Method for preparing turmeric-bacterial cellulose membrane based on response surface method optimization and application of turmeric-bacterial cellulose membrane

Abstract

The invention discloses a method for preparing a turmeric-bacterial cellulose membrane based on response surface method optimization, and belongs to the technical field of biological fermentation. The method comprises the following steps: inoculating an artificial flora into turmeric powder sweet water initial fermentation liquor, further selecting an optimal turmeric powder sweet water initial fermentation liquor formula and fermentation conditions through a single-factor influence test and a Box-Behnken response surface test by taking the yield of bacterial cellulose as an evaluation index, and fermenting to prepare a turmeric-bacterial cellulose membrane; the turmeric powder matrix used in the method is preprocessed, antibacterial active ingredients of the turmeric powder matrix can be fully released, and the prepared bacterial cellulose membrane has the advantages of being high in yield, high in total phenol content, high in antibacterial activity, good in oxidation resistance and the like; on the basis, glycerol is adopted to modify the bacterial cellulose film so as to obtain the bio-based antibacterial preservative film, and the film can meet different packaging requirements, has relatively good barrier property, good smooth and flat degree and proper air permeability, and has relatively good application prospects in the fields of food preservation and packaging.

Description

Technical Field

[0001] This patent relates to a method and application for optimizing the preparation of turmeric-bacterial cellulose membrane based on response surface methodology, and belongs to the field of bio-fermentation technology. Background Art

[0002] Kombucha film is a biofilm produced by symbiotic bacteria during the fermentation process of kombucha beverages. Composed of bacterial cellulose, it floats on the surface of the beverage, helping to protect the internal community from external bacteria during the fermentation process. Compared to common plant cellulose, kombucha bacterial cellulose has unique water resistance, antioxidant properties, high surface area, and high porosity, showing broad application prospects in food preservation and packaging.

[0003] As a traditional Chinese medicinal herb, turmeric is rich in functional ingredients such as curcumin, turmerone, elemene, furadiene, curcuminone, bisacurone, cyclocurcumin, glycyrrhizin A, and germacrone. It possesses significant antimicrobial and antioxidant properties, making it an ideal plant-based fermentation substrate. Therefore, turmeric can be used as an antimicrobial active component to effectively enhance the antimicrobial properties of kombucha film, expanding its potential applications.

[0004] Existing research on kombucha is mostly centered around the control of the taste of its beverages, while the application of the bacterial cellulose membrane associated with its surface is rarely studied. Although the turmeric-bacterial cellulose membrane associated with turmeric-kombucha beverages has the functional components of both turmeric and kombucha, there are still many aspects that need to be improved in its development and application in food preservation: (1) kombucha bacterial cellulose production. Improving kombucha bacterial cellulose production is a prerequisite for promoting the development and utilization of kombucha bacterial cellulose; (2) mechanical strength. Improving the mechanical strength of kombucha bacterial cellulose is an important issue for realizing the application of kombucha bacterial cellulose in the field of food preservation packaging. Furthermore, the cell wall of turmeric is mainly composed of cellulose, hemicellulose, and lignin in different proportions. There are significant obstacles to the release of its intrinsic active polyphenol antibacterial components and the absorption and utilization of kombucha bacterial cellulose. This also limits the antibacterial and antimicrobial properties of turmeric-bacterial cellulose membranes and affects their application in the field of food preservation packaging. Summary of the Invention

[0005] In order to solve the problems in the prior art, the present invention provides a method for optimizing the preparation of turmeric-bacterial cellulose film based on the response surface methodology. According to the method, an artificial bacterial community is inoculated into an initial fermentation broth of turmeric powder and sugar water for fermentation and culture, and the response surface methodology is used to optimize the preparation of a high-yield turmeric-bacterial cellulose film. The turmeric powder matrix used can fully release its antibacterial active ingredients after pre-processing, and the prepared bacterial cellulose has the advantages of high antibacterial and antifungal activity, good antioxidant performance, and the like. On this basis, the bacterial cellulose is modified with glycerol to obtain a bio-based antibacterial fresh-keeping film, which has high mechanical strength, good barrier performance, good smoothness and appropriate air permeability, and has good application prospects in the field of food preservation packaging.

[0006] The technical solutions of the present invention are as follows: One of the objects of the present invention is to provide a method for optimizing the preparation of turmeric-bacterial cellulose membrane based on response surface methodology, wherein the preparation method comprises the following steps: S1. Preparation of a mixed culture mother solution: After activating artificial strains of Candida sp., Lodderomyces elongisporus, and Komagataeibacter sp., 15% of each culture medium was inoculated into a tea-sugar liquid medium for cultivation. Subsequently, the three culture solutions were mixed at a concentration ratio of 1:1:1, and the mixture was again inoculated into the tea-sugar liquid medium at a 15% inoculum to obtain a mixed culture mother solution. S2. Pre-processing of turmeric powder matrix: treating turmeric powder in water using an ultrasonic cell disruptor to obtain a turmeric powder matrix dispersion, wherein the ultrasonic blasting conditions are optimized using response surface methodology; S3. Preparation of turmeric-bacterial cellulose membrane: mixing a turmeric powder matrix dispersion with sucrose to obtain a turmeric powder syrup initial fermentation liquid, inoculating the mixed culture mother liquid into the turmeric powder syrup initial fermentation liquid, and placing the mixed culture mother liquid in a fermentation tank sealed with multiple layers of sterilized gauze. Optimizing the optimal formula and fermentation conditions of the turmeric powder syrup initial fermentation liquid using bacterial cellulose yield as an indicator by response surface methodology, and fermenting and culturing the turmeric-bacterial cellulose membrane. The optimal formula of the initial fermentation liquid of turmeric powder syrup comprises: 14.6 g / L turmeric powder, 42.6 g / L sucrose and water, and the fermentation culture conditions include: mixed culture mother liquor inoculation amount of 9.8%, culture temperature of 29.5 ° C, and culture time of 9 days; Furthermore, the tea syrup liquid culture medium in step S1 is prepared by adding 3.5% (w / v) sucrose and boiling water to tea water obtained by boiling and extracting 1.5% (w / v) black tea; Furthermore, the activation in step S1 comprises the following steps: inoculating Candida and Lodeella longispora on yeast culture medium, respectively, and culturing at 35°C for 3 days; inoculating Bacillus komagata on acetic acid bacteria culture medium, and culturing at 30°C for 3 days; Furthermore, the yeast culture medium is prepared by mixing 10.0 g of yeast extract, 15.0 g of peptone, 20.0 g of anhydrous glucose, 20.0 g of agar, and diluting the volume to 1000 mL with double-distilled water, and sterilizing by high pressure; Furthermore, the acetic acid bacteria culture medium is prepared by adding 10.0 g of yeast extract, 5.0 g of peptone, 50.0 g of anhydrous glucose, 20.0 g of agar, and diluting the volume to 1000 mL with double distilled water, and sterilizing by high pressure; cooling to about 50 ° C, adding 2% anhydrous ethanol and 10.0 g of CaCO3 sterilized by dry heat at 165 ° C for 2 h; Furthermore, the specific steps of the response surface methodology in step S2 are as follows: a. Single factor effect test; using an ultrasonic disruptor to ultrasonically blast turmeric powder in water to obtain a turmeric powder matrix dispersion, mixing the turmeric powder matrix dispersion with sucrose to obtain a turmeric powder syrup initial fermentation liquid, the formula of the turmeric powder syrup initial fermentation liquid is: 10 g / L turmeric powder matrix dispersion, 35 g / L sucrose; the mixed culture mother liquor described in step S1 is inoculated into the turmeric powder syrup initial fermentation liquid and placed in a fermenter with a tank mouth wrapped by multiple layers of sterilized gauze to ferment and culture to obtain an initial turmeric-bacterial cellulose film, wherein the fermentation culture conditions include: a mixed culture mother liquor inoculation amount of 15%, a culture temperature of 25°C, and a culture time of 9 days; then, with power, time, and solid-liquid ratio as variables and the total phenol content of bacterial cellulose as an evaluation index, a single factor effect test is carried out to screen out the optimal levels of power, time, and solid-liquid ratio for ultrasonic blasting; the optimal levels are solid-liquid ratio of 1:30~1:50 g / mL, ultrasonic power of 100~140 W, and time of 10~20 min; b. Box-Behnken response surface experiment: The power, time, and material-liquid ratio of the ultrasonic blasting were used as the independent variable range, the total phenol content of the turmeric-bacterial cellulose membrane was used as the response value, and the formula of the initial fermentation liquid of turmeric powder and sugar water of the turmeric-bacterial cellulose membrane and the fermentation culture conditions were the same as those in step a. A response surface experiment was designed according to the Box-Behnken principle, and a multiple regression equation was obtained between the total phenol content of the bacterial cellulose and each variable through multiple regression fitting; the multiple regression equation is: Y=3.33+0.0513A++0.0138B+0.0675C-0.0350AB-0.0425AC-0.0075BC-0.1585A²-0.2385B²-0.1310 C²; Among them: A is the material-liquid ratio, B is the power, and C is the time.

