Heavy metal adsorbing sugar orange pectin, and preparation method and application thereof

Abstract

This invention discloses a heavy metal adsorption pectin from mandarin orange peel, its preparation method, and its applications. The invention obtains highly efficient heavy metal adsorption mandarin orange pectin from waste mandarin orange peel residue through steps including raw material drying and pulverization, solid-state fermentation modification, combined assisted extraction, alcohol precipitation separation, purification, and freeze-drying. The preparation method described in this invention is simple to operate, quick, low-cost, and environmentally friendly. The prepared mandarin orange pectin has a high yield, few impurities, and exhibits high heavy metal adsorption performance and antioxidant activity, showing significant application prospects in the food and biopharmaceutical industries. This technology achieves effective utilization of waste mandarin orange peel residue, reducing environmental pollution, increasing the added value of mandarin orange products, and improving enterprise economic benefits.

Description

Technical Field

[0001] This invention relates to the separation, extraction, modification, and application technology of natural plant polysaccharides, belonging to the field of agricultural and sideline product processing technology, specifically to a sugar orange pectin that adsorbs heavy metals and its preparation method and application. Background Technology

[0002] Satsuma mandarin oranges (Citrus reticulata Blanco cv. Shatangju), commonly known as October mandarin oranges, originated in Sihui, Guangdong, China, and are one of the most widely cultivated citrus varieties in South China. Their superior growth habits and high commercial value make them an important economic crop in southern China. In recent years, with the rapid development of the citrus processing industry, Satsuma mandarin oranges have been widely used to produce various processed products, such as canned fruit, flavored beverages, and jams. However, this has also led to a large amount of processing byproducts, mainly Satsuma mandarin orange peel pomace. Satsuma mandarin orange peel pomace is rich in various bioactive components, including flavonoids, pectin, dietary fiber, and essential oils. Among them, pectin, as a natural high-molecular-weight compound, is widely present in the cell walls of higher plants. Acidic pectin exhibits good gelling and emulsifying stability, is safe and non-toxic, and possesses biocompatibility, exhibiting various biological activities such as antibacterial, hemostatic, anti-inflammatory, and antidiarrheal properties. Therefore, it has wide applications in the food, biopharmaceutical, medical and health, chemical, and environmental protection fields.

[0003] Currently, commercial pectin is mainly derived from citrus peel residue. With the rapid development of the pectin market and the increasing demand year by year, citrus peel residue, as an underutilized pectin raw material, has enormous development potential. However, commercial pectin prepared using traditional acid extraction methods suffers from problems such as lengthy extraction processes, high energy consumption, low extraction rates, large molecular weight, low solubility, low antioxidant activity, and unstable quality, limiting its application in the food and biopharmaceutical fields.

[0004] Studies have shown that degraded pectin has a significant adsorption and purification effect on wastewater containing heavy metals, and may also chelate heavy metals in the body, alleviating their toxic effects on the human body. Therefore, developing a new process for efficiently extracting degraded pectin from mandarin orange peel to increase product added value and reduce environmental pollution has become an urgent problem to be solved in the citrus industry. Summary of the Invention

[0005] To address the shortcomings and deficiencies of the existing technologies, the primary objective of this invention is to provide a method for preparing mandarin orange pectin that adsorbs heavy metals. This method uses mandarin orange peel residue as raw material, which undergoes drying and pulverization, solid-state fermentation modification, combined assisted extraction, alcohol precipitation separation, purification, and freeze-drying to obtain mandarin orange pectin with high-efficiency heavy metal adsorption. The preparation method of this invention utilizes mixed fermentation modification with Aspergillus niger, Monascus purpureus, and Aspergillus oryzae, combined with assisted extraction to improve the extraction efficiency of mandarin orange pectin, while simultaneously enhancing its antioxidant activity and heavy metal adsorption performance. Furthermore, this preparation method is characterized by low energy consumption, high extraction rate, and environmental safety.

