Processing method of eggplant with high anthocyanin stability

Abstract

The application relates to the field of fruit and vegetable processing technology and discloses a processing method of eggplants with high anthocyanin stability, which comprises the following steps: preparing an auxiliary color precursor by mixing potassium bicarbonate, ferulic acid and sodium caseinate, mixing the auxiliary color precursor with low-methoxyl pectin, sodium hexametaphosphate and calcium lactate at 40-45 DEG C, adding gluconic acid-delta-lactone, and adjusting the pH to 6.2-6.5 to prepare an impregnation solution; placing the cut purple-skin eggplant pieces in the impregnation solution for penetration, heating the eggplant pieces to 92-95 DEG C at a rate of 3-5 DEG C / min and keeping the temperature, and finally cooling and dehydrating the eggplant pieces. The application constructs a chemical clock by using the acid production characteristics of lactone under heating, triggers the isoelectric condensation of proteins to form hydrophobic microzones to isolate water and triggers the crosslinking of polysaccharides to construct an interpenetrating polymer network in sequence after homogeneous low-resistance mass transfer. The method effectively blocks the high-temperature hydration degradation of anthocyanin and maintains the macroscopic texture of the heated tissue.

Description

Technical Field

[0001] This invention relates to the field of fruit and vegetable processing technology, specifically to a method for processing eggplant with high anthocyanin stability. Background Technology

[0002] Eggplant is a common vegetable rich in anthocyanins. Its purplish-red color mainly comes from delphinidin derivatives, which have significant nutritional and commercial value. In the pre-processing stage of industrial processing such as canning, quick-freezing, and dehydrated vegetables, materials usually need to be blanched at a high temperature of over 90°C to inactivate endogenous enzymes such as polyphenol oxidase and peroxidase in order to prevent enzymatic browning during processing and storage.

[0003] To address the issue of high-temperature blanching easily damaging pigment stability, traditional industrial processing often employs methods such as adding auxiliary pigments and adjusting the pH of the system for color protection. Conventional processes typically add phenolic acids such as ferulic acid to the blanching solution, utilizing their π-π conjugated stacking with anthocyanins to form complexes, thereby resisting thermal degradation. Some processing methods also introduce calcium ions and hydrophilic polysaccharides such as pectin into the system, attempting to form polysaccharide gels in fruit and vegetable tissues to maintain their mechanical texture after heating; or directly add acidity regulators such as citric acid to maintain the processing system at a constant low pH, thereby stabilizing the anthocyanin flavonoid configuration.

[0004] Conventional auxiliary coloring relies heavily on non-covalent intermolecular bonding. While the system remains stable at room temperature, molecular thermal motion increases dramatically in high-temperature aqueous environments, easily disrupting the existing thermodynamic equilibrium. This leads to the significant detachment and dissociation of auxiliary pigments, exposing free anthocyanins directly to polar water molecules, making them susceptible to nucleophilic attack and hydration degradation, resulting in product fading. Directly acidifying the impregnation solution and combining it with polysaccharides and calcium salts to maintain texture creates acidic conditions that promote rapid coordination cross-linking of macromolecules on the fruit and vegetable skin. This prematurely formed dense network hinders mass transfer, preventing external auxiliary coloring components from penetrating deeply into the internal thin-walled cells, resulting in extremely uneven distribution of the color-protecting agent. Therefore, this invention provides a method for processing eggplant with high anthocyanin stability to address the shortcomings of existing technologies. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for processing eggplant with high anthocyanin stability. This method solves the problem that in the current industrial blanching process of purple eggplant, materials often require high-temperature treatment above 90°C to inactivate polyphenol oxidase. In this high-temperature aqueous environment, anthocyanins are easily degraded by hot water and transformed into colorless substances. Furthermore, the non-covalent complexes formed by conventionally added phenolic acid co-pigments and anthocyanins are prone to thermodynamic dissociation upon heating, thus limiting their color-protecting effect.

[0006] To achieve the above objectives, the present invention provides a method for processing eggplant with high anthocyanin stability, employing the following technical solution: A method for processing eggplant with high anthocyanin stability includes the following steps: S1. Select purple eggplants, wash them, remove the stems, cut them into chunks, drain and set aside; S2. Place the amphiphilic co-color precursor in a reaction vessel and maintain the temperature at 40-45℃. Add low-methoxyl pectin, sodium hexametaphosphate, and calcium lactate while stirring, and continue stirring. Then add gluconate-δ-lactone and stir. Adjust the pH value to 6.2-6.5 using an alkaline adjuster to obtain the impregnation solution. The amphiphilic co-color precursor is prepared from potassium bicarbonate, ferulic acid, and sodium caseinate in purified water. S3. Place the cut eggplant pieces in the soaking solution, start the external circulation pump, and soak at a temperature of 40-45℃. S4. Stop the external circulation, raise the center temperature of the system inside the reactor to 92-95°C at a heating rate of 3-5°C / min, and then keep it at that temperature. S5. Remove the eggplant pieces after heat preservation and place them in an ice water bath to cool. S6. Place the cooled eggplant pieces in a centrifugal dehydrator for dehydration to obtain processed eggplant pieces with high anthocyanin stability.

