A method for preparing an edible film using oil bodies and the resulting product

Abstract

The present invention provides a method for preparing an edible film using oil bodies, comprising the steps of: 1) dissolving chitosan in an organic acid solution with a mass concentration of 0.5-2%, heating at 50-60 °C and magnetically stirring until there are no suspended impurities; 2) dissolving a surfactant in water to form a solution; mixing and stirring the chitosan solution, the surfactant solution, glycerol, and oil bodies prepared in step 1), heating in a water bath at 50 °C and stirring until there are no suspended impurities; 3) spreading the mixed solution on a flat surface and forming a film after drying. The present invention utilizes oil bodies of oilseeds, which are inexpensive and widely sourced, to explore the application of oil bodies as components of edible packaging materials in the storage and preservation of fruits, providing a safe, economical, and simple new preservation technology method for the storage, transportation, and marketing of fruits.

Description

Technical Field

[0001] The present invention belongs to the technical field of food processing, and particularly relates to a preparation method and application of a fresh-keeping film. Background Art

[0002] In recent years, with the general improvement of people's environmental protection awareness, using green and environmentally friendly edible film packaging to replace plastic food packaging has become the future development trend of food packaging. An edible film is a thin film formed by edible materials through intermolecular interactions, and usually plasticizers and cross-linking agents need to be added. The edible film covers the surface or inside of food, and ensures food quality and extends the food shelf life by blocking oxygen, water vapor and preventing solute migration.

[0003] Currently, the existing products in the edible film market generally have problems such as weak antioxidant and antibacterial properties, insufficient mechanical strength, poor heat-sealing property and water resistance (Chen Yamin, Chen Fusheng, Yang Hongshun. Research progress of edible films in fresh-keeping of fruits and vegetables [J]. Agricultural Machinery, 2012(30): 106-109.). When oleosomes are used instead of oils in edible films of other substrates, due to the unique hydrophilic properties of oleosomes and the interactions between polymers, the compatibility state between the film components can be effectively improved, the antioxidant characteristics of the film can be enhanced, and the properties of the edible film can be improved.

[0004] Oleosomes are discrete organelles rich in triacylglycerol that provide energy for the growth, development and metabolic activities of seeds in plants, and are commonly present in higher eukaryotes. They play an energy storage role during seed germination and growth. Natural oleosomes have a unique membrane structure. Proteins, phospholipids, etc. on the surface of the oleosome membrane interact to form a tight and stable charged layer, effectively preventing the aggregation of oleosomes due to interaction. Natural oleosomes can maintain good stability both in the plant body and in the external environment, and will not aggregate, fuse, etc. when the external environment and the oleosome structure change little, and have good solubility in water.

[0005] Endogenous non-oil body proteins interact with oil body proteins through intermolecular forces, affecting the physicochemical stability of natural oil bodies. At the same time, endogenous non-oil body proteins also contain some endogenous enzymes, which may hydrolyze triglycerides in the oil bodies or the oil body membranes, thereby affecting the stability of natural oil bodies (Karkani O A, Nenadis N, Nikiforidis C V, et al. Effect of recovery methods on the oxidative and physical stability of oil body emulsions[J]. Food Chemistry, 2013, 139(1-4): 640-648.) Summary of the Invention

[0006] To solve the deficiencies of the existing technology, the present invention proposes a method for preparing an edible film using oil bodies.

[0007] The second object of the present invention is to propose the application of the product obtained by the said method.

[0008] The technical solution for achieving the above objects of the present invention is as follows:

[0009] A method for preparing an edible film using oil bodies, which comprises the steps of:

[0010] 1) Dissolve chitosan in an organic acid solution with a mass concentration of 0.5-2%, heat at 50-60 °C and stir magnetically until there are no suspended impurities to obtain a chitosan solution; the organic acid is one of acetic acid, formic acid or oxalic acid;

[0011] 2) Dissolve the surfactant in water to make a solution; mix the chitosan solution prepared in step 1), the solution of the surfactant, glycerol, and oil bodies, heat in a water bath at 50 °C and stir until there are no suspended impurities to obtain an oil body coating solution; the surfactant is one or more of sodium carboxymethyl cellulose, sodium lauryl sulfate (SLS), and sodium hydroxypropyl methylcellulose, with a mass concentration of 3-5%;

[0012] 3) Spread the oil body coating solution prepared in step 2) on a flat surface and form a film after drying.

[0013] Further, in step 1), dissolve 2-3 g of chitosan in 100 mL of the organic acid solution, heat at 50-60 °C and stir.