[0006] The primary objective of this invention is achieved through the following technical solution:

[0007] A method for preparing mandarin orange pectin for adsorbing heavy metals includes the following steps:

[0008] (1) Drying and pulverizing: Dry the washed and boiled sugar orange peel residue to constant weight, pulverize it, and pass it through a 50-mesh sieve to obtain sugar orange peel residue powder;

[0009] (2) Solid-state fermentation modification: The sugar orange peel residue powder obtained in step (1) is sterilized, dried, and then mixed with an appropriate amount of sterile distilled water. Mixed bacteria are inoculated and solid-state fermentation modification is carried out on it. After fermentation, it is sterilized, dried and pulverized to prepare sugar orange peel residue powder.

[0010] (3) Combined assisted extraction: The fermented mandarin orange peel residue powder obtained in step (2) is mixed with distilled water, the pH value of the mixture is adjusted with hydrochloric acid, and a surfactant is added for combined assisted extraction under ultrasonic conditions to obtain mandarin orange pectin mixed mother liquor. After centrifugation and concentration, mandarin orange pectin extract is obtained.

[0011] (4) Alcohol precipitation separation: The extract of mandarin orange pectin in step (3) was decolorized with activated carbon, and anhydrous ethanol was added to precipitate and separate the crude mandarin orange pectin.

[0012] (5) Purification and freeze drying: Wash the crude tangerine pectin from step (4) with ethanol solution, remove the protein by Sevage method, then further purify by water dialysis, and finally freeze dry to obtain tangerine pectin adsorbed with heavy metals.

[0013] Preferably, the mixed strains mentioned in step (2) are Aspergillus niger (GDMCC3.562), Monascus anka (CGMCC3.554), and Aspergillus oryzae (CGMCC3.951), which are cultured for 3-5 days and then prepared to a concentration of 3×10⁻⁶. 6 CFU / mL spore suspension.

[0014] Preferably, the mixed strain inoculation in step (2) has a mixed inoculation volume ratio of Aspergillus niger: Monascus purpureus: Aspergillus oryzae of 1-2:1-2:1-2, an inoculation amount of 10%-30%, an initial moisture content of 40%-80%, a fermentation time of 2-6 days, and a fermentation temperature of 24℃-36℃.

[0015] Preferably, the combined assisted extraction conditions in step (3) are as follows: the mixing ratio of fermented sugar orange peel residue powder to distilled water is 1:20-30 (g / mL), the pH value of the mixture is 1.5-2.5, the ultrasonic duty cycle is 60-80%, the ultrasonic power density is 7-11 W / mL, the ultrasonic time is 20-30 min, and the amount of surfactant is 5-9 g / L.

[0016] Preferably, the surfactant in step (3) is one of sodium dodecyl sulfate (SDS), Tween-20, Tween-80, hexadecyltrimethylammonium bromide, sodium salt of 3-allyloxy-2-hydroxy-1-propanesulfonate, disodium lauryl sulfosuccinate, lauramide propyl hydroxysulfonate betaine, disodium fatty alcohol polyoxyethylene ether (3) sulfosuccinate, monolauryl phosphate, cocamidopropyl hydroxysulfonate betaine, and polyethylene glycol 8000.

[0017] Preferably, the concentration in step (3) is carried out under vacuum at 40-60°C, and the mixed mother liquor of mandarin orange pectin is concentrated to 20-40% of its original volume.

[0018] Preferably, in step (4), the volume ratio of anhydrous ethanol to mandarin orange pectin extract is 2:1.

[0019] Preferably, the ethanol washing in step (5) involves washing the separated pectin with a 60% ethanol solution 2-3 times; the dialysis is performed by dialysis purification of the crude tangerine pectin obtained in step (5) using an RC dialysis membrane from ViSkase (USA) with a molecular weight cutoff of 3500 Da for 48-72 h.

[0020] The mandarin orange pectin prepared by the above method has the characteristics of low molecular weight, low degree of esterification, and good solubility. It also has improved antioxidant capacity and enhanced heavy metal adsorption capacity, and is expected to be widely used in food, medicine, daily necessities, cosmetics and water heavy metal pollution control.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] (1) The preparation method of the heavy metal adsorbing mandarin orange pectin prepared by the present invention uses mandarin orange peel residue as raw material, which can improve the resource utilization rate of mandarin orange waste products, reduce environmental pollution, and improve the economic benefits of enterprises.

