Method for preparing tomato peel polyester and derivative based on biological method

Abstract

The invention belongs to the technical field of biological materials, and particularly relates to a method for preparing tomato skin polyester and derivatives based on a biological method, and the method realizes efficient extraction and functional modification of polyester in tomato skin through a biological refining process combining microbial fermentation and enzyme catalysis. The multifunctional polyester material with various application potentials is prepared. The polyester material prepared by the invention has excellent mechanical properties, thermal stability and biocompatibility. The method not only can give full play to the resource potential in the tomato peel, but also can meet the application requirements in different fields through functional modification, and has a wide development prospect.

Description

Technical Field

[0001] This invention belongs to the field of biomaterials technology, specifically relating to a method for preparing polyester and derivatives from tomato peels based on biological methods. This method achieves efficient extraction and functional modification of polyester from tomato peels through a biorefining process combining microbial fermentation and enzyme catalysis, resulting in the preparation of multifunctional polyester materials with various application potentials. Background Technology

[0002] Tomatoes are one of the most widely cultivated crops globally, primarily used to produce tomato sauce, juice, canned goods, and various other food products. However, tomato processing generates a significant amount of waste, with tomato skins accounting for 8% of the total tomato weight. Despite this, tomato skins are rich in nutrients such as carbohydrates, protein, fat, fiber, and minerals, as well as antioxidants like vitamin E, vitamin C, carotenoids, flavonoids, and phenols. Improper disposal of these wastes not only pollutes the environment but also wastes the valuable resources they contain.

[0003] Currently, the main methods for disposing of tomato peels are landfilling, incineration, and use as animal feed. CN202410369948.8 discloses a method for preparing organic fertilizer using microbial inoculants fermented with tomato byproducts and cotton stalks. However, this method does not fully utilize the high-value components in tomato peels. Researchers have also begun to explore extracting active ingredients from tomato peel residue. CN202311832375.X discloses a method for extracting protein from tomato peels using enzymatic methods. CN202311478592.3 discloses a modified macroporous resin, its preparation method, and methods for separating and purifying total flavonoids from tomato peel residue, as well as its applications. CN202210867656.8 discloses a method for simultaneously extracting lycopene and polysaccharides. CN202010800358.8 discloses a method for preparing high-purity lycopene. However, further application research after extraction is lacking, and the processing technology is cumbersome.

[0004] Chemical hydrolysis involves treating tomato skins with strong acids or alkalis, hydrolyzing the cuticle components into free hydroxy fatty acid monomers, which are then synthesized into polyesters through esterification. However, this method requires large amounts of chemical reagents and generates significant wastewater, causing environmental pollution. Enzymatic hydrolysis utilizes specific enzymes to break down the bonds between the cuticle and cell walls, releasing the cuticle components. This method is relatively environmentally friendly, but the cost of enzymes is high, and the hydrolysis efficiency is affected by various factors such as temperature, pH, and substrate concentration.

[0005] In recent years, microbial fermentation, as an emerging biomass conversion technology, has shown great potential in the field of biomaterial preparation. By screening microbial strains capable of degrading tomato peels and producing polyesters, cuticle can be extracted under relatively mild conditions. However, polyester materials extracted solely through fermentation may not meet diverse functional and performance requirements. Given the limitations of existing extraction methods, developing a more efficient, environmentally friendly, and performance-controllable technology for extracting and modifying polyesters from tomato peels is particularly important. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing polyester and its derivatives from tomato peels based on a biological process. This method can improve the extraction efficiency and purity of polyester by optimizing hydrolysis and polymerization conditions, while reducing production costs and realizing the resource utilization of waste.

