Novel lotus root bluing inhibitor as well as preparation method and application thereof

Abstract

The invention provides a novel lotus root blue stain inhibitor. The novel lotus root blue stain inhibitor is prepared from the following components: oxalic acid, EDTA-Na2, VC, tea saponin and the balance of water, wherein the concentration of oxalic acid is 0.2%-0.4%, the concentration of EDTA-Na2 is 0.2%-0.4%, the concentration of VC is 0.1%-0.2%, and the concentration of theasaponin is 0.5%-1%. A natural preservative and a bacteriostatic agent tea saponin are added into the prepared inhibitor, so that the use of chemical and synthetic preservatives is reduced, and the inhibitor is more green and safer; the blue stain inhibitor can effectively slow down the loss of active substances such as polyphenol caused by damage to cell walls and cell membranes, so that the formation of polyphenol-iron blue chelate is reduced, and the blue stain of the lotus roots is reduced; and the blue stain inhibitor can also slow down the loss of nutrient substances of the lotus roots, and has a very good fresh-keeping effect on the lotus roots.

Description

Technical Field

[0001] The present invention belongs to the technical field of food preservation, and particularly relates to a novel lotus root blueing inhibitor, a preparation method thereof, and an application thereof. Background Art

[0002] Lotus root is an aquatic rhizomatous herbaceous plant belonging to the Nelumbonaceae family and is widely cultivated in regions such as China, India, and South Korea. In recent years, lotus root has been popular among consumers due to its therapeutic properties and nutritional value. However, lotus root is prone to browning during storage, which directly affects the market value and consumer appeal of lotus root. Therefore, it is crucial to perform appropriate post-harvest treatment on lotus root to inhibit its browning and maintain its industrial processing quality.

[0003] Currently popular lotus root preservation technologies mainly include physical methods such as ultrasonic and microwave pretreatment; and chemical methods such as soaking with EDTA-Na2, ascorbic acid, oxalic acid, 24-epibrassinolide, acetic acid, etc. Nevertheless, ultrasound also has certain disadvantages and adverse effects on fruits and vegetables, including damage to their tissues and cells. Microwave processing involves a large amount of initial investment, complex technology, and various other challenges. In addition, existing preservatives often require higher doses when used alone and there are certain safety issues. Therefore, various preservatives are often used in combination to minimize safety hazards. At the same time, the increasing awareness of personal health has driven the demand for green preservatives.

[0004] It is generally believed that the browning of lotus root is the result of enzymatic browning, which is why most methods aimed at preventing this browning focus on inhibiting the involved enzymatic processes. However, non-enzymatic browning such as the release of bioactive compounds polyphenols from plant tissues due to abrasion or other physiological damage can lead to the formation of blue-violet phenol-iron complexes, which seriously affects the appearance of lotus root and the acceptance of lotus root by consumers.

[0005] Therefore, it is of great significance to focus on the inhibition of blueing and the preservation effect in the non-enzymatic browning of lotus root rather than focusing on the enzymatic browning of lotus root. Summary of the Invention

[0006] In view of this, the present invention provides a lotus root blueing inhibitor with good effect, environmental protection, safety, and low price, and an application of the blueing inhibitor in the preservation of lotus root.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A novel lotus root blueing inhibitor, the inhibitor is composed of the following components: oxalic acid, EDTA-Na2, VC, tea saponin, and the balance is water; Among them, by mass concentration: the concentration of oxalic acid is 0.2% - 0.4%, the concentration of EDTA-Na2 is 0.2% - 0.4%, the concentration of VC is 0.1% - 0.2%, and the concentration of tea saponin is 0.5% - 1%.

[0008] In some specific embodiments, preferably, in the inhibitor, the concentration of oxalic acid is 0.3%, the concentration of EDTA-Na2 is 0.35%, the concentration of VC is 0.15%, and the concentration of tea saponin is 0.5%.