[0023] (2) The preparation method of the heavy metal adsorbing mandarin orange pectin prepared by the present invention uses surfactant-ultrasound combined assisted extraction technology, which significantly improves the yield of mandarin orange pectin; and the surfactant can reduce the interfacial tension between the solid and the liquid, increase the viscosity of the solution, and reduce the damage of ultrasound to the microstructure of pectin.

[0024] (3) The preparation method of the heavy metal adsorbing mandarin orange pectin prepared by the present invention also has the characteristics of simple operation, low cost, green safety and easy promotion.

[0025] (4) The tangerine pectin for adsorbing heavy metals prepared by the present invention has a lower molecular weight and degree of esterification, and improved solubility, antioxidant activity and heavy metal adsorption characteristics. It can be used in the production of health products and pharmaceuticals with high requirements for antioxidant effect, heavy metal adsorption in food and beverages and industrial wastewater, water pollution treatment and other fields, with huge economic and social benefits. Attached Figure Description

[0026] Figure 1 This is a comparison chart of the DPPH free radical scavenging ability of the mandarin orange pectin prepared in Examples 1-3 and Comparative Examples 1-3;

[0027] Figure 2 This is a comparison chart of the hydroxyl radical scavenging capabilities of the mandarin orange pectin prepared in Examples 1-3 and Comparative Examples 1-3;

[0028] Figure 3 Cd content of mandarin orange pectin prepared in Examples 1-3 and Comparative Examples 1-3 2+ Comparison chart of heavy metal adsorption capacity;

[0029] Figure 4 Pb of mandarin orange pectin prepared in Examples 1-3 and Comparative Examples 1-3 2+ Comparison chart of heavy metal adsorption capacity;

[0030] Figure 5 This is a flow chart illustrating the preparation process of the heavy metal-adsorbing mandarin orange pectin described in this invention. Detailed Implementation

[0031] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings, but the scope of protection and implementation of the present invention are not limited thereto.

[0032] In the following examples and comparative examples, the D-galacturonic acid content in mandarin orange pectin was determined using the carbazole colorimetric method, and a standard curve was plotted using D-galacturonic acid as a standard substance. The galacturonic acid (GalA) content of mandarin orange pectin was calculated using the following formula:

[0033] GalA (%) = Mass of galacturonic acid in the dried extract / Total mass of the extract × 100.

[0034] The extraction rate of mandarin orange pectin was calculated using the following formula:

[0035] Extraction rate (%) = mass of extracted mandarin orange pectin products / total mass of raw materials × 100.

[0036] In the following examples and comparative examples, the protein content was determined using the Coomassie Brilliant Blue method, with bovine serum albumin as the standard substance to plot a standard curve. The protein content in the extract was calculated using the following formula:

[0037] Protein content (%) = Protein content in dried extract / Total mass of extract × 100.

[0038] The antioxidant activity and total reducing power of the mandarin orange pectin prepared in the following examples are determined by the following methods:

[0039] The method for determining DPPH free radical scavenging ability is as follows:

[0040] Take 2 mL of 0.1 mmol / L DPPH-ethanol solution in a test tube, add 1 mL of mandarin orange pectin solution of different concentrations, mix well, and react the resulting mixture at room temperature for 30 min in the dark. After the reaction is complete, measure the absorbance A1 at 517 nm (measure the absorbance A2 by replacing the sample with distilled water). At the same time, mix the sample solution with the ethanol solution and measure the absorbance A0 as described above. Calculate the DPPH free radical scavenging capacity (%) using the following formula:

[0041] DPPH(%)=(1-(A2-A0) / A1)×100

[0042] The method for determining hydroxyl radical scavenging ability is as follows:

[0043] Add 1 mL of 9 mmol / L FeSO4 solution, 1 mL of 9 mmol / L salicylic acid solution, and 1 mL of 9 mmol / L H2O2 solution sequentially to pectin solutions of different concentrations. Incubate the resulting mixtures in a water bath at 37°C for 15 min (using distilled water instead of the sample for absorbance measurement A0). Determine the hydroxyl radical scavenging capacity (%) using the following formula:

[0044] OH(%) = (A0 - A1) / A0 × 100

[0045] (2) The method for determining the heavy metal adsorption capacity of the mandarin orange pectin prepared in the following examples and comparative examples is as follows:

