CN112724435A - 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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- CN112724435A CN112724435A CN202011595200.8A CN202011595200A CN112724435A CN 112724435 A CN112724435 A CN 112724435A CN 202011595200 A CN202011595200 A CN 202011595200A CN 112724435 A CN112724435 A CN 112724435A
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- almond oil
- polylactic acid
- film
- pla
- degradable
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Images
Classifications
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- 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
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- 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
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- 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 the apricot kernel oil, crushing the apricot kernels, drying for later use, weighing a proper amount of coarse almond powder, placing the coarse almond powder into an extraction tube, adding a normal hexane solution into an extraction bottle, refluxing in a soxhlet extractor, placing the solution into a rotary evaporator after the reflux is finished, evaporating the solvent to obtain the apricot kernel oil, and storing the apricot kernel oil in a refrigerator for later use; secondly, preparing the almond oil/polylactic acid film, mixing polylactic acid, trichloromethane solution and almond oil, stirring, ultrasonically extracting, 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, endows the film with certain antioxidant activity, and is 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 people are non-degradable petroleum-based plastics, but the environmental problem caused by the non-degradability of the packaging materials causes people to think again how to solve the troublesome problem. Therefore, researchers gradually focus on biodegradable materials, and the performance of the modified biomaterial is comparable to that of the traditional material, so that the modified biomaterial is expected to be a substitute of a non-degradable material.
Polylactic acid is a biodegradable material prepared by fermenting plant resources widely existing in the nature into lactic acid and polymerizing the lactic acid. The polylactic acid material can be subjected to self-degradation in nature after being discarded, and cannot cause any burden to the environment, so that the polylactic acid material is a well-known safe and environment-friendly biopolymer material. Polylactic acid also has the characteristics of biocompatibility and ease of processing. The method is widely applied to the fields of packaging, biomedicine and the like. However, the polylactic acid film has the defects of high brittleness and low water vapor barrier performance, and the application of the polylactic acid film in the packaging industry is limited.
The almond oil has strong antioxidant activity, but is limited in application due to the influence of hydrophobicity and high volatility, and can be added into a PLA film matrix as an active substance, so that the loss of the almond oil can be reduced, a biological film also has antioxidant property, and in addition, the hydrophobicity of the almond oil can reduce the contact chance of water molecules on the surface of a polylactic acid film, thereby improving the water vapor barrier property of the almond oil. However, the wild apricot seeds are often used as a waste material, but if the almond oil is extracted from the wild apricot seeds, the concept of changing waste into valuable and fully utilizing the crop waste is undoubtedly provided, and the strategy of the current sustainable development is completely met.
According to the invention, the almond oil extracted from the apricot kernel is blended with the polylactic acid to prepare the degradable plastic film, the high performance of the polylactic acid and the antioxidant activity of the almond oil are integrated, the traditional petroleum-based plastic can be partially replaced, the defects of the single polylactic acid are overcome, the application range of the polylactic acid is widened, meanwhile, the apricot seed waste is fully utilized, the cost is saved, the important economic and environmental protection significance is achieved, and a thought is provided for developing a new 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, endow the film with certain antioxidant activity and are ideal degradable packaging materials.
In order to achieve the above purpose, the solution of the invention is: a preparation method of a degradable almond oil polylactic acid film comprises the following steps:
(1) extraction of mountain apricot kernel oil
Cleaning wild apricot kernels with running water, drying, pulverizing into powder for later use, weighing a proper amount of coarse almond powder, placing the coarse almond powder into an extraction tube, adding a normal hexane solution into an extraction bottle, refluxing in a soxhlet extractor, placing the solution into a rotary evaporator after the reflux is finished, evaporating the solvent to obtain almond oil, and storing the almond oil in a refrigerator for later use;
(2) preparation of almond oil/polylactic acid film
Weighing 2g of polylactic acid in a beaker, adding 30mL of trichloromethane 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 in a ventilated place, and tearing off to form a film.
Preferably, the solution in the step (2) is sealed by a preservative film during stirring.
Preferably, the mass ratio of the almond oil to the polylactic acid in the preparation process of the film is 0.2: 1 adding almond oil.
Preferably, the almond oil is added into the film in a mass ratio of 0.4:1 of the almond oil to the polylactic acid in the preparation process of the film.
Preferably, the almond oil is added into the film in a mass ratio of 0.6:1 of the almond oil to the polylactic acid in the preparation process of the film.
Preferably, the almond oil is added into the film in a mass ratio of 0.8:1 of the almond oil to the polylactic acid in the preparation process of the film.
Preferably, the almond oil is added into the film in a mass ratio of the almond oil to the polylactic acid of 1: 1.
The invention also provides an 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:
the method selects green and environment-friendly polylactic acid and wild almond as raw materials, and utilizes the principle of solvent reflux and siphon to extract wild almond oil by a cable extractor, so that the coarse powder of the wild almond is continuously extracted by normal hexane solution to obtain the purified wild almond; 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 keeps the high performances of biodegradability and the like of the polylactic acid, but also improves the flexibility and the water vapor barrier property.
From the experimental data of DSC, as the content of the almond oil increases, Tg becomes smaller, which shows that the temperature at which molecular chains need to change is reduced, the flexibility of the film is improved, and TC, Tm and the crystallinity are all reduced compared with pure polylactic acid, which shows that the addition of the almond oil only plays a role in plasticization because the almond oil can form easily deformable oil drops in a PLA gel matrix to play a role in plasticization, but does not play a role in improving the crystallinity; the reason why the water vapor barrier property is improved is that the almond oil itself has hydrophobicity, and the contact of water vapor with the film is reduced, so that the water vapor is blocked.
In addition, the experimental data of free radical scavenging show that the almond oil also endows the film with certain antioxidant activity, overcomes the defects of single polylactic acid and widens the application range of the polylactic acid.
The preparation method is simple and feasible, the prepared almond oil/polylactic acid film belongs to food grade, has good toughness and degradability, has good water vapor permeability, can prolong the storage life of foods such as fruits and vegetables and the like as a fresh-keeping packaging material, has better toughness than the existing fresh-keeping film, and is an ideal green packaging material.
