Method for removing fishy smell of eucheuma

Abstract

The invention relates to the technical field of food fermentation, in particular to a method for removing fishy smell of eucheuma, which comprises the following steps: pretreating eucheuma; mixing the pretreated eucheuma with a lactobacillus plantarum solution, and fermenting in a fermentation tank; the fermentation tank comprises a reciprocating pump and an air supply system; after fermentation is completed, removing the bacterial liquid, cleaning the eucheuma, and draining water to obtain frond of the eucheuma; after fermentation, washing the eucheuma, carrying out alkali treatment, washing to be neutral, boiling glue in a water bath, and centrifuging to obtain algal glue; the eucheuma is treated by adopting a microbial fermentation technology, chemical substances are not introduced, the cost is low, and the operation is simple; through the pressurized injection technology combining the reciprocating pump with the air supply system, the bacterial liquid is used for impacting the surface of the eucheuma to form pits, so that various substances can be conveniently separated out, the contact area between the bacterial liquid and the eucheuma is increased, a better fermentation effect is achieved, and the fermentation time is shortened; the damage to a carrageenan network structure and the degradation of a molecular chain in a microbial fermentation process are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of food fermentation, and particularly relates to a method for removing the fishy smell of Eucheuma. Background Art

[0002] Eucheuma ( Eucheuma muricatum ) is one of the large algal populations in the world and has important economic value. Many studies have shown that various dietary nutrients such as active polysaccharides rich in Eucheuma have a positive regulatory effect on human health. However, due to the strong and unpleasant volatile substances such as algal fishy smell in Eucheuma, it is difficult to remove during the processing, making it unacceptable to consumers and seriously affecting the development and promotion of Eucheuma and its processed products. Therefore, in the processing of Eucheuma, higher requirements are put forward for the technology of retaining flavor substances and removing fishy smell substances.

[0003] In order to reduce the fishy smell of algae, current studies have separated or masked fishy smell substances by physical methods to reduce the bad flavor brought by fishy smell substances. Although it has high safety, the removal effect is not ideal; there is also the use of chemical reagents such as acids and alkalis, but it is easy to produce chemical residues that are difficult to remove and a large amount of chemical waste in such processes. The microbial fermentation deodorization technology has gradually been applied to the removal of peculiar smells in foods due to its advantages of natural environmental protection, high nutrient retention rate, and high safety. Microbial fermentation mainly relies on the metabolic function of microorganisms to metabolize and convert fishy smell substances into odorless small molecule substances.

[0004] However, although microbial fermentation of Eucheuma can achieve a good deodorization effect, the gel strength of the carrageenan obtained by extraction is significantly decreased compared with the carrageenan extracted without microbial fermentation. This is because the enzymes and organic acids produced during the microbial fermentation process easily damage the network structure of carrageenan and degrade the molecular chain, resulting in a change in the molecular weight of carrageenan and a decrease in gel strength, thus greatly affecting the quality of carrageenan products.

[0005] Therefore, a method for removing the fishy smell of Eucheuma is needed, which can improve the existing microbial deodorization to ensure the removal of fishy smell while avoiding the problem of reducing the quality of carrageenan. Summary of the Invention

[0006] The technical problem to be solved by the present invention is: to provide a method for removing the fishy smell of Eucheuma, which can improve the existing microbial deodorization to ensure the removal of fishy smell while reducing the problem of quality decline of carrageenan.