[0014] Among them, in step 2), the oil bodies are one or more of the oil bodies of peanuts, white sesame seeds, walnuts, and rapeseeds.

[0015] Preferably, in the present invention, the oil bodies are operated according to the aqueous phase extraction method, and the extraction process flow is: soaking → pressing → centrifuging → scraping. Specifically, soaking: the oil seeds are soaked in pure water and stirred for 8 - 15 hours; pressing: after soaking, the seeds and water are squeezed through a twin-screw juicer to obtain an extraction pulp; centrifuging: the extraction pulp is reserved for centrifuging; scraping: the upper layer of the emulsion is scraped off after centrifuging.

[0016] The non-oil body proteins attached to the outer layer during the extraction process are also key factors in maintaining the stability of natural oil bodies. When using the aqueous phase extraction method to extract oil bodies from plant seeds, plant endogenous non-oil body proteins will adhere to the outside of the oil body membrane during the grinding and soaking processes, forming a second protein membrane outside the oil body membrane, thus affecting the stability of natural oil bodies.

[0017] More preferably, the oil seeds are soaked in pure water at a material-liquid ratio of 1:(6 - 8) (g:ml) and stirred on a magnetic stirrer for 10 - 15 hours; after soaking, the seeds and water are squeezed through a twin-screw juicer to obtain an extraction pulp; the extraction pulp is reserved for centrifuging at low temperature and high speed, and the centrifuging conditions are: centrifugal force 10000g, centrifuging time 30 min, centrifuging temperature 4°C; the upper layer of the emulsion is scraped off after centrifuging.

[0018] A preferred technical solution of the present invention is that in step 2), the raw material ratio is: 20 ml of chitosan solution, 15 - 25 ml of sodium carboxymethylcellulose solution, 1 - 5 g of glycerol, and 0.5 - 3.5 g of oil bodies.

[0019] Further, in step 3), first, the mixed solution prepared in step 2) is placed in an ultrasonic cleaner and water-bathed at 50°C for ultrasonic treatment for 10 min; after mixing evenly, it is placed in a culture dish; left standing for 48 h until the bubbles disappear; and the film is peeled off after drying.

[0020] Further preferably, the thickness of the edible film is 0.4 - 0.6 mm.

[0021] Application of the edible film prepared by the method of the present invention in food preservation.

[0022] The said application is to soak the fruits in the oil body coating liquid for 25 - 35 s and air-dry them naturally, and the fruits are strawberries, grapes, apples or blueberries.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention utilizes oil and fat bodies that are inexpensive and widely sourced to explore the application of oil and fat bodies as components of edible packaging materials in the storage and preservation of fruits, providing a safe, economical, and simple new preservation technology method for the storage, transportation, and marketing of fruits. In the experiment, the extraction and comprehensive determination of the properties of four types of oil and fat bodies, the improvement of the properties of edible films by sesame oil and fat bodies with different contents, and the actual preservation effect of the oil and fat body coating solution provide a theoretical basis for the application of the oil and fat body coating solution in the field of fruit preservation. Explore the application prospects of plant oil and fat bodies in the field of edible films, improve the conversion rate and processing and utilization level of vegetable oil products, develop high-quality agricultural derivative products based on vegetable oil and fat bodies, promote agricultural efficiency increase, and create a modern green agricultural economy.

[0025] (1) There are significant differences in the contents of water, protein, and fat in the oil and fat bodies from four different sources. Among them, the rapeseed oil and fat body has the lowest fat content and the highest protein content. The absolute value of the Zeta potential of the peanut oil and fat body is the highest, at 30.77 ± 0.93 mV. The average particle sizes of the peanut oil and fat body and the sesame oil and fat body are the smallest and are significantly lower than those of the other two oil and fat bodies, showing good emulsion stability. The peroxide value and thiobarbituric acid value of the sesame oil and fat body change minimally during the storage period and are the lowest at the end, having the best oxidation stability. Considering various properties, the sesame oil and fat body is selected as the best additive component to be applied to the edible film.

[0026] (2) The sesame oil and fat body can significantly improve the appearance, water vapor permeability, solubility, and elongation of the edible film, and the performance remains almost unchanged when the addition content of the oil and fat body is continuously increased. As the addition amount of the oil and fat body increases, the appearance, softness, and tensile strength of the edible film show a trend of first increasing and then decreasing. When the addition content of the oil and fat body is 1.19%, the comprehensive performance and economic benefits are the best. Therefore, the optimal addition content of the oil and fat body in the edible film is determined to be 1.19%.