[0007] c. Optimizing the process parameters of the model using Design-Expert software based on the multiple regression equation to determine the optimal conditions for ultrasonic blasting. Under these conditions, an ultrasonic cell disruptor was used to ultrasonically blast the turmeric powder in water to obtain the turmeric powder matrix dispersion; wherein the optimal conditions were: power 41 W, time 16 min, and a solid-liquid ratio of 1:41.

[0008] Furthermore, the specific steps of the response surface methodology in step S3 are as follows: a. Single factor effect test: The turmeric powder matrix dispersion described in step S2 is mixed with sucrose to obtain a turmeric powder syrup initial fermentation liquid, and the culture time is fixed at 9 days. The mixed culture mother liquid described in step S1 is inoculated into the turmeric powder syrup initial fermentation liquid and placed in a fermenter for fermentation and culture. A single factor effect test is performed with the amount of turmeric powder added, the amount of sucrose added, the inoculum size of the mixed culture mother liquid, and the culture temperature as variables. The optimal levels of turmeric powder addition, sucrose addition, mixed culture mother liquid inoculum size, and culture temperature are screened using the turmeric-bacterial cellulose film yield as the measurement index; the optimal levels are: turmeric powder addition 12.5-17.5 g / L, sucrose addition 20-60 g / L, inoculum size 8%-12%, and culture temperature 25-35 ° C. b. Box-Behnken response surface experiment: The culture time was fixed at 9 days. Based on the results of the single factor effect experiment, the amount of turmeric powder added, the amount of sucrose added, the inoculum size of the mixed culture mother solution, and the culture temperature were used as independent variables, and their optimal levels were used as the independent variable range. The yield of turmeric-bacterial cellulose film was used as the response value. A response surface experiment was designed according to the Box-Behnken principle. Through multiple regression fitting, a multiple regression equation was obtained between the yield of turmeric-bacterial cellulose film and each variable. The multiple regression equation is: Y=2.14-0.1017A+0.2292B-0.0767C-0.0275D-0.0025AB+0.0225AC+0.0000D+0.0700BC-0.0950BD+0.0075 CD-0.3266 A²-0.8828 B²-0.2666 C²-0.2528 D²; Wherein: A is the amount of turmeric added, B is the sucrose concentration, C is the culture temperature, and D is the inoculum size of the mixed culture mother solution.

[0009] c. Based on the above multiple regression equation, the process parameters were optimized using Design-Expert software to determine the optimal formula and fermentation conditions for the initial fermentation liquid of turmeric powder and sugar water for producing turmeric-bacterial cellulose membrane.

[0010] The second purpose of the present invention is to apply the turmeric-bacterial cellulose film to the field of food preservation and packaging.

[0011] The present invention also provides an antibacterial bio-based fresh-keeping film, and a preparation method thereof comprises the following steps: soaking a turmeric-bacterial cellulose film in a glycerol solution, taking it out and drying it to obtain the antibacterial bio-based fresh-keeping film.

[0012] Furthermore, the glycerol solution is prepared by mixing glycerol and distilled water, and the glycerol concentration may be 0-30%; preferably, the glycerol concentration is 20%.

[0013] Different from the prior art, the present invention has the following beneficial effects: 1. The present invention inoculates a mixed culture mother liquor prepared by activating artificial strains of Candida sp., Lodderomyces elongisporus, and Komagataeibacter sp. into an initial fermentation broth of turmeric powder and sugar solution to produce a turmeric-bacterial cellulose membrane through in situ fermentation. The bacterial cellulose contains functional components of turmeric and has better biological activity than traditional kombucha bacterial cellulose. The turmeric powder matrix used in the bacterial cellulose is pre-processed by ultrasonic blasting. The ultrasonic blasting pre-processing conditions are optimized using response surface methodology to fully release the antibacterial active components of turmeric. The total phenol content, antioxidant properties, and antibacterial activity of the resulting bacterial cellulose are significantly improved.

[0014] 2. The formula of the initial fermentation liquid of turmeric powder and sugar water and the fermentation culture conditions of the turmeric-bacterial cellulose membrane of the present invention are optimized by response surface methodology. The preferred fermentation culture conditions are more conducive to the decomposition of polyphenol components of turmeric powder by microorganisms, thereby increasing the active ingredients of the fermentation liquid. At the same time, the optimization of the fermentation liquid formula and fermentation culture conditions can effectively increase the yield and thickness of the kombucha bacterial cellulose. The thicker bacterial cellulose can sink into the fermentation liquid in the later stage of fermentation culture, thereby increasing the contact area between the bacterial cellulose and the fermentation liquid, which can effectively promote the bacterial cellulose to absorb the active ingredients in the fermentation liquid. The above measures have significantly improved the yield of the prepared turmeric-bacterial cellulose membrane. At the same time, its performance in antibacterial, antibacterial, and antioxidant aspects has also been further optimized and improved.

[0015] 3. The bio-based antibacterial cling film made from the turmeric-bacterial cellulose film provided by the present invention can meet different packaging needs, has good barrier properties, good smoothness and appropriate air permeability; compared with previous technologies, the present invention introduces turmeric as an antibacterial functional ingredient, which can effectively improve the antibacterial properties of the bio-based antibacterial cling film; the present invention uses glycerol-modified bacterial cellulose film to make a bio-based antibacterial cling film, and its elongation at break is significantly improved; the introduction of glycerol softens the rigid structure of the film, and improves the flexibility, ductility and processability of the cling film; glycerol interspersed between polymer chains can reduce the intermolecular attraction to a certain extent, reduce the dense structure of the cling film, and make the cling film have appropriate air permeability; at the same time, the introduction of glycerol makes the cling film exhibit better smoothness.

[0016] 4. The antimicrobial bio-based cling film prepared in the present invention is applied to the fresh-keeping packaging of blueberries. The packaged blueberries are superior to those without film coating or those coated with other films in terms of sensory evaluation scores, hardness, total bacterial count, and rotten fruit rate. After long-term storage, the blueberries coated with the antimicrobial bio-based cling film of the present invention have better performance in appearance, spoilage, and total bacterial count. The antimicrobial bio-based cling film is environmentally friendly and pollution-free. After 15 days of burial in the soil, the film is almost completely degraded. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a single factor experimental diagram of the effect of different ultrasonic blasting conditions of turmeric powder on the total phenol content of bacterial cellulose in Example 1, where (a) is the material-liquid ratio, (b) is the time, and (c) is the power.

