Processing method for maintaining crispness and flavor of guava product

Abstract

The invention relates to a processing method for maintaining crispness and flavor of guava products, an acidic permeation composition used in the processing method and application of the acidic permeation composition, and belongs to the technical field of food processing. The method comprises the following steps: carrying out vacuum pulse permeation treatment on guava fruit blocks by adopting an acidic permeation composition containing trehalose, D-xylose, calcium lactate, L-cysteine and low-molecular-weight chitosan; then, the fruit blocks are soaked in a buffer solution with the high pH value to be subjected to pH response triggering treatment, and composition components are subjected to in-situ crosslinking in fruit block tissue; and finally performing low-temperature curing and low-temperature hot air drying. The invention further provides an acidic permeable composition containing the components and application of the acidic permeable composition. By means of the method, a microcosmic support network can be constructed in guava tissue, drying shrinkage is effectively resisted, and the prepared guava product has the advantages of being crisp in texture, high in natural flavor retention rate, low in volume shrinkage rate and full in shape.

Description

TECHNICAL FIELD

[0001] The present application relates to a processing method of Psidium guajava, in particular to a processing method for maintaining the crispness and flavor of Psidium guajava products. BACKGROUND

[0002] Psidium guajava is a kind of fruit with rich nutrition and unique flavor, and its deep-processed products have broad market prospects. Fruit and vegetable drying is a key technical means to extend the shelf life and improve the added value of products, among which hot air drying is widely used due to its simple equipment and controllable cost.

[0003] However, the traditional direct hot air drying process often faces severe technical bottlenecks when dealing with fruits and vegetables such as Psidium guajava with relatively dense organizational structure. During the drying process, with the rapid evaporation of water, strong liquid surface tension and capillary contraction force will cause irreversible collapse and shrinkage of the cell organization inside the fruit and vegetable. This destruction of the organizational structure eventually leads to hard, dense and lack of crispness of the product, and the taste is severely deteriorated, which is far from the crispy taste expected by consumers. At the same time, long-term heating will also trigger Maillard reaction and caramelization reaction, which not only causes the browning of the product color, but also causes the large loss of its original natural aroma substances and produces unpleasant cooking flavor, which seriously affects the overall quality of the product.

[0004] In order to improve this situation, high sugar permeation pretreatment or vacuum freeze drying technology is often used in the prior art. However, high sugar permeation often masks the natural flavor of the fruit and causes the product to become tough, while vacuum freeze drying can produce a crisp product, but its energy consumption is huge and the equipment investment is high, which is difficult to meet the needs of large-scale industrial production.

[0005] Therefore, it has become a technical problem to be solved in the field of fruit and vegetable processing to develop a technology that can effectively maintain the organizational structure of fruits and vegetables, give the product excellent crisp texture and maintain its natural flavor under normal pressure or low-cost drying conditions. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a processing method for Psidium guajava products with excellent crispness and flavor retention characteristics, which can effectively inhibit the problems such as organizational collapse, hardening and flavor deterioration of Psidium guajava during drying, as well as the composition and application thereof.

[0007] In a first aspect, the present application provides a processing method for maintaining the crispness and flavor of Psidium guajava products, which adopts the following technical solution: Step one, a vacuum pulse permeation treatment is performed on Psidium guajava pieces using an acidic permeation composition containing trehalose, D-xylose, calcium lactate, L-cysteine and low molecular weight chitosan; Step two, immerse the guava pieces treated in step one in a buffer solution with a pH higher than the acidic permeation composition for pH-responsive trigger treatment; Step three, subject the guava pieces treated in step two to low-temperature ripening treatment; Step four, subject the guava pieces treated in step three to low-temperature hot air drying.

[0008] By adopting the technical solution, the application uses a step-by-step pH-responsive in-situ crosslinking mechanism to construct a micro support network in the guava tissue, thereby effectively resisting the shrinkage stress in the drying process. The technical principle is described in detail as follows: Pre-treatment and efficient permeation stage (step one): The core goal of this stage is to uniformly transport all functional components to the inside of the guava pieces with high permeation efficiency.

