An enzymatic treatment method for enzyme-mediated defruiting and polyphenol conversion of olives

Abstract

This invention relates to the field of food processing, and provides an enzyme-mediated enzymatic treatment method for olive de-astringency and polyphenol conversion, solving the problems of high pollution from chemical methods and severe browning from traditional enzymatic methods in existing olive de-astringency technologies, resulting in poor product appearance, strong astringent taste, and loss of nutritional active ingredients. The method includes the following steps: S1, preparing an olive raw material slurry; S2, adding laccase to the olive raw material slurry, adding a citrate-sodium citrate buffer solution to adjust the reaction environment, and then adding a color-protecting agent to obtain a first solution system; S3, carrying out an enzymatic reaction in the first solution system obtained in step S2 under water bath conditions; S4, after the enzymatic reaction is completed, obtaining a second solution system, subjecting the second solution system to enzyme inactivation treatment, and obtaining a de-astringent olive product after cooling and centrifugation; wherein the color-protecting agent is citric acid; the de-astringency rate of the de-astringent olive product is >62.0%, and the browning degree is ≤0.219.

Description

Technical Field

[0001] This invention relates to the field of food processing, and more particularly to an enzyme-mediated enzymatic treatment method for olive deastringency and polyphenol conversion. Background Technology

[0002] Olives, also known as green olives, are the fruit of the olive tree, a plant belonging to the genus *Olive* in the family Burseraceae. As a traditional Chinese medicine, dried olives are used medicinally, possessing properties that clear heat and detoxify, soothe the throat, and promote saliva production. As a food, olives are rich in antioxidants such as vitamin C, polyphenols, and vitamin E. Their unique taste, initially astringent but later sweet, is widely loved. Fuzhou ranks among the top in Fujian Province in terms of olive planting area and yield, mainly distributed along the Minjiang River in Minhou and Minqing counties. Relying on excellent soil and water resources and a long history of cultivation, olives have become an important local specialty industry, driving rural economic growth.

[0003] The astringency of fruits mainly originates from tannins and other polyphenolic compounds. According to the standard GB / T 10221-2021 Sensory Analysis Terminology, astringency is a complex sensation induced by substances such as persimmon tannin and blackthorn tannin, manifested as contraction, tightening, or wrinkling of the oral skin or mucous membrane. Currently, the evaluation index system for astringency mainly includes three methods: sensory evaluation, physicochemical detection (tannin content), and instrumental detection (electronic tongue). Among them, sensory evaluation scores based on the sensation of contraction at the tip of the tongue according to corresponding scoring standards; physicochemical detection uses tannin content as the core chemical indicator; and the electronic tongue is a new type of analytical instrument that simulates the human taste mechanism and can be used for rapid determination of astringency intensity. In olives, astringency is significantly correlated with soluble tannin content. Since tannin content directly determines the strength of astringency in fruit, deastringency removal becomes an essential and crucial step in processing. Currently, deastringency removal technologies mainly employ various strategies such as chemical treatment, physical-assisted chemical methods, fermentation / natural fermentation, and biological enzymatic methods. Traditional chemical treatment is the most common method in industrial production, mainly using low-salt, dilute alkali (usually sodium hydroxide, baking soda, edible soda ash, or quicklime) to rapidly hydrolyze tannins. However, this method suffers from nutrient loss and generates large amounts of aniline-containing wastewater, creating environmental problems. Physical-assisted chemical methods combine modern technologies, including ultrasound, vacuum permeation, CO2 treatment, or ethanol soaking, to improve astringency removal efficiency or taste, but these methods have high equipment costs. Fermentation relies on natural or microbial forces, using plant fermentation broth or lactic acid bacteria to gradually decompose tannins through slow enzymatic reactions, but this process is time-consuming. In contrast, the increasingly developed green technology of bio-enzyme directly adds specific enzymes (such as tanninase) to break the glycosidic bonds in tannins, converting them into milder-tasting monomeric phenolic compounds. This method better preserves the sensory qualities of olives, is gentler, and has environmental advantages.