[0018] Figure 2 (a), (b), and (c) are respectively the three-dimensional response surface diagrams of the effects of power and material-liquid ratio on the total phenol content of the membrane in Example 1, the three-dimensional response surface diagrams of the effects of material-liquid ratio and time on the total phenol content of the membrane, and the three-dimensional response surface diagrams of the effects of power and time on the total phenol content of the membrane Figure 3 Figure 1 is a single factor experimental diagram of the effects of different turmeric powder syrup recipes and bacterial cellulose fermentation conditions on bacterial cellulose yield in Example 1, wherein (a) is the effect of turmeric powder addition on membrane yield, (b) is the effect of sucrose addition on membrane yield, (c) is the effect of fermentation temperature on membrane yield, and (d) is the effect of inoculum size on membrane yield.

[0019] Figure 4 The response diagrams of the two-factor interaction on membrane yield in Example 1: (a) is the response surface of inoculum size and temperature, (b) is the response surface of sucrose addition amount and turmeric powder addition amount, (c) is the response surface of inoculum size and turmeric powder addition amount, (d) is the response surface of temperature and sucrose addition amount, (e) is the response surface of inoculum size and sucrose addition amount, and (f) is the response surface of temperature and turmeric powder.

[0020] Figure 5 (a), (b), and (c) are the effects of different glycerol concentrations on the elongation at break, breaking strength, and water vapor permeability of the membrane.

[0021] Figure 6 These are photos of the antibacterial bio-based cling film of Example 5 being bent, folded, stretched, twisted, and knotted.

[0022] Figure 7 The scanning electron microscope images of Example 1 (left) and Example 5 (right) are shown.

[0023] Figure 8 The infrared spectra of the samples of Example 1, Comparative Example 1 and Example 5 are shown.

[0024] Figure 9 The sensory evaluation panel's evaluation results on the samples.

[0025] Figure 10 The order is changes in the hardness of stored blueberry fruits, changes in the rate of rotten fruit, changes in titratable acid content, changes in weight loss rate, and changes in the total number of colonies.

[0026] Figure 11 This is the change of film quality during the period of burial of plastic wrap. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with the accompanying drawings and preferred embodiments. The given embodiments are only for illustrating the present invention, rather than for limiting the scope of the present invention.

[0028] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources. The methods in the following embodiments are all conventional methods unless otherwise specified.

[0029] Example 1 This embodiment provides a method for optimizing the preparation of turmeric-bacterial cellulose membrane based on response surface methodology, comprising the following steps: S1. Preparation of mixed culture mother liquor: Artificial strains of Candida sp. and Lodderomyces elongisporus were inoculated on yeast culture medium and activated at 35°C for 3 days; Komagataeibacter sp was inoculated on acetic acid bacteria culture medium and activated at 30°C for 3 days; the three activated fermentation broths were then inoculated into tea sugar water liquid culture medium at a 15% inoculum size and cultured for 3 days at a temperature of 25-30°C. Subsequently, 5 mL of each of the three culture broths was taken, mixed, and again inoculated into tea sugar water liquid culture medium at a 15% inoculum size to obtain a mixed culture mother liquor; The yeast culture medium is prepared by mixing 10.0 g of yeast extract, 15.0 g of peptone, 20.0 g of anhydrous glucose, 20.0 g of agar, and diluting the volume to 1000 mL with double-distilled water, and sterilizing by high pressure. The acetic acid bacteria culture medium was prepared by adding 10.0 g of yeast extract, 5.0 g of peptone, 50.0 g of anhydrous glucose, 20.0 g of agar, and diluting the volume to 1000 mL with double-distilled water, followed by autoclaving; cooling to about 50 °C, adding 2% anhydrous ethanol, and 10.0 g of CaCO3 sterilized by dry heat at 165 °C for 2 h; The tea sugar liquid culture medium is prepared by adding 3.5% (w / v) sucrose and boiling water to the tea water obtained by boiling and extracting 1.5% (w / v) black tea; S2. Pre-processing of turmeric powder matrix: ultrasonic cell disruptor was used to ultrasonically blast turmeric powder in water. The total phenol content of bacterial cellulose was used as an indicator, and the optimal ultrasonic blasting conditions were optimized by response surface methodology to obtain turmeric powder matrix dispersion. Among them, the best ultrasonic blasting conditions were power 41 W, time 16 min, and material-liquid ratio 1:41; S3. Preparation of turmeric-bacterial cellulose membrane: mixing a turmeric powder matrix dispersion with sucrose to obtain a turmeric powder syrup initial fermentation broth, inoculating the mixed culture mother liquor into the turmeric powder syrup initial fermentation broth, and fermenting the mixture in a fermenter. Optimizing the optimal formula and fermentation conditions of the turmeric powder syrup initial fermentation broth using bacterial cellulose yield as an indicator by response surface methodology to obtain the turmeric-bacterial cellulose membrane; The formula of the initial fermentation liquid of turmeric powder syrup is: 14.6 g / L turmeric powder matrix dispersion, 42.6 g / L sucrose, and the fermentation culture conditions include: mixed culture mother liquor inoculation amount of 9.8%, culture temperature of 29.5 ° C, and culture time of 9 days.

[0030] The formula of the turmeric powder syrup initial fermentation liquid and the fermentation culture conditions are optimized by response surface methodology.

[0031] The yield of the turmeric-bacterial cellulose membrane prepared in this example in the fermentation broth was 2.05±0.13 g / L.

[0032] The specific steps of the response surface method in step S2 in this embodiment are as follows: (1) Single-factor experiment Turmeric powder is ultrasonically blasted in water using an ultrasonic disruptor to obtain a turmeric powder matrix dispersion, and the turmeric powder matrix dispersion is mixed with sucrose to obtain a turmeric powder syrup initial fermentation liquid, wherein the formula of the turmeric powder syrup initial fermentation liquid is: 10 g / L turmeric powder matrix dispersion, 35 g / L sucrose; the mixed culture mother liquid described in step S1 is inoculated into the turmeric powder syrup initial fermentation liquid and placed in a fermenter for fermentation and culture to obtain a turmeric-bacterial cellulose film, wherein the fermentation culture conditions include: a mixed culture mother liquid inoculation amount of 15%, a culture temperature of 25°C, and a culture time of 9 days; then, using power, time, and material-liquid ratio as variables and the total phenol content of the bacterial cellulose as an evaluation index, the effects of changes in the three factors on the total phenol content of the obtained bacterial cellulose are explored, and the optimal level of each variable is screened out: 1) Effect of power on the total phenol content of bacterial cellulose: A single-factor experiment was conducted with power as the variable, with a fixed time of 10 min and a fixed solid-liquid ratio of 1:30. The total phenol content of the produced bacterial cellulose was tested. 2) Effect of solid-liquid ratio on the total phenol content of bacterial cellulose: A single-factor experiment was conducted with the solid-liquid ratio as the variable, with the time fixed at 10 min and the power fixed at 100 W, and the solid-liquid ratio set at 1:20, 1:30, 1:40, 1:50, and 1:60, to test the total phenol content of the prepared bacterial cellulose. 3) Effect of time on the total phenol content of bacterial cellulose: The solid-liquid ratio was fixed at 1:30, the power was fixed at 100 W, and the time was set to 5 min, 10 min, 15 min, 20 min and 25 min, respectively. A single-factor experiment with time as the variable was conducted to test the total phenol content of the prepared bacterial cellulose membranes.

[0033] (2) Box-Behnken response surface experiment The results of the single factor test are as follows Figure 1 As shown in the figure, the optimal level of each factor in the single factor experiment was used as the independent variable range, and the total phenol content of turmeric-bacterial cellulose film was used as the response value. The response surface experiment was designed according to the Box-Behnken principle. The formula and fermentation conditions of the initial fermentation liquid of bacterial cellulose with turmeric powder and sugar water were the same as those in the single factor experiment in step (1). The optimal level of each variable selected in the response surface experiment is shown in Table 1. The design scheme and results of the response surface experiment are shown in Table 2.