[0009] For the preparation method of the above inhibitor, add oxalic acid, EDTA-Na2, VC, and tea saponin into water, and stir well to dissolve to obtain it.

[0010] For the application of the above inhibitor in the preservation of lotus roots, during specific application, place the washed lotus roots in the inhibitor for soaking, drain the water after soaking, and then perform vacuum packaging and refrigeration.

[0011] Furthermore, the soaking time is 0.5 - 1.5 h; the refrigeration temperature is 2 - 5 °C.

[0012] In some specific embodiments, preferably, the soaking time is 1 h; the refrigeration temperature is 4 °C.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: The inhibitor prepared by the present invention adds natural preservatives and bacteriostatic agent tea saponin, reduces the use of chemical and synthetic preservatives, and is more green and safe. Using the inhibitor prepared by the present invention for the preservation of lotus roots, during the entire 60-day period, the lotus roots still maintain a good appearance (only slightly turn blue, and after 60 days, the total phenol content is 12.08 - 12.39 mg / g dw, the total iron content is 66.45 - 115.39 μg / g dw, reducing the formation of polyphenol-iron blue chelates). In addition, the nutritional value and safety can also be better maintained. Among them, after 60 days, the protein content is 1.10 - 1.15 mg / g fw, the reducing sugar content is 66.23 - 91.27 mg / g fw, the soluble solid content is 7.06 - 7.31 mg / g fw; the total number of colonies is 6.16 - 6.29 lg(CFU / g), and the total number of molds and yeasts is 3.73 - 3.79 lg(CFU / g). Description of the Drawings

[0014] Figure 1 Shows the effects of different treatments on the appearance of lotus roots during 60-day storage; Figure 2 Shows the effects of different treatments on the total phenol (a), protein content (b), reducing sugar (c), soluble solids (d), pH (e), and titratable acid (f) of lotus roots during 60-day storage; Figure 3 Effect of different treatments on total colony count (a), total mold and yeast count (b), electrolyte leakage rate (c), malondialdehyde (d), hardness (e), and soluble quinone (f) of lotus root during 60-day storage; Figure 4 Effect of different treatments on the cell wall of lotus root peel cells on the 60th day; among them, (A 1 ) is the cell wall of lotus root peel after storage for 60 days with deionized water immersion treatment (CK1), 200×; (B 1 ) is the cell wall of lotus root peel in Group 2 after storage for 60 days, 200×; (C 1 ) is the cell wall of fresh lotus root peel, 200×; (A 2 ) is the cell wall of lotus root peel after storage for 60 days with deionized water immersion treatment, 500×; (B 2 ) is the cell wall of lotus root peel in Group 2 after storage for 60 days, 500×; (C 2 ) is the cell wall of fresh lotus root peel, 500×; Figure 5 Effect of different treatments on total phenols (a), iron content (b), and phenol content (c) of lotus root peel during storage on the 60th day. Specific implementation mode

[0015] The present invention will be further described in detail below with specific embodiments, so that those skilled in the art can understand the present invention more clearly.

[0016] Source and physicochemical parameters of key test materials: The lotus root used is "Elian No. 5", produced in Wuhan City, Hubei Province. Lotus roots with uniform shape and size and no damage are selected and delivered to the laboratory within 6 hours after picking.

[0017] The packaging bags used are Xianqu vacuum packaging bags (16 filaments on both sides, 20×30 cm), purchased from Taizhou City, Zhejiang Province.

[0018] The tea saponin used is purchased from Tiancheng Biotechnology Co., Ltd.

[0019] Example 1 This example provides a lotus root blueing inhibitor, specifically as follows: Add 6 g of oxalic acid, 7 g of EDTA-Na2, 3 g of VC, and 10 g of tea saponin to 1 kg of deionized water, stir well, and then add 1 kg of deionized water to obtain a lotus root blueing inhibitor.