Drawings
FIG. 1 is an SEM image of pure polylactic acid and almond oil/polylactic acid films of different concentrations according to the present invention;
FIG. 2 is a FTIR plot of pure polylactic acid and varying concentrations of almond oil/polylactic acid films in accordance with the present invention;
FIG. 3 is a DSC of pure polylactic acid and varying concentrations of almond oil/polylactic acid films in accordance with the present invention;
FIG. 4 is a bar graph of DPPH, H2O2 radical clearance rates for pure polylactic acid and varying concentrations of almond oil/polylactic acid films in accordance with the present invention;
FIG. 5 is a graph of sensory scores of the CK group and the test group of the present invention during storage;
FIG. 6 is a graph showing the tendency of weight loss during storage in the CK group and the test group according to the present invention;
FIG. 7 is a graph showing the trend of hardness change during storage in the CK group and the test group according to the present invention;
FIG. 8 is a graph showing the decay tendency of the CK group and the test group during storage according to the present invention;
FIG. 9 is a graph showing the trend of TSS during storage in the CK group and the test group according to the present invention;
FIG. 10 is a graph showing the trend of TA changes during storage in the CK group and the test group according to the present invention;
FIG. 11 is a graph showing the trend of Vc during storage in the CK group and the test group according to the present invention;
FIG. 12 is a graph showing the POD activity profiles during storage in the CK group and the test group according to the present invention;
FIG. 13 is a graph showing the trend of the change in PPO activity during storage in the CK group and the test group according to the present invention;
FIG. 14 is a graph showing the trend of MDA changes during storage in the CK group and the test group according to the present invention.
Detailed Description
The invention relates to a degradable almond oil/polylactic acid film which can be applied to the fresh-keeping storage of various fruits and vegetables. For convenience of description, the almond oil/polylactic acid film prepared by the preparation method of the present invention is used for fresh-keeping storage of cherry tomatoes as an example. However, the present invention is not limited thereto, and the almond oil/polylactic acid film of the present invention can be used in packaging fruits and vegetables as far as it is concerned with the preservation of fruits and vegetables, such as storage, transportation, and the like.
The preparation method of the almond oil/polylactic acid film provided by the invention comprises the following two steps: firstly, the apricot kernel oil is extracted from apricot kernels by a soxhlet extraction method, wherein the soxhlet extractor comprises an extraction bottle, an extraction pipe and a condensation pipe, a siphon pipe and a connecting pipe are respectively arranged on two sides of the extraction pipe, the joint of each part is tight and airtight, solid substances are continuously extracted by pure solvents by utilizing the principles of solvent backflow and siphon, and the solvent is saved, and the extraction efficiency is high; secondly, the almond oil/polylactic acid composite membrane is prepared by adopting a solvent volatilization method.
The method comprises the following specific steps:
(1) extraction of mountain apricot kernel oil
S1, crushing: cleaning wild apricot kernels with running water, drying at room temperature, and pulverizing the wild apricot kernels into powder by a pulverizer to increase the solid-liquid contact area;
s2, extracting: manufacturing a cylindrical filter paper cylinder by using filter paper, weighing 15g of the coarse almond powder obtained in the step S1, filling the coarse almond powder into the filter paper cylinder, folding and sealing the opening end, and putting the filter paper cylinder into an extraction tube;
accurately measuring 100ml of n-hexane solution, placing the n-hexane solution in an extraction bottle, connecting the lower end of the extraction tube with the extraction bottle containing the n-hexane solution, connecting the upper end of the extraction tube with a condenser tube, introducing condensed water into the condenser tube, heating the extraction bottle to 80 ℃ to boil the n-hexane solution, gasifying the n-hexane solution, lifting the n-hexane solution into the condenser tube through a connecting tube, condensing the condensed n-hexane solution into liquid, dripping the liquid into the extraction tube, extracting coarse almond powder by using the n-hexane solution, flowing the n-hexane solution containing almond oil into the extraction bottle through the siphon tube when the liquid level of the n-hexane solution in the extraction tube reaches the highest position of the siphon tube, continuously heating, gasifying, lifting and condensing the n-hexane solution flowing into the extraction bottle, dripping the heated, gasified, lifted and condensed into the extraction tube, repeating the steps repeatedly, and refluxing for 12 hours, obtaining purified almond oil n-hexane solution;
putting 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 the almond oil, and placing the almond oil in a refrigerator at 4 ℃ for later use.
The extraction and purification of the almond oil achieves the purposes of extraction and separation by utilizing the solvent with high solubility to the required components in the solid mixture and low solubility to impurities.
(2) Preparation of almond oil/polylactic acid film
S1, weighing 2g of polylactic acid in a beaker, adding 30mL of trichloromethane solution, placing on a magnetic stirrer, and fully stirring for 1h at 25 ℃ and at the rotating speed of 5000 r/min;
s2, after the solution is uniformly stirred, mixing the almond oil and the polylactic acid according to the mass ratio of 0: 1-1: 1, putting the almond oil obtained in the step (1) into a beaker, putting the beaker on a magnetic stirrer, and fully stirring for 7 hours at the temperature of 25 ℃ and the rotating speed of 5000 r/min;
s3, after stirring, carrying out ultrasonic auxiliary extraction for 10min, and then centrifuging for 5min at the rotation speed of the centrifuge of 8000 r/min;
s4, pouring the solution into a polytetrafluoroethylene plate with 20cm of gamma and 20cm of gamma, drying for 12 hours at normal temperature in a ventilated place, and tearing off to form the film.
In order to avoid experimental errors caused by volatilization of trichloromethane, the beaker needs to be sealed by a preservative film in the whole stirring process.
The present invention will be described in detail below with reference to specific examples.
Example 1:
weighing 2g of polylactic acid in a beaker, adding 30mL of trichloromethane solution, then placing the beaker on a magnetic stirrer, fully stirring for 8h at 25 ℃ and the rotation speed of 5000r/min, after stirring, carrying out ultrasonic-assisted extraction for 10min, then centrifuging for 5min at the rotation speed of 8000r/min by a centrifuge, finally pouring the solution into a polytetrafluoroethylene plate of 20cm x 20cm, drying for 12h at normal temperature in a ventilated place, and tearing off to obtain a coatPLA film as a blank control.
