阅读说明：本技术 一种对香豆酸接枝改性淀粉和可降解保鲜膜及其制备方法 (P-coumaric acid grafted modified starch and degradable preservative film and preparation method thereof ) 是由 李淑珍 黄泳斐 李立 于 2019-12-27 设计创作，主要内容包括：本发明涉及一种对香豆酸接枝改性淀粉和可降解保鲜膜及其制备方法,其特征在于：淀粉分子中葡萄糖单元环上3,5位上的羟基上的氢原子被对香豆酸取代；(1)密闭容器中加入溶剂DMSO,加入摩尔比3：9：2的对香豆酸、琥珀酸酐和DMAP,50-60℃反应12-18h；(2)氮气氛围中将CDI加到容器中,CDI：对香豆酸摩尔比为6:5,60-70℃反应8-12h；(3)将淀粉溶解在DMSO中,加入容器,淀粉与对香豆酸摩尔比为1:1,75-90℃反应36-48h,加入4-6倍丙酮,离心；(4)沉淀洗涤后溶于DMSO中,用透析袋透析,进一步用蒸馏水透析,透析液冻干,得PCA-g-S。本发明优点：采用CDI介导制备对香豆酸接枝改性淀粉,反应条件温和；接枝率高；副产物无毒且可移除；可降解保鲜膜具有高效广谱抗菌抗氧化性能,可以有限抑制食品微生物生长,延长食品贮藏期,对人体无害。(The invention relates to p-coumaric acid grafted modified starch, a degradable preservative film and a preparation method thereof, which are characterized by comprising the following steps: the hydrogen atoms on the hydroxyl groups on the 3 and 5 positions of the glucose unit ring in the starch molecule are replaced by p-coumaric acid; (1) adding a solvent DMSO into a closed container, and adding a mixture of DMSO and DMSO in a molar ratio of 3: 9: 2, p-coumaric acid, succinic anhydride and DMAP, and reacting for 12-18h at 50-60 ℃; (2) CDI was added to the vessel under nitrogen atmosphere, CDI: reacting for 8-12h at 60-70 ℃ with the mol ratio of p-coumaric acid of 6: 5; (3) dissolving starch in DMSO, adding into a container, reacting at 75-90 deg.C for 36-48h with the molar ratio of starch to p-coumaric acid of 1:1, adding 4-6 times of acetone, and centrifuging; (4) washing the precipitate, dissolving in DMSO, dialyzing with dialysis bag, further dialyzing with distilled water, and lyophilizing the dialysate to obtain PCA-g-S. The invention has the advantages that: the CDI mediated preparation of the p-coumaric acid grafted modified starch is adopted, and the reaction conditions are mild; the grafting rate is high; the by-products are non-toxic and removable; the degradable preservative film has high-efficiency broad-spectrum antibacterial and antioxidant properties, can inhibit the growth of food microorganisms to a limited extent, prolongs the storage period of food, and is harmless to human bodies.)

1. a p-coumaric acid grafted modified starch is characterized in that: the hydrogen atoms on the hydroxyl groups on the 3 and 5 positions of the glucose unit ring in the starch molecule are replaced by p-coumaric acid, and the structure is shown as follows:

wherein

2. The method for preparing the p-coumaric acid graft-modified starch according to claim 1, characterized by comprising the following steps:

(1) succinylation of p-coumaric acid: adding solvent anhydrous dimethyl sulfoxide (DMSO) into a closed container, and adding a mixture of dimethyl sulfoxide (DMSO) and dimethyl sulfoxide (DMSO) in a molar ratio of 3: 9: 2, succinic anhydride and 4-Dimethylaminopyridine (DMAP) at the temperature of between 50 and 60 ℃ for 12 to 18 hours to obtain succinylated p-coumaric acid;

(2) succinylated p-coumaric acid was grafted onto starch using a CDI mediated reaction: introducing nitrogen into the container, adding N, N-Carbonyldiimidazole (CDI) into the container in the step (1), and controlling the content of N, N-carbonyldiimidazole: the mol ratio of p-coumaric acid is 6:5, continuously stirring, and reacting for 8-12 hours at 60-80 ℃;

(3) dissolving starch in anhydrous dimethyl sulfoxide at a molar ratio of starch to p-coumaric acid of 1:1, adding into a container under N₂In the atmosphere, 75-9Continuously stirring at 0 ℃ for reacting for 36-48h, adding acetone with the volume 4-6 times of the total solution after the reaction is finished, and centrifuging to obtain a precipitate;

(4) washing the precipitate with ethanol, dissolving in anhydrous dimethyl sulfoxide (DMSO), dialyzing with dialysis bag with cut-off (MWCO) of 8000-14000Da, further dialyzing with distilled water, and lyophilizing the dialysate in a lyophilizer to obtain the p-coumaric acid grafted modified starch, which is recorded as PCA-g-S.

3. The degradable preservative film prepared from the p-coumaric acid grafted 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 PCA-g-S, 6-8 parts of PLA and 1-2 parts of PBST.

4. The method for preparing the degradable preservative film by grafting the p-coumaric acid modified starch according to claim 1, which is characterized by comprising the following steps:

(1) PLA, PBST and PCA-g-S are mixed according to the mass ratio of 1-2: 6-8: 1-2, mixing, 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) drying the composite master batch at 50-60 ℃ for 0.5-1h, and casting by a casting machine to prepare the PLA-PBSA- (PCA-g-S) preservative film.

5. The method for preparing the degradable preservative film by grafting the p-coumaric acid modified starch according to 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 preservative film is controlled to be 50-55 mu m.