[0020] Example 2 This example provides a lotus root blueing inhibitor, specifically as follows: Add 6 g of oxalic acid, 7 g of EDTA-Na2, 3 g of VC and 20 g of saponin to 1 kg of deionized water. After stirring well, add another 1 kg of deionized water to obtain the lotus root browning inhibitor.

[0021] Example 3 This example provides a lotus root browning inhibitor, which is as follows: Add 4 g of oxalic acid, 8 g of EDTA-Na2, 2 g of VC and 20 g of saponin to 1 kg of deionized water. After stirring well, add another 1 kg of deionized water to obtain the lotus root browning inhibitor.

[0022] Comparative Example 1 In this comparative example, lotus roots were directly soaked in deionized water, and the other treatment methods remained unchanged.

[0023] Comparative Example 2 This comparative example provides a lotus root browning inhibitor, which is as follows: In terms of mass concentration, the inhibitor contains 0.9% sodium alginate, 2% EDTA-Na2, 5% glycerol and 0.5% potassium sorbate, and the balance is water.

[0024] Comparative Example 3 This comparative example provides a lotus root browning inhibitor, and its specific preparation is basically the same as that of Example 1, except that: saponin was not added, and the rest remained unchanged.

[0025] Comparative Example 4 This comparative example provides a lotus root browning inhibitor, and its specific preparation is basically the same as that of Example 1, except that: the oxalic acid was replaced with an equal amount of acetic acid, and the rest remained unchanged.

[0026] Furthermore, in order to understand the specific effects of the above inhibitors, the following experiments were also carried out: Using "Elian No. 5" as the experimental raw material, which is produced in Wuhan City, Hubei Province. Select lotus roots with uniform shape and size and no damage, and deliver them to the laboratory within 6 hours after picking; Wash the just-picked lotus roots with tap water and drain the water, and then soak them in each of the above-prepared inhibitors and deionized water for 1 hour respectively. The mass ratio of the inhibitor, deionized water and lotus root is 2:1. After soaking, drain the water, package them in vacuum bags, 600 ± 100 g per bag, and store them at 4°C for 60 days. Measure the appearance changes, chromaticity values, total phenols, proteins, reducing sugars, soluble solids, pH, titratable acids, total colony counts, molds and yeasts, electrolyte leakage rates, malondialdehyde, hardness and soluble quinone contents of the lotus roots every 15 days, as well as the changes in the microstructure of the lotus root peel cell wall, total phenols, total iron and phenolic components on the 60th day. The specific analysis results are as follows: (1)Determination of appearance and chromaticity The appearance of lotus roots with different storage times was photographed using a camera (EDO 6D Mark II, Canon, Japan), and the chromaticity of the lotus roots was recorded using a colorimeter (Ultra Scan VIS, Hunter Lab Color Management Company of America). 、 、 represent brightness (black is ) / darkness (white is ), redness (positive value) / greenness (negative value), and yellowness (positive value) / blueness (negative value), respectively. 、 、 represent brightness (where corresponds to black, corresponds to white), red (represented by positive values) and green (represented by negative values), and yellow (represented by positive values) and blue (represented by negative values), respectively. The total color difference (ΔE) and browning index (BI) of the lotus roots were calculated using the following formula:

[0027]

[0028] where L 0 , a 0 , and b 0 are the initial values, and L i , a i , and b i are the measured values for each experiment.

[0029] Table 1 Effects of different treatments on the chromaticity of lotus roots during 60 days of storage

[0030] In Table 1, CK1 represents the control group 1, CK2 represents the control group 2, CK3 represents the control group 3, CK4 represents the control group 4, Group1 represents the example group 1, and Group2 represents the example group 2.

[0031] As can be seen from Table 1: As the storage time increases, the values of L* and b* gradually decrease, while the values of a* and ΔE increase steadily, with the most obvious change in CK1. However, the inhibitory effects of CK2, CK3, and CK4 on the blue discoloration of lotus roots are lower than those of Group1 and Group2. The change trend of the BI value is similar to that of ΔE, indicating that as the storage time extends, the quality of lotus roots deteriorates, resulting in an increase in both ΔE and BI values. Compared with the CK4 group, the color protection effect of the CK3 group is better.

