Extraction process and application of polyphenols based on sweet potato peel

Abstract

The invention relates to the technical field of preservation, and discloses a sweet potato peel-based polyphenol substance extraction process and application thereof, and the extraction process comprises the following steps: S1, pretreatment; s2, freezing; s3, grinding is conducted; s4, filtering; s5, soaking; s6, heating is conducted; s7, performing centrifugation; s8, suction filtration; s9, evaporating and concentrating; s10, performing purification; and S11, freezing to obtain a finished product. According to the extraction process of the polyphenols based on the sweet potato peels, the polyphenols can be extracted from the sweet potato peels, the extraction efficiency is high, the extracted polyphenols are high in antioxidant activity effect, and fresh milk can be kept fresh through application of the polyphenols.

Description

Technical Field

[0001] The invention relates to the field of freshness preservation, and more specifically, to an extraction process of polyphenols based on sweet potato peels and application thereof. Background Art

[0002] In modern society, with the popularization of healthy eating concepts and the increasing requirements for food nutritional value and safety, dairy products, especially fermented milk, have become an important part of the daily diet of many consumers due to their unique taste and rich nutrients. Fermented milk is rich in protein, calcium and vitamin B2. At the same time, the probiotics produced during its fermentation process have significant health benefits, such as promoting digestion and absorption and maintaining intestinal health. However, due to its high biological activity, fermented milk is susceptible to microbial contamination and oxidative damage during storage and transportation, which not only damages the quality of the product, but also limits its shelf life. Therefore, how to effectively improve the quality of fermented milk and extend its shelf life has become a key challenge in the field of dairy research.

[0003] Sweet potato (Dioscorea esculenta) is one of the most important food crops in the world. Its roots are rich in starch, dietary fiber, vitamins and minerals, especially β-carotene, vitamin C, potassium, calcium, etc. These nutrients make sweet potato a nutritious food and widely used in human daily diet. In addition, sweet potato contains a variety of bioactive substances, such as polysaccharides, flavonoids, protein hydrolysates, etc., which have antioxidant, anti-inflammatory and antibacterial functions. Therefore, the application of sweet potato in the food industry has attracted more and more attention.

[0004] Studies have shown that sweet potatoes and their extracts can be used as food additives to improve the texture, taste, color, and shelf life of food. As a food ingredient with broad application prospects, sweet potatoes provide rich resources and development potential for the food industry. However, there are some challenges in the extraction and purification of sweet potato peel polyphenols, such as low extraction efficiency and high cost. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides an extraction process of polyphenols based on sweet potato peel and application thereof.

[0006] A process for extracting polyphenols from sweet potato peels comprises the following steps:

[0007] S1. Pretreatment: cleaning and washing the sweet potato peels;

[0008] S2, freezing: placing the sweet potato peels into a vacuum freeze drying chamber for freezing;

[0009] S3, grinding: grinding the frozen sweet potato peel into powder;

[0010] S4, filtering: filtering the ground powder;

[0011] S5, soaking: soaking the filtered powder;

[0012] S6. Heating: heating the soaking liquid in a water bath;

[0013] S7, centrifugation: centrifuging the soaking liquid to obtain a supernatant;

[0014] S8, suction filtration: use a Buchner funnel to filter the supernatant to obtain a filtrate;

[0015] S9, evaporation and concentration: evaporating and concentrating the obtained filtrate;

[0016] S10, purification: purifying the obtained polyphenol extract using a macroporous adsorption resin method;

[0017] S11. Freezing: placing the obtained polyphenol extract in a vacuum freezer at -80 degrees Celsius for 48 hours, attaching a label, and obtaining the finished product.

[0018] Preferably: the sweet potato skin is sweet potato skin or purple potato skin.

[0019] Preferably: in S2, the freezing temperature is -80°C and the freezing time is 24 hours.

[0020] Preferably: in S5, the soaking liquid is an ethanol solution, the concentration of the ethanol solution is 65%, the material-liquid ratio is 1:15 (g / ml), and the soaking time is 30 minutes.

[0021] Preferably, in S5, the soaking liquid is an ethanol solution, the concentration of the ethanol solution is 75%, the material-liquid ratio is 1:20 (g / ml), and the soaking time is 30 minutes.

[0022] Preferably, in S5, the soaking liquid is an ethanol solution, the concentration of the ethanol solution is 85%, the material-liquid ratio is 1:25 (g / ml), and the soaking time is 30 minutes.

[0023] Preferably, in S6, the heating temperature is 60°C and the heating time is 40 minutes.

[0024] Preferably, in S6, the heating temperature is 50°C and the heating time is 50 minutes.

[0025] Preferably, in S6, the heating temperature is 70°C and the heating time is 30 minutes.

[0026] An application of polyphenols based on sweet potato peels in the preservation of fresh milk.

[0027] An application of polyphenols based on sweet potato peels, wherein a preferred application method is: adding the polyphenols from the sweet potato peels into fresh milk.

