Nano-silver hydrogel for monitoring freshness of sauced chicken meat product as well as preparation method and application of nano-silver hydrogel

Abstract

The invention relates to the technical field of hydrogel, in particular to nano-silver hydrogel for monitoring freshness of sauced chicken meat products and a preparation method and application thereof.The preparation method comprises the steps that 1, gelatin is weighed and dissolved in pure water, stirring is performed under heating till complete dissolution, polyvinylpyrrolidone and a silver nitrate solution are sequentially added into the solution after the solution is cooled to the room temperature, and stirring is performed to obtain a mixed solution; stirring in a dark environment to form a gelatin / Ag < + > solution, and reacting the mixed sample in a high-pressure sterilization pot to obtain an AgNP solution; and 2) weighing the prepared AgNP solution, adding agar powder, stirring while heating to completely dissolve the agar powder, degassing, weighing the sample solution, pouring into a culture dish, and standing and solidifying at normal temperature to obtain the nano-silver hydrogel. Through the innovative nano-silver formula and the combination of the characteristic that the sauce braised meat product is marinated by adopting the high-salt-concentration marinating soup, and based on the specific combination of silver ions and chloride ions, the color change of the hydrogel film and the prolonging of the shelf life are realized in the storage period.

Description

Technical Field

[0001] The invention relates to the technical field of hydrogels, and specifically relates to a nano silver hydrogel for monitoring the freshness of marinated chicken products, a preparation method and an application thereof. Background Art

[0002] Among traditional Chinese meat products, marinated meat products have a long history, and classic products such as the traditional four famous chickens are timeless. In addition, marinated meat products have a high market share, with about 5,000 tons of marinated meat products consumed by consumers every year. Among them, freshly prepared marinated meat products can better guarantee their flavor quality because they are not sterilized, but they also have a short shelf life and are difficult to monitor.

[0003] At present, edible hydrogel film is the most common method for monitoring the shelf life of meat products, especially aquatic products. The principle is to use the increase in pH during the storage of aquatic products to induce the color change of the color-developing substance to characterize the change in its freshness. However, after the marinated meat products are marinated, their pH changes are small during the storage process, usually fluctuating within 0.5 units, resulting in the traditional edible hydrogel film not being suitable for monitoring the freshness of marinated meat products.

[0004] Therefore, it is of great significance to develop a method that can be used to characterize the freshness of marinated cooked meat products during their shelf life and extend their shelf life. Summary of the invention

[0005] The purpose of the present invention is to provide a nanosilver hydrogel for monitoring the freshness of braised chicken products, a preparation method and an application thereof, based on the reaction between chloride ions and nanosilver structures to achieve color change during the shelf life and extend the shelf life, providing a new technical idea for the freshness characterization and shelf life extension of cooked meat products.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing a nanosilver hydrogel for monitoring the freshness of a braised chicken product comprises the following steps:

[0008] (1) Preparation of Nanosilver

[0009] Weigh gelatin and dissolve it in pure water. Stir under heating until completely dissolved. After cooling to room temperature, add polyvinyl pyrrolidone (PVP) and silver nitrate solution to the solution in sequence. Stir under light-proof environment to form gelatin / Ag + Solution, react the mixed sample in an autoclave to obtain an AgNP solution;

[0010] (2) Preparation of Nanosilver Hydrogel

[0011] The prepared AgNP solution was weighed, agar powder was added, and the agar powder was completely dissolved by stirring under heating. After degassing, the sample solution was weighed and poured into a culture dish, and allowed to stand at room temperature to solidify, thereby obtaining the nanosilver hydrogel.

[0012] Wherein, in step (1), the mass volume ratio of gelatin to pure water is 1:180 to 1:45; the mass volume ratio of gelatin to polyvinyl pyrrolidone is 1:2 to 2:1; the mass volume ratio of gelatin to silver nitrate solution is 1:20 to 1:5; and the concentration of the silver nitrate solution is 0.1 mol / L.

