An edible whey protein film loaded with amino acids, its preparation method and application

Abstract

The invention discloses an edible whey protein film loaded with amino acids and its preparation method and application, wherein the whey protein film is prepared by film-forming treatment of a film-forming liquid comprising whey protein, a nutrient enhancer, glycerol and water, wherein the nutrient enhancer is a non-protein amino acid; the whey protein film preparation method is as follows: (1) whey protein is dissolved in water, and water bath treatment is performed after adjusting pH with an alkaline solution, and cooling is taken out after termination to obtain an alkaline whey protein solution; (2) glycerol and a nutrient enhancer are added to the above solution, and the mixture is stirred until completely dissolved to obtain a film-forming liquid; (3) the film-forming liquid is subjected to a film-forming treatment to obtain an edible whey protein film. The present invention adds physiologically active L-taurine, L-theanine or L-citrulline to a whey protein solution to prepare an edible whey protein film having significantly improved mechanical properties, swelling properties, air permeability, solubility and thermoplasticity, thereby achieving a common improvement in the processing functionality and nutritional functionality of the whey protein film.

Description

Technical Field

[0001] The present invention relates to the field of food biomass material processing, and particularly relates to a whey protein film loaded with amino acids, a preparation method thereof and an application thereof. Background Art

[0002] Food packaging can effectively overcome adverse factors encountered during the storage, transportation, sales, etc. of food, such as high temperature, high humidity, direct sunlight, oxygen, etc., to ensure the quality and safety of food and extend the shelf life of food. At present, petroleum-based polymers such as plastics are widely used in the food packaging industry. Although this kind of packaging material is cheap and easy to obtain, it is difficult to be degraded and utilized, so it is easy to accumulate in large quantities in the environment, and various adverse effects generated will affect all aspects of human survival and even cause irreversible damage. With the continuous development of society, the degree of attention and protection awareness of the environment by humans have been continuously increasing. In order to replace petroleum-based materials represented by plastics, countries are implementing sustainable development strategies and striving to find green and environmentally friendly alternatives. Among them, biodegradable materials are not only non-toxic and environmentally friendly, but also edible, can be used as carriers of active ingredients, and can effectively maintain the nutrition and flavor of packaged food. In recent years, the demand for biodegradable materials in the food packaging industry has also been increasing. Therefore, this field has great environmental and commercial potential and is an important part of the food packaging industry.

[0003] The most common biodegradable matrix materials applied to food packaging films are proteins and polysaccharides. When prepared by the wet method, they form gels with a network structure through various intermolecular interactions and can obtain films after losing some moisture. Such films are easily degradable and do not pollute the environment; moreover, they have good barrier properties and can effectively prevent adverse factors such as water vapor, oxygen, and ultraviolet rays in the air from infiltrating to avoid affecting the quality of food; at the same time, they can also serve as carriers for nutrients, active ingredients, antibacterial ingredients, etc., improving the added value of food packaging. Among them, whey protein is recommended for application in food packaging films due to its excellent gel-forming properties. At the same time, whey protein films can also act as carriers for various active ingredients and encapsulate antibacterial agents, thereby playing a role in protecting sensitive active ingredients and controlling food surface contamination to improve the quality of food and extend the shelf life. More importantly, the advantages shown by whey protein films in many aspects, such as excellent oxygen barrier performance, better elasticity and transparency, more solvent resistance, odorless, high nutritional value, etc., are far greater than those of competitive protein films or polysaccharide films. However, films containing only whey protein may have structural defects, with general mechanical properties and a relatively high water vapor transmission rate. Even though there are many research results (such as adding glycerol plasticizer) that can effectively improve the various properties of whey protein films, the improvement in mechanical properties, thermal properties, structure, etc. is still not ideal, or it cannot be scaled up and industrially produced due to other complex factors. Therefore, there is still room for further improvement in improving the physical and mechanical properties of whey protein films. At the same time, the encapsulation and loading of active substances are a technical requirement for the food industry. Summary of the Invention

[0004] Object of the Invention: To solve the technical problems existing in the prior art, the present invention aims to provide an edible whey protein film loaded with amino acids with excellent processing functions and nutritional functions. Moreover, the present invention also provides a preparation method and application of the edible whey protein film.

