Preparation method of electrochemically modified sweet potato residue pectin, product and application thereof

Abstract

The application discloses a preparation method of electrochemically modified sweet potato residue pectin, and products and applications of the electrochemically modified sweet potato residue pectin. The sweet potato residue pectin is modified by using an electrochemical method, and the process is simple, green and efficient, and an anode modified pectin with high antibacterial activity and a cathode modified pectin with excellent wide-pH gel performance can be simultaneously prepared. Application researches show that the cathode modified pectin is combined with cinnamaldehyde to form stable milk gels, and the evaporation of water and the volatility of cinnamaldehyde can effectively delay strawberry spoilage; the anode modified pectin coating can significantly prolong the shelf life of refrigerated beef by 2 days, inhibit the growth of microorganisms and maintain the meat color and quality. The application provides a new idea for green modification of the sweet potato residue pectin and expands the application potential of the sweet potato residue pectin in food preservation and functional materials.

Description

Technical Field

[0001] This invention relates to the fields of food processing, natural polymer modification and food preservation technology, specifically to a method for preparing electrochemically modified sweet potato residue pectin, its products and applications. Background Technology

[0002] Sweet potato residue is a major byproduct of the starch industry and is rich in pectin. However, natural sweet potato residue pectin (SPP) typically suffers from weak gelling properties (forming gels only under acidic conditions) and limited antibacterial activity, restricting its high-value application in the food industry. Traditional pectin modification methods, such as chemical methods (acid and alkali treatment) or enzymatic methods, have drawbacks such as complex processes, low efficiency, high cost, and a tendency to cause pectin degradation or chemical residues. Furthermore, they are difficult to significantly improve both the gelling and antibacterial properties of pectin simultaneously.

[0003] In recent years, electrochemical modification technology has shown great potential in the field of biomolecule modification due to its advantages such as mild conditions, environmental friendliness, controllable processes, and ease of operation. Currently, electrochemical modification is mostly used for small molecule compounds or specific proteins. However, research on the systematic electrochemical modification of polysaccharides such as pectin, especially the acquisition of modified products with different prominent functions (strong antibacterial properties and excellent gelling properties) at both the anode and cathode using the same process, has not been reported. Furthermore, how to efficiently apply modified pectin to food preservation systems to construct slow-release antibacterial gels or edible coatings remains a pressing technical problem to be solved. Summary of the Invention

[0004] One of the objectives of this invention is to provide a method for preparing electrochemically modified sweet potato residue pectin. This method is simple, green, and efficient, and can simultaneously prepare anolyte-modified pectin (AM8h) with high antibacterial activity and cathodic-modified pectin (CM8h) with excellent wide pH gelation properties.

[0005] A second objective of this invention is to provide modified sweet potato residue pectin obtained by the above method.

[0006] The third objective of this invention is to provide applications of the above-mentioned modified sweet potato residue pectin, suitable for the preservation of fruits and meats.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing electrochemically modified sweet potato residue pectin, comprising the following steps: (1) Dissolve sweet potato residue pectin (SPP) extracted by hydrothermal method in electrolyte solution to prepare a pectin solution with a concentration of 0.5% ~ 2% w / v; (2) Add the above pectin solution in equal amounts to the anode and cathode chambers of the H-type electrolytic cell, and separate the two chambers with a dialysis membrane with a molecular weight cutoff of 1000 kDa. (3) Electrolysis reaction for 2 to 8 hours under DC regulated power supply, voltage 20~40 V, room temperature, and continuous stirring; (4) After the reaction is completed, the reaction solutions in the anode chamber and the cathode chamber are collected respectively, and their pH is adjusted to neutral with acid or base to obtain the anode modified pectin solution (denoted as AMnh, or AM8h if the reaction lasts for 8 hours) and the cathode modified pectin solution (denoted as CMnh, or CM8h if the reaction lasts for 8 hours). The solutions are stored at low temperature for later use.

[0008] Preferably, the electrolyte solution in step (1) is a sodium chloride solution of 0.1% to 0.2% w / v; and the concentration of the pectin solution is 1% w / v.

[0009] Preferably, the electrolysis voltage in step (3) is 30 V, the reaction time is 8 hours, and the stirring speed is 150 rpm.

[0010] In a second aspect, the present invention provides a modified sweet potato residue pectin, including anodic modified sweet potato residue pectin and cathode modified sweet potato residue pectin, which is prepared by the preparation method described in the first aspect of the present invention.