[0007] The technical solution adopted by the present invention to achieve the above objectives is as follows: This invention provides a method for preparing tomato peel polyester and its derivatives based on a biological method, comprising the following steps: (1) Tomato skin pretreatment: The tomato skin was washed and cleaned, crushed and then added to the proline betaine pretreatment system. After the treatment was completed, the tomato skin was homogenized to obtain tomato skin pulp. (2) Enzymatic hydrolysis: Add water to the tomato peel pulp, add cellulase and pectinase to carry out enzymatic hydrolysis, and obtain tomato peel hydrolysate; (3) Fermentation treatment: Water is added to the enzymatic hydrolysate of tomato peel to obtain a mixture. Then ammonium sulfate, magnesium sulfate and yeast extract are added to the mixture. After mixing and sterilization, Yeast lipolyticis is inoculated and fermented. After the fermentation is completed, ultrasonic treatment is performed to obtain the fermentation product. (4) Centrifugation: The fermentation product is centrifuged, the supernatant is collected, and then extracted with a mixed solvent. The solvent is removed by vacuum distillation of the extract to obtain crude polyester. After purification of the crude polyester, tomato skin polyester is obtained. (5) Modify the polyester in tomato peel to obtain a polyester derivative of tomato peel.

[0008] Preferably, in step (1), the amount of the proline betaine pretreatment system added accounts for 3-5% of the weight of the tomato skin; the proline betaine pretreatment system is composed of proline betaine, urea and water in a mass ratio of 1:0.1:10; and the homogenate is homogenized to 200 mesh.

[0009] Preferably, in step (2), the volume ratio of tomato peel pulp to water is 1:1; the amount of cellulase added is 0.2% w / v; the amount of pectinase added is 0.1% w / v; and the enzymatic hydrolysis is carried out at pH 5.0 and a temperature of 48-50℃ for 4 hours.

[0010] Preferably, in step (3), the volume ratio of the tomato peel enzymatic hydrolysate to water is 1:1.5-2; the amount of ammonium sulfate added accounts for 0.5%-0.8% of the weight of the mixture; the amount of magnesium sulfate added accounts for 0.2%-0.3% of the weight of the mixture; the amount of yeast extract added accounts for 2%-3% of the weight of the mixture; and the amount of Yersinia lipolyticis inoculated accounts for 3%-5% of the volume of the mixture.

[0011] Preferably, in step (3), the fermentation is carried out at 28°C for 72 hours with shaking culture at 130-150 rpm; the ultrasonic treatment is carried out using an ultrasonic cell disruptor with a treatment frequency of 500-800 kHz, a pulse ratio of 1:1 to 1:2, and a time of 30-40 min.

[0012] Preferably, in step (4), the centrifugation is performed at 4000-5000 rpm for 15-20 min; the mixed solvent is composed of ethyl acetate / methanol in a volume ratio of 7:3.

[0013] Preferably, in step (4), the purification is first passed through a silica gel column and then eluted using a chloroform / methanol mixed solvent.

[0014] Preferably, in step (4), the gradient elution procedure is as follows: at room temperature, elution is performed sequentially with 20-30%, 50-60%, and 80-90% chloroform / methanol mixed solvent.

[0015] Preferably, in step (5), the specific process of the modification is as follows: acetic anhydride-pyridine solution is added to the tomato peel polyester to carry out an ester exchange reaction; then hydrogen peroxide is added to the reaction solution to carry out the reaction to obtain the tomato peel polyester derivative.

[0016] Preferably, the transesterification reaction is carried out at 80-85°C for 6 hours; the concentration of acetic anhydride in the pyridine solution is 20-22 wt%; the mass ratio of tomato peel polyester to acetic anhydride is 1:0.08-0.1; the amount of hydrogen peroxide added accounts for 10% of the mass of tomato peel polyester; after adding hydrogen peroxide, the reaction is carried out at room temperature for 24-26 hours.

[0017] The tomato peels used in this invention are the peels from tomato processing waste.

[0018] The beneficial effects of this invention are as follows: (1) This invention selects tomato peel as a raw material for biotransformation, effectively utilizing food processing waste. Utilizing tomato peel not only reduces production costs but also effectively achieves resource recycling, reduces environmental pollution, and embodies the concepts of green chemistry and sustainable development. The preparation method provided by this invention can effectively release the original polyester in tomato peel, while microorganisms utilize the nutrients in the tomato peel to synthesize more polyester.

