Method for removing fishy smell of Eucheuma

Abstract

The present invention relates to the field of food fermentation technology, and specifically to a method for removing the fishy smell of Eucheuma. The method comprises pre-treating Eucheuma; mixing the pre-treated Eucheuma with a Lactobacillus plantarum liquid and placing the mixture in a fermentation tank for fermentation; the fermentation tank comprises a reciprocating pump and an air supply system; after the fermentation is completed, removing the bacterial liquid, cleaning the Eucheuma and draining the water to obtain the algal body of the Eucheuma; after the fermentation is completed, the Eucheuma is cleaned, subjected to an alkali treatment, washed to neutrality, boiled in a water bath, and centrifuged to obtain the algal gel; the present invention processes the Eucheuma by adopting microbial fermentation technology, does not introduce chemical substances, has low cost, and is simple to operate; the bacterial liquid is used to impact the surface of the Eucheuma by using a reciprocating pump combined with a pressurized injection technology of the air supply system to form pits, thereby facilitating the precipitation of various substances, increasing the contact area between the bacterial liquid and the Eucheuma, achieving a better fermentation effect, shortening the fermentation time, and reducing the damage to the carrageenan network structure and the degradation of the molecular chain during the microbial fermentation process.

Description

Technical Field

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

[0002] Eucheuma Eucheuma muricatum Eucheuma (Euchee) is one of the world's largest algae groups and holds significant economic value. Numerous studies have shown that the active polysaccharides and other dietary nutrients found in Eucheuma have positive regulatory effects on human health. However, Eucheuma's strong, unpleasant algal odor and other volatile compounds are difficult to remove during processing, making it difficult for consumers to accept and severely hindering the development and promotion of Eucheuma and its processed products. Therefore, Eucheuma processing places higher demands on technologies that preserve flavor and remove odorous compounds.

[0003] To reduce the fishy odor of algae, current research involves physical methods to separate or mask the odorous substances, reducing the unpleasant flavor they cause. While these methods are safe, they are not ideal. Another approach involves the use of chemical reagents such as acids and alkalis, but these processes can easily produce difficult-to-remove chemical residues and generate significant amounts of chemical waste. Microbial fermentation, however, is increasingly being used for food odor removal due to its environmentally friendly, high nutrient retention, and safety advantages. Microbial fermentation primarily relies on microbial metabolism to convert odorous substances into odorless small molecules.

[0004] However, although microbial fermentation of Eucheuma can achieve a good deodorizing effect, the gel strength of the extracted carrageenan is significantly lower than that of carrageenan that has not been extracted through microbial fermentation. This is because the enzymes and organic acids produced during the microbial fermentation process can easily destroy the network structure of carrageenan and degrade the molecular chains, causing the molecular weight of carrageenan to change and the gel strength to decrease, which greatly affects the quality of the carrageenan product.

[0005] Therefore, there is a need for a method for removing the fishy smell of Eucheuma that can improve the existing microbial fishy smell removal to ensure that the fishy smell is removed 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 that can improve the existing microbial fishy smell removal to ensure that the fishy smell is removed while reducing the quality degradation of carrageenan.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0008] A method for removing the fishy smell of Eucheuma, comprising:

[0009] Step S1, pre-treating Eucheuma;

[0010] Step S2: mixing the pretreated Eucheuma with the Lactobacillus plantarum liquid. The value is 0.8-1.2, and the number of viable bacteria is 1× CFU / mL, the inoculation amount is 0.5-2% v / v; after the mixing is completed, it is placed in a fermentation tank for fermentation; the fermentation tank includes a controller, a tank body, a reciprocating pump, and an air supply system, the tank body includes a top cover and a main body, the top cover and the main body form a closed space when they cooperate, the top cover is provided with an inlet and a camera arranged toward the main body, the inlet is provided with a nozzle, the bottom of the side wall of the main body is provided with an outlet, and the main 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 provided in the pump body to divide the pump body into a pump liquid space and a connecting rod. The top of the pump liquid space is provided with a liquid outlet one-way valve, and the bottom is provided with a liquid inlet one-way valve, the liquid outlet one-way valve is connected to the inlet, and the liquid inlet one-way valve is connected to the outlet through a pipeline, and the outlet is provided with a first solenoid valve; the connecting space is connected to the outside and is arranged toward 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; the two ends of the first connecting rod are respectively movably connected to the side of the piston facing the connecting space and the free end; the gas replenishing system includes a gas cylinder and a second solenoid valve, and the gas cylinder is connected to the pump body and the pipeline respectively through the second solenoid valve;