Technical Field

The invention belongs to the technical field of novel high polymer materials, and relates to p-coumaric acid 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. However, PLA has limited its use in many fields due to its high brittleness; the adipic acid-terephthalic acid-butylene terephthalate copolymer (PBAT) which is also used as a full-biodegradable material has good toughness, and the two can make up for the weakness by compounding, so the composite material is a good blending material system. However, the cost of fully biodegradable materials is high, which makes many manufacturers prohibitive.

Starch is a macromolecule formed by the dehydration polymerization of a plurality of glucose molecules, and generally contains about 20% amylose and 80% amylopectin. 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. P-coumaric acid, namely p-hydroxycinnamic acid, is widely present in various vegetable such as green pepper, carrot, tomato, strawberry, pineapple and garlic, and is rich in p-coumaric acid. The coumaric acid has different degrees of inhibition effects on staphylococcus aureus, dysentery bacillus, escherichia coli and pseudomonas aeruginosa. It is noteworthy that the existing research has mainly focused on the grafting of chitosan onto phenolic compounds.   however, the research on phenolic compound grafted starch is very limited.

Disclosure of Invention

The invention aims to provide p-coumaric acid grafted modified starch, a degradable preservative film and a preparation method thereof.

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

a p-coumaric acid grafted modified starch is characterized in that: the hydrogen atoms on the hydroxyl groups on the 3 and 5 positions of the glucose unit ring in the starch molecule are replaced by p-coumaric acid, and the structure is shown as follows:

wherein

。

A preparation method of p-coumaric acid grafted modified starch is characterized by comprising the following steps:

(1) succinylation of p-coumaric acid: to a closed vessel, the solvent anhydrous dimethyl sulfoxide (DMSO, 25-30 ml) was added, and the molar ratio was 3: 9: 2 (0.4925 g), succinic anhydride (0.90 g) and 4-dimethylaminopyridine (DMAP, 0.24 g) at 50-60 ℃ for 12-18h to obtain succinylated p-coumaric acid;

(2) succinylated p-coumaric acid was grafted onto starch using a CDI mediated reaction: n, N-carbonyldiimidazole (CDI, 0.486 g) was charged into the vessel of step (1) by introducing nitrogen into the vessel, and controlling the ratio of CDI: the mol ratio of p-coumaric acid is 6:5, the mixture is continuously stirred and reacts for 8 to 12 hours at the temperature of between 60 and 80 ℃ until CO is not released any more₂；

(3) Dissolving starch (0.49 g) in anhydrous dimethyl sulfoxide (DMSO, 25-30 ml) at a molar ratio of starch to p-coumaric acid of 1:1, adding into a container, and reacting at 75-90 deg.C under stirring for 36-48 hr (N)₂Atmosphere), adding acetone with the volume 4-6 times of the total solution volume after the reaction is finished, and then centrifuging for 12-15min at 1200-5000 rpm to obtain a precipitate;

(4) washing the precipitate with ethanol for 3-5 times to remove p-coumaric acid activated by p-coumaric acid, CDI and imidazole, dissolving in anhydrous dimethyl sulfoxide (DMSO), dialyzing with dialysis bag with cut-off volume (MWCO) of 8000-14000Da (20-28 h), further dialyzing with distilled water (45-50 h), and freeze-drying the dialyzate in a freeze-drying machine at-55 deg.C to-45 deg.C for 36-50h to obtain the p-coumaric acid grafted modified starch, which is recorded as PCA-g-S.

The degradable preservative film prepared from the p-coumaric acid grafted modified starch is characterized by being prepared from the following raw materials in parts by weight:

1-2 parts of PCA-g-S, 6-8 parts of PLA and 1-2 parts of PBST.

A method for preparing a degradable preservative film by grafting modified starch on p-coumaric acid is characterized by comprising the following steps:

(1) mixing PLA, PBST and PCA-g-S according to the proportion, 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) drying the composite master batch at 50-60 ℃ for 0.5-1h, and casting by a casting machine to prepare the PLA-PBSA- (PCA-g-S) preservative film.

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 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.

The CDI mediated reaction takes N, N-Carbonyl Diimidazole (CDI) as an activating agent, and realizes the grafting reaction of p-coumaric acid and starch in dimethyl sulfoxide sulfone (DMSO); the CDI can react with carboxyl of p-coumaric acid to convert the p-coumaric acid into imidazole-activated p-coumaric acid, and then the starch and the imidazole-activated p-coumaric acid are subjected to homogeneous reaction to realize esterification. The main advantage of the CDI mediated reaction is the higher yield of starch ester obtained under mild reaction conditions. In addition, carbon dioxide and imidazole by-products are non-toxic and completely removable.

The invention has the advantages that: the method for preparing the p-coumaric acid grafted modified starch by adopting the CDI mediated reaction has mild reaction conditions; the grafting rate is high; the by-products are non-toxic and removable; the degradable preservative film prepared from the p-coumaric acid grafted modified starch prepared by the invention has high-efficiency broad-spectrum antibacterial and antioxidant performance, is safe and harmless to human bodies, effectively avoids the problems of concentration reduction and non-durable antibacterial effect caused by long-time preservation loss of an antibacterial agent, and also eliminates potential harm of the leaked antibacterial agent to human health.

Description of the drawings:

FIG. 1 is a synthesis of p-coumaric acid graft-modified starch by CDI-mediated reaction;

FIG. 2 shows the antioxidant property of the PLA/PBST/PCA-g-S preservative film;

FIG. 3 shows the total number of colonies of snakeheads preserved by PLA/PBST/PCA-g-S preservative film;

FIG. 4 shows the colony count of broccoli preserved by PLA/PBST/PCA-g-S preservative film.

Detailed Description