[0007] In order to solve the above technical problem, the technical solution adopted by the present invention is: A method for removing the fishy smell of Eucheuma, comprising Step S1, the pretreatment of Eucheuma; Step S2: Mix the pretreated Eucheuma with the Lactobacillus plantarum liquid. The value of the Lactobacillus plantarum liquid is 0.8 - 1.2, the viable count is 1× CFU / mL, and the inoculation amount is 0.5 - 2% v / v. After mixing, place it in a fermentation tank for fermentation. The fermentation tank includes a controller, a tank body, a reciprocating pump, and a gas supply system. The tank body includes a top cover and a main body. When the top cover and the main body are combined, a closed space is formed. An inlet and a camera facing the main body are provided on the top cover. A nozzle is provided on the inlet. An outlet is provided at the bottom of the side wall of the main body. A heating device, a stirring device, and a temperature sensor are also provided inside the main body. The reciprocating pump includes a pump body, a piston, a first connecting rod, a second connecting rod, and a reciprocating motor. The piston is arranged in the pump body and divides the pump body into a liquid pumping space and a connecting space. A liquid outlet check valve is provided at the top of the liquid pumping space, and a liquid inlet check valve is provided at the bottom. The liquid outlet check valve is communicated with the inlet, and the liquid inlet check valve is communicated with the outlet through a pipeline. A first solenoid valve is provided on the outlet. The connecting space is communicated with the outside and faces the reciprocating motor. One end of the second connecting rod is fixedly connected to the reciprocating motor, and the other end is a free end. Two ends of the first connecting rod are respectively movably connected to one side of the piston facing the connecting space and the free end. The gas supply system includes a gas cylinder and a second solenoid valve. The gas cylinder is communicated with the pump body and the pipeline through the second solenoid valve respectively; The fermentation includes: Open the top cover, mix the pretreated Eucheuma with the Lactobacillus plantarum liquid and add it to the main body, then close the top cover to form a seal. The controller controls the opening of the instant heating device according to the temperature sensor, and at the same time starts the stirring device, the reciprocating motor, and the first solenoid valve. The stirring motor stirs in real time. The reciprocating motor works, and the movement of the piston makes the Lactobacillus plantarum liquid enter the liquid pumping space, thereby causing the liquid level in the main body to drop, and part of the Eucheuma is exposed outside the Lactobacillus plantarum liquid. The movement of the piston causes the liquid pumping space to be squeezed to achieve a primary pressurization. While the liquid pumping space is being squeezed, the second solenoid valve is opened to send gas into the liquid pumping space to achieve a secondary pressurization. After pressurization, the Lactobacillus plantarum liquid sprayed out by the nozzle impacts the exposed Eucheuma under high pressure, thereby causing damage to the surface of the Eucheuma. Pits are formed at the damaged parts of the surface of the Eucheuma to increase the contact area with the Lactobacillus plantarum liquid. The controller determines whether the degree of damage to the surface of the Eucheuma reaches the expectation according to the camera. If not, continue to impact until it reaches the expectation. If so, the controller controls the opening of the second solenoid valve, sends the gas in the gas cylinder into the pump body and the pipeline, discharges the bacterial liquid in the pump body and the pipeline, and then closes the reciprocating motor, the stirring device, the first solenoid valve, and the second solenoid valve until the fermentation is completed; Step S3: After the fermentation is completed, remove the bacterial liquid, wash the Eucheuma clean and drain the water to obtain the thallus of Eucheuma; Step S4: After the fermentation of Eucheuma is completed, wash it, perform alkali treatment, wash it to neutrality, boil the glue in a water bath for 1.5 - 2 h, and centrifuge to obtain algin.

[0008] Preferably, take 10 g of the thallus obtained in step S3, transfer it to a 60 mL headspace vial, place it in a water bath at 70 °C for 30 min to equilibrate, adsorb it with an aged extraction head for 30 min, then insert the extraction head into the GS-MS sample port, desorb for 5 min, and analyze it using the GS-MS detection method.

[0009] Preferably, take 10 g of the alginate obtained in step S4, transfer it to a 60 mL headspace vial, place it in a water bath at 70 °C for 30 min to equilibrate, adsorb it with an aged extraction head for 30 min, then insert the extraction head into the GS-MS sample port, desorb for 5 min, and analyze it using the GS-MS detection method.

[0010] Preferably, the GS-MS detection method includes: GC conditions: The chromatographic column is Rtx-5MS, the carrier gas is high-purity helium with a purity of 99.999%, the column flow rate is 3 mL / min, and splitless injection is used; Temperature programming: Programmed temperature rise, the inlet temperature is 230 °C, the initial temperature is 40 °C, then it is heated to 54 °C at a rate of 1 °C / min, heated to 80 °C at a rate of 12 °C / min, heated to 170 °C at a rate of 3 °C / min, heated to 220 °C at a rate of 5 °C / min, and held for 3 min. The total program is 59.17 min; MS conditions: The ion source temperature is 220 °C, the ionization mode is EI, the ionization energy is 70 eV, the interface temperature is 250 °C, the ion fragment scanning range is 35 - 500 m / z, and the solvent delay time is 2.5 min.

[0011] Preferably, the GS-MS detection method further includes: qualitative and quantitative analysis of volatile flavor components, and the qualitative and quantitative analysis of volatile flavor components includes qualitative analysis and quantitative analysis; Qualitative analysis includes: Perform similarity retrieval using a mass spectrometry database, select substances with a mass spectrometry matching degree greater than 80%, and then combine the base peak and characteristic ion peaks; Compare the retention time obtained from the qualitative analysis of the n-alkane standard product with the retention time of the volatile flavor components in the sample; Compare and identify according to the retention index calculated by formula 1: Formula 1 where n: the number of carbon atoms of the n-alkane; RIx: the retention index of the component to be measured; RTx: the retention time of the component to be measured; RTn: the retention time of the n-alkane Cn; RTn+1: the retention time of the n-alkane Cn+1.

[0012] Preferably, quantitative analysis includes: Formula 2 According to the qualitative analysis results, the internal standard method is adopted for relative quantification. Cyclohexanone is used as the internal standard substance, and the quantitative analysis results are calculated according to Formula 2.