[0011] Fermentation includes: opening the top cover, mixing the pretreated Eucheuma and Lactobacillus plantarum liquid, adding it to the main body, and then closing the top cover to form a seal; the controller controls the opening of the heating device according to the temperature sensor, and simultaneously starts the stirring device, the reciprocating motor, and the first solenoid valve, and the stirring motor stirs in real time; the reciprocating motor works by causing the Lactobacillus plantarum liquid to enter the pump liquid space through the movement of the piston, thereby lowering the liquid level in the main body, and part of the Eucheuma is exposed outside the Lactobacillus plantarum liquid; the piston movement squeezes the pump liquid space to achieve a pressurization, and while the pump liquid space is squeezed, the second solenoid valve opens to send liquid into the pump liquid space. The gas is pressurized again, and the Lactobacillus plantarum liquid sprayed from the nozzle after pressurization is subjected to high-pressure impact on the exposed Eucheuma, thereby damaging the surface of the Eucheuma. The damaged parts of the Eucheuma surface form potholes, which increase the contact area with the Lactobacillus plantarum liquid. The controller obtains information from the camera to determine whether the degree of damage on the Eucheuma surface meets the expectation. If not, the impact continues until the expected degree is achieved. If so, the controller controls the opening of the second solenoid valve, sends the gas from 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.

[0012] Step S3: After the fermentation is completed, the bacterial liquid is removed, and the Eucheuma is cleaned and drained to obtain the Eucheuma algae;

[0013] Step S4: After the fermentation is completed, the Eucheuma is washed and treated with alkali, washed until neutral, boiled in a water bath for 1.5-2 hours, and centrifuged to obtain algin.

[0014] Preferably, 10 g of the algae obtained in step S3 is transferred to a 60 mL headspace bottle, placed in a 70 °C water bath for equilibration for 30 min, and adsorbed on the aged extraction head for 30 min. The extraction head is then inserted into the GS-MS sample port, desorbed for 5 min, and analyzed using the GS-MS detection method.

[0015] Preferably, 10 g of the algin obtained in step S4 is transferred to a 60 mL headspace bottle, placed in a 70°C water bath for equilibration for 30 min, and adsorbed on the aged extraction head for 30 min. The extraction head is then inserted into the GS-MS sample port, desorbed for 5 min, and analyzed using the GS-MS detection method.

[0016] Preferably, the GS-MS detection method comprises:

[0017] GC conditions: Rtx-5MS column, 99.999% pure helium as carrier gas, 3 mL / min column flow rate, splitless injection;

[0018] Temperature program: programmed temperature, injection port temperature 230 °C, initial temperature 40 °C, then increase to 54 °C at 1 °C / min, increase to 80 °C at 12 °C / min, increase to 170 °C at 3 °C / min, increase to 220 °C at 5 °C / min, hold for 3 min, total program time 59.17 min;

[0019] Mass spectrometry conditions were as follows: ion source temperature 220 °C, ionization mode EI, ionization energy 70 eV, interface temperature 250 °C, ion fragmentation scan range 35-500 m / z, and solvent delay time 2.5 min.

[0020] Preferably, the GS-MS detection method further comprises: qualitative and quantitative analysis of volatile flavor components, wherein the qualitative and quantitative analysis of volatile flavor components comprises qualitative analysis and quantitative analysis;

[0021] Qualitative analysis includes:

[0022] A similarity search was performed using the mass spectrum database to select substances with a mass spectrum match greater than 80%, and then combined with base peaks and characteristic ion peaks;

[0023] The retention times of n-alkane standards obtained by qualitative analysis of volatile flavor components were compared with the retention times of volatile flavor components in the samples;

[0024] Calculate the retention index according to formula 1 for qualitative comparison:

[0025] Formula 1

[0026] Wherein, n is the number of carbon atoms in normal alkane; RIx is the retention index of the component to be measured; RTx is the retention time of the component to be measured; RTn is the retention time of normal alkane Cn; RTn+1 is the retention time of normal alkane Cn+1.

[0027] Preferably, the quantitative analysis includes:

[0028] Formula 2

[0029] Based on the qualitative analysis results, the internal standard method was used for relative quantification, with cyclohexanone as the internal standard, and the quantitative analysis results were calculated and output according to Formula 2.