[0009] Construction of an acidic environment: the pH value of the permeation composition is maintained in the acidic range of 4.0-4.5. Under this pH condition, the amino groups (-NH2) on the low-molecular-weight chitosan molecular chain are protonated into positively charged ammonium ions (-NH3 + ), so that they have good water solubility and permeability. At the same time, the polysaccharide pectin naturally present in the fruit and vegetable tissue has a high degree of protonation of the carboxyl groups (-COOH) at this pH, and the electrostatic repulsion between the molecular chains is weakened, which is conducive to the penetration of external substances.

[0010] Physical reinforcement of vacuum pulse: vacuum pulse treatment effectively removes the gas in the interstitial gaps of the guava pieces by negative pressure; after the atmospheric pressure is restored, the permeation liquid can quickly and deeply fill these gaps under the driving of the atmospheric pressure difference, realizing efficient and uniform permeation of all functional components and laying a material foundation for the subsequent in-situ crosslinking reaction.

[0011] pH-responsive trigger in-situ crosslinking stage (step two): This stage is the core innovative step of the application, which triggers the in-situ crosslinking reaction of the pre-permeated functional components in the tissue by precisely controlling the change of the environmental pH value.

[0012] Change of pH environment: transfer the permeated pieces to a weakly acidic buffer solution with a pH value of 5.5-6.0, and the pH value inside and outside the tissue is rapidly increased.

[0013] Formation mechanism of in-situ crosslinking network: First re-crosslinking: with the increase of the pH value, the carboxyl groups (-COOH) on the pectin molecular chain are largely deprotonated and converted into negatively charged carboxylate ions (-COO - ). These -COO -ionically bond with pre-impregnated divalent calcium ions (Ca 2+ ) to form a classic "egg-box model" gel network structure.

[0014] Second cross-linking: meanwhile, strong electrostatic attraction occurs between the positively charged chitosan molecular chains (-NH3 + ) and the negatively charged pectin molecular chains (-COO - ), forming a polyelectrolyte complex.

[0015] Synergistic effect: the two cross-linking reactions occur simultaneously in the intercellular space of Psidium guajava tissue, forming a three-dimensional gel network that is supported by the "pectin-calcium" network and the "pectin-chitosan" network. This network structure is generated in situ within the tissue and serves as a microskeletal support.

[0016] Network stabilization and drying setting phase (steps three and four): Low-temperature maturation: sufficient time is given for the cross-linked network to stabilize and strengthen, resulting in a more uniform and robust structure.

[0017] Low-temperature drying: during the drying and dehydration process, the three-dimensional network formed above effectively resists the capillary contraction force caused by water migration, preventing severe cell wall shrinkage and tissue structure collapse. Therefore, the final product can maintain a high porosity and low volume shrinkage, macroscopically exhibiting a crisp texture rather than the dry hardness of traditional dried products.

[0018] Flavor retention: D-xylose and L-cysteine in the infiltration solution, as well as the low-temperature drying process, together inhibit the generation of undesirable flavor substances and the loss of heat-sensitive aroma substances caused by Maillard reaction and Strecker degradation during the drying process, thereby maximizing the retention of the original natural flavor of Psidium guajava.

[0019] Preferably, in step one, the process parameters of vacuum pulse infiltration treatment are: vacuum degree of -0.075 MPa to -0.085 MPa, vacuum holding time of 8-12 minutes, soaking time after returning to normal pressure of 12-18 minutes, and repeating cycles of 2-3 times. By adopting the above technical solution, the optimal penetration depth and uniformity of functional components can be ensured without excessive damage to the fruit and vegetable tissue.

[0020] Preferably, in step two, the pH value of the buffer solution is 5.5-6.0, and the pH response triggering treatment time is 3-5 minutes. By adopting the above technical solution, this pH range is the optimal interval for triggering pectin deprotonation and initiating cross-linking reaction, which is mild and efficient; this time range ensures sufficient cross-linking reaction.