[0007] By employing the above technical solution, this invention utilizes a heat-driven acidity regulation mechanism to initiate multi-level phase transitions of macromolecules sequentially during heating, thereby constructing an interpenetrating polymer network in situ within the intercellular spaces of eggplant cells and intervening in pigment degradation at a physical spatial level. The specific reaction process and mechanism are as follows: During the impregnation stage at 40–45℃ and pH 6.2–6.5, both sodium caseinate and low-methoxyl pectin in the system are in a dissociated state and carry the same negative charge. Due to the electrostatic repulsion between polymer chains, the system is not prone to macromolecular condensation phase separation. At the same time, sodium hexametaphosphate in the system fixes the free calcium ions dissociated from calcium lactate through coordination chelation, which limits the premature cross-linking of low-methoxyl pectin. The above rheological state is conducive to maintaining a low macroscopic viscosity of the impregnation solution. The co-color precursor composed of sodium caseinate and ferulic acid can diffuse into the spongy tissue of eggplant along the concentration gradient, promoting the π-π conjugation of the aromatic ring of ferulic acid with intracellular anthocyanins, completing the initial co-color assembly.

[0008] During a heating process at a rate of 3–5 °C / min to 92–95 °C, gluconate-δ-lactone undergoes a ring-opening hydrolysis reaction under thermal conditions. The main reaction equation is: C6H... 10 O6 + H2O → C6H12 O7→C6H 11 O7 - +H + The hydrolysis reaction accelerates with increasing temperature, providing a continuous proton source for the system. This results in a smooth decrease in the pH of the tissue microenvironment over time, thus providing a time-controlled basis for subsequent macromolecular phase transitions.

[0009] When the system is heated and the pH of the microenvironment drops to around 4.6, it reaches the isoelectric point of sodium caseinate. At this point, the net surface charge of sodium caseinate molecules approaches zero, and with the disappearance of intermolecular electrostatic repulsion, spontaneous liquid-solid phase separation easily occurs. Molecular chain segments then fold and aggregate inward, forming a protein condensate phase in situ. Because the co-chromogenic complex formed by ferulic acid and anthocyanins has lipophilic properties, it is usually preferentially allocated and encapsulated within the hydrophobic region generated by protein aggregation. This hydrophobic region lowers the local dielectric constant, repelling the entry of external polar water molecules and spatially restricting the hydration degradation pathway of anthocyanins through nucleophilic attack by high-temperature free water molecules.

[0010] As the temperature continued to rise to 92–95°C, the pH of the system further decreased to around 4.0. Under the influence of this temperature and proton concentration, the polyphosphate chains of sodium hexametaphosphate degraded, and the increased hydrogen ions competed for coordination with it, weakening its chelating ability for calcium ions and causing the system to release more free calcium ions in situ. Calcium ions then coordinated with galacturonic acid residues on the low-methoxyl pectin chains distributed around the hydrophobic region, with the reaction shown as: 2R-COO - +Ca 2+ →(R-COO)2Ca. Through coordination, the polysaccharide chains fold and cross-link, forming a metal ion polysaccharide network structure with a certain strength.

[0011] In addition to relying on a rigid polysaccharide backbone to restrict the irreversible macroscopic thermal aggregation of protein molecules at their isoelectric point at 95°C, thus helping to maintain the mechanical morphology of fruit and vegetable tissues, this physical structure also provides corresponding physical steric hindrance, which to some extent restricts the translational degrees of freedom of the internal auxiliary color complexes and inhibits the tendency of thermodynamic dissociation under high temperature conditions.

[0012] Preferably, the amphiphilic co-chromogenic precursor is prepared from 0.08–0.12 parts by weight of potassium bicarbonate, 0.15–0.20 parts by weight of ferulic acid, and 0.40–0.60 parts by weight of sodium caseinate in purified water, based on 100.00 parts by weight of purified water. When preparing the impregnation solution, the amount of low-methoxyl pectin added is 0.50–0.70 parts by weight, the amount of sodium hexametaphosphate is 0.25–0.30 parts by weight, the amount of calcium lactate is 0.15–0.20 parts by weight, and the amount of glucono-δ-lactone is 0.40–0.50 parts by weight.

[0013] By adopting the above technical solution, the mass ratio of each component meets the stoichiometric requirements of the phase change reaction. Under a specific heating trajectory, the protein and polysaccharide system with the above-mentioned content can generate a volume-matched condensed phase and cross-linked network, which helps to reduce fluid mass transfer blockage caused by excessively high macromolecular concentrations, or improve the problem of insufficient three-dimensional support strength caused by excessively low concentrations.

[0014] Preferred method for preparing amphiphilic co-chromogenic precursor includes the following steps: injecting purified water into a reaction vessel, heating and maintaining the temperature at 40-45°C; adding potassium bicarbonate and ferulic acid sequentially to the purified water, starting mechanical stirring, and stirring continuously for 5-8 minutes; while maintaining stirring, adding sodium caseinate, and stirring continuously at a constant temperature for 20-30 minutes to obtain the amphiphilic co-chromogenic precursor.

[0015] By employing the above-mentioned technical solution, potassium bicarbonate promotes the dissociation of the free carboxyl groups of ferulic acid, transforming it into a water-soluble salt state. Subsequently added sodium caseinate undergoes non-covalent assembly with ferulic acid through hydrophobic interactions. Stepwise stirring facilitates the thorough dispersion of ferulic acid in the aqueous phase, improving the homogeneity of the complex and providing a relatively stable precursor solution for subsequent targeted penetration.

[0016] Preferably, purple-skinned eggplants are cut into pieces with a side length of 1.0 to 1.5 cm; based on 100.00 parts by weight of purified water, the weight of the eggplant pieces is 20.00 to 30.00 parts by weight.