[0030] Preferably, step S1 further comprises: washing, removing impurities and drying the Eucheuma, adding glucose water with a mass concentration of 1-5%, the ratio of Eucheuma to glucose water being 1:10-50 g / mL, and cooling to room temperature after pasteurization.

[0031] Preferably, step S2 further comprises:

[0032] The pretreated Eucheuma is mixed with Lactobacillus plantarum liquid. The value is 0.8-1.2, and the number of viable bacteria is 1× CFU / mL, the inoculum amount is 0.5-2% v / v, and the inoculum amount is 2% inoculated at 37°C; after mixing, it is placed in a fermentation tank for fermentation for 2-4 hours.

[0033] Preferably, step S4 further comprises:

[0034] A 10% mass fraction NaOH solution and a 12% mass fraction KCl solution were mixed in a volume ratio of 1:1 to form a mixed solution, which was added to Eucheuma and placed in a water bath at 60-65°C for 3-4 hours. After the water bath, the Eucheuma was separated from the mixed solution and repeatedly soaked in water at a ratio of Eucheuma to water of 1:100-200 g / mL, each soaking for 30-90 minutes until the pH of the Eucheuma reached 7; water was added to the Eucheuma at a ratio of Eucheuma to water of 1:20-30 g / mL, and the Eucheuma was placed in a water bath at 100°C for 1.5-2 hours. The mixture was centrifuged while hot, and the supernatant was separated to obtain alginate.

[0035] Preferably, a pressure balancing valve is provided on the top cover.

[0036] The present invention has the beneficial effects of treating Eucheuma and its processed products using microbial fermentation technology, and analyzing the differences in volatile components of the samples through quantitative descriptive sensory evaluation combined with HP-SPME-GC-MS (headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry). The present invention utilizes a green and safe microbial fermentation process to treat samples, which does not introduce chemical substances, is low-cost, and is simple to operate, making it an effective means of improving flavor. Pressurized spraying technology is employed to impact the surface of Eucheuma with a bacterial liquid, forming pits that facilitate the precipitation of various substances and increase 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 damage to the carrageenan network structure and molecular chain degradation during the microbial fermentation process, thereby maintaining the performance of the carrageenan gel strength. The destruction of the Eucheuma structure can also shorten the water bath time for subsequent algin extraction and improve the gel yield. The combination of subjective sensory evaluation and objective instrumental analysis can better explain the relationship between food flavor chemical components and sensory experience, thereby clarifying the mechanism of flavor removal and synergistic enhancement. After treatment with Lactobacillus plantarum shock fermentation technology, the algal odor of Eucheuma algae and its processed product algin was significantly weakened through quantitative sensory evaluation. GS-MS detection of its representative undesirable flavor substances, including 1-octen-3-ol, 1-octen-3-one, hexanal, octanal, nonanal, (E)-4-decenal and 2,4-(E,E)-nonadienal, was significantly reduced, and the deodorization effect was significant. At the same time, the number of acid and ester substances increased, producing odors such as fermentation aroma, floral aroma and sweet aroma. In summary, it is shown that fermentation with Lactobacillus plantarum has the effect of removing fishy smell and enhancing flavor, and can ensure the strength of carrageenan by shortening the fermentation time; by adopting the form of a reciprocating pump, the traditional centrifugal pump is prone to failure due to the rapid temperature change of the bacterial liquid caused by frictional heat generated by the high-speed rotation of the impeller, and the pressure generated by the reciprocating pump is large, which can be suitable for mass production of food; the primary pressurization of the reciprocating pump plus the secondary pressurization of the gas (to achieve gas volume change) can achieve a faster speed when the bacterial liquid is sprayed out, ensuring sufficient kinetic energy and the presence of gas can make the bacterial liquid droplets small enough due to the impact of the airflow during spraying. Combined with stirring, the sea cucumber in the fermentation tank can be evenly and locally broken. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Shown is a radar chart of sensory evaluation of Eucheuma algae and their processed products (algin) according to the examples and comparative examples of the present invention;

[0038] Figure 2 Shown are total ion currents of volatile flavor substances in Eucheuma algae and their processed products (algin) according to the examples and comparative examples of the present invention;

[0039] Figure 3 Shown are the types of volatile flavor compounds of Eucheuma algae and its processed products (algin) according to the examples and comparative examples of the present invention;