[0013] Preferably, step S1 further includes: cleaning and removing impurities from Eucheuma, drying it in the sun, adding glucose water with a mass concentration of 1-5%, and the ratio of Eucheuma to glucose water is 1:10-50 g / mL. After pasteurization, it is cooled to room temperature.

[0014] Preferably, step S2 further includes: Mixing the pretreated Eucheuma with Lactobacillus plantarum liquid, and the value of the Lactobacillus plantarum liquid is 0.8-1.2, the viable count is 1× CFU / mL, the inoculation amount is 0.5-2% v / v, and the inoculation amount of 2% is inoculated at 37 °C; after mixing, it is placed in a fermenter for fermentation for 2-4 h.

[0015] Preferably, step S4 further includes: Mixing a 10% NaOH solution and a 12% KCl solution in a volume ratio of 1:1 to form a mixed solution and adding it to Eucheuma. It is water-bathed at 60-65 °C for 3-4 h. After the water bath is completed, Eucheuma is separated from the mixed solution and soaked repeatedly with water. The ratio of Eucheuma to water is 1:100-200 g / mL, and each soaking lasts for 30-90 min until the pH of Eucheuma is 7; adding water to Eucheuma, the ratio of Eucheuma to water is 1:20-30 g / mL, and it is water-bathed at 100 °C for 1.5 h-2 h. Centrifuge while it is hot, separate and take the supernatant to obtain alginate.

[0016] Preferably, a pressure balance valve is provided on the top cover.

[0017] The beneficial effects of the present invention are as follows: By adopting the microbial fermentation technology to process Eucheuma and its processed products, and at the same time analyzing the differences in the volatile components of the samples through quantitative descriptive sensory evaluation combined with HP-SPME-GC-MS (headspace solid-phase microextraction combined with gas chromatography-mass spectrometry); The present invention uses the microbial fermentation technology method of green and safe processing to process the samples, which neither introduces chemical substances, has low cost and simple operation, and is a good means to improve the flavor. By adopting the pressure jet technology, potholes are formed on the surface of Eucheuma by using the bacterial liquid to impact, which is convenient for the precipitation of various substances, and at the same time increases the contact area between the bacterial liquid and Eucheuma, thereby achieving a better fermentation effect and shortening the fermentation time. Shortening the fermentation time can reduce the damage to the carrageenan network structure and the degradation of molecular chains during the microbial fermentation process, achieving the performance purpose of maintaining the gel strength of carrageenan. The destruction of the Eucheuma structure can also shorten the water bath time for obtaining alginate subsequently, and can also increase the alginate yield; At the same time, the combination of subjective sensory evaluation and objective instrument analysis can better explain the relationship between the flavor chemical components of food and the sensory experience, so as to clarify the mechanism of flavor removal and enhancement. After being treated by the impact fermentation technology of Lactobacillus plantarum, through quantitative descriptive sensory evaluation, the algal odor of Eucheuma thallus and its processed product alginate is significantly weakened. Through GS-MS detection, the relative contents of the odorant representatives: 1-octen-3-ol, 1-octen-3-one, hexanal, octanal, nonanal, (E)-4-decenal and 2,4-(E,E)-nona-2,4-dienal and other off-flavor substances are significantly reduced, and the deodorization effect is significant; At the same time, the types and numbers of acids and esters increase, and odors such as fermentation fragrance, floral fragrance and sweet fragrance are produced. In summary, it shows that the fermentation of Lactobacillus plantarum has the effect of deodorization and flavor enhancement, and can ensure the strength of carrageenan by shortening the fermentation time; By adopting the form of reciprocating pump, the traditional centrifugal pump is prone to failure due to the sudden change in the temperature of the bacterial liquid caused by the high-speed rotation and friction of the impeller, and the reciprocating pump generates a large pressure, which is suitable for mass production in food work; The primary pressurization of the reciprocating pump plus the secondary pressurization of the gas (realizing gas variable volume) can achieve a faster speed when the bacterial liquid is ejected, ensuring sufficient kinetic energy and the bacterial liquid droplets can be impacted small enough by the airflow due to the presence of the gas when ejected. Coupled with stirring, the Eucheuma in the fermentation tank can be evenly and locally broken. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The figure shows the sensory evaluation radar chart of Eucheuma thallus and its processed product (alginate) of the embodiment and comparative example of the present invention; Figure 2 The figure shows the total ion chromatogram of the volatile flavor substances of Eucheuma thallus and its processed product (alginate) of the embodiment and comparative example of the present invention; Figure 3The figure shows the types of volatile flavor compounds in the thalli of Eucheuma muricatum and its processed products (algal gum) in the examples and comparative examples of the present invention; Figure 4 The figure shows the contents of volatile flavor compounds in the thalli of Eucheuma muricatum and its processed products (algal gum) in the examples and comparative examples of the present invention; Figure 5 The figure shows a schematic structural diagram of the fermenter used in the examples of the present invention; Label description: 1. Tank body; 11. Top cover; 12. Body; 13. Nozzle; 2. Reciprocating pump; 21. Pump body; 22. Piston; 23. First connecting rod; 24. Second connecting rod; 25. Reciprocating motor; 26. Pumping liquid space; 27. Liquid outlet check valve; 28. Liquid inlet check valve; 3. Air supplementing system; 31. Gas cylinder; 32. Second solenoid valve; 4. Pipeline; 41. First solenoid valve. Detailed implementation manners

