Microcapsule for fishy smell removal and water retention of aquatic products and preparation method of microcapsule

Abstract

The invention discloses a microcapsule for fishy smell removal and water retention of aquatic products and a preparation method of the microcapsule, and belongs to the technical field of food preservation. The microcapsule is prepared by the following method: adding Arabic gum and maltodextrin into purple perilla hydrolat, adding water for dissolving, centrifuging, and taking supernatant, so as to obtain a purple perilla hydrolat solution; then adding the zanthoxylum oil into the perilla hydrolat solution drop by drop, and homogenizing to prepare an emulsion; and carrying out spray drying on the emulsion to obtain the microcapsule. The microcapsule prepared by the invention is small in particle size, low in surface oil content, high in encapsulation efficiency, good in thermal stability and outstanding in antioxidant effect. The microcapsule can be used for fishy smell removal and water retention of aquatic products, and can slow down the fat oxidation rate of the aquatic products, inhibit the growth of harmful microorganisms, reduce the generation of rotten metabolites and fishy smell substances, reduce the juice loss rate of the aquatic products and improve the water retention effect of the aquatic products, so that the refreshing time and shelf life of the aquatic products can be finally prolonged; therefore, the method has important application prospect and value in the field of food preservation.

Description

Technical Field

[0001] The present invention belongs to the technical field of food preservation, and particularly relates to a microcapsule for removing fishy smell and retaining water of aquatic products and a preparation method thereof. Background Art

[0002] The white shrimp (Penaeus vannamei), also known as Litopenaeus vannamei, belongs to the family Penaeidae, the genus Penaeus, and the subgenus Litopenaeus. It is native to the coastal waters of the Pacific Ocean in Central and South America and is currently the shrimp species with the highest aquaculture production among the three major cultured shrimps. In recent years, its production has been increasing continuously.

[0003] Although the white shrimp is very nutritious, the endogenous enzyme activity in the shrimp is very high. In addition, the water content in the shrimp meat reaches 70%, and the protein content is more than 15%. Therefore, the shrimp spoils very quickly after death. How to better maintain the freshness of the shrimp is very important. When the shrimp body dies, a series of physical, chemical, and physiological changes will occur in its body, resulting in a significant decrease in the hardness and elasticity of the shrimp meat. As the storage time lengthens, nitrogen-containing substances such as proteins in the shrimp body will decompose to produce a large amount of biogenic amines, such as cadaverine, histamine and other harmful substances, making the shrimp inedible. Therefore, during the process of catching, transporting, and storing shrimp, people usually adopt corresponding measures to inhibit the enzyme activity and the reproduction of microorganisms in the shrimp body, so as to meet the needs of consumers. At present, the preservation technologies of white shrimp include low-temperature refrigeration preservation, micro-freezing preservation, vacuum packaging preservation, chemical preservation, biological preservation, ultra-high pressure preservation, irradiation preservation, etc. With the extensive application of enzyme preparations, bioactive substances, and some microorganisms that can produce bacteriocins in food, biological preservation is currently more emphasized. It mainly delays oxidation by using a preservative to block the contact between aquatic products and oxygen, or the biological preservation substance itself has very good antibacterial effects, thereby controlling the activities of microorganisms to extend the storage period of aquatic products.

[0004] In recent years, with the continuous increase of food safety issues, the research and development of natural preservatives have been increasingly emphasized. In the research of food preservatives, plant-derived preservatives have attracted much attention due to their natural, safe, and effective characteristics. Therefore, developing a natural preservative has important application value and significance. Summary of the Invention

[0005] The present invention provides a preparation method of a microcapsule for removing fishy smell and retaining water of aquatic products, comprising the following steps:

[0006] Add gum arabic and maltodextrin to perilla hydrosol, dissolve with water, centrifuge and take the supernatant to obtain perilla hydrosol solution; then add prickly ash oil dropwise to the perilla hydrosol solution, homogenize to make an emulsion; spray-dry the emulsion to obtain microcapsules.

[0007] In the above preparation method, each component is selected from the following mass parts:

[0008] Perilla hydrosol 5 - 10 parts, gum arabic 0.1 - 1 part, maltodextrin 1 - 3 parts, prickly ash oil 1 - 5 parts, water 50 - 100 parts.

[0009] In a specific embodiment, each component is selected from the following mass parts:

[0010] Perilla hydrosol 7.5 parts, gum arabic 0.5 part, maltodextrin 2 parts, prickly ash oil 2.5 parts, water 87.5 parts.

[0011] In the above preparation method, the prickly ash oil is the core material, and the perilla hydrosol, gum arabic and maltodextrin are the wall materials; the oil - to - wall ratio is selected from 1:2 - 1:6, preferably 1:4.

[0012] In the above preparation method, the gum arabic and maltodextrin are solid components, and the prickly ash oil and perilla hydrosol are liquid components; the solid - to - liquid ratio is selected from 1:2 - 1:6, preferably 1:4.

[0013] In the above preparation method, the mass ratio of the gum arabic to the maltodextrin is selected from 1:2 - 1:6, preferably 1:4.

[0014] In the above preparation method, the conditions of homogenization are selected as: homogenize for 1 - 5 min under the condition of 8000 - 12000 rpm.

[0015] In the above preparation method, the conditions of spray - drying are selected as: the sample injection speed is 5 - 10 mL / min, and the spray temperature is 100 - 150 °C.

[0016] In the present invention, peanut protein can also be added as a wall material to the above - mentioned scheme to prepare microcapsules. Specifically, during the preparation of perilla hydrosol solution, peanut protein is added to perilla hydrosol together with gum arabic and maltodextrin. The dosage of the peanut protein is 0.5 - 2% of the total amount of the emulsion.

[0017] The present invention provides microcapsules for removing fishy smell and retaining water in aquatic products prepared by the above method.