[0046] First, a heavy metal standard solution was prepared using Cd(NO3)2·4H2O and Pb(OAc)2·3H2O. Cd(NO3)2·4H2O and Pb(OAc)2·3H2O were dissolved in ultrapure water (both metal cations were expressed as M...). 2+ (As a substitute) Prepare M at a concentration of 20 mg / L 2+ Prepare the solution. Transfer 10 mL of M solution into a 25 mL beaker. 2+ Solution; adjust M with 0.5 mol / L HNO3 solution or NaOH solution. 2+ The pH of the solution was 5.0; then 20 mg of different pectin samples were added; the mixture was stirred at 500 r / min and 30 ℃ for 40 min; samples were taken by dialysis and the M value was determined by AAS. 2+ Concentration. Pectin's effect on M 2+ The adsorption capacity Qe (mg / g) is calculated using the following formula.

[0047] Qe=(C0V-C(V+V0)) / M

[0048] In the formula, C0 is M 2+ Initial concentration of solution (mg / L);

[0049] C represents the adsorbed M 2+ Solution concentration (mg / L);

[0050] V indicates the initial pour into the dialysis bag. M represents the initial pour. 2+ Volume of the solution (L);

[0051] V0 represents the volume (L) of ultrapure water used for dialysis in the beaker.

[0052] M indicates the amount of pectin used (g).

[0053] M was determined directly using AAS with the untreated solution after the reaction. 2+ The concentration of [specific concentration] was used as a control group.

[0054] Example 1

[0055] (1) Pretreatment: Dry the washed and boiled sugar orange peel residue to constant weight, crush it, pass it through a 50-mesh sieve, then sterilize it at high temperature and dry it;

[0056] (2) Solid-state fermentation modification: After pretreatment, sterilized tangerine peel residue was taken, and sterile distilled water was added to the initial moisture content of 30%. The mixture was mixed and inoculated with a mixed strain of Aspergillus niger, Aspergillus rubrum and Aspergillus oryzae (2:1:1). The inoculation amount was 30%, the fermentation time was 6 days, and the fermentation temperature was 30℃. Solid-state fermentation modification was carried out. After the fermentation was completed, the residue was sterilized, dried and pulverized to obtain tangerine fermented peel residue powder.

[0057] (3) Combined assisted extraction: The fermented mandarin orange peel residue powder was mixed with distilled water at a ratio of 1:25 (g / mL). The pH of the mixture was adjusted to 1.8 with hydrochloric acid, the amount of SDS was 7 g / L, the ultrasonic power density was 9 w / mL, the ultrasonic time was 25 min, and the duty cycle was 75%. Combined assisted extraction was performed to obtain the mandarin orange pectin mixed mother liquor. The mixture was centrifuged at 5000 rpm for 10 min to remove insoluble matter and obtain a clear mandarin orange pectin extract.

[0058] (4) The extract of mandarin orange pectin obtained in step (3) is concentrated under vacuum at 55°C to 1 / 3 of the original volume. Two volumes of anhydrous ethanol are added, and the mixture is centrifuged at 6000 rpm for 10 min. The precipitate is taken and washed three times with 60% ethanol. The protein is removed by the Sevage method, and then further purified by dialysis with water. Finally, it is freeze-dried to obtain mandarin orange pectin.

[0059] Example 2

[0060] (1) Pretreatment: Dry the washed and boiled sugar orange peel residue to constant weight, crush it, pass it through a 50-mesh sieve, then sterilize it at high temperature and dry it;

[0061] (2) Solid-state fermentation modification: After pretreatment, sterilized sugar orange peel residue was taken, and sterile distilled water was added to the initial moisture content of 30%. The mixture was mixed and inoculated with a mixed strain of Aspergillus niger, Aspergillus rubrum and Aspergillus oryzae (1:2:1). The inoculation amount was 30%, the fermentation time was 6 days, and the fermentation temperature was 30℃. The solid-state fermentation modification was carried out. After the fermentation was completed, it was sterilized, dried and ground to obtain sugar orange fermented peel residue powder.