[0005] Technical Solution: The edible whey protein film loaded with amino acids according to the present invention is prepared by subjecting a film-forming solution containing a nutritional fortifier, whey protein, glycerol, and water to film-forming treatment.

[0006] Furthermore, the nutritional fortifier is a non-protein amino acid selected from one or more of L-taurine, L-theanine, or L-citrulline, and the concentration of the nutritional fortifier in the film-forming solution is 0.25 - 2.0 g / L, preferably 0.5 g / L.

[0007] Furthermore, the mass ratio of glycerol to whey protein in the film-forming solution is 1:2 - 1:3, preferably 1:2.5.

[0008] Furthermore, the pH of the film-forming solution is 8.0.

[0009] Furthermore, the whey protein is whey protein isolate (WPI) or whey protein concentrate (WPC).

[0010] The method for preparing the amino acid-loaded edible whey protein film of the present invention comprises the following steps:

[0011] (1) Take whey protein and dissolve it in water to obtain a whey protein solution. Adjust the pH of the whey protein solution with an alkali solution and then perform a water bath treatment. After completion, take it out and cool to obtain a whey protein solution;

[0012] (2) Add glycerol and a nutritional fortifier to the alkaline whey protein solution and stir well until completely dissolved to obtain a film-forming solution;

[0013] (3) Perform a film-forming treatment on the film-forming solution to obtain the amino acid-loaded edible whey protein film.

[0014] Furthermore, in step (1), the pH of the whey protein solution is adjusted using a NaOH solution with a concentration of 2 mol / L, and the pH is adjusted to 8.0; the conditions for the water bath treatment are: heating at 85 - 95 °C for 20 - 35 min.

[0015] Furthermore, in step (3), the process of the film-forming treatment is: evenly spread the film-forming solution on a substrate material, air-dry it naturally, and then equilibrate it for 24 - 48 h under the conditions of a temperature of 24 - 30 °C and a relative humidity of 50 - 60%.

[0016] The application of the amino acid-loaded edible whey protein film of the present invention as a carrier for active substances or an additive for modifying packaging film materials.

[0017] Principle of the invention: In the present invention, non-protein amino acids are added to the whey protein film to improve its physical and mechanical properties. Taurine, theanine, and citrulline all belong to non-protein amino acids, and they can all be extracted from natural foods. Adding them appropriately to foods is not only non-toxic and harmless but also produces various physiological activities beneficial to the human body. For example, taurine has important physiological functions such as anti-inflammatory, antioxidant, participating in bile acid conjugation, stabilizing membrane structure, maintaining calcium homeostasis, regulating osmotic pressure, and immunomodulation. Theanine shows unique effects in aspects such as antioxidant, immunomodulation, and inhibiting neurotransmission to calm the mood. And citrulline participates in important biological processes such as arginine synthesis, nitrogen balance, anabolic processes, protein synthesis, growth and development, intestinal homeostasis, and muscle performance. Currently, natural taurine, theanine, and citrulline have been approved for use as nutritional fortifiers in foods.

[0018] Taurine can stabilize the number of hydrogen bonds between proteins and aqueous solvents, and can induce the formation of the most ordered solvent structure, enhancing the stability of the native structure of proteins. Theanine can regulate protein metabolism through specific pathways. In other related studies, it has also been found that through cholesterol metabolism and retinol metabolism pathways, theanine can improve dextran sulfate sodium-induced inflammatory bowel disease. Citrulline can quench with bovine serum albumin at different pH values, changing the structure and function of proteins, and thus may change its distribution behavior in the solution system, thereby affecting the protein homeostasis. The potential interactions between these non-protein amino acids and proteins provide a basis for their application in foods. However, at present, these non-protein amino acids have not been added to the protein film system to improve the functionality of the film; in addition, such addition can also achieve the use of protein films to load bioactive substances. By evaluating the effects of three non-protein amino acids on the mechanical properties, optical properties, water-related physical properties, thermal properties, and microstructure of whey protein films, it was found that these non-protein amino acids have a great promoting effect on the functionality of protein films.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0020] (1) The present invention confirms that whey protein can be loaded with L-taurine, L-theanine or L-citrulline in the form of a thin film, and also systematically expounds that L-taurine, L-theanine and L-citrulline can significantly improve the functionality of whey protein films without destroying the excellent transparency and visual sensory quality of the whey protein films themselves;