[0004] Chinese Patent Publication No. CN116158506A discloses a greening processing equipment and method for olive fruits, including the following steps: S10 primary cleaning, washing the harvested olive fruits with clean water to remove surface dirt; S20 removal of bitter glycosides from the olive fruits, soaking the olive fruits in a sodium hydroxide alkaline solution of a set concentration for a set time; S30 secondary cleaning, rinsing the surface of the olive fruits with clean water to remove the alkaline solution; S40 dealkalization, soaking the olive fruits in an organic acid citric acid aqueous solution to remove the alkali; S50 color protection and preservation treatment, applying a color-protecting agent to the olive fruits for color protection. This technical solution uses sodium hydroxide alkaline solution to soak the olive fruits, which presents environmental problems such as nutrient loss and the generation of large amounts of aniline-containing wastewater.

[0005] Chinese Patent Publication No. CN106819755A discloses a reagent and method for removing astringency and turbidity from fruit juice. The reagent comprises cross-linked gelatin and an aluminum-magnesium layered bimetallic hydroxide. The cross-linked gelatin has a degree of cross-linking of 0.5-1 and a molecular weight greater than 300,000. The aluminum-magnesium molar ratio of the aluminum-magnesium layered bimetallic hydroxide is 0.3-3. This invention has excellent astringency and turbidity removal effects on fruit juices with a bitter taste and high turbidity, achieving a tannin removal rate of over 70% and increasing light transmittance to over 90%. However, while removing turbidity and increasing light transmittance, it cannot solve the color protection problem, resulting in poor product appearance and color. Furthermore, this method produces a large amount of solid precipitate, which may leave gel residue.

[0006] The green technology of bio-enzymatic methods has broad application prospects in the field of olive deep processing and comprehensive utilization, covering multiple aspects such as fruit and vegetable juice processing and quality improvement, functional component extraction, cosmetics, and antibacterial applications. In fruit and vegetable juice processing and quality improvement, to address the astringency problem of olives, compound hydrolytic enzymes can decompose large-molecule astringent substances within minutes; compound clarifying enzymes can degrade pectin and tannins, improving clarity and reducing astringency. In the extraction of functional components, cellulase and pectinase assist in the extraction of olive polyphenols and oleuropein, offering advantages such as high extraction efficiency and low oxidative loss, and enabling high-value utilization of by-products such as olive pomace and olive leaves. In the cosmetics field, lipases can convert oleuropein into hydroxytyrosol, or proteases can be used to prepare tyrosinase-inhibiting peptides. The resulting products have anti-inflammatory, antioxidant, and melanin-inhibiting effects, suitable for functional cosmetics. In antibacterial applications, enzymatic hydrolysis of green olives and abalone blood produces glycopeptides with enhanced antibacterial activity; enzymatically hydrolyzed olive pomace polyphenols also exhibit concentration-dependent antibacterial effects and can be used as natural antibacterial agents. Summary of the Invention

[0007] Therefore, in view of the above problems, the present invention provides an enzyme-mediated enzymatic treatment method for olive de-astringency and polyphenol conversion, which solves the problems of high pollution from chemical methods and severe browning from traditional enzymatic methods in existing olive de-astringency technologies, resulting in poor product appearance, strong astringent taste and loss of nutritional active ingredients.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: An enzyme-mediated method for olive de-astringency and polyphenol conversion includes the following steps: S1. Preparation of olive raw material slurry; S2. Add laccase to the olive raw material slurry, add citrate-sodium citrate buffer to adjust the reaction environment, and then add a color-protecting agent to obtain the first solution system; S3. The first solution system obtained in step S2 is subjected to an enzymatic reaction under water bath conditions; S4. After the enzymatic reaction is completed, a second solution system is obtained. The second solution system is subjected to enzyme inactivation treatment, and after cooling and centrifugation, the de-astringent olive product is obtained. The color-protecting agent is citric acid; the deastringency rate of the deastringent olive product is >62.0%, and the browning degree is ≤0.219.