[0032] From Figure 1The results showed that: with the extension of storage time, the appearance of each treatment group gradually deteriorated. The quality of CK2, Group1, and Group2 was better than that of CK1, and CK3 was better than CK4. After 60 days of storage, the epidermal color of the lotus root remained more transparent, showing an inconspicuous light blue color. This indicates that the blue variation inhibitor (CK2) and Group1 and Group2 can both reduce the formation of blue pigments in the lotus root. However, after 60 days of storage, CK1 showed an obvious blue transformation.

[0033] It can be seen that on the basis of the formula of this application, removing tea saponin (i.e., CK3 group) and replacing oxalic acid with acetic acid (i.e., CK4 group) resulted in a worse appearance preservation effect than the complete formula of this application (i.e., Group1 and Group2 groups). Therefore, further, the substance content and colony situation of the lotus roots preserved in CK1, CK2, CK3, Group1, and Group2 groups were further explored subsequently.

[0034] (2) Determination of total phenols, proteins, reducing sugars, and soluble solids The phenolic compounds in the lotus root were extracted by the homogenization method, and then the total phenol content was determined by the Folin-Ciocalteu method. The total phenol content was expressed as an equivalent amount of gallic acid (y = 2.3278x + 0.0353, R 2 = 0.9992), with the unit of mg GAE / g fw.

[0035] The protein content was determined by the Coomassie Brilliant Blue staining method. The absorbance was measured using a microplate reader (Multiskan SkyHigh, Thermo Field, USA). The protein content in the lotus root was expressed as the protein content per gram of fresh tissue weight (mg / g FW), and the calculation formula was as follows:

[0036] In the formula, c 1 and V 1 are the protein concentration and volume of the sample extract, respectively, and m 0 is the fresh weight of the sample taken.

[0037] The reducing sugars were extracted by the homogenization method. After extraction, the extract and the residue were placed in a 50 mL centrifuge tube and heated in a water bath at 80 °C for 30 min to ensure that all reducing sugars in the lotus root were completely released. After heating, the mixture was taken out and cooled to room temperature. The reducing sugar extract was filtered and diluted with distilled water in a 100 mL volumetric flask for future use as the reducing sugar extract. Before measurement, the sample was diluted tenfold. Then, 1 mL of the diluted sample was mixed with 0.5 mL of distilled water and 3 mL of DNS. After boiling in a water bath for 5 min and cooling to room temperature, the absorbance was measured at 540 nm with a 200 μL sample.

[0038] The soluble solids were determined using an HT4-101 handheld refractometer: The extracted lotus root supernatant was placed on the refractometer to measure the refractive index of the lotus root juice, which reflects the soluble solids content (%) of the lotus root during storage.

[0039] Figure 2 It shows the effects of different treatments on the contents of nutrients such as total phenols (2a), proteins (2b), reducing sugars (2c), and soluble solids (2d) in lotus roots during 60 days of storage.

[0040] As can be seen from the figure: As the storage time extended, the contents of total phenols and proteins in each group gradually decreased. On the 60th day, the total phenols in CK1, CK2, CK3, Group1, and Group2 were 0.35 ± 0.0040, 0.40 ± 0.0017, 0.36 ± 0.0017, 0.42 ± 0.0097, and 0.39 ± 0.028 mg GAE / g fw, respectively. The protein contents in each group on the 60th day were 0.36 ± 0.016, 0.86 ± 0.070, 0.58 ± 0.078, 1.13 ± 0.024, and 0.76 ± 0.069 mg / g fw, respectively. The decrease in the soluble protein content indicates that as the storage time extended, the synthesis and metabolism ability of lotus roots gradually declined. Compared with CK1, CK2, CK3, Group1, and Group2 could significantly reduce the loss of phenolic compounds and the degradation of proteins during storage.