[0027] (3) Under the normal temperature strawberry storage environment, the treatment with the edible coating of the oil and fat body can effectively delay the deterioration of the strawberry appearance, inhibit the decay and spoilage of strawberries, and extend the shelf life by 2 days. It can reduce the respiratory losses of water, soluble solids, and titratable acids during storage, delay the post-harvest ripening of strawberries, is beneficial to the fresh storage of strawberries, and can increase the direct economic benefit by 12.36 yuan / kg. Description of the Drawings

[0028] Figure 1 It is the in vitro microstructure of the oil and fat body. From left to right in the figure are walnut oil and fat body, peanut oil and fat body, sesame oil and fat body, and rapeseed oil and fat body.

[0029] Figure 2 It is the particle size distribution diagram of the oil and fat body.

[0030] Figure 3 It is the particle size of the oil and fat body after adding SDS

[0031] Figure 4 Comparison of the particle sizes of oleosomes before and after adding SDS

[0032] Figure 5 Figure showing the change in the thiobarbituric acid value of oleosomes over time.

[0033] Figure 6 is the thickness of the edible film;

[0034] Figure 7 is the transparency of the edible film;

[0035] Figure 8 is the water vapor transmission rate of the edible film;

[0036] Figure 9 is the dissolution rate of the edible film;

[0037] Figure 10 are the tensile strength and elongation rate of the edible film;

[0038] Figure 11 is the effect of different coating treatments on the sensory quality of strawberries during storage;

[0039] Figure 12 is the effect of different coating treatments on the hardness of strawberries during storage;

[0040] Figure 13 Effect of different coating treatments on the weight loss rate of strawberries during storage;

[0041] Figure 14 is the effect of different coating treatments on the soluble solids of strawberries during storage;

[0042] Figure 15 is the effect of different coating treatments on the pH and titratable acid of strawberries during storage. Detailed implementation manners

[0043] The present invention will be further described below with reference to specific embodiments. The following embodiments are only used to explain the present invention in detail and do not limit the present invention.

[0044] Unless otherwise specified, the technical means used in the specification are all well-known technical means in the art. The raw materials used are all commercially available.

[0045] Example 1

[0046] In this example, walnuts, peanuts, sesame seeds, and rapeseeds were selected as oil raw materials to prepare oil bodies by the aqueous extraction method. The basic composition, microstructure, Zeta potential, particle size distribution, hydroperoxide value, and thiobarbituric acid value of the four oil seeds and oil bodies were studied to evaluate their feasibility as food raw materials, and oil bodies with strong emulsion stability and oxidation stability were selected for subsequent applications.

[0047] Naturally air-dried peanuts, white sesame seeds, walnuts, and rapeseeds were selected and operated according to the aqueous extraction method. The extraction process flow was: soaking → pressing → centrifuging → scraping.

[0048] The specific extraction steps were as follows: The oil seeds were soaked in pure water at a material-liquid ratio of 1:7 (m:v) and stirred on a magnetic stirrer for 12 hours; after soaking, the seeds and water were extruded through a twin-screw juicer to obtain the extraction pulp; the extraction pulp was retained for low-temperature high-speed centrifugation, and the centrifugation conditions were: centrifugal force 10,000 g, centrifugation time 30 min, and centrifugation temperature 4°C; after centrifugation, the upper layer of the emulsion was scraped and placed in a centrifuge tube and stored in a 4°C refrigerator away from light for later use.

[0049] The composition, microstructure, Zeta potential, particle size, hydroperoxide value, and thiobarbituric acid value of the obtained oil bodies were detected.

[0050] Table 1 Composition of oil bodies

[0051]

[0052] The microscopic observation results of the oil body emulsion are as Figure 1 shown. It can be seen from the observation results that there are significant differences in the size and morphology of oil bodies from different sources. It can be judged from the images that after aqueous extraction, the peanut and sesame oil bodies can maintain relatively independent and complete structures and can be evenly dispersed in the water medium, and the volume and morphology of the oil bodies are relatively uniform. Obvious aggregation phenomena occurred in the walnut and rapeseed oil bodies, and there were significant differences in volume and morphology among the oil bodies, and the membrane structures of some oil bodies may have been damaged.

[0053] The absolute value of the Zeta potential of the peanut oil body was (30.77 ± 0.93) mV, which was significantly higher than that of the walnut oil body (27.30 ± 0.17) mV, the sesame oil body (24.50 ± 0.17) mV, and the rapeseed oil body (18.93 ± 0.65) mV. The highest absolute value of the potential of the peanut oil body indicates that the electrostatic repulsion between particles in the peanut oil body emulsion is large, it is not easy to aggregate, and the stability is high.