[0013] Wherein, in the step (1), the gelatin / Ag mixture is stirred at a speed of 1200 r / min for 10 min in a light-proof environment. + Solution.

[0014] Wherein, in the step (1), the reaction conditions of the sample in the high pressure sterilizer are 121° C., 0.12 MPa, and the reaction time is 20 min.

[0015] Wherein, in the step (2), the mass volume ratio of agar powder to AgNP solution is 2 to 3:100.

[0016] Wherein, in the step (2), heating is performed at 1200 r / min and 80° C. for 10 min to completely dissolve the agar powder.

[0017] The nano silver hydrogel prepared by the present invention can be used to monitor the freshness of braised chicken products, comprising the following steps:

[0018] (1) Braised chicken with soy sauce

[0019] Raw material pretreatment: fresh or thawed chicken breasts are blanched at 90-100℃; after blanching, the chicken breasts are placed in braising soup for stewing;

[0020] Braising: add onion, sugar, refined salt, star anise, pepper, angelica dahurica, and cloves to water, and cook at 90-100℃ for 30min; then add the blanched chicken breast, and cook at 90-100℃ for 20-30min; after braising, remove the chicken breast and pre-cool at room temperature;

[0021] (2) Monitoring the freshness of meat products

[0022] The pre-cooled braised chicken was cut into small pieces, placed on the nanosilver hydrogel, and then placed in a disposable culture dish and stored at 4°C. The nanosilver hydrogel changed from brown to off-white within 3 days of storage of the braised chicken; the nanosilver hydrogel extended the shelf life of unpackaged braised chicken from 4 days to 6 days at 4°C.

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

[0024] The present invention prepares nanosilver hydrogel through an innovative nanosilver formula, and combines the characteristics of braised meat products that are braised in a brine with a relatively high salt concentration, based on the specific binding of silver ions and chloride ions, to achieve color change of the hydrogel film and extension of the shelf life during the storage period. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 pH changes for braised chicken at 4°C.

[0026] Figure 2 UV-visible absorption spectra and colors of gelatin and AgNP solutions.

[0027] Figure 3 AgNP and Cl - UV-Vis spectra (a) and selectivity histograms (b) after reaction with other anions.

[0028] Figure 4 The color response of nanosilver hydrogel to braised chicken during storage. Blank: Color change of nanosilver hydrogel at 4°C. Control: Color response of chicken cooked in water without braising soup to nanosilver hydrogel. 3%, 4%, 5%: Color response of chicken cooked in braising soup containing 3%, 4%, 5% salt to nanosilver hydrogel.

[0029] Figure 5 The effect of AgNP hydrogel on the total colony count of chicken.

[0030] Figure 6 Changes in V-Vis spectrum (a), color (b), particle size (c), Zeta potential (d), and CD spectrum (e) of AgNPs reacting with different concentrations of NaCl.

[0031] Figure 7 UV-visible spectra (a), color (b), particle size (c), zeta potential (d), and CD spectra (e) of AgNPs with different concentrations of NaCl and H 2 Changes in S response. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Example 1

[0034] A method for preparing a nanosilver hydrogel for monitoring the freshness of a braised chicken product comprises the following steps:

[0035] (1) Preparation of Nanosilver

[0036] Weigh 1g gelatin and dissolve it in 100mL pure water. Heat it on a constant temperature magnetic stirrer until it is completely dissolved. After cooling to room temperature, add 1g PVP and 10mL 0.1mol / L silver nitrate solution to the solution in sequence. Stir at 1200r / min for 10min in a light-proof environment to form a gelatin / Ag + The mixed sample was transferred into a 250 mL conical flask and placed in an autoclave at 121°C, 0.12 MPa, and reacted for 20 min. The solution after removal was reddish brown, indicating the formation of nanosilver.