[0034] Table 1 Factors and levels of ultrasonic blasting response surface test

[0035] Table 2 Design scheme and results of ultrasonic blasting response surface test Test No. A. Material-liquid ratio B. Time (min) C. Power (W) Phenol content 1 40 120 15 3.37 2 40 120 15 3.31 3 40 100 10 2.84 4 40 120 15 3.32 5 40 120 15 3.34 6 50 120 20 3.10 7 50 120 10 3.07 8 40 140 10 2.93 9 30 100 15 2.85 10 30 120 20 3.10 11 40 120 15 3.32 12 50 140 15 2.95 13 30 140 15 2.90 14 40 140 20 3.07 15 30 120 10 2.90 16 40 100 20 3.01 17 50 100 15 3.04 Through multiple regression fitting, the regression equation between the total phenol content of bacterial cellulose and each variable was obtained: Y=3.33+0.0513A++0.0138B+0.0675C-0.0350AB-0.0425AC-0.0075BC-0.1585A²-0.2385B²-0.1310 C²; Among them, A is the material-liquid ratio, B is the power, and C is the time.

[0036] Based on the above regression model, a response surface analysis diagram was drawn to study the effects of ultrasonic blasting conditions such as material-liquid ratio, power, and time on the total phenol content of bacterial cellulose. Figure 2 As shown. The above regression model was subjected to variance analysis, as shown in Table 3: The F value was 50.58, P < 0.0001, indicating that the model has a high significance. The lack of fit term was 0.1306, which exceeded 0.05 and the difference was not significant, indicating that the error between the model and the experimental value was small. This model can be used to predict and analyze the total phenol content of the membrane. The correlation coefficient R of the model 2 = 0.9849, indicating a good fit between the measured and predicted total phenolic content values ​​of the membranes. The experimental data are highly reliable and can be used to theoretically predict the total phenolic content of turmeric fermented membranes. The adjusted correlation coefficient R² = 0.9654 indicates that this mathematical model explains 96.54% of the variability in the total phenolic content of the membranes. The linear terms A (material-liquid ratio) and C (time) have extremely significant effects on the total phenolic content of the membranes (P < 0.01). The F-value indicates that the significance of the influence of each factor on the total phenolic content of the bacterial cellulose membranes is as follows: time > material-liquid ratio > power.

[0037] Table 3 Variance analysis of ultrasonic blasting regression model

[0038] Note: **: p < 0.01, extremely significant difference; *: p < 0.05, significant difference.

[0039] (3) Optimal process conditions Based on the above multivariate regression equation, the process parameters were optimized using Design-Expert software to determine the optimal ultrasonic blasting conditions. The optimal conditions were: power 41.28 W, duration 16.17 min, and a solid-liquid ratio of 1:41.28. Under these conditions, the predicted total phenolic content of the bacterial cellulose was 3.34 mg / g. Considering actual operation, the optimal process conditions were adjusted to power 41 W, duration 16 min, and a solid-liquid ratio of 1:41.

[0040] Three parallel experiments were carried out under this optimized condition, and the total phenol content of bacterial cellulose was verified to be 3.24 mg / g, which was close to the data predicted by the response surface optimization method, indicating that the regression model has a good prediction effect. The process of crushing turmeric powder to ferment and produce film to increase the phenol content is reliable.

[0041] The specific steps of the response surface method in step S3 in this embodiment are as follows: (1) Single-factor experiment The culture time was fixed at 9 days. The mixed culture mother liquor was inoculated into the initial fermentation liquid of turmeric powder and sugar water and placed in a fermenter for fermentation culture. A single factor effect test was conducted with the amount of turmeric powder added, the amount of sucrose added, the inoculation amount of the mixed culture mother liquor, and the culture temperature as variables. The bacterial cellulose film yield was used as the measurement indicator to screen out the optimal levels of turmeric powder addition, sucrose addition, mixed culture mother liquor inoculation amount, and culture temperature. The specific steps of the single factor effect test are as follows: 1) Effect of turmeric powder addition on bacterial cellulose film yield: In a single-factor experiment with turmeric powder addition as the variable, turmeric powder addition was set at 0.75%, 1%, 1.25%, 1.75%, and 2%, respectively. 200 mL of distilled water, 3.5% sucrose, and 10% yeast inoculum were added to 250 mL beakers, mixed thoroughly, sealed with gauze, and fermented at 25 °C for 9 days. The membranes were then dried and weighed. 2) Effect of bacterial solution addition amount on bacterial cellulose film yield: In a single-factor experiment with inoculum size as the variable, the bacterial solution inoculum size was set at 5%, 10%, 15%, 20%, and 25%, respectively. The sucrose addition amount was 3.5%, the turmeric powder addition amount was 1.5%, and 200 mL of distilled water was dispensed into 250 mL beakers. After thorough mixing, the beakers were sealed with gauze and fermented at 25 °C for 9 days. The membranes were then dried and weighed. 3) Effect of sugar addition on bacterial cellulose film yield: In a single-factor experiment with sucrose addition as the variable, sucrose addition was set at 2%, 4%, 6%, 8%, and 12%, turmeric powder addition was 1.5%, bacterial liquid addition was 10%, and 200 mL of distilled water was dispensed into 250 mL beakers. After thorough mixing, the mixture was sealed with gauze and fermented at 25 °C for 9 days. The membranes were then dried and weighed. 4) Effect of fermentation temperature on cellulose film yield: In a single-factor experiment with fermentation temperature as the variable, the fermentation temperatures were set at 20 °C, 25 °C, 30 °C, 35 °C, and 40 °C. The added amounts of turmeric powder were 1.5%, sucrose were 3.5%, and the inoculum size was 10%. 200 mL of distilled water were divided into 250 mL beakers, mixed thoroughly, sealed with gauze, and fermented at 25 °C for 9 days. The membranes were then dried and weighed.

[0042] (2) Response surface experiment The results of the single factor test are as follows Figure 3 As shown in Figure 4, based on the results of the single factor effect test, the amount of turmeric powder added, the amount of sucrose added, the inoculum size of the mixed culture mother liquid, and the culture temperature were used as independent variables, their optimal levels were used as the independent variable range, the yield of turmeric-bacterial cellulose film was used as the response value, and the culture time was fixed at 9 days. The response surface experiment was designed according to the Box-Behnken principle. The optimal levels of the various variables selected in the response surface experiment are shown in Table 4, and the design scheme and results of the response surface experiment are shown in Table 5.

[0043] Through multiple regression fitting, the multiple regression equation between the yield of turmeric-bacterial cellulose film and each variable was obtained: Y=2.14-0.1017A+0.2292B-0.0767C-0.0275D-0.0025AB+0.0225AC+0.0000D+0.0700BC-0.0950BD+0.0075 CD-0.3266 A²-0.8828 B²-0.2666 C²-0.2528 D²; Among them, A is the amount of turmeric added, B is the sucrose concentration, C is the culture temperature, and D is the inoculum size of the mixed culture mother solution.

[0044] Based on the above regression model, a response surface analysis diagram was drawn to study the effects of turmeric powder addition, sucrose addition, mixed culture mother liquid inoculation amount, and culture temperature on bacterial cellulose production. Figure 4 The above regression model was subjected to variance analysis, as shown in Table 6.

[0045] An analysis of variance analysis was conducted based on the experimental results. As shown in Table 4, the model's F-value was 43.86, with a P value of <0.0001, indicating that the model was significant. The lack-of-fit term was 0.1234, indicating a nonsignificant difference, indicating that the error between the model and the experimental values ​​was small. This model can be used to predict and analyze the yield of bacterial cellulose membranes. The model's correlation coefficient, R², was 0.9777, indicating a good fit between the actual measured and predicted values ​​for bacterial cellulose membrane yield, demonstrating that the experimental data can be used to theoretically predict bacterial cellulose membrane yield. The adjusted correlation coefficient, R², was 0.9554, indicating that this mathematical model can explain 95.54% of the variability in cellulose membrane yield. Sucrose concentration and turmeric addition had extremely significant effects on bacterial cellulose membrane yield (P<0.01), while temperature had a significant effect (P<0.05).