[0062] (3) Combined assisted extraction: The fermented mandarin orange peel residue powder was mixed with distilled water at a ratio of 1:25 (g / mL). The pH of the mixture was adjusted to 1.8 with hydrochloric acid. The amount of SDS was 7 g / L. The ultrasonic power density was 9 W / mL, the ultrasonic time was 25 min, and the duty cycle was 75%. Combined assisted extraction was performed to obtain a mixed mother liquor of mandarin orange pectin. The mixture was centrifuged at 5000 rpm for 10 min to remove insoluble matter and obtain a clear mandarin orange pectin extract.

[0063] (4) The extract of mandarin orange pectin obtained in step (3) is concentrated under vacuum at 55°C to 1 / 3 of the original volume. Two volumes of anhydrous ethanol are added, and the mixture is centrifuged at 6000 rpm for 10 min. The precipitate is taken and washed three times with 60% ethanol. The protein is removed by the Sevage method, and then further purified by dialysis with water. Finally, it is freeze-dried to obtain mandarin orange pectin.

[0064] Example 3

[0065] (1) Pretreatment: Dry the washed and boiled sugar orange peel residue to constant weight, crush it, pass it through a 50-mesh sieve, then sterilize it at high temperature and dry it;

[0066] (2) Solid-state fermentation modification: After pretreatment, sterilized tangerine peel residue was taken, and sterile distilled water was added to the initial moisture content of 30%. The mixture was mixed and inoculated with a mixed strain of Aspergillus niger, Aspergillus rubrum and Aspergillus oryzae (1:1:3). The inoculation amount was 30%, the fermentation time was 6 days, and the fermentation temperature was 30℃. Solid-state fermentation modification was carried out. After the fermentation was completed, the residue was sterilized, dried and ground to obtain tangerine fermented peel residue powder.

[0067] (3) Combined assisted extraction: The fermented mandarin orange peel residue powder was mixed with distilled water at a ratio of 1:25 (g / mL). The pH of the mixture was adjusted to 1.8 with hydrochloric acid, the amount of SDS was 7 g / L, the ultrasonic power density was 9 w / mL, the ultrasonic time was 25 min, and the duty cycle was 75%. Combined assisted extraction was performed to obtain the mandarin orange pectin mixed mother liquor. The mixture was centrifuged at 5000 rpm for 10 min to remove insoluble matter and obtain a clear mandarin orange pectin extract.

[0068] (4) The extract of mandarin orange pectin obtained in step (3) is concentrated under vacuum at 55°C to 1 / 3 of the original volume. Two volumes of anhydrous ethanol are added, and the mixture is centrifuged at 6000 rpm for 10 min. The precipitate is taken and washed three times with 60% ethanol. The protein is removed by the Sevage method, and then further purified by dialysis with water. Finally, it is freeze-dried to obtain mandarin orange pectin.

[0069] Comparative Example 1

[0070] (1) Pretreatment: Dry the washed and boiled sugar orange peel residue to constant weight, crush it, pass it through a 50-mesh sieve, then sterilize it at high temperature and dry it;

[0071] (2) Solid-state fermentation modification: After pretreatment, add sterile distilled water to the initial moisture content of 30%, mix, inoculate with Aspergillus niger, the inoculation amount is 30%, fermentation time is 6 days, fermentation temperature is 30℃, solid-state fermentation modification is carried out, sterilize after fermentation, dry and grind to obtain tangerine fermented peel residue powder.

[0072] (3) Combined assisted extraction: The fermented mandarin orange peel residue powder was mixed with distilled water at a ratio of 1:25 (g / mL). The pH of the mixture was adjusted to 1.8 with hydrochloric acid, the amount of SDS was 7 g / L, the ultrasonic power density was 9 w / mL, the ultrasonic time was 25 min, and the duty cycle was 75%. Combined assisted extraction was performed to obtain the mandarin orange pectin mixed mother liquor. The mixture was centrifuged at 5000 rpm for 10 min to remove insoluble matter and obtain a clear mandarin orange pectin extract.

[0073] (4) The extract of mandarin orange pectin obtained in step (3) is concentrated under vacuum at 55°C to 1 / 3 of the original volume. Two volumes of anhydrous ethanol are added, and the mixture is centrifuged at 6000 rpm for 10 min. The precipitate is taken and washed three times with 60% ethanol. The protein is removed by the Sevage method, and then further purified by dialysis with water. Finally, it is freeze-dried to obtain mandarin orange pectin.