[0018] The present invention provides the application of the above microcapsules in removing fishy smell and retaining water in aquatic products.

[0019] The beneficial effects of the present invention are as follows:

[0020] The microcapsules of the present invention are prepared from prickly ash oil, perilla hydrosol, gum arabic, and maltodextrin. The microcapsules have small particle size, low surface oil content, high encapsulation efficiency, good thermal stability, and outstanding antioxidant effect. The microcapsules can be used for removing fishy smell and retaining water in aquatic products, can slow down the fat oxidation rate of aquatic products, inhibit the growth of harmful microorganisms, reduce the generation of spoilage metabolites and fishy smell substances, lower the juice loss rate of aquatic products, improve their water retention effect, and ultimately can extend the freshness preservation period and shelf life of aquatic products, thus having important application prospects and value in the field of food freshness preservation. In addition, there is a synergistic effect between prickly ash oil and perilla hydrosol in the microcapsules in terms of removing fishy smell and retaining water, which further optimizes the application of prickly ash oil and perilla hydrosol in removing fishy smell and retaining water, not only can fully reduce the usage amounts of prickly ash oil and perilla hydrosol, but also can further improve the freshness preservation effect of aquatic products. Description of the Drawings

[0021] Figure 1 Effect of temperature on the encapsulation efficiency of microcapsules;

[0022] Figure 2 Effect of injection speed on the encapsulation efficiency of microcapsules;

[0023] Figure 3 Effect of solid-liquid ratio on the encapsulation efficiency of microcapsules;

[0024] Figure 4 Effect of oil-wall ratio on the encapsulation efficiency of microcapsules;

[0025] Figure 5 Effect of GA:MD ratio on the encapsulation efficiency of microcapsules;

[0026] Figure 6 Scanning electron micrograph of microcapsules;

[0027] Figure 7 Thermal stability analysis diagram of microcapsules;

[0028] Figure 8 Infrared spectrum analysis diagram of microcapsules;

[0029] Figure 9 Antioxidant activity analysis of microcapsules; where A is the DPPH scavenging rate, B is the hydroxyl radical scavenging rate, and C is the lipid hydroperoxide scavenging rate;

[0030] Figure 10 Measurement of inhibition zone;

[0031] Figure 11 SEM images of shrimp meat during storage; where A is Control-0, B is Control-4, C is Control-8, D is PZM-4, and E is PZM-8;

[0032] Figure 12 is the juice loss rate of shrimp meat during storage. Detailed implementation mode

[0033] In the present invention, gum arabic (GA), maltodextrin (MD) and perilla hydrosol are used as wall materials, and prickly ash oil is used as core material. Among them, gum arabic (GA) and maltodextrin (MD) are only used as wall materials to improve physical indexes and properties such as the embedding rate of the core material, and they have no biological functions such as antibacterial and deodorizing.

[0034] Perilla hydrosol (pH = 5.0 - 6.0) is purchased from Henan Zhongxiang Biotechnology Co., Ltd. Peanut protein is purchased from Shanghai Xintai Industrial Co., Ltd.

[0035] Other materials used in the present invention, unless otherwise stated, can be obtained through commercial channels. Other terms used in the present invention, unless otherwise explained, generally have the meanings commonly understood by those of ordinary skill in the art. The present invention will be further described in detail below with reference to specific examples and data. The following examples are only for illustrating the present invention and do not limit the scope of the present invention in any way.

[0036] Example 1

[0037] Prepare microcapsules, the steps are as follows:

[0038] Add 0.5 g of gum arabic and 2 g of maltodextrin to 7.5 g of perilla hydrosol, add 87.5 mL of deionized water to dissolve and then centrifuge to take the supernatant to obtain perilla hydrosol solution; then drop 2.5 g of prickly ash oil (PPO) into the perilla hydrosol solution drop by drop, and use a high-speed disperser for homogenization (12000 rpm, 3 min) during the addition process to make an emulsion; add the emulsion to a spray drying device at a speed of 130 °C and 9 mL / min for spray drying to obtain microcapsules (PZM).

[0039] I. Influence of different pretreatment conditions on the encapsulation rate of microcapsules

[0040] Taking the preparation conditions in Example 1 as the standard, study the influence of different temperatures, injection rates, solid-liquid ratios, oil-wall ratios, and MD:GA ratios on the encapsulation rate of microcapsules (PZM).

[0041] In Example 1, the oil-wall ratio [(prickly ash oil):(perilla hydrosol + gum arabic + maltodextrin)] = 1:4, the solid-liquid ratio [(gum arabic + maltodextrin):(prickly ash oil + perilla hydrosol)] = 1:4, and MD:GA = 4:1.

[0042] The experimental design is shown in Table 1:

[0043] Table 1 Pretreatment experimental design

[0044]

[0045] The test results are as Figures 1 - 5 shown below:

[0046] The conditions of the microcapsule preparation process screened by the above single-factor experiments are as follows: injection temperature 130 °C, injection rate 9 mL / min, oil-to-wall ratio = 1:4, MD:GA = 4:1, solid-to-liquid ratio = 1:4.

[0047] II. Response surface experiment design

[0048] Based on the results of the single-factor experiments, a four-factor and three-level response surface experiment was designed with the injection port temperature (X1), injection rate (X2), ratio of oil to wall material (X3), and ratio of GA to MD (X4). With the microcapsule encapsulation rate (Y) as the index, the optimal embedding process was determined. The Design expert 13 was used to perform multiple fitting regression analysis on the experimental results, and the binary multiple regression equation of the embedding rate (Y) with respect to the injection port temperature (X1), injection rate (X2), ratio of oil to wall material (X3), and ratio of GA to MD (X4) was obtained:

[0049] Y = 91.41 + 0.2608X1 - 0.3783X2 + 0.1817X3 + 0.1625X4 + 0.685X1X2 + 0.265X1X3 - 0.4675X1X4 - 0.4075X2X3 + 0.4375X3X4 - 1.48X1 2 - 1.82X2 2 - 1.39X3 2 - 0.9216X4 2 .

