CN112724435B - Degradable almond oil/polylactic acid film and preparation method and application thereof - Google Patents
Degradable almond oil/polylactic acid film and preparation method and application thereof Download PDFInfo
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- CN112724435B CN112724435B CN202011595200.8A CN202011595200A CN112724435B CN 112724435 B CN112724435 B CN 112724435B CN 202011595200 A CN202011595200 A CN 202011595200A CN 112724435 B CN112724435 B CN 112724435B
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- almond oil
- polylactic acid
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- 235000019489 Almond oil Nutrition 0.000 title claims abstract description 154
- 239000008168 almond oil Substances 0.000 title claims abstract description 154
- 229920006381 polylactic acid film Polymers 0.000 title claims abstract description 56
- 238000002360 preparation method Methods 0.000 title claims abstract description 27
- 229920000747 poly(lactic acid) Polymers 0.000 claims abstract description 192
- 239000004626 polylactic acid Substances 0.000 claims abstract description 192
- 238000003860 storage Methods 0.000 claims abstract description 58
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 30
- 238000000605 extraction Methods 0.000 claims abstract description 29
- 238000003756 stirring Methods 0.000 claims abstract description 29
- 235000012055 fruits and vegetables Nutrition 0.000 claims abstract description 25
- HEDRZPFGACZZDS-UHFFFAOYSA-N Chloroform Chemical compound ClC(Cl)Cl HEDRZPFGACZZDS-UHFFFAOYSA-N 0.000 claims abstract description 22
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical compound CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 claims abstract description 19
- 238000005303 weighing Methods 0.000 claims abstract description 17
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- 239000000843 powder Substances 0.000 claims abstract description 13
- 239000002904 solvent Substances 0.000 claims abstract description 11
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- 239000001944 prunus armeniaca kernel oil Substances 0.000 claims abstract description 7
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- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 description 4
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- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
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- 235000011389 fruit/vegetable juice Nutrition 0.000 description 2
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 2
- 239000010931 gold Substances 0.000 description 2
- 229910052737 gold Inorganic materials 0.000 description 2
- LHGVFZTZFXWLCP-UHFFFAOYSA-N guaiacol Chemical compound COC1=CC=CC=C1O LHGVFZTZFXWLCP-UHFFFAOYSA-N 0.000 description 2
- 238000002329 infrared spectrum Methods 0.000 description 2
- 239000004310 lactic acid Substances 0.000 description 2
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- 239000004570 mortar (masonry) Substances 0.000 description 2
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- KJFMBFZCATUALV-UHFFFAOYSA-N phenolphthalein Chemical compound C1=CC(O)=CC=C1C1(C=2C=CC(O)=CC=2)C2=CC=CC=C2C(=O)O1 KJFMBFZCATUALV-UHFFFAOYSA-N 0.000 description 2
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- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
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- 235000013809 polyvinylpolypyrrolidone Nutrition 0.000 description 2
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- BJEPYKJPYRNKOW-REOHCLBHSA-N (S)-malic acid Chemical compound OC(=O)[C@@H](O)CC(O)=O BJEPYKJPYRNKOW-REOHCLBHSA-N 0.000 description 1
- HOLHYSJJBXSLMV-UHFFFAOYSA-N 2,6-dichlorophenol Chemical compound OC1=C(Cl)C=CC=C1Cl HOLHYSJJBXSLMV-UHFFFAOYSA-N 0.000 description 1
- RVBUGGBMJDPOST-UHFFFAOYSA-N 2-thiobarbituric acid Chemical compound O=C1CC(=O)NC(=S)N1 RVBUGGBMJDPOST-UHFFFAOYSA-N 0.000 description 1
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- SXZYCXMUPBBULW-SKNVOMKLSA-N L-gulono-1,4-lactone Chemical compound OC[C@H](O)[C@H]1OC(=O)[C@@H](O)[C@H]1O SXZYCXMUPBBULW-SKNVOMKLSA-N 0.000 description 1
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- DGEZNRSVGBDHLK-UHFFFAOYSA-N [1,10]phenanthroline Chemical compound C1=CN=C2C3=NC=CC=C3C=CC2=C1 DGEZNRSVGBDHLK-UHFFFAOYSA-N 0.000 description 1
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- BJEPYKJPYRNKOW-UHFFFAOYSA-N alpha-hydroxysuccinic acid Natural products OC(=O)C(O)CC(O)=O BJEPYKJPYRNKOW-UHFFFAOYSA-N 0.000 description 1
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- MGJZITXUQXWAKY-UHFFFAOYSA-N diphenyl-(2,4,6-trinitrophenyl)iminoazanium Chemical compound [O-][N+](=O)C1=CC([N+](=O)[O-])=CC([N+]([O-])=O)=C1N=[N+](C=1C=CC=CC=1)C1=CC=CC=C1 MGJZITXUQXWAKY-UHFFFAOYSA-N 0.000 description 1
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/18—Manufacture of films or sheets
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
- B65D65/00—Wrappers or flexible covers; Packaging materials of special type or form
- B65D65/38—Packaging materials of special type or form
- B65D65/46—Applications of disintegrable, dissolvable or edible materials
- B65D65/466—Bio- or photodegradable packaging materials
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
- C08J2367/04—Polyesters derived from hydroxy carboxylic acids, e.g. lactones
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2491/00—Characterised by the use of oils, fats or waxes; Derivatives thereof
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A40/00—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production
- Y02A40/90—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production in food processing or handling, e.g. food conservation
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W90/00—Enabling technologies or technologies with a potential or indirect contribution to greenhouse gas [GHG] emissions mitigation
- Y02W90/10—Bio-packaging, e.g. packing containers made from renewable resources or bio-plastics
Abstract
The invention discloses a preparation method of a degradable almond oil/polylactic acid film, which comprises the following two steps: firstly, extracting apricot kernel oil, namely firstly crushing the apricot kernel, drying for later use, weighing a proper amount of apricot kernel coarse powder, placing the powder in an extraction tube, adding an n-hexane solution into an extraction bottle, refluxing in a Soxhlet extractor, placing the solution in a rotary evaporator after finishing, evaporating a solvent to obtain the almond oil, and storing in a refrigerator for later use; secondly, preparing an almond oil/polylactic acid film, mixing polylactic acid, a chloroform solution and the almond oil, stirring, carrying out ultrasonic extraction and centrifuging, and finally preparing the almond oil/PLA film. The almond oil/PLA film can be used for fresh-keeping storage of fruits and vegetables, ensures the biodegradability of polylactic acid, improves the flexibility and the water vapor barrier property of the film to a certain extent, and endows the film with certain antioxidant activity, thus being an ideal degradable packaging material.
Description
Technical Field
The invention relates to the technical field of high polymer materials, in particular to a degradable almond oil polylactic acid film and a preparation method and application thereof.
Background
At present, most of the packaging materials used by us are non-degradable petroleum-based plastics, but the environment problem caused by the non-degradability of the packaging materials is that we have to think again how to solve the troublesome problem. Thus, researchers gradually focus on biodegradable materials, and the performance of the biodegradable materials after modification treatment can be comparable to that of traditional materials, so that the biodegradable materials are expected to become substitutes for non-degradable materials.
Polylactic acid is a biodegradable material prepared by fermenting plant resources widely existing in nature into lactic acid and polymerizing the lactic acid. The polylactic acid material can be self-degraded in nature after being discarded, and does not cause any burden to the environment, so that the polylactic acid material is a safe and environment-friendly biological polymer material. Polylactic acid also has the characteristics of biocompatibility and easy processing. At present, the method is widely applied to the fields of packaging, biomedicine and the like. However, polylactic acid films have the defects of high brittleness and low water vapor barrier property, and limit the application of the polylactic acid films in the packaging industry.
The almond oil has extremely strong antioxidant activity, is limited in application due to the influence of hydrophobicity and high volatility, and can reduce loss of the almond oil and oxidation resistance of a biological film when being added into a PLA film matrix as an active substance, and in addition, the hydrophobicity of the almond oil can reduce the contact opportunity of water molecules on the surface of the polylactic acid film, so that the water vapor barrier property of the almond oil is improved. However, the apricot seeds are often used as a waste material, but if the almond oil is extracted from the apricot seeds, the apricot seeds are certainly a concept of changing waste into valuables and fully utilizing crop waste, and the method completely accords with the current strategy of sustainable development.
According to the invention, the almond oil extracted from the apricot kernel and the polylactic acid are blended to prepare the degradable plastic film, so that the high performance of the polylactic acid and the antioxidation activity of the almond oil are combined, the traditional petroleum-based plastic can be partially replaced, the defect of pure polylactic acid is overcome, the application range of the polylactic acid is widened, meanwhile, the waste materials of the apricot seeds are fully utilized, the cost is saved, and the degradable plastic film has important economic and environmental protection significance, and provides a thought for developing a novel food fresh-keeping film.
Disclosure of Invention
The invention aims to provide a degradable almond oil/polylactic acid film, a preparation method and application thereof, which ensure the biodegradability of polylactic acid, improve the flexibility and the water vapor barrier property of the film to a certain extent, and endow the film with certain antioxidant activity, thus being an ideal degradable packaging material.
To achieve the above object, the solution of the present invention is: a preparation method of a degradable almond oil polylactic acid film comprises the following steps:
(1) Extraction of apricot kernel oil
Cleaning semen Armeniacae amarum with running water, drying, pulverizing into powder, weighing appropriate amount of semen Armeniacae amarum coarse powder, placing into an extraction tube, adding n-hexane solution into an extraction bottle, refluxing in a Soxhlet extractor, placing the solution into a rotary evaporator after finishing, evaporating solvent to obtain oleum Armeniacae amarum, and storing in a refrigerator;
(2) Preparation of almond oil/polylactic acid film
Weighing 2g of polylactic acid in a beaker, adding 30mL of chloroform solution, stirring on a magnetic stirrer, adding the almond oil obtained in the step (1) into the beaker after the solution is uniformly stirred, placing the beaker in the magnetic stirrer for stirring, performing ultrasonic extraction and centrifugation after stirring, finally pouring the solution into a container, drying at a ventilation position, and tearing off to form a film.
Preferably, the solution in the step (2) is sealed by a preservative film in the stirring process.
Preferably, the mass ratio of almond oil to polylactic acid in the preparation process of the film is 0.2:1 adding almond oil.
Preferably, almond oil is added in the mass ratio of 0.4:1 of almond oil to polylactic acid in the preparation process of the film.
Preferably, almond oil is added in the mass ratio of 0.6:1 of almond oil to polylactic acid in the preparation process of the film.
Preferably, almond oil is added in the mass ratio of 0.8:1 of almond oil to polylactic acid in the preparation process of the film.
Preferably, almond oil is added in the mass ratio of almond oil to polylactic acid of 1:1 in the preparation process of the film.
The invention also provides application of the almond oil/polylactic acid film in fruit and vegetable fresh-keeping.
After the scheme is adopted, the gain effect of the invention is as follows:
according to the invention, green and environment-friendly polylactic acid and apricot kernel are selected as raw materials, and the apricot kernel oil is extracted by a Soxhlet extractor, so that the apricot kernel coarse powder is continuously extracted by normal hexane solution by utilizing the principle of solvent reflux and siphon, and the purification is obtained; the purified almond oil and polylactic acid are prepared into an almond oil/polylactic acid film by a solvent volatilization method, and the film not only maintains high performances such as biodegradability and the like of the polylactic acid, but also improves flexibility and water vapor barrier property.
From DSC experimental data, as the content of the almond oil increases, tg becomes smaller, the temperature required to change the molecular chain is reduced, the film flexibility is improved, TC, tm and crystallinity are reduced compared with that of pure polylactic acid, and the almond oil is only plasticized, because the almond oil can form easily deformed oil drops in a PLA gel matrix, but the almond oil does not have the effect of improving the crystallinity; the reason for the improvement of the water vapor barrier property is that the almond oil itself has a hydrophobic property, and the contact between the water vapor and the film can be reduced, thereby blocking the contact.
In addition, experimental data of free radical scavenging show that the almond oil also endows the film with a certain antioxidant activity, solves the defects existing in pure polylactic acid, and widens the application range of polylactic acid.
The preparation method is simple and easy to implement, the prepared almond oil/polylactic acid film belongs to food grade, has good toughness and degradability, also has good water vapor permeability, can prolong the storage life of foods such as fruits and vegetables as a fresh-keeping packaging material, has toughness superior to that of the existing fresh-keeping film, and is an ideal green packaging material.
Drawings
FIG. 1 is an SEM image of a pure polylactic acid and almond oil/polylactic acid film of the present invention of varying concentrations;
FIG. 2 is a FTIR graph of the pure polylactic acid and almond oil/polylactic acid films of the present invention in varying concentrations;
FIG. 3 is a DSC chart of the present invention pure polylactic acid and almond oil/polylactic acid films of varying concentrations;
FIG. 4 is a bar graph of DPPH, H2O2 radical scavenging rate for the present invention pure polylactic acid and almond oil/polylactic acid films of varying concentrations;
FIG. 5 is a graph of the sensory scores of the CK and test groups of the present invention during storage;
FIG. 6 is a graph showing the trend of weight loss during storage of the CK and test groups of the present invention;
FIG. 7 is a graph showing the hardness change trend during storage of the CK and test groups of the present invention;
FIG. 8 is a graph showing the change in decay during storage of the CK and test groups of the present invention;
FIG. 9 is a graph showing the trend of TSS change during storage for the CK and test groups of the present invention;
FIG. 10 is a graph showing the trend of TA change during storage for the CK and test groups of the present invention;
FIG. 11 is a graph showing the trend of Vc change during storage of the CK and test groups of the invention;
FIG. 12 is a graph showing the change in POD activity during storage of the CK group and the test group of the present invention;
FIG. 13 is a graph showing the change in PPO activity during storage of the CK group and the test group of the present invention;
FIG. 14 is a graph showing MDA change trend during storage of the CK group and the test group of the present invention.
Detailed Description
The invention relates to a degradable almond oil/polylactic acid film which can be applied to fresh-keeping storage of various fruits and vegetables. For convenience of explanation, the almond oil/polylactic acid film prepared by the preparation method of the invention is used for fresh-keeping storage of cherry tomatoes. However, the present invention is not limited thereto, and the almond oil/polylactic acid film of the present invention may be used in packaging fruits and vegetables as long as it is related to preservation and storage of fruits and vegetables, such as storage, transportation, etc.
The preparation method of the almond oil/polylactic acid film provided by the invention comprises the following two steps: firstly, the method adopts a Soxhlet extraction method to extract the apricot kernel oil from the apricot kernel, wherein the Soxhlet extractor is composed of an extraction bottle, an extraction pipe and a condensation pipe, two sides of the extraction pipe are respectively provided with a siphon pipe and a connecting pipe, and the connecting parts of the extraction pipe are tightly and air-tight, and the device utilizes the solvent reflux and siphon principle to continuously extract solid substances by pure solvent, thereby saving solvent and having high extraction efficiency; secondly, preparing the almond oil/polylactic acid composite film by adopting a solvent volatilization method.
The method comprises the following specific steps:
(1) Extraction of apricot kernel oil
S1, crushing: cleaning semen Armeniacae amarum with running water, drying at room temperature, and pulverizing semen Armeniacae amarum into powder with pulverizer to increase contact area of the reinforcing liquid;
s2, extracting: manufacturing a cylindrical filter paper cylinder by using filter paper, weighing 15g of the almond coarse powder obtained in the step S1, putting the almond coarse powder into the filter paper cylinder, folding and sealing the open end, and putting the almond coarse powder into an extraction pipe;
accurately measuring 100ml of normal hexane solution, placing the lower end of an extraction tube in an extraction bottle, connecting the lower end of the extraction tube with the extraction bottle containing the normal hexane solution, connecting the upper end of the extraction tube with a condensation tube, heating the extraction bottle to 80 ℃ after condensed water is introduced into the condensation tube, boiling the normal hexane solution, gasifying the normal hexane solution, ascending the condensation tube into the condensation tube, condensing the condensed liquid into the liquid, dripping the condensed liquid into the extraction tube, leaching almond coarse powder for extraction, flowing the normal hexane solution containing almond oil into the extraction bottle through the siphon when the liquid level of the normal hexane solution in the extraction tube reaches the highest position of the siphon, continuously heating, ascending and condensing the normal hexane solution flowing into the extraction bottle, dripping the normal hexane solution into the extraction tube, circularly reciprocating in such a way, continuously extracting the almond coarse powder by the pure normal hexane solution after refluxing for 12 hours, and enriching the extracted almond oil in the extraction bottle to obtain purified almond oil normal hexane solution;
and (3) placing the purified almond oil n-hexane solution into a rotary evaporator, evaporating the solvent at 50 ℃ and the rotating speed of 60r/min to obtain almond oil, and placing the almond oil in a refrigerator at 4 ℃ for standby.
The almond oil is extracted and purified by utilizing the solvent to have high solubility of the required components in the solid mixture and low solubility of impurities so as to achieve the aim of extraction and separation.
(2) Preparation of almond oil/polylactic acid film
S1, weighing 2g of polylactic acid in a beaker, adding 30mL of chloroform solution, placing on a magnetic stirrer, and fully stirring for 1h at 25 ℃ and a rotating speed of 5000 r/min;
s2, after the solution is uniformly stirred, the mass ratio of the almond oil to the polylactic acid is 0: 1-1:1, placing the almond oil obtained in the step (1) into a beaker, placing the beaker on a magnetic stirrer, and fully stirring for 7h at 25 ℃ and a rotating speed of 5000 r/min;
s3, after stirring is completed, carrying out ultrasonic-assisted extraction for 10min, and centrifuging for 5min under the condition that the rotating speed of a centrifuge is 8000 r/min;
s4, pouring the solution into a polytetrafluoroethylene plate with 20cm gamma of 20cm, drying the solution for 12 hours at normal temperature at a ventilation position, and tearing off the solution to form the film.
In order to avoid experimental errors caused by volatilization of chloroform, the beaker is sealed by a preservative film in the whole stirring process.
Hereinafter, the present invention will be described in detail with reference to specific examples.
Example 1:
weighing 2g of polylactic acid in a beaker, adding 30mL of chloroform solution, placing the beaker on a magnetic stirrer, fully stirring for 8h at 25 ℃ and a rotation speed of 5000r/min, performing ultrasonic-assisted extraction for 10min after stirring is completed, centrifuging for 5min at a centrifuge rotation speed of 8000r/min, finally pouring the solution into a polytetrafluoroethylene plate with 20cm & lt 20 & gt cm, drying at normal temperature for 12h at a ventilation position, and tearing off to obtain a neatPLA film serving as a blank control.
Example 2:
weighing 2g of polylactic acid in a beaker, adding 30mL of chloroform solution, placing the beaker on a magnetic stirrer, fully stirring for 1h at 25 ℃ and a rotating speed of 5000r/min, and after the solution is uniformly stirred, mixing the almond oil obtained in the step (1) according to the mass ratio of 0.2 with the polylactic acid: 1 adding into beaker, placing the beaker on magnetic stirrer, stirring thoroughly at 25deg.C and rotation speed of 5000r/min for 7 hr, ultrasonic-assisted extraction for 10min after stirring, centrifuging at centrifugal machine rotation speed of 8000r/min for 5min, pouring the solution into 20cm polytetrafluoroethylene plate, drying at ventilation site at normal temperature for 12 hr, and tearing to obtain oleum Armeniacae amarum/PLA composite membrane marked AKEO/PLA 0.2 。
Example 3:
weighing 2g of polylactic acid in a beaker, adding 30mL of chloroform solution, placing the beaker on a magnetic stirrer, fully stirring for 1h at 25 ℃ and the rotating speed of 5000r/min, and after the solution is uniformly stirred, mixing the almond oil obtained in the step (1) according to the mass ratio of 0.4 with the polylactic acid: 1 adding into beaker, placing the beaker on magnetic stirrer, stirring thoroughly at 25deg.C and rotation speed of 5000r/min for 7 hr, ultrasonic-assisted extraction for 10min after stirring, centrifuging at centrifugal machine rotation speed of 8000r/min for 5min, pouring the solution into 20cm polytetrafluoroethylene plate, drying at ventilation site at normal temperature for 12 hr, and tearing to obtain oleum Armeniacae amarum/PLA composite membrane marked AKEO/PLA 0.4 。
Example 4:
weighing 2g of polylactic acid into a beaker, adding 30mL of chloroform solution, placing the beaker on a magnetic stirrer, and fully placing the beaker under the conditions of 25 ℃ and rotational speed of 5000r/minStirring for 1h, and after the solution is uniformly stirred, mixing the almond oil obtained in the step (1) with polylactic acid according to the mass ratio of 0.6:1 adding into beaker, placing the beaker on magnetic stirrer, stirring thoroughly at 25deg.C and rotation speed of 5000r/min for 7 hr, ultrasonic-assisted extraction for 10min after stirring, centrifuging at centrifugal machine rotation speed of 8000r/min for 5min, pouring the solution into 20cm polytetrafluoroethylene plate, drying at ventilation site at normal temperature for 12 hr, and tearing to obtain oleum Armeniacae amarum/PLA composite membrane marked AKEO/PLA 0.6 。
Example 5:
weighing 2g of polylactic acid in a beaker, adding 30mL of chloroform solution, placing the beaker on a magnetic stirrer, fully stirring for 1h at 25 ℃ and the rotating speed of 5000r/min, and after the solution is uniformly stirred, mixing the almond oil obtained in the step (1) according to the mass ratio of 0.8 with the polylactic acid: 1 adding into beaker, placing the beaker on magnetic stirrer, stirring thoroughly at 25deg.C and rotation speed of 5000r/min for 7 hr, ultrasonic-assisted extraction for 10min after stirring, centrifuging at centrifugal machine rotation speed of 8000r/min for 5min, pouring the solution into 20cm polytetrafluoroethylene plate, drying at ventilation site at normal temperature for 12 hr, and tearing to obtain oleum Armeniacae amarum/PLA composite membrane marked AKEO/PLA 0.8 。
Example 6:
weighing 2g of polylactic acid in a beaker, adding 30mL of chloroform solution, placing the beaker on a magnetic stirrer, fully stirring for 1h at 25 ℃ and a rotating speed of 5000r/min, and after the solution is uniformly stirred, mixing the almond oil obtained in the step (1) according to a mass ratio with the polylactic acid of 1:1, placing the beaker on a magnetic stirrer, fully stirring for 7 hours under the condition of 25 ℃ and 5000r/min, extracting for 10 minutes under the assistance of ultrasound after stirring, centrifuging for 5 minutes under the condition of 8000r/min, finally pouring the solution into a polytetrafluoroethylene plate with 20cm of gamma and 20cm, drying for 12 hours at normal temperature in a ventilation place, and tearing off to obtain an almond oil/PLA composite film, wherein the almond oil/PLA composite film is marked as AKEO/PLA 1.0 。
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings and the examples.