[0011] Anodically modified sweet potato residue pectin (AM8h), with a degree of esterification (DE) higher than 70%, still belongs to high-methoxyl pectin (HMP); it is resistant to foodborne pathogens such as Escherichia coli (E. coli). E. coli ) and Staphylococcus aureus ( S. aureus It exhibits significantly enhanced antibacterial activity, with a minimum inhibitory concentration (MIC) of 20 mg / mL. Its antibacterial mechanisms include disrupting bacterial cell membrane integrity, inducing cell membrane potential depolarization, causing oxidative stress (ROS accumulation), and inhibiting bacterial nucleic acid expression.

[0012] The cathode-modified sweet potato residue pectin (CM8h) has an esterification degree (DE) of less than 50%, transforming from high methoxyl pectin (HMP) to low methoxyl pectin (LMP). It exhibits excellent calcium ion-responsive gelation ability and can form stable hydrogels that do not drip when inverted under the following wide range of conditions: pectin concentration 0.6% ~ 1.0% (w / v), calcium chloride concentration 37.5 ~ 62.5 mg / g (based on dry pectin), and pH range 4.0 ~ 12.0.

[0013] Thirdly, the present invention provides a slow-release antibacterial gel for fruit preservation, which is composed of the cathode-modified sweet potato residue pectin (CM8h) described in the second aspect, calcium ions, and the natural antibacterial agent cinnamaldehyde. The amount of cinnamaldehyde added is 2% to 4% of the total weight of the gel; the calcium ions are provided by calcium chloride at a concentration of 41.67 to 62.5 mg / g (calculated based on dry CM8h).

[0014] The preparation method of the sustained-release antibacterial gel is as follows: prepare a 1% to 2% CM8h solution, adjust the pH to 7, add calcium chloride and cinnamaldehyde of the above concentration, vortex mix and let stand to form an emulsion gel.

[0015] Fourthly, this invention provides the application of the slow-release antibacterial gel described in the third aspect in the preservation of perishable fruits such as strawberries. The application method is as follows: the fruit and the slow-release antibacterial gel are placed together in a sealed or semi-sealed container. The evaporation of water in the gel network drives the slow volatilization of cinnamaldehyde, creating an antibacterial atmosphere around the fruit, thereby inhibiting mold growth, delaying fruit softening, and reducing nutrient loss.

[0016] Fifthly, the present invention provides an edible antibacterial coating for meat preservation, which is composed of the anodic modified sweet potato residue pectin (AM8h) solution described in the second aspect, wherein the concentration of the solution is 1% to 3% (w / v).

[0017] Sixthly, the present invention provides the application of the edible antibacterial coating described in the fifth aspect in the preservation of refrigerated meats such as beef and pork. The application method is as follows: immerse fresh meat pieces in the coating solution for 30-60 seconds, remove them, drain or allow the surface liquid to air dry, and then store them under refrigeration conditions.

[0018] This coating can inhibit the growth of microorganisms on the surface of meat products through its antibacterial activity, slow down lipid oxidation and myoglobin discoloration, and reduce the rate of volatile basic nitrogen (TVB-N) formation, thereby extending the sensory and microbiological shelf life of meat products.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. A green and efficient electrochemical method is used to modify sweet potato residue pectin. The process is mild and does not require a large amount of chemical reagents. The same electrolysis process can obtain AM8h with outstanding antibacterial properties and CM8h with excellent gelation properties at the anode and cathode, respectively, realizing the efficient and multifunctional utilization of waste biomass. Moreover, the process equipment is simple and the parameters are easy to control, and it has the potential for industrial scale-up.

[0020] 2. Anodic modified pectin AM8h exhibits significantly enhanced antibacterial activity compared to natural pectin, enabling the construction of edible coatings to extend the shelf life of chilled beef; Cathode modified pectin CM8h overcomes the environmental limitations of traditional pectin gels, forming stable gels under wide pH and low concentration conditions, and can also construct a cinnamaldehyde slow-release emulsion gel system to achieve active slow-release preservation of strawberries.

[0021] 3. The green and safe physical preservation systems constructed by the two modified sweet potato residue pectin have provided a new natural source solution for the food preservation field and a new material for the development of natural food preservatives, greatly expanding the application potential of pectin in various food systems. Attached Figure Description

[0022] Figure 1 : Preservation effect of CM8h / cinnamaldehyde composite gel on strawberries. (A) Changes in appearance of strawberries stored at 28℃ for 0-5 days (comparison); (B) Changes in weight loss rate of strawberries during storage; (C) Changes in firmness of strawberries during storage; (D) Changes in soluble solids content of strawberries during storage.