[0050] The method for measuring the encapsulation rate is as follows:

[0051] Before each experiment, the weight of the container without the sample needs to be kept constant. The specific method is determined as follows: The glass beaker is dried in a forced-air drying oven at 80 °C for 1 h, and then transferred to a glass desiccator until it reaches room temperature, with a weight of A0. Petroleum ether (5 mL) and microcapsules (0.5 g) are vigorously shaken at room temperature for 5 min, the solvent is filtered and recovered, and the residue is washed with petroleum ether (5 mL). The surface oil amount is calculated based on the mass difference of the pre-weighed glass beaker (A2).

[0052] The extractor is treated in the same way as the glass beaker, with a weight of A1: Accurately weigh microcapsules (0.5 g), and extract with petroleum ether in a Soxhlet apparatus at 80 °C for 4 h. After extraction, the solvent is completely evaporated to a constant weight. The total oil amount is calculated based on the mass difference of the pre-weighed extractor (A3).

[0053] The calculation formula is as follows:

[0054] EE(%) = 1 - (surface oil content / total oil content) × 100%; Surface oil content = A2 - A0; Total oil content = A3 - A1.

[0055] The results of the four-factor and three-level response surface experiment are shown in Table 2:

[0056] Table 2 Response surface experiment design and results

[0057]

[0058] According to the analysis by Design-Expert 13 software, the temperature is 141.37 °C, the injection rate is 8.81 mL / min, the oil-to-wall ratio is 4.163, the ratio of MD and GA is 4.06, and the optimal encapsulation rate is 91.451%. Considering the accuracy of the instrument and the operability of the experiment, the optimal microencapsulation process conditions are modified to: temperature is 140 °C, injection rate is 9 mL / min, oil-to-wall ratio is 1:4, and the ratio of MD and GA is 4:1. Microcapsules are prepared according to this optimal condition (where the solid-to-liquid ratio = 1:4), and finally microcapsules with an encapsulation rate of 92.38% are obtained.

[0059] III. Microcapsule Characterization

[0060] The microcapsules prepared under the optimal conditions of the above response surface method were subjected to structural characterization.

[0061] 1. Particle size and moisture determination

[0062] Particle size determination: The microcapsules were dissolved in deionized water, and the supernatant was taken by centrifugation. The supernatant collected was added to a dynamic light scattering instrument to measure the particle size of the microcapsules.

[0063] Moisture determination: An appropriate amount of microcapsule powder was placed on the tray of a moisture analyzer and dried to a constant weight, and the weight difference before and after drying was recorded to calculate the moisture content.

[0064] The measurement results are shown in Table 3:

[0065] Table 3 Characterization of microcapsules

[0066] Sample Particle size (μm) Surface oil content (%) Moisture content (%) Entrapment efficiency (%) PZM 2.15±0.10 0.42±0.09 3.75±0.28 92.38±1.33

[0067] As can be seen from Table 4, the particle size of the microcapsules encapsulated with gum arabic, maltodextrin and perilla pure dew remains in the μm level, the surface oil content is low, and the encapsulation rate is as high as 92.38 ± 1.33%. It is proved that PZM can effectively convert prickly ash oil from liquid to solid particles.

[0068] 2. Microscopic morphology detection

[0069] The apparent morphology of the microcapsules was observed using a scanning electron microscope. The samples were attached to the experimental table with double-sided conductive tape and sputter-coated with gold. The scanning electron microscope was operated at 10 kV, with a working distance of 9.5 mm and a magnification of 800 times.

[0070] The test results are as Figure 6 shown:

[0071] The surface of the microcapsules formed by spray drying is smooth and dense. It can be seen from the figure that a cyst-like structure has formed on the surface of the microcapsules, and no oily substances can be seen on the surface. This proves that the microcapsules have been successfully prepared. The appearance of wrinkles on the surface of some particles is due to the too high inlet temperature, which causes the water to evaporate too quickly.

[0072] 3. Thermal stability analysis

[0073] To verify the effectiveness of the encapsulation process, differential scanning calorimetry (DSC) analysis was performed on prickly ash oil (PPO), gum arabic (GA), maltodextrin (MD), and microcapsules (PZM). The samples were weighed in a 150 μL airtight alumina crucible, and the thermal behavior of the samples was analyzed in the temperature range of 25 - 600 °C. The scans were carried out under nitrogen with a ramp rate of 10 °C / min. The thermal degradation profile of the microcapsules was determined by DSC.

[0074] The test results are as Figure 7 shown:

[0075] The degradation of PPO starts at 100 °C and then continues to volatilize until complete carbonization at 500 °C. This behavior is the combined result of the different thermal stabilities of the components of PPO. In contrast, the microcapsules are basically stable up to 200 °C, decompose faster than PPO, and reach complete carbonization at 550 °C. The temperature-related mass loss of the microcapsules occurs in three main stages. In the initial stage (20 - 200 °C), the gradual mass loss is related to the evaporation of water and the release of volatile substances. In the second stage (200 - 400 °C), all groups show a sharp decline, which is due to the rupture of the capsule wall, oil leakage, and the thermal decomposition of oil and other components. In the third stage (400 - 550 °C), the mass loss is slow, corresponding to the complete carbonization and thermal decomposition of the residual polysaccharides.

[0076] The above thermal stability experiments prove that the microcapsules have better thermal stability, can prevent the degradation of prickly ash oil at high temperatures, and better maintain the bioactive substances in prickly ash oil, especially the decomposition of thermosensitive substances.

[0077] 4. Infrared spectroscopy detection

[0078] The FTIR spectra of the microcapsules and their raw materials were recorded on an iS50 FTIR at room temperature, with a wavenumber range of 500 - 4000 cm -1 , and a resolution of 4 cm -1 .