[0028] An application of polyphenols based on sweet potato peels, wherein a preferred application method is: adding the polyphenols and the natural antioxidant tea polyphenols into fresh milk in a ratio of 3:7.

[0029] The beneficial effects of the present invention are as follows: the present invention proposes a process for extracting polyphenols based on sweet potato peels, which can realize the extraction of polyphenols from sweet potato peels, has high extraction efficiency, and the polyphenols after extraction have strong antioxidant activity. The application of the polyphenols proposed by the present invention can realize the preservation of fresh milk. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a standard curve diagram of gallic acid in Example 7 of the present invention;

[0031] Figure 2 is a curve diagram of the scavenging effect of various components of purple potato peel polyphenols on ABTS free radicals in Example 7 of the present invention;

[0032] Figure 3 is a curve diagram of the scavenging effect of various components of sweet potato peel polyphenols on ABTS free radicals in Example 7 of the present invention;

[0033] Figure 4 is a curve diagram of the scavenging effect of various components of purple potato peel polyphenols on DPPH free radicals in Example 7 of the present invention;

[0034] Figure 5 is a curve diagram of the scavenging effect of various components of sweet potato peel polyphenols on DPPH free radicals in Example 7 of the present invention;

[0035] Figure 6 is a graph showing the adsorption kinetics of sweet potato peel polyphenols by HP-20 macroporous resin in Example 8 of the present invention;

[0036] Figure 7 is a graph showing the adsorption kinetics of purple sweet potato peel polyphenols by HP-20 macroporous resin in Example 8 of the present invention;

[0037] Figure 8 is a graph showing the desorption kinetics of sweet potato peel polyphenols by HP-20 macroporous resin in Example 8 of the present invention;

[0038] Fig. 9 is a graph showing the desorption kinetics of purple sweet potato peel polyphenols by 10HP-20 macroporous resin in Example 8 of the present invention;

[0039] Fig.10is a graph showing the effect of the polyphenol concentration of the sweet potato peel polyphenol extract on the adsorption effect of the HP-20 macroporous resin in Example 8 of the present invention;

[0040] Fig.11 This is a graph showing the effect of the polyphenol concentration of the purple sweet potato peel polyphenol extract on the adsorption effect of the HP-20 macroporous resin in Example 8 of the present invention. DETAILED DESCRIPTION

[0041] The subject matter described herein will now be discussed with reference to example embodiments. It should be understood that the discussion of these embodiments is only to enable those skilled in the art to better understand and implement the subject matter described herein, and the functions and arrangements of the elements discussed may be changed without departing from the scope of protection of the contents of this specification. Each example may omit, replace or add various processes or components as needed. In addition, the features described relative to some examples may also be combined in other examples.

[0042] Example 1

[0043] In this embodiment, a process for extracting polyphenols from sweet potato peels is proposed, comprising the following steps:

[0044] S1. Pretreatment: cleaning and washing the sweet potato peels;

[0045] S2, freezing: placing the sweet potato peels into a vacuum freeze drying chamber for freezing;

[0046] S3, grinding: grinding the frozen sweet potato peel into powder;

[0047] S4, filtering: filtering the ground powder;

[0048] S5, soaking: soaking the filtered powder;

[0049] S6. Heating: heating the soaking liquid in a water bath;

[0050] S7, centrifugation: centrifuging the soaking liquid to obtain a supernatant;

[0051] S8, suction filtration: use a Buchner funnel to filter the supernatant to obtain a filtrate;

[0052] S9, evaporation and concentration: evaporating and concentrating the obtained filtrate;

[0053] S10, purification: purifying the obtained polyphenol extract using a macroporous adsorption resin method;

[0054] S11. Freezing: placing the obtained polyphenol extract in a vacuum freezer at -80 degrees Celsius for 48 hours, attaching a label, and obtaining the finished product.

[0055] in:

[0056] Sweet potato skin is sweet potato skin or purple potato skin.

[0057] In S2, the freezing temperature is -80°C and the freezing time is 24 hours.

[0058] In S5, the soaking liquid is an ethanol solution, the concentration of the ethanol solution is 65%, the material-liquid ratio is 1:15 (g / ml), and the soaking time is 30 minutes.

[0059] In S6, the heating temperature is 60°C and the heating time is 40 minutes.

[0060] Example 2

[0061] In this embodiment, a process for extracting polyphenols from sweet potato peel is proposed. The extraction process proposed in this embodiment is different from that in Example 1 in that:

[0062] In S2, the freezing temperature is -80°C and the freezing time is 24 hours.

[0063] In S5, the soaking liquid is an ethanol solution, the concentration of the ethanol solution is 75%, the material-liquid ratio is 1:20 (g / ml), and the soaking time is 30 minutes.

[0064] In S6, the heating temperature is 50°C and the heating time is 50 minutes.