[0023] Figure 2 : The preservation effect of AM8h coating on refrigerated beef. (A) Changes in the surface of beef at 4℃ for different days with 3% A8; (B) Changes in beef color L* for different days; (C) Changes in beef color a* for different days; (D) Changes in beef color b* for different days; (E) Beef color for different days ΔE Changes; (F) Changes in beef weight over different days; (G) Changes in beef pH over different days; (H) Changes in beef microbial colonies over different days; (I) Changes in beef TVB-N over different days. Detailed Implementation

[0024] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0025] Example 1: Electrochemically Modified Sweet Potato Residue Pectin Sweet potato residue pectin (SPP) extracted by hydrothermal method was dissolved in 0.1% ~ 0.2% w / v sodium chloride solution to prepare a pectin solution with a concentration of 1% w / v. The above pectin solution was added in equal amounts to the anode and cathode chambers of an H-type electrolytic cell (250 mL). Both the anode and cathode were platinum electrodes, and the two chambers were separated by a regenerated cellulose dialysis membrane with a molecular weight cutoff of 1000 kDa. Electrolysis was carried out for 8 hours under DC regulated power supply, at a voltage of 30 V, room temperature, and continuous stirring at 150 rpm / min. After the reaction is complete, the reaction solutions from the anode and cathode chambers are collected separately, and their pH is adjusted to neutral with acid or alkali to obtain the anode-modified pectin solution (denoted as AM8h) and the cathode-modified pectin solution (denoted as CM8h), which are stored at low temperature for later use.

[0026] The performance of anode-modified sweet potato residue pectin and cathode-modified sweet potato residue pectin were characterized by the following tests: Anodically modified sweet potato residue pectin (AM8h), with an esterification degree (DE) higher than 70% as determined by acid-base titration, still belongs to high-methoxyl pectin (HMP). Adding 0.5% to 3% (w / v) of AM8h to plates and using a spreader method, it was tested against foodborne pathogens such as Escherichia coli. E. coli ) and Staphylococcus aureus ( S. aureus Observations revealed that it has significantly enhanced antibacterial activity, with a minimum inhibitory concentration (MIC) of 20 mg / mL. Kit tests showed that it disrupts bacterial cell membrane integrity, induces cell membrane depolarization, causes oxidative stress (ROS accumulation), and inhibits bacterial nucleic acid expression.

[0027] The degree of esterification (DE) of the cathode-modified sweet potato residue pectin (CM8h) was less than 50% as determined by acid-base titration. Alkali treatment of CM8h yielded low-methoxyl pectin (LMP). LMP exhibits excellent calcium ion-responsive gelling ability and can form a stable hydrogel that does not drip when inverted under the conditions of pectin concentration of 0.6% ~ 1.0% (w / v), calcium chloride concentration of 37.5 ~ 62.5 mg / g (based on dry pectin), and pH range of 4.0 ~ 12.0.

[0028] Example 2: Preparation of CM8h / cinnamaldehyde composite sustained-release gel and its application in strawberry preservation. 1. Preparation of composite gel: CM8h was prepared into a 2% (w / v) solution (pH=7), and CaCl2 was added to a final concentration of 62.5 mg / g. Then, cinnamaldehyde was added at concentrations of 1%, 2%, and 4% of the total gel weight, respectively. The mixture was vortexed for 5 seconds and allowed to stand to form an emulsion gel. A CM8h gel without cinnamaldehyde was used as a control.

[0029] 2. Strawberry Preservation Experiment: Select strawberries of uniform size and ripeness, place 5 strawberries and a semi-circular composite gel (or control gel) in each sealed container, and incubate at 28℃. Observe the appearance and mold growth of the strawberries daily, and measure the weight loss rate, firmness, and soluble solids content.

[0030] 3. Results: such as Figure 1As shown, the CM8h gel containing 2% cinnamaldehyde exhibited the best preservation effect. By the third day of storage, obvious mold spots had appeared in the control group and the 1% cinnamaldehyde group, while the strawberries in the 2% and 4% cinnamaldehyde groups remained intact. Furthermore, the strawberries in the 2% cinnamaldehyde group showed the slowest decrease in firmness and loss of soluble solids. This indicates that the CM8h gel can effectively load and slowly release cinnamaldehyde, achieving synergistic preservation of strawberries.

[0031] Example 3: Preparation of AM8h edible coating and its application in beef preservation 1. Coating preparation: Prepare a 2% (w / v) aqueous solution of AM8h.

[0032] 2. Beef Preservation Experiment: Fresh beef was cut into uniform small pieces (approximately 3.5 × 3.5 × 1 cm). The experimental group of beef was immersed in AM8h solution for 30 seconds, then removed and air-dried; the control group was immersed in distilled water for the same amount of time. The treated beef pieces were placed in sterile petri dishes and stored in a refrigerator at 4°C.