[0019] To describe in detail the technical content, achieved object and effects of the present invention, the following is described in conjunction with the implementation manners and with reference to the drawings.

[0020] The test materials used in the present invention are all ordinary commercially available products and can be purchased in the market; The Eucheuma muricatum raw material involved in the present invention comes from Green New (Fujian) Food Co., Ltd.; Lactobacillus plantarum subsp. bulgaricus: Purchased from China Center of Industrial Culture Collection (CICC6076). Examples

[0021] Refer to Figures 1 - 5 ; A method for removing the fishy smell of Eucheuma muricatum, comprising: Step S1. Pretreat Eucheuma muricatum: Wash, remove impurities and dry Eucheuma muricatum, then add glucose water with a mass concentration of 2%, and the ratio of Eucheuma muricatum to glucose water is 1:30 g / mL, and cool to room temperature after pasteurization.

[0022] Step S2: Ferment Eucheuma muricatum with Lactobacillus plantarum (using 2% sugar water, liquid-to-material ratio of 30:1 ml / g, the value of the Lactobacillus plantarum liquid is 0.8 - 1.2, and the viable count is 1× CFU / mL, the inoculum amount is 0.5 - 2% v / v, and 2% of the inoculum amount is inoculated and fermented at 37°C for 2 h); the fermentation tank includes a controller, a tank body 1, a reciprocating pump 2, and a gas supplementing system 3. The tank body 1 includes a top cover 11 and a body 12. When the top cover 11 and the body 12 are combined, a closed space is formed. An inlet and a camera facing the body 12 are provided on the top cover 11. A nozzle 13 is provided on the inlet. An outlet is provided at the bottom of the side wall of the body 12. A heating device, a stirring device, and a temperature sensor are also provided inside the body 12; the reciprocating pump 2 includes a pump body 21, a piston 22, a first connecting rod 23, a second connecting rod 24, and a reciprocating motor 25. The piston 22 is arranged inside the pump body 21 to divide the body 12 into a liquid pumping space 26 and a connecting space. A liquid outlet check valve 27 is provided at the top of the liquid pumping space 26, and a liquid inlet check valve 28 is provided at the bottom. The liquid outlet check valve 27 is communicated with the inlet, and the liquid inlet check valve 28 is communicated with the outlet through a pipeline 4. A first solenoid valve 41 is provided on the outlet; the connecting space is communicated with the outside and faces the reciprocating motor 25; one end of the second connecting rod 24 is fixedly connected to the reciprocating motor 25, and the other end is a free end; both ends of the first connecting rod 23 are respectively movably connected to one side of the piston 22 facing the connecting space and the free end; the gas supplementing system 3 includes a gas cylinder 31 and a second solenoid valve 32. The gas cylinder 31 is communicated with the pump body 21 and the pipeline 4 through the second solenoid valve 32; Fermentation includes: pre-sterilizing the fermenter. After sterilization is completed, open the top cover 11, mix the pretreated Eucheuma and Lactobacillus plantarum liquid and add them into the main body 12, then close the top cover 11 to form a seal; the controller controls the activation of the instant heating device (heating to 37 °C) according to the temperature sensor, and at the same time starts the stirring device, the reciprocating motor 25, and the first solenoid valve 41. The stirring motor stirs in real time; the reciprocating motor 25 operates to make the Lactobacillus plantarum liquid enter the liquid pumping space 26 through the movement of the piston 22, thereby causing the liquid level in the main body 12 to drop, and part of the Eucheuma is exposed outside the Lactobacillus plantarum liquid; the movement of the piston 22 causes the liquid pumping space 26 to be squeezed to achieve a primary pressurization. While the liquid pumping space 26 is being squeezed, the second solenoid valve 32 is opened to send gas into the liquid pumping space 26 to achieve secondary pressurization (the second solenoid valve 32 is closed when the liquid pumping space 26 expands). After pressurization, the Lactobacillus plantarum liquid ejected from the nozzle 13 impacts the exposed Eucheuma under high pressure, thereby causing damage to the surface of the Eucheuma. Pits are formed at the damaged parts on the surface of the Eucheuma to increase the contact area with the Lactobacillus plantarum liquid; the controller determines whether the degree of damage on the surface of the Eucheuma reaches the expectation based on the camera (for example, the degree of damage is that there are damages on the surface of the Eucheuma, but the whole Eucheuma does not break due to these damages). If not, continue to impact until it reaches the expectation. If so, the controller controls the opening of the second solenoid valve 32, sends the gas in the gas cylinder 31 (the gas is nitrogen or sterilized compressed air) into the pump body 21 and the pipeline 4, discharges the bacterial liquid in the pump body 21 and the pipeline 4, and then closes the reciprocating motor 25, the stirring device, the first solenoid valve 41, and the second solenoid valve 32 until fermentation is completed; Step S3: After fermentation is completed, remove the bacterial liquid, wash the Eucheuma clean and drain the water to obtain the thallus of Eucheuma; take 10 g of the obtained thallus and transfer it to a 60 mL headspace vial, place it in a water bath at 70 °C for 30 min to equilibrate, adsorb it with an aged extraction head for 30 min, then insert the extraction head into the GS-MS sample port and desorb it for 5 min, and analyze it using the GS-MS detection method.