[0065] Example 3

[0066] In this embodiment, a process for extracting polyphenols from sweet potato peel is proposed. The extraction process proposed in this embodiment is different from that in Example 1 in that:

[0067] In S2, the freezing temperature is -80°C and the freezing time is 24 hours.

[0068] In S5, the soaking liquid is an ethanol solution, the concentration of the ethanol solution is 85%, the material-liquid ratio is 1:25 (g / ml), and the soaking time is 30 minutes.

[0069] In S6, the heating temperature is 70°C and the heating time is 30 minutes.

[0070] Example 4

[0071] In this embodiment, an application of polyphenols based on sweet potato peels is proposed, and the application in fresh milk preservation is proposed. The application method in this embodiment is: adding the polyphenols based on sweet potato peels into fresh milk.

[0072] Example 5

[0073] In this embodiment, an application of polyphenols based on sweet potato peels is proposed for the preservation of fresh milk. The application method in this embodiment is: adding polyphenols and natural antioxidant tea polyphenols into fresh milk in a ratio of 3:7.

[0074] Example 6

[0075] In this embodiment, the preservation effect of fresh milk is compared by means of comparative experiments.

[0076] Prepare fresh milk and divide it into six groups in equal amounts:

[0077] Experimental Group 1: Polyphenols were extracted according to the extraction process proposed in Example 1 and added to fresh milk.

[0078] Experimental Group 2: Polyphenols were extracted according to the extraction process proposed in Example 2 and added to fresh milk.

[0079] Experimental group 3: Polyphenols extracted according to the extraction process proposed in Example 3 and added to fresh milk

[0080] Experimental Group 4: According to the polyphenols extracted by the extraction process proposed in Example 1, the polyphenols and the natural antioxidant tea polyphenols were added into the fresh milk at a ratio of 3:7.

[0081] Comparative group 1: no substance was added.

[0082] Comparison group 2: Adding natural antioxidant tea polyphenols into fresh milk.

[0083] Evaluation of fresh milk from the sensory perspective:

[0084] Sensory evaluation table of experimental group 1

[0085]

[0086] Sensory evaluation table of experimental group 2

[0087]

[0088] Sensory evaluation table of experimental group 3

[0089]

[0090] Sensory evaluation table of experimental group 4

[0091]

[0092] Sensory evaluation table of comparison group 1

[0093]

[0094] Sensory evaluation table of comparison group 2

[0095]

[0096] As can be seen from the table above, fresh milk with added polyphenols has improved odor, color, texture and taste.

[0097] The antibacterial percentage of the experimental group and the control group was determined, and the following results were obtained:

[0098]

[0099] As can be seen from the above table, the antibacterial rate is higher when polyphenols are added.

[0100] Example 7

[0101] In this example, the effect of multiple factors on the polyphenol extraction was investigated and evaluated. Common influencing factors include extraction temperature, extraction time, solvent concentration, and the ratio of material to solvent.

[0102] 1 Materials and Methods

[0103] 1.1 Materials and reagents

[0104] Sweet potato (commercially available), anhydrous ethanol (commercially available), packaging bag (commercially available), ABTS mother solution (commercially available), DPPH solution (commercially available), beaker (commercially available), purified water (Hangzhou Wahaha Beverage Co., Ltd.), filter bag (commercially available, food grade).

[0105] 1.2 Experimental design steps

[0106] In the optimization of sweet potato peel polyphenol extraction, several factors and levels can be considered and coded.

[0107] 1.2.1 Extraction temperature

[0108] Choosing the appropriate extraction temperature is crucial to the extraction effect of polyphenols. The levels can be low temperature, medium temperature and high temperature.

[0109] Sweet Potato Skins:

[0110]

[0111] Purple potato skin:

[0112]

[0113]

[0114] It can be concluded that 60℃ is the best temperature for extracting sweet potato peel.

[0115] 1.2.2 Extraction time

[0116] The extraction time affects the extraction speed and extraction rate of polyphenols.

[0117] Sweet Potato Skins:

[0118]

[0119] Purple potato skin:

[0120]

[0121]

[0122] It can be concluded that the best extraction temperature for sweet potato peel is 50 minutes, and the best extraction temperature for sweet potato peel is 40 minutes.

[0123] 1.2.3 Solvent concentration

[0124] The concentration of the solvent will affect the dissolution and extraction of polyphenols.

[0125] Sweet Potato Skins:

[0126]

[0127] Purple potato skin:

[0128]

[0129] It can be concluded that 65% of sweet potato ethanol concentration is best, and 75% of purple potato peel concentration is best.

[0130] 1.2.4 Material-liquid ratio

[0131] The solid-liquid ratio will affect the extraction effect of polyphenols.

[0132] Sweet Potato Skins:

[0133]

[0134] Purple potato skin:

[0135]

[0136] It can be concluded that the best ratio of sweet potato: ethanol is 1:15, and the best ratio of purple potato peel: ethanol is 1:30.