[0079] The detection results are as Figure 8 shown below:

[0080] FTIR analysis provides information on the molecular structure and chemical bonds of molecules of any size. All samples had broad absorption peaks at 3000 - 3500 cm -1 , corresponding to the hydroxyl groups of polysaccharides. PPO had a strong stretching vibration peak corresponding to -CH=CH- at 3100 - 2700 cm -1 , indicating the presence of unsaturated fatty acids, which were also present in the spectrum of the microcapsules, indicating that the oil was effectively encapsulated. GA and MD had weak absorption peaks at 2930 cm -1 , characteristic of C-H bonds. All samples had strong characteristic peaks related to C-C bonds near 1000 cm -1 . No new absorption peaks appeared in the spectrum of the microcapsules, indicating that the chemical structures of PPO and the encapsulant did not change during the preparation of the microcapsules.

[0081] 5. Antioxidant effect

[0082] (1) DPPH scavenging rate

[0083] At room temperature, the microcapsules (200 mg) were mixed with deionized water (10 mL) by ultrasound (400 W) for 1 min, and then centrifuged at 1611 g for 10 min. The supernatant (2 mL) of each sample was mixed with DPPH (2 mL, 1 mmol / L, absolute ethanol), and the same volume of water as the control, and incubated in the dark at room temperature for 30 min. Finally, the absorbance at 517 nm was measured using a UV-visible spectrophotometer with ethanol as the blank. Using VC as the positive control, the above experiment was repeated to calculate the DPPH radical scavenging activity (SA DPPH ), and the calculation formula is as follows:

[0084] SA DPPH (%) = 1 - (A 样品 - A 对照 ) / A 空白 ×100%.

[0085] (2) Hydroxyl radical scavenging rate

[0086] Add 2 mL of the sample to be tested, 2 mL of the sample to be tested and 2 mL of distilled water into three test tubes respectively. Then add 2 mL of FeSO4 (6 mmol / L) and 2 mL of H2O2 (6 mmol / L) into the three test tubes respectively. Mix each test tube evenly and let it stand for 10 min. Then add 2 mL of salicylic acid (6 mmol / L), 2 mL of distilled water and 2 mL of salicylic acid (6 mmol / L) into the three test tubes respectively. Mix each test tube evenly and let it stand for 30 min. Adjust the "0" point with distilled water and measure the absorbance at 510 nm. The absorbance values of the three reaction solutions are A i , A j and A0. Calculate the scavenging rate of the sample to be tested for hydroxyl radicals according to the following formula:

[0087] Scavenging rate (%) = [1 - (A i - A j ) / A0] × 100%.

[0088] (3) Scavenging rate of lipid hydroperoxides

[0089] Prepare liposome PBS dispersion system (LLS) and TBARS reagent: Dissolve 15 g of TCA, 0.375 g of TBA and 2.1 mL of HCl in 100 mL of distilled water to prepare a mixed solution. Add 300 mg of lecithin into 30 mL of PBS (PH = 7.4) to prepare LLS. Add 1.0 mL (LLS), 1.0 mL of FeCl3 (0.4 mmol / L) solution, 1.0 mL of ascorbic acid (0.4 mmol / L) solution and 1.0 mL of sample solution (sample group) or 1.0 mL of distilled water (blank group) into a test tube in sequence, mix well with a vortex mixer, place it in a water bath at 37 °C in the dark for 60 min, then add 2.0 mL of TCA-TBA-HC1 mixed solution, mix well with a vortex mixer, place it in a water bath at 95 °C for 15 min, quickly cool it, centrifuge at a speed of 4000 r / min for 10 min, take the supernatant, adjust the "0" point with distilled water at 532 nm, and measure the absorbance value A of the sample and the absorbance value A0 of the blank group. Calculate the inhibition rate of the sample against liposome peroxidation according to the following formula:

[0090] Inhibition rate = (1 - A / A0) × 100%.

[0091] The test results are as Figure 9 shown:

[0092] Since PPO itself has certain antioxidant activity, the DPPH scavenging rate, hydroxyl radical scavenging rate and lipid hydroperoxide scavenging rate of PPO and PZM showed a similar range on the 0th day, and then decreased over time. Due to the rapid oxidation of PPO within 15 days, the DPPH scavenging rate showed a linear decrease ( Figure 9A). The scavenging rates of hydroxyl radicals and lipid hydroperoxides decreased exponentially with time ( Figure 9 B, Figure 9 C) and the scavenging rate of free radicals by PZM was significantly higher than that of PPO. Microencapsulation effectively isolated environmental factors such as light, heat, and oxygen through a physical barrier, reducing the degradation of antioxidant components (such as phenols and flavonoids) in PPO. Unencapsulated PPO may lose active ingredients due to volatilization or oxidation during storage or experiments, while microencapsulation significantly increased the retention rate of these components. The antioxidant capacity of the microcapsules was significantly higher than that of PPO (p<0.05).

[0093] 6. Antibacterial performance test

[0094] The Pseudomonas aeruginosa screened from shrimp was inoculated into LB solid medium by the filter paper method. 100 mg of perilla hydrosol, prickly ash oil, and microcapsules were added to sterile drug sensitivity test papers respectively, with sterile water as the negative control and ampicillin (1 mg / mL) as the positive control. After culturing at 37 °C for 24 h, the diameter of the inhibition zone was measured.

[0095] The test results are shown in Table 4 and Figure 10 as follows:

[0096] Table 4 Inhibition zone size

[0097] Sample PPO Perilla hydrosol PZM Negative control Positive control Inhibition zone (mm) 4.09±0.88 7.35±1.44 11.8±0.05 ND 20.21±1.2

[0098] ND indicates not detected.