[0040] Figure 4 Shown is a graph showing the content of volatile flavor compounds in Eucheuma algae and their processed products (algin) according to the examples of the present invention and the comparative example;

[0041] Figure 5 Shown is a simplified structural diagram of a fermentation tank used in an embodiment of the present invention;

[0042] Explanation of the numbers: 1. Tank body; 11. Top cover; 12. Main body; 13. Nozzle; 2. Reciprocating pump; 21. Pump body; 22. Piston; 23. First connecting rod; 24. Second connecting rod; 25. Reciprocating motor; 26. Pump liquid space; 27. Liquid outlet one-way valve; 28. Liquid inlet one-way valve; 3. Air supply system; 31. Gas cylinder; 32. Second solenoid valve; 4. Pipeline; 41. First solenoid valve. DETAILED DESCRIPTION

[0043] To illustrate the technical content, achieved objectives and effects of the present invention in detail, the following description is given in conjunction with the embodiments and accompanying drawings.

[0044] The test materials used in the present invention are all common commercial products and can be purchased in the market;

[0045] The Eucheuma raw material involved in the present invention comes from Lvxin (Fujian) Food Co., Ltd.

[0046] Lactobacillus plantarum subsp. bulgaricus: purchased from China Industrial Culture Collection Center (CICC6076). Example

[0047] Reference Figure 1-Figure 5 A method for removing the fishy smell of Eucheuma, comprising:

[0048] Step S1, pre-treating the Eucheuma: washing, removing impurities, and drying the Eucheuma, then adding 2% glucose water with a mass concentration of 1:30 g / mL of Eucheuma to glucose water, pasteurizing, and cooling to room temperature.

[0049] Step S2: Lactobacillus plantarum fermentation of Eucheuma (using 2% sugar water, liquid-to-material ratio 30:1 ml / g, the Lactobacillus plantarum liquid The value is 0.8-1.2, and the number of viable bacteria is 1× CFU / mL, the inoculation amount is 0.5-2% v / v, and the inoculation amount is 2% and inoculated at 37°C for fermentation for 2h); the fermentation tank includes a controller, a tank body 1, a reciprocating pump 2, and an air supply system 3. The tank body 1 includes a top cover 11 and a main body 12. The top cover 11 and the main body 12 form a closed space when they cooperate. The top cover 11 is provided with an inlet and a camera arranged toward the main body 12. The inlet is provided with a nozzle 13. The bottom of the side wall of the main body 12 is provided with an outlet. The main body 12 is also provided with a heating device, a stirring device and a temperature sensor; 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 provided in the pump body 21 to divide the main body 12 into a pump liquid space 26 and a connecting space. A liquid outlet one-way valve 27 is provided at the top of the pump liquid space 26, and a liquid inlet one-way valve 28 is provided at the bottom. The liquid outlet one-way valve 27 is connected to the inlet, and the liquid inlet one-way valve 28 is connected to the outlet through a pipe 4. A first solenoid valve 41 is provided on the outlet; the connecting space is connected to the outside and is arranged toward 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; the two ends of the first connecting rod 23 are respectively movably connected to the side of the piston 22 facing the connecting space and the free end; the gas replenishing system 3 includes a gas cylinder 31 and a second solenoid valve 32, and the gas cylinder 31 is connected to the pump body 21 and the pipe 4 respectively through the second solenoid valve 32;

[0050] Fermentation includes: sterilizing the fermentation tank in advance, opening the top cover 11 after sterilization, mixing the pretreated Eucheuma and Lactobacillus plantarum liquid and adding it to the main body 12, and then closing the top cover 11 to form a seal; the controller controls the opening of the heating device according to the temperature sensor (heating to 37°C), and at the same time starts the stirring device, the reciprocating motor 25, and the first solenoid valve 41, and the stirring motor stirs in real time; the reciprocating motor 25 works by the movement of the piston 22 to make the Lactobacillus plantarum liquid enter the pump liquid space 26, thereby lowering the liquid level in the main body 12, and part of the Eucheuma plantarum is exposed outside the Lactobacillus plantarum liquid; the movement of the piston 22 squeezes the pump liquid space 26 to achieve a pressurization, and at the same time the pump liquid space 26 is squeezed, the second solenoid valve 32 is opened to send gas into the pump liquid space 26 to achieve a second pressurization (the second solenoid valve 32 is closed when the pump liquid space 26 expands), and after pressurization, the Lactobacillus plantarum liquid sprayed from the nozzle 13 is subjected to a high-pressure impact toward the exposed Eucheuma plantarum, thereby causing the Eucheuma plantarum to The damaged parts of the Eucheuma surface form pits to increase the contact area with the Lactobacillus plantarum liquid. The controller obtains information from the camera to determine whether the damage degree of the Eucheuma surface meets the expectations (for example, the damage degree is that the Eucheuma surface is damaged, but the Eucheuma as a whole is not broken due to these damages). If not, the impact is continued until the expected degree is reached. If so, the controller controls the opening of the second solenoid valve 32, and the gas (nitrogen or sterilized compressed air) in the gas cylinder 31 is sent into the pump body 21 and the pipeline 4 to discharge 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 the fermentation is completed.