[0054] There is a certain correlation between the stability of the oil body emulsion and the particle size distribution. When the particle size distribution of the emulsion droplets in the emulsion system is uniform and the individual particle size is small, the creaming speed is slower and the overall stability of the emulsion is stronger. The particle size distributions of the four oil bodies are asFigure 2 As shown, the particle size distributions of the three types of oil bodies other than rapeseed oil bodies show a single-peak distribution, indicating that relatively uniform oil bodies were obtained. The particle size distribution of the rapeseed oil body emulsion shows three peaks in total, and there are also two peaks in the relatively high particle size range of 10 - 100 μm. See Figure 3 , after adding SDS, the average volume particle size of a single rapeseed oil body is 2.08 ± 0.78 μm, indicating that relatively serious aggregation may have occurred in the rapeseed oil bodies in the original emulsion environment. After adding SDS to the particle size distribution, the surface tension between particles will be enhanced, and the repulsive force between ions will increase. What is measured is the particle size of a single independent molecule. The greater the difference between the actual measurement and after adding SDS, the more aggregation there is and the more unstable it is.

[0055] As Figure 2 can be seen, the average volume particle sizes D [4,3] of peanuts and sesame seeds are significantly lower than those of walnuts and rapeseed oil bodies, and the D [4,3] of rapeseed oil bodies is the largest. The average volume particle sizes of the oil body emulsions from small to large are: sesame oil body emulsion < peanut oil body emulsion < walnut oil body emulsion < rapeseed oil body. The average surface area particle size D [3,2] of peanuts is significantly lower than those of sesame seeds, walnuts, and rapeseed oil bodies, and the D [3,2] of rapeseed oil bodies is the largest. The difference between D [4,3] and D [3,2] of the oil bodies can reflect the morphological distribution of the oil bodies to a certain extent. The smaller the difference between D [4,3] and D [3,2] , the more concentrated and uniform the particle size distribution of the oil body particles. As can be seen from Figure 4 , the difference between D [4,3] and D [3,2] of rapeseed oil bodies is the largest, significantly higher than those of the other three types of oil bodies, indicating that the particle size distribution range of rapeseed oil body particles in the oil body emulsion is the largest, which is consistent with the previous direct microscopic observation results.

[0056] The primary oxidation degrees of the four types of oil bodies are: sesame oil body emulsion < rapeseed oil body emulsion < walnut oil body emulsion < peanut oil body. The secondary oxidation degrees of the four types of oil bodies are: sesame oil body emulsion < rapeseed oil body emulsion < walnut oil body emulsion < peanut oil body.

[0057] In this example, the basic composition, emulsion stability, and oxidation stability of four kinds of oil bodies were analyzed. Emulsion stability: peanut oil body, sesame oil body > walnut oil body > rapeseed oil body. Oxidation stability: sesame oil body > rapeseed oil body > walnut oil body > peanut oil body. Although the peanut oil body has the smallest particle size, its hydroperoxide value and thiobarbituric acid value are significantly higher than those of the other three oil bodies, and its oxidation stability is poor. Therefore, it was excluded in the subsequent experiments. The sesame oil body has a smaller particle size and less aggregation degree in the emulsion, with good stability. At the same time, its hydroperoxide value and thiobarbituric acid value ( Figure 5 ) are lower than those of the other three oil bodies, and its oxidation stability is good. Therefore, the sesame oil body was selected to be added to the film component in the subsequent experiments.

[0058] Example 2

[0059] Fresh sesame oil bodies were extracted using the same extraction method as in Example 1.

[0060] The specific film-making steps are as follows: Dissolve 2.5 g of chitosan in 100 mL of 1% acetic acid solution, heat in a water bath at 55 °C and stir magnetically until there are no suspended impurities; dissolve 3.75 g of sodium carboxymethylcellulose in 100 mL of deionized water; mix 20 g of chitosan solution, 20 g of sodium carboxymethylcellulose solution, 2 g of glycerol, and a certain mass of oil bodies (the formula is shown in Table 2), heat in a water bath at 50 °C and stir until there are no suspended impurities to obtain an oil body coating solution; ultrasonically clean in a water bath at 50 °C for 10 min; after mixing evenly, invert it in a 90-mm petri dish; let it stand for 48 h until the bubbles disappear; place it in an oven at 45 °C for 10 h to dry and then peel off the film.

[0061] Table 2 Formulation for preparing oil body composite film

[0062]

[0063] The obtained film was subjected to sensory evaluation (color, softness, moisture regain, integrity), using a 20-point standard. Using a sensory evaluation standard table, the color, softness, moisture regain, and integrity of each group of edible films were scored sensorially.