[0099] It can be Figure 10 seen that except for sterile water, the other 4 samples all had inhibitory effects on Pseudomonas aeruginosa. And except for the positive control, the antibacterial effect of perilla hydrosol was better than that of prickly ash oil. PZM showed a better antibacterial effect than when prickly ash oil and perilla hydrosol were used alone, proving that the synergistic effect of perilla hydrosol and prickly ash oil had a better effect of removing fishy smell and antibacterial. As can be seen from Table 5, the inhibitory effect of prickly ash oil on Pseudomonas aeruginosa was weak, and the inhibition zone <5 mm. The inhibitory effect of perilla hydrosol on Pseudomonas aeruginosa was moderately sensitive, and the inhibition zone >5 mm. The inhibitory effect of PZM on Pseudomonas aeruginosa was highly sensitive, and the inhibition zone >10 mm.

[0100] Thus, it can be seen that at the same dosage, the antibacterial effect of the microcapsules was significantly better than that of perilla hydrosol and prickly ash oil, indicating that there was a synergistic effect between perilla hydrosol and prickly ash oil, and their combination had a better inhibitory effect on Pseudomonas aeruginosa and could greatly inhibit the generation of fishy smell.

[0101] IV. Fishy smell removal test

[0102] Add 0.1 g of microcapsules to 10 g of shrimp paste (Litopenaeus vannamei), refrigerate at 4 °C, and test every 4 days. Name them Blank-0 (Control-0), Blank-4 (Control-4), Blank-8 (Control-8), microcapsule-treated for 4 days (PZM-4), and microcapsule-treated for 8 days (PZM-8).

[0103] 1. Detection of TBA content

[0104] Pretreatment: Use a malondialdehyde (MDA) detection kit to detect the spoilage time of shrimp meat, and add microcapsules for comparative detection of the storage period.

[0105] Peroxides formed by the oxidation of unsaturated fats in shrimp meat will decompose to produce MDA, which will react with thiobarbituric acid (TBA) to produce a colored compound. By calculating the MDA content, the oxidation situation of meat during storage can be determined, which is also an important indicator for judging the freshness of aquatic products.

[0106] The test results are shown in Table 5 as follows:

[0107] Table 5 Changes in TBA content of shrimp meat treated with microcapsules

[0108] Group TBA content (mg / kg) Control-0 0.233 Control-4 0.897 Control-8 2.031 PZM-4 0.517 PZM-8 0.702

[0109] As can be seen from Table 5, at the beginning of storage, the TBA content of Control-0 was 0.233 mg / kg. As the storage time extended, the TBA contents of both the Control group and the PZM group were continuously increasing. At the 4th day of storage, the TBA value of the shrimp meat in the Control-4 group increased rapidly and reached the threshold. At the 8th day of the storage period, the TBA value of the shrimp meat in the Control group was 2.031 mg / kg, which was significantly higher than that of the PZM group (P < 0.05). This indicates that microcapsules can slow down the fat oxidation rate of Litopenaeus vannamei and extend the shelf life of shrimp meat.

[0110] 2. Detection of odor substances

[0111] GC-MS detection: Analyze the volatile substances of shrimp meat by solid-phase microextraction method. Weigh 2 g of the minced sample accurately into a 15 mL headspace vial, add 1 mL of normal saline and 2-octanol as an internal standard (0.025 mg / mL), and cover the bottle cap. Insert the DVB / CAR / PDMS fiber into the headspace vial, place the bottle in a constant temperature water bath at 60 °C for 20 min to extract the sample. Immediately after extraction, move the needle to the GC injection port and desorb at 250 °C for 10 min, and at the same time activate the instrument for collection.

[0112] GC-MS analysis was performed using a TQ8050NX gas chromatograph-mass spectrometer and a DB-WAX fused silica capillary column (30 m × 0.25 mm, 0.25 μm). The carrier gas was He with a purity of 99.999%, and the flow rate was 1.0 mL / min. The chromatographic column was first heated to 40 °C and held for 2 min, then heated at 6 °C / min to 220 °C, and then heated at 20 °C / min to 280 °C and held for 10 min. The electron ionization energy was 70 eV, the inlet temperature was 270 °C, the ion source temperature was 230 °C, and the mass scanning range was 30 - 330 m / z. According to the total ion current chromatogram of volatile compounds, similarity searches were performed using the NIST05 database, and the compounds were characterized in combination with their RI. The RI of volatile compounds was calculated based on the peak order of n-alkanes in the same sample under the same analytical conditions, and 2-octanol was used for quantitative analysis. In addition, the odor activity value (OAV) was calculated as the ratio of concentration to threshold, and key volatile compounds in differently heat-treated white shrimp meat were screened by combining differential substance analysis. The thresholds of the volatile compounds involved in this experiment were all based on the water system.

[0113] The detection results are shown in Tables 6 and 7:

[0114] Table 6 Concentrations of volatile compounds in shrimp meat

[0115]

[0116]

[0117]

[0118]

[0119] ND indicates not detected.

[0120] A total of 80 major volatile compounds, including aldehydes, alkenes, alcohols, ketones, esters, alkanes, acids, benzene, phenols, amines, and indole, were detected by GC-MS after different treatments of shrimp meat. The content of indole in the Control group increased significantly with storage time because tryptophan decomposed to form indole, and the microcapsule treatment inhibited microbial activity and blocked the spoilage pathway. Hexadecanoic acid methyl ester, a lipid oxidation product, increased in content in the Control group but was not detected in the microcapsule treatment group, proving that the antioxidant effect of the anti-corrosion treatment inhibited lipid oxidation and reduced the formation of off-flavor substances. Linalool had a relatively high proportion. PZM was rich in terpene compounds such as linalool, which was released into the shrimp meat during the treatment. At the same time, the anti-corrosion effect reduced the decomposition of linalool by microorganisms. Perillaldehyde and thymol, which accounted for a relatively large proportion in PZM, were released into the shrimp meat during the treatment, imparting a herbal aroma. At the same time, they synergistically inhibited microorganisms with prickly ash oil and reduced the formation of spoilage metabolites, showing a better preservation effect.