[0051] Step S3: After the fermentation is completed, the bacterial liquid is removed, the Eucheuma is cleaned and drained to obtain the Eucheuma algae; 10 g of the obtained algae is transferred to a 60 mL headspace bottle, placed in a 70°C water bath for equilibration for 30 minutes, and adsorbed on an aged extraction head for 30 minutes. Subsequently, the extraction head is inserted into the GS-MS sample port, desorbed for 5 minutes, and analyzed using the GS-MS detection method.

[0052] Step S4: A 10% by mass NaOH solution and a 12% by mass KCl solution were mixed in a 1:1 volume ratio to form a mixed solution, which was added to the Eucheuma salsa and incubated in a water bath at 60-65°C for 3-4 hours. After the water bath, the Eucheuma salsa was separated from the mixed solution and repeatedly soaked in water at a ratio of 1:100-200 g / mL for 30-90 minutes each time until the pH of the Eucheuma salsa reached 7. Water was added to the Eucheuma salsa at a ratio of 1:20-30 g / mL, and the solution was incubated in a water bath at 100°C for 1.5-2 hours. The solution was centrifuged while hot, and the supernatant was separated to obtain algin. 10 g of the obtained algin was transferred to a 60 mL headspace vial, equilibrated in a 70°C water bath for 30 minutes, and adsorbed on an aged extraction tip for 30 minutes. The extraction tip was then inserted into the GS-MS sample port, desorbed for 5 minutes, and analyzed using the GS-MS detection method.

[0053] GS-MS detection methods include:

[0054] GC conditions: Rtx-5MS column (30 m × 0.25 mm × 0.25 µm), 99.999% pure helium as carrier gas, 3 mL / min column flow rate, splitless injection;

[0055] Temperature program: programmed temperature, injection port temperature 230 °C, initial temperature 40 °C, then increase to 54 °C at 1 °C / min, increase to 80 °C at 12 °C / min, increase to 170 °C at 3 °C / min, increase to 220 °C at 5 °C / min, hold for 3 min, total program time 59.17 min;

[0056] Mass spectrometry conditions were as follows: ion source temperature 220 °C, ionization mode EI, ionization energy 70 eV, interface temperature 250 °C, ion fragmentation scan range 35-500 m / z, and solvent delay time 2.5 min.

[0057] The GS-MS detection method further includes: qualitative and quantitative analysis of volatile flavor components, wherein the qualitative and quantitative analysis of volatile flavor components includes qualitative analysis and quantitative analysis;

[0058] Qualitative analysis includes:

[0059] Mass spectrometry databases (NIST20, NIST20s, and FNFSC1.3) were used for similarity search, and substances with a mass spectrum match greater than 80% were selected, and then combined with base peaks and characteristic ion peaks;

[0060] Standards of normal alkanes ( - ) comparing the retention time obtained by qualitative analysis of volatile flavor components with the retention time of volatile flavor components in the sample;

[0061] The retention index calculated according to formula 1 was compared qualitatively with the retention index reported on the website (https: / / webbook.nist.gov / ):

[0062] Formula 1

[0063] Wherein, n is the number of carbon atoms in normal alkane; RIx is the retention index of the component to be measured; RTx is the retention time of the component to be measured; RTn is the retention time of normal alkane Cn; RTn+1 is the retention time of normal alkane Cn+1.

[0064] Quantitative analysis includes:

[0065] Formula 2

[0066] Based on the qualitative analysis results, the internal standard method was used for relative quantification, with cyclohexanone as the internal standard, and the quantitative analysis results were calculated and output according to Formula 2.