[0064] Table 3 Sensory evaluation criteria for independent films

[0065]

[0066] The thickness, transparency, water vapor transmission coefficient, tensile strength, and elongation rate of the product were measured.

[0067] Sensory evaluation of the edible film: As can be seen from Table 4, after adding oleosomes, the appearance and softness of the edible film have been significantly improved. Since chitosan itself is yellow, adding oleosomes can improve the yellowing phenomenon of the film, and the appearance quality is further enhanced. At the same time, adding oleosomes can reduce the water evaporation during the film drying process, increase the water content of the film, and improve the softness of the film. However, when the addition amount of oleosomes is too large, the softness of the film will be too large, lacking rigidity and prone to breakage, resulting in a decrease in integrity, which is also not conducive to the fresh-keeping effect of fruits and vegetables. Moreover, when the addition amount of oleosomes is relatively large, a large amount of lipids float to the surface of the film during heating in the film drying process, showing the phenomenon of floating oil, which has an adverse impact on both the fresh-keeping function and the edible quality of the edible film. Considering the four sensory evaluation characteristics, when the addition amount of oleosomes is 0.5 g, the appearance and softness of the film are significantly improved, without oil leakage and breakage, and the overall sensory performance is the best.

[0068] Table 4 Sensory evaluation of the edible film

[0069]

[0070] The thickness of the film prepared in this example is between 0.4 and 0.5 mm. A thinner and more uniform film has less impact on the appearance color of fruits and vegetables after film covering, and has higher commercial value. From Figure 6 it can be seen that with the increase in the concentration of sesame oleosomes, the thickness of the composite film increases. When the addition amount of sesame oleosomes is not more than 2.5 g, there is no significant effect on the film thickness. When the addition amount of sesame oleosomes is 3.5 g, the film thickness is significantly higher than that of other composite films with lower concentrations. When the amount of oleosomes is excessive, the compatibility between oleosomes and other film components is poor, and the uniformity of the coating emulsion is worse, resulting in uneven distribution after the film dries.

[0071] The optical properties of the edible film will affect consumers' acceptance of fruit and vegetable products. Generally, the higher the transparency of the edible film, the less adverse impact on the sensory quality of fruits and vegetables after film covering. From Figure 7 it can be seen that the transparency of the film decreases overall after adding oleosomes. When the addition amount is not more than 1.5 g, there is no significant change in transparency. When the addition amount is greater than 2.5 g, the transparency decreases significantly. It may be that when the addition amount of oleosomes in the coating solution reaches a certain concentration, the particle sizes and sedimentation rates of oleosomes and other substances in the composite film are quite different, resulting in significant differences in particle distribution after film formation, and the light transmittance decreases due to the reflection of light. At the same time, after adding oleosomes to the coating solution, the oleosomes are dispersed in the coating solution system to form an emulsion system, and the coating solution presents an emulsion appearance, and the transparency of the film interface decreases due to light scattering.

[0072] Water vapor transmission rate of the edible film: The edible film can reduce the transfer rate of water vapor between fruits and vegetables and the external environment, effectively reduce the water loss of fruits and vegetables during storage, and delay the shrinkage of fruits and vegetables due to water loss. Therefore, the lower the water vapor transmission rate of the edible film, the more effective it is for fruit and vegetable preservation. The water vapor transmission coefficients of the edible films with different added amounts of oleosomes are as Figure 8 shown. After adding oleosomes, the water vapor transmission coefficients of the composite films in each treatment group decreased significantly, and there was no obvious difference among the groups with different added amounts. When sesame oleosomes were added to the coating solution, part of the oleosomes melted during the heating and drying process of the film solution, and floated to the film surface to form a lipid hydrophobic layer due to their lower specific gravity. Due to the hydrophobic characteristics of the lipid layer on the film surface, it can greatly reduce the diffusion rate and adsorption of water vapor in the film, significantly improve the water vapor permeability of the film, and enhance the moisture barrier property of the film. When the added amount of oleosomes was 0.5 - 2.5 g, the water vapor transmission coefficients of the composite films were basically the same. When the added amount of oleosomes increased to 3.5 g, the water vapor transmission coefficient of the composite film decreased further. This may be because the obvious increase in film thickness caused the macromolecular substances to aggregate with each other, resulting in an enhanced hindrance effect on water vapor.