[0137] 1.2.6 Sample preparation

[0138] Pre-treat sweet potato peels and prepare fresh purple potato peels and sweet potato peels, and pre-freeze them in a vacuum drying oven at -80°C for 24 hours.

[0139] 1.2.7 Crushing

[0140] The frozen purple potato peel and sweet potato peel were ground into powder by a grinder, and sieved with a mesh sieve (100 mesh). The purple potato peel and sweet potato peel obtained above were weighed (0.1g accuracy), wherein the sweet potato peel powder was 130.15g and the purple potato peel powder was 60.33g.

[0141] 1.2.8 Extraction of polyphenols

[0142] Select 65% ethanol solution as the solvent to soak the sweet potato peels, according to the sweet potato peel: 65% ethanol

[0143] =1:15 (g / ml) of solid-liquid ratio for soaking for 30 minutes; select 75% ethanol solution as the solvent to soak the purple potato peel, according to the purple potato peel: 75% ethanol = 1:30 (g / ml) of solid-liquid ratio for soaking for 30 minutes.

[0144] 1.2.9 Water bath heating

[0145] The heating conditions of the sweet potato peel soaking liquid in the water bath were 60°C for 50 min, and the heating conditions of the purple potato peel soaking liquid in the water bath were 70°C for 50 min.

[0146] 1.2.10 Centrifugal separation

[0147] The extract was centrifuged at 8000 rpm for 5 minutes to obtain a supernatant.

[0148] 1.2.11 Vacuum filtration

[0149] The supernatant was filtered using a Buchner funnel to obtain a filtrate.

[0150] 1.2.12 Evaporation and concentration

[0151] The obtained filtrate was concentrated by evaporation.

[0152] 1.2.13 Freezing

[0153] The extracted polyphenols are placed in a vacuum freezer, stored at minus 80 degrees Celsius for 48 hours, and labeled to obtain the finished product.

[0154] 1.2.14 Weighing

[0155] The finished products are weighed and compared to select the optimal conditions.

[0156] 1.3 Measurement of polyphenol content

[0157] 1.3.1 Testing instruments

[0158] UV spectrophotometer

[0159] 1.3.2 Test results

[0160] 1.3.1 Preparation of mother liquor

[0161] 100 mg of sweet potato peel and 100 mg of purple potato peel polyphenol samples were taken respectively, and then placed in 65% and 75% ethanol respectively to prepare 1 mg / ml polyphenol mother solution.

[0162] 1.3.2 Absorbance determination

[0163] Take 5ml in a 50ml volumetric flask and dilute with distilled water (i.e. dilute 10 times). Take 0.5ml sample + 2.5ml Folin phenol + 1.7ml sodium carbonate solution, extract with a pipette, mix well, store in dark (cover with a wet cloth, place the colorimetric tube in a dark environment for 1h), and prepare gallic acid solution as a standard. Wash 8 10ml colorimetric tubes, mark them, and transfer 0, 0.1, 0.2, 0.4, 0.6.0.8, 1.0, 1.2ml of standard solution according to the mark, place the colorimetric tube in a dark environment for 1h, measure its absorbance at 760nm, repeat 3 times, take the average value to draw a standard curve, and get the linear regression equation of Y = 0.4142X + 0.0055 (R2 = 0.999), which has a good linear relationship.

[0164] Standard curve table of absorbance determination value of gallic acid

[0165]

[0166] Gallic acid standard curve (see Figure 1 )

[0167] 1.3.3 Spectrometry

[0168] Then the polyphenol solutions were placed in UV-visible spectrophotometers to measure the UV absorption spectrum, thereby detecting the polyphenol content. Purple potato peel polyphenols and sweet potato peel polyphenols were measured in three groups in parallel.

[0169] Sweet potato peel polyphenols:

[0170]

[0171] The average polyphenol content in sweet potato peel is 0.022.

[0172] Purple potato peel polyphenols:

[0173]

[0174] The average polyphenol content in sweet potato peel is 0.025.

[0175] According to the linear equation Y = 0.4142X + 0.0055, sweet potato skin polyphenols: 0.222 = 0.4142X + 0.0055, X = 0.0398358. Purple potato skin polyphenols: 0.225 = 0.4142X + 0.0055, X = 0.0470787

[0176] Then sweet potato peel polyphenol concentration (mg / g) = 0.0398358*10*0.5 / 1 = 0.1992 (mg / g)

[0177] Purple sweet potato peel polyphenol concentration (mg / g) = 0.0470787*10*0.5 / 1 = 0.23539 (mg / g)

[0178] 1.4 Study on antioxidant activity

[0179] Based on the optimal extraction process of polyphenols, the scavenging ability of dandelion polyphenols on DPPH free radicals and ABTS free radicals was studied respectively.

[0180] 1.4.1 Determination of DPPH free scavenging ability.