[0121] Table 7 Changes in OAV of shrimp meat during storage

[0122]

[0123]

[0124] ND indicates not detected.

[0125] The main flavors of the Control group and the PZM group are shown in Table 7, and there are significant differences in the OAV of flavor substances during the storage time. After screening, the primary flavor detected in all samples is linalool, which mainly contributes to floral and woody scents. The aroma of the Control group degraded within 8 days, while the OAV of the microcapsule-treated group remained relatively high. The sustained-release effect of the microcapsules enabled its continuous release in shrimp meat, and PZM had a better retention effect on linalool. β-Myrcene and D-Limonene contribute to citrus scent, and their partial degradation over storage time is due to the direct introduction of terpene compounds in prickly ash oil and the decrease in concentration caused by oxidation or volatilization during storage. The flavor of perillaldehyde in the PZM group was obvious due to the addition of perilla hydrosol, which imparted a fresh and herbal scent to the shrimp meat and remained stable during storage, attributed to the antibacterial effect slowing down its degradation. Thymol did not reach a significant value but contributed to the herbal scent. It is a by-product of the antibacterial components in perilla hydrosol, with a low concentration but supplementary effect on the flavor. Indole in the Control group showed a putrid odor on the 4th day of storage and increased significantly on the 8th day, as it was produced by the microbial metabolism of tryptophan, indicating increased spoilage. 3-Methyl-1-butanol continued to increase during the storage period and had a fermented off-odor, which could be interpreted as a microbial metabolite and accumulated with the spoilage process. The antibacterial components of the microcapsules (such as perillaldehyde) could inhibit spoilage bacteria and reduce the production of off-odor substances.

[0126] 3. Detection of Amino Acid Content

[0127] Weigh 1 g of shrimp meat into a hydrolysis tube, add 10 mL of 6 mol / L hydrochloric acid, fill with high-purity nitrogen, and seal. Place the hydrolysis tube in a constant-temperature drying oven at 105 °C for 22 h of hydrolysis, then take it out and cool. Open the hydrolysis tube, filter the hydrolysis solution, and make up the volume to 50 mL with deionized water. Pipette 0.5 mL of the filtrate onto an evaporating dish and dry it in a vacuum dryer at 55 °C. Dissolve the residue with 1 mL of 0.02 mol / L hydrochloric acid and filter. It is for amino acid analyzer analysis.

[0128] The detection results are shown in Table 8:

[0129] Table 8 Changes in Amino Acid Content in Shrimp Meat

[0130]

[0131] As can be seen from Table 8, the contents of aspartic acid, glutamic acid, etc. in the Control group decreased significantly after 8 days of storage, indicating that amino acids were largely consumed by microorganisms. The reduction of sulfur-containing amino acids such as methionine may be related to their participation in putrefactive metabolism to produce hydrogen sulfide. Lysine and histidine may be decarboxylated to produce biogenic amines such as putrescine and histamine, further reducing the content of free amino acids. The content of proline increased in Control-4 and Control-8, which may be due to the production of proline by microbial metabolic activities as an osmoprotectant, or the release of stored proline from shrimp cells during spoilage. The increase of glycine in PZM-8 may be related to the antioxidant effect of perilla hydrosol, which slowed down the decomposition of glycine. The lysine content of PZM-8 was significantly higher than that of the control group because PZM contains antibacterial components (such as phenols and terpenoids), which inhibit the growth of microorganisms and thus reduce the decomposition of amino acids. Cystine was not detected in Control-4 and Control-8, which may be due to the preferential decomposition of sulfur-containing amino acids by microorganisms to produce volatile sulfides (such as H2S), or data loss due to insufficient detection limit. The total amino acid content of the treatment group was significantly higher than that of the blank group, indicating that microcapsule treatment effectively delayed the spoilage process of shrimp meat.

[0132] 4. Detection of biogenic amine content

[0133] Biogenic amines were extracted from 5 mL of the sample with 0.4 M perchloric acid and transferred to a screw-cap vial. 0.2 mL of 2 M NaOH solution, 0.3 mL of saturated NaHCO3 solution and 1.0 mL of dansyl chloride solution (10 mg / mL) were added to the vial, and it was stirred in the dark at 40 °C for 0.5 h, and then dansyl chloride was precipitated with ammonia water. The supernatant was placed in a volumetric flask and made up to 50 mL with acetonitrile. After filtration with a Millipore filter (pore size 0.45 μm), HPLC analysis was carried out. The mixed acetonitrile (A) and water (B) of the gradient elution system were used for the gradient elution process. B was 35% A + 65% B at 1 minute, 20% A + 80% B at 5 minutes, 10% A + 90% B at 6 minutes and 8% A + 92% B at 16 minutes. The biogenic amine content was determined by an Agilent 1100 liquid chromatography system, using a C18 column, 7 μm, 4.6 cm × 150 mm, with a diode array detector (254 nm). A series of diluted standard solutions containing cadaverine, histamine, tyramine, spermidine and spermine (in 0.4 M perchloric acid) were prepared from the standard stock solution to obtain the standard curve of each biogenic amine.

[0134] The detection results are shown in Table 9:

[0135] Table 9 Changes in biogenic amine content

[0136]

[0137] ND indicates not detected.