[0046] Table 4 Independent variables and levels of response surface experiment on the formula of turmeric-bacterial cellulose membrane fermentation broth and fermentation conditions

[0047] Table 5 Design and results of response surface experiment on the formulation and fermentation conditions of turmeric-bacterial cellulose membrane fermentation broth Test No. Turmeric powder addition amount (g / L) Sucrose addition amount (g / L) Cultivation temperature (°C) Mixed culture mother liquor inoculation amount (%) Bacterial cellulose yield (g / L) 1 15 60 30 12 1.01 2 12.5 40 30 8 1.75 3 15 40 25 8 1.71 4 15 40 30 10 2.18 5 17.5 60 30 10 1.01 6 15 20 25 10 0.86 7 15 60 35 10 1.4 8 17.5 40 30 12 1.51 9 15 40 30 10 2.21 10 15 60 30 8 1.33 11 15 40 30 10 2.15 12 12.5 20 30 10 0.79 13 15 40 25 12 1.62 14 12.5 60 30 10 1.2 15 15 40 30 10 2.13 16 17.5 40 35 10 1.33 17 15 40 35 8 1.55 18 15 20 30 8 0.75 19 17.5 40 25 10 1.56 20 17.5 40 30 8 1.47 21 15 40 35 12 1.59 22 15 60 25 10 1.3 23 12.5 40 35 10 1.63 24 15 20 35 10 0.68 25 15 20 30 12 0.81 26 17.5 20 30 10 0.61 27 12.5 40 25 10 1.75 28 15 40 30 10 2.05 29 12.5 40 30 12 1.79 Table 6 Variance analysis of the regression model of turmeric-bacterial cellulose membrane fermentation broth formula and fermentation conditions

[0048] Note: **: p < 0.01, extremely significant difference; *: p < 0.05, significant difference.

[0049] (3) Optimal process conditions Based on the above multiple regression equation, the process parameters were optimized using Design-Expert software to determine the optimal formula and fermentation conditions for the initial fermentation broth of turmeric powder and sugar solution for producing turmeric-BC membranes. The optimal process conditions were: a turmeric powder syrup initial fermentation broth containing 14.5972 g / L of turmeric powder, 42.5791 g / L of sucrose, and water; a culture temperature of 29.3266 °C; and an inoculum size of 9.83984% of the mixed culture mother liquor. Under these conditions, the predicted yield of turmeric-BC membranes was 2.17323 g / L. Considering practical operation, the optimal process conditions were adjusted to: a turmeric powder syrup initial fermentation broth containing 14.6 g / L of turmeric powder, 42.6 g / L of sucrose, and water; a culture temperature of 29.5 °C; and an inoculum size of 9.8% of the mixed culture mother liquor.

[0050] It has been verified that the actual yield of turmeric-bacterial cellulose membrane produced under these conditions in the fermentation broth is 2.05±0.13 g / L, which is close to the data predicted by the response surface optimization method mentioned above. The regression model has a good prediction effect, and this method is reliable for studying the process of turmeric-bacterial cellulose membrane.

[0051] Comparative Example 1 This comparative example provides a turmeric-bacterial cellulose membrane, which differs from Example 1 in that the formula and fermentation conditions of the turmeric powder tea syrup liquid culture medium are different, and the turmeric powder matrix is ​​not pretreated by ultrasonic blasting. The preparation method thereof comprises the following steps: S1. Preparation of mixed culture mother liquor: Candida sp. and Lodderomyces elongisporus were inoculated on yeast culture medium and activated at 35°C for 3 days; Komagataeibacter sp was inoculated on acetic acid bacteria culture medium and activated at 30°C for 3 days; the three activated fermentation broths were then inoculated into tea sugar water liquid culture medium at a 15% inoculum size and cultured for 3 days at a temperature of 25-30°C. Subsequently, 5 mL of each of the three culture broths was taken, mixed, and again inoculated into tea sugar water liquid culture medium at a 15% inoculum size to obtain a mixed culture mother liquor; The yeast culture medium is prepared by mixing 10.0 g of yeast extract, 15.0 g of peptone, 20.0 g of anhydrous glucose, 20.0 g of agar, and diluting the volume to 1000 mL with double-distilled water, and sterilizing by high pressure. The acetic acid bacteria culture medium was prepared by adding 10.0 g of yeast extract, 5.0 g of peptone, 50.0 g of anhydrous glucose, 20.0 g of agar, and diluting the volume to 1000 mL with double-distilled water, followed by autoclaving; cooling to about 50 °C, adding 2% anhydrous ethanol, and 10.0 g of CaCO3 sterilized by dry heat at 165 °C for 2 h; The tea sugar liquid culture medium is prepared by adding 3.5% (w / v) sucrose and boiling water to the tea water obtained by boiling and extracting 1.5% (w / v) black tea; S2. Preparation of turmeric-bacterial cellulose membrane: inoculating the mixed culture mother liquid into the initial fermentation liquid of turmeric powder and sugar water and placing the mixture in a fermentation tank, and fermenting and culturing the mixture in a dark, cool and well-ventilated environment to obtain the turmeric-bacterial cellulose membrane; The formula of the initial fermentation liquid of turmeric powder syrup includes: 10 g / L turmeric powder, 35 g / L sucrose, and the fermentation conditions are: mixed culture mother liquid inoculation amount 15%, culture temperature 25 ° C, and culture time 9 days.

[0052] The yield of the turmeric-bacterial cellulose membrane in the fermentation broth of this comparative example was 1.0 g / L.

[0053] Example 2 This embodiment provides a bio-based antibacterial cling film, and the preparation method thereof comprises the following steps: cutting the turmeric-bacterial cellulose film obtained in Example 1 into a 5 cm × 2 cm film sheet, soaking it in a glycerol solution for 2 seconds, taking it out and vacuum drying it at 40 ° C for 24 hours to obtain the antibacterial bio-based cling film.

[0054] The glycerol solution is a mixture of glycerol and water, and the glycerol concentration can be 0-25%. In this embodiment, the glycerol concentration is 5%.

[0055] Example 3 This embodiment provides a bio-based antibacterial cling film, and the preparation method thereof comprises the following steps: cutting the turmeric-bacterial cellulose film obtained in Example 1 into a 5 cm × 2 cm film sheet, soaking it in a glycerol solution for 2 seconds, taking it out and vacuum drying it at 40 ° C for 24 hours to obtain the antibacterial bio-based cling film.

[0056] The glycerol solution is a mixture of glycerol and water, and the glycerol concentration can be 0-30%. In this embodiment, the glycerol concentration is 10%.

[0057] Example 4 This embodiment provides a bio-based antibacterial cling film, and the preparation method thereof comprises the following steps: cutting the turmeric-bacterial cellulose film obtained in Example 1 into a 5 cm × 2 cm film sheet, soaking it in a glycerol solution for 2 seconds, taking it out and vacuum drying it at 40 ° C for 24 hours to obtain the antibacterial bio-based cling film.

[0058] The glycerol solution is a mixture of glycerol and water, and the glycerol concentration can be 0-30%. In this embodiment, the glycerol concentration is 15%.

[0059] Example 5 This embodiment provides a bio-based antibacterial cling film, and the preparation method thereof comprises the following steps: cutting the turmeric-bacterial cellulose film obtained in Example 1 into a 5 cm × 2 cm film sheet, soaking it in a glycerol solution for 2 seconds, taking it out and vacuum drying it at 40 ° C for 24 hours to obtain the antibacterial bio-based cling film.

[0060] The glycerol solution is a mixture of glycerol and water, and the glycerol concentration can be 0-30%. In this embodiment, the glycerol concentration is 20%.