[0037] (2) Preparation of Nanosilver Hydrogel

[0038] Weigh 100 mL of the prepared AgNP solution into a beaker, then add 2 g of agar powder into the beaker, and heat on a magnetic stirrer at 1200 r / min and 80°C for 10 min to completely dissolve the agar powder. After degassing, weigh 30 mL of the above sample solution with a measuring cylinder and pour it into a polystyrene culture dish with a diameter of 90 mm, and let it stand at room temperature to solidify to obtain nanosilver hydrogel.

[0039] The application of the nano silver hydrogel in improving the freshness of marinated chicken products comprises the following steps:

[0040] (1) Braised chicken with soy sauce

[0041] a. Raw material pretreatment: fresh or thawed chicken breasts are blanched at 95°C for 5 minutes; after blanching, the chicken breasts are placed in braising soup for stewing;

[0042] b. Braising: Add 1kg of onion, 4kg of sugar, 5kg of refined salt to 100kg of water, then put in 0.5kg each of star anise, pepper, angelica dahurica and cloves, and cook at 95℃ for 30min; then add the blanched chicken breast and cook at 90-100℃ for 25min; after braising, remove the chicken breast and precool it at room temperature.

[0043] (2) Freshness monitoring

[0044] a. Cut the pre-cooled marinated chicken into small pieces and place them on a 4cm 2 The AgNP hydrogel was placed in a disposable culture dish and stored at 4 °C.

[0045] b. The color of AgNP hydrogel changed from brown to off-white within 3 days of storage of braised chicken. In addition, AgNP hydrogel extended the shelf life of unpackaged braised chicken from 4 days to 6 days at 4°C.

[0046] Example 2

[0047] A method for preparing a nanosilver hydrogel for monitoring the freshness of a braised chicken product comprises the following steps:

[0048] (1) Preparation of Nanosilver

[0049] Weigh 1.5 g of gelatin and dissolve it in 120 mL of pure water. Heat it on a constant temperature magnetic stirrer until it is completely dissolved. After cooling to room temperature, add 1.5 g of PVP and 15 mL of 0.1 mol / L silver nitrate solution to the solution in sequence. Stir at a speed of 1200 r / min for 10 min in a light-proof environment to form a gelatin / Ag + The mixed sample was transferred into a 250 mL conical flask and placed in an autoclave at 121°C, 0.12 MPa, and reacted for 20 min. The solution after removal was reddish brown, indicating the formation of nanosilver.

[0050] (2) Preparation of Nanosilver Hydrogel

[0051] Weigh 100 mL of the prepared AgNP solution into a beaker, then add 2.5 g of agar powder into the beaker, and heat on a magnetic stirrer at 1200 r / min and 80°C for 10 min to completely dissolve the agar powder. After degassing, weigh 30 mL of the above sample solution with a measuring cylinder and pour it into a polystyrene culture dish with a diameter of 90 mm, and let it stand at room temperature to solidify to obtain nanosilver hydrogel.

[0052] The application of the nano silver hydrogel in improving the freshness of marinated chicken products comprises the following steps:

[0053] (1) Braised chicken with soy sauce

[0054] a. Raw material pretreatment: fresh or thawed chicken breasts are blanched at 99°C for 5 minutes; after blanching, the chicken breasts are placed in braising soup for stewing;

[0055] b. Braising: Add 1kg of onion, 4kg of sugar, 5kg of refined salt to 100kg of water, then put in 0.5kg each of star anise, pepper, angelica dahurica and cloves, and cook at 99℃ for 30min; then add the blanched chicken breast and cook at 99℃ for 20min; after braising, remove the chicken breast and precool it at room temperature.

[0056] (2) Freshness monitoring

[0057] a. Cut the pre-cooled marinated chicken into small pieces and place them on a 4cm 2 The AgNP hydrogel was placed in a disposable culture dish and stored at 4 °C.