[0017] By adopting the above technical solution, the material size and corresponding liquid-to-solid mass ratio control the mass transfer distance and concentration gradient between the solid and liquid phases. A suitable specific surface area helps maintain the penetration rate of the auxiliary color precursor into the eggplant spongy tissue and reduces the temperature difference between the central and surface areas during blanching.

[0018] Preferably, the stirring time after adding low-methoxyl pectin, sodium hexametaphosphate and calcium lactate is 15 to 20 minutes.

[0019] By adopting the above technical solution, the longer processing time provides sufficient time for polysaccharide hydration and ion chelation, which is conducive to sodium hexametaphosphate fully capturing free calcium ions in the system, reducing early cross-linking of polysaccharides caused by excessively high local concentrations, and thus better maintaining the macroscopic homogeneous state of the impregnation solution.

[0020] Preferably, the alkalinity regulator is an aqueous solution of potassium bicarbonate with a concentration of 0.8–1.2 mol / L.

[0021] By employing the above-mentioned technical solution and adjusting the initial acidity with a weakly alkaline salt solution of this concentration, an appropriate buffer capacity can be established for the system. This makes the acidity change during the initial stage of gluconate-δ-lactone hydrolysis smoother, helping to reduce the risk of premature isoelectric aggregation of proteins caused by a sudden drop in local acidity.

[0022] Preferably, the immersion time is 15 to 20 minutes; the heat treatment time is 4 to 6 minutes.

[0023] By adopting the above technical solution, the constant temperature immersion for 15 to 20 minutes is conducive to the diffusion equilibrium of macromolecular complexes in eggplant tissue; while the high temperature holding treatment for 4 to 6 minutes can meet the inactivation conditions of endogenous enzymes such as polyphenol oxidase, and at the same time promote the cross-linking and solidification of polysaccharide network.

[0024] Preferably, the temperature of the ice water bath is 0-4°C, and the cooling process is carried out until the center temperature of the eggplant pieces drops to 20-25°C.

[0025] By adopting the above technical solution, the forced cooling treatment after blanching rapidly reduces the thermodynamic kinetic energy of the system, blocks the hydrolysis reaction of residual lactones, and fixes the physical morphology of the formed polymer interpenetrating network, which helps to alleviate the phenomenon of excessive softening of the tissue caused by residual heat.

[0026] Preferably, the dehydration speed is 400-500 rpm and the dehydration time is 2-3 min.

[0027] By adopting the above technical solution, the centrifugation parameters can remove free water from the surface of the tissue without damaging the integrity of the external macroscopic structure of the eggplant pieces, thereby reducing the surface water activity of the product and providing a relatively stable physical interface for subsequent packaging or freezing processing.

[0028] Preferably, at the end of the heat preservation treatment, the final pH value of the system in the reactor drops to 3.8-4.2.

[0029] By adopting the above technical solution, the final pH value is controlled within this range, exceeding the critical proton concentration for sodium hexametaphosphate to stably chelate calcium ions, thus promoting the release of calcium ions and the completion of the polysaccharide cross-linking reaction.

[0030] This invention provides a method for processing eggplant with high anthocyanin stability. It has the following beneficial effects: 1. This invention achieves dynamic adjustment of the system's acidity during the heating process by adding gluconate-δ-lactone to the impregnation solution and utilizing its slow hydrolysis and acid production kinetics. This results in the system being in a low-viscosity state with repulsion of like charges in the macromolecules during the initial impregnation stage, reducing the mass transfer resistance caused by premature cross-linking of polysaccharides on the eggplant surface. This facilitates the even distribution of the auxiliary color precursor composed of sodium caseinate and ferulic acid deep into the eggplant tissue, solving the technical problem that traditional acidic color-protecting solutions easily cause epidermal closure and thus hinder internal mass transfer.

[0031] 2. This invention combines the acidity decrease trajectory during the heating process and utilizes the charge neutralization effect of sodium caseinate near its isoelectric point to induce protein aggregation phase separation in situ in the intercellular spaces of eggplant cells. The hydrophobic regions generated by aggregation can preferentially allocate and encapsulate lipophilic co-chromophores. This microstructure reduces the local dielectric constant and, at the physical level, reduces the frequency of direct contact between high-temperature polar water molecules and anthocyanins, thereby inhibiting the hydration degradation process and thermodynamic dissociation tendency of anthocyanins under high-temperature blanching conditions.

[0032] 3. This invention utilizes the calcium-degrading properties of sodium hexametaphosphate at specific high temperatures and proton concentrations to trigger ionic cross-linking of low-methoxyl pectin after the formation of the hydrophobic protein condensate phase, constructing a polymer interpenetrating network. The rigid outer polysaccharide backbone provides a physical constraint boundary for the internal protein condensate phase, limiting irreversible macroscopic thermal aggregation of proteins at sustained high temperatures. This not only maintains the stability of the physical barrier separating pigments but also provides internal spatial mechanical compensation for heated fruit and vegetable tissues, improving the textural softening phenomenon that easily occurs after conventional blanching of eggplants. Attached Figure Description