Example 2:
weighing 2g of polylactic acid in a beaker, adding 30mL of chloroform solution, then 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) with the polylactic acid according to the mass ratio of 0.2: 1 adding into a beaker, placing the beaker on a magnetic stirrer, fully stirring for 7h at 25 ℃ and at the rotating speed of 5000r/min, performing ultrasonic-assisted extraction for 10min after stirring, centrifuging for 5min at the rotating speed of 8000r/min by a centrifuge, finally pouring the solution into a polytetrafluoroethylene plate of 20cm x 20cm, drying at normal temperature for 12h in a ventilated place, tearing off to obtain an almond oil/PLA composite membrane marked as AKEO/PLA0.2。
Example 3:
weighing 2g of polylactic acid in a beaker, adding 30mL of chloroform solution, then 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) with the polylactic acid according to the mass ratio of 0.4:1 adding into a beaker, placing the beaker on a magnetic stirrer, stirring for 7h at 25 deg.C and 5000r/min, ultrasonic-assisted extracting for 10min, centrifuging at 8000r/min for 5min, and pouring the solution into a container with a volume of 20cDrying at room temperature for 12 hr in Teflon plate with gamma of 20cm, and tearing to obtain almond oil/PLA composite membrane labeled AKEO/PLA0.4。
Example 4:
weighing 2g of polylactic acid in a beaker, adding 30mL of chloroform solution, then 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) with the polylactic acid according to the mass ratio of 0.6:1 adding into a beaker, placing the beaker on a magnetic stirrer, fully stirring for 7h at 25 ℃ and at the rotating speed of 5000r/min, performing ultrasonic-assisted extraction for 10min after stirring, centrifuging for 5min at the rotating speed of 8000r/min by a centrifuge, finally pouring the solution into a polytetrafluoroethylene plate of 20cm x 20cm, drying at normal temperature for 12h in a ventilated place, tearing off to obtain an almond oil/PLA composite membrane marked as AKEO/PLA0.6。
Example 5:
weighing 2g of polylactic acid in a beaker, adding 30mL of chloroform solution, then 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) with the polylactic acid according to the mass ratio of 0.8:1 adding into a beaker, placing the beaker on a magnetic stirrer, fully stirring for 7h at 25 ℃ and at the rotating speed of 5000r/min, performing ultrasonic-assisted extraction for 10min after stirring, centrifuging for 5min at the rotating speed of 8000r/min by a centrifuge, finally pouring the solution into a polytetrafluoroethylene plate of 20cm x 20cm, drying at normal temperature for 12h in a ventilated place, tearing off to obtain an almond oil/PLA composite membrane marked as AKEO/PLA0.8。
Example 6:
weighing 2g of polylactic acid in a beaker, adding 30mL of chloroform solution, then placing the beaker on a magnetic stirrer, fully stirring for 1h at 25 ℃ and at the rotating speed of 5000r/min, and after the solution is uniformly stirred, mixing the almond oil obtained in the step (1) with the polylactic acid according to the mass ratio of 1:1, placing the beaker on a magnetic stirrer, fully stirring for 7 hours at the temperature of 25 ℃ and the rotating speed of 5000r/min, after stirring,extracting with ultrasound for 10min, centrifuging at 8000r/min for 5min, pouring the solution into a polytetrafluoroethylene plate of 20cm x 20cm, drying at normal temperature in ventilated place for 12 hr, and tearing to obtain almond oil/PLA composite membrane labeled AKEO/PLA1.0。
Preferred embodiments of the present invention will be described below with reference to the accompanying drawings and the above-described examples.
Experimental example 1:
this example shows the film surface observation of the pure PLA, almond oil/PLA composite films obtained in examples 1 to 6. Before the experiment, each composite film is dried for 12 hours in vacuum at 50 ℃, then each composite film is cut into a slender square strip with the width of about 2mm, a thin layer of gold or platinum is sprayed on the surface of a sample by an ion sputtering instrument, the sample after the gold spraying is sent to a sample chamber along with a sample table, and then the surface of the film can be observed. FIG. 1 is an SEM image of pure polylactic acid and almond oil/polylactic acid films of different concentrations according to the present invention.
As shown in FIG. 1, wherein a) neatPLA, b) AKEO/PLA0.2、c)AKEO/PLA0.4、d)AKEO/PLA0.6E) and f) AKEO/PLA0.8G) and h) AKEO/PLA1.0From the figure, it can be seen that AKEO/PLA0.2、AKEO/PLA0.4、AKEO/PLA0.6The three almond oil/PLA composite films have no great difference with the PLA film in surface appearance, are relatively flat, which shows that the almond oil and the polylactic acid are well fused, and have no great influence on the PLA film surface appearance, while the AKEO/PLA composite films have the advantages of good fusion performance, good surface appearance, good surface0.8、AKEO/PLA1.0The surfaces of the two almond oil/PLA composite films are rough because the almond oil passes through the PLA film in the volatilization process during the drying process to cause rough and uneven surfaces of the films.
Experimental example 2:
this example was conducted by subjecting pure PLA and almond oil/PLA composite films obtained in examples 1 to 6 to an infrared spectroscopic experiment. Before the experiment, each film is cut into a square with 2cm gamma and 2cm and placed in an infrared spectrometer, the molecular structure components of the sample are analyzed, after an air background atlas 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 isFTIR profiles of pure polylactic acid and varying concentrations of almond oil/polylactic acid films of the present invention, wherein a) neatPLA, b) AKEO/PLA0.2、c)AKEO/PLA0.4、d)AKEO/PLA0.6、e)AKEO/PLA0.8、f)AKEO/PLA1.0。
As shown in FIG. 2, the neatPLA was at about 3480cm-1Has a weaker absorption peak, which indicates that a small amount of-OH exists, 3000cm-1Is the stretching vibration of-CH-in the PLA structure, 1760cm-1Is characterized by-C ═ O stretching vibration, 1460cm-1、1380cm-1Is in-CH-bending vibration, 1200cm-1、1100cm-1about-C-O-stretching vibration of 870cm-1Is a-C-C-stretching vibration. The absorption peak of the almond oil/PLA composite membrane is 3500cm-1～3400cm-1Nearby weak absorption peaks of-OH and-NH stretching vibration at 3000cm-1～2800cm-1Is in-CH-telescopic vibration, 1750cm-1The neighborhood is the characteristic peak of ester carbonyl (-C ═ O stretching vibration), and the peak at this position shifts to a smaller wave number with the increase of the content of almond oil, which may occur because the almond oil is complexed with PLA to cause the PLA conformation to change and the molecular order to change. 1460cm-1、1380cm-1near-CH-bending vibration, 1250-1000 cm-1Nearby is-C-O-telescopic vibration of 870cm-1near-C-C-stretching vibration, the spectrum shows that the pure PLA film is basically consistent with the infrared spectrum characteristic bands of other five groups of almond oil/PLA films, which shows that the active almond oil has no obvious influence on the chemical structure of the film.