[0023] Step S4: Mix a NaOH solution with a mass fraction of 10% and a KCl solution with a mass fraction of 12% in a volume ratio of 1:1 to form a mixed solution, add it to Eucheuma, and perform a water bath at 60 - 65 °C for 3 - 4 h. After the water bath is completed, separate Eucheuma from the mixed solution, soak it repeatedly with water. The ratio of Eucheuma to water is 1:100 - 200 g / mL, and each soaking lasts for 30 - 90 min until the pH of Eucheuma is 7. Add water to Eucheuma, with the ratio of Eucheuma to water being 1:20 - 30 g / mL, perform a water bath at 100 °C for 1.5 - 2 h, centrifuge while it is hot, separate and take the supernatant to obtain alginate. Take 10 g of the obtained alginate and transfer it to a 60 mL headspace vial, place it in a water bath at 70 °C to equilibrate for 30 min, adsorb it with an aged extraction head for 30 min, then insert the extraction head into the GS-MS sample port, desorb it for 5 min, and perform analysis using the GS-MS detection method.

[0024] The GS-MS detection method includes: GC conditions: The chromatographic column is Rtx-5MS (30 m × 0.25 mm × 0.25 µm), the carrier gas is high-purity helium with a purity of 99.999%, the column flow rate is 3 mL / min, and splitless injection is used; Temperature programming: Programmed temperature rise, the injection port temperature is 230 °C, the initial temperature is 40 °C, then it is heated to 54 °C at a rate of 1 °C / min, heated to 80 °C at a rate of 12 °C / min, heated to 170 °C at a rate of 3 °C / min, heated to 220 °C at a rate of 5 °C / min, and held for 3 min. The total program is 59.17 min; MS conditions: The ion source temperature is 220 °C, the ionization mode is EI, the ionization energy is 70 eV, the interface temperature is 250 °C, the ion fragment scanning range is 35 - 500 m / z, and the solvent delay time is 2.5 min.

[0025] The GS-MS detection method further includes: qualitative and quantitative analysis of volatile flavor components, and the qualitative and quantitative analysis of volatile flavor components includes qualitative analysis and quantitative analysis; Qualitative analysis includes: Perform similarity searches using a mass spectrometry database (NIST20, NIST20s, FFNSC1.3), select substances with a mass spectrometry matching degree greater than 80%, and then combine the base peak and characteristic ion peaks; n-alkane standards ( - ) Compare the retention time obtained from the qualitative analysis of volatile flavor components with the retention time of volatile flavor components in the sample; Compare and qualitatively analyze the retention index calculated according to Formula 1 with the retention index reported on the website (https: / / webbook.nist.gov / ): Formula 1 Wherein, n: the number of carbon atoms of the n-alkane; RIx: the retention index of the component to be measured; RTx: the retention time of the component to be measured; RTn: the retention time of the n-alkane Cn; RTn+1: the retention time of the n-alkane Cn+1.

[0026] Quantitative analysis includes: Formula 2 According to the qualitative analysis results, the internal standard method is used for relative quantification. Cyclohexanone is used as the internal standard, and the quantitative analysis results are calculated according to Formula 2.

[0027] Comparative example Step S1: The operation is the same as that of Step S1 in the embodiment, and will not be repeated here; Step S2: The Eucheuma is washed and drained, 10 g of the thallus is taken and transferred to a 60 mL headspace vial, placed in a water bath at 70 °C for 30 min to equilibrate, and sensory evaluation is carried out; Step S3: 10 g of the thallus is taken and transferred to a 60 mL headspace vial, placed in a water bath at 70 °C for 30 min to equilibrate, adsorbed by the aged extraction head for 30 min, and then the extraction head is inserted into the GS-MS sample port and desorbed for 5 min for GS-MS analysis.