[0021] Preferably, the temperature of the low-temperature curing in step three is 4-6℃, and the time is 4-6 hours; and / or, the temperature of the low-temperature hot air drying in step four is 50-60℃. By adopting the above technical solution, the low-temperature curing is conducive to the stability of the network structure, and the drying temperature of 50-60℃ is the best temperature interval considering the drying efficiency and the retention of flavor and nutrients.

[0022] Preferably, before the step one, the method further comprises a pretreatment step of peeling and cutting the Psidium guajava fruits. By adopting the above technical solution, uniform raw materials are provided for subsequent infiltration and drying treatment, and the stability of the quality of the final product is ensured.

[0023] In a second aspect, the present application provides an acidic infiltration composition for processing Psidium guajava products, which adopts the following technical solution: An acidic infiltration composition for processing Psidium guajava products, which is prepared from the following raw materials in the weight fractions: trehalose: 18.0-22.0 parts; D-xylose: 1.5-2.5 parts; calcium lactate: 0.6-1.0 parts; L-cysteine: 0.06-0.10 parts; low molecular weight chitosan: 0.15-0.25 parts.

[0024] By adopting the above technical solution, each component in the composition has a clear functional positioning and synergistic effect: Low molecular weight chitosan: as a core structural builder, it dissolves and carries a positive charge under acidic conditions, and forms an electrostatic interaction with pectin to form a support network when the pH is subsequently increased. The low molecular weight (5.0×10 4 -1.5×10 5 Da) chitosan is selected because it has a lower viscosity and is more easily infiltrated into the interior of the fruit and vegetable tissue.

[0025] Calcium lactate: as another core structural builder, it provides Ca 2+ ions to form a "egg lattice model" cross-linking structure with pectin, which synergistically enhances the chitosan network.

[0026] Trehalose: as an excellent protective agent and filler, its high glass transition temperature helps to form a stable amorphous glass matrix in the later drying stage, further fixing the porous structure and effectively protecting the bioactive substances.

[0027] D-xylose and L-cysteine: as flavor protectants, they synergistically inhibit non-enzymatic browning reactions during thermal processing, reducing the generation of undesirable flavors and color changes.

[0028] Acidic environment (pH 4.0-4.5): is the prerequisite for the implementation of the whole technical solution, which ensures the dissolution and protonation of chitosan, and prepares conditions for the subsequent pH response trigger mechanism.

[0029] Preferably, the low molecular weight chitosan has a weight average molecular weight of 5.0*10 4 -1.5*10 5 Da, and a deacetylation degree of 85.0%-95.0%. By adopting the above technical solution, the chitosan with the above molecular weight range has good permeability and reactivity, and the higher deacetylation degree means more amino groups, i.e. more positive charge sites, which is conducive to forming a stronger cross-linking network.

[0030] Preferably, the pH value of the composition is 4.0-4.5. By adopting the above technical solution, accurate control of the pH in this range is the key to ensuring that the chitosan is completely dissolved and protonated, while the fruit and vegetable tissues are not excessively acidified.

[0031] Preferably, the composition comprises the following components by weight: trehalose: 20 parts; D-xylose: 2.0 parts; calcium lactate: 0.8 parts; L-cysteine: 0.08 parts; low molecular weight chitosan: 0.2 parts. By adopting the above technical solution, this ratio is an optimized specific embodiment, and the synergistic effect of each component is remarkable.

[0032] In a third aspect, the application provides an application of the acidic penetration composition, which adopts the following technical solution: The application of the acidic penetration composition is used for enhancing the brittleness and flavor retention capacity of guava products after processing.

[0033] By adopting the above technical solution, a new technical approach is provided for the field of deep processing of fruits and vegetables. The core value of the application lies in that by combining a specially designed composition with a specific processing technology, the internal physical structure of fruit and vegetable raw materials can be actively and controllably modified, thereby overcoming the inherent defects of traditional drying technology, and producing new fruit and vegetable products with high quality, crispy texture and natural flavor which cannot be achieved by traditional technology.