[0009] Furthermore, in step S1, the olive raw material slurry includes olive juice, olive pulp homogenate, or olive extract.

[0010] Furthermore, in step S2, the amount of laccase added is 30U-50U per 0.01g of olive raw material slurry.

[0011] Furthermore, in step S2, the pH value of the citrate-sodium citrate buffer solution is 4.0-5.0, and the concentration is 0.1 mol / L.

[0012] Furthermore, in step S3, the enzymatic reaction takes 2-6 hours.

[0013] Furthermore, in step S3, the water bath temperature for the enzymatic reaction is 30℃-70℃.

[0014] Furthermore, in step S4, the enzyme inactivation treatment is performed at 90°C for 5 minutes.

[0015] By adopting the aforementioned technical solution, the beneficial effects of the present invention are as follows: 1. This technical solution is the first to apply laccase to the degradation of olive tannins. By utilizing the strong oxidizing activity of laccase on phenolic substances, it can achieve efficient deastringency in a weakly acidic environment. The removal rate of olive tannins is >62.0%, which is far higher than the treatment effect of traditional tannin enzymes or physical methods. Moreover, the reaction conditions are mild and the energy consumption is low, making it suitable for industrial production.

[0016] 2. Addressing the industry pain point that laccase catalysis easily leads to phenolic oxidation and browning, this technical solution innovatively adopts a citric acid-sodium citrate buffer system. By utilizing the chelating effect of citrate on metal ions and the principle of inhibiting enzyme active sites in an acidic environment, a balance between high deastringency rate and low browning is achieved. Specifically, in the citrate system, by adjusting the amount of citric acid, the browning degree can be significantly reduced while maintaining a tannin removal rate of >62.0%, overcoming the defect of severe enzyme activity inhibition by color-protecting agents in the phosphate system.

[0017] 3. Compared to traditional alkaline deastringency methods and chemical treatment methods, this technical solution uses a fully biological enzymatic process, leaving no harmful chemical residues and meeting food safety standards. Furthermore, this process is not only suitable for olive juice and dried fruit processing, but can also be extended to the processing of other tannin-rich fruits and vegetables such as persimmons, plums, and tea, demonstrating high versatility and market potential. Attached Figure Description

[0018] Figure 1 This is a standard curve of gallic acid in an embodiment of the present invention; Figure 2 This is a diagram illustrating the color-protecting effect of citric acid on laccase enzymatic deacidification in an embodiment of the present invention. Figure 3 This is a graph showing the effect of different enzyme amounts on the degradation rate of olive polyphenols in the embodiments of the present invention. Detailed Implementation Example 1

[0019] An enzyme-mediated method for olive de-astringency and polyphenol conversion includes the following steps: (1) Preparation of olive raw material slurry (1-1) Prepare raw materials: fresh olives, the variety is sandalwood olive, harvested from Minqing County, Fuzhou; (1-2) Remove the pits from fresh olives and prepare olive fruit homogenate to obtain olive raw material slurry; (2) Blending the reaction system Laccase was added to the olive raw material slurry, and citrate-sodium citrate buffer was added to adjust the reaction environment. Then, a color-protecting agent was added to obtain the first solution system. The laccase (10000U / mL, obtained by fermentation of Aspergillus oryzae): a food enzyme, sourced from Cangzhou Xiasheng Enzyme Biotechnology Co., Ltd. The amount of olive raw material slurry weighed is 1g; before adding laccase, 60mL of water is added to the olive raw material slurry and washed into a 250mL conical flask, extracted in a boiling water bath for 30min, cooled and then diluted to 100mL to obtain tannin extract, and then 2.50mL of tannin extract is taken. The amount of laccase added is 40U per 0.01g of olive raw material slurry; The citrate-sodium citrate buffer solution has a pH of 5.0 and a concentration of 0.1 mol / L; the tannin extract is brought to a final volume of 10 mL using the citrate-sodium citrate buffer solution. The color-protecting agent is citric acid, with a concentration of 7.5 g / L and an addition amount of 1 mL; (3) Enzyme-catalyzed reaction The first solution system obtained in step S2 is subjected to an enzymatic reaction under water bath conditions; The enzymatic reaction time is 2 hours; the water bath temperature for the enzymatic reaction is 50°C. (4) Enzyme inactivation treatment After the enzymatic reaction is completed, a second solution system is obtained. The second solution system is subjected to enzyme inactivation treatment, and after cooling and centrifugation, the de-astringent olive product is obtained. The enzyme inactivation treatment was performed at 90°C for 5 minutes. Example 2