[0138] The fishy substances mainly come from putrescine and cadaverine. Putrescine is produced from arginine / ornithine. The content of putrescine in Control-8 increased to 4544 mg / L (1.20 mg / L in Control-0), indicating that the microbial metabolic activity is extremely strong in the late stage of spoilage. Cadaverine is produced from lysine. The cadaverine content in Control-8 reached 118 mg / L (0.70 mg / L in Control-0), further verifying the direct correlation between amino acid decomposition and biogenic amine production. Histamine is produced from histidine. The histamine content in Control-8 is 2.93 mg / L, which may pose a food safety risk. The total amount of biogenic amines increased sharply: the total amount of biogenic amines in Control-8 reached 4689 mg / L (13.15 mg / L in Control-0), indicating that the shrimp meat has deteriorated severely and its quality has decreased significantly in the late stage of spoilage.

[0139] Biogenic amines (such as putrescine and cadaverine) have a putrid smell and bitterness, resulting in an obvious fishy smell in the shrimp meat. High concentrations of histamine and tyramine may cause poisoning symptoms such as headache and vomiting; cadaverine and putrescine have cytotoxicity. Amino acids (such as glutamic acid and lysine) are consumed in large amounts, leading to a decline in the nutritional quality of the shrimp meat. Histamine was not detected in PZM-8 (2.93 mg / L in Control-8), indicating that the combined treatment with perilla hydrosol has a stronger inhibitory effect on the activity of histidine-containing decarboxylase. The total amount of biogenic amines in the treatment group remained at 12.9 - 14.5 mg / L (4689 mg / L in Control-8), close to the level of fresh shrimp meat (13.15 mg / L in Control-0), proving that the anti-corrosion treatment can significantly delay spoilage. Tryptamine was detected in the treatment group: the tryptamine content in the PZM group was 0.921 mg / L and 1.04 mg / L respectively (not detected in the Control group), which may be because the preservative changed the microbial community structure or inhibited the further degradation of tryptamine.

[0140] V. Water-holding effect test

[0141] Fresh shrimp meat was selected, washed and crushed to obtain shrimp paste. The microcapsules were added to the shrimp meat according to a mass ratio of 1:10 and stirred evenly to prepare the shrimp paste.

[0142] 1. Microscopic morphology of shrimp meat

[0143] The shrimp meat was sliced and fixed in 2.5% glutaraldehyde. After taking out the shrimp meat, it was dehydrated in a gradient of 30%, 50%, 70%, 90%, and 100% ethanol for 10 minutes each. After dehydration, the sample was taken out from 100% ethanol and placed in the sample chamber of a critical point dryer for critical point drying. The drying time was about 1 hour. After drying, the sample was taken out from the sample chamber of the critical point dryer, fixed on the sample stage with conductive tape, and sputter-coated with gold for testing using a scanning electron microscope (SEM).

[0144] The test results are as follows Figure 11 shown below

[0145] As Figure 11 shown in A, the muscle fibers of fresh shrimp meat (at 0 d) are arranged neatly under a magnification of 15,000 times, and there is no fracture. As the storage time prolongs, the myofiber structure of the shrimp shows differential changes. At the 4th day of storage ( Figure 11 B), the surface of the muscle fibers of the shrimp meat in the Control-4 group becomes rough, and there are many filamentous substances attached to the surface, which may be due to the loss and migration of water during storage. At the same time, the muscle fibers become loose, while in the PZM-4 group ( Figure 11 D), the surface of the muscle fibers of the shrimp meat is relatively smooth and the muscle fibers are compact. This is consistent with the results of amino acids and TBA, indicating that proteins in the shrimp meat decompose and fats are continuously oxidized to produce MDA during storage, and the PZM group can inhibit lipid oxidation. When stored for 8 days, the surface of Control-8 is still rough, and obvious fracture phenomena occur in the muscle fibers of the shrimp meat ( Figure 11 C), while the surface of the muscle fibers of the shrimp meat in the PZM group is smooth and the muscle fibers are arranged neatly ( Figure 11 E). The research shows that the degradation and denaturation of shrimp meat proteins during cold storage will lead to the fracture of myofibrils, and the migration of muscle tissue water during storage will make the myofiber structure of the shrimp meat rough and loose. These phenomena indicate that the microcapsule has good antioxidant and oxidase inhibitory activities, can delay protein degradation, and thus play a role in preserving the shrimp meat

[0146] 2. Juice loss rate

[0147] Cut a meat sample of about 5 g and put it into a self-sealing bag. Measure the weight of the self-sealing bag in advance and record it as m1. On the day of measurement, weigh the meat and the self-sealing bag and record it as m2. Take out the meat sample and weigh the self-sealing bag and the juice, and record it as m3. The calculation formula for the juice loss rate is as follows: Juice loss rate (%) = (m3 - m1) / (m2 - m1) × 100%

[0148] The test results are as follows Figure 12 shown below

[0149] Juice loss is caused by the decrease in the water-holding capacity of the shrimp meat during storage. The water contained in the shrimp meat will affect the taste, texture, and tenderness, which is one of the important indicators for evaluating product quality. As can be seen from Figure 12 , the juice loss rate of the samples in each treatment increases with the prolongation of time, and the increase rate of the juice loss rate is the highest in the initial stage and then slows down. During storage, the juice loss rate of the control group is the largest, reaching 7.55% at the 8th day, showing a significant difference from other groups (p < 0.05). PZM can significantly improve the water-holding capacity of the shrimp meat surface

[0150] 3. Analysis of Shrimp Meat Texture

[0151] Cut the meat samples into pieces about 1 cm × 1 cm × 1 cm, place them on the texture analyzer stage perpendicular to the muscle fiber direction for measurement, and use a P50 probe for testing. The main test parameters are Strain (compression ratio): 50%, Pre-Test Speed: 4 mm / s, Test Speed: 1 mm / s, Post-Test Speed: 4 mm / s, and obtain indicators such as the hardness and elasticity of shrimp meat.

[0152] Through texture profile analysis, study the effect of PZM treatment on the muscle texture characteristics of shrimp meat. During storage, the physical properties for structural evaluation are shown in Table 10.