[0028] Step S4: After the fermentation is completed, the Eucheuma is washed and drained, alkali-treated, washed to neutral, boiled to make glue, and centrifuged; Step S5: 10 g of the alginate is taken and transferred to a 60 mL headspace vial, placed in a water bath at 70 °C for 30 min to equilibrate, adsorbed by the aged extraction head for 30 min, and then the extraction head is inserted into the GS-MS sample port and desorbed for 5 min for GS-MS analysis.

[0029] Result analysis: 1. Carry out sensory evaluation The quantitative descriptive sensory evaluation method is adopted. The evaluation panel consists of 12 trained evaluators (8 females and 4 males, aged 22-25 years). According to the odor description words of algae in the literature, the panel discusses the aroma attribute words of the samples until all members agree on their attributes. Finally, algal odor, fatty odor, grassy odor, mushroom odor, fermented sour odor and floral odor are selected as the odor profile description words of the Eucheuma thallus and alginate. The flavor intensity evaluation adopts a five-point scale (0 points means no aroma, and 5 points means the strongest aroma); 10 g of samples (Comparative Example (algae), Example (algae), Comparative Example (algin), and Example (algin)) were placed in 60 mL headspace vials, equilibrated in a 70°C water bath for 30 minutes, randomly numbered, and sensory evaluations were conducted by evaluators in a clean environment at 25 ± 2°C. Each sample was evaluated three times by evaluators, and the average value was calculated for each sample. The sensory evaluation radar chart was constructed by scoring the main flavor sensory attributes (algae flavor, grassy flavor, floral flavor, fat flavor, mushroom flavor, and fermented sour flavor). The results are shown in the figure below. Figure 1 As shown in Figure 2, after fermentation with Lactobacillus plantarum, the algae, grassy, and mushroom aromas of the algae and its processed product, algin, were significantly reduced, while the floral, fatty, and fermented sour aromas were significantly enhanced. Furthermore, the overall odor value of the algae was significantly higher than that of its processed product, algin.

[0030] 2. HP-SPME-GC-MS (Headspace Solid Phase Microextraction Combined with Gas Chromatography-Mass Spectrometry) was used to analyze the differences in volatile components of the samples To further clarify the effect of plant lactic acid bacteria fermentation on the volatile compounds of fishy smell in Eucheuma and its processed products, this study used HP-SPME technology combined with GS-MS detection to extract and identify volatile compounds, and conducted qualitative analysis of volatile compounds through database comparison and manual analysis. The results are as follows Figures 2 - 3 As shown in the figure, 42 volatile compounds were identified in the comparative example (algae), including 17 aldehydes, 8 alcohols, 11 ketones, 2 esters, 2 olefins, and 2 other compounds. In the example (algae), 48 volatile compounds were identified, including 18 aldehydes, 8 alcohols, 8 ketones, 4 esters, 6 acids, 2 olefins, and 2 other compounds. In the algae samples, the number of compounds primarily distinguished from acids, esters, and other compounds increased after fermentation with Lactobacillus plantarum. This is because the growth and metabolism of Lactobacillus plantarum involve redox reactions and esterification reactions of odorous components such as aldehydes and alcohols during fermentation. This also demonstrates that fermentation can increase the variety of volatile flavor compounds. In the comparative example (algin), 38 volatile compounds were identified, including 16 aldehydes, 5 alcohols, 12 ketones, 3 esters, and 2 other compounds. In the example (algin), 36 volatile compounds were identified, including 11 aldehydes, 8 alcohols, 9 ketones, 5 esters, 1 olefin, and 2 other compounds. The number of volatile flavor compounds in the algin showed little variation. High-pressure spraying damages the Eucheuma itself, maximizing the precipitation of various substances and increasing the bacterial liquid contact area, thereby improving fermentation efficiency. This is one of the reasons why the example (algin) produces more volatile compounds.

[0031] To further clarify the content variation trend of volatile flavor chemicals in Eucheuma and its processed products after fermentation by plant lactic acid bacteria, this study conducted a quantitative analysis of its volatile flavor chemicals (internal standard method). Figure 4 Among them, aldehydes are the most numerous and abundant volatile flavor compounds, followed by ketones and alcohols.