[0019] (2) This invention innovatively combines natural extraction with microbial fermentation technology in the manufacturing process of polyester. This method avoids the high temperature and high pressure conditions required by traditional chemical synthesis methods, reduces energy consumption and environmental pollution, and effectively improves resource utilization. This invention not only focuses on the preparation of polyester, but also further introduces specific functional groups (such as hydroxyl and carboxyl groups) through chemical catalytic functionalization modification, thereby endowing polyester with more functional properties.

[0020] (3) The polyester material prepared by this invention has excellent mechanical properties, thermal stability and biocompatibility. This method can not only make full use of the resource potential of tomato peel, but also meet the application needs of different fields through functional modification, and has broad development prospects. Detailed Implementation

[0021] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0022] The cellulase and pectinase used in this invention were purchased from Yisheng Biotechnology (Shanghai) Co., Ltd.

[0023] The Yersinia lipolyticis yeast used in this invention was purchased from Wuhan Gray Algae Biotechnology Co., Ltd. (product number: HZB119831).

[0024] Example 1 (1) Pretreatment of tomato skin: Tomato skin pretreatment: Wash the tomato skins in the tomato processing waste, wash away impurities, mechanically crush to a particle size of less than 1-2 mm, add 4% of the tomato skin weight of proline betaine pretreatment system (proline betaine, urea and water are composed in a mass ratio of 1:0.1:10) for treatment, and then use a homogenizer to crush it to 200 mesh; (2) Enzymatic hydrolysis: Add 1 volume of water to the ground tomato skin, add 0.2% w / v of cellulase and 0.1% w / v of pectinase, pH=5.0, temperature 50 ℃, time 4 hours; then inactivate the enzymes.

[0025] (3) Fermentation treatment: Add twice the volume of water to the enzyme-inactivated tomato peel pulp, add 0.8% ammonium sulfate, 0.2% magnesium sulfate, and 3% yeast extract to the above mixture, mix well and sterilize, then inoculate with 5% of the fermentation liquid volume of Yersinia lipolytica, ferment at 28℃ for 72 hours, and culture with shaking (130-150 rpm). After the culture is completed, use an ultrasonic cell disruptor to treat the cells at a frequency of 800 kHz, a pulse ratio of 1:1, and a time of 40 min.

[0026] (4) Centrifugation: After ultrasonic crushing, centrifugation is performed at 4000 rpm for 20 min, and the supernatant is collected.

[0027] (5) Organic solvent extraction: Five extractions were performed using a mixed solvent of ethyl acetate / methanol (volume ratio 7:3). The solvent was removed by vacuum distillation of the extract to obtain crude polyester.

[0028] (6) Purification: Further purification was carried out by column chromatography (silica gel column) using a gradient elution with a chloroform / methanol mixed solvent. The specific elution procedure was as follows: at room temperature, elution was carried out sequentially with 20%, 50%, and 80% chloroform / methanol mixed solvent to obtain tomato skin polyester with high purity. (7) Tomato peel polyester and acetic anhydride were added to a 22wt% acetic anhydride-pyridine solution at a mass ratio of 0.1 and reacted at 80-85℃ for 6h; then hydrogen peroxide of 10% of the mass of tomato peel polyester was added to the reaction solution and reacted at room temperature for 26h to obtain tomato peel polyester derivative.

[0029] The tomato peel polyester derivative prepared in Example 1 has the following molecular weights: Mw4155, Mn3637, glass transition temperature (Tg): -16.3℃, and melting point (Tm): 48.6℃.

[0030] Example 2 (1) Pretreatment of tomato skin: Tomato skin pretreatment: Wash the tomato skins in the tomato processing waste, wash away impurities, mechanically crush to a particle size of less than 1-2 mm, add 5% of the tomato skin weight of proline betaine pretreatment system (proline betaine, urea and water are composed in a mass ratio of 1:0.1:10) for treatment, and then use a homogenizer to crush it to 200 mesh; (2) Enzymatic hydrolysis: Add an equal volume of water to the ground tomato skins, add 0.2% w / v cellulase and 0.1% w / v pectinase, pH=5.0, temperature 50 ℃, time 4 hours. Then inactivate the enzymes.