[0074] Comparative Example 2

[0075] (1) Pretreatment: Dry the washed and boiled sugar orange peel residue to constant weight, crush it, pass it through a 50-mesh sieve, then sterilize it at high temperature and dry it;

[0076] (2) Solid-state fermentation modification: After pretreatment, sterilized tangerine peel residue was taken, and sterile distilled water was added to the initial moisture content of 30%. The mixture was mixed, and Aspergillus niger was inoculated with an inoculation amount of 30%. The fermentation time was 6 days and the fermentation temperature was 30℃. Solid-state fermentation modification was carried out on it. After the fermentation was completed, it was sterilized, dried and pulverized to obtain tangerine fermented peel residue powder.

[0077] (3) Ultrasonic extraction: The fermented mandarin orange peel residue powder was mixed with distilled water at a ratio of 1:25 (g / mL). The pH of the mixture was adjusted to 1.8 with hydrochloric acid. Ultrasonic extraction was performed with an ultrasonic power density of 9w / mL, an ultrasonic time of 25min, and a duty cycle of 75% to obtain a mixed mother liquor of mandarin orange pectin. The mixture was centrifuged at 5000rpm for 10min to remove insoluble matter and obtain a clear mandarin orange pectin extract.

[0078] (4) The extract of mandarin orange pectin obtained in step (3) is concentrated under vacuum at 55°C to 1 / 3 of the original volume. Two volumes of anhydrous ethanol are added, and the mixture is centrifuged at 6000 rpm for 10 min. The precipitate is taken and washed three times with 60% ethanol. The protein is removed by the Sevage method, and then further purified by dialysis with water. Finally, it is freeze-dried to obtain mandarin orange pectin.

[0079] Comparative Example 3

[0080] (1) Pretreatment: Dry the washed and boiled sugar orange peel residue to constant weight, crush it, pass it through a 50-mesh sieve, then sterilize it at high temperature and dry it;

[0081] (2) Solid-state fermentation modification: After pretreatment, add sterile distilled water to the initial moisture content of 30%, mix, inoculate with Monascus purpureus strain, the inoculation amount is 30%, fermentation time is 6 days, fermentation temperature is 30℃, solid-state fermentation modification is carried out, sterilize after fermentation, dry and grind to obtain tangerine peel residue powder.

[0082] (3) Combined assisted extraction: The fermented mandarin orange peel residue powder was mixed with distilled water at a ratio of 1:25 (g / mL). The pH of the mixture was adjusted to 1.8 with hydrochloric acid, the amount of SDS was 7 g / L, the ultrasonic power density was 9 w / mL, the ultrasonic time was 25 min, and the duty cycle was 75%. Combined assisted extraction was performed to obtain the mandarin orange pectin mixed mother liquor. The mixture was centrifuged at 5000 rpm for 10 min to remove insoluble matter and obtain a clear mandarin orange pectin extract.

[0083] (4) The extract of mandarin orange pectin obtained in step (3) is concentrated under vacuum at 55°C to 1 / 3 of the original volume. Two volumes of anhydrous ethanol are added, and the mixture is centrifuged at 6000 rpm for 10 min. The precipitate is taken and washed three times with 60% ethanol. The protein is removed by the Sevage method, and then further purified by dialysis with water. Finally, it is freeze-dried to obtain mandarin orange pectin.

[0084] Table 1. Yields, composition, and functional properties of Examples 1-3 and Comparative Examples 1-3

[0085] Extraction rate (%) GalA (%) Protein content (%) Degree of esterification (%) Example 1 <![CDATA[11.66±0.34 a ]]> <![CDATA[75.66±1.14 a ]]> <![CDATA[2.42±0.28 f ]]> <![CDATA[33.11±0.75 e ]]> Example 2 <![CDATA[11.47±0.19 ab ]]> <![CDATA[73.29±0.88 b ]]> <![CDATA[2.94±0.09 c ]]> <![CDATA[35.23±0.34 d ]]> Example 3 <![CDATA[11.15±0.26 b ]]> <![CDATA[71.66±1.34 c ]]> <![CDATA[2.38±0.21 e ]]> <![CDATA[39.84±0.70 c ]]> Comparative Example 1 <![CDATA[8.18±0.42 d ]]> <![CDATA[70.99±1.53 d ]]> <![CDATA[3.09±0.14 b ]]> <![CDATA[44.26±0.88 b ]]> Comparative Example 2 <![CDATA[6.77±0.55 e ]]> <![CDATA[67.30±0.75 e ]]> <![CDATA[2.82±0.27 d ]]> <![CDATA[47.40±0.51 a ]]> Comparative Example 3 <![CDATA[9.48±0.35 c ]]> <![CDATA[71.30±0.75 c ]]> <![CDATA[3.25±0.44 a ]]> <![CDATA[45.40±0.37 b ]]>