[0033] 3. Index determination: Samples were taken every 2 days to determine the sensory color, pH value, total bacterial count and volatile basic nitrogen (TVB-N) value of beef.

[0034] 4. Results: such as Figure 2 As shown, AM8h coating treatment significantly delayed the spoilage of beef.

[0035] Appearance and color: By day 10, the beef in the coated group remained bright red, while the control group had noticeably darkened and browned. Colorimeter data showed that the a* value (redness) of the coated group decreased more slowly.

[0036] Microbiological indicators: such as Figure 2 During the early storage period (0-4 days), the total bacterial count in the coated group was significantly lower than that in the control group. By day 6, the total bacterial count in the control group had exceeded 10. 4 CFU / g enters the sub-fresh level, while the coating group remains in the fresh level (<10). 4 (CFU / g), extending shelf life by approximately 2 days.

[0037] Chemical indicators: such as Figure 2 The rate of increase in TVB-N value in the coated group was consistently slower than that in the control group, indicating that protein degradation and putrefaction processes were slowed down.

[0038] pH value: The pH value of the coating group also increased more slowly than that of the control group.

[0039] In summary, the electrochemical modification method provided by this invention can efficiently endow sweet potato residue pectin with new functional properties, and its application in food antibacterial preservation and gel carrier has significant effects, showing good development prospects and market potential.

[0040] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing electrochemically modified sweet potato residue pectin, characterized in that, Includes the following steps: (1) Dissolve the pectin extracted from sweet potato residue by hydrothermal method in an electrolyte solution to prepare a pectin solution with a concentration of 0.5% ~ 2% w / v; (2) Add the above pectin solution in equal amounts to the anode and cathode chambers of the H-type electrolytic cell, and separate the two chambers with a dialysis membrane with a molecular weight cutoff of 1000 kDa. (3) Electrolysis reaction for 2 to 8 hours under DC regulated power supply, voltage 20~40 V, room temperature, and continuous stirring; (4) After the reaction is completed, the reaction solutions in the anode chamber and the cathode chamber are collected respectively, and their pH is adjusted to neutral with acid or alkali to obtain anode modified pectin solution and cathode modified pectin solution, which are stored at low temperature for later use.

2. The method for preparing electrochemically modified sweet potato residue pectin according to claim 1, characterized in that, The electrolyte solution in step (1) is a sodium chloride solution with a concentration of 0.1% to 0.2% w / v; the pectin solution has a concentration of 1% w / v.

3. The method for preparing electrochemically modified sweet potato residue pectin according to claim 1, characterized in that, The electrolysis voltage in step (3) is 30 V, the reaction time is 8 hours, and the stirring speed is 150 rpm.

4. A modified sweet potato residue pectin, characterized in that, Prepared by the preparation method according to any one of claims 1 to 3, comprising anoly modified sweet potato residue pectin and cathode modified sweet potato residue pectin.

5. A slow-release antibacterial gel for fruit preservation, characterized in that, The sustained-release antibacterial gel is composed of cathode-modified sweet potato residue pectin, calcium ions, and cinnamaldehyde as described in claim 4, wherein the amount of cinnamaldehyde added is 2% to 4% of the total weight of the gel; the calcium ions are provided by calcium chloride, and the calcium ion concentration is 41.67 to 62.5 mg / g based on dry cathode-modified sweet potato residue pectin.

6. The sustained-release antibacterial gel for fruit preservation according to claim 5, characterized in that, The method for preparing the sustained-release antibacterial gel is as follows: the cathode-modified sweet potato residue pectin is prepared into a solution with a mass concentration of 1% to 2%, the pH is adjusted to 7, calcium chloride and cinnamaldehyde are added, and the mixture is vortexed and allowed to stand to form an emulsion gel.

7. The application of the sustained-release antibacterial gel according to claim 5 or 6 in the preservation of perishable fruits such as strawberries, characterized in that, The application method is as follows: Place the fruit and the slow-release antibacterial gel together in a sealed or semi-sealed container. The evaporation of water in the gel network drives the slow volatilization of cinnamaldehyde, forming an antibacterial atmosphere around the fruit, thereby inhibiting mold growth, delaying fruit softening and nutrient loss.

8. An edible antibacterial coating for meat preservation, characterized in that, The coating comprises the anolyte modified sweet potato residue pectin as described in claim 4, wherein the concentration of the anolyte modified sweet potato residue pectin in the coating is 1% to 3% (w / v).

9. The application of the edible antibacterial coating according to claim 8 in the preservation of refrigerated meat, characterized in that, The application method is as follows: Soak fresh meat pieces in the coating solution for 30-60 seconds, remove them and drain or air dry the surface liquid, and then refrigerate them.

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