[0153] Table 10 Changes in Shrimp Meat Texture during Storage

[0154] Index Control-0 Control-4 Control-8 PZM-4 PZM-8 Hardness 344±8.60 300±5.28 209±6.12 320±5.33 290±7.21 Elasticity 2.95±0.05 2.01±0.09 0.91±0.09 2.56±0.01 1.98±0.02 Recovery 0.25±0.02 0.18±0.01 0.10±0.02 0.20±0.01 0.15±0.03

[0155] As the storage time increases, the hardness of shrimp meat in different treatment groups shows a downward trend. The hardness of shrimp meat in the microcapsule treatment group is significantly higher than that of the control group during the storage period (p < 0.05). This can be explained that prickly ash oil and perilla hydrosol have the ability to inhibit the growth of microorganisms and the activities of endogenous enzymes in meat (such as collagenase, cathepsin, and calpain), delaying the degradation process of myofibrillar protein and collagen. The decrease in elasticity is caused by the degradation of proteins into small molecules, resulting in the destruction of the protein network structure. The elasticity of each component generally shows a downward trend, and the control group has the largest decrease (p < 0.05), which is because the addition of perilla hydrosol can enhance the water-holding capacity of shrimp meat and keep the fresh texture of shrimp meat. Resilience refers to the degree to which meat returns to its original shape under external pressure. Resilience has a certain correlation with elasticity and generally shows a downward trend. Compared with the shrimp meat samples in the blank group, the samples in the PZM group show better hardness, elasticity, and resilience, indicating that PZM with a slow-release effect can better maintain the texture of shrimp meat, and the better the texture maintenance effect on shrimp meat.

[0156] On the basis of the above technical solutions, the present invention also attempts to use peanut protein as a wall material to prepare microcapsules, as shown in Example 2 below.

[0157] Example 2

[0158] Prepare microcapsules, and the steps are as follows:

[0159] Add 1.5 g of peanut protein, 0.5 g of arabic gum and 2 g of maltodextrin to 7.5 g of perilla hydrosol. After adding 86 mL of deionized water and dissolving, centrifuge and take the supernatant to obtain perilla hydrosol solution. Then, add 2.5 g of prickly ash oil (PPO) dropwise to the perilla hydrosol solution, and homogenize it using a high-speed disperser during the addition process (12,000 rpm, 3 min) to prepare an emulsion. Add the emulsion to a spray drying device at a speed of 130 °C and 9 mL / min for spray drying to obtain microcapsules (PPM).

[0160] The embedding effects of different wall materials are shown in Table 11 as follows:

[0161] Table 11 Comparison of embedding effects of different wall materials

[0162] Group Entrapment efficiency (%) Example 1 92.38±0.76 Example 2 93.65±0.22

[0163] As can be seen from Table 11, adding peanut protein can improve the embedding effect of microcapsules on prickly ash oil.

[0164] The effects of the microcapsules described in Example 2 on the texture of shrimp meat during storage are shown in Table 12 as follows:

[0165] Table 12 Changes in the texture of shrimp meat during storage

[0166] Index PPM-4 PPM-8 Hardness 360±2.85 310±5.04 Elasticity 3.25±0.10 2.11±0.04 Recovery 0.30±0.01 0.22±0.01

[0167] As can be seen from Table 12, after adding peanut protein, the hardness, elasticity and resilience of shrimp meat have been improved to varying degrees, and the water-holding effect of shrimp meat has been enhanced within 8 days of storage.

[0168] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention in other forms. Any person skilled in the art may use the technical content disclosed above to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing microcapsules for removing fishy smell and retaining water in aquatic products, characterized in that: The steps include: Gum arabic and maltodextrin are added to perilla hydrosol, water is added to dissolve the solution, and then the solution is centrifuged to obtain the supernatant to obtain a perilla hydrosol solution; then pepper oil is added dropwise to the perilla hydrosol solution, and the solution is homogenized to prepare an emulsion; and the emulsion is spray-dried to obtain microcapsules.

2. The preparation method according to claim 1, characterized in that: Each component is selected from the following mass parts: 5-10 parts of perilla hydrosol, 0.1-1 part of gum arabic, 1-3 parts of maltodextrin, 1-5 parts of Sichuan pepper oil, and 50-100 parts of water.

3. The preparation method according to claim 2, characterized in that: Each component is selected from the following mass parts: 7.5 parts of perilla hydrosol, 0.5 parts of gum arabic, 2 parts of maltodextrin, 2.5 parts of Sichuan pepper oil, and 87.5 parts of water.

4. The preparation method according to claim 1, characterized in that: The prickly ash oil is the core material, and the perilla hydrosol, gum arabic and maltodextrin are the wall materials; the oil-to-wall ratio is selected from 1:2 to 1:

6.

5. The preparation method according to claim 1, characterized in that: The gum arabic and maltodextrin are solid components, and the pepper oil and perilla hydrosol are liquid components; the solid-liquid ratio is selected from 1:2 to 1:

6.

6. The preparation method according to claim 1, characterized in that: The mass ratio of gum arabic to maltodextrin is selected from 1:2 to 1:

6.

7. The preparation method according to claim 1, characterized in that: The homogenization condition is selected from: homogenization at 8000-12000 rpm for 1-5 min; the spray drying condition is selected from: injection speed of 5-10 mL / min, spray temperature of 100-150° C.

8. The preparation method according to claim 1, characterized in that: In the process of preparing the perilla hydrosol solution, in addition to adding gum arabic and maltodextrin, peanut protein is also added; the amount of the peanut protein accounts for 0.5-2% of the total amount of the emulsion.

9. Microcapsules for removing fishy smell and retaining water in aquatic products prepared by the method according to any one of claims 1 to 8.

10. Use of the microcapsule according to claim 9 in removing odor and retaining water in aquatic products.

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