Example 3:
in this experimental example, mechanical properties of the pure PLA and almond oil/PLA composite films obtained in examples 1 to 6 were tested, using GB/T1040.3-2006 as a standard, cutting a sample film into rectangular sample strips of 100 × 15mm with a cutting knife, an initial distance between clamps of 100mm, a gauge length of 50mm, a tensile speed of 20mm/min, and environmental conditions of temperature (23 ± 2) ° c and relative humidity (50 ± 5)%, measuring tensile strength and elongation at break of the composite film, testing 3 parallel samples per group to reduce errors, recording tensile strength and elongation at break of the samples during each test, and averaging. And analyzing the stress change degree according to the average value. The thickness of the composite film was measured by a micrometer screw, and the thickness of the composite film in the center position and four corner directions was randomly measured, and the average value thereof was taken as shown in table 1.
Table 1 shows the mechanical properties of the pure PLA and almond oil/PLA composite films of examples 1-6
*. the level of significance of the difference in mean values was 0.05.
It can be seen from table 1 that the addition of almond oil increases the elongation at break of PLA films, and there is a significant difference (P < 0.05) between pure PLA and each almond oil/PLA composite film; and the tensile strength and the elastic modulus both decrease with the increase of the content of the almond oil. In tensile strength, there is a significant difference (P < 0.05) between pure PLA and the respective almond oil/PLA composite films, but almond oil/PLA0.6With almond oil/PLA0.8The difference between the two is not significant (P is more than 0.05); in addition to almond oil/PLA, pure PLA has an elastic modulus0.2The composite membrane has no significant difference with other composite membranes (P is less than 0.05).
Example 4:
this example performs DSC tests 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 membrane sample, packaging in a crucible, heating from room temperature to 210 ℃ at a speed of 10 ℃/min under a nitrogen atmosphere with a gas flow rate of 50mL/min, keeping the temperature for 5min to eliminate heat history, then cooling to room temperature at the same speed, heating for the second time to 210 ℃, and recording the change of enthalpy change along with temperature during the second heating, as shown in Table 2. The crystallinity of the material is calculated as follows:
in the formula: Δ Hm is the melting enthalpy of the material; the Delta Hm0 is the enthalpy value of the polylactic acid at 100% crystallization of 93.6J/g.
TABLE 2 thermal Properties of pure PLA and Almond oil/PLA composite films
FIG. 3 is a DSC of pure polylactic acid and almond oil/polylactic acid films of varying concentrations according to the present invention. Combining table 2 and fig. 3, it can be seen that Tg becomes smaller as the almond oil content increases, indicating that the temperature at which the molecular chain starts to change is decreased, demonstrating that the film flexibility is improved. The Tc is respectively reduced from 110.21 ℃ of pure PLA to 107.01 ℃, 109.68 ℃, 109.68 ℃, 109.50 ℃ and 109.91 ℃ of the almond oil/PLA composite membrane. Compared with pure PLA, Tm168.26 ℃ of the almond oil/PLA composite film is reduced to a minimum value of 166.91 ℃, which further shows that the almond oil improves the mobility of PLA molecules to play a role in plasticization, so that the temperature is shifted to a low temperature. This is attributed to the dispersion of almond oil into the PLA structure, which can form easily deformable oil droplets in the PLA gel matrix to plasticize. However, the crystallinity of the almond oil/PLA composite film is also reduced compared with that of pure PLA, which indicates that the almond oil cannot improve the crystallinity of the PLA.
Example 5:
in this example, the opacity and water vapor permeability of the pure PLA and almond oil/PLA composite films obtained in examples 1 to 6 were measured by gravimetric method. The experiment utilizes anhydrous calcium chloride to adsorb moisture, and the water vapor transmission coefficient (WVP) is determined by the weight gain of the anhydrous calcium chloride. First, 1g of dry anhydrous calcium chloride was put into a bottle having an inner diameter of 120mm and a used area of 113.04mm2The film was sealed and then placed in a 25 ℃ drying cabinet containing saturated NaCl to ensure 75% relative humidity, anhydrous calcium chloride in the cup to ensure 0% humidity, and the amount of water vapor absorbed through the film was measured every 12 hours for each container, as shown in Table 3. The specific calculation formula is as follows:
in the formula: Δ m is the mass increase, g, over time t; l is the film thickness, m; a is effective area, mm 2; t is the interval time of two times after the quality is stable, h; and delta P is the difference between the water vapor pressure inside and outside the cup. Note: saturated vapor pressure of water 3170Pa at 25 ℃.
In addition, the sample was cut into a rectangle and placed in a cuvette for blank control (nothing). Absorbance at 600nm was measured and the average was taken 3 times per set of measurements as shown in Table 3. The calculation formula is as follows:
in the formula: a. the600Is the absorbance at 600 nm; d is the thickness mm of the film.