[0058] b. The color of AgNP hydrogel changed from brown to off-white within 3 days of storage of braised chicken. In addition, AgNP hydrogel extended the shelf life of unpackaged braised chicken from 4 days to 6 days at 4°C.

[0059] Example 3

[0060] A method for preparing a nanosilver hydrogel for monitoring the freshness of a braised chicken product comprises the following steps:

[0061] (1) Preparation of Nanosilver

[0062] Weigh 2g of gelatin and dissolve it in 180mL of pure water. Heat it on a constant temperature magnetic stirrer until it is completely dissolved. After cooling to room temperature, add 2g of PVP and 20mL of 0.1mol / L silver nitrate solution to the solution in sequence. Stir at a speed of 1200r / min for 10min in a light-proof environment to form a gelatin / Ag + The mixed sample was transferred into a 250 mL conical flask and placed in an autoclave at 121°C, 0.12 MPa, and reacted for 20 min. The solution after removal was reddish brown, indicating the formation of nanosilver.

[0063] (2) Preparation of Nanosilver Hydrogel

[0064] Weigh 100 mL of the prepared AgNP solution into a beaker, then add 3 g of agar powder into the beaker, and heat on a magnetic stirrer at 1200 r / min and 80°C for 10 min to completely dissolve the agar powder. After degassing, weigh 30 mL of the above sample solution with a measuring cylinder and pour it into a polystyrene culture dish with a diameter of 90 mm, and let it stand at room temperature to solidify to obtain nanosilver hydrogel.

[0065] The application of the nano silver hydrogel in improving the freshness of marinated chicken products comprises the following steps:

[0066] (1) Braised chicken with soy sauce

[0067] a. Raw material pretreatment: fresh or thawed chicken breasts are blanched at 99°C for 5 minutes; after blanching, the chicken breasts are placed in braising soup for stewing;

[0068] b. Braising: Add 1kg of onion, 4kg of sugar, 5kg of refined salt to 100kg of water, then put in 0.5kg each of star anise, pepper, angelica dahurica and cloves, and cook at 95℃ for 30min; then add the blanched chicken breast and cook at 99℃ for 30min; after braising, remove the chicken breast and precool it at room temperature.

[0069] (2) Freshness monitoring

[0070] a. Cut the pre-cooled marinated chicken into small pieces and place them on a 4cm 2The AgNP hydrogel was placed in a disposable culture dish and stored at 4 °C.

[0071] b. The color of AgNP hydrogel changed from brown to off-white within 3 days of storage of braised chicken. In addition, AgNP hydrogel extended the shelf life of unpackaged braised chicken from 4 days to 6 days at 4°C.

[0072] In order to highlight the beneficial effects of the present invention, some exploratory experiments carried out in the early stage are cited as examples for comparison.

[0073] Comparative experiment 1

[0074] Nanosilver materials were prepared by using gelatin as a reducing agent combined with high temperature reaction. The specific results are as follows:

[0075] (a) pH changes of braised chicken at 4°C

[0076] like Figure 1 As shown in the figure, the pH of cooked meat increased from 6.28 to 6.46 when stored at 4°C. It can be seen that the shelf life increased by only 0.18 within 7 days, which is far from the color development reaction of the hydrogel film based on pH changes. Therefore, it is urgent to develop a hydrogel color development and antibacterial film that does not rely on pH changes in meat products.

[0077] (b) Previous studies have found that salt in the brine during chicken stewing enters the muscle through osmosis, and the salt entering the muscle has a potential color development effect. Therefore, the effect of NaCl on the size and potential of the main components in the nanosilver preparation material was studied. The specific results are as follows:

[0078] Table 1 Effect of NaCl on main components

[0079]