[0031] (3) Fermentation treatment: Add twice the volume of water to the enzyme-inactivated tomato peel pulp, add 0.6% ammonium sulfate, 0.3% magnesium sulfate, and 3% yeast extract to the above mixture, mix well and sterilize, then inoculate with 4% of the fermentation liquid volume of Yersinia lipolytica, ferment at 28℃ for 72 hours, and culture with shaking. After the culture is completed, use an ultrasonic cell disruptor to treat the cells at a frequency of 800 kHz, a pulse ratio of 1:1, and a time of 40 min.

[0032] (4) Centrifugation: After ultrasonic crushing, centrifugation is performed at 4000 rpm for 20 min, and the supernatant is collected.

[0033] (5) Organic solvent extraction: Five extractions were performed using a mixed solvent of ethyl acetate / methanol (volume ratio 7:3). The solvent was removed by vacuum distillation of the extract to obtain crude polyester.

[0034] (6) Purification: Further purification was carried out by column chromatography (silica gel column) using a gradient elution with a chloroform / methanol mixed solvent. The specific elution procedure was as follows: at room temperature, elution was carried out sequentially with 20%, 50%, and 80% chloroform / methanol mixed solvent to obtain tomato skin polyester with high purity. (7) Tomato peel polyester and acetic anhydride were added to a 22wt% acetic anhydride-pyridine solution at a mass ratio of 1:0.1 and reacted at 80-85℃ for 6h. Then, hydrogen peroxide of 10% of the mass of tomato peel polyester was added to the reaction solution and reacted at room temperature for 26h. After centrifugation and washing, the tomato peel polyester derivative was obtained.

[0035] Comparative Example 1 (1) Pretreatment of tomato skin: Tomato skin pretreatment: Wash the tomato skins in the tomato processing waste, wash away impurities, mechanically crush them to a particle size of less than 1-2 mm, add 4% urea aqueous solution (urea and water are composed in a mass ratio of 10.1:10) to treat the tomato skins, and then use a homogenizer to crush them to 200 mesh. The other steps are the same as in Example 1.

[0036] Comparative Example 2 (1) Pretreatment of tomato skin: Tomato skin pretreatment: Wash the tomato skins in the tomato processing waste, wash away impurities, mechanically crush them to a particle size of less than 1-2 mm, add water accounting for 4% of the weight of the tomato skins, stir evenly, and then use a homogenizer to crush them to 200 mesh. The other steps are the same as in Example 1.

[0037] Example 1 The extraction rates of tomato peel polyesters prepared in the examples and comparative examples were statistically analyzed. The extraction rate was calculated using the following formula: Polyester extraction rate from tomato peel - (actual mass of extracted polyester / total mass of polyester in raw material) × 100%.

[0038] Note: The total mass of polyester in tomato skin is calculated based on the theoretical polyester content in tomato skin (based on the theoretical polyester content being 2.5% of the total).

[0039] The specific results are shown in Table 1.

[0040] Table 1 Example 2 The extracted tomato peel polyester derivatives were subjected to antibacterial performance testing. The specific testing method was as follows: (1) Prepare a concentration of 10 7 CFU / mL of Escherichia coli and Staphylococcus aureus bacterial suspension; (2) Add an equal amount of tomato skin polyester derivative and incubate at 37°C for a certain time (2, 4, 6 h); set up a blank control group (bacterial suspension without any treatment).

[0041] (3) Take the cultured mixture, dilute it serially, spread it on agar plates, and count the number of viable bacteria (CFU / mL) after culturing.

[0042] Calculate the antibacterial rate: Inhibition rate (%) = [(Number of viable bacteria in control group - Number of viable bacteria in treatment group) / Number of viable bacteria in control group] × 100% The specific results are shown in Table 2.

[0043] Table 2

Claims

1. A method for preparing tomato peel polyester and its derivatives based on a biological method, characterized in that, Includes the following steps: (1) Tomato skin pretreatment: The tomato skin was washed and cleaned, crushed and then added to the proline betaine pretreatment system. After the treatment was completed, the tomato skin was homogenized to obtain tomato skin pulp. (2) Enzymatic hydrolysis: Add water to the tomato peel pulp, add cellulase and pectinase to carry out enzymatic hydrolysis, and obtain tomato peel hydrolysate; (3) Fermentation treatment: Water is added to the enzymatic hydrolysate of tomato peel to obtain a mixture. Then ammonium sulfate, magnesium sulfate and yeast extract are added to the mixture. After mixing and sterilization, Yeast lipolyticis is inoculated and fermented. After the fermentation is completed, ultrasonic treatment is performed to obtain the fermentation product. (4) Centrifugation: The fermentation product is centrifuged, the supernatant is collected, and then extracted with a mixed solvent. The solvent is removed by vacuum distillation of the extract to obtain crude polyester. After purification of the crude polyester, tomato skin polyester is obtained. (5) Modify the polyester in tomato peel to obtain a polyester derivative of tomato peel.

2. The method according to claim 1, characterized in that, In step (1), the amount of proline betaine pretreatment system added accounts for 3-5% of the weight of tomato skin; the proline betaine pretreatment system is composed of proline betaine, urea and water in a mass ratio of 1:0.1:10; the homogenate is homogenized to 200 mesh.

3. The method according to claim 1 or 2, characterized in that, In step (2), the volume ratio of tomato peel pulp to water is 1:1; the amount of cellulase added is 0.2% w / v; the amount of pectinase added is 0.1% w / v; and the enzymatic hydrolysis is carried out at pH 5.0 and a temperature of 48-50℃ for 4 hours.

4. The method according to claim 1 or 3, characterized in that, In step (3), the volume ratio of the tomato peel hydrolysate to water is 1:1.5-2; the amount of ammonium sulfate added accounts for 0.5%-0.8% of the weight of the mixture; the amount of magnesium sulfate added accounts for 0.2%-0.3% of the weight of the mixture; the amount of yeast extract added accounts for 2%-3% of the weight of the mixture; and the amount of Yeast lipolyticis inoculated accounts for 3%-5% of the volume of the mixture.

5. The method according to claim 1 or 4, characterized in that, In step (3), the fermentation is carried out at 28°C for 72 hours with shaking culture at 130-150 rpm; the ultrasonic treatment is carried out using an ultrasonic cell disruptor with a treatment frequency of 500-800kHz, a pulse ratio of 1:1 to 1:2, and a time of 30-40 min.

6. The method according to claim 1, characterized in that, In step (4), the centrifugation is performed at 4000-5000 rpm for 15-20 min; the mixed solvent is composed of ethyl acetate / methanol in a volume ratio of 7:

3.

7. The method according to claim 1 or 6, characterized in that, In step (4), the purification process involves passing the material through a silica gel column and then eluting it using a gradient elution with a chloroform / methanol mixed solvent.

8. The method according to claim 7, characterized in that, In step (4), the gradient elution procedure is as follows: at room temperature, elution is performed sequentially with 20-30%, 50-60%, and 80-90% chloroform / methanol mixed solvent.

9. The method according to any one of claims 1-8, characterized in that, In step (5), the specific process of the modification is as follows: acetic anhydride-pyridine solution is added to the tomato peel polyester to carry out an ester exchange reaction; then hydrogen peroxide is added to the reaction solution to carry out the reaction and obtain the tomato peel polyester derivative.

10. The method according to claim 8, characterized in that, The transesterification reaction is carried out at 80-85℃ for 6 hours; the concentration of acetic anhydride in the pyridine solution is 20-22 wt%; the mass ratio of tomato peel polyester to acetic anhydride is 1:0.08-0.1; the amount of hydrogen peroxide added is 10% of the mass of tomato peel polyester; after adding hydrogen peroxide, the reaction is carried out at room temperature for 24-26 hours.

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