TABLE 3 opacity values and WVP values of pure PLA and Almond oil/PLA composite films
As can be seen from Table 3, the WVP of pure PLA reached 1.34. + -. 0.05 x 10-9 g.m/h.pa.m2As almond oil increases, the WVP value gradually decreases and there is a significant difference (p < 0.05) from pure PLA because the hydrophobicity of almond oil reduces the chance of water vapor coming into contact with the film, blocking it out; AKEO/PLA0.8WVP is increased to 2.60 + -0.04 x 10 compared with other composite membranes-9g·m/h·pa·m2Possibly due to the fact that almond oil volatilizes to form uneven holes on the surface of the film. With the further increase of the content of the almond oil, AKEO/PLA1.0With AKEO/PLA0.8There was no significant difference (p > 0.05).
In addition, the opacity of each almond oil/PLA composite film is obviously reduced compared with pure PLA (p is less than 0.05), and when the mass ratio of the almond oil to the polylactic acid is 0.6: at 1, there was no significant difference in further increasing the opacity of almond oil (p > 0.05).
Example 6:
almond oil is a natural antioxidant, and when combined with a film, the antioxidant function of the almond oil does not disappear, and in order to verify the influence of adding almond oil/polylactic acid films with different concentrations on the antioxidant performance, the experimental example tests the antioxidant performance of the pure PLA and the almond oil/PLA composite film obtained in the examples 1-6.
(1) DPPH radical scavenging test
Firstly, preparing 0.1mM DPPH solution, accurately weighing 3.9mg DPPH, fixing the volume to 100mL in a brown bottle by using absolute ethyl alcohol, shaking up, storing in dark at room temperature, and preparing for use on site; then preparing composite membrane extract, respectively weighing 500mg of neatpLA and AKEO/PLA0.2、AKEO/PLA0.4、AKEO/PLA0.6、AKEO/PLA0.8、AKEO/PLA1.0Dissolving in 15mL of absolute ethanol solution, performing ultrasonic treatment for 2h, and centrifuging at 8000r/min for 20min to mix completely; and finally, mixing 2mL of composite membrane extracting solution and 2mL of PPH solution, placing the mixture at room temperature in a dark place for incubation for 1h, repeatedly measuring the absorbance at 517nm for three times, and taking the average value +/-standard deviation. The inhibition rate was calculated by the formula:
I(％)＝[1-(Asample/ADPPH)]×100％
in the formula: i is the inhibition rate; a. thesampleIs DPPH solution containing membrane extract; a. theDPPHIs a DPPH solution without membrane extract.
(2)H2O2Free radical scavenging test
First, 0.1% H was prepared2O2Accurately measuring the stock solution to obtain 0.333mLH2O2Adding phosphoric acid buffer solution with pH of 7.4 to 100mL, preparing, and preparing composite membrane extractive solution (the same procedure as above) by weighing 500mg of neatpLA and AKEO/PLA respectively0.2、AKEO/PLA0.4、AKEO/PLA0.6、AKEO/PLA0.8、AKEO/PLA1.0Dissolving in 15mL of absolute ethanol solution, performing ultrasonic treatment for 2h, and centrifuging at 8000r/min for 20 min. Finally taking 1mL of composite membrane extract and 1mLH2O21mL of phenanthroline solution, 1mL of LFeSO4The mixture was incubated at room temperature in the dark for 30min and the absorbance at 230nm was measured (triplicate). H of sample liquid without film2O2The mixture was used as a blank and the absorbance at 230nm was measured (in triplicate). The mixed solution without membrane sample solution (1mL of absolute ethanol instead) was used as a blank. The inhibition rate was calculated by the formula:
I(％)＝[1-(Asample/ADPPH)]×100％
in the formula: i is the inhibition rate; asampe is H containing membrane solution2O2Absorbance of the solution mixture; ADPPH is H without membrane liquid2O2Absorbance of the solution mixture.
FIG. 4 is a bar graph of DPPH, H2O2 radical scavenging rates of pure polylactic acid and almond oil/polylactic acid films of different concentrations of the present invention, wherein 1-6 correspond to neat PLA, AKEO/PLA, respectively0.2、AKEO/PLA0.4、AKEO/PLA0.6、AKEO/PLA0.8、AKEO/PLA1.0Along with the increase of the concentration of almond oil, the DPPH free radical clearance rate of the composite membrane shows an increasing trend, which is increased from 0 percent of pure PLA to 24.20 percent, and the minimum concentration of AEKO/PLA0.2The antioxidant 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 the composite films of each sample and pure PLA. From FIG. 4, it can be seen that H2O2The clearance rate of free radicals is lower than that of DPPH free radicals, but the clearance rate of pure PLA and each composite membrane still has obvious difference (p is less than 0.05), so that the antioxidant activity of the almond oil can be increased after the almond oil and the PLA are blended and compounded.
Experimental example 8:
the experiment takes cherry tomatoes as an example, the fresh-keeping effect of the pure PLA and the almond oil/PLA composite film (namely, a test group) obtained in the examples 1 to 6 on the cherry tomatoes is tested, and a group of control group (CK) is added, wherein the cherry tomatoes in the group do not have any protection measures.
A) Sensory evaluation
The test was conducted by using 10-point scale, and sensory evaluation was conducted by 10 evaluators having sensory evaluation experience, and the detailed evaluation was shown in table 4.
TABLE 4 cherry tomato sensory evaluation criteria
Fig. 5 is a graph of sensory scores of the CK groups and the test groups of the present invention during storage. As shown in figure 5, the sensory scores of the test group and the CK group are gradually reduced along with the prolonging of the storage time, the scores are respectively almond oil/PLA composite film > pure PLA > CK group, and the almond oil is added into the PLA to maintain the freshness of the cherry tomatoes to a certain degree, wherein the AEKO/PLA is kept during the whole storage period0.6、AEKO/PLA0.8、AEKO/PLA1.0The sensory score is relatively high, which shows that the almond oil with a certain content has a certain antioxidation effect in the film. AEKO/PLA at the end of storage0.6The highest score indicates that the almond oil/PLA film at this concentration can better maintain freshness, color, mouthfeel, etc. in the stored cherry tomatoes.