[0181] Prepare sweet potato polyphenol extract solutions of different concentrations. Take 1.0 ml of sample solution of different concentrations + 3.0 ml of DPPH solution, mix well, let stand at room temperature for 30 minutes, at a wavelength of 517 nm, record as A1, take 1.0 ml of sample solution of different concentrations + 3.0 ml of anhydrous ethanol, mix well, let stand at room temperature for 30 minutes, at a wavelength of 517 nm, record as A2, use 1.0 ml of 85% ethanol + 3.0 ml of anhydrous ethanol, record as A0, use VC positive control, all determination steps are the same as above.

[0182]

[0183] 1.4.2 ABTS assay

[0184] ABTS assay is a commonly used method for determining antioxidant activity, especially for evaluating antioxidant properties in food, medicine and biological samples. During the assay, the ABTS solution and sample are usually mixed and reacted for a period of time, and then the absorbance is measured. By comparing the absorbance of the control group, the content and activity of antioxidant substances in the sample can be evaluated. Take 0.15ml of sample solution of different concentrations + 2.85ml ABTS working solution and mix them evenly, react at room temperature in the dark for 10 minutes, measure at a wavelength of 734nm, record as A1, 0.15ml85% ethanol + 2.85mlABTS is recorded as A0, take 0.15ml of sample solution of different concentrations + 2.85ml distilled water, record as A2, blank zero adjustment: 0.15ml85% ethanol + 2.85ml distilled water, use VC positive control, all assay steps are the same as above.

[0185]

[0186] 2. Results and Analysis

[0187] 2.1 The scavenging effects of various components of purple potato peel polyphenols on ABTS free radicals (see the table below and Figure 2 ).

[0188]

[0189] 2.2 The scavenging effects of various components of sweet potato peel polyphenols on ABTS free radicals (see the table below and Figure 3 ).

[0190]

[0191]

[0192] 2.3 The scavenging effect of various components of purple potato peel polyphenols on DPPH free radicals (see the table below and Figure 4 ).

[0193]

[0194]

[0195] 2.4 The scavenging effects of various components of sweet potato peel polyphenols on DPPH free radicals (see the table below and Figure 5 ).

[0196]

[0197]

[0198] 3. Discussion

[0199] The optimal process parameter combination was obtained through the optimized sweet potato peel polyphenol extraction process. Under this condition, the extraction rate of sweet potato peel polyphenol was significantly improved, and the antioxidant activity was also significantly enhanced. The optimized process parameters played a positive role in the extraction effect of sweet potato peel polyphenol, providing a basis for further development of the application of sweet potato peel polyphenol.

[0200] Sweet potato peel polyphenols and purple potato peel polyphenols are antioxidant substances in plant components. They have the effects of scavenging free radicals in the body, anti-oxidation, and anti-aging. Sweet potato peel polyphenols and purple potato peel polyphenols have obvious scavenging effects on two free radicals, DPPH and ABTS. As antioxidant substances in plant components, polyphenols, flavonoids, and polysaccharides coexist in plants. Whether they work independently or synergistically is of great significance not only for exploring plant biological functions, but also for developing and utilizing natural plant products. The comparison of DPPH and ABTS provides a methodological basis for studying component antioxidant or synergistic antioxidant effects.

[0201] Example 8

[0202] This example is an experiment on the purification process of sweet potato peel polyphenols.

[0203] 1 Materials and Methods

[0204] 1.1 Instruments and Equipment

[0205] Electronic analytical balance (Talent series, Sartorius, Germany), UV5200 UV-visible spectrophotometer (Shanghai Yuanxi Instrument Co., Ltd.), air bath constant temperature shaker (Shanghai Ziren Instrument Co., Ltd.), circulating water vacuum pump (Shanghai Xiande Experimental Instrument Co., Ltd.)

[0206] 1.2 Materials and reagents

[0207] Sweet potato peel polyphenols, purple potato peel polyphenols, D101 macroporous adsorption resin, HP-20 macroporous adsorption resin, and AB-8 macroporous adsorption resin Folin phenol (1.0 Normal) were purchased from Shanghai Ruji Biotechnology Development Co., Ltd., and NaOH, HCL, anhydrous ethanol and other domestic analytical grade materials were used.

[0208] 1.2.1 Experimental Materials

[0209] The sweet potato peel polyphenols used in this experiment were extracted by students in the previous study.

[0210] 1.3 Experimental methods

[0211] 1.3.1 Screening of macroporous resin types

[0212] The three selected macroporous resins, AB-8, D101 and HP-20, were soaked in anhydrous ethanol for 24 hours respectively to fully swell, washed with deionized water until there was no alcohol smell, then soaked in 5% hydrochloric acid for 12 hours, washed with deionized water until neutral, and then soaked in 5% sodium hydroxide solution for 12 hours. After washing with deionized water until neutral, the surface moisture was absorbed with filter paper and set aside.

[0213] Weigh 1.0g of three types of macroporous resins respectively, place them in 50ml conical flasks, add equal volumes of 1.0mg / ml sweet potato peel polyphenol extract, shake in a constant temperature water bath shaker (25℃, 160rpm) for 24h, filter the supernatant, determine the polyphenol content, and calculate the adsorption amount and adsorption rate of the resin according to the following formula:

[0214]

[0215] Wherein: Q is the adsorption amount (mg / g), C0 is the concentration of polyphenols in the extract before adsorption (mg / mL), C1 is the concentration of polyphenols in the filtrate at adsorption equilibrium (mg / mL), V1 is the volume of the polyphenol extract (mL), m is the mass of the resin (g), and A is the adsorption rate (%).

[0216] The fully adsorbed resin was washed with deionized water until there was no extract on the surface, and the excess water was absorbed with filter paper. Then, it was placed in a 50 mL conical flask, and an equal volume of 75% ethanol solution was added. The resin was shaken in a constant temperature water bath shaker (25°C, 120 rpm) for desorption for 24 h. The supernatant was filtered and the polyphenol concentration was determined. The desorption rate was calculated as follows:

[0217]

[0218] Where: D is the desorption rate (%), C2 is the concentration of polyphenols in the filtrate after desorption (mg / mL), V2 is the volume of the desorption liquid (mL), m is the mass of the resin (m), and Q is the adsorption amount (mg / g).

[0219] Macroporous resins suitable for polyphenol purification were selected based on adsorption capacity, adsorption rate and desorption rate.

[0220] 1.3.2 Adsorption and desorption kinetics of macroporous resin

[0221] Accurately weigh 1.0g of macroporous resin into a 200mL conical flask, add 30mL of 1.0mg / mL extract, and oscillate and adsorb in a constant temperature water bath shaker (25℃, 160rpm) for 12h. Start timing from 0, draw 0.1mL of supernatant every 1h and measure the polyphenol concentration to calculate the adsorption amount. Draw a static adsorption curve with time as the horizontal axis and adsorption amount as the vertical axis.

[0222] The resin after full adsorption was washed with deionized water until there was no extract on the surface, and the surface moisture was dried with filter paper, then placed in a 200 mL conical flask, 30 mL of ethanol solution was added (65% ethanol solution was added to the sweet potato peel polyphenol extract group, and 75% ethanol solution was added to the purple potato peel polyphenol extract group), and desorbed for 12 hours by shaking in a constant temperature water bath shaker (25°C, 160rpm), and a portion of the supernatant was taken every 1 hour, and the polyphenol concentration was measured to calculate the desorption rate. The desorption kinetic curve was drawn with time as the horizontal axis and the resolution rate as the vertical axis.

[0223] 1.3.3 Effect of sweet potato peel polyphenol concentration on the adsorption capacity of macroporous resin

[0224] Accurately weigh 1.0 g of the most suitable macroporous resin into a 200 mL conical flask, add 30 mL of extract with different polyphenol concentrations (0.5 mg / mL, 1.0 mg / mL, 2.0 mg / mL, 3.0 mg / mL, 4.0 mg / mL, 5.0 mg / mL), shake in a constant temperature water bath shaker (25°C, 160 rpm) for 12 h, filter the supernatant, determine the polyphenol content, and calculate the adsorption amount.

[0225] 1.3.4 Effect of ethanol concentration of eluent on the desorption capacity of macroporous resin

[0226] Accurately weigh 1.0 g of the macroporous resin adsorbed to saturation into a 200 mL conical flask, add 30 mL of ethanol solution of different concentrations (the ethanol concentrations of the eluents of the sweet potato peel polyphenol extract group were 45%, 55%, 65%, 75%, and 85%, respectively, and the ethanol concentrations of the eluents of the purple potato peel polyphenol extract group were 55%, 65%, 75%, 85%, and 95%, respectively), shake on a constant temperature water bath shaker (25°C, 160 rpm) for 12 hours, filter the supernatant, determine the polyphenol concentration, and calculate the desorption rate.

[0227] 1.3.5 Purification of sweet potato peel polyphenol extract

[0228] After determining the optimal adsorption saturation time, polyphenol concentration and ethanol concentration of the eluent, accurately weigh 10g of macroporous resin, load it into the column with distilled water, inject 60ml of the optimal sweet potato peel polyphenol solution concentration into the loaded column, and elute at a flow rate of 1mL / min with the optimal ethanol concentration of the eluent. Collect 100ml of the eluent, which can be fully eluted under this condition, and finally calculate the purification rate.

[0229] 2 Results and analysis

[0230] 2.1 Screening of macroporous resin types

[0231] It is not difficult to see from Table 1 and Table 2 that different types of macroporous resins show different adsorption and desorption capacities for sweet potato peel polyphenols, which may be related to the polarity differences between the macroporous resins. Among the three types of macroporous resins D101, HP-20, and AB-8, the adsorption amount and adsorption rate of the HP-20 type macroporous resin for sweet potato peel polyphenols are higher than those of the other two resins. In addition, the adsorption effect of the AB-8 type macroporous resin is the worst. Therefore, it may be because the polarity of the HP-20 type macroporous resin is too small to have a strong adsorption capacity for sweet potato peel polyphenols, which makes it easy for polyphenols to be eluted from the macroporous resin, resulting in a higher adsorption and desorption effect. Therefore, this experiment chose to use the HP-20 type macroporous resin as the purification resin for the sweet potato peel polyphenol extract.

[0232] Table 1 Adsorption amount and adsorption rate of different types of macroporous resins

[0233]

[0234]

[0235] Table 2 Desorption rate of different types of macroporous resins

[0236]

[0237] 2.2 Effect of adsorption time on the adsorption capacity of macroporous resin

[0238] Figure 1 This is the static adsorption curve of sweet potato peel polyphenols by HP-20 macroporous resin. Figure 2 This is the static adsorption curve of HP-20 macroporous resin for purple sweet potato peel polyphenols. Figure 1 It can be seen that the adsorption of sweet potato peel polyphenols by HP-20 macroporous resin can be divided into two stages: from 0 to 2h, the adsorption of sweet potato peel polyphenols by macroporous resin increases rapidly with time; after 2h, the adsorption of sweet potato peel polyphenols by macroporous resin remains basically unchanged, indicating that the resin adsorption has reached saturation. Figure 2 It can be seen that the adsorption of purple sweet potato peel polyphenols by HP-20 macroporous resin can be divided into two stages: from 0 to 2h, the adsorption of purple sweet potato peel polyphenols by macroporous resin increases rapidly with time; after 2h, the adsorption of purple sweet potato peel polyphenols by macroporous resin remains basically unchanged, indicating that the resin adsorption has reached saturation.

[0239] Table 3 Effect of adsorption time of sweet potato peel polyphenols on the adsorption capacity of macroporous resin

[0240]

[0241]

[0242] Table 4 Effect of adsorption time of purple sweet potato peel polyphenols on the adsorption capacity of macroporous resin

[0243]

[0244] 2.3 Effect of desorption time on the adsorption capacity of macroporous resin

[0245] Figure 3 The desorption kinetics curve of sweet potato peel polyphenols by HP-20 perforated resin is shown. Figure 4 The desorption kinetics of purple sweet potato peel polyphenols by HP-20 macroporous resin is shown. Figure 3 It can be seen that the desorption rate of HP-20 macroporous resin increases rapidly from 0 to 2 hours, and the desorption almost reaches equilibrium after 2 hours. Figure 4It can be seen that the desorption rate of HP-20 macroporous resin increases rapidly from 0 to 2h, and the desorption almost reaches equilibrium after 2h.

[0246] Table 5 Effect of desorption time of sweet potato peel polyphenols on the adsorption capacity of macroporous resin

[0247]

[0248] Table 6 Effect of desorption time of purple sweet potato peel polyphenols on the adsorption capacity of macroporous resin

[0249]

[0250]

[0251] 2.4 Effect of sweet potato peel polyphenol concentration on the adsorption capacity of macroporous resin

[0252] Figure 5 The effect of polyphenol concentration of sweet potato peel polyphenol extract on the adsorption of HP-20 macroporous resin is shown. Figure 5 It can be seen that when the concentration of sweet potato peel polyphenol extract increases, the adsorption of sweet potato peel polyphenol by HP-20 macroporous resin gradually decreases with the increase of concentration. It is not difficult to see from the figure that when the concentration of sweet potato peel polyphenol extract is 0.5 mg / mL, the adsorption of sweet potato peel polyphenol by HP-20 macroporous resin is the largest, indicating that the adsorption of polyphenol by macroporous resin reaches saturation at this time.

[0253] Figure 6 The effect of polyphenol concentration of purple sweet potato peel polyphenol extract on the adsorption effect of HP-20 macroporous resin was shown. Figure 6 It can be seen that when the concentration of the purple sweet potato peel polyphenol extract increases, the adsorption of sweet potato peel polyphenol by HP-20 macroporous resin gradually decreases with the increase of concentration. It is not difficult to see from the figure that when the concentration of the purple sweet potato peel polyphenol extract is 0.5 mg / mL, the adsorption of purple sweet potato peel polyphenol by HP-20 macroporous resin is the largest, indicating that the adsorption of polyphenol by the macroporous resin reaches saturation at this time.

[0254] Therefore, in this experiment, the concentration of polyphenols in the extract should be controlled at 0.5 mg / mL when loading.

[0255] Table 7 Effect of sweet potato peel polyphenol concentration on the adsorption capacity of macroporous resin

[0256]

[0257]

[0258] 2.5 Effect of ethanol concentration of eluent on the desorption capacity of macroporous resin

[0259] Table 8 reflects the effect of the ethanol concentration of the eluent on the desorption effect of the HP-20 macroporous resin. According to the table, we can see that when the sweet potato peel polyphenol extract is eluted with ethanol as the eluent, the desorption rate changes with the increase of the ethanol concentration of the eluent. When the ethanol concentration of the eluent is 65%, the desorption rate reaches the maximum and the desorption effect is the best.

[0260] Similarly, when the purple sweet potato peel polyphenol extract is eluted with ethanol as the eluent, the desorption rate changes with the increase of the ethanol concentration of the eluent. When the ethanol concentration of the eluent is 75%, the desorption rate reaches the maximum and the desorption effect is the best.

[0261] Therefore, in this experiment, 65% ethanol was used to elute the polyphenol extracts from sweet potato slices, and 75% ethanol was used to elute the polyphenol extracts from purple potato peels.

[0262] Table 8 Effect of ethanol concentration of eluent on desorption effect of HP-20 macroporous resin

[0263]

[0264]

[0265] 3 Conclusion

[0266] In this experiment, macroporous resin was used to purify sweet potato peel polyphenols by adsorption. Before the experiment, we selected three types of resins: D101, HP-20, and AB-8. Among them, HP-20 macroporous resin had the best adsorption and desorption effect on sweet potato peel polyphenol extract, so HP-20 macroporous resin was selected for this experiment. Then, according to the adsorption and desorption kinetic curves of the macroporous resin, the optimal adsorption saturation time and desorption saturation time, as well as the concentration of sweet potato peel polyphenol extract (0.5 mg / mL) were determined. According to the effect of the ethanol concentration of the eluent on the desorption effect of the HP-20 macroporous resin, in this experiment, 65% ethanol was used to elute the sweet potato slice polyphenol extract, and 75% ethanol was used to elute the purple potato peel polyphenol extract.

[0267] Under the conditions of determining the best adsorption saturation time, polyphenol concentration and ethanol concentration of the eluent, accurately weigh 10g of macroporous resin, load it into the column with distilled water, inject 60ml of 0.5mg / mL sweet potato peel polyphenol solution into the loaded column, and carry out at a flow rate of 1mL / min. The sweet potato peel polyphenol extract is eluted with 65% ethanol, and the purple potato peel polyphenol extract is eluted with 75% ethanol. Collect 100ml of eluent. Under this condition, the elution can be fully performed, and finally the purification rate is calculated. Finally, the purification rates of the two sweet potato peels are 40%.

[0268] The above describes an embodiment of the present embodiment, but the present embodiment is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present embodiment, ordinary technicians in this field can also make many forms, all of which are within the protection of the present embodiment.

Claims

1. A process for extracting polyphenols from sweet potato peels, characterized in that: The steps include: S1. Pretreatment: cleaning and washing the sweet potato peels; S2, freezing: placing the sweet potato peels into a vacuum freeze drying chamber for freezing; S3, grinding: grinding the frozen sweet potato peel into powder; S4, filtering: filtering the ground powder; S5, soaking: soaking the filtered powder; S6. Heating: heating the soaking liquid in a water bath; S7, centrifugation: centrifuging the soaking liquid to obtain a supernatant; S8, suction filtration: use a Bush funnel to filter the supernatant to obtain a filtrate; S9, evaporation and concentration: evaporating and concentrating the obtained filtrate; S10, purification: purifying the obtained polyphenol extract using a macroporous adsorption resin method; S11. Freezing: placing the obtained polyphenol extract in a vacuum freezer at -80 degrees Celsius for 48 hours, attaching a label, and obtaining the finished product.

2. The process for extracting polyphenols from sweet potato peels according to claim 1, characterized in that: Sweet potato skin is sweet potato skin or purple potato skin.

3. The process for extracting polyphenols from sweet potato peels according to claim 1, characterized in that: In S2, the freezing temperature is -80°C and the freezing time is 24 hours.

4. The process for extracting polyphenols from sweet potato peels according to claim 1, characterized in that: In S5, the soaking liquid is an ethanol solution, the concentration of the ethanol solution is 65%, the material-liquid ratio is 1:15 (g / ml), and the soaking time is 30 minutes.

5. The process for extracting polyphenols from sweet potato peels according to claim 1, characterized in that: In S5, the soaking liquid is an ethanol solution, the concentration of the ethanol solution is 75%, the material-liquid ratio is 1:20 (g / ml), and the soaking time is 30 minutes.

6. The process for extracting polyphenols from sweet potato peels according to claim 1, characterized in that: In S5, the soaking liquid is an ethanol solution, the concentration of the ethanol solution is 85%, the material-liquid ratio is 1:25 (g / ml), and the soaking time is 30 minutes.

7. The process for extracting polyphenols from sweet potato peels according to claim 1, characterized in that: In S6, the heating temperature is 60°C and the heating time is 40 minutes.

8. The process for extracting polyphenols from sweet potato peels according to claim 1, characterized in that: In S6, the heating temperature is 50°C and the heating time is 50 minutes.

9. The process for extracting polyphenols from sweet potato peels according to claim 1, characterized in that: In S6, the heating temperature is 70°C and the heating time is 30 minutes.

10. An application of polyphenols based on sweet potato peels, characterized in that: Application in fresh milk preservation.

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