[0067] Comparative Example

[0068] Step S1 is the same as step S1 in the embodiment and will not be described again here;

[0069] Step S2: Wash and drain the Eucheuma truncatula, transfer 10 g of the algae into a 60 mL headspace bottle, and equilibrate in a 70 °C water bath for 30 min for sensory evaluation.

[0070] Step S3: 10 g of algae was transferred to a 60 mL headspace bottle, which was then placed in a 70 °C water bath for equilibration for 30 min. The aged extraction tip was then adsorbed for 30 min. The extraction tip was then inserted into the GS-MS sample port and desorbed for 5 min before being analyzed by GS-MS.

[0071] Step S4: After the fermentation is completed, the Eucheuma is washed and drained, treated with alkali, washed until neutral, boiled, and centrifuged;

[0072] Step S5: 10 g of alginate was transferred to a 60 mL headspace bottle, which was then placed in a 70°C water bath for equilibration for 30 min. The aged extraction tip was adsorbed for 30 min, and then the extraction tip was inserted into the GS-MS sample port for desorption for 5 min before being analyzed by GS-MS.

[0073] Result analysis:

[0074] 1. Conduct sensory evaluation

[0075] A quantitative descriptive sensory evaluation method was used by a panel of 12 trained evaluators (8 women, 4 men, aged 22-25 years). Based on literature describing the odor of algae, the panel discussed the aroma attributes of the samples until all members agreed on the attributes. Ultimately, the odor profile descriptors for Eucheuma algae and algin were selected as "algal," "fatty," "grassy," "mushroomy," "fermented," and "floral." Flavor intensity was evaluated on a five-point scale (0 indicates no aroma, 5 indicates the strongest aroma).

[0076] 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.

[0077] 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

[0078] 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 Figure 2-3As 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.

[0079] 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.

[0080] 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).

[0081] 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.

[0082] 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: include Step S1, pre-treating Eucheuma; Step S2: mixing the pretreated Eucheuma with the Lactobacillus plantarum liquid. The value is 0.8-1.2, and the number of viable bacteria is 1× CFU / mL, the inoculation amount is 0.5-2% v / v; after the mixing is completed, it is placed in a fermentation tank for fermentation; the fermentation tank includes a controller, a tank body, a reciprocating pump, and an air supply system, the tank body includes a top cover and a main body, the top cover and the main body form a closed space when they cooperate, the top cover is provided with an inlet and a camera arranged toward the main body, the inlet is provided with a nozzle, the bottom of the side wall of the main body is provided with an outlet, and the main 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 provided in the pump body to divide the pump body into a pump liquid space and a connecting rod. The top of the pump liquid space is provided with a liquid outlet one-way valve, and the bottom is provided with a liquid inlet one-way valve, the liquid outlet one-way valve is connected to the inlet, and the liquid inlet one-way valve is connected to the outlet through a pipeline, and the outlet is provided with a first solenoid valve; the connecting space is connected to the outside and is arranged toward 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; the two ends of the first connecting rod are respectively movably connected to the side of the piston facing the connecting space and the free end; the gas replenishing system includes a gas cylinder and a second solenoid valve, and the gas cylinder is connected to the pump body and the pipeline respectively through the second solenoid valve; Fermentation includes: opening the top cover, mixing the pretreated Eucheuma and Lactobacillus plantarum liquid, adding it to the main body, and then closing the top cover to form a seal; the controller controls the opening of the heating device according to the temperature sensor, and simultaneously starts the stirring device, the reciprocating motor, and the first solenoid valve, and the stirring motor stirs in real time; the reciprocating motor works by causing the Lactobacillus plantarum liquid to enter the pump liquid space through the movement of the piston, thereby lowering the liquid level in the main body, and part of the Eucheuma is exposed outside the Lactobacillus plantarum liquid; the piston movement squeezes the pump liquid space to achieve a pressurization, and while the pump liquid space is squeezed, the second solenoid valve opens to send liquid into the pump liquid space. The gas is pressurized again, and the Lactobacillus plantarum liquid sprayed from the nozzle after pressurization is subjected to high-pressure impact on the exposed Eucheuma, thereby damaging the surface of the Eucheuma. The damaged parts of the Eucheuma surface form potholes, which increase the contact area with the Lactobacillus plantarum liquid. The controller obtains information from the camera to determine whether the degree of damage on the Eucheuma surface meets the expectation. If not, the impact continues until the expected degree is achieved. If so, the controller controls the opening of the second solenoid valve, sends the gas from 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, the bacterial liquid is removed, and the Eucheuma is cleaned and drained to obtain the Eucheuma algae; Step S4: After the fermentation is completed, the Eucheuma is washed and treated with alkali, washed until neutral, boiled in a water bath for 1.5-2 hours, and centrifuged to obtain algin.