[0080] Note: Data are expressed as mean ± standard deviation. Lowercase letters (af) indicate significant differences within the same column (P<0.05). Gelatin (without NaCl), gelatin (with NaCl): 100 μL of 1M NaCl solution was added to 10 mL of gelatin solution. PVP (without NaCl), PVP (with NaCl): 100 μL of 1M NaCl solution was added to 10 mL of PVP solution. 0.01 M AgNO3 (without NaCl), 0.01 M AgNO 3 (with NaCl): in 10mL AgNO 3In the solution, 100μL 1M NaCl solution was not added or added. Gelatin + PVP (without NaCl), gelatin + PVP (with NaCl): In 10mL gelatin and PVP solution, 100μL 1M NaCl solution was not added or added. Gelatin-PVP (without NaCl), gelatin-PVP (with NaCl): Gelatin and PVP were reacted at high temperature and then mixed to prepare 10mL gelatin and PVP solution, and 100μL 1M NaCl solution was not added or added. AgNP (without NaCl), AgNP (with NaCl): In the prepared nanosilver solution, 100μL 1M NaCl solution was not added or added.

[0081] Table 1 shows the changes in particle size and potential of different reaction materials when NaCl is added or not. It can be seen from group 6 that after adding NaCl, the particle size becomes larger and the absolute value of potential becomes lower. These results can prove that NaCl affects the results of each component of nanosilver at room temperature.

[0082] The difference between groups 9 and 10 and groups 7 and 8 is that the gelatin and PVP in groups 9 and 10 were treated with high temperature. From the results, it can be seen that regardless of whether NaCl is contained, the particle size decreases after high temperature treatment. The results show that high temperature treatment further affects the structure of gelatin and PVP.

[0083] Groups 11 and 12 show the changes in particle size and potential of nanosilver prepared by high temperature method with NaCl added. The nanosilver prepared by high temperature method is significantly smaller than the particle size of silver nitrate at room temperature. Since PVP is the macromolecule that stabilizes the result, gelatin plays a reducing role, reducing silver nitrate to nanosilver at high temperature. And under the same salt ion conditions, the particle size of the prepared nanosilver increased from 23.80nm to 64.87nm, an increase of 172%, which is the group with the most significant particle size change among all results; in addition, the absolute value of the potential of nanosilver without NaCl added is 23.89 times that of nanosilver with NaCl added, which is also the group with the most significant particle size change among all results. These results show that the sensitivity of the particle size and potential of nanosilver prepared by high temperature to NaCl is greatly enhanced, which is an unexpected effect.

[0084] (c) The results of preparing nanosilver using gelatin as a reducing agent combined with a high temperature method and its selectivity for chloride ions are as follows:

[0085] like Figure 2 As shown in Figure 2, the AgNP sol is reddish brown, and due to the surface plasmon resonance of silver nanoparticles, its UV absorption visible spectrum shows a strong broad absorption peak around 420-430nm, while the blank group (AgNO 3The solution was colorless and had no absorption peak in the range of 300-800nm, which indicated the formation of AgNPs. The main reason for the formation of AgNPs is that gelatin converts Ag into + Ions are reduced to Ag 0 , and then Ag 0 AgNPs are composed of aggregates. The SPR band is caused by the size, shape, morphology, dielectric conduction and oscillation of the formed nanoparticles. The shape of AgNPs is always related to SPR, that is, the well-defined spherical AgNPs form only one peak at 420nm. From the figure, it can be seen that the single peak of λmax near 420nm is absorbed in the spectrum, which indicates that the synthesized AgNPs are spherical.

[0086] In order to explore whether the AgNPs prepared in the present invention are also selective for other common anions, under the same experimental conditions, CH 3 COO - OH - 、NO 3 - 、SO 4 2- 、NO 3 - Common anions, such as Figure 3 As shown in the figure, from the UV spectrum and the corresponding selectivity histogram, it can be seen that compared with other common anions, Cl - The response to AgNPs was particularly significant.