[0041] Figure 2 As shown in c, on the 30th day, the peak value of the reducing sugar content in CK1 was 121.54 ± 1.76 mg / g fw. The CK2, CK3, Group1, and Group2 groups reached the peak on the 45th day, which were 85.20 ± 5.03, 99.12 ± 8.70, 84.86 ± 6.36, and 86.22 ± 7.71 mg / g fw, respectively. Then, as the storage time extended, the soluble solids content decreased significantly ( Figure 2 d). The results indicate that the lotus roots treated with the preservation treatment can reduce the starch decomposition caused by low-temperature stress and reduce the sugar consumption caused by the respiration of lotus roots. The change trend of soluble solids reflects the change trend of reducing sugars; specifically, the CK1 group reached the peak at 15 days and then decreased rapidly. For the blueing inhibitor treatment groups, especially CK2, CK3, and Group1 and Group2, they could significantly delay the decrease in the soluble solids level. In summary, compared with the CK1 group, CK2, CK3, Group1, and Group2 showed more favorable effects, indicating that these four inhibitors may slow down the deterioration of the quality of lotus roots.

[0042] (3) Determination of pH and titratable acid Determination of pH: Mix 10 g of fresh lotus root with an equal amount of distilled water, and then blend to make juice.

[0043] Determination of titratable acid: Take 20 mL of lotus root extract and mix it with phenolphthalein, then titrate with 0.1 M NaOH. The end point of the titration shows a faint red color in the solution and persists for at least one minute, and then record the volume of NaOH used. The calculation formula for the content of titratable acid in lotus root is:

[0044] where V 0 and V 1 are the volumes of NaOH consumed in titrating distilled water and the filtrate, respectively (mL); V 2 represents the volume of the filtrate obtained from the sample during titration (mL), and V t represents the total volume of the prepared filtrate (mL); m represents the mass of the sample (g), and f represents the conversion factor (0.067 g / mmol).

[0045] Figure 2 Shows the effects of different treatments on the pH (2e) and titratable acid (2f) of lotus root during 60 days of storage.

[0046] As can be seen from the figure: Each treatment has a significant effect on the initial pH value and the pH value at the 60th day of lotus root. Subsequently, due to the utilization of organic acids and their conversion to sugars, compared with the CK2 group, the pH values of CK3, Group1, and Group2 increased significantly. In the later stage, the metabolism of microorganisms and the production of acids caused the pH of CK1 to decrease significantly.

[0047] Storage and treatment time have a considerable impact on the titratable acid of lotus root. During low-temperature storage, the content of titratable acid in lotus root treated in the CK3 group was significantly lower than that in the treatment groups CK2, Group1, and Group2. After 60 days of storage, the titratable acids in lotus root treated with CK2, Group1, and Group2 were 1.38 times, 1.31 times, and 1.38 times higher than that in the CK1 group, respectively.

[0048] (4) Determination of total number of colonies, molds, and yeasts The determination of the total number of colonies was carried out according to the plate counting method of GB 4789.2-2022. The determination of the total number of molds and yeasts was carried out according to the plate counting method of GB 4789.15-2016. The results are expressed as lg (CFU / g).

[0049] Figure 3 Shows the total number of bacteria (3a) and the number changes of molds and yeasts (3b) in lotus root after different treatments.

[0050] As can be seen from the figure: with the extension of storage time, the total number of bacteria and the presence of molds and yeasts both increased steadily. In terms of antibacterial effect, CK2, Group1, and Group2 were superior to CK3. This study showed that oxalic acid, ascorbic acid, and tea saponin had antibacterial properties, comparable to CK2. In addition, the main spoilage organisms of lotus root were bacteria, which played an important role in the initial spoilage of lotus root, while molds and yeasts played a major role in the later spoilage of lotus root. In summary, the existing formulations Group1 and Group2 could effectively inhibit spoilage bacteria, molds, and yeasts in lotus root, and had good fresh-keeping effects on lotus root.