[0033] Figure 1 This is a flowchart of the preparation method of the present invention; Figure 2 The above is an online monitoring graph of the changes in the physicochemical parameters of the impregnation solution during the programmed heating process of the present invention. (a) is a graph of the pH value change of each group of impregnation solutions during the programmed heating process, and (b) is a graph of the apparent viscosity change of each group of impregnation solutions during the programmed heating process. Figure 3 The figures show the thermodynamic stability of anthocyanins and the parameters of skin color in this invention. (a) shows the distribution of total anthocyanin retention rate in each group of eggplant samples, and (b) shows the skin color of each group of eggplant samples. * Value test distribution chart; Figure 4 The following are physical test diagrams of the texture characteristics of eggplant according to the present invention, wherein (a) is a distribution diagram of the hardness test of each group of eggplant samples, and (b) is a distribution diagram of the elasticity test of each group of eggplant samples. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0036] The eggplant raw materials used in this invention are commercially available fresh purple-skinned long eggplants with a moisture content ranging from 90% to 93%. Sodium caseinate (CAS number 9005-46-3) is a commercially available food-grade product with a weight-average molecular weight distribution ranging from 20kDa to 30kDa and a protein isoelectric point ranging from 4.5 to 4.7. Low-methoxyl pectin (CAS number 9000-69-5) is a commercially available food-grade product with a degree of esterification of galacturonic acid residues ranging from 30% to 35% and a weight-average molecular weight ranging from 50kDa to 80kDa. Ferulic acid (CAS number 1135-24-6), potassium bicarbonate (CAS number 298-14-6), calcium lactate (CAS number 814-80-2), sodium hexametaphosphate (CAS number 10124-56-8), and glucono-δ-lactone (CAS number 90-80-2) are all commercially available conventional food-grade products.

[0037] Preparation Example 1: This preparation example provides a method for preparing an amphiphilic auxiliary chromogenic precursor, including the following steps: (1) Inject 100.00 parts by weight of purified water into a reactor equipped with a mechanical stirrer and a jacket temperature control system, and heat and keep the temperature constant to 40°C.

[0038] (2) Add 0.08 parts by weight of potassium bicarbonate and 0.15 parts by weight of ferulic acid to the purified water in the reactor, turn on the mechanical stirrer, set the speed to 200 rpm, and stir continuously for 5 min.

[0039] (3) While maintaining stirring, add 0.40 parts by mass of sodium caseinate at a constant speed, adjust the stirring speed to 250 rpm, and continue stirring at a constant temperature for 20 min to obtain the amphiphilic auxiliary color precursor.

[0040] Preparation Example 2: This preparation example provides a method for preparing an amphiphilic auxiliary chromogenic precursor, including the following steps: (1) Inject 100.00 parts by weight of purified water into a reactor equipped with a mechanical stirrer and a jacket temperature control system, and heat and keep the temperature constant to 42°C.

[0041] (2) Add 0.10 parts by weight of potassium bicarbonate and 0.18 parts by weight of ferulic acid to the purified water in the reactor in sequence, turn on the mechanical stirrer, set the speed to 220 rpm, and stir continuously for 6 min.

[0042] (3) While maintaining stirring, add 0.50 parts by mass of sodium caseinate at a constant speed, adjust the stirring speed to 280 rpm, and continue stirring at a constant temperature for 25 min to obtain the amphiphilic auxiliary color precursor.

[0043] Preparation Example 3: This preparation example provides a method for preparing an amphiphilic auxiliary chromogenic precursor, including the following steps: (1) Inject 100.00 parts by weight of purified water into a reactor equipped with a mechanical stirrer and a jacket temperature control system, and heat and keep the temperature constant to 45°C.

[0044] (2) Add 0.12 parts by mass of potassium bicarbonate and 0.20 parts by mass of ferulic acid to the purified water in the reactor, turn on the mechanical stirrer, set the speed to 250 rpm, and stir continuously for 8 minutes.

[0045] (3) While maintaining stirring, add 0.60 parts by mass of sodium caseinate at a constant speed, adjust the stirring speed to 300 rpm, and continue stirring at a constant temperature for 30 min to obtain the amphiphilic auxiliary color precursor.

[0046] See attached document Figure 1 Example 1: This embodiment provides a method for processing eggplant with high anthocyanin stability, including the following steps: S1. Select purple eggplants, wash and remove the stems, cut them into pieces with a side length of 1.0cm, drain the water, and weigh out 20.00 parts by weight for later use.

[0047] S2. The amphiphilic auxiliary color precursor obtained in Preparation Example 1 was placed in a reaction vessel and the temperature was maintained at 40°C. 0.50 parts by weight of low-methoxyl pectin, 0.25 parts by weight of sodium hexametaphosphate and 0.15 parts by weight of calcium lactate were added at a stirring speed of 250 rpm and stirred continuously for 15 min. 0.40 parts by weight of gluconate-δ-lactone were added and stirred for 5 min. The pH value was adjusted to 6.2 with 0.8 mol / L potassium bicarbonate aqueous solution to obtain the impregnation solution.

[0048] S3. Place 20.00 parts by weight of eggplant pieces obtained in step S1 into the soaking solution obtained in step S2, start the external circulation pump, and soak at 40°C for 15 minutes.

[0049] S4. Stop the external circulation and raise the center temperature of the system inside the reactor to 92°C at a heating rate of 3°C / min. Hold at this temperature for 4 minutes.

[0050] S5. Remove the eggplant pieces and place them in an ice water bath at 0℃ until the center temperature of the eggplant pieces drops to 20℃.