[0073] Dissolution rate of the edible film: The dissolution rate of the edible film will have a certain impact on the taste of fruit and vegetable products after coating. Within a certain range, the higher the water dissolution rate of the film, the easier it can be removed by simple rinsing before eating, and it can melt in the mouth during eating, and the impact on the taste of the fruit and vegetable products themselves can be ignored. As Figure 9 shown, the solubility of the oleosome film generally showed an upward trend with the increase in the added amount of oleosomes, and there was no significant difference among the groups with different added amounts. The increase in the water dissolution rate may be because after the oleosomes were compounded with chitosan and sodium carboxymethylcellulose to form a film, it had a certain impact on the internal crosslinking degree of the film solution, resulting in an increase in the water solubility of the film.

[0074] Tensile strength and elongation rate of the edible film: The mechanical properties of the edible film can be represented by the tensile strength and elongation rate. Good mechanical properties of food film packaging materials are the premise for ensuring the integrity of packaged products. The influence of different contents of oleosomes on the elongation rate of the edible film is as Figure 10 shown. After adding oleosomes, the elongation rate of the edible film increased significantly. When the added concentration of oleosomes continued to increase, the elongation rate remained almost unchanged. This shows that a certain amount of oleosomes can effectively improve the flexibility of the edible film, soften the film structure and enhance the film ductility.

[0075] From Figure 10It can be seen that as the addition amount of oleosomes increases continuously, the tensile strength of the oleosome edible film shows a trend of first increasing and then decreasing. When the addition amount is 0.5 g, the tensile strength of the film is the largest. Subsequently, as the addition amount of oleosomes increases, the tensile strength gradually decreases. And when the addition amount reaches 2.5 g, the tensile strength of the composite film is even significantly lower than that of the control group. This may be because a small amount of oleosomes can act as a lubricating material to improve the mutual sliding performance of macromolecules in the film, thereby increasing the tensile strength of the film. However, when the addition amount of oleosomes is too large, it will affect the interaction between chitosan and carboxymethyl cellulose molecules in the original film, resulting in a decrease in tensile strength.

[0076] The addition amount of oleosomes will have a significant impact on the sensory quality, water vapor permeability, solubility and mechanical strength of the edible film. After adding oleosomes to the edible film, it has better appearance quality, softness, water vapor barrier ability and solubility, and can improve the fresh-keeping performance of fruits and vegetables of the edible film. However, a high content of oleosomes will lead to a decrease in film integrity and surface oiling phenomenon, resulting in a decrease in transparency and tensile strength. When the addition amount of oleosomes is 0.5 g, the moisture regain, integrity and transparency of the film are less affected, and there is no significant difference from the control group. And it can effectively improve the compatibility of macromolecular substances in the film and increase the tensile strength. Considering the test results of various film properties and economic costs, when the addition amount is 0.5 g, the overall performance of the film is the best and the film-making cost is the lowest. Therefore, 1.19% is selected as the optimal addition amount of sesame oleosomes in the edible film.

[0077] Example 3

[0078] This example provides a method for preparing an edible film with oleosomes, including the steps:

[0079] 1) Dissolve 2.5 g of chitosan in 100 mL of 1% acetic acid solution, heat it in a water bath at 55 °C and stir magnetically until there are no suspended impurities to obtain a chitosan solution;

[0080] 2) Dissolve 3.75 g of sodium carboxymethyl cellulose in 100 mL of deionized water; mix 20 g of the chitosan solution, 20 g of the sodium carboxymethyl cellulose solution, 2 g of glycerol, and 0.5 g of sesame oleosomes (the extraction method is the same as that in Example 1), heat it in a water bath at 50 °C and stir until there are no suspended impurities;

[0081] 3) Spread the oleosome coating solution prepared in step 2) on a 90-mm bacterial culture dish, let it stand for 48 h until the bubbles disappear; place it in an oven at 45 °C for 10 h to dry and then peel off the film.

[0082] Example 4: Applied to strawberry fresh-keeping

[0083] The experimental variety was Hongyan strawberries from Xiaotangshan, Beijing. After the strawberries used in the experiment were washed and dried on the surface, they were randomly divided into three groups, with 20 strawberries in each treatment group. The experimental strawberry samples were soaked in the oleosome coating solution (prepared in Example 3) and the control coating solution without oleosomes for 30 s and then air-dried naturally, and stored at room temperature of 20-25 °C. The changes in the quality indicators of the strawberries were measured every 1 day. The strawberries in the water treatment group were used as the blank control, and each experiment was repeated three times.