[0051] (5)Determination of electrolyte leakage rate, malondialdehyde, hardness, and soluble quinone Determination of electrolyte leakage rate: Take 15 pieces of lotus root peel with a diameter of 5 mm, add 20 mL of deionized water, and store at room temperature for 30 min for initial measurement (L 0 ). Subsequently, place the peel in a boiling water bath for 15 min, and after cooling to room temperature, record the reading of the sample with a conductivity meter (DDS-307) (L t ). The result of relative electrolyte leakage is expressed as the ratio of L 0 to L t (%)

[0052] Extraction of malondialdehyde: Take 10 g of lotus root for each group, then add 20 mL of 5% trichloroacetic acid solution pre-cooled to 4 °C to the sample, and homogenize with a high-speed homogenizer (XHF-D, Ningbo Xinzhi Biotechnology Co., Ltd.) at a speed of 10000 rpm / min for 1 min. Centrifuge the supernatant at 10000 rpm for 10 min to obtain the malondialdehyde extract. Take 2 mL of the extract and mix it with 2 mL of 0.67% (m / v) thiobarbituric acid solution to determine the malondialdehyde content. At the same time, 2 mL of trichloroacetic acid is used as a blank control. Place the sample in a boiling water bath for 30 min, cool to room temperature, centrifuge again, collect the supernatant, and measure the absorbance values of the sample at 450, 532, and 600 nm. The calculation of malondialdehyde content is as follows:

[0053] The hardness of lotus root was measured using a texture analyzer (TA.XT) (TA.XT.PLUS, SMS companies of the United Kingdom). The key parameters are summarized as follows: initial test speed: 2 mm / s; test speed: 1 mm / s; recording speed: 1 mm / s; compression ratio: 30%; dwell time: 5 s. The hardness (g) of the specimen is defined as the highest peak value reached during the compression process.

[0054] The method for determining soluble quinone is summarized as follows: Measure its absorbance value at 437 nm, and the soluble quinone content is expressed as (OD437 )g -1 is represented by FW.

[0055] Figure 3 Shows the changes in electrolyte leakage rate (3c), malondialdehyde content (3d), hardness (3e) and soluble quinone (3f) in lotus roots treated differently.

[0056] As can be seen from the figure: The electrolyte leakage rate of lotus roots without added preservatives (CK1) increased significantly with the extension of storage time and reached 77.87±4.15% after 60 d; while the electrolyte leakage rates of lotus roots treated with CK2 and Group1 increased slowly with time. Oxalic acid and ascorbic acid may help maintain the integrity of the membrane, reduce the oxidation of fatty acids in the cell membrane, and ultimately reduce the electrolyte leakage in processed agricultural products by reducing lipoxygenase activity. In addition, saponins exhibit effective antibacterial properties and can reduce tissue damage caused by microorganisms.

[0057] The malondialdehyde content gradually increased during storage. However, over time, the malondialdehyde level in the lotus roots of the CK1 group increased rapidly; at the same time, the malondialdehyde levels of CK2, CK3, Group1, and Group2 also increased gradually, but were still significantly lower than that of the CK1 group (p<0.05); on the 45th d and the 60th d, the malondialdehyde levels of Group1 and Group2 were the lowest.

[0058] With the extension of storage time, the hardness of lotus roots in each group decreased, and the hardness of lotus roots soaked in oxalic acid, ascorbic acid, EDTA-Na2 and tea saponin decreased significantly.

[0059] Compared with the initial level measured on the 0th day, the soluble quinone concentrations of all treatments increased significantly. However, on the 45th d and the 60th d, the soluble quinone levels of other treatment groups were lower than that of the CK1 group. The increase in soluble quinone indicates an increase in the reactions related to browning. The results show that the combination of oxalic acid, EDTA-Na2 and ascorbic acid can significantly reduce the formation of brown pigments.