[0032] Aldehydes have a low odor threshold and are important volatile flavor compounds in algae and aquatic products. Among these, compounds associated with fishy odors, such as hexanal, heptanal, octanal, (E)-2-octenal, nonanal, (E)-4-decenal, (E,E)-2,4-nonadienal, (E)-2-decenal, and (E,E)-2,4-decadienal, are common in Eucheuma and its processed algae gel. Octanal and nonanal are the most abundant. After fermentation in a fermenter, the content of these fishy odor-related compounds decreased. Compared to the comparative example, the fishy odor removal rate of the example (algae and gel) was greater than 50%. Therefore, potential conversion reactions occur during the fermentation process. Unsaturated alcohols are generally produced by the enzymatic decomposition of fatty acids or the reduction of carbonyl compounds. They possess distinctive mushroom, earthy, and metallic odors. 1-Octen-3-ol is a typical representative component. After fermentation, the 1-octen-3-ol removal rate in Example (algae) reached 55%, and in Example (algain) the removal rate reached 9%. Ketone compounds are typically produced by the degradation of polyunsaturated fatty acids or microbial oxidation, contributing to the distinctive aroma. However, enones often have an unpleasant odor and can interact synergistically with aldehydes. 1-Octen-3-one, widely recognized as being highly correlated with the fishy odor of seaweed, was found in Example (algae) at a 70% removal rate after fermentation compared to the control sample, while no 1-octen-3-one was found in Example (algain). After fermentation with Lactobacillus plantarum, the Example (algae) produces acidic substances. This is because during the growth and metabolism of Lactobacillus plantarum, aldehydes are converted into acidic substances through its own acid dehydrogenase. The acidic substances are further converted into esters and other compounds, giving the algae a unique flavor, showing lactic acid fermentation flavor, sweetness, and floral fragrance. After fermentation, the ester content of the Example (algae) increased by 5.5 times, while there was no significant change in the Example (algin).

[0033] This study found that Eucheuma (algae) is the key to the production of fishy substances. Through microbial fermentation combined with high-pressure spray technology, the fishy smell of Eucheuma (algae) and its processed products (algin) can be effectively removed, and it also makes a certain contribution to the improvement of the flavor of Eucheuma and its processed products.

[0034] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's description and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for removing the fishy smell of Eucheuma, characterized in that, including Step S1: Pretreatment of Eucheuma Step S2: Mix the pre-treated Eucheuma with the Lactobacillus plantarum liquid, where the value is 0.8 - 1.2, the viable count is 1× CFU / mL, and the inoculum amount is 0.5 - 2% v / v; after mixing, place it in a fermentation tank for fermentation; the fermentation tank includes a controller, a tank body, a reciprocating pump, and an air supplement system. The tank body includes a top cover and a body. When the top cover and the body are combined, a closed space is formed. The top cover is provided with an inlet and a camera facing the body. The inlet is provided with a nozzle. The bottom of the side wall of the body is provided with an outlet. The body is also provided with a heating device, a stirring device, and a temperature sensor; the reciprocating pump includes a pump body, a piston, a first connecting rod, a second connecting rod, and a reciprocating motor. The piston is arranged in the pump body and divides the pump body into a pump liquid space and a connection space. The top of the pump liquid space is provided with a liquid outlet check valve, and the bottom is provided with a liquid inlet check valve. The liquid outlet check valve is communicated with the inlet, and the liquid inlet check valve is communicated with the outlet through a pipeline. The outlet is provided with a first solenoid valve; the connection space is communicated with the outside and faces the reciprocating motor; one end of the second connecting rod is fixedly connected to the reciprocating motor, and the other end is a free end; both ends of the first connecting rod are respectively movably connected to the side of the piston facing the connection space and the free end; the air supplement system includes a gas cylinder and a second solenoid valve. The gas cylinder is communicated with the pump body and the pipeline through the second solenoid valve; The fermentation includes: opening the top cover, mixing the pretreated Eucheuma with Lactobacillus plantarum liquid, adding them into the main body, and then closing the top cover to form a seal; the controller controls the activation of the instant heating device according to the temperature sensor, and at the same time starts the stirring device, the reciprocating motor, and the first solenoid valve. The stirring motor stirs in real time; the reciprocating motor works, and the movement of the piston causes the Lactobacillus plantarum liquid to enter the liquid pumping space, thereby reducing the liquid level in the main body, and part of the Eucheuma is exposed outside the Lactobacillus plantarum liquid; the movement of the piston squeezes the liquid pumping space to achieve a primary pressurization. When the liquid pumping space is squeezed, the second solenoid valve opens to send gas into the liquid pumping space to achieve a secondary pressurization. After pressurization, the Lactobacillus plantarum liquid sprayed by the nozzle impacts the exposed Eucheuma at high pressure, thereby causing damage to the surface of the Eucheuma, and potholes are formed at the damaged part of the Eucheuma surface to increase the contact area with the Lactobacillus plantarum liquid; the controller determines whether the damage degree on the surface of the Eucheuma reaches the expectation according to the camera. If not, continue to impact until it reaches the expectation. If so, the controller controls the opening of the second solenoid valve, sends the gas in the gas cylinder into the pump body and the pipeline to discharge the bacterial liquid in the pump body and the pipeline, and then closes the reciprocating motor, the stirring device, the first solenoid valve, and the second solenoid valve until the fermentation is completed; Step S3: After the fermentation is completed, remove the bacterial liquid, wash the Eucheuma clean and drain the water to obtain the thallus of Eucheuma; Step S4: After the fermentation ends, wash the Eucheuma, perform alkali treatment, wash it to neutral, boil the glue in a water bath for 1.5 - 2 h, and centrifuge to obtain algin; 2. The method for removing the fishy smell of Eucheuma according to claim 1, wherein Take 10 g of the thallus obtained in Step S3 and transfer it to a 60 mL headspace vial, place it in a 70 °C water bath for 30 min to equilibrate, adsorb it with an aged extraction head for 30 min, then insert the extraction head into the GS-MS sample port, desorb it for 5 min, and analyze it using the GS-MS detection method; 3. The method for removing the fishy smell of Eucheuma according to claim 1, characterized in that, Take 10 g of the algin obtained in Step S4 and transfer it to a 60 mL headspace vial, place it in a 70 °C water bath for 30 min to equilibrate, adsorb it with an aged extraction head for 30 min, then insert the extraction head into the GS-MS sample port, desorb it for 5 min, and analyze it using the GS-MS detection method; 4. The method for removing the fishy smell of Eucheuma according to any one of claims 2 or 3, characterized in that, The GS-MS detection method includes: GC conditions: The chromatographic column is Rtx-5MS, the carrier gas is high-purity helium with a purity of 99.999%, the column flow rate is 3 mL / min, and splitless injection; Temperature programming: Programmed temperature rise, the inlet temperature is 230 °C, the initial temperature is 40 °C, then it rises to 54 °C at a rate of 1 °C / min, rises to 80 °C at a rate of 12 °C / min, rises to 170 °C at a rate of 3 °C / min, rises to 220 °C at a rate of 5 °C / min, and holds for 3 min. The total program is 59.17 min; MS conditions: The ion source temperature is 220 °C, the ionization mode is EI, the ionization energy is 70 eV, the interface temperature is 250 °C, the ion fragment scanning range is 35 - 500 m / z, and the solvent delay time is 2.5 min.