[0084] Sensory determination of strawberries (appearance, color, smell): The sensory quality of strawberries is an index that comprehensively evaluates the fruits through appearance, color, and smell, and is the most intuitive factor affecting the commercial value of strawberries. As Figure 11 shown, the sensory scores of the appearance, color, and smell of the strawberries in each treatment group showed a downward trend. The fresh-keeping effects of the appearance and color of the coating treatment group were better than those of the blank control group and the control film group, and the fresh-keeping effect of the smell was basically the same. Obvious mold contamination appeared on the surface of the strawberries in the blank control group and the control film group on the 3rd day, the surface was dark red and shrank severely due to water loss, and the appearance and color scores were significantly lower than those of the oleosome film group, losing the commercial value of strawberries. The oleosome film group had a relatively good fresh-keeping effect on the 3rd day, with little difference in appearance and color from fresh strawberries. And due to the improved glossiness of the oleosome-coated surface, there were only a small number of water stain spots, and the overall quality of the strawberries was good.

[0085] Decay rate and decay index: Strawberries are prone to physical damage during post-harvest storage and transportation, leading to the invasion of microorganisms and decay. As the storage time prolonged, the decay rate and decay index of the strawberries in each treatment group showed an increasing trend. The growth trend of decay in the oleosome film group increased relatively slowly. Decay began to appear in the blank control group and the control film group on the 2nd day, and then the decay intensified and they quickly lost their edible value. However, no decay occurred in the oleosome film group within the first 2 days, the strawberry fruits were intact in shape and had good color. Slight decay began to appear after the 3rd day. At the end of storage, the decay rate and decay index of the blank control group reached 35.72% and 10.64%, respectively, and those of the control film group reached 30.04% and 8.72%, respectively, while the decay rate and decay index of the oleosome film group were only 16.67% and 6.25%. Thus, it can be seen that the oleosome coating can effectively delay the decay and deterioration process of strawberries and can extend the shelf life of strawberries by 2 days under normal temperature conditions. Research shows that tocopherols and active sterols in sesame oleosomes have antioxidant and antibacterial properties and can inhibit the growth of spoilage bacteria.

[0086] Firmness: As Figure 12As shown, the strawberry firmness of each treatment group showed a downward trend with the extension of storage time. During storage, the strawberry firmness of the oil body film group was generally higher than that of the blank control group and the control film group. The downward trend of firmness in each treatment group was relatively slow within the first 2 days, and there was little difference among the treatment groups. The downward trend of firmness increased starting from the 3rd day, which might be related to the appearance of rotting strawberries on the 3rd day. There was no significant difference in firmness among different levels of the oil body film group from the 1st to the 4th day, while the firmness of the oil body film group was significantly lower than the initial firmness on the 4th day, and the firmness of the blank control group was significantly lower than the initial firmness on the 3rd day. This indicates that the oil body film can keep strawberries in a relatively suitable gas environment, can inhibit the post-harvest ripening of fruits to a certain extent, and enable strawberries to maintain an appropriate firmness during storage.

[0087] See Figure 13 , the strawberries in the oil body film group were protected by a dense coating on the surface, reducing the direct contact between the strawberry surface and the external gas environment, effectively preventing the evaporation and dissipation of strawberry moisture, and being able to effectively reduce the water loss and oxidative deterioration of strawberries, and effectively reducing the weight loss rate. Moreover, the antibacterial components contained in sesame oil bodies themselves can inhibit the activity of microorganisms and reduce the pathological water loss of strawberries.

[0088] Soluble solid content: Soluble solids mainly refer to soluble sugars. The soluble solid content can directly reflect the sugar content in strawberry fruits and is an important indicator for measuring the ripeness and freshness of fruits. As Figure 14 can be seen, the soluble solid content of strawberries in each treatment group showed a downward trend over time. The decline of the soluble solid content in the oil body film treatment group was the slowest and the total decline was the smallest. After 5 days of storage, the soluble solid content of the oil body film treatment group was significantly higher than that of the blank control group and the control film group, indicating that the treatment with the oil body film can inhibit the conversion of soluble sugars in strawberries into alcohol substances to a certain extent, can significantly delay the post-harvest ripening of strawberries, and is beneficial to the fresh storage of strawberries.