[0021] (2) The present invention has found the optimal addition amounts of L-taurine, L-theanine and L-citrulline, and their concentrations are all 0.5 g / L; it has also discovered that the above three non-protein amino acids can be used as additives in protein matrix food systems;

[0022] (3) The present invention combines L-taurine, L-theanine and L-citrulline with whey protein respectively, achieving a common improvement in the selection of additives, the processing functionality and nutritional value of protein films. Description of the Drawings

[0023] Figure 1 It is a physical diagram of the whey protein film loaded with L-taurine, L-theanine or L-citrulline of the present invention;

[0024] Figure 2 It is the effect of the whey protein film loaded with L-taurine, L-theanine or L-citrulline of the present invention on the color of the whey protein film;

[0025] Figure 3 It is the effect of the whey protein film loaded with L-taurine, L-theanine or L-citrulline of the present invention on the mechanical properties of the whey protein film (A: tensile strength; B: elongation at break);

[0026] Figure 4 Effects of the present invention's loaded L-taurine, L-theanine or L-citrulline on the hydration properties of whey protein films (A: Swelling property; B: Solubility; C: Water vapor permeability);

[0027] Figure 5 Effects of the present invention's loaded L-taurine, L-theanine or L-citrulline on the thermal properties of whey protein films (A: Mass retention rate; B: Rate of change of mass retention);

[0028] Figure 6 Scanning electron microscope images of the present invention's loaded L-taurine, L-theanine or L-citrulline on whey protein films;

[0029] Figure 7 Fourier transform infrared spectra of the present invention's loaded L-taurine, L-theanine or L-citrulline on whey protein films. Detailed implementation manners

[0030] Next, the present invention will be further described in conjunction with specific embodiments and the accompanying drawings.

[0031] Example 1: The preparation method of the edible whey protein film loaded with amino acids according to the present invention includes the following steps:

[0032] (1) Weigh the isolated whey protein (WPI) powder and dissolve it in ultrapure water to make a whey protein isolate solution (60 g / L). After magnetic stirring for 3 hours, adjust the pH to 8.0 with 2 mol / L NaOH solution and calibrate it. Then place the solution in a water bath at 90 °C for 30 minutes. After the solution cools to room temperature, an alkaline WPI solution is obtained;

[0033] (2) Add glycerol with a mass ratio of 1:2.5 to the whey protein and the nutritional fortifier L-taurine with a concentration of 0.25 g / L to the alkaline WPI solution, and stir magnetically again to obtain a film-forming solution;

[0034] (3) Take 10 mL of the film-forming solution and spread it evenly on a 10 cm × 10 cm horizontal plexiglass plate. After natural air drying, peel off the film, and then equilibrate it at a temperature of 24 °C and a relative humidity of 50% for 24 hours to obtain the edible whey protein film loaded with amino acids.

[0035] Example 2: The difference from Example 1 is that: in step (2), the concentration of L-taurine is 0.5 g / L.

[0036] Example 3: The difference from Example 1 is that: in step (2), the concentration of L-taurine is 1 g / L.

[0037] Example 4: The difference from Example 1 is that in step (2), the concentration of L-taurine is 2 g / L.

[0038] Example 5: The difference from Example 1 is that in step (2), the nutritional fortifier is L-theanine, and the concentration of L-theanine is 0.25 g / L.

[0039] Example 6: The difference from Example 5 is that in step (2), the concentration of L-theanine is 0.5 g / L.