B) Weight loss
The fruits and vegetables contain a large amount of water, and have important significance for maintaining the appearance and the quality of the fruits and vegetables. The loss of water is one of the most important reasons for reducing the weight of the fruits and vegetables, and directly influences the texture and the nutritional ingredients of the fruits and vegetables. Fig. 6 is a graph showing the tendency of weight loss during storage in the CK group and the test group according to the present invention. The test is carried out by a gravimetric method, and the calculation formula is as follows:
weight loss ratio (%) - (mass before storage-mass after storage)/mass after storage
As shown in fig. 6, the weight loss ratio of the cherry tomatoes increases with the increase of the storage time, and the weight loss ratio of the test group is less than that of the CK group, which indicates that the fruit weight is reduced due to water loss caused by transpiration and respiration of the cherry tomatoes during the storage process, and the weight reduction can be effectively inhibited to a certain extent by the film package, so as to achieve 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. The weight loss ratios of the test groups were 8.40% for neatPLA and 8.40% for AEKO/PLA, respectively, when stored for 21 days0.2 8.20％、AEKO/PLA0.47.62％、AEKO/PLA0.6 7.57％、AEKO/PLA0.8 8.32％、AEKO/PLA1.08.35%, indicating that the PLA film functioned somewhatParticularly, after the almond oil is added, the water resistance of the film is improved due to the hydrophobicity of the almond oil, and the weight loss rate of the cherry tomatoes is reduced.
C) Hardness of
The hardness of the fruit is related to the organization structure and the maturity of the fruit, and the hardness indirectly reflects the texture, the sensory quality and the nutritional components of the fruit. The hardness of the fruit is measured by GY-3 in this test. FIG. 7 is a graph showing the trend of hardness change during storage in the CK group and the test group according to the present invention.
As shown in fig. 7, the protopectin component gradually decomposed due to water loss of the cherry tomatoes during storage, and the hardness of all the group cherry tomatoes decreased with increasing storage time. After 21 days of storage, the stiffness of the cherry tomatoes decreased from the initial 4.13kg/cm2 to 1.50kg/cm of neatPLA respectively2，AEKO/PLA0.2Is 1.53kg/cm2、AEKO/PLA0.4Is 1.60kg/cm2、AEKO/PLA0.6Is 2.00kg/cm2、AEKO/PLA0.8Is 1.63kg/cm2、AEKO/PLA1.0Is 1.83kg/cm2Except for AEKO/PLA0.6Has a hardness of 2.00kg/cm2The rest groups are lower than 2.00kg/cm2Description of AEKO/PLA0.6Can better maintain the freshness of the cherry tomatoes and reduce the softening degree.
D) Index of decay
The rot rate is one of important indexes for sensory evaluation of fruits and vegetables, and reflects the rot degree of the fruits and vegetables in the storage process. The test takes the water stain-like disease spots on the surface of the fruit as the basis for judging the fruit rot, and the test is divided into 6 grades, 0 grade and no rot according to the fruit rot area; grade 1, the rotten area of the fruit is less than 25%; grade 2, the rotten surface accounts for 25 to 50 percent of the fruit area; grade 3, the rotten area is 50-75% larger than the area of the fruits; grade 4, rotten area is more than 75%; grade 5, complete rotting; FIG. 8 is a graph showing the tendency of decay of the CK group and the test group of the present invention during storage.
The decay index was calculated as follows:
as shown in FIG. 8, no decay occurred in both CK group and test group from 0 to 3 days; at 7d, 10% and 5% of CK group and neatPLA respectively have rotting phenomena, and the rest groups have no rotting phenomena; at 21d, the CK group rotting rate reaches 23%, the neurPLA rotting rate is 15%, and AEKO/PLA0.2、AEKO/PLA0.4、AEKO/PLA0.6、AEKO/PLA0.8、AEKO/PLA1.0The rotting rates of (A) are 12.5%, 10%, 5%, 7.5%, respectively, AEKO/PLA0.6The lowest decay rate of (A) indicates AEKO/PLA0.6Can better maintain the freshness of the cherry tomatoes and reduce the rotting rate.
E) Soluble Solids (TSS) assay
In this test, a proper amount of cherry tomato is weighed, chopped, ground and filtered to obtain a juice, and then the juice is tested by an Abbe refractometer. As a result, as shown in FIG. 9, the TSS trend in both the CK group and the test group during storage was a sharp decrease in the initial period of storage, a small increase in the range of 3d to 14d, and a decrease in the latter period.
The reduction in the early stage of storage is caused by that the cherry tomatoes continuously consume the nutrient substances of soluble sugar to provide the physiological activity of the cherry tomatoes for maintaining the physiological activity of the cherry tomatoes; the small increase in the middle storage period is caused by the fact that cherry tomatoes belong to fruits and vegetables with breathing jump, and the conversion of nutrient substances and the accumulation of saccharides are continuously carried out in the after-ripening process, so that soluble solid matters show an increasing trend; the later period of storage is reduced because the nutrient substances consumed for maintaining self respiration are far more than the nutrient substances accumulated by the self, so the soluble solid matters show a small reduction trend. The TSS of each almond oil/PLA film is higher than pure PLA and CK groups, and the change trend is slow, wherein, the TSS of each almond oil/PLA film is AEKO/PLA0.6The level remained high during storage, indicating AEKO/PLA0.6Can better maintain the TSS of the cherry tomatoes and reduce the consumption of nutrient substances.
F) Determination of Titratable Acid (TA) content
TA is one of the important components forming the flavor quality of fruits and vegetables, and the nutrients of the cherry tomatoes are not obtained from plants after being picked, so that the nutrients of the cherry tomatoes have to be consumed during the storage process to maintain the physiological activity of the cherry tomatoes. In the test, 1g of cherry tomato is chopped, distilled water is used for fixing the volume to 20mL, after filtration, 1-2 drops of phenolphthalein indicator are dropped into the filtrate, 0.1mol/LNaOH is used for dropping the indicator to reddish color, the indicator does not fade within 30s, and the consumed NaOH volume (V) is recorded, and FIG. 10 is a graph showing the change trend of TA in the CK group and the test group during storage.
The calculation method is as follows:
in the formula: c is the concentration of the standard titration, mol/L; v is the volume of NaOH standard solution consumed in calibration, mL; k is the conversion coefficient of the main acid, namely 1mmol NaOH is equivalent to the gram number of the main acid (malic acid is used as the conversion coefficient in the test); m is the sample weight.