[0061] Example 6 This embodiment provides a bio-based antibacterial cling film, and the preparation method thereof comprises the following steps: cutting the turmeric-bacterial cellulose film obtained in Example 1 into a 5 cm × 2 cm film sheet, soaking it in a glycerol solution for 2 seconds, taking it out and vacuum drying it at 40 ° C for 24 hours to obtain the antibacterial bio-based cling film.

[0062] The glycerol solution is a mixture of glycerol and water, and the glycerol concentration can be 0-30%. In this embodiment, the glycerol concentration is 25%.

[0063] Comparative Example 2 This comparative example provides a bio-based cling film, and the preparation steps of the bio-based antibacterial cling film include: soaking the turmeric-bacterial cellulose film prepared in Example 1 in water to remove the culture medium, bacteria and impurities remaining on the surface, washing the film with 75% ethanol to change the film from yellow to white, and soaking and boiling it in a 0.2 mol / L NaOH solution for five minutes to remove the biological activity of the bacterial cellulose, and then immersing it in a 20% glycerol solution. After drying, the bio-based cling film is obtained.

[0064] Performance Testing (1) Bioactivity test of turmeric-bacterial cellulose membrane The fermentation conditions of the turmeric-bacterial cellulose film prepared in Example 1 and the formula of the initial fermentation broth of turmeric powder and sugar water were optimized by response surface methodology. The bacterial cellulose yield could reach 2.05±0.13 g per liter of fermentation broth, while the bacterial cellulose yield prepared by the conventional method in Comparative Example 1 was only 1 g per liter of fermentation broth. It can be seen that the bacterial cellulose yield in Example 1 is significantly better than that in Comparative Example 1, and is more suitable for the promotion and utilization of kombucha bacterial cellulose.

[0065] Table 7 shows the bioactivity test of turmeric-bacterial cellulose film. The intrinsic polyphenol components of turmeric are fully released and absorbed thanks to the ultrasonic blasting pre-processing of the turmeric powder matrix. The bioactivity characteristics of the bacterial cellulose in Example 1 are significantly enhanced. The total phenol content of the bacterial cellulose in Comparative Example 1 is 2.5 ± 0.11 mg / g, and the total phenol content of the bacterial cellulose in Example 1 is the highest, 3.41 ± 0.61 mg / g. The results show that the polyphenol content of the bacterial cellulose pre-processed by ultrasonic blasting is improved. At the same time, thanks to the optimization of the fermentation conditions and the initial fermentation liquid formula of turmeric powder syrup by response surface methodology, the optimized fermentation culture conditions also further promote the microbial decomposition of the polyphenol components of turmeric powder and increase the active ingredients of the fermentation liquid. At the same time, the optimization of the fermentation liquid formula and fermentation culture conditions can effectively increase the yield and thickness of the kombucha bacterial cellulose. The thicker bacterial cellulose can sink into the fermentation liquid in the later stage of fermentation culture, and the contact area between the bacterial cellulose and the fermentation liquid is increased, which promotes the bacterial cellulose to absorb the active ingredients in the fermentation liquid. The scavenging rates of the bacterial cellulose in comparative example 1 for the antioxidant detection reagents DPPH and ABTS were 64.33% and 62.34%, respectively, while those of the bacterial cellulose in Example 1 were increased to 75.33% and 83.33%, respectively. It can be seen that the antioxidant performance of the bacterial cellulose in Example 1 is significantly improved; the antibacterial test results are also similar to those of the antioxidant performance, and the sample in Example 1 has better performance in antioxidant and antibacterial properties.

[0066] In summary, the turmeric-bacterial cellulose film prepared by the method for preparing turmeric-bacterial cellulose film based on response surface methodology as described in Example 1 has a high yield and has better performance in terms of total phenol content, antibacterial and sterilization activity, and antioxidant properties. It is superior to the turmeric-bacterial cellulose film prepared by the conventional method and is more suitable for the promotion and application of kombucha bacterial cellulose.

[0067] Table 7 Biological activity characteristics of bacterial cellulose in Example 1 and Comparative Example 1

[0068] (2) Structural characterization of bio-based antibacterial cling film As described in Examples 2 to 6, the present invention soaks the turmeric-bacterial cellulose film prepared by the method described in Example 1 in a glycerol solution to prepare a bio-based antibacterial cling film; the bio-based antibacterial cling films of Examples 2 to 6 are tested for mechanical strength, barrier properties, and micromorphology.

[0069] The mechanical properties of the membrane were measured by texture analyzer; Figure 5 As shown in Examples 2-6, the effect of glycerol on the mechanical properties of the membranes: the membrane elongation at break is positively correlated with the glycerol concentration. The membrane elongation at break is only 2% when not impregnated with glycerol, while it reaches 16% when impregnated with 30% glycerol. A small amount of glycerol can slightly improve the breaking strength of the bacterial cellulose. After impregnation with a small amount of glycerol, the breaking strength of the membrane is slightly increased. However, when the glycerol concentration exceeds 20%, the bacterial cellulose is significantly softened, and the breaking strength decreases significantly.

[0070] The introduction of glycerol weakens the polymer-polymer interaction and reduces the intermolecular friction between the polymer chains of the plastic wrap, which allows the plastic wrap to deform without breaking, thereby improving the flexibility, ductility and processability of the plastic wrap. Figure 6 These are photos of the bending, folding, twisting and knotting of the sample of Example 5, which show that the sample has good flexibility and ductility.

[0071] The barrier property test of plastic wrap uses the cup method to determine the moisture barrier property of the sample. The test steps are as follows: 3g of calcium chloride is placed at the bottom of a triangular vial with the same diameter as the bottle mouth, and the bottle mouth sealing film sample is sealed. The change in mass reflects the water vapor transmission rate. The water vapor transmission rate is calculated as follows:

[0072] Where: ∆m is the amount of water vapor migration (g); S is the area of ​​the membrane (m 2 ); t is the measurement time (h).

[0073] like Figure 5As shown, the water vapor transmission rates of the cling films of Examples 2-6 gradually increased with increasing amounts of glycerol added. The water vapor transmission rate of the bacterial cellulose of Example 1, which was not modified with glycerol, was 8.13%. Glycerol infiltration effectively improves the air permeability of the cling film. This is due to the fact that glycerol, as a small molecule, can intercalate between polymer chains, reducing intermolecular attraction to a certain extent, increasing the free volume of the system, and reducing the dense structure of the cling film, thus achieving appropriate air permeability. After glycerol modification, the film with a loose structure is expected to be used for the preservation of breathable foods.

[0074] like Figure 7 As shown in FIG, the microscopic morphology of the films of Example 1 and Example 5 before and after glycerol modification was compared, and the results showed that the addition of glycerol can make the surface of the film smooth; this is because the introduction of glycerol increases the cohesion and compatibility of the polymer in the cling film, improves the interfacial adhesion, and makes the cling film exhibit better smoothness.

[0075] In summary, the bio-based cling film prepared by modifying the turmeric-bacterial cellulose membrane of Example 1 with glycerol has good mechanical strength, appropriate air permeability and high surface smoothness; among Examples 2 to 6, the comprehensive performance of the sample of Example 5 with a glycerol concentration of 20% is the best.

[0076] The total phenol content, antioxidant properties, and antibacterial properties of the sample of Example 5 were tested and compared with those of Example 1. The results are shown in Table 8. The results show that the glycerol infiltration modification does not significantly damage the total phenol content, antioxidant properties, and antibacterial properties of the turmeric-bacterial cellulose membrane itself.

[0077] Table 8 Biological activity characteristics of bacterial cellulose of Example 1 and plastic wrap of Example 5

[0078] The present invention also conducted FT-IR test on the samples of Example 1, Comparative Example 1 and Example 5, and the results were as follows: Figure 8 The main characteristic peaks of each sample appear at 3300 cm -1 (OH), 2900 cm -1 (CH), 1700 cm -1 (O=CH), 1600cm -1 (C=C) and 1000 cm -1 (COC), where 1600 cm -1 The peaks are characteristic peaks of aromatic compounds, and the remaining peaks are characteristic peaks of bacterial cellulose.