[0089] pH and titratable acid content: Strawberries contain various organic acids, and malic acid was used as the basis in the calculation process. Acidity affects the flavor and edible quality of strawberries and is an important indicator for judging the freshness and commercial value of strawberries. As Figure 15It can be seen that the pH of strawberries in each treatment group first increases and then decreases with the increase of storage time, and the titratable acid first decreases and then increases. The organic acids in strawberries are consumed as respiratory substrates in the early stage of storage. As the maturity increases, the acidity will first gradually decrease, which can reflect the consumption degree of nutrients in the early stage of storage. After the 3rd day, spoilage occurred in strawberries in each treatment group, and the acidity decreased again due to the acid production by microbial fermentation. At the 3rd day, the content of titratable acid in the control group was significantly lower than that in the oil body membrane group, indicating that during the previous storage process, the decomposition amount of organic acids in strawberries in the control group was larger, and the loss of strawberry nutrients and taste was more serious. At the 5th day in the later stage of storage, the content of titratable acid in the control group was significantly higher than that in the oil body membrane group, probably because the spoilage degree of the control group was more serious and more acid was produced by microorganisms, indicating that the oil body membrane on the strawberry surface can delay the loss of organic acids and the spoilage process in strawberries, and can effectively extend the fresh-keeping period of strawberries.

[0090] Economic benefits of film coating for fresh-keeping: The economic benefits of this film coating fresh-keeping process were calculated by accounting for strawberries treated with oil body film coating and stored at room temperature for 2 days. Refer to Table 5. The average selling time of boxed strawberries in the fresh food chain supermarket is 3 days. The selling price of boxed strawberries is 114.29 yuan / kg (40 yuan / box, 350g / box), and the selling price after the proposed fresh-keeping treatment is the selling price in the Beijing chain supermarket. The cost of treating 1 kg of strawberry fruits was counted, and the cost was 10.50 yuan / kg. Assuming a daily sales volume of 20% for calculation and a total sales volume of 1 kg, it can be calculated that the final selling unit price of traditional strawberries is 78.86 yuan / kg, and the final selling unit price of fresh-keeping strawberries is 101.72 yuan / kg. Considering the fresh-keeping cost, the economic benefit per kg of strawberries can be directly increased by 12.36 yuan after film coating treatment.

[0091] Table 5 Details of simulated strawberry sales status

[0092]

[0093] Although the present invention has been described above through embodiments, those skilled in the art should understand that without departing from the spirit and essence of the present invention, the improvements and modifications made to the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing an edible film using oil bodies, characterized in that, Including the steps: 1) Dissolve 2 - 3 g of chitosan in 100 mL of organic acid solution, heat and stir at 50 - 60 °C to obtain a chitosan solution; the organic acid is one of acetic acid, formic acid or oxalic acid; 2) Dissolve the surfactant in water to make a solution; mix and stir the chitosan solution prepared in step 1), the solution of the surfactant, glycerol, and oleosome, heat in a water bath at 50 °C and stir until there are no suspended impurities to obtain an oleosome coating solution; the surfactant is sodium carboxymethyl cellulose with a mass concentration of 3 - 5%; the oleosome is the oleosome of white sesame seeds, and the oleosome is extracted according to the water - phase extraction method. The operation of the water - phase extraction method is as follows: soak the oil - bearing seeds in pure water and stir for 8 - 15 hours; after soaking, squeeze the seeds and water together through a twin - screw juicer to obtain an extraction pulp; keep the extraction pulp for centrifugation, and scrape the upper layer of the emulsion after centrifugation; In step 2), the proportion of raw materials is: 20 mL of chitosan solution, 20 mL of sodium carboxymethyl cellulose solution, 2 g of glycerol, and 0.5 g of oleosome; 3) Spread the oleosome coating solution prepared in step 2) on a flat surface and form a film after drying.

2. The method for preparing an edible film using liposomes according to claim 1, characterized in that, The oil seeds are soaked in pure water at a material-liquid ratio of 1:(6 - 8) (g:mL) and stirred on a magnetic stirrer for 10 - 15 hours; after soaking, the seeds and water are extruded through a twin-screw juicer to obtain an extraction pulp; the extraction pulp is reserved for low-temperature high-speed centrifugation, and the centrifugation conditions are: centrifugal force 10000 g , centrifugation time 30 min, centrifugation temperature 4°C; Scrape the upper layer of the emulsion after centrifugation.

3. The method for preparing an edible film using liposomes according to claim 1, characterized in that, In step 3), first place the mixed solution prepared in step 2) in an ultrasonic cleaner and perform ultrasonic treatment at 50 °C for 10 min in a water bath; after mixing evenly, place it in a petri dish; let it stand for 48 h until the bubbles disappear; form a film after drying.

4. The method for preparing an edible film using liposomes according to claim 1, wherein The thickness of the edible film is 0.4 - 0.6 mm.

5. Use of the oil body coating solution prepared by the method according to any one of claims 1 to 4 in food preservation, characterized in that, Soak the fruits in the oleosome coating solution for 25 - 35 s and air - dry naturally. The fruits are strawberries, grapes, apples or blueberries.

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