[0087] The above results show that gelatin PVP acts as a stabilizer and gelatin as a reducing agent to reduce AgNO in one step through a one-pot method. 3 In the synthesis of AgNP, PVP combines with the proline of gelatin through the carboxyl group in the structure due to hydrogen bonding, forming a gelatin-PVP complex with gelatin in the gelatin structure. The gelatin-PVP complex plays a spatial stabilizing role on the surface of AgNP, mainly because the hydrophobic groups of gelatin are adsorbed on the surface of AgNP, while the segments containing hydrophilic groups stretch in water. According to Zeta potential measurement, AgNP is positively charged, which indicates that there is a large amount of Ag on the surface of AgNP. + When NaCl was added, the Ag adsorbed on the AgNP + With Cl - It is easy to react chemically to generate AgCl particles attached to the surface of AgNP, and the gelatin-PVP structure with a steric stabilization effect on the surface is affected by Na + and Cl - The effect causes the electrostatic interaction between the ionized groups on the gelatin molecular chain to be shielded, and the change in molecular conformation causes the aggregation of gelatin molecules while disturbing the stable state of gelatin-PVP.

[0088] Comparative test 2

[0089] The color reaction and inhibitory effect of nanosilver hydrogel on braised chicken are as follows:

[0090] Figure 4 The prepared AgNP hydrogel showed the color change of chicken samples. As the storage time increased, the color of the nanosilver hydrogel remained stable without obvious color change. Compared with chicken marinated in water, chicken marinated in broth containing 3%, 4%, and 5% salt content caused a significant change in the color of the nanosilver hydrogel. The L * value, a * Value and b * The value decreased significantly within 7 days, and the color of the AgNP hydrogel changed from yellow to grayish white.

[0091] The total number of colonies is an important indicator for evaluating microbial contamination during the storage of meat products. Figure 5 As shown in the figure, after 7 days of storage, the total viable counts (TVC) of chicken samples in the AH-0%, AH-3%, AH-4% and AH-5% groups with AgNP hydrogel were significantly reduced compared with the CON group without AgNP hydrogel (P<0.05). With the extension of storage time, the total colony count increased significantly (P<0.05). According to the national standard GB 2726-2016 "National Food Safety Standard Cooked Meat Products", the total colony count of products made from fresh (frozen) livestock and poultry products as the main raw materials is ≤50000 cfu / g (i.e. 4.70 log CFU / g). The total colony count of chicken in the CON group reached the specified limit on the 4th day, while that in the AH-0% group exceeded the limit on the 6th day. This shows that the AgNP hydrogel has a certain antibacterial effect.

[0092] The above results show that nanosilver prepared with gelatin can be used as a color reaction for the freshness of cooked meat products, which is fundamentally different from the traditional method of judging the freshness of raw meat by pH changes. It is based on the reaction between the change of salt content in the braising soup and nanosilver, which causes its color change. On the other hand, it can extend the shelf life of braised chicken from 4 days to 6 days, which has unexpected effects.

[0093] Comparative test 3

[0094] The mechanism of the color reaction of nanosilver hydrogel to braised chicken is as follows:

[0095] Figure 6 The results show that the UV absorption increases with the Cl -The increase in absorbance can be attributed to the Cl - and Ag + The reaction between AgCl and AgNP leads to the formation of AgCl precipitates. These precipitates adhere to the surface of AgNPs, creating a "black hole" effect and enhancing the UV absorbance. In addition, the half-peak width of the UV absorption spectrum indicates the uniformity of the particle size. Narrower half-peak width and better symmetry correspond to a more uniform particle size distribution of the synthesized AgNPs. - With the increase of content, the uniformity of AgNP decreases ( Figure 6 a), which is consistent with the Cl - and Ag + The results are consistent with those of the previous studies that the reaction between them destroyed the original spatial structure of AgNP.