[0051] S6. Place the cooled eggplant pieces in a centrifugal dehydrator and dehydrate at 400 rpm for 2 minutes to obtain processed eggplant pieces with high anthocyanin stability. Example 1

[0052] This embodiment provides a method for processing eggplant with high anthocyanin stability, including the following steps: S1. Select purple eggplants, wash and remove the stems, cut them into pieces with a side length of 1.2cm, drain the water, and weigh 25.00 parts by weight for later use.

[0053] S2. The amphiphilic auxiliary color precursor obtained in Preparation Example 2 was placed in a reaction vessel and the temperature was maintained at 42°C. 0.60 parts by mass of low-methoxyl pectin, 0.28 parts by mass of sodium hexametaphosphate and 0.18 parts by mass of calcium lactate were added at a stirring speed of 250 rpm and stirred continuously for 18 min. 0.45 parts by mass of gluconate-δ-lactone were added and stirred for 5 min. The pH value was adjusted to 6.4 with 1.0 mol / L potassium bicarbonate aqueous solution to obtain the impregnation solution.

[0054] S3. Place 25.00 parts by weight of eggplant pieces obtained in step S1 into the soaking solution obtained in step S2, start the external circulation pump, and soak at 42°C for 18 minutes.

[0055] S4. Stop the external circulation and raise the center temperature of the system inside the reactor to 94°C at a heating rate of 4°C / min. Hold at this temperature for 5 minutes.

[0056] S5. Remove the eggplant pieces and place them in an ice water bath at 2°C until the center temperature of the eggplant pieces drops to 22°C.

[0057] S6. Place the cooled eggplant pieces in a centrifugal dehydrator and dehydrate at 450 rpm for 2 minutes to obtain processed eggplant pieces with high anthocyanin stability. Example 2

[0058] This embodiment provides a method for processing eggplant with high anthocyanin stability, including the following steps: S1. Select purple eggplants, wash and remove the stems, cut them into pieces with a side length of 1.5cm, drain the water, and weigh out 30.00 parts by weight for later use.

[0059] S2. The amphiphilic auxiliary color precursor obtained in Preparation Example 3 was placed in a reaction vessel and the temperature was maintained at 45°C. 0.70 parts by weight of low-methoxyl pectin, 0.30 parts by weight of sodium hexametaphosphate and 0.20 parts by weight of calcium lactate were added at a stirring speed of 250 rpm and stirred continuously for 20 min. 0.50 parts by weight of gluconate-δ-lactone were added and stirred for 5 min. The pH value was adjusted to 6.5 with 1.2 mol / L potassium bicarbonate aqueous solution to obtain the impregnation solution.

[0060] S3. Place 30.00 parts by weight of eggplant pieces obtained in step S1 into the soaking solution obtained in step S2, start the external circulation pump, and soak at 45°C for 20 minutes.

[0061] S4. Stop the external circulation and raise the center temperature of the system inside the reactor to 95°C at a heating rate of 5°C / min, and hold at this temperature for 6 minutes.

[0062] S5. Remove the eggplant pieces and place them in an ice water bath at 4°C until the center temperature of the eggplant pieces drops to 25°C.

[0063] S6. Place the cooled eggplant pieces in a centrifugal dehydrator and dehydrate at 500 rpm for 3 minutes to obtain processed eggplant pieces with high anthocyanin stability. Example 3

[0064] This embodiment provides a method for processing eggplant with high anthocyanin stability, including the following steps: S1. Select purple eggplants, wash and remove the stems, cut them into pieces with a side length of 1.2cm, drain the water, and weigh 20.00 parts by weight for later use.

[0065] S2. The amphiphilic auxiliary color precursor obtained in Preparation Example 2 was placed in a reaction vessel and the temperature was maintained at 42°C. 0.60 parts by mass of low-methoxyl pectin, 0.28 parts by mass of sodium hexametaphosphate and 0.18 parts by mass of calcium lactate were added at a stirring speed of 250 rpm and stirred continuously for 18 min. 0.45 parts by mass of gluconate-δ-lactone were added and stirred for 5 min. The pH value was adjusted to 6.4 with 1.0 mol / L potassium bicarbonate aqueous solution to obtain the impregnation solution.

[0066] S3. Place 20.00 parts by weight of eggplant pieces obtained in step S1 into the soaking solution obtained in step S2, start the external circulation pump, and soak at 42°C for 18 minutes.

[0067] S4. Stop the external circulation and raise the center temperature of the system inside the reactor to 94°C at a heating rate of 4°C / min. Hold at this temperature for 5 minutes.

[0068] S5. Remove the eggplant pieces and place them in an ice water bath at 2°C until the center temperature of the eggplant pieces drops to 25°C.

[0069] S6. Place the cooled eggplant pieces in a centrifugal dehydrator and dehydrate at 450 rpm for 2 minutes to obtain processed eggplant pieces with high anthocyanin stability.

[0070] Comparative Example 1: Compared with Example 2, the difference is that: no amphiphilic auxiliary color precursor and impregnation solution were prepared, and the same amount of purified water was used in both steps S2 and S3, that is, only pure water was used for impregnation and heating, and the rest were the same.

[0071] Comparative Example 2: Compared with Example 2, the difference is that gluconate-δ-lactone was not added in the preparation of the impregnation solution in step S2, and the initial pH value of the impregnation solution was directly adjusted to 4.0 with 1.0 mol / L hydrochloric acid aqueous solution at the end of step S2. All other aspects are the same.

[0072] Comparative Example 3: The difference from Example 2 is that sodium caseinate was not added when preparing the amphiphilic co-color precursor; all other aspects are the same.