Since part of the organic acids in cherry tomatoes are converted into sugars and the other part is consumed by respiration, the TA changes during storage as shown in fig. 10, showing an overall downward trend. After 21 days of storage, TA content was AEKO/PLA0.6＞AEKO/PLA0.4＞AEKO/PLA0.2＝AEKO/PLA0.8＞neatPLA＞AEKO/PLA1.0Is > CK and AEKO/PLA0.6The change trend is slow in the whole storage process, and the preservation effect is better than that of other composite films.
G) Determination of vitamin C (Vc) content
The cherry tomatoes contain rich vitamins which are important indexes for measuring the nutritive value of fruits and vegetables. In the test, 5g of cherry tomatoes are weighed, 50mL of 2% oxalic acid solution is added, the cherry tomatoes are ground into homogenate and filtered to obtain a filtrate, a filter cake can be washed by a small amount of 2% oxalic acid solution for several times, the filtrates are combined, the volume of the filtrate is recorded, 4mL of 0.1mg/mL filtrate is accurately sucked into a conical flask, 16mL of 1% oxalic acid solution is added, 2, 6-dichlorophenol indigo is titrated to light red (15-time fading is the end point), the volume of the used dye solution is recorded, and the amount of ascorbic acid which can be oxidized by 1mL of the dye solution is calculated. Accurately sucking the sample extracting solution, carrying out the same operation as the titration method in the step 2, and taking 20mL of oxalic acid as a blank control. The content of reduced ascorbic acid in 100g of the sample was calculated by substituting the following formula:
in the formula: v1The volume of dye consumed for titrating the sample, mL; v2The volume of dye consumed to titrate the blank, mL; v is the total volume of the sample extracting solution; v3To titrate the volume of sample taken; m is1The amount of ascorbic acid which can be oxidized by 1mL of dye, mg; m is2To measure the weight of the sample, g.
Vitamin in fruits and vegetables is subjected to oxidative decomposition along with the prolonging of time and the stable characteristic of Vc, and figure 11 is a change trend graph of Vc in a storage period of a CK group and a test group.
As shown in FIG. 11, both the CK group and the test group showed a gradual decrease in storage period, and after 21 days of storage, the content of Vc was apricot oil/PLA film > pure PLA film > CK group, in which AEKO/PLA film0.6The content remained high throughout the storage, indicating that AEKO/PLA0.6Has better fresh-keeping effect than other almond oil/PLA films.
H) Measurement of POD enzyme Activity
POD enzyme is one of the enzymatic defense systems for protecting fruits and vegetables when they are exposed to stress.
(1) Preparation of an enzyme extract: weighing 3g of cherry tomato in a mortar, adding 3mL of extracting solution (1mMPEG, 4% PVPP and 1% Triton X-100), grinding into slurry in ice bath, centrifuging at 4 deg.C and 1200r/min for 30min, collecting supernatant as enzyme extracting solution, and storing at low temperature for later use.
(2) And (3) enzyme activity determination: 3mL of 25mmol guaiacol solution and 0.5mL of enzyme extract were added to a test tube, and 200. mu. L of 0.5mol/LH was added2O2After rapid mixing, the enzyme reaction system was rapidly started and timing was immediately started. Pouring the reaction solution into a cuvette, placing the cuvette in a spectrophotometer, and starting to record the OD of the reaction system at 15s470The value is the initial value and then recorded every 60s for at least 6 ODs470Value, repeated three times.
(3) Data processing: the increase of 0.01 per 60s absorbance value per gram fresh weight is 1 POD enzyme activity unit, and the calculation formula is as follows:
in the formula: delta OD470The absorbance change value of the reaction mixed liquor is obtained; Δ t is the enzymatic reaction time; m is sample mass, g;
v is the total volume of the sample extracting solution, mL; vs is the volume of the sample of extract, mL, taken at the time of the assay.
FIG. 12 is a graph showing the trend of POD activity during storage in the CK group and the test group according to the present invention.
As shown in FIG. 12, the overall enzyme trend was upward, then downward, and finally upward. The POD activity is enhanced to protect the fruit and vegetable organisms after the cherry tomatoes leave the plant matrix at 0-3d due to the stress of the surrounding environment, wherein the activity of each composite membrane is higher than that of pure PLA and CK groups, which shows that the activity of the slow enzyme for senescence of the organisms is higher, and the fruit and vegetable organisms can be further protected better; during the period of 7-14 days, the enzyme activity begins to decrease due to the gradual senescence of fruits and vegetables, but the AEKO/PLA is compared with that of CK group and test group0.6Still at a higher activity; in the final storage period of 14-21 days, the fruit and vegetable are not only aged, but also catalyzed by POD H2O2The peroxide produced damages the cell membrane, and the body recalls the POD enzymatic defense system, so that the POD activity tends to increase at a later stage, but the AEKO/PLA activity increases0.6The enzyme activity was minimal, thus indicating that the plasma membrane of cherry tomato cells in this thin film packaging material is less damaged.
I) Determination of PPO enzyme Activity
In the aging process of after-ripening or the storage and processing process after picking, the tissue browning of fruits and vegetables is closely related to the polyphenol oxidase activity in the tissues, so that the PPO enzyme activity reflects the aging degree of fruits in the storage process to a certain extent.
(1) Preparation of an enzyme extract: weighing 3g of cherry tomato in a mortar, adding 3mL of extracting solution (1mMPEG, 4% PVPP and 1% Triton X-100), grinding into slurry in ice bath, centrifuging at 4 deg.C and 1200r/min for 30min, collecting supernatant as enzyme extracting solution, and storing at low temperature for later use.
(2) And (3) enzyme activity determination: 4.0mL of 50mmol acetic acid buffer solution, 1mL of 50mmol catechol solution and 100 mu L enzyme extracting solution are sequentially added into a test tube, an enzyme reaction system is quickly started after the mixture is quickly mixed, and timing is immediately started at the same time. Pouring the reaction solution into a cuvette, placing the cuvette in a spectrophotometer, and starting to record the OD of the reaction system at 15s420The value is the initial value and then recorded every 60s for at least 6 ODs420Value, repeated three times.