[0096] In this experiment, the average particle size of AgNPs synthesized by one-pot method was 23.80±3.53nm ( Figure 6 c). PVP can interact with the hydrophilic groups of gelatin and embed into the gelatin matrix, providing steric hindrance. The hydrophobic groups of gelatin can interact with the hydrophobic silver nanoparticles. These effects are crucial for the stability of AgNPs prepared by the one-pot method. With the increase of NaCl concentration, the particle size of AgNPs increased significantly from 23.80nm to 64.86nm ( Figure 6 c). Figure 6 The results of d showed that with the increase of NaCl concentration, the zeta potential of AgNP decreased significantly from 13.83mV to 0.55mV (P<0.05). The results of zeta potential and particle size showed that the surface Cl - and Ag + The reaction between them reduces the surface charge of AgNPs due to charge neutralization. Since electrostatic interaction is an important force to maintain the spatial structure of AgNPs, the reduction of electrostatic repulsion between AgNPs leads to the aggregation and larger particle size of AgNPs, as well as the reduction of AgNP stability. These results are consistent with the results of UV spectroscopy.

[0097] UV-CD spectroscopy was used to analyze the effect of NaCl on the secondary structure of gelatin in AgNPs, e.g. Figure 6 e. The results showed that there were two different peaks in the CD spectrum: a positive peak at 220 nm and a negative peak at 199 nm, which is consistent with the typical CD spectrum characteristics of gelatin. As the NaCl concentration increased, the absolute value of the negative peak decreased significantly, while there was no significant difference in the absolute value of the positive peak at 220 nm. The decrease in the absolute value of the negative peak in the gelatin CD spectrum indicates that the aggregation of gelatin molecules is enhanced. Therefore, this finding indicates that gelatin molecules exhibit a higher degree of aggregation with increasing NaCl concentration, which is consistent with the results of Zeta potential, particle size and UV spectrum.

[0098] Figure 7 Shows H 2 The effect of S on the appearance, UV spectrum, particle size, zeta potential and circular dichroism of the above NaCl-AgNP solution. 2 When S gas was injected into the NaCl-AgNP solution, the absorbance value of the maximum absorption peak at 420 nm increased significantly with the increase of NaCl concentration ( Figure 7 a), the visual appearance of the solution gradually changed from transparent yellow to gray ( Figure 7 b) Due to Ag 2 The solubility product constant of S is much lower than that of AgCl. 2 S, HS - and S 2- In the presence of 2 S.

[0099] AgNP surface Ag 2 The formation of S layer significantly changed the extinction characteristics of AgNP surface plasmon resonance spectrum. The concentration of NaCl changed the Ag 2 The S layer plays a vital role in visual color ( Figure 7 b) Injection of H 2 After S, the particle size of AgNPs further increased from 64.87 nm to 116.63 nm, and the Zeta potential decreased significantly, indicating that the synthesized AgNPs 2 The stability further deteriorated under the influence of S. After adding NaCl, the absolute value of the negative peak of the gelatin CD spectrum decreased significantly, but there was no significant difference in the absolute value of the negative peak when the NaCl concentration increased. 2 S, the absolute value of the negative peak of the CD spectrum of gelatin decreased significantly in the presence of NaCl, but there was no significant difference in the absolute value of the negative peak of the CD spectrum of gelatin when the NaCl concentration increased.

[0100] In the one-pot method used in this experiment, gelatin converts Ag + Ions are reduced to Ag 0 , unreduced Ag + Adsorbed on Ag 0 Surface, Ag 0 The PVP binds to the hydrophobic residues of gelatin through hydrophobic interactions. At the same time, PVP is embedded in the three-dimensional structure of gelatin through hydrogen bonds between the PVP carboxyl groups and the proline of gelatin, which plays a vital role in stabilizing the spatial conformation of gelatin. Therefore, the gelatin-PVP complex acts as a framework for AgNPs, and the nanosilver particles are located on the gelatin-PVP skeleton through hydrophobic interactions. During storage, NaCl in the marinated chicken re-migrates to the surface of the meat and contacts with the AgNP hydrogel. Subsequently, Cl -Ag on the surface of AgNP + The NaCl reaction caused the AgCl particles to adhere to the AgNP surface. At the same time, the electrostatic interaction between the ionized groups on the gelatin molecular chain was shielded, resulting in increased aggregation of gelatin molecules and reduced stability of the gelatin-PVP complex. 2 In the presence of S, the AgCl particles are further converted into black Ag attached to the surface of AgNPs. 2 S particles, gelatin-PVP complexes further aggregated, causing the visual color of AgNPs to change to off-white. This is the mechanism of the freshness response of gelatin-stabilized AgNP hydrogels to color reaction when in contact with marinated chicken.