[0073] Comparative Example 4: Compared with Example 2, the difference is that low-methoxyl pectin, sodium hexametaphosphate and calcium lactate were not added in the preparation of the impregnation solution in step S2, while the rest are the same.

[0074] Comparative Example 5: Compared with Example 2, the difference is that sodium caseinate, gluconate-δ-lactone and sodium hexametaphosphate were not added. The impregnation solution was prepared directly using ferulic acid, low methoxy pectin and calcium lactate in the original mass proportions. All other aspects are the same.

[0075] Test Example 1: Test Description: This experiment aims to record the physicochemical evolution of the system with temperature changes by comparing the rheological characteristics and pH change trajectories of the impregnation solutions in the examples and comparative examples during the heating process, and to evaluate the impact of different process steps on the macroscopic fluid state of the system.

[0076] The testing steps are as follows: (1) Take 200 mL of the initial impregnation solution prepared in Example 2, Comparative Example 2 and Comparative Example 4 respectively as test samples and place them in the sample measurement cell of the rheometer with temperature control jacket.

[0077] (2) Insert the online pH composite electrode probe, which has been calibrated with standard buffer solution, into the measuring cell simultaneously, set the rheometer measurement system to continuous shear mode, and set the constant shear rate to 50 s. -1 .

[0078] (3) Set the jacket heating program, control the sample temperature to rise from 42.0℃ to 94.0℃, control the heating rate to 4℃ / min, and the heating process takes 13 minutes.

[0079] (4) During the heating process, the real-time center temperature, real-time pH value and apparent viscosity data of each group of samples are recorded synchronously every 2 minutes using the data acquisition system. Recording is stopped after the measurement is completed.

[0080] The test data is shown in Table 1: Table 1: Real-time pH and apparent viscosity test data of each group of impregnation solutions during programmed temperature rise.

[0081] See attached document Figure 2 According to the data in Table 1, during the testing process from the initial heating stage to 66.3℃, the apparent viscosity of the systems in Example 2 and Comparative Example 4 decreased with increasing temperature, while the pH value remained stable. This physicochemical state reflects the acid-producing process of gluconic acid-δ-lactone hydrolysis regulating the pH of the system. During this stage, the macromolecular components maintain a state of like charge repulsion, keeping the system at a low apparent viscosity, thus providing the basic fluid conditions for the penetration of the amphiphilic complex. In contrast, Comparative Example 2, due to its initial setting of a constant slightly acidic environment, had an apparent viscosity of 3854.2 mPa·s at 42.1℃. This viscosity data shows that the system without dynamic acidity regulation has already triggered macromolecular cross-linking in the initial stage, and the higher system viscosity will create interfacial obstacles for subsequent mass exchange processes.

[0082] As the heating process continued, when the temperature reached approximately 74.5°C, the pH values ​​of both Example 2 and Comparative Example 4 decreased to the range of 4.65 to 4.68, and the apparent viscosity of both groups of test samples showed a slight upward trend. This upward range of apparent viscosity corresponds to the physicochemical process where the system pH value approaches the isoelectric point of sodium caseinate. In the region near the isoelectric point, the net surface charge of protein molecules tends to zero, the electrostatic repulsion between molecules weakens, and the molecular chain segments undergo aggregated phase separation. The changes in the above rheological data correspond to the initial formation stage of hydrophobic condensation regions at the microscopic level.

[0083] During the high-temperature range of the later heating stage, when the system reached the end of the heat treatment, the pH value of the example spontaneously dropped to the range of 3.8–4.2. Under the combined effects of this acidity and high temperature, the apparent viscosity of Example 2 increased from 158.7 mPa·s to 4731.5 mPa·s. The increase in apparent viscosity corresponds to the structural dissociation behavior of polyphosphate under conditions of increased temperature and proton concentration. This behavior reduces the chelating effect of sodium hexametaphosphate on free calcium ions, promoting the release of calcium ions and their participation in the cross-linking reaction of low-methoxyl pectin. In contrast, the apparent viscosity of Comparative Example 4, without the addition of polysaccharide substrate, did not increase in the same temperature range, but instead showed a decline with increasing temperature. This difference reflects that the protein condensate phase, lacking the constraint of a cross-linked network, is difficult to maintain its original structural state in a continuously heated environment. The evolution of apparent viscosity in Example 2 reflects the solidification process of the polysaccharide network on the periphery of the protein condensate phase. This process forms a multi-scale polymer interpenetrating network, providing a constrained environment for the internal molecules at the physical spatial level.

[0084] Test Example 2: Test Description: This experiment aims to test the anthocyanin retention rate and red-green color intensity (a) in the epidermis of eggplants after each treatment group. * The physical values ​​of the pigment system were compared to the effects of different physicochemical interventions on the thermal degradation of the pigment system.

[0085] The testing steps are as follows: (1) Fresh, untreated purple eggplants and semi-finished eggplants obtained from Examples 1 to 4 and Comparative Examples 1 to 5 were selected as test subjects.

[0086] (2) The epidermal tissue of each group of test subjects was scraped with a stainless steel scraper, placed in a freeze dryer for drying, then crushed and passed through a 60-mesh sieve to obtain epidermal dry powder samples.