2. The method for removing the fishy smell of Eucheuma according to claim 1, wherein: 10 g of the algae obtained in step S3 was transferred to a 60 mL headspace bottle and placed in a 70 °C water bath for equilibration for 30 min. The aged extraction tip was adsorbed for 30 min, and then the extraction tip was inserted into the GS-MS sample port for desorption for 5 min. The sample was then analyzed using the GS-MS detection method.

3. The method for removing the fishy smell of Eucheuma according to claim 1, wherein: 10 g of the algin obtained in step S4 was transferred to a 60 mL headspace bottle, placed in a 70 °C water bath for equilibration for 30 min, and adsorbed on the aged extraction head for 30 min. The extraction head was then inserted into the GS-MS sample port and desorbed for 5 min. The sample was then analyzed 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: GS-MS detection methods include: GC conditions: Rtx-5MS column, 99.999% pure helium as carrier gas, 3 mL / min column flow rate, splitless injection; Temperature program: programmed temperature, injection port temperature 230 °C, initial temperature 40 °C, then increase to 54 °C at 1 °C / min, increase to 80 °C at 12 °C / min, increase to 170 °C at 3 °C / min, increase to 220 °C at 5 °C / min, hold for 3 min, total program 59.17 min; Mass spectrometry conditions were as follows: ion source temperature 220 °C, ionization mode EI, ionization energy 70 eV, interface temperature 250 °C, ion fragmentation scan range 35-500 m / z, and solvent delay time 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, wherein the qualitative and quantitative analysis of volatile flavor components includes qualitative analysis and quantitative analysis; Qualitative analysis includes: A similarity search was performed using the mass spectrum database to select substances with a mass spectrum match greater than 80%, and then combined with base peaks and characteristic ion peaks; The retention times of n-alkane standards obtained by qualitative analysis of volatile flavor components were compared with the retention times of volatile flavor components in the samples; Calculate the retention index according to formula 1 for qualitative comparison: Formula 1 Wherein, n is the number of carbon atoms in normal alkane; RIx is the retention index of the component to be measured; RTx is the retention time of the component to be measured; RTn is the retention time of normal alkane Cn; RTn+1 is the retention time of normal alkane Cn+1.

6. The method for removing the fishy smell of Eucheuma according to claim 5, characterized in that: Quantitative analysis includes: Formula 2 Based on the qualitative analysis results, the internal standard method was used for relative quantification, with cyclohexanone as the internal standard, and the quantitative analysis results were calculated and output according to Formula 2.

7. The method for removing the fishy smell of Eucheuma according to claim 1, characterized in that: Step S1 further includes: washing, removing impurities and drying the Eucheuma, adding glucose water with a mass concentration of 1-5%, the ratio of Eucheuma to glucose water being 1:10-50 g / mL, and cooling to room temperature after pasteurization.

8. The method for removing the fishy smell of Eucheuma according to claim 1, characterized in that: Step S2 further comprises: The pretreated Eucheuma was mixed with the Lactobacillus plantarum solution, and after mixing, the mixture was placed in a fermentation tank for fermentation for 2-4 hours.

9. The method for removing the fishy smell of Eucheuma according to claim 1, characterized in that: Step S4 further comprises: A 10% mass fraction NaOH solution and a 12% mass fraction KCl solution were mixed in a volume ratio of 1:1 to form a mixed solution, which was added to Eucheuma and incubated in a water bath at 60-65°C for 3-4 hours. After the water bath, the Eucheuma was separated from the mixed solution and repeatedly soaked in water at a ratio of Eucheuma to water of 1:100-200 g / mL, each soaking for 30-90 minutes, until the pH of the Eucheuma reached 7; water was added to the Eucheuma at a ratio of 1:20-30 g / mL, and the Eucheuma was in a water bath at 100°C for 1.5-2 hours. The mixture was centrifuged while hot, and the supernatant was separated to obtain alginate.

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

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