[0040] Example 7: The difference from Example 5 is that in step (2), the concentration of L-theanine is 1 g / L.

[0041] Example 8: The difference from Example 5 is that in step (2), the concentration of L-theanine is 2 g / L.

[0042] Example 9: The difference from Example 1 is that in step (2), the nutritional fortifier is L-citrulline, and the concentration of L-citrulline is 0.25 g / L.

[0043] Example 10: The difference from Example 9 is that in step (2), the concentration of L-citrulline is 0.5 g / L.

[0044] Example 11: The difference from Example 9 is that in step (2), the concentration of L-citrulline is 1 g / L.

[0045] Example 12: The difference from Example 9 is that in step (2), the concentration of L-citrulline is 2 g / L.

[0046] Comparative Example 1: The difference from Example 1 is that in step (2), no nutritional fortifier is added.

[0047] Example 13: Perform performance measurements on the edible whey protein film loaded with amino acids prepared in Examples 1-12 and Comparative Example 1, including:

[0048] (1) Measurement of film thickness: Randomly (excluding the edges) take 6 points on the film sample to be measured, measure its thickness with a micrometer with a precision of 0.01 mm, and then calculate the average film thickness.

[0049] (2) Measurement of film transparency: Measure the absorption spectrum of the film sample at 200-800 nm with a UV spectrophotometer. Cut the sample into rectangular pieces (3.5 cm × 0.8 cm) and attach them to one side of the cuvette. After measurement, measure its thickness with a micrometer. Calculate the transparency at 600 nm, and the formula is:

[0050] A 600is the absorbance of the film at 600 nm, and X is the film thickness (mm);

[0051] The calculation formula for the transmittance (T%) is:

[0052] T% = 100 × 10 -A (3) Measurement of film color: Use a color difference meter to measure the color of the film. For the white standard plate, L = 94.75, a = 5.04, and b = -1.91. The CIELab scale is used to measure the brightness of the film (L* = 0 for black, L* = 100 for white), the red-green chromaticity (+a* is redder, -a* is greener), and the yellow-blue chromaticity (+b* is yellower, -b* is bluer). Place the film on the white standard plate and select five points to measure its color.

[0053] Color difference ΔE 2 =(L * - L) 2 +(a * - a) 2 +(b * - b) 2

[0054] (4) Measurement of the mechanical properties of the film: Cut the sample into a strip-shaped film of 1.9 cm × 10 cm, and use a TA.XT plus texture analyzer to measure its tensile properties. The trigger force is 5 g, the distance between the upper and lower clamps is 60 mm, and the crosshead tensile speed is set to 0.8 mm / min. The tensile strength (TS) and elongation at break (EAB) are calculated by the following formulas:

[0055]

[0056] where F is the maximum tensile force, A is the cross-sectional area of the film sample, L is the length of the film at break, and L0 is the initial length of the film.

[0057] (5) Measurement of the water vapor permeability (WVP) of the film: According to the standard weight measurement method, add dry silica gel (relative humidity 0%) to a beaker with a diameter of 3.5 cm and a height of 5 cm, cover the beaker mouth with the film sample and tie it tightly. Place the sample in a constant temperature and humidity chamber (23°C, relative humidity 50%). Monitor the weight increment of the beaker within 12 hours and record the weight every 2 hours. The calculation formula for water vapor permeability is as follows:

[0058]

[0059] where w: weight gain (g); x: film thickness (mm); t: time (h); A: sealing area (m 2 ); Δp: water vapor pressure difference inside and outside the beaker (Pa).