[0087] (3) Accurately weigh 1.00g of each group of epidermal powder samples, add 25mL of prepared methanol extraction solution containing 0.1% hydrochloric acid, shake and extract for 2 hours at room temperature in the dark, collect the supernatant after centrifugation at 4000rpm for 10 minutes, and repeat the extraction of the residue once. Combine the supernatants and make up to 50mL.

[0088] (4) Take the above-mentioned extract after volume adjustment and dilute it with potassium chloride buffer at pH 1.0 and sodium acetate buffer at pH 4.5 at a volume ratio of 1:4. After standing for equilibration for 20 minutes, use a UV-Vis spectrophotometer to measure the absorbance of the solution at wavelengths of 530 nm and 700 nm. Calculate the total anthocyanin concentration by combining the extinction coefficient and compare it with the concentration of the fresh reference sample to obtain the retention rate.

[0089] (5) Take a whole eggplant semi-finished product from each group, and use a handheld colorimeter calibrated with a standard white board to conduct multi-point tests on the skin area, and record the a value in the color difference system. * The value was calculated by taking the average of 8 different measurement points in each group to reflect the apparent purplish-red color retention of the sample.

[0090] The test data is shown in Table 2: Table 2: Total anthocyanin retention rate and skin color of eggplant samples in each group a * Value test data

[0091] See attached document Figure 3 Compared with the data in Table 2, Comparative Example 1, which underwent conventional pure water heating treatment, showed lower values ​​in pigment retention rate and color index, reflecting the tendency of anthocyanins to degrade in a heated aqueous environment. Examples 1 to 4, after undergoing the same heating endpoint conditions, exhibited lower anthocyanin retention rates and α-color indices. * The values ​​remain in a relatively high range. This data distribution reflects the influence of the constructed multi-component formulation system on the physical state of the microenvironment of anthocyanin molecules during the heat processing stage.

[0092] Comparative Example 2 was set to a slightly acidic environment directly during the impregnation stage, without employing a progressive acidity adjustment step during the heating process. Its test data differed from the examples. The slightly acidic conditions induced premature cross-linking of the polysaccharide system on the tissue surface, and the resulting polymer network hindered mass transfer of the chromophore precursor to the internal cellular sites. These results demonstrate the objective correlation between the temporal separation of the mass transfer process and the network curing process in mesoscopic network construction.

[0093] Comparative Examples 3 and 5, which did not contain specific protein components or employ specific ion-masking substances, exhibited lower pigment retention data compared to the examples. Conventional hydrophilic cross-linked networks retain free water, making it difficult to physically reduce the contact frequency between water molecules and anthocyanin structures. In the examples, by controlling the phase separation and aggregation of macromolecular components at their isoelectric points, localized low dielectric constant regions were formed. These regions spatially reduce the probability of polar water molecules contacting the co-color complex.

[0094] Comparative Example 4, which did not include the polysaccharide substrate and crosslinking trigger for external curing, showed a lower pigment retention rate than the Example Group. The lack of spatial constraint in the protein condensate phase makes it prone to aggregation and rearrangement under heat, exposing the pigment system to an exposed thermal degradation environment. In the Examples, the polysaccharide network generated in situ through ionic crosslinking constituted the physical boundary of the protein condensate phase, demonstrating the mechanistic relationship between polymer interpenetrating networks in maintaining structural boundaries and influencing pigment stability.

[0095] Test Example 3: Test Description: This experiment aims to evaluate the effects of various immersion and heating conditions on the macroscopic physical and mechanical properties of eggplant tissue. By comparing the differences in hardness and elasticity values ​​of samples under specific compression deformation, the effects of different processes on maintaining the mechanical structure of the product are verified.

[0096] The testing steps are as follows: (1) Prepare fresh, untreated purple eggplants and eggplant semi-finished products processed in Examples 1 to 4, Comparative Examples 1, 2, and 4 as test subjects.

[0097] (2) Use a cutting tool to trim the eggplant pieces in each group into cubic specimens with a size of 10mm×10mm×10mm in order to reduce the influence of geometric differences on the mechanical test signal. Prepare 10 parallel specimens for each group.

[0098] (3) Start the texture analyzer, install the P / 36R cylindrical flat-bottom probe, and calibrate the instrument's load sensor and displacement sensor.

[0099] (4) Set the test parameters of the texture profile analysis program. The pre-test running speed is set to 2.0 mm / s, the test running speed is set to 1.0 mm / s, the post-test return speed is set to 2.0 mm / s, the target compressibility deformation is set to 30%, the time interval between two compression cycles is set to 5.0 s, and the trigger force is set to 0.05 N.

[0100] (5) Place the sample on the test platform, start the program to obtain the force-time response curve, extract the maximum peak force of the first compression cycle from the data processing software as the hardness value of the sample, extract the ratio of the work done in the second compression to the work done in the first compression as the elastic value of the sample, and record and calculate the average result of each group of samples.

[0101] The test data is shown in Table 3: Table 3: Hardness and elasticity test data of eggplant samples in each group

[0102] See attached document Figure 4 Compared with the data in Table 3, the hardness and elasticity values ​​of Comparative Example 1 under conventional aqueous phase heating conditions are at a low level. This value variation corresponds to the depolymerization behavior of polysaccharides in the cell walls of fruits and vegetables in the heating environment, reflecting that the tissue matrix is ​​unable to maintain its original physical and mechanical state in the absence of exogenous structural support. The hardness and elasticity parameters in Examples 1 to 4 are distributed within a range close to that of fresh reference samples, demonstrating that the constructed cross-linked network system plays a supporting role in the spatial framework within the tissue, and to a certain extent mitigates the tissue softening trend caused by the heating process.