[0079] Compared with Comparative Example 1, the bacterial cellulose of Example 1 preferably prepared by the response surface methodology has all the characteristic peaks of the bacterial cellulose of Comparative Example 1 prepared by the conventional method, but the characteristic peaks are shifted to higher wavenumbers and the peak areas are reduced; after the turmeric powder is pretreated, the turmeric powder is more easily incorporated into the bacterial cellulose matrix and interacts with the bacterial cellulose fibrils, thereby reducing the vibration absorption.

[0080] Compared with Example 5, no new characteristic peaks were formed in Example 1; this may be because glycerol contains a large number of hydroxyl groups, which enhances the characteristic peaks here. After glycerol was added, no new characteristic peaks and chemical bonds were found, indicating that glycerol, turmeric powder and bacterial cellulose were physically blended.

[0081] (3) Blueberry packaging and preservation test of bio-based antibacterial cling film The bio-based antibacterial cling film prepared in Example 5 was selected for blueberry packaging and preservation testing.

[0082] Experimental Grouping: Fresh, untreated blueberries that were plump, intact, and of roughly uniform color and size were selected for the test. Twenty blueberries (weighing 25 ± 0.5 g) were placed in a 6 cm diameter Petri dish and grouped according to the type of membrane used. Specifically, the blueberries coated with G-BC-CUR (Example 5) served as the experimental group, while those coated with G-BC (Comparative Example 2), wrapped with cling film, and uncoated served as the CK group. The storage temperature was set at 4°C and the humidity was constant to simulate blueberry storage and transportation. The storage period was 15 days, with samples collected every three days for analysis.

[0083] A sensory panel comprised of six graduate students (aged 22-30, three males and three females) evaluated blueberries from different treatments based on five criteria: morphology, color, flavor, aroma, and texture. Each blueberry sample group was randomly numbered and provided to the panelists. The evaluation results were averaged across all six participants, using the criteria shown in Table 9.

[0084] Table 9 Sensory evaluation criteria for blueberries

[0085] The sensory properties of blueberries in each group Figure 9The results show that sensory scores of blueberries coated with different films varied. After three days of storage, the sensory scores of blueberries in the CK group decreased more significantly than those in the other experimental groups, and by the ninth day, the CK group had lost its edible value. From three to six days of storage, the sensory scores of blueberries in the G-BC-CUR group were lower than those in the plastic wrap and G-BC groups. This is because the turmeric aroma of the G-BC-CUR film contributes to the lower odor scores. In the later stages of storage, the G-BC-CUR film achieved the highest sensory score (54.66), followed by the G-BC group (41.66), and the plastic wrap group (29.66). This may be because the active ingredients in the G-BC-CUR plastic wrap inhibited the growth of harmful bacteria and delayed oxidation of the blueberries.

[0086] 2) Storage blueberry firmness test The hardness of blueberries during storage was measured using a texture analyzer. A stainless steel probe with a diameter of 2 mm was selected and the measuring speed was 1.0 mm / s. The peak height of the first peak was the maximum force, which was used to express the hardness in N.

[0087] like Figure 10 As shown in (a), the hardness of blueberries in the CK group decreased rapidly, the hardness of blueberries coated with the film decreased more slowly, and the hardness of blueberries coated with the G-BC-CUR group decreased the slowest. It can be seen that the antibacterial bio-based cling film can effectively inhibit the hardness loss of blueberries.

[0088] 3) Blueberry rot rate test during storage The bad fruit rate is calculated as follows:

[0089] Depend on Figure 10 As shown in Figure b, both the uncoated and coated groups showed varying degrees of decay. After 15 days of storage, the blueberries in the G-BC-CUR film group remained fresh, with slight changes in color and size, and a rotten fruit rate of 16.66%. The rotten fruit rate in the CK group reached 53.33%. Some blueberries in the G-BC and plastic wrap groups exuded pus and were covered with mold, with rotten fruit rates of 40% and 30%, respectively.

[0090] 4) Determination of titratable acid content in blueberries at different storage periods The blueberry sample was determined by titration using 0.1 mol / L sodium hydroxide solution. Accurately weigh 3.00 g of the blueberry sample and grind it into a homogenous slurry using a grinder. Transfer the blueberry homogenate to a 150 mL volumetric flask, dilute to volume, shake well, heat at 60°C for 0.5 h, let it stand for 30 min, and filter to obtain a filtrate. Titration of blueberry filtrate: Take 50 mL of blueberry filtrate and titrate with sodium hydroxide solution (0.1 mol / L). Use a pH meter to determine the titration end point. When the pH = 8.2 does not change within 30 s, the titration is complete. Record the volume of alkali solution consumed in the titration, and then use distilled water as a blank control. Calculate the titratable acid content in the blueberry tissue based on the consumption of sodium hydroxide solution, expressed as a percentage (%), and the calculation formula is as follows:

[0091] Where: V—total volume of fruit extract, mL; Vs—the volume of blueberry filtrate required for titration, mL; C—concentration of sodium hydroxide titrant, mol / L; V1—volume of sodium hydroxide solution consumed, mL; V0—volume of sodium hydroxide solution consumed in titrating distilled water, mL; m—blueberry mass, g; f—conversion coefficient (0.067), g / mmol.

[0092] The change of titratable acid content can reflect the flavor and quality of blueberries during storage. The change of titratable acid content of blueberries during storage is as follows: Figure 10 As shown in Figure c, the titratable acid content of blueberry fruit decreased with the extension of storage time. The titratable acid content of blueberries before storage was 3%. On the 15th day, the titratable acid content of blueberries in the CK (unpacked), fresh-keeping paper packaging, G-BC packaging, and G-BC-CUR packaging groups decreased by 1.44%, 1.10%, 1.15%, and 0.7%, respectively.

[0093] 5) Determination of blueberry weight loss during storage The weight loss rate of blueberries was determined by weighing method, and the calculation formula is as follows:

[0094] like Figure 10As shown in Figure d, due to water loss during storage through transpiration and respiration, all blueberries experienced varying degrees of weight loss within 15 days of storage. The weight loss rate of blueberries in the CK group was significantly higher than that in the experimental group. Without film wrapping, blueberries lost water more rapidly, reducing their shelf life. The weight loss rates of blueberries in the cling film and G-BC film groups were 12.9% and 12.1%, respectively, while the weight loss rate of G-BC-CUR was 8.86%. These results indicate that G-BC-CUR film can reduce the weight loss of blueberries during storage.

[0095] 6) Determination of total bacterial count in stored blueberries The test was conducted in accordance with GB 4789.15-2016 “National Food Safety Standard - Microbiological Examination of Food - Mold and Yeast Count”.

[0096] Depend on Figure 10 As shown in Figure e, the total number of fungi reference standard GH / T 1229-2018 "Frozen Blueberries" stipulates that the total number of colonies in blueberry fruits is limited to no more than 10 4 CFU / g. As time went on, the total colony count of blueberries in the CK group, G-BC group, and cling film group increased, among which the total colony count of blueberries coated with G-BC-CUR was lower, indicating that the antibacterial bio-based cling film has good antibacterial properties.