[0101] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing nanosilver hydrogel for monitoring the freshness of marinated chicken products, characterized in that: The following steps are involved: (1) Preparation of Nanosilver Weigh gelatin and dissolve it in pure water. Stir under heating until it is completely dissolved. After cooling to room temperature, add polyvinyl pyrrolidone and silver nitrate solution to the solution in sequence. Stir under light-proof environment to form gelatin / Ag + Solution, react the mixed sample in an autoclave to obtain an AgNP solution; (2) Preparation of Nanosilver Hydrogel The prepared AgNP solution was weighed, agar powder was added, and the agar powder was completely dissolved by stirring under heating. After degassing, the sample solution was weighed and poured into a culture dish, and allowed to stand at room temperature to solidify, thereby obtaining the nanosilver hydrogel.

2. The method for preparing nano silver hydrogel according to claim 1, wherein: In the step (1), the mass volume ratio of gelatin to pure water is 1:180 to 1:45; the mass volume ratio of gelatin to polyvinyl pyrrolidone is 1:2 to 2:1; the mass volume ratio of gelatin to silver nitrate solution is 1:20 to 1:5; and the concentration of the silver nitrate solution is 0.1 mol / L.

3. The method for preparing nano silver hydrogel according to claim 2, wherein: In the step (1), the gelatin / Ag mixture is stirred at a speed of 1200 r / min for 10 min in a light-proof environment. + Solution.

4. The method for preparing nano silver hydrogel according to claim 3, wherein: In the step (1), the reaction conditions of the sample in the high pressure sterilizer are 121° C., 0.12 MPa, and the reaction time is 20 min.

5. The method for preparing nano silver hydrogel according to claim 4, characterized in that: In the step (2), the mass volume ratio of agar powder to AgNP solution is 2 to 3:

100.

6. The method for preparing the nano silver hydrogel according to claim 5, characterized in that: In the step (2), heating is performed at 1200 r / min and 80° C. for 10 min to completely dissolve the agar powder.

7. The nano silver hydrogel prepared by the preparation method according to any one of claims 1 to 6.

8. The use of the nanosilver hydrogel according to claim 7 in monitoring the freshness of marinated chicken products, characterized in that: The following steps are involved: (1) Stewing of braised chicken; (2) Monitoring the freshness of meat products The pre-cooled marinated chicken was cut into small pieces, placed on the nanosilver hydrogel, and then placed in a disposable culture dish and stored at 4°C.

9. The use of the nanosilver hydrogel according to claim 8 in monitoring the freshness of marinated chicken products, characterized in that: The nanosilver hydrogel changed from brown to grayish white within 3 days of storage of braised chicken in soy sauce; the nanosilver hydrogel extended the shelf life of unpackaged braised chicken in soy sauce from 4 days to 6 days at 4°C.

10. The use of the nanosilver hydrogel according to claim 9 in monitoring the freshness of marinated chicken products, characterized in that: The step (1) specifically comprises: Raw material pretreatment: fresh or thawed chicken breasts are blanched at 90-100℃; after blanching, the chicken breasts are placed in braising soup for stewing; Braising: Add onion, sugar, and salt to the water, then put in star anise, pepper, angelica, and cloves, and cook at 90-100℃ for 30 minutes; then add the blanched chicken breast and cook at 90-100℃ for 20-30 minutes; after braising, remove the chicken breast and pre-cool it at room temperature.

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