[0060] (6) Determination of the swelling ratio of the membrane: Cut the membrane into pieces with a size of 2.5 cm x 1.8 cm, weigh it, and record it as W1. After soaking it in distilled water for 30 minutes, remove the surface water droplets with absorbent paper and weigh it, record it as W2. Use W a to represent the water absorption rate, and the calculation formula is as follows:

[0061]

[0062] (7) Determination of the solubility of the membrane: Cut the membrane into pieces with a size of 2.5 cm × 2.0 cm, place it in a drying oven at 65 °C for 40 hours, and weigh (m1). After immersing it in 20 mL of distilled water for 24 hours, dry the sample at 65 °C again for 40 hours and weigh (m2). The solubility of the thin film is calculated as follows:

[0063]

[0064] (8) Thermogravimetric determination of the membrane: Use a TG209F1 thermogravimetric analyzer to perform thermogravimetric analysis on the thin film. Weigh about 5 - 8 mg of the sample in an aluminum flat pan in advance, heat the temperature from 30 °C to 600 °C, and the heating rate is 10 °C / min. The flow rate of the purified gas nitrogen is 20 mL / min. Record the mass as a function of temperature; then take the derivative of the above curve to obtain the first derivative function.

[0065] (9) Infrared spectrum determination of the membrane: Use Fourier transform infrared spectroscopy to obtain information on the structure and interactions of the thin film sample, and then perform qualitative analysis. At the same time, collect spectral data in the wavenumber range of 4000 - 400 cm -1 When preparing the sample, grind the freeze-dried thin film sample with potassium bromide particles and press it into a circular tablet.

[0066] (10) Microstructure determination of the membrane: Cut the cross-section of the membrane with a sharp blade. First, use a sputtering coater to coat the thin film sample with gold, and then under a vacuum of 10 -3 Pa, use an acceleration voltage of 10 kV to capture images of the surface and cross-section of the thin film sample at scales of 50 μm and 100 μm through a scanning electron microscope.

[0067] The above determination results are shown in Table 1 and Figures 1-7 as follows.

[0068] As Figure 1 shown, the whey protein membranes loaded with L-taurine, L-theanine or L-citrulline of the present invention all have good appearances and are visually transparent and uniform.

[0069] As Figure 2 shown, the L * , a * , b of the whey protein membrane loaded with L-theanine and the whey protein membrane loaded with L-citrulline* The values are roughly the same and there are no significant differences with the change in amino acid concentration. However, the whey protein film loaded with L-taurine has significant color changes with different addition concentrations. The films loaded with amino acids are brighter, redder, and bluer than the control, but the whey protein film loaded with a high concentration of L-taurine (2 g / L) has a smaller a* and a larger b*. All films have a high L* and are relatively stable. There are significant differences in the total color difference between the films loaded with amino acids and the films without amino acids. The addition of three non-protein amino acids all affects the color of the whey protein film, but visually the films are transparent and uniform.

[0070] As Figure 3 shown, compared with the control without amino acids, the tensile strength values of the films loaded with three non-protein amino acids all increase significantly. The tensile strength of all three whey protein films reaches the maximum when the added amino acid concentration reaches 0.5 g / L, and the overall curve shows a trend of first increasing and then decreasing with the concentration. At the same concentration, the whey protein film added with L-theanine has the highest tensile strength. Most of the phenomena presented by the elongation at break value curve are exactly opposite to the tensile strength curve. Films with high tensile strength show low elongation at break values.

[0071] As Figure 4 shown, at lower concentrations (0.25, 0.5, 1 g / L), the reduction effects of the three non-protein amino acids on the water vapor permeability of the whey protein film are consistent. The water vapor permeability of the film added with L-citrulline is the highest, followed by L-taurine, and the lowest is L-theanine. The addition of the three amino acids all increases the swelling rate and solubility of the whey protein film, and all three amino acids show the maximum swelling rate of the whey protein film when the addition concentration is 0.25 g / L. As the amino acid content increases, both the swelling rate curve and the solubility curve show a trend of first increasing and then decreasing. At low concentrations (0.25, 0.5 g / L), the whey protein film added with L-citrulline shows the highest solubility. At higher concentrations (1, 2 g / L), the whey protein film added with L-taurine has the largest solubility, and the swelling rates from large to small are L-theanine, L-citrulline, and L-taurine.