[0086] As shown in Table 1, the extraction rates of mandarin orange pectin obtained from Examples 1-3 were all higher than those of Comparative Examples 1-3. Compared with Comparative Example 2, the extraction rates were increased by 29.84%, 28.68%, and 26.64%, respectively, while the GalA content increased by 6.17%, 3.14%, and 0.93% compared with Comparative Example 1, respectively. Furthermore, the protein content of Examples 1-3 was reduced by 21.68%, 4.85%, and 22.98% compared with Comparative Example 1, respectively, and the degree of esterification (DE) was reduced by 25.19%, 20.40%, and 9.99%, respectively. These findings indicate that the mandarin orange pectin prepared by the method of this invention has a high GalA content, fewer protein impurities, high purity, and excellent quality. Moreover, its lower degree of esterification and molecular weight are more conducive to chelating heavy metal cations.

[0087] Figure 1 As shown, the mandarin orange pectin prepared in Examples 1-3 exhibited higher antioxidant activity compared to that prepared in Comparative Examples 1-3. At a pectin solution concentration of 5 mg / mL, the DPPH free radical scavenging abilities reached 94.01%, 90.00%, 86.38%, 82.58%, 76.38%, and 81.47%, respectively. Figure 2As shown, compared with the pectin prepared in Examples 1-3 and Comparative Examples 1-3, the -OH radical scavenging ability of Satsuma mandarin orange pectin was significantly improved, reaching maximum values ​​of 91.21%, 73.89%, 83.42%, 78.86%, and 81.42%, respectively, at a pectin solution concentration of 5 mg / mL. The DPPH and -OH radical scavenging abilities of Examples 1-3 were both higher than those of Comparative Examples 1-3. This is partly because the Satsuma mandarin orange pectin backbone degraded after mixed fermentation modification, exposing more active sites such as reducing hydroxyl groups and active substances such as proteins and phenols, which is beneficial for pectin to scavenge DPPH and -OH radicals. On the other hand, studies have shown that the antioxidant activity of pectin is related to the synergistic effect of different domains of its structure; in Example 1, the homogalacturonic acid domains involving more GalA exhibited greater antioxidant activity. Furthermore, the degraded pectin backbone was stretched out, making it more spatially conducive to the binding of external free radicals, resulting in higher antioxidant activity.

[0088] Figure 3 and Figure 4 Cd content of mandarin orange pectin prepared in Examples 1-3 and Comparative Examples 1-3, respectively. 2+ Pb 2+ Heavy metal adsorption capacity; Examples 1-3 on Cd 2+ and Pb 2+ The adsorption capacity of the mandarin orange pectin in Example 1 was higher than that of Comparative Examples 1-3, and the adsorption capacity of the mandarin orange pectin in Example 1 was better than that of Comparative Examples 1-3. 2+ Pb 2+ Adsorption properties, of which the pectin Cd in Example 1 2+ The adsorption capacity reached 10.808 mg / g, and the adsorption rate was 92.75%, Pb 2+ The adsorption capacity reached 12.108 mg / g, with an adsorption rate of 95.75%. This indicates that the deeply modified pectin obtained in Example 1 through mixed-culture fermentation (2:1:1) for 6 days exhibits a high degree of degradation, low esterification, and the greatest cation chelating capacity, demonstrating a higher adsorption effect than comparative examples with other mixed-culture inoculation ratios, fermentation times, and inoculation amounts. The adsorption of metal cations by Satsuma mandarin pectin primarily occurs through the binding of cations to carboxyl anions and hydroxyl active sites on the pectin side chains. According to the "soft attracts soft, hard attracts hard" acid-base theory, carboxyl anions (hard bases) bind to Pb... 2+ (Border acid) has a higher binding affinity than Cd. 2+ (Soft acid).