[0034] The application provides a processing method for brittleness and flavor retention of guava products. The method has the following beneficial effects: 1、The present application significantly improves the crisp texture of guava products, effectively avoids the defects of traditional dry products such as dryness, toughness, etc., and the low molecular weight chitosan and calcium ions are introduced into the fruit tissue inside under acidic conditions by vacuum pulse infiltration, and then the two components are triggered to have a double crosslinking reaction with endogenous pectin in the fruit by an independent pH increasing step, which constructs a micro three-dimensional network skeleton inside the tissue, which plays a key supporting role in the subsequent drying process, effectively resisting the tissue collapse caused by capillary contraction force, so that the final product forms a porous and crisp physical structure.

[0035] 2、The present application maximizes the natural flavor and color of guava, significantly inhibits the deterioration during processing, and the D-xylose and L-cysteine in the acidic infiltration composition can be used as an effective inhibitor of non-enzymatic browning reaction, reducing the adverse flavor and color deepening caused by Maillard reaction, and the low temperature hot air drying technology used at the end of the process gently removes the water, avoids the destruction of heat-sensitive aroma substances and natural pigments by high temperature, so that the flavor characteristics of the product are closer to fresh guava.

[0036] 3、The guava products prepared by the present application have lower volume shrinkage and better rehydration performance, and the product form is full and stable, since the in-situ formed crosslinked network effectively maintains the internal structure of the product, avoiding severe shrinkage during drying, so that the volume and appearance of the product are better maintained. At the same time, this porous stable structure also provides a convenient channel for the re-entry of water, so that the product can quickly and uniformly absorb water when it needs to be rehydrated, and the rehydration ratio is much higher than that of traditional dense dry products, improving the eating quality and application convenience of the product. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be described below in a clear and complete manner. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0038] The main raw materials and reagents used in the following examples and comparative examples are as follows, and the reagents not specifically described are commercially available analytical pure or higher grade products.

[0039] The guava (Psidium guajava L.) raw material is "Zhenzhu" guava produced in Zhangzhou, Fujian, China, and the harvesting standard is 70-80% maturity, complete fruit shape, no disease and insect pests on the surface and no mechanical damage.

[0040] Trehalose is a commercially available food grade product with the chemical name of a-D-glucopyranosyl-(1→1)-a-D-glucopyranoside dihydrate and CAS number 6138-23-4.

[0041] D-xylose is a commercially available food grade product with the chemical name of a pentulose and CAS number 58-86-6.

[0042] Calcium lactate is a commercially available food grade product with the chemical name of (S)-2-hydroxypropanoic acid, calcium salt, pentahydrate and CAS number 5743-47-5.

[0043] L-cysteine is a commercially available food grade product with the chemical name of (R)-2-amino-3-mercapto propanoic acid and CAS number 52-90-4.

[0044] Citric acid is a commercially available analytical grade product with the chemical name of 2-hydroxypropane-1,2,3-tricarboxylic acid and CAS number 77-92-9.

[0045] Sodium citrate dihydrate is a commercially available analytical grade product with the chemical name of 2-hydroxy-1,2,3-propanetricarboxylic acid, disodium salt and CAS number 144-33-2.

[0046] Low molecular weight chitosan is a non-commercially available custom-made polymer. The low molecular weight chitosan used in the present application has a weight average molecular weight (Mw) ranging from 5.0 x 10 4 to 1.5 x 10 5 Da (determined by gel permeation chromatography) and a degree of deacetylation (DD) ranging from 85.0% to 95.0% (determined by 1H nuclear magnetic resonance spectroscopy). This material is prepared from commercially available high molecular weight chitosan raw material by subsequent enzymatic or physical degradation and purification as described in the subsequent preparation examples.

