fillets with distilled water, remove the surface enzyme solution and drain. Use a meat grinder to grind the enzymatically hydrolyzed fish pieces once every 5 seconds, repeat 10 times, beat into fish paste and measure relevant parameters, such as Figure 4 The sensory test results are shown in Figure 5 shown.

[0068] from Figure 4It can be seen that with the increase in the number of freeze-thaw cycles, the degreasing rate, acid value, and POV generally show an upward trend. This is because the freeze-thaw process causes damage to the cell structure and accelerates the separation and dissolution of fat. In this experiment, the degreasing rate of the 90-min group was higher than that of the other two groups. From the perspective of acid value, 30min<60min<90min. Longer soaking will lead to higher fat hydrolysis and oxidation, resulting in higher acid value. The peroxide value was higher in the two groups with shorter soaking time in the early stage. Long-term soaking (90min) may reduce the primary oxidation of fat in some way, which may be related to the antioxidant substances in the soaking process. From the perspective of TBA, 90min was the lowest at the beginning, and it increased as oxidation continued to intensify, which may be because long-term soaking accelerated the deep oxidation of fat.

[0069] From sensory data ( Figure 5 ), appropriately shortening the immersion time in enzyme solution can effectively improve the sensory quality of fish, especially reduce the fishy smell, thereby increasing the acceptance of fish. However, too short an immersion time may lead to insufficient reaction, while too long an immersion time may damage the fish tissue and increase the experimental time cost.

[0070] Therefore, the optimal soaking time range is 25 to 35 minutes.

[0071] Example 3

[0072] After removing the head, tail and internal organs of the fresh fish, wash, peel, debone and cut the fish body into fish fillets about 1.5 cm thick with a mass of about 60 g, and drain after washing; add glycine (Gly)-sodium hydroxide (NaOH) buffer solution with a mass ratio of 1:1, 1:2, and 1:3 to the beaker, weigh a certain amount of enzyme in proportion using a weighing instrument, and the enzyme addition amount after mixing is 300U / ml; adjust the pH of the solution to 7; adjust the temperature of the water bath to 50°C, completely immerse the beaker, and the soaking time is 90 minutes; after the enzymatic hydrolysis is completed, wash the enzymatically hydrolyzed fish fillets with distilled water, remove the surface enzyme solution and drain. Use a meat grinder to grind the enzymatically hydrolyzed fish pieces once every 5 seconds, repeat 10 times, beat into fish paste and measure relevant parameters, such as Figure 6 The sensory test results are shown in Figure 7 shown.

[0073] from Figure 6 It can be seen that when the fish liquid ratio is 1:1, the degreasing rate is the highest. When the fish liquid ratio is 1:1, the POV increases significantly with the increase in the number of freeze-thaw cycles, and exceeds 1:2 and 1:3. This may be because the lower fish liquid ratio may lead to a more concentrated oxidation reaction and generate more peroxides. The TBA value is the highest at 1:2, and 1:1 is relatively lower, indicating that the 1:1 fish liquid ratio is more conducive to the removal of fishy substances. From the perspective of acid value, the fish liquid ratio is the lowest at 1:1.

[0074] from Figure 7 From the above, it can be seen that appropriately reducing the fish-liquid ratio can reduce the fishy smell. As the number of freeze-thaw cycles increases, the fishy smell becomes heavier. At the same time, too low a fish-liquid ratio cannot completely immerse the fish meat, which may cause an insufficient reaction. Therefore, the optimal fish-liquid ratio range is 1:0.8 to 1:1.2.

[0075] Example 4

[0076] After removing the head, tail and internal organs of the fresh fish, wash, peel, debone and cut the fish body into fish fillets about 1.5 cm thick with a mass of about 60 g, and drain after washing; add glycine (Gly)-sodium hydroxide (NaOH) buffer solution of equal mass to the fish fillets to a beaker, weigh a certain amount of enzyme in proportion using a weighing instrument, and after mixing, the enzyme addition amount is 300U / ml; adjust the pH of the solution to 5, 7, and 9 respectively; adjust the temperature of the water bath to 50°C, completely immerse the beaker, and the soaking time is 90 minutes; after the enzymatic hydrolysis is completed, wash the enzymatically hydrolyzed fish fillets with distilled water, remove the surface enzyme solution and drain. Use a meat grinder to grind the enzymatically hydrolyzed fish pieces once every 5 seconds, repeat 10 times, make fish paste and measure relevant parameters, such as Figure 8 The sensory test results are shown in Fig. 9 shown.

[0077] from Figure 8 It can be seen that the degreasing rate is the highest at pH = 7, the lowest at pH = 5, and even lower at pH = 9. From the perspective of acid value, pH = 7 is the lowest, so it is most conducive to the removal of fishy substances. As fat oxidation continues to intensify, POV increases significantly. Finally, pH = 7 and 9 are higher. The TBA value is the highest under alkaline conditions, which may be because under alkaline conditions, fat oxidation reactions are more likely to generate secondary products, resulting in an increase in the TBA value. Under neutral conditions, the oxidation reaction is relatively mild.

[0078] from Fig. 9 From the above, we can see that most of the fishy smell indicators at pH = 7 have decreased, and other indicators are not much different from the other two groups, which is a more ideal choice.

[0079] In summary, the optimal pH range is 6.5-7.5.