[0020] The difference from Example 1 is that the amount of citric acid added is 2 mL. All other technical aspects are the same as in Example 1. Example 3

[0021] The difference from Example 1 is that the amount of citric acid added is 3 mL. All other technical aspects are the same as in Example 1. Example 4

[0022] The difference from Example 1 is that the amount of citric acid added is 4 mL. All other technical aspects are the same as in Example 1.

[0023] Comparative Example 1 The difference from Example 1 is that citric acid is not added. All other technical aspects are the same as in Example 1.

[0024] Comparative Example 2 The difference from Example 1 is that laccase is not added, but 1 mL of citric acid is added. All other technical aspects are the same as in Example 1.

[0025] Comparative Example 3 The difference from Example 1 is that laccase is not added, but 2 mL of citric acid is added. All other technical aspects are the same as in Example 1.

[0026] Comparative Example 4 The difference from Example 1 is that laccase is not added, but 3 mL of citric acid is added. All other technical aspects are the same as in Example 1.

[0027] Comparative Example 5 The difference from Example 1 is that laccase is not added, but 4 mL of citric acid is added. All other technical aspects are the same as in Example 1.

[0028] Comparative Example 6 The difference from Example 2 is that in step (2), laccase is added to the olive raw material slurry, and disodium hydrogen phosphate-sodium dihydrogen phosphate buffer is added to adjust the reaction environment. Other technical solutions are the same as in Example 2.

[0029] Comparative Example 7 The difference from Comparative Example 6 is that citric acid is not added. All other technical aspects are the same as Comparative Example 6.

[0030] Comparative Example 8 The difference from Comparative Example 6 is that laccase is not added. All other technical aspects are the same as Comparative Example 6.

[0031] The deastringency effect of the deastringent olive products prepared in Examples 1-4 and Comparative Examples 1-8 was evaluated by color, tannin removal rate, and browning degree.

[0032] The astringency of olive fruit is highly significantly positively correlated with the content of soluble tannins, but not significantly correlated with the content of insoluble tannins. A soluble tannin content of 0.2% is usually used as the threshold for determining whether the fruit has lost its astringency.