[0060] (6) Microstructure of the cell wall of lotus root skin on the 60th d The ultrastructure of the cell wall of lotus root peel was studied using a scanning electron microscope (SEM, JSM-6390LV, NTC, Japan). Under the microscope, the fresh lotus root peel and lotus root peel of the CK1 and Group3 treatment groups were cut into three 3 mm×3 mm squares with a thickness of 200 μm. The sliced tissues were washed 3-4 times with 0.1 M phosphate buffer solution (PBS, pH 7.2). Subsequently, the samples were fixed overnight in 4% polyformaldehyde tissue fixative. After fixation, the samples were dehydrated and rinsed 3-4 times with PBS again before dehydration. The tissue samples were dehydrated using ethanol solutions of different concentrations (30, 50, 70, 80, 90, 95, and 100%), with 100% ethanol dehydration for 30 min and the dehydration time for all other concentrations being 15 min. During the 70% ethanol dehydration step, vacuum was applied to eliminate air trapped in the tissue. Finally, the treated tissue samples were freeze-dried. In the SEM analysis, the samples were initially coated with a layer of gold spray and then observed at magnifications of 200× and 500×.

[0061] Figure 4 The microscopic structural changes of the lotus root peel cell wall on the 60th day after different treatments are shown.

[0062] As can be seen from the figure: obvious shrinkage and certain damage occurred in the cell wall of the CK1 group ( Figure 4 A1 and A2), which means the damage of the cell membrane structure and the possible leakage of phenolic substances and other active substances. While the structures of Group2 ( Figure 4 B1 and B2) and the fresh lotus root cell wall ( Figure 4 C1 and C2) were relatively complete without obvious damage. This shows that the Group2 blueing inhibitor has a certain protective effect on the lotus root cell wall and cell membrane.

[0063] (7)Determination of total phenols, total iron, and phenolic substances in the lotus root peel on the 60th d On the 60th day of storage, the lotus seed coats (about 1 mm thick) of each treatment group were freeze-dried using a freeze dryer (LGJ-18, Beijing Songyuan Huaxing Technology Development Co., Ltd.) and then ground into powder. Subsequently, polyphenols were extracted and the total phenolic content was measured. The types and contents of polyphenols in lotus seed coats were determined using a high-performance liquid chromatograph (HPLC, Agilent Technology (China) Co., Ltd.) combined with an XDB-C18 liquid chromatography column (4.6 mm × 250 mm, 5 μm). Mobile phase A was an aqueous solution of 0.4% (v / v) formic acid, and mobile phase B was acetonitrile. The injection volume was 10 μL, and the flow rate was 1 mL / min. The detection wavelength was 280 nm, and the column temperature was 25 °C. The program for running the samples on the gradient was as follows: 0 min, 95% A; 3 min, 80% A; 35 min, 10% A; 37 min, 10% A; 39 min, 90% A; 40 min, 95% A.

[0064] Samples of each treatment group were soaked in 1 mol / L hydrochloric acid at room temperature for 1.5 h, and then 5 mL of the soaking solution was diluted 100 times. The diluted solution was transferred to a 25 mL volumetric flask, 5 mL of 1 mol / L sodium acetate and 5 mL of 1.5 g / L o-phenanthroline were added, and the volume was adjusted to the mark. This process was repeated three times, and the absorbances of the samples at wavelengths of 510 nm and 390.5 nm were measured and calculated using the provided formula.

[0065]

[0066]

[0067] In the formula, m 1 , k 1 , V 1 are the concentration of Fe 2+ (μg / g dw), the dilution factor used when measuring Fe 2+ and the volume of the Fe 2 + solution to be measured (L); m 2 , k 2 , V 2 represent the concentration of Fe 3+ (μg / g dw), the dilution multiple of the Fe 3+ to be measured and the volume of the Fe 3+ solution to be measured (L).