[0080] Example 5

[0081] After removing the head, tail and internal organs of the fresh fish, wash, peel, debone and cut the fish body into fish fillets about 1.5 cm thick with a mass of about 60 g, and drain after washing; add glycine (Gly)-sodium hydroxide (NaOH) buffer solution of equal mass to the fish fillets to a beaker, weigh a certain amount of enzyme in proportion using a weighing instrument, and the enzyme addition amount after mixing is 300U / ml; adjust the pH of the solution to 7; adjust the temperature of the water bath to 30°C, 40°C, and 50°C respectively, and immerse the beaker completely, and the soaking time is 90 minutes respectively; after the enzymatic hydrolysis is completed, wash the enzymatically hydrolyzed fish fillets with distilled water, remove the surface enzyme solution and drain. Use a meat grinder to grind the enzymatically hydrolyzed fish pieces once every 5 seconds, repeat 10 times, beat into fish paste and measure relevant parameters, such as Fig.10 The sensory test results are shown in Fig.11 shown.

[0082] from Fig.10 It can be seen that the degreasing rate is the highest at 50℃. POV increases with the increase of temperature and increases significantly with the increase of freeze-thaw times. From the perspective of TBA, the 50℃ group in the later period is the highest. The acid value is the lowest at 30℃, indicating that the removal effect of fishy substances is better at this temperature.

[0083] from Fig.11 It can be seen that within the selected range, as the temperature increases, the fishy smell and related fat flavor substances increase. This shows that high temperature is not suitable for removing fishy smell, but too low a temperature may require a longer reaction time.

[0084] In summary, the optimal temperature selection range is 25-35°C.

[0085] Example 6

[0086] After removing the head, tail and internal organs of the fresh fish, wash, peel, debone and cut the fish body into fish fillets about 1.5 cm thick with a mass of about 60 g. Drain after washing; add glycine (Gly)-sodium hydroxide (NaOH) buffer solution of equal mass to the fish fillets to a beaker, weigh a certain amount of enzyme in proportion using a weighing instrument, and after mixing, the enzyme addition amount is 100U / ml; the fish-liquid ratio is 1:1; adjust the pH of the solution to 7; adjust the water bath temperature to 30°C, completely immerse the beaker, and the soaking time is 30 minutes; after the enzymatic hydrolysis is completed, wash the enzymatically hydrolyzed fish fillets with distilled water, remove the surface enzyme solution and drain. Use a meat grinder to grind the enzymatically hydrolyzed fish pieces once every 5 seconds, repeat 10 times, beat into fish paste and measure relevant parameters. Specifically, Fig.12 shown.

[0087] Comparative Example 1

[0088] The neutral lipase in Example 1 was replaced by alkaline lipase. The addition amount of alkaline lipase was 300 U / ml. Other conditions or parameters were the same as those in Example 1.

[0089] The protein content of the fish fillets in Example 1 (neutral lipase addition amount is 300U / ml) and Comparative Example 1 was detected. The protein content of the fish fillets treated with alkaline lipase was reduced from 16.74% to 15.88%, while the protein content of the fish fillets treated with neutral protease was only reduced from 16.74% to 16.70%. Fig.13 As shown, almost no change occurred.

[0090] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for removing freshwater fish odor substances by enzyme defatting, characterized in that: The method comprises the following steps: treating fish fillets with neutral lipase in a glycine-sodium hydroxide buffer solution, wherein the addition amount of the neutral lipase in the treatment system is 80-300 U / ml.

2. The method according to claim 1, characterized in that: The material-liquid ratio of the buffer solution to the fish fillet is 1:0.8 to 1:

3.

3. The method according to claim 1 or 2, characterized in that: The neutral lipase is used to treat the fish fillet for 25 to 90 minutes.

4. The method according to any one of claims 1 to 3, characterized in that: The temperature of the fish fillet treated with the neutral lipase is 25-50°C.

5. The method according to any one of claims 1 to 4, characterized in that: The pH of the fish fillet treated with the neutral lipase is 6.5-9.

6. The method according to any one of claims 1 to 5, characterized in that: The method comprises treating fish fillets with neutral lipase in a glycine-sodium hydroxide buffer solution; The neutral lipase is added in an amount of 80 to 120 U / ml in the treatment system; The material-liquid ratio of the buffer solution to the fish fillet is 1:0.8 to 1:1.2; The neutral lipase treatment time of the fish fillet is 25 to 35 minutes; The temperature of the fish fillet treated with neutral lipase is 25-35°C; The pH of the fish fillet treated with the neutral lipase is 6.5-7.

5.

7. A method for reducing the content of hexanal, 1-octen-3-ol, octanal and / or nonanal in fish fillets, characterized in that: The method comprises the following steps: treating fish fillets with neutral lipase in a glycine (Gly)-sodium hydroxide (NaOH) buffer solution at 25-50°C and pH 6.5-9, wherein the addition amount of the neutral lipase in the treatment system is 80-300 U / ml.

8. The method according to claim 7, characterized in that The material-liquid ratio of the buffer solution to the fish fillet is 1:0.8 to 1:

3.

9. The method according to claim 7, characterized in that: The neutral lipase is used to treat the fish fillet for 25 to 90 minutes.

10. Use of the method according to any one of claims 1 to 6, or the method according to any one of claims 7 to 9 in processing fish fillet products.

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