[0097] 6) Biodegradability test of plastic wrap To evaluate the biodegradability of the films, soil burial degradation tests were conducted. 0.5g of each of G-BC (Comparative Example 2) and G-BC-CUR (Example 5) was cut, covered with nylon screen (20 mesh), and buried in soil at a depth of 8-10 cm. The biodegradability of the films was evaluated using the weight loss rate, calculated as follows:

[0098] like Figure 11 As shown, during the initial soil burial, the bacterial cellulose membranes absorbed soil moisture, causing the mass of both G-BC and G-BC-CUR membranes to increase by 20%. After the third day, the bacterial cellulose membranes were gradually degraded by soil microorganisms, and after the eighth day, the membrane mass decreased by approximately 50%. After 15 days of soil burial, the bacterial cellulose membranes were completely degraded, with the G-BC membrane degrading the fastest. Due to the antibacterial properties of the G-BC-CUR membrane, the degradation rate of the G-BC-CUR membrane was slower than that of the G-BC membrane.

Claims

1. A method for optimizing the preparation of turmeric-bacterial cellulose membrane based on response surface methodology, characterized in that: The steps include: S1. Preparation of a mixed culture mother solution: After activating artificial strains of Candida sp., Lodderomyces elongisporus, and Komagataeibacter sp., 15% of each culture medium was inoculated into a tea-sugar liquid medium for cultivation. Subsequently, the three culture solutions were mixed at a concentration ratio of 1:1:1, and the mixture was again inoculated into a tea-sugar liquid medium at a 15% inoculum to obtain a mixed culture mother solution. The tea sugar liquid culture medium is prepared by adding 3.5% (w / v) sucrose and boiling water to the tea water obtained by boiling and extracting 1.5% (w / v) black tea; S2. Pre-processing of turmeric powder matrix: ultrasonic cell disruptor is used to perform ultrasonic blasting on turmeric powder in water to obtain turmeric powder matrix dispersion; S3. Preparation of turmeric-bacterial cellulose membrane: mixing a turmeric powder matrix dispersion with sucrose to obtain a turmeric powder syrup initial fermentation liquid, inoculating the mixed culture mother liquid into the turmeric powder syrup initial fermentation liquid, and placing the mixed culture mother liquid in a fermentation tank sealed with multiple layers of sterilized gauze. Using bacterial cellulose yield as an evaluation indicator, the optimal formula and fermentation conditions of the turmeric powder syrup initial fermentation liquid were selected through single factor effect tests and Box-Behnken response surface experiments, and the turmeric-bacterial cellulose membrane was obtained by fermentation and culture. The optimal formula of the initial fermentation liquid of turmeric powder syrup is: 14.6 g / L turmeric powder matrix dispersion, 42.6 g / L sucrose, and the optimal fermentation culture conditions include: mixed culture mother liquor inoculation amount of 9.8%, culture temperature of 29.5 ° C, and culture time of 9 days.

2. The method for optimizing the preparation of turmeric-bacterial cellulose membrane based on response surface methodology according to claim 1, wherein: The specific steps of using an ultrasonic cell disruptor to ultrasonically blast the turmeric powder in water in step S2 are as follows: a. Single factor effect test: Using an ultrasonic disruptor, turmeric powder was ultrasonically blasted in water to obtain a turmeric powder matrix dispersion. A single factor effect test of ultrasonic blasting conditions was conducted with power, time, and solid-liquid ratio as variables. The total phenol content of bacterial cellulose was used as the evaluation index to screen out the optimal levels of power, time, and solid-liquid ratio. b. Box-Behnken response surface experiment: With the optimal levels of power, time, and material-liquid ratio as the independent variable range and the total phenol content of the membrane as the response value, a response surface experiment was designed according to the Box-Behnken principle. The multiple regression equation between the total phenol content of the bacterial cellulose and each variable was obtained through multiple regression fitting; c. Optimizing the process parameters of the model using Design-Expert software according to the multiple regression equation to determine the optimal conditions for ultrasonic blasting. Under the optimal conditions, ultrasonic cell disruptor was used to ultrasonically blast the turmeric powder in water to obtain the turmeric powder matrix dispersion; Among them, the optimal conditions are: power 41 W, time 16 min, material-liquid ratio 1:41; The preparation method of bacterial cellulose comprises the following steps: (1) The turmeric powder matrix dispersion was mixed with sucrose to prepare the turmeric powder syrup initial fermentation liquid. The formula of the turmeric powder syrup initial fermentation liquid was: 10 g / L turmeric powder matrix dispersion, 35 g / L sucrose; (2) The mixed culture mother liquid is inoculated into the initial fermentation liquid of turmeric powder and sugar water and placed in a fermenter for fermentation to obtain the bacterial cellulose. The fermentation conditions include: the mixed culture mother liquid inoculation amount is 15%, the culture temperature is 25 ° C, and the culture time is 9 days.

3. The method for optimizing the preparation of turmeric-bacterial cellulose membrane based on response surface methodology according to claim 2, wherein: The multiple regression equation in step b is: Y=3.33+0.0513A+0.0138B+0.0675C-0.0350AB-0.0425AC-0.0075BC-0.1585A²-0.2385B²-0.1310 C²; where A is the material-liquid ratio, B is the power, and C is the time.

4. The method for optimizing the preparation of turmeric-bacterial cellulose membrane based on response surface methodology according to claim 1, wherein: The specific steps of the single factor effect test in step S3 are as follows: The culture time is fixed at 9 days, the mixed culture mother liquor is inoculated into the initial fermentation liquor of turmeric powder and sugar water and placed in a fermenter for fermentation and culture, a single factor influence test is carried out with the amount of turmeric powder added, the amount of sucrose added, the inoculation amount of the mixed culture mother liquor and the culture temperature as variables, and the bacterial cellulose film yield is used as a measurement index to screen out the optimal levels of the amount of turmeric powder added, the amount of sucrose added, the inoculation amount of the mixed culture mother liquor and the culture temperature.

5. The method for optimizing the preparation of turmeric-bacterial cellulose membrane based on response surface methodology according to claim 4, characterized in that: The optimal levels of the turmeric powder addition amount, sucrose addition amount, mixed culture mother liquid inoculation amount, and culture temperature are: turmeric powder addition amount 12.5-17.5 g / L, sucrose addition amount 20-60 g / L, inoculation amount 8%-12%, and culture temperature 25-35 °C.

6. The method for optimizing the preparation of turmeric-bacterial cellulose membrane based on response surface methodology according to claim 5, characterized in that: The specific steps of the Box-Behnken response surface experiment are as follows: The culture time is fixed at 9 days, the amount of turmeric powder added, the amount of sucrose added, the inoculation amount of the mixed culture mother liquid, and the optimal level of the culture temperature are used as the independent variable range, and the yield of turmeric-bacterial cellulose film is used as the response value. A response surface experiment is designed according to the Box-Behnken principle, and a multiple regression equation between the yield of turmeric-bacterial cellulose film and each variable is obtained through multiple regression fitting; then, according to the multiple regression equation, the process parameters of the model are optimized using Design-Expert software to determine the optimal formula of the initial fermentation liquid of turmeric powder sugar water and the final fermentation conditions for producing turmeric-bacterial cellulose film.

7. The method for optimizing the preparation of turmeric-bacterial cellulose membrane based on response surface methodology according to claim 6, characterized in that: The multiple regression equation is: Y=2.14-0.1017A+0.2292B-0.0767C-0.0275D-0.0025AB+0.0225AC+0.0000D+0.0700BC-0.0950BD+0.0075 CD-0.3266 A²-0.8828 B²-0.2666 C²-0.2528 D²; Wherein: A is the amount of turmeric added, B is the sucrose concentration, C is the culture temperature, and D is the inoculum size of the mixed culture mother solution.

8. The turmeric-bacterial cellulose film prepared by the method of claim 1 is applied to the fields of food preservation and packaging.

9. An antibacterial bio-based fresh-keeping film, characterized in that: The preparation method comprises the following steps: soaking the turmeric-bacterial cellulose film prepared by the method according to claim 1 into a glycerol solution, taking it out and drying it to obtain the antibacterial bio-based fresh-keeping film.

10. The antimicrobial bio-based fresh-keeping film according to claim 9, characterized in that: The glycerol concentration of the glycerol solution is 20%.

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