[0068] Figure 5 Shows the changes in total phenols (5a), total iron (5b) and phenolic substances (5c) in lotus seed coats on the 60th day.

[0069] As can be seen from the figure: On the 60th day, the total phenols in CK1 were slightly lower than those in the CK3 group and significantly lower than those in CK2, Group1, and Group2. The research results show that without adding preservatives or soaking with oxalic acid, ascorbic acid, and EDTA-Na2, the polyphenols in lotus root peel underwent significant oxidative degradation after 60 days of storage. In addition, the formation of polyphenol-iron chelates also affected the determination of total phenols. As Figure 5 shown in 2+ Figure 3+ b, the total contents of Fe 2+ and Fe 2+ showed a trend opposite to that of total phenols, and the iron ion content in the CK1 group was significantly higher than that in other groups. This is related to the increased formation of blue pigments in CK1 because polyphenol-iron chelators are often insoluble or poorly soluble in ethanol and water, resulting in lower measured iron contents during the extraction process. In addition, iron ions mainly exist in the form of Fe3+, and only CK2 and Group2 contain some Fe 3+ . This indicates that the preservative formulations in CK2 and Group2 have effective antioxidant properties, significantly slowing down the oxidation of Fe

[0070] The main phenolic compounds found in the lotus root peel of different treatment groups include levodopa, gallocatechin, epigallocatechin, catechin, and epicatechin, as shown in Table 2 for details.

[0071] Table 2 Changes in polyphenol contents in lotus root peel after 60 days of storage under different treatments

[0072] The research results show that the o-phenol content of levodopa in lotus root peel is the highest. However, the content of levodopa in CK1 is significantly lower than that in CK2, Group1, and Group2, showing a stronger blue change, indicating that more levodopa-iron chelates are formed in these two groups. In addition, the contents of gallocatechin and epigallocatechin in CK3 and Group2 are also significantly higher than those in the CK1 group, possibly because the chelates formed involve different types and amounts of polyphenols and iron. The experimental group Group2 contains a higher content of phenolic substances but does not show obvious blue discoloration, indicating the protective effect of the blue discoloration inhibitor on the integrity of its tissue.

[0073] From the above tests, it can be seen that: The inhibitor prepared by the present invention can achieve a good fresh-keeping effect on lotus root and reduce the occurrence of blue discoloration during the storage of lotus root.

[0074] In the present invention, the specific raw materials not described are all existing substances and can be directly purchased from the market.

[0075] The above are only the preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A novel lotus root blueing inhibitor, characterized in that: The inhibitor is composed of the following components: oxalic acid, EDTA-Na2, VC, tea saponin, and the balance is water; Among them, in terms of mass concentration: oxalic acid concentration is 0.2%~0.4%, EDTA-Na2 concentration is 0.2%~0.4%, VC concentration is 0.1%~0.2%, and tea saponin concentration is 0.5~1%.

2. The inhibitor according to claim 1, characterized in that The inhibitor has an oxalic acid concentration of 0.3%, an EDTA-Na2 concentration of 0.35%, a VC concentration of 0.15%, and a tea saponin concentration of 0.5%.

3. A method for preparing the inhibitor according to any one of claims 1 or 2, characterized in that: Add oxalic acid, EDTA-Na2, VC and tea saponin into water and stir thoroughly to dissolve.

4. Use of the inhibitor according to any one of claims 1 or 2 in the preservation of lotus roots, characterized in that: When used, soak the washed lotus root in the inhibitor, drain the water after soaking, vacuum pack it, and refrigerate it.

5. The use according to claim 4, characterized in that: The soaking time is 0.5-1.5 hours; the refrigeration temperature is 2-5°C.

6. The use according to claim 5, characterized in that: The soaking time is 1 hour; the refrigeration temperature is 4°C.

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