[0103] Comparative Example 2 did not employ a progressive acidity control method over heating time. Its test sample exhibited a higher hardness value than the fresh reference sample, and its elasticity index was lower. Combined with the direct introduction of an acidic environment during the impregnation stage, these data characteristics reflect early cross-linking behavior of polysaccharide macromolecules in the superficial tissue region. The cross-linked network formed on the surface hinders mass exchange of fluids inside and outside the tissue, resulting in a macroscopically mechanically characterized by high external hardness but limited overall deformation recovery. These physical characterization results highlight the necessity of using lactone compounds to implement phase transition timing control to construct a more uniformly distributed mesoscopic network.

[0104] Comparative Example 4, which did not contain the components responsible for building the polysaccharide network, showed numerical differences in its mechanical test parameters compared to the Example group. In the absence of external polysaccharide network spatial constraints, protein molecules at their isoelectric point state exhibited thermal aggregation during heating. These protein aggregates distributed within the tissue altered the original structural continuity and failed to form a well-elastic network support system. The relatively low hardness and elasticity parameters of this sample reflect the difficulty of a single hydrophobic aggregate microdomain independently maintaining the structural stability of the tissue's mesoscopic boundary in a heated system. This comparative data supports the logical connection between polymer interpenetrating networks and their role in influencing thermodynamic changes in tissues.

Claims

1. A method for processing eggplant with high anthocyanin stability, characterized in that, Includes the following steps: S1. Select purple eggplants, wash them, remove the stems, cut them into chunks, drain and set aside; S2. The amphiphilic co-color precursor is placed in a reaction vessel, and the temperature is maintained at 40-45℃. Low-methoxyl pectin, sodium hexametaphosphate, and calcium lactate are added while stirring. Stirring is continued. Then gluconate-δ-lactone is added and stirred. The pH value is adjusted to 6.2-6.5 using an alkaline regulator to obtain the impregnation solution. The amphiphilic co-color precursor is prepared by potassium bicarbonate, ferulic acid, and sodium caseinate in purified water. S3. Place the eggplant pieces obtained in step S1 into the soaking solution obtained in step S2, start the external circulation pump, and soak at a temperature of 40-45°C. S4. Stop the external circulation, raise the center temperature of the system inside the reactor to 92-95°C at a heating rate of 3-5°C / min, and then keep it at that temperature. S5. Remove the eggplant pieces after heat preservation and place them in an ice water bath to cool. S6. Place the cooled eggplant pieces in a centrifugal dehydrator for dehydration to obtain processed eggplant pieces with high anthocyanin stability.

2. The eggplant processing method with high anthocyanin stability according to claim 1, characterized in that, The amphiphilic cochromogenic precursor was prepared from 0.08–0.12 parts by weight of potassium bicarbonate, 0.15–0.20 parts by weight of ferulic acid, and 0.40–0.60 parts by weight of sodium caseinate in 100.00 parts by weight of purified water. In step S2, the amount of low-methoxyl pectin added is 0.50-0.70 parts by weight, the amount of sodium hexametaphosphate is 0.25-0.30 parts by weight, the amount of calcium lactate is 0.15-0.20 parts by weight, and the amount of glucono-δ-lactone is 0.40-0.50 parts by weight.

3. The eggplant processing method with high anthocyanin stability according to claim 2, characterized in that, The preparation method of the amphiphilic auxiliary chromogenic precursor includes the following steps: Pour purified water into the reaction vessel, heat and maintain the temperature at 40-45℃; Add potassium bicarbonate and ferulic acid to purified water in sequence, turn on mechanical stirring, and continue stirring for 5-8 minutes. While maintaining stirring, sodium caseinate was added, and the mixture was stirred at a constant temperature for 20–30 minutes to obtain the amphiphilic co-chromogenic precursor.

4. The eggplant processing method with high anthocyanin stability according to claim 1, characterized in that, In step S1, the purple eggplant is cut into pieces with a side length of 1.0 to 1.5 cm; based on 100.00 parts by weight of purified water, the weight of the eggplant pieces is 20.00 to 30.00 parts by weight.

5. The eggplant processing method with high anthocyanin stability according to claim 1, characterized in that, In step S2, the continuous stirring time after adding low-methoxyl pectin, sodium hexametaphosphate, and calcium lactate is 15-20 minutes.

6. The eggplant processing method with high anthocyanin stability according to claim 1, characterized in that, In step S2, the alkaline regulator is an aqueous solution of potassium bicarbonate with a concentration of 0.8–1.2 mol / L.

7. The eggplant processing method with high anthocyanin stability according to claim 1, characterized in that, In step S3, the immersion time is 15 to 20 minutes; in step S4, the heat preservation treatment time is 4 to 6 minutes.

8. The eggplant processing method with high anthocyanin stability according to claim 1, characterized in that, In step S5, the temperature of the ice water bath is 0-4°C, and the cooling process continues until the center temperature of the eggplant pieces drops to 20-25°C.

9. The eggplant processing method with high anthocyanin stability according to claim 1, characterized in that, In step S6, the dehydration process is carried out at a rotation speed of 400-500 rpm for 2-3 minutes.

10. The eggplant processing method with high anthocyanin stability according to claim 1, characterized in that, In step S4, when the heat preservation treatment ends, the final pH value of the system in the reactor drops to 3.8-4.2.

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