[0033] The calculation process for tannin removal rate: a. Plotting the standard curve A standard curve for tannin detection was established based on the standard NY / T 1600-2008, "Determination of Tannin Content in Fruits, Vegetables and Their Products - Spectrophotometric Method". Accurately weigh 0.0571 g of gallic acid monohydrate reference standard, add deionized water to a final volume of 50 mL. The concentration of this gallic acid monohydrate standard solution is 1.038 mg / mL. Dilute it 10 times to obtain the working solution. Accurately pipette 0.2, 0.3, 0.4, 0.5, 0.6, and 0.7 mL of the working solution into 10 mL colorimetric tubes, add 1.0 mL of Folin-Ciocalteu reagent, shake well, let stand for 3 min, add 3.0 mL of 75 g / L sodium carbonate solution, and dilute to volume. After reacting at room temperature in the dark for 2 h with shaking, measure the absorbance at 765 nm. Plot the standard curve with absorbance Y as the ordinate and gallic acid concentration X (μg) as the abscissa. The soluble tannin content in fresh olives was determined spectrophotometrically, and the tannin content was expressed as gallic acid. The gallic acid standard curve is shown below. Figure 1 As shown, the linear regression equation is y = 0.0141x + 0.0718. r 2 =0.9994, gallic acid showed a good linear relationship in the range of 20.76-72.66 μg; b. Calculate the tannin content of olives The tannin content of olives is X (calculated as gallic acid). The tannin content of olives is calculated according to formula (1). (1) In formula (1): The tannin content X (calculated as gallic acid) in the sample, mg / g; C—Tannin content in the sample solution, μg; V—Dilution factor of the tannin extract stock solution; M—Weight of fresh olives, in g; c. Calculation of tannin removal rate Take a certain volume of tannin extract, filter it in rapid quantitative filter paper, take the filtrate and determine its tannin content X1, and calculate the tannin removal rate according to formula (2). (2) In formula (2): X—Tannin content in the sample before deastringency treatment, mg / g; X1—Tannin content in the sample after deastringency treatment, mg / g.

[0034] Determination of browning degree in fresh olives: Because the pigments produced by the browning reaction have significant absorption at 420 nm, the absorbance value D at 420 nm represents the degree of browning; the larger the D at 420 nm, the more severe the browning. Accurately pipette a certain volume of olive extract, use a 1 cm cuvette, and with distilled water as a reference, measure the optical density at a wavelength of 420 nm.

[0035] The descaling and color-protecting effects of Examples 1-4 and Comparative Examples 1-8 are shown in Table 1.

[0036] Table 1. Evaluation of the color-protecting effect of citric acid on laccase de-acidification.

[0037] Although laccase can efficiently remove tannins from olives, the tannin extract turns significantly yellow and brown after the enzymatic reaction, severely affecting the product's appearance. To address this issue, citric acid was introduced as a color-protecting agent. In disodium hydrogen phosphate-sodium dihydrogen phosphate buffer (Table 1), citric acid exhibits excellent color-protecting effects, significantly reducing the browning degree of tannin-containing systems (regardless of whether laccase is added). While the introduction of citric acid reduced the browning degree from 0.190 to 0.140, demonstrating some color-protecting ability, it also caused a significant decrease in the tannin removal rate of laccase from 60.3% to 43.7%, severely inhibiting the deastringency efficiency. This may be because, in the phosphate buffer, the carboxyl oxygen atom in the citric acid molecule specifically coordinates with the copper ion in the active site of laccase, occupying the enzyme's active site and thus hindering the catalytic oxidation of tannin substrates by laccase.

[0038] refer to Figure 2 In Examples 1-4, the color-protecting effect of citric acid on laccase enzymatic deastringency was as follows: In the citric acid-sodium citrate buffer system, laccase effectively catalyzed the oxidative deastringency reaction of olive tannins. Without the addition of citric acid, the tannin deastringency rate significantly increased to 67.5%, but the solution color deepened to yellow. Figure 2 The presence of enzymatic browning was observed. As the amount of citric acid added increased from 1 mL to 4 mL, the tannin deastringency rate of laccase showed a slow decreasing trend (from 66.1% to 62.4%), and the absorbance value of the solution significantly decreased from 0.219 to 0.174, with a lighter color. This indicates that the addition of citric acid effectively inhibited the oxidative color development reaction caused by laccase, exhibiting a good color-protecting effect. In contrast, the absorbance value of citric acid in the control group (comparative examples 1-5) remained at a low level (0.022-0.024), and the color remained similar to that of the tannins, indicating that citric acid itself does not possess deastringency-removing ability and only acts as an acidic color-protecting agent. In conclusion, in the citric acid-sodium citrate buffer system, laccase can effectively remove the astringency of olive tannins. Furthermore, by adjusting the amount of citric acid, a high deastringency rate (>62%) can be maintained while significantly inhibiting enzymatic browning, achieving a dual effect of deastringency removal and color protection. This provides a feasible solution for color protection and quality improvement in olive processing. Example 5