[0047] Preparation Example 1: Enzymatic preparation of low molecular weight chitosan (target molecular weight 5.0 x 10 4 - 1.0 x 10 5 Da) A chitosan with a weight average molecular weight of 3.5 x 10 5Da, 100 g, was added to 9900 ml of 2% (v / v) acetic acid aqueous solution and stirred to dissolve at 50°C for 4 hours to form a homogeneous chitosan solution. The pH of the solution was adjusted to 5.0 with 1 mol / L hydrochloric acid. Chitosanase (source: Streptomyces griseus, enzyme activity ≥ 500 U / mg) was added to the solution at an amount of 0.05% (w / w) of the dry weight of chitosan. The enzymatic reaction was carried out in a constant temperature water bath at 50°C, and the change in molecular weight of the reaction solution was monitored in real time by gel permeation chromatography (GPC) during the reaction. When the weight average molecular weight decreased to about 6.5×10 4 Da, the reaction solution was quickly heated to 100°C and maintained for 15 minutes to completely inactivate the enzyme and terminate the enzymatic reaction. After the reaction solution was cooled to room temperature, 2 mol / L sodium hydroxide solution was slowly added dropwise and stirred to adjust the pH to 9.0, at which point the chitosan precipitated to form a white precipitate. The precipitate was collected by centrifugation and washed repeatedly with deionized water until the washing solution was neutral. The washed product was pre-frozen at -80°C for 12 hours and then dried in a freeze dryer for 48 hours. A white flocculent solid, low molecular weight chitosan, was obtained. The product was determined to have a weight average molecular weight of 6.2×10 4 Da and a deacetylation degree of 90.8%.

[0048] Preparation Example 2: Preparation of low molecular weight chitosan by physical and chemical method (target molecular weight 1.0×10 5 -1.5×10 5 Da) A commercially available chitosan powder with a weight average molecular weight of 3.8×10 5 Da and a deacetylation degree of 94.5% was weighed out at 100 g and dispersed in 1000 ml of 8% (w / v) hydrochloric acid solution. The suspension was transferred to a three-necked flask equipped with mechanical stirring and a reflux condenser and heated to react at 80°C. During the reaction, samples were taken at regular intervals to monitor the degradation process by measuring the viscosity of the solution and estimating the molecular weight by the Mark-Houwink equation. When the molecular weight decreased to the target range, the reaction system was quickly cooled in an ice water bath to terminate the degradation reaction. An excess amount of 2 mol / L sodium hydroxide solution was added to the cooled reaction solution to adjust the pH to 10.0 to precipitate the chitosan completely. The subsequent purification steps were the same as in Preparation Example 1: the precipitate was collected by centrifugation, washed with deionized water until it was neutral, and finally freeze-dried to obtain a white powdery solid. The product was determined to have a weight average molecular weight of 1.4×10 5 Da and a deacetylation degree of 93.6%. Example 1

[0049] The present example provides a processing method for maintaining the crispness and flavor of psidium guajava products, specifically comprising the following steps: (1) Raw material pretreatment: Fresh guava fruits were washed, peeled, and cut into 1.5 cm x 1.5 cm x 1.5 cm cubes.

[0050] (2) Preparation of acidic permeation solution: 20 parts by weight of trehalose, 2.0 parts by weight of D-xylose, 0.8 parts by weight of calcium lactate, 0.08 parts by weight of L-cysteine, and 0.2 parts by weight of low-molecular-weight chitosan prepared using Preparation Example 1 were weighed and dissolved in 200 parts by weight of deionized water. The pH of the solution was adjusted to 4.2 using citric acid to prepare the acidic permeation solution.

[0051] (3) Vacuum pulse permeation treatment: The guava fruit cubes were immersed in the above acidic permeation solution at a solid-to-liquid ratio of 1:5 (w / v), vacuumed to -0.08 MPa and maintained for 10 minutes, and then soaked at normal pressure for 15 minutes. This was one cycle, and a total of 2 cycles were performed.

[0052] (4) pH-responsive in-situ crosslinking: A sodium citrate buffer solution having a pH of 5.8 was prepared. The permeated guava fruit cubes were removed and immediately immersed in the buffer solution for 4 minutes.

[0053] (5) Low-temperature maturation: The crosslinked fruit cubes were removed, rinsed with deionized water, and then dried. The dried cubes were placed in a 5°C cold storage environment for 5 hours.