Experimental example 1:
this experimental example was conducted to observe the film surface of the pure PLA, almond oil/PLA composite film obtained in examples 1 to 6. Before the experiment, each composite film was dried under vacuum at 50 ℃ for 12 hours, then each composite film was cut into elongated square strips with a width of about 2mm, a thin layer of gold or platinum was sprayed on the surface of the sample by an ion sputtering apparatus, and the samples after the gold spraying were sent to a sample chamber along with a sample stage, and then the film surface was observed. FIG. 1 is an SEM image of the pure polylactic acid and almond oil/polylactic acid films of the present invention in varying concentrations.
As shown in FIG. 1, wherein a) neatPLA, b) AKEO/PLA 0.2 、c)AKEO/PLA 0.4 、d)AKEO/PLA 0.6 AKEO/PLA, e) and f) 0.8 AKEO/PLA, g) and h) 1.0 From the figure, AKEO/PLA was found 0.2 、AKEO/PLA 0.4 、AKEO/PLA 0.6 The three almond oil/PLA composite films are not greatly different from the PLA film in surface morphology, are all relatively smooth, indicate that the almond oil and the polylactic acid are well fused, have no great influence on the PLA film in surface morphology, and are AKEO/PLA 0.8 、AKEO/PLA 1.0 The surface of the two almond oil/PLA composite films is rough, because the almond oil can lead to rough and uneven film surface through the PLA film in the volatilization process in the drying process.
Experimental example 2:
this experimental example an infrared spectrum experiment was performed on the pure PLA, almond oil/PLA composite film obtained in examples 1-6. Before the experiment, each film is sheared into squares with 2cm gamma of 2cm and placed in an infrared spectrometer, the molecular structural components of the sample are analyzed, after the air background spectrum is collected by the infrared spectrometer, the infrared spectrogram of each film is respectively tested, and the test range is 400cm -1 ～4000cm -1 . FIG. 2 is a FTIR of a purified polylactic acid and almond oil/polylactic acid film of the present invention in various concentrations, wherein a) neatPLA, b) AKEO/PLA 0.2 、c)AKEO/PLA 0.4 、d)AKEO/PLA 0.6 、e)AKEO/PLA 0.8 、f)AKEO/PLA 1.0 。
As shown in FIG. 2, the neatPLA is present at about 3480cm -1 There is a weaker absorption peak, indicating that a small amount of-OH is present, 3000cm -1 Is telescopic vibration of-CH-in PLA structure, 1760cm -1 The position is-C=O stretching vibration of 1460cm -1 、1380cm -1 The place is-CH-bending vibration, 1200cm -1 、1100cm -1 Nearby is-C-O-stretching vibration 870cm -1 is-C-C-stretching vibration. While the absorption peak of the almond oil/PLA composite film is 3500cm -1 ～3400cm -1 The nearby weak absorption peaks are-OH and-NH stretching vibration, and the absorption peak is 3000cm -1 ～2800cm -1 The position is-CH-telescopic vibration, 1750cm -1 The characteristic peak (-c=o stretching vibration) of the ester carbonyl group is nearby, and the peak at this position moves to a smaller wave number with increasing almond oil content, which is probably due to the change in PLA conformation caused by the recombination of almond oil and PLA, and the change in molecular order. 1460cm -1 、1380cm -1 near-CH-bending vibration 1250-1000 cm -1 Nearby is-C-O-telescopic vibration 870cm -1 The vicinity is-C-C-stretching vibration, and the spectrum shows that the infrared spectrum characteristic bands of the pure PLA film are basically consistent with those of other five groups of almond oil/PLA films, so that the active almond oil has no obvious influence on the chemical structure of the film.
Example 3:
the mechanical properties of the pure PLA, almond oil/PLA composite films obtained in examples 1-6 were tested, using GB/T1040.3-2006 as a standard, cutting the sample film into rectangular bars of 100 x 15mm with a cutting knife, measuring the initial distance between clamps by 100mm, the gauge length by 50mm, the stretching speed by 20mm/min, the environmental conditions of temperature (23+ -2) DEG C and relative humidity (50+ -5)%, measuring the tensile strength and elongation at break of the composite film, testing 3 parallel samples per group, recording the tensile strength and elongation at break of the samples in each test process, and taking the average value. And analyzing the stress variation degree according to the average value. The thickness of the composite film was measured by a screw micrometer, and the center position and the thicknesses in the four angular directions of the composite film were randomly measured, and the average values thereof were taken as shown in table 1.
Table 1 shows the mechanical properties of the pure PLA and almond oil/PLA composite films of examples 1 to 6
* The significance level of the mean difference was 0.05.
It can be seen from table 1 that the addition of almond oil increases the elongation at break of the PLA film, and that there is a significant difference (P < 0.05) between pure PLA and each almond oil/PLA composite film; while the tensile strength and the elastic modulus decrease with increasing almond oil content. There was a significant difference in tensile strength (P < 0.05) between pure PLA and each almond oil/PLA composite film, but almond oil/PLA 0.6 With almond oil/PLA 0.8 The difference between them is not significant (P > 0.05); in the elastic modulus, pure PLA is used in addition to almond oil/PLA 0.2 Besides no significant difference, the film has significant difference (P < 0.05) with other composite films.
Example 4:
this experimental example DSC was performed on the thermal properties of the pure PLA, almond oil/PLA composite films obtained in examples 1-6. Weighing 5-8mg of almond oil/PLA composite film sample, packaging in a crucible, heating from room temperature to 210 ℃ at a speed of 10 ℃/min under nitrogen atmosphere with a gas flow rate of 50mL/min, keeping constant temperature for 5min to eliminate heat history, cooling to room temperature at the same speed, heating to 210 ℃ for the second time, and recording the change condition of enthalpy change along with temperature during the second heating, wherein the change condition is shown in Table 2. The crystallinity of the material is calculated as follows:
wherein: Δhm is the enthalpy of fusion of the material; ΔHm0 is 93.6J/g of enthalpy value at 100% crystallization of polylactic acid.
TABLE 2 thermal performance parameters of pure PLA and Almond oil/PLA composite films
FIG. 3 is a DSC chart of the inventive pure polylactic acid and almond oil/polylactic acid films of varying concentrations. From a combination of Table 2 and FIG. 3, it can be seen that Tg decreases as the almond oil content increases, indicating that a decrease in temperature is required to initiate a change in molecular chains, demonstrating an increase in film flexibility. Tc was reduced from 110.21℃for pure PLA to 107.01 ℃ 109.68 ℃ 109.68 ℃ 109.50 ℃ 109.91 ℃for almond oil/PLA composite films, respectively. Compared with pure PLA, the temperature of the almond oil/PLA composite film is reduced to a minimum value of 166.91 ℃ at Tm168.26 ℃, which further indicates that the almond oil improves the fluidity of PLA molecules so as to play a plasticizing role, so that the temperature moves to a low temperature. This is due to the fact that almond oil is dispersed into the PLA structure, which can form easily deformed oil droplets in the PLA gel matrix to exert a plasticizing effect. However, the crystallinity of the almond oil/PLA composite film is also reduced compared with pure PLA, indicating that the almond oil cannot improve the crystallinity of the PLA.
Example 5:
this experimental example the opacity and water vapor transmission properties of the pure PLA, almond oil/PLA composite films obtained in examples 1-6 were tested by gravimetric methods. The experiment uses anhydrous calcium chloride to absorb water, and the water vapor transmission coefficient (WVP) is measured by weight gain of the anhydrous calcium chloride. Firstly, 1g of dry anhydrous calcium chloride with a use area of 113.04mm is put into a bottle with an inner diameter of 120mm 2 The film was then placed in a 25 ℃ dry box with saturated NaCl to ensure 75% relative humidity, and anhydrous calcium chloride placed in the cup to ensure 0% humidity, measured every 12 hours, and the amount of water vapor absorbed through the film was measured for each container, expressed as mean ± standard deviation, as shown in table 3. The specific calculation formula is as follows:
wherein: Δm is the increase in mass in time t, g; l is the thickness of the film, m; a is the effective area, mm2; t is the interval time of two times after the quality is stable, and h; ΔP is the difference in vapor pressure between the inside and outside of the cup. And (3) injection: saturated vapor pressure of water at 25℃3170Pa.
In addition, the sample was cut into rectangular shapes, placed in a cuvette, and a blank control was made (what was not placed). Absorbance at 600nm was measured and averaged 3 times per group as shown in table 3. The calculation formula is as follows:
wherein: a is that 600 Absorbance at 600 nm; d is the thickness of the film mm.
TABLE 3 opacity and WVP values for pure PLA and almond oil/PLA composite films
As is clear from Table 3, the WVP value of pure PLA reaches 1.34.+ -. 0.05 x 10-9 g.m/h.pa.m 2 As almond oil increases, the WVP value gradually decreases and there is a significant difference (p < 0.05) from pure PLA, because of the hydrophobicity of almond oil, reducing the chance of water vapor coming into contact with the membrane, blocking it out; AKEO/PLA 0.8 Increased WVP to 2.60+ -0.04 gamma 10 compared to other composite membranes -9 g·m/h·pa·m 2 Possibly due to the evaporation of almond oil to form uneven holes in the surface of the film. With further increase of almond oil content AKEO/PLA 1.0 With AKEO/PLA 0.8 There was no significant difference (p > 0.05).
In addition, the opacity of each almond oil/PLA composite film was significantly reduced (p < 0.05) compared to pure PLA, and as the almond oil content increased, when the mass ratio of almond oil to polylactic acid was 0.6:1, there was no significant difference in opacity (p > 0.05) already with further increase of almond oil.
Example 6:
the almond oil is a natural antioxidant, and the antioxidation function of the almond oil is not lost when the almond oil is combined with the film, so that the antioxidation performance of the pure PLA and the almond oil/PLA composite films obtained in the examples 1-6 is tested for verifying the influence of the almond oil/polylactic acid films with different concentrations on the antioxidation performance.
(1) DPPH radical scavenging test
FirstPreparing 0.1mM DPPH solution, accurately weighing 3.9mgDPPH, fixing the volume to 100mL in a brown bottle by absolute ethyl alcohol, shaking uniformly, placing at room temperature, keeping away from light, and preparing for use at present; then preparing a composite membrane extract, and respectively weighing 500mgneatPLA and AKEO/PLA 0.2 、AKEO/PLA 0.4 、AKEO/PLA 0.6 、AKEO/PLA 0.8 、AKEO/PLA 1.0 Dissolving in 15mL absolute ethanol solution, performing ultrasonic treatment for 2h, centrifuging at 8000r/min for 20min to fully mix; finally, 2mL of the composite membrane extract and 2mL of the LDPPH solution are mixed, incubated for 1h at room temperature in a dark place, absorbance is measured at 517nm and is repeatedly measured for three times, and the average value is taken to be +/-standard deviation. The inhibition ratio was calculated by the formula:
I(％)＝[1-(A sample /A DPPH )]×100％
wherein: i is the inhibition rate; a is that sample Is DPPH solution containing membrane extract; a is that DPPH The solution was DPPH without the membrane extract.
(2)H 2 O 2 Free radical scavenging test
First, 0.1% H was prepared 2 O 2 Stock solution, accurately measured 0.333mLH 2 O 2 The volume is fixed to 100mL by a phosphate buffer solution with pH=7.4, the solution is prepared at present, and then a composite membrane extracting solution (the steps are the same as the above) is prepared, and 500mgneatPLA and AKEO/PLA are respectively weighed 0.2 、AKEO/PLA 0.4 、AKEO/PLA 0.6 、AKEO/PLA 0.8 、AKEO/PLA 1.0 Dissolved in 15mL of absolute ethanol solution, treated by ultrasonic for 2h and centrifuged at 8000r/min for 20min. Finally, 1mL of composite membrane extract and 1mLH are taken 2 O 2 1mL phenanthroline, 1 mLFASO 4 The mixture was incubated at room temperature in the absence of light for 30min, and absorbance was measured at 230nm (repeated three times). H without Membrane sample fluid 2 O 2 The absorbance was measured at 230nm for the control mixture (three replicates). A mixed solution without the membrane sample solution (1 mL of absolute ethanol instead) was used as a blank. The inhibition ratio was calculated by the formula:
I(％)＝[1-(A sample /A DPPH )]×100％
wherein: i is the inhibition rate; asmple containing membrane solutionH 2 O 2 Absorbance of the solution mixture; ADPPH is H without membrane liquid 2 O 2 Absorbance of the solution mixture.
FIG. 4 is a bar graph of DPPH and H2O2 radical scavenging rates for the films of the present invention with pure polylactic acid and almond oil/polylactic acid of varying concentrations, where 1-6 correspond to neatPLA and AKEO/PLA, respectively 0.2 、AKEO/PLA 0.4 、AKEO/PLA 0.6 、AKEO/PLA 0.8 、AKEO/PLA 1.0 With the increase of the concentration of the almond oil, the DPPH free radical clearance of the composite membrane shows an ascending trend, the DPPH free radical clearance is increased from almost 0 to 24.20 percent of pure PLA, and the minimum concentration AEKO/PLA is increased 0.2 The antioxidation activity of the composite film is improved by about 17 percent compared with that of a pure PLA film. There was a significant difference (P < 0.05) between each sample composite film and pure PLA. From FIG. 4, it can be seen that H 2 O 2 The free radical clearance is lower than DPPH free radical clearance, but the pure PLA and each composite film have obvious difference (p is less than 0.05), so the antioxidation activity of the almond oil can be increased after the almond oil and the PLA are mixed and compounded.
Experimental example 8:
in the experiment, cherry tomatoes are taken as an example, the fresh-keeping effect of the pure PLA and almond oil/PLA composite film obtained in the examples 1-6 (namely, the test group) on the cherry tomatoes is tested, and meanwhile, a group of control group (CK) is added, and the cherry tomatoes in the group do not take any protective measures.
A) Sensory evaluation
The test uses 10 scores and 10 panelists with sensory evaluation experience perform sensory scores, the specific score details are shown in table 4.
TABLE 4 cherry tomato sensory evaluation criteria
FIG. 5 is a graph of the sensory scores of the CK and test groups of the present invention during storage. As shown in FIG. 5, with the increase of storage time, the sensory scores of the test group and the CK group gradually decrease, and the score of the almond oil/PLA composite film > pure PLA > CK group indicates that the almond oil can be added into the PLA to a certain degreeMaintaining freshness of cherry tomato, wherein AEKO/PLA is maintained during storage 0.6 、AEKO/PLA 0.8 、AEKO/PLA 1.0 The sensory score is relatively high, which indicates that certain content of almond oil plays a certain role in resisting oxidation in the film. AEKO/PLA at the end of storage 0.6 The highest score indicates that the almond oil/PLA film at the concentration can better maintain the freshness, the color, the taste and the like of the cherry tomatoes in storage.
B) Weightlessness
The fruits and vegetables contain a large amount of water, and have important significance for maintaining the appearance and quality of the fruits and vegetables. The loss of water is one of the most important reasons for the weight reduction of fruits and vegetables, and directly affects the texture and nutritional ingredients of the fruits and vegetables. FIG. 6 is a graph showing the change in weight loss during storage of the CK group and the test group of the present invention. The test is carried out by a weight method, and the calculation formula is as follows:
weight loss (%) = (mass before storage-mass after storage)/mass after storage
As shown in fig. 6, the weight loss rate of cherry tomatoes increases with the extension of the storage time, the weight loss rate of the test group is less than that of the CK group, which indicates that the transpiration and respiration of cherry tomatoes can cause water loss during the storage process to reduce the weight of fruits, and the film packaging can effectively inhibit the weight reduction to a certain extent, thereby achieving the fresh-keeping effect. Since the cherry tomatoes in the CK group have no protective measures, the free water loss is serious, and the weight loss rate of the CK group reaches 22.2% only on the 7 th day. At 21d storage, the weight loss rates of the test groups were, respectively, neatPLA 8.40%, AEKO/PLA 0.2 8.20％、AEKO/PLA 0.4 7.62％、AEKO/PLA 0.6 7.57％、AEKO/PLA 0.8 8.32％、AEKO/PLA 1.0 8.35%, the PLA film plays a certain role in fresh-keeping, and especially after the almond oil is added, the hydrophobicity of the almond oil can improve the water-blocking performance of the film and reduce the weight loss rate of cherry tomatoes.
C) Hardness of
Fruit firmness is related to fruit tissue structure and maturity, and the magnitude of the firmness value indirectly reflects the texture, sensory quality and nutritional composition of the fruit. The hardness of the fruits was measured in this test using GY-3. FIG. 7 is a graph showing the change in hardness during storage of the CK group and the test group of the present invention.
As shown in fig. 7, as the water of cherry tomatoes is lost during storage, the protopectin component is gradually decomposed, and the hardness of all the cherry tomatoes is reduced with the increase of the storage time. After 21d of storage, the hardness of cherry tomatoes was reduced from the initial 4.13kg/cm2 to a neatPLA of 1.50kg/cm, respectively 2 ，AEKO/PLA 0.2 1.53kg/cm 2 、AEKO/PLA 0.4 1.60kg/cm 2 、AEKO/PLA 0.6 2.00kg/cm 2 、AEKO/PLA 0.8 1.63kg/cm 2 、AEKO/PLA 1.0 1.83kg/cm 2 Except AEKO/PLA 0.6 Has a hardness of 2.00kg/cm 2 The rest groups are less than 2.00kg/cm 2 Description of AEKO/PLA 0.6 Can better maintain the freshness of cherry tomatoes and reduce the softening degree.
D) Decay index
The rotting rate is one of important indexes of sensory evaluation of fruits and vegetables, and reflects the rotting degree of the fruits and vegetables in the storage process. In the test, the occurrence of water stain-like lesions on the surface of the fruit is used as the judging basis of the rot of the fruit, and the fruit is classified into 6 grades, namely 0 grade according to the rot area of the fruit, and no rot exists; grade 1, fruit rotting area less than 25%;2, the rotten surface accounts for 25% -50% of the fruit area; grade 3, the rotting area is more than 50% -75% of the fruit area; grade 4, the decay area is more than 75%;5, completely rotting; FIG. 8 is a graph showing the change in decay during storage of the CK group and the test group of the present invention.
The decay index is calculated as follows:
as shown in FIG. 8, no decay phenomenon occurs in the CK group and the test group in 0-3 d; at 7d, 10% and 5% of rot phenomena occur in the CK group and the neatPLA respectively, and the rest groups have no rot phenomena; at 21d, the decay rate of CK group reaches 23%, the decay rate of neatPLA is 15%, AEKO/PLA 0.2 、AEKO/PLA 0.4 、AEKO/PLA 0.6 、AEKO/PLA 0.8 、AEKO/PLA 1.0 The decay rates of (2) were 12.5%, 10%, 5%, 7.5%, and AEKO/PLA, respectively 0.6 The decay rate of (C) was the lowest, indicating AEKO/PLA 0.6 Can better maintain the freshness of cherry tomatoes and reduce the decay rate.
E) Soluble Solids (TSS) assay
In the test, a proper amount of cherry tomatoes are weighed, crushed, ground and filtered to obtain juice, and then the juice is tested by an Abbe refractometer. As shown in FIG. 9, the TSS changes in both the CK group and the test group during storage were abruptly decreased at the initial stage of storage, and were slightly increased at 3d-14d, and decreased at the later stage.
The storage period is reduced because the cherry tomatoes can continuously consume the nutrient substance of the soluble sugar to provide the physiological activity for maintaining the physiological activity; the cherry tomatoes are of respiratory transition type fruits and vegetables, and the conversion of nutrients and accumulation of saccharides are continuously carried out in the after-ripening process, so that the soluble solids are in an ascending trend; the later storage period is reduced because the nutrient consumed for maintaining the breathing of the patient can be far larger than the nutrient accumulated by the patient, so the soluble solid matters also show a small reduction trend. Each almond oil/PLA film TSS is higher than pure PLA and CK groups and has a slow variation trend, wherein AEKO/PLA 0.6 Remains high during storage, indicating AEKO/PLA 0.6 Can better maintain TSS of cherry tomatoes and reduce nutrient consumption.
F) Determination of Titratable Acid (TA) content
TA is one of the important components constituting the flavor quality of fruits and vegetables, and nutrients of cherry tomatoes are not obtained from plants after picking, so that the nutrients must be consumed during storage to maintain the physiological activity. In the test, 1g of cherry tomatoes are chopped, distilled water is used for fixing the volume to 20mL, 1-2 drops of phenolphthalein indicator are dripped into the filtrate after filtration, 0.1mol/LNaOH is dripped into reddish color, the color is not faded within 30s, the volume (V) of consumed NaOH is recorded, and FIG. 10 is a graph showing the variation trend of TA during storage of the CK group and the test group of the invention.
The calculation method is as follows:
wherein: c is the concentration, mol/L of standard titration; v is the volume of NaOH standard solution consumed in calibration, mL; k is the conversion factor of the primary acid, i.e., 1 mmole of NaOH corresponds to the grams of the primary acid (malic acid is used as the conversion factor in this test); m is the sample weight.
Part of organic acid in cherry tomato is converted into saccharide, and the other part is used for respiratory consumption, so that the variation trend of TA in the storage process is shown in figure 10, and the overall descending trend is shown. After 21d storage, TA content was AEKO/PLA 0.6 ＞AEKO/PLA 0.4 ＞AEKO/PLA 0.2 ＝AEKO/PLA 0.8 ＞neatPLA＞AEKO/PLA 1.0 > CK, and AEKO/PLA 0.6 The change trend is slow in the whole storage process, and the fresh-keeping effect is better than that of other composite films.
G) Determination of vitamin C (Vc) content
The cherry tomatoes contain rich vitamins, and the vitamins are important indexes for measuring the nutritional value of fruits and vegetables. In the test, 5g of cherry tomatoes are weighed, 50mL of 2% oxalic acid solution is added, cherry tomatoes are ground into homogenate, filtrate is obtained by filtration, a filter cake can be washed for several times by a small amount of 2% oxalic acid solution, the filtrate is combined, after the volume of the filtrate is recorded, 4mL of 0.1mg/mL of filtrate is accurately sucked into a conical flask, 16mL of 1% oxalic acid solution is added, 2, 6-dichlorophenol indigo is used for titration until light red (the color in 15 does not fade, namely, the end point) is reached, the volume of the dye solution is recorded, and the amount of ascorbic acid which can be oxidized by 1mL of dye solution is calculated. Accurately sucking the sample extract, and operating the titration method in the same way as 2, and taking 20mL of oxalic acid as a blank control. Substituting the formula to calculate the content of the reduced ascorbic acid in 100g of the sample:
wherein: v (V) 1 Volume of dye consumed for titration of the sample, mL; v (V) 2 Volume of dye consumed for titration of blank, mL; v is the sample extractionTaking the total volume of the liquid; v (V) 3 For titration of the volume of sample taken; m is m 1 1mL of ascorbic acid, mg, capable of oxidizing the dye; m is m 2 To measure the weight of the sample g.
The vitamin in the fruits and vegetables is oxidized and decomposed along with the time and the stability of Vc, and fig. 11 is a graph showing the change trend of Vc in the CK group and the test group of the invention during storage.
As shown in FIG. 11, the CK group and the test group showed a tendency to gradually decrease during storage, and after 21d of storage, vc was contained in each almond oil/PLA film > pure PLA film > CK group, wherein AEKO/PLA 0.6 Maintains a high level throughout storage, indicating AEKO/PLA 0.6 Compared with other almond oil/PLA film, the fresh-keeping effect is better.
H) Determination of POD enzyme Activity
POD enzyme is one of enzymatic defense systems for protecting fruits and vegetables when they are forced.
(1) Preparation of enzyme extract: 3g cherry tomato is weighed in a mortar, 3mL of extracting solution (1 mMPEG, 4% PVPP and 1% Triton X-100) is added, the mixture is fully ground into slurry in an ice bath, the slurry is centrifuged at 4 ℃ for 30min at 1200r/min, and the supernatant is collected to obtain an enzyme extracting solution, and the enzyme extracting solution is preserved at a low temperature for standby.
(2) Enzyme activity measurement: 3mL of 25mmol guaiacol solution and 0.5mL of enzyme extract were added to the test tube, and finally 200. Mu.L of 0.5mol/LH was added 2 O 2 The enzyme reaction system was started rapidly after rapid mixing, and timing was started immediately. Pouring the reaction solution into a cuvette, placing into a spectrophotometer, and recording the reaction system at OD at 15s 470 The value is the initial value, then record every 60s, record at least 6 OD 470 Values were repeated three times.
(3) And (3) data processing: the absorbance value per 60s per gram fresh weight was increased by 0.01 to 1 POD enzyme activity unit, and the formula was calculated as follows:
wherein: ΔOD (delta OD) 470 The absorbance change value of the reaction mixed solution; Δt is the enzymatic reaction time; m is the mass of the sample, g;
v is the total volume of the sample extracting solution, and mL; vs is the volume of the sample extract taken at the time of measurement, mL.
FIG. 12 is a graph showing the change in POD activity during storage of the CK group and the test group of the present invention.
As shown in fig. 12, the overall enzyme change trend was a trend of rising first, then falling, and finally rising again. The POD is enhanced to protect the fruit and vegetable bodies because the cherry tomatoes are stressed by the surrounding environment after leaving the plant parent body in 0-3d, wherein the activity of each composite film is higher than that of pure PLA and CK groups, so that the activity of the slow-aging enzyme activity of the body is higher, and the fruit and vegetable bodies can be further and better protected; as fruits and vegetables gradually begin to age during 7-14d, enzyme activity begins to decrease, but AEKO/PLA compared to CK and test groups 0.6 Still at higher activity; fruit and vegetable are aged and POD catalyzed H in the end stage of storage for 14-21 days 2 O 2 The peroxide produced will damage the cell membrane, so the body remodelles the POD enzymatic defense system, and the POD activity will tend to increase in the later stage, but at this time AEKO/PLA 0.6 The enzyme activity is the lowest, thus indicating that the cherry tomato cytoplasmic membrane in the film packaging material is less damaged.
I) Assay of PPO enzyme Activity
In the aging process of after ripening or in the storage processing process after harvest, tissue browning of fruits and vegetables is closely related to polyphenol oxidase activity in tissues, so that the activity of PPO enzyme reflects the aging degree of fruits in the storage process to a certain extent.
(1) Preparation of enzyme extract: weighing 3g cherry tomato, placing in a mortar, adding 3mL of extract (1 mMPEG, 4% PVPP and 1% Triton X-100), sufficiently ice-bathing, grinding into slurry, centrifuging at 4deg.C and 1200r/min for 30min, collecting supernatant as enzyme extract, and preserving at low temperature for use.
(2) Enzyme activity measurement: into a test tube, 4.0mL of 50mmol acetic acid buffer solution, 1mL of 50mmol catechol solution and 100. Mu.L of enzyme extract were added in this orderTaking liquid, quickly mixing, quickly starting an enzyme reaction system, and immediately starting timing. Pouring the reaction solution into a cuvette, placing into a spectrophotometer, and recording the reaction system at OD at 15s 420 The value is the initial value, then record every 60s, record at least 6 OD 420 Values were repeated three times.
(3) And (3) data processing: the absorbance value per 60s per gram fresh weight was increased by 0.01 to 1 POD enzyme activity unit, and the formula was calculated as follows:
wherein: ΔOD (delta OD) 420 The absorbance change value of the reaction mixed solution; Δt is the enzymatic reaction time; v is the total volume of the sample extracting solution, and mL; vs is the volume of the sample extract, mL, measured; m is the mass of the sample and g.
FIG. 13 is a graph showing the change in PPO activity during storage of the CK group and the test group of the present invention.
As can be seen from fig. 13, the activity of PPO enzyme overall showed an upward trend, and PPO relatively slowly increased during the 0-7d storage period, since cherry tomatoes were relatively in a fresh stage in the early stage, cherry tomato pulp remained relatively low in PPO activity, and the aging-starting PPO activity of cherry tomatoes gradually began to rapidly increase with the lapse of time. CK group PPO was always at higher activity than test group during the whole storage period, AEKO/PLA 0.6 The enzyme activity was the lowest and remained in a slower rising trend, indicating that the package could be kept fresh.
J) Determination of Malondialdehyde (MDA) content
In the aging process of post maturation of fruit and vegetable tissues or in the process of diseases, cold injury or other injury of cells, superoxide anion free radicals and hydroxyl free radicals generated by the fruit and vegetable tissues can induce unsaturated acid in membrane lipid to prevent peroxidation and generate lipid free radicals. Lipid radicals can further induce peroxidation of membrane lipids leading to increased cell membrane permeability, cell damage or death. Wherein MDA is one of the main products of lipid peroxidation, the degree of loss of cells can be reflected by measuring the MAD content.
(1) Preparation of the extract: 1.0g cherry tomato sample is weighed, 5mL10% trichloroacetic acid is added, the mixture is ground into homogenate, the mixture is centrifuged for 20min at 10000r/min at 4 ℃, and the supernatant is collected and stored at a low temperature for standby.
(2) Determination of MDA content: 2mL of the supernatant and 0.67% thiobarbituric acid were added to the tube, mixed, heated in a boiling water bath for 20min, cooled and centrifuged once more, and absorbance values of the supernatant were measured at 450nm, 532nm and 600nm, respectively. Repeated three times.
(3) And (3) data processing: the MDA content per gram of cherry tomato is calculated according to the absorbance value and expressed in mu mol/g. The calculation formula is as follows:
wherein: c is MDA content in the reaction mixture, and mu mol/L; v is the total volume of the sample extracting solution, and mL; vs is the volume of the sample extract, mL, measured; m is the mass of the sample and g.
FIG. 14 is a graph showing MDA change trend during storage of the CK group and the test group of the present invention.
As can be seen from fig. 14, the MDA content is always in an upward trend during the whole storage period, the CK group is most obviously increased during the first 7d period, and the MDA content is still continuously increased after 7d period, because as the fruits continuously breathe, the active oxygen free radicals are continuously increased, so that the active oxygen in the fruits continuously accumulate, lipid peroxidation reaction is promoted in the fruits, and the MDA content is continuously increased. As can be seen from the figure, AEKO/PLA throughout storage 0.6 The MDA content of the cherry tomato always keeps a slower rising trend, which indicates that the cherry tomato cells are less damaged under the packaging condition.
As can be seen from the above experimental examples 1 to 7, the results of the properties of the different amounts of the apricot kernel oil added are also different, the mechanical strength of the polylactic acid is not significantly improved but the elongation at break is significantly improved, and the water vapor barrier property is also improved (wherein AEKO/PLA 0.6 Water vapor barrier propertiesMost preferably; meanwhile, the addition of the almond oil has no influence on the chemical structure of the polylactic acid, but the surface of the PLA film becomes uneven along with the increase of the content of the almond oil, so that the AEKO/PLA is considered in the comprehensive view 0.6 The film has the best performance effect, so experimental example 8 is further verified, and the result shows that the AEKO/PLA is really effective in the fresh-keeping performance of the cherry tomatoes 0.6 Can maintain good nutritional quality of cherry tomato.
While several embodiments of the invention have been described, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments may be implemented in various other ways, and various omissions, substitutions, and changes may be made without departing from the scope of the invention. Such embodiments and modifications are included in the scope and spirit of the invention, and are included in the invention described in the claims and their equivalents.
Claims (9)
1. The preparation method of the degradable almond oil/polylactic acid film is characterized by comprising the following steps of:
(1) Extraction of apricot kernel oil
Cleaning semen Armeniacae amarum with running water, drying, pulverizing into powder, weighing appropriate amount of semen Armeniacae amarum coarse powder, placing into an extraction tube, adding n-hexane solution into an extraction bottle, refluxing in a Soxhlet extractor, placing the solution into a rotary evaporator after finishing, evaporating solvent to obtain oleum Armeniacae amarum, and storing in a refrigerator;
(2) Preparation of almond oil/polylactic acid film
Weighing 2g of polylactic acid in a beaker, adding 30mL of chloroform solution, stirring on a magnetic stirrer, adding the almond oil obtained in the step (1) into the beaker according to the mass ratio of the almond oil to the polylactic acid of 0.2-1:1 after the solution is uniformly stirred, stirring the beaker in the magnetic stirrer, performing ultrasonic extraction after stirring, centrifuging, finally pouring the solution into a container, drying at a ventilation position, and tearing off to form a film.
2. The method for preparing a degradable almond oil/polylactic acid film according to claim 1, wherein the solution in the step (2) is sealed by a preservative film in the stirring process.
3. The method for preparing the degradable almond oil/polylactic acid film according to claim 1, wherein the mass ratio of the almond oil to the polylactic acid in the film preparation process is 0.2:1 adding almond oil.
4. The method for preparing the degradable almond oil/polylactic acid film according to claim 1, wherein the mass ratio of the almond oil to the polylactic acid in the film preparation process is 0.4:1 adding almond oil.
5. The method for preparing the degradable almond oil/polylactic acid film according to claim 1, wherein the mass ratio of the almond oil to the polylactic acid in the film preparation process is 0.6:1 adding almond oil.
6. The method for preparing the degradable almond oil/polylactic acid film according to claim 1, wherein the mass ratio of the almond oil to the polylactic acid in the film preparation process is 0.8:1 adding almond oil.
7. The method for preparing the degradable almond oil/polylactic acid film according to claim 1, wherein the almond oil is added in the mass ratio of the almond oil to the polylactic acid of 1:1 in the preparation process of the film.
8. The degradable almond oil/polylactic acid film is characterized by being prepared by the preparation method of the degradable almond oil/polylactic acid film according to any one of claims 1-7.
9. The application of the degradable almond oil/polylactic acid film is characterized in that the degradable almond oil/polylactic acid film disclosed in claim 8 is used for fresh-keeping storage of fruits and vegetables.
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| CN109294191A (en) * | 2018-09-29 | 2019-02-01 | 安徽大力熊环保塑料科技有限公司 | A method of addition Ginkgo biloba polysaccharide-Fructus Perillae quintessence oil microcapsules prepare compound degradable Antimicrobial preservative food product packing film |
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