[0039] The difference from Example 1 is as follows: The olive raw material slurry is olive juice. The preparation process is as follows: pit fresh olives, add water to fresh olives according to the ratio of fresh olives to water of 10g:1000mL, homogenize with a juicer, filter through gauze, centrifuge at 4000r / min for 10min and take 200mL of supernatant juice, add 50U of laccase per 0.01g of olive raw material slurry, the enzymatic reaction time is 2h, and the water bath temperature of the enzymatic reaction is 40℃.

[0040] Example 5 investigated the changes in quality indicators (soluble solids, total sugar, tannins, total phenols, and total acid) of olive juice before and after enzymatic hydrolysis, as shown in Table 2. Significant changes in these indicators occurred after laccase treatment. First, the soluble solids content decreased from 6.13% to 5.63%, indicating that some macromolecules were decomposed. Second, the total sugar content slightly increased, indicating that polysaccharides such as starch were hydrolyzed into monosaccharides by the enzyme, slightly enhancing the sweetness of the juice. Most significantly, the tannin and total phenol contents decreased, from 6.40 mg / g to 2.83 mg / g and from 6.71 mg / g to 3.25 mg / g, respectively, indicating that laccase effectively decomposed phenolic substances in the juice, reducing astringency. Furthermore, the total acid content slightly increased from 0.79% to 0.85%, possibly due to the production of acidic products during enzymatic hydrolysis. Overall, laccase treatment reduced astringent components and slightly increased sweetness, improving the flavor characteristics of the juice.

[0041] Table 2 Changes in quality indicators of olive juice before and after laccase treatment Action system Soluble solids / % Total sugar / % Tannins (mg / g) Total phenols (mg / g) Total acid / % juice 6.13 2.33 6.40 6.71 0.79 Fruit juice + laccase 5.63 2.42 2.83 3.25 0.85 Example 6

[0042] The difference from Example 1 is as follows: The olive raw material slurry is an olive extract. The preparation process is as follows: crush fresh olives and take 1g of sample. Add 60% ethanol and extract by ultrasonication at 30℃ for 40min. Centrifuge at 4000r / min for 10min and take the supernatant. Add 50U of enzyme at 0.01g olive mass at 40℃ and enzymatically hydrolyze for 2h. Place the enzymatic hydrolysate in a -18℃ refrigerator to terminate the enzymatic hydrolysis reaction. Then filter with a 0.45μm microporous membrane and take the filtrate for detection of olive polyphenols. The detection conditions are: (a) Chromatographic conditions: use an Agilent XDBC18 (2.1mm×100mm, 1.8μm) column, mobile phase A is water, mobile phase B is acetonitrile; injection volume is 5μL; flow rate is 0.2mL·min −1 Column temperature 40℃; linear gradient elution program: 0–4 min, 1%–7% B; 4–13 min, 7%–40% B; 13–14 min, 40%–90% B; 14–18 min, 1% B; 18–20 min, 1% B. (b) Mass spectrometry conditions: electrospray ionization (ESI) source, negative ion detection mode; sheath gas temperature 250℃; sheath gas flow rate 11.0 L·min −1 Drying gas temperature: 300℃; Drying gas flow rate: 8.0 L / min −1 The atomizing gas pressure was 45 psi; the capillary voltage was 3.5 kV; the scanning mode was full scan, and the scanning range was 100 to 1200 m / z.

[0043] Comparative Example 9 The difference from Example 6 is that the amount of laccase added is 5U. All other technical aspects are the same as in Example 6.

[0044] Comparative Example 10 The difference from Example 6 is that the amount of laccase added is 10U. All other technical aspects are the same as in Example 6.