[0054] (6) Low-temperature hot-air drying: The matured fruit cubes were dried in a hot air at 55°C until a constant weight was obtained to obtain the final product. Example 2

[0055] The present embodiment provides a processing method for maintaining the crispness and flavor of guava products, which specifically comprises the following steps: (1) Raw material pretreatment: Fresh guava fruits were washed, peeled, and cut into 1.5 cm x 1.5 cm x 1.5 cm cubes.

[0056] (2) Preparation of acidic permeation solution: 18 parts by weight of trehalose, 1.5 parts by weight of D-xylose, 0.6 parts by weight of calcium lactate, 0.06 parts by weight of L-cysteine, and 0.15 parts by weight of low-molecular-weight chitosan prepared using Preparation Example 1 were weighed and dissolved in 180 parts by weight of deionized water. The pH of the solution was adjusted to 4.0 using citric acid to prepare the acidic permeation solution.

[0057] (3) Vacuum pulse permeation treatment: The guava fruit cubes were immersed in the above acidic permeation solution at a solid-to-liquid ratio of 1:5 (w / v), vacuumed to -0.075 MPa and maintained for 8 minutes, and then soaked at normal pressure for 12 minutes. This was one cycle, and a total of 2 cycles were performed.

[0058] (4) pH-responsive trigger in-situ cross-linking: A sodium citrate buffer solution with pH 5.5 was prepared. The permeated guavas were fished out and drained immediately, and then immersed in the buffer solution for 3 minutes.

[0059] (5) Low-temperature maturation: The guavas after cross-linking were fished out, rinsed with deionized water and drained, and then placed in a 4°C refrigeration environment for maturation for 4 hours.

[0060] (6) Low-temperature hot air drying: The guavas after maturation were dried in a hot air at 50°C to constant weight to obtain the final product. Example 3

[0061] The present example provides a processing method for maintaining the crispness and flavor of guava products, which specifically comprises the following steps: (1) Raw material pretreatment: Fresh guava fruits were taken, washed, peeled, and then cut into 1.5 cm x 1.5 cm x 1.5 cm cubes.

[0062] (2) Preparation of acidic permeation solution: According to parts by weight, 22 parts of trehalose, 2.5 parts of D-xylose, 1.0 part of calcium lactate, 0.10 part of L-cysteine, and 0.25 part of low molecular weight chitosan prepared by Preparation Example 2 were weighed and dissolved in 220 parts of deionized water. The pH value of the solution was adjusted to 4.5 with citric acid to prepare an acidic permeation solution.

[0063] (3) Vacuum pulse permeation treatment: The guava cubes were immersed in the above-mentioned acidic permeation solution at a solid-liquid ratio of 1:5 (w / v), vacuumed to -0.085 MPa and maintained for 12 minutes, and then returned to normal pressure for soaking for 18 minutes, which was one cycle, and a total of 3 cycles were performed.

[0064] (4) pH-responsive trigger in-situ cross-linking: A sodium citrate buffer solution with pH 6.0 was prepared. The permeated guavas were fished out and drained immediately, and then immersed in the buffer solution for 5 minutes.

[0065] (5) Low-temperature maturation: The guavas after cross-linking were fished out, rinsed with deionized water and drained, and then placed in a 6°C refrigeration environment for maturation for 6 hours.

[0066] (6) Low-temperature hot air drying: The guavas after maturation were dried in a hot air at 60°C to constant weight to obtain the final product.

[0067] Comparative Example 1: Compared with Example 1, the difference is that the pretreated guava raw material does not go through any permeation, cross-linking or maturation steps, and is directly dried using the same low-temperature hot air drying step.

[0068] Comparative Example 2: The difference compared with Example 1 is that the step (3) penetration treatment does not use vacuum pulse method, but the guavas are soaked in the same acidic penetration solution under normal pressure, the total soaking time is the same as the total penetration time of Example 1 (50 minutes), and the rest are the same.

[0069] Comparative Example 3: The difference compared with Example 1 is that the acidic penetration solution of step (2) is directly mixed with all components of the crosslinking trigger buffer of step (4) to form a single treatment solution, then the same vacuum pulse penetration treatment as Example 1 is used, and after treatment, the independent pH trigger step is omitted and directly enters the low-temperature curