CN110885381A

CN110885381A - Catechin graft modified starch, degradable preservative film and preparation method thereof

Info

Publication number: CN110885381A
Application number: CN201911381605.9A
Authority: CN
Inventors: 任鹏; 黄泳斐; 李立
Original assignee: Bengbu Tiancheng Packaging Technology Co Ltd
Current assignee: Bengbu Tiancheng Packaging Technology Co Ltd
Priority date: 2019-12-27
Filing date: 2019-12-27
Publication date: 2020-03-17
Anticipated expiration: 2039-12-27
Also published as: CN110885381B

Abstract

The invention relates to catechin grafted modified starch, a degradable preservative film and a preparation method thereof, which are characterized in that: oxidizing and reducing an initiation system by using ascorbic acid and hydrogen peroxide, and grafting antioxidant chlorogenic acid on 2,3 and 5 positions of a glucose unit ring in a starch molecule; (1) in a closed container, starch is dissolved in acetic acid solution, followed by the addition of catechins and ascorbic acid, controlling the ratio of catechins: ascorbic acid: the mass ratio of the starch is 5.225: 1.08:6, adding an initiator H in a nitrogen atmosphere₂O₂Reacting for 15-20h at room temperature; (2) adding the reaction mixture into a cut-off membrane with the molecular weight of 8000-14000 Da, dialyzing in distilled water for 60-72h, and freeze-drying the dialysate at-45 to-50 ℃ for 36-48h to obtain C-g-S; C-g-S, PLA and PBST are mixed according to the mass ratio of 1-2: 6-8: 1-2, preparing the preservative film. The invention has the advantages that: the catechin grafted modified starch is prepared by adopting a free radical induced grafting method, and the initiator has good affinity with the environment, no pollution and low price; the degradable preservative film has efficient broad-spectrum antibacterial and antioxidant properties, is safe and harmless to human health, and can effectively prolong the shelf life of food.

Description

Catechin graft modified starch, degradable preservative film and preparation method thereof

Technical Field

The invention belongs to the technical field of novel high polymer materials, and particularly relates to catechin grafted modified starch, a degradable preservative film and a preparation method thereof.

Background

With the increasing severity of global environmental pollution, the environmental problems brought to the earth by traditional petroleum-based materials are increasingly prominent, and the emergence of fully biodegradable materials can effectively relieve the petroleum consumption and solve the problem of environmental pollution. With the enhancement of environmental protection consciousness of people, the fully biodegradable material is continuously favored by people.

Polylactic acid (PLA) is receiving attention because of its high mechanical strength, good processability and outstanding biocompatibility. But the application of PLA in many fields is limited due to the defect of high brittleness of PLA, and the adipic acid-terephthalic acid-butylene terephthalate copolymer (PBAT) which is also used as a full-biodegradable material has good toughness, and the composition of the two can make up for the deficiency, so the PLA is a good blending material system; however, the cost of the fully biodegradable material is high, so that many manufacturers can be prohibited to use, and the addition of the starch can effectively reduce the production cost.

Starch is a macromolecule formed by the dehydration polymerization of multiple glucose molecules, and generally contains about 20% amylose and 80% amylopectin. The development and utilization of starch has been an active area. To expand the applications of starch, chemical, physical, enzymatic and genetic methods have been used to modify the structure of starch. The graft copolymerization starch is a starch reprocessing product newly developed in recent years, has wide application due to a plurality of excellent performances, and is known as a third generation derivative of starch. Since the northern research center of the U.S. department of agriculture in 1969 was the first to successfully perform graft copolymerization of starch and use for the production of degradable plastics and super absorbent resins, development and research of starch have been conducted in various countries of the world. In general, the hydroxyl groups present in starch are the most reactive sites for chemical modification reactions. Functionalization with antioxidant molecules is a promising approach to improve the properties of natural polymers, opening up new applications in biomedicine and packaging materials. The resulting antioxidant-polymer conjugate combines the advantages of both components, having higher stability and slower decomposition rates than low molecular weight molecules, but at the same time having the unique properties of antioxidant molecules.

Phenolic compounds are natural antioxidant molecules widely distributed in fruits, edible plants and vegetables. Catechin (Chlorogenacic) is depside composed of caffeic acid (Caffeeic acid) and quinic acid (Quinicacid), and 3-O-caffeoylquinic acid (3-O-caffeoylquinic acid) is a phenylpropanoid compound produced by plant body through shikimic acid pathway in aerobic respiration process. Polyphenols such as catechin are called "seventh group nutrients", and are widely used in the health care industry. Catechins are effective phenolic antioxidants with antioxidant capacity greater than caffeic acid, p-hydroxybenzoic acid, ferulic acid, syringic acid, Butylated Hydroxyanisole (BHA) and tocopherols. Catechin can form hydrogen radical with antioxidant effect because of containing certain amount of R-OH group to eliminate the activity of free radical such as hydroxyl radical and superoxide anion, thereby protecting tissue from damage caused by oxidation. Catechin has wide bioactivity, and the research on the bioactivity of catechin in modern science has been deeply carried out in various fields such as food, health care, medicine, daily chemical industry and the like.

The existing research mainly focuses on the grafting of the phenolic compound on the chitosan. However, the research on the phenolic compound grafted starch is very limited.

Disclosure of Invention

The invention aims to provide catechin grafted modified starch, a degradable preservative film and a preparation method thereof; the catechin grafted modified starch is synthesized by grafting catechin free radicals to a starch main chain by adopting an ascorbic acid/hydrogen peroxide oxidation reduction pair.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a catechin grafting modified starch is characterized in that: antioxidant molecule chlorogenic acid is grafted on 2,3 and 5 positions of a glucose unit ring in a starch molecule, and the structure is shown as follows:

wherein

。

A preparation method of catechin grafted modified starch is characterized by comprising the following steps:

(1) in a closed vessel (2L three-necked round-bottomed flask), starch (6-12 g) was dissolved in an acetic acid solution (1-3%, 500-: ascorbic acid: the mass ratio of the starch is 5.225: 1.08: 6 (molar ratio of catechin to ascorbic acid is 3: 1), slowly introducing nitrogen, and adding H in nitrogen atmosphere₂O₂As an initiator (1-3 mol/L,10-20 ml), reacting for 15-20h at room temperature;

(2) after the reaction is finished, adding the reaction mixture into a cut-off membrane with the molecular weight of 8000-14000 Da, dialyzing in distilled water for 60-72h to remove unreacted antioxidant, and freeze-drying the dialyzate at-45 to-50 ℃ for 36-48h to obtain the catechin grafted starch named as C-g-S.

A degradable preservative film prepared from catechin grafted modified starch is characterized by being prepared from the following raw materials in parts by weight: 1-2 parts of C-g-S; 6-8 parts of PLA; PBST 1-2 parts.

A method for preparing a degradable preservative film by using catechin grafted modified starch is characterized by comprising the following steps:

(1) mixing PLA, PBST and C-g-S according to the proportion, fully and uniformly stirring, blending and extruding by a double-screw extrusion device, cooling by a water tank, and cutting to obtain composite master batches with uniform size;

(2) and (3) placing the composite master batch in an air-blast drying oven, drying at 50-60 ℃ for 0.5-1h, and preparing the PLA-PBSA- (C-g-S) preservative film by tape casting through a plastic extrusion device and a casting machine.

Further, the temperature of the zone from the feed end of the extrusion device to the die head 1 to 7 is 110-175 ℃, and the rotating speed of the twin-screw is 45-55 rpm; the temperature of the region 1 to 7 from the feed end of the casting machine to the die head is 110-175 ℃, the single screw rotating speed is 45-55 rpm, the coiling rotating speed of the casting machine is 2.8-3.2rpm, and the thickness of the film is controlled to be 50-55 mu m.

The present invention employs a free radical induced grafting method, a grafting reaction between an antioxidant molecule and a biopolymer is performed in a one-step reaction by using a redox initiator system (reaction formula below). At room temperature H₂O₂Oxidation of ascorbic acid and formation of ascorbate and hydroxyl radicals, thus initiating the reaction; the reaction process comprises two steps: a first step of activating starch chains to perform a radical reaction; the second step covalently binds an antioxidant molecule to the preformed macro-radical. This method is very useful for the synthesis of protein or polysaccharide antioxidant conjugates, and does not produce toxic reaction by-products at room temperature and retains the antioxidant through degradation processes.

The invention has the advantages that: in the reaction of free radical induced grafting, the hydrogen peroxide system initiator has good affinity with the environment, no pollution and low price; the degradable preservative film prepared by the catechin grafted modified starch effectively solves the problems that the concentration of an antibacterial agent is reduced and the antibacterial effect is not durable due to long-term storage of the antibacterial agent, eliminates potential harm of the leaked antibacterial agent to human health, can realize complete biodegradation of materials, has high-efficiency broad-spectrum antibacterial and antioxidant properties, is safe and harmless to human health, and can prolong the shelf life of food.

Description of the drawings:

FIG. 1 is a graph showing ascorbic acid and hydrogen peroxide interaction;

FIG. 2 is a diagram of the synthesis of catechin grafted modified starch by a free radical induced reaction;

FIG. 3 shows the antioxidant property of the PLA/PBST/C-g-S preservative film;

FIG. 4 shows the total number of colonies of snakeheads preserved by PLA/PBST/C-g-S preservative film;

FIG. 5 shows the total number of colonies of broccoli preserved by PLA/PBST/C-g-S preservative film.

Detailed Description

Example 1

A preparation method of catechin grafted modified starch comprises the following specific implementation steps:

(1) in a 2L three-necked round bottom flask, 6g starch was dissolved in 600ml 1% acetic acid solution, then 1.08g ascorbic acid and 5.31g catechin were added to the flask, 15ml1mol/L H was added after slowly passing an oxygen-free nitrogen stream for 40 minutes with stirring₂O₂The solution is reacted for 18 hours at 25 ℃ in the nitrogen atmosphere by initiating reaction;

(2) after the reaction is finished, adding the reaction mixture into a cut-off membrane with the molecular weight of 14000 Da, and dialyzing in distilled water for 65h to remove unreacted antioxidant; and finally, freeze-drying the dialysate at-50 ℃ for 48 hours to obtain the catechin grafted modified starch named as C-g-S.

A method for preparing a degradable preservative film by using catechin grafted modified starch comprises the following specific implementation steps:

(1) mixing PLA, PBST and C-g-S according to the mass ratio of 7:1:2, fully and uniformly stirring, blending and extruding by a double-screw extrusion device, cooling by a water tank, and cutting to obtain composite master batches with uniform size;

(2) placing the composite master batch in a blast drying oven, drying at 55 ℃ for 40min, and preparing a PLA-PBSA- (C-g-S) preservative film (marked as C) by tape casting through a plastic extrusion device and a casting machine; wherein the temperatures of the feed end of the extrusion device to the regions 1 to 7 of the die head are respectively 110 ℃, 165 ℃, 170 ℃, 170 ℃, 170 ℃, 170 ℃, 165 ℃ and the rotating speed of the twin screw is 50 rpm; the temperatures of the regions 1 to 7 from the feed end of the casting machine to the die head are respectively 110 ℃, 160 ℃, 175 ℃, 175 ℃, 170 ℃, 170 ℃, 170 ℃, 50rpm of single screw rotation speed, 3rpm of the coiling rotation speed of the casting machine, and the thickness of the film is controlled to be 50 μm.

Comparative example 1

(1) Mixing PLA and PBST according to the mass ratio of 8:2, fully and uniformly stirring, blending and extruding by a double-screw extrusion device, cooling by a water tank, and cutting to obtain composite master batches with uniform size;

(2) placing the composite master batch in a blast drying oven, drying at 55 ℃ for 40min, and preparing a PLA-PBSA preservative film (marked as A) by tape casting through a tape casting machine; wherein the temperatures of the feed end of the extrusion device to the regions 1 to 7 of the die head are respectively 110 ℃, 165 ℃, 170 ℃, 170 ℃, 170 ℃, 170 ℃, 165 ℃ and the rotating speed of the twin screw is 50 rpm; the temperatures of the regions 1 to 7 from the feed end of the casting machine to the die head are respectively 110 ℃, 160 ℃, 175 ℃, 175 ℃, 170 ℃, 170 ℃, 170 ℃, 50rpm of single screw rotation speed, 3rpm of the coiling rotation speed of the casting machine, and the thickness of the film is controlled to be 50 μm.

Comparative example 2

(1) Mixing PLA, PBST and ungrafted corn starch according to a weight ratio of 7:1:2, fully and uniformly stirring, blending and extruding by a double-screw extrusion device, cooling by a water tank, and cutting to obtain composite master batches with uniform size;

(2) drying the composite master batches in a blast drying oven at 55 ℃ for 40min, and then preparing a PLA-PBSA-ungrafted starch preservative film (marked as B) by tape casting through a tape casting machine, wherein the temperatures of the regions from the feed end of the extrusion device to a die head 1 to a die head 7 are respectively 110 ℃, 165 ℃, 170 ℃, 170 ℃, 170 ℃, 170 ℃, 165 ℃ and the rotating speed of a double screw is 50 rpm; the temperatures of the regions 1 to 7 from the feed end of the casting machine to the die head are respectively 110 ℃, 160 ℃, 175 ℃, 175 ℃, 170 ℃, 170 ℃, 170 ℃, 50rpm of single screw rotation speed, 3rpm of the coiling rotation speed of the casting machine, and the thickness of the film is controlled to be 50 μm.

As shown in fig. 1 and 2, Ascorbic Acid (AA) is a water-soluble ketolide with two ionizable hydroxyl groups, which can be ionized to produce an ascorbic acid monoanion (ascih) that first forms an ascorbic acid group (Asc) and then a dehydroascorbic acid (DHA). H ₂0₂The oxidation of AA may be accelerated, producing more Asc. Starch molecules may form fractionsIntermolecular hydrogen bonds. Asc can abstract hydrogen atoms from starch and generate carbon-centered radicals along the starch chain, resulting in a substantial reduction in inter-and intramolecular hydrogen bonds. Subsequently, a large number of catechin groups are grafted onto the starch, further reducing the hydrogen bonding interactions between the starch chains.

Fig. 3 is a graph for testing the oxidation resistance of the film by detecting the scavenging capacity of the 1, 1-diphenyl-2-trinitrophenylhydrazine (DPPH) free radical, and it can be seen that the difference between the oxidation resistance of the film a without starch and the oxidation resistance of the film B without starch grafted is not great, but the oxidation resistance of the film C with the catechin grafted and modified starch is greatly improved, which indicates that the film C also has the functions of scavenging the free radical and resisting oxidation, and the food can be preserved by using the film C, so that the food oxidation can be inhibited.

From the colony total number chart of the fresh-keeping snakehead shown in FIG. 3, the colony total number of the fresh snakehead is 3.272logcfu/g, so that A, B film can obtain the secondary freshness index 10 of the total bacteria number already at the 6 th day⁶logcfu/g, which indicates that the fish food exceeds the use limit, the total number of the C film bacterial colonies exceeds the secondary freshness index on the 8 th day, the shelf life of the snakehead can be effectively prolonged by catechin grafted modified starch for 2 days, in the total number of the fresh broccoli bacterial colonies diagram in FIG. 4, the total number of the fresh broccoli bacterial colonies is 2.893logcfu/g, and the total number of the microbial bacterial colonies of the fresh broccoli is positively correlated with the refrigeration time of the broccoli sample. A. The two films reach 10 days after storing broccoli⁶log cfu/g, the film C added with the catechin grafted modified starch exceeds the second-level freshness index at the 14 th day, and the film C can effectively prolong the shelf life of broccoli for 4 days, which shows that the catechin grafted modified starch has antibacterial performance, can effectively delay food spoilage and prolong the shelf life of food in the actual preservation process.

As can be seen from Table 1, the PLA/PBAT/starch preservative film prepared by adding ungrafted corn starch influences the mechanical property and the air permeability of the film, but the oxidation resistance and the antibacterial property of the preservative film are not improved, and the addition of the grafted starch positively influences the physicochemical property of the film, thus confirming the feasibility of the scheme. The bacteriostatic action of catechin is not caused by inhibiting respiratory metabolism, but can inhibit the logarithmic growth phase of staphylococcus aureus and escherichia coli; increase the permeability of bacterial cell membrane, cause the leakage of protein and carbohydrate in bacterial cells, and disorder the bacterial metabolism. Catechin can destroy the cell wall and membrane structure of Escherichia coli in a short time, increase cell permeability, and cause cell electrolyte, enzyme, DNA and RNA to leak out, NPN permeates into the cell membrane wall, thereby affecting the stability of cell structure and gradually killing cell. The catechin has good bacteriostatic action on gram-negative bacteria escherichia coli and gram-positive bacteria staphylococcus aureus, but has stronger activity against staphylococcus aureus than escherichia coli. The bacteriostatic effect of the membrane is influenced by the self bacteriostatic mechanism besides the grafting rate, which shows that catechin is successfully grafted on the main chain of the starch. The bacteriostatic effect of catechin on staphylococcus aureus can be seen to be more remarkable than that of escherichia coli through a bacteriostatic test in table 2. The antioxidant catechin can exist in the starch in a chemical bond form with the main chain of the starch, so that the antioxidant capacity and the antibacterial performance of the membrane are obviously improved.

Table 1 shows the mechanical barrier performance indexes of the PLA/PBST/C-g-S preservative film:

table 2 shows the antibacterial performance indexes of the PLA/PBST/C-g-S preservative film:

Claims

1. a catechin grafting modified starch is characterized in that: antioxidant molecule chlorogenic acid is grafted on 2,3 and 5 positions of a glucose unit ring in a starch molecule, and the structure is shown as follows:

wherein

。

2. A preparation method of catechin grafted modified starch is characterized by comprising the following steps:

(1) in a closed container, starch is dissolved in a solvent acetic acid solution, and then catechin and ascorbic acid are added to control the ratio of catechin: ascorbic acid: the mass ratio of the starch is 5.225: 1.08: 6, slowly introducing nitrogen, and adding H in a nitrogen atmosphere₂O₂As an initiator, reacting for 15-20h at room temperature;

(2) after the reaction is finished, adding the reaction mixture into a cut-off membrane with the molecular weight of 8000-14000 Da, dialyzing in distilled water for 60-72h, and freeze-drying the dialyzate at-45 to-50 ℃ for 36-48h to obtain the catechin grafted starch named as C-g-S.

3. The degradable preservative film prepared from the catechin grafted and modified starch according to claim 1, which is characterized by being prepared from the following raw materials in parts by weight: 1-2 parts of C-g-S; 6-8 parts of PLA; PBST 1-2 parts.

4. The method for preparing the degradable preservative film by using the catechin grafted modified starch as claimed in claim 3, which is characterized by comprising the following steps:

(1) according to the mass ratio of C-g-S, PLA to PBST of 1-2: 6-8: 1-2, mixing, fully stirring, blending and extruding by a double-screw extrusion device, cooling by a water tank, and cutting to obtain composite master batches with uniform size;

(2) and (3) placing the composite master batch in a blast drying oven, drying at 50-60 ℃ for 0.5-1h, and preparing the PLA-PBSA- (CA-g-S) preservative film by tape casting through an extrusion device and a casting machine.

5. The method for preparing the degradable preservative film by using the catechin grafted modified starch as claimed in claim 4, wherein the method comprises the following steps: the temperature of the feed end of the extrusion device in a region from 1 to 7 of the die head is 110-175 ℃, and the rotating speed of the twin-screw is 45-55 rpm; the temperature of the region 1 to 7 from the feed end of the casting machine to the die head is 110-175 ℃, the rotating speed of the single screw is 45-55 rpm, the coiling rotating speed of the casting machine is 2.8-3.2rpm, and the thickness of the film is controlled to be 50-55 mu m.