[0072] As Figure 5 shown, during the process of the continuous and equal weight decrease of the four whey protein films, the film added with L-taurine (0.5 g / L) has the highest residual mass value. Compared with the control, the change in the thermal stability of the film added with L-theanine (0.5 g / L) is not obvious, while the film added with L-citrulline (0.5 g / L) reduces the thermal stability of the film instead.

[0073] As Figure 6As shown, the pores in the protein network structure of the control whey protein film are larger and disordered. After adding non-protein amino acids, the network structure of the film becomes very regular, uniform, the pores shrink, and a layered structure appears. This change will lead to an increase in its tensile strength, a decrease in water vapor transmission rate, and an improvement in thermal stability.

[0074] As Figure 7 shown, the whey protein film added with non-protein amino acids and the control film show similar absorption main peaks, and the added amino acids will significantly enhance the amplitude of the main peak. Near 3434.95 cm -1 , the enhancement of the amplitude of the absorption main peak may be due to the increase in the number of O-H and N-H groups. Near 2923.53 cm -1 , it is due to the increase in the number of C-H groups. Near 1633 cm -1 , the three added amino acids cause cross-linking of the whey protein film through intermolecular hydrogen bonds, which in turn leads to an increase in the amplitude of the main peak. This cross-linking effect results in the maximum tensile strength of the whey protein film at an amino acid addition concentration of 0.5 g / L; a decrease in the swelling rate and solubility; while L-taurine improves the thermal stability of the film, and L-citrulline reduces the thermal stability of the film. As the amino acid addition concentration increases, the degree of enhancement of the amplitude of the absorption main peak in the infrared spectrum gradually weakens, which may be caused by hydrophobic interaction and electrostatic interaction.

[0075] As shown in Table 1, in the ultraviolet wavelength range (200 - 350 nm), both the films with and without added non-protein amino acids have very low light transmittance (<0.14%), proving that these films have good ultraviolet barrier properties. However, in the visible light range, the films have relatively high light transmittance, which corresponds to a low opacity value, indicating good film transparency. The light transmittance of the film loaded with L-theanine decreases as the addition amount of the additive increases.

[0076] Table 1 Light transmittance and opacity of edible whey protein films in Examples 1 - 12 and Comparative Example 1 at each wavelength

[0077]

Claims

1. An edible whey protein film loaded with amino acids, characterized in that, The whey protein film is prepared by subjecting a film-forming solution composed of a nutritional fortifier, whey protein, glycerol, and water to a film-forming treatment; The nutritional fortifier is a non-protein amino acid, L-theanine or L-citrulline; the concentration of the nutritional fortifier L-citrulline in the film-forming solution is 0.25 - 2.0 g / L, and the concentration of L-theanine is 0.5 g / L; the preparation method of the edible whey protein film comprises the following steps: (1) Take whey protein and dissolve it in water to obtain a 60 g / L whey protein solution, adjust the pH of the whey protein solution with an alkali solution, then perform a water bath treatment, and after completion, take it out and cool to obtain an alkaline whey protein solution; (2) Add glycerol and a nutritional fortifier with a mass ratio of 1:2.5 to the whey protein to the alkaline whey protein solution, and stir well until completely dissolved to obtain a film-forming solution; (3) Perform a film-forming treatment on the film-forming solution to obtain an edible whey protein film loaded with amino acids.

2. The edible whey protein film according to claim 1, characterized in that, In step (1), the NaOH solution is used to adjust the pH of the whey protein solution.

3. The edible whey protein film according to claim 1, characterized in that, In step (1), the conditions of the water bath treatment are: heating at 85 - 95 °C for 20 - 35 min.

4. The edible whey protein film according to claim 1, characterized in that, In step (3), the process of the film-forming treatment is: evenly spread the film-forming solution on a substrate material, air-dry it naturally, and then equilibrate it for 24 - 48 h under the conditions of a temperature of 24 - 30 °C and a relative humidity of 50 - 60%.

5. Use of an edible whey protein film loaded with amino acids according to claim 1 as a carrier for active substances.

Images