[0089] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing heavy metal adsorbing citrus grandis pectin, characterized by, Includes the following steps: (1) Drying and pulverizing: Dry the washed and boiled sugar orange peel residue to constant weight, pulverize it, and pass it through a 50-mesh sieve to obtain sugar orange peel residue powder; (2) Solid-state fermentation modification: The sugar orange peel residue powder obtained in step (1) is sterilized, dried, and then mixed with an appropriate amount of sterile distilled water. Mixed bacteria are inoculated and solid-state fermentation modification is performed on it. After fermentation, it is sterilized, dried, pulverized, and passed through a 50-mesh sieve to obtain sugar orange peel residue powder. (3) Combined assisted extraction: The fermented mandarin orange peel residue powder obtained in step (2) is mixed with distilled water, the pH value of the mixture is adjusted with hydrochloric acid, and a surfactant is added for combined assisted extraction under ultrasonic conditions to obtain mandarin orange pectin mixed mother liquor. After centrifugation and concentration, mandarin orange pectin extract is obtained. (4) Alcohol precipitation separation: The extract of mandarin orange pectin in step (3) was decolorized with activated carbon, and anhydrous ethanol was added to precipitate and separate the crude mandarin orange pectin. (5) Purification and freeze drying: Wash the crude mandarin orange pectin from step (4) with ethanol solution, remove the protein in it by Sevage method, then further purify by water dialysis, and finally freeze dry to obtain mandarin orange pectin. The mixed strains inoculated in step (2) are Aspergillus niger, Aspergillus rubrum, and Aspergillus oryzae. After culturing for 3-5 days, a solution with a concentration of 3×10⁻⁶ is prepared. 6 CFU / mL spore suspension; the inoculation mixed strain has a mixed inoculation volume ratio of Aspergillus niger: Monascus purpureus: Aspergillus oryzae of 1-2:1-2:1-2, an inoculation amount of 10%-30%, an initial moisture content of 40%-80%, a fermentation time of 2-6 days, and a fermentation temperature of 24℃-36℃; The combined assisted extraction conditions in step (3) are as follows: the mixing ratio of fermented sugar orange peel residue powder to distilled water is 1:20-30 g / mL, the pH value of the mixture is 1.8-2.5, the ultrasonic duty cycle is 60-80%, the ultrasonic power density is 7-11 W / mL, the ultrasonic time is 20-30 min, and the amount of surfactant is 5-9 g / L.

2. The method for preparing mandarin orange pectin for adsorbing heavy metals according to claim 1, characterized in that, The surfactant mentioned in step (3) is one of sodium dodecyl sulfate, Tween-20, Tween-80, hexadecyltrimethylammonium bromide, sodium salt of 3-allyloxy-2-hydroxy-1-propanesulfonate, disodium lauryl sulfosuccinate, lauramide propyl hydroxysulfonate betaine, disodium fatty alcohol polyoxyethylene ether (3) sulfosuccinate, monolauryl phosphate, cocamidopropyl hydroxysulfonate betaine, and polyethylene glycol 8000.

3. The method for preparing mandarin orange pectin for adsorbing heavy metals according to claim 1, characterized in that, The concentration in step (3) is carried out at 40-60°C under vacuum conditions, concentrating the mixed mother liquor of mandarin orange pectin to 20-40% of its original volume.

4. The method for preparing mandarin orange pectin for adsorbing heavy metals according to claim 1, characterized in that, The washing with ethanol solution in step (5) involves washing the separated pectin with 60% ethanol solution 2 to 3 times; the dialysis is performed by dialysis purification of the crude tangerine pectin obtained in step (5) using an RC dialysis membrane from ViSkase in the United States with a molecular weight cutoff of 3500 Da for 48-72 h.

5. A type of mandarin orange pectin for adsorbing heavy metals prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the heavy metal adsorbing tangerine pectin according to claim 5 in the fields of food, medicine, and daily necessities.

7. The application of the heavy metal-adsorbing mandarin orange pectin according to claim 5 in the cosmetics field.

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