[0045] Comparative Example 11 The difference from Example 6 is that the amount of laccase added is 25U. All other technical aspects are the same as in Example 6.

[0046] Example 6 investigated the transformation of phenolic compounds and their metabolites related to astringency after laccase deastringency treatment. Figure 3 As shown, the degradation of olive polyphenol compounds by enzyme amount is as follows: with increasing enzyme amount, the degradation of four substrates (gallic acid, 3-...) decreases. O The degradation rates of gallic quinic acid, geraniol, and geraniol isomers generally showed an increasing trend, but the sensitivity of different substrates to the enzyme varied significantly. Geraniol isomers and geraniol were highly sensitive substrates; at low enzyme levels (10 U), the degradation rates rapidly reached 92.7% and 81.3%, respectively, and approached 100% at 25 U. Gallic acid and 3- O Gallic quinic acid is a moderately sensitive substrate; its degradation rate increases linearly with increasing enzyme concentration, only approaching complete degradation at high enzyme concentrations (50 U). Ellagic acid, however, is hardly degraded by this enzyme, with its degradation rate remaining consistently low (-12.7% to 12.7%), a stark contrast to the other four substrates. Its degradation rate increases rather than decreases in low enzyme concentrations (<50 U), possibly due to the enzymatic conversion of geraniol, a polyphenolic compound of ellagitannins, and its isomers into ellagic acid.

[0047] In summary, this technical solution reveals the substrate-specific transformation law of laccase on olive polyphenols: it exhibits high sensitivity to geraniol and its isomers, which cause strong astringency (the degradation rate can reach 100% at low enzyme concentrations), while showing resistance to degradation and even enrichment of ellagic acid, which has high nutritional value. This selective degradation not only significantly reduces astringency but also slightly increases the sweetness of the juice (increases the total sugar content) through enzymatic hydrolysis of starch and other polysaccharides, achieving a reduction in astringency and an increase in sweetness, thus improving the overall quality of the product.

[0048] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.

Claims

1. A method for enzyme-mediated deastringency removal and polyphenol conversion of olives, characterized in that, Includes the following steps: S1. Preparation of olive raw material slurry; S2. Add laccase to the olive raw material slurry, add citrate-sodium citrate buffer to adjust the reaction environment, and then add a color-protecting agent to obtain the first solution system; S3. The first solution system obtained in step S2 is subjected to an enzymatic reaction under water bath conditions; S4. After the enzymatic reaction is completed, a second solution system is obtained. The second solution system is subjected to enzyme inactivation treatment, and after cooling and centrifugation, the de-astringent olive product is obtained. The color-protecting agent is citric acid; the deastringency rate of the deastringent olive product is >62.0%, and the browning degree is ≤0.

219.

2. The enzyme-mediated deastringency and polyphenol conversion method for olives according to claim 1, characterized in that, In step S1, the olive raw material slurry includes olive juice, olive pulp homogenate, or olive extract.

3. The enzyme-mediated deastringency and polyphenol conversion method for olives according to claim 1, characterized in that, In step S2, the amount of laccase added is 30U-50U per 0.01g of olive raw material slurry.

4. The enzyme-mediated deastringency and polyphenol conversion method for olives according to claim 1, characterized in that, In step S2, the pH value of the citrate-sodium citrate buffer solution is 4.0-5.0, and the concentration is 0.1 mol / L.

5. The enzyme-mediated deastringency and polyphenol conversion method for olives according to claim 1, characterized in that, In step S3, the enzymatic reaction takes 2-6 hours.

6. The enzyme-mediated deastringency and polyphenol conversion method for olives according to claim 1, characterized in that, In step S3, the water bath temperature for the enzymatic reaction is 30℃-70℃.

7. The enzyme-mediated deastringency and polyphenol conversion method for olives according to claim 1, characterized in that, In step S4, the enzyme inactivation treatment is performed at 90°C for 5 minutes.

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