5. The method for removing the fishy smell of Eucheuma according to claim 4, characterized in that, The GS-MS detection method further includes: qualitative and quantitative analysis of volatile flavor components, and the qualitative and quantitative analysis of volatile flavor components includes qualitative analysis and quantitative analysis; The qualitative analysis includes: Performing similarity retrieval using a mass spectrometry database, selecting substances with a mass spectrometry matching degree greater than 80%, and then combining the base peak and characteristic ion peaks; Comparing the retention time obtained from the qualitative analysis of the n-alkane standard product with the retention time of the volatile flavor components in the sample; Performing comparative qualitative analysis by calculating the retention index according to Formula 1: Formula 1 Wherein, n: the number of carbon atoms of the n-alkane; RIx: the retention index of the component to be measured; RTx: the retention time of the component to be measured; RTn: the retention time of the n-alkane Cn; RTn+1: the retention time of the n-alkane Cn+1.

6. The method for removing the fishy smell of Eucheuma according to claim 5, wherein, The quantitative analysis includes: Formula 2 According to the results of the qualitative analysis, relative quantification is performed using the internal standard method, with cyclohexanone as the internal standard, and the quantitative analysis results are calculated and output according to Formula 2.

7. The method for removing the fishy smell of Eucheuma according to claim 1, wherein Step S1 further includes: cleaning and removing impurities from Eucheuma, drying it in the sun, adding glucose water with a mass concentration of 1-5%, and the ratio of Eucheuma to glucose water is 1:10-50 g / mL, followed by pasteurization and then cooling to room temperature.

8. The method for removing the fishy smell of Eucheuma according to claim 1, characterized in that, Step S2 further includes: Mix the pre-treated Eucheuma with the Lactobacillus plantarum solution, where the value is 0.8 - 1.2, the viable count is 1× CFU / mL, the inoculation amount is 0.5 - 2% v / v, and an inoculation amount of 2% is added at 37 °C; after mixing, place it in a fermenter and ferment for 2 - 4 h.

9. The method for removing the fishy smell of Eucheuma according to claim 1, wherein, Step S4 further includes: Mixing a 10% NaOH solution and a 12% KCl solution in a volume ratio of 1:1 to form a mixed solution, adding it to Eucheuma, performing a water bath at 60-65 °C for 3-4 h, separating Eucheuma from the mixed solution after the water bath, soaking it repeatedly with water, with the ratio of Eucheuma to water being 1:100-200 g / mL, soaking for 30-90 min each time until the pH of Eucheuma is 7; adding water to Eucheuma, with the ratio of Eucheuma to water being 1:20-30 g / mL, performing a water bath at 100 °C for 1.5-2 h, centrifuging while it is hot, separating and taking the supernatant to obtain alginate.

10. The method for removing the fishy smell of Eucheuma according to claim 1, characterized in that, A pressure balance valve is provided on the top cover.

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