(3) Data processing: the increase of 0.01 per 60s absorbance value per gram fresh weight is 1 POD enzyme activity unit, and the calculation formula is as follows:
in the formula: delta OD420The absorbance change value of the reaction mixed liquor is obtained; Δ t is the enzymatic reaction time; v is the total volume of the sample extracting solution, mL; vs is the volume of the extracted solution of the sample in mL; m is the sample mass, g.
FIG. 13 is a graph showing the trend of the change in PPO activity during storage in the CK group and the test group of the present invention.
As can be seen from fig. 13, the activity of PPO enzyme showed an overall rising trend, with relatively slow rise of PPO during storage at 0-7d, since cherry tomato was still relatively fresh in the early stages, so cherry tomato flesh remained relatively low in PPO activity, and with time the cherry tomato gradually started to rapidly increase in aged PPO activity. The CK group PPO was always at a higher activity, AEKO/PLA, than the test group throughout the storage period0.6The enzyme activity was minimal and remained on a relatively slow rising trend, indicating that the package could be kept fresh.
J) Determination of Malondialdehyde (MDA) content
Superoxide anion free radicals and hydroxyl free radicals generated in the aging process of the fruit and vegetable tissues or in cells suffering from diseases, cold damage or other injuries can induce the peroxidation of acid-proof substances after the unsaturation in membrane lipid to generate lipid free radicals. Lipid free radicals can further induce peroxidation of membrane lipids leading to increased cell membrane permeability, cell damage or cell death. The extent of cell loss can be reflected by measuring the amount of MAD, with MDA being one of the major products of lipid peroxidation.
(1) Preparing an extracting solution: weighing 1.0g cherry tomato sample, adding 5mL 10% trichloroacetic acid, grinding into homogenate, centrifuging at 4 deg.C 10000r/min for 20min, collecting supernatant, and storing at low temperature for use.
(2) And (3) measuring the MDA content: 2mL of the supernatant and 0.67% thiobarbituric acid were added to a test tube, mixed, heated in a boiling water bath for 20min, cooled and centrifuged again, and then the absorbance values of the supernatants were measured at 450nm, 532nm and 600nm, respectively. This was repeated three times.
(3) Data processing: from the absorbance values, the MDA content per gram of cherry tomato was calculated and expressed as μmol/g. The calculation formula is as follows:
in the formula: c is the MDA content in the reaction mixed liquid, mu mol/L; v is the total volume of the sample extracting solution, mL; vs is the volume of the extracted solution of the sample in mL; m is the sample mass, g.
FIG. 14 is a graph showing the trend of MDA changes during storage in the CK group and the test group according to the present invention.
As can be seen from fig. 14, the MDA content is always increasing during the whole storage period, the CK group is most significantly increased during the first 7d period, and the MDA content of the test group is still increased after 7d period, because the active oxygen radicals are continuously increased along with the continuous respiration of the fruit, which causes the active oxygen inside the fruit to be continuously accumulated, and the lipid peroxidation reaction inside the fruit is promoted, so the MDA content is continuously increased. As can be seen from the figure, AEKO/PLA was present throughout the storage period0.6The MDA content of the product is kept relatively slowA slow rising trend, indicating less damage to cherry tomato cells under this packaging condition.
As can be seen from the above experimental examples 1-7, the almond oil has different performance results according to different addition amounts, but the almond oil has obviously improved elongation at break and improved water vapor barrier property (of which AEKO/PLA) although the mechanical strength of polylactic acid is not obviously improved0.6The best water vapor barrier performance); meanwhile, the addition of the almond oil has no influence on the chemical structure of polylactic acid, but the surface of a PLA film becomes uneven along with the increase of the content of the almond oil, so that the AEKO/PLA is considered to be combined0.6The performance effect of the film is best, and the experimental example 8 is further verified, so that the result shows that the AEKO/PLA is indeed in the fresh-keeping performance of the cherry tomato0.6Can maintain the good nutritional quality of cherry tomatoes.
While several embodiments of the invention have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. These new embodiments may be implemented in various other forms, and various omissions, substitutions, and changes may be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.
Claims (9)
1. A preparation method of a degradable almond oil/polylactic acid film is characterized by comprising the following steps:
(1) extraction of mountain apricot kernel oil
Cleaning wild apricot kernels with running water, drying, pulverizing into powder for later use, weighing a proper amount of coarse almond powder, placing the coarse almond powder into an extraction tube, adding a normal hexane solution into an extraction bottle, refluxing in a soxhlet extractor, placing the solution into a rotary evaporator after the reflux is finished, evaporating the solvent to obtain almond oil, and storing the almond oil in a refrigerator for later use;
(2) preparation of almond oil/polylactic acid film
Weighing 2g of polylactic acid in a beaker, adding 30mL of trichloromethane 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 in a ventilated place, 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 during stirring.
3. The method for preparing a degradable almond oil/polylactic acid film according to claim 1, wherein the mass ratio of the almond oil to the polylactic acid in the preparation process of the film is 0.2: 1 adding almond oil.
4. The method for preparing a degradable almond oil/polylactic acid film according to claim 1, wherein the mass ratio of the almond oil to the polylactic acid in the preparation process of the film is 0.4:1 adding almond oil.
5. The method for preparing a degradable almond oil/polylactic acid film according to claim 1, wherein the mass ratio of the almond oil to the polylactic acid in the preparation process of the film is 0.6:1 adding almond oil.
6. The method for preparing a degradable almond oil/polylactic acid film according to claim 1, wherein the mass ratio of the almond oil to the polylactic acid in the preparation process of the film is 0.8:1 adding almond oil.
7. The method for preparing a degradable almond oil/polylactic acid film according to claim 1, wherein the almond oil is added into the film according to the mass ratio of the almond oil to the polylactic acid of 1: 1.
8. A degradable almond oil/polylactic acid film is characterized by being prepared by the preparation method of the degradable almond oil/polylactic acid film as claimed in any one of claims 1 to 7.
9. The application of the degradable almond oil/polylactic acid film is characterized in that the degradable almond oil/polylactic acid film as claimed in claim 8 is used for fresh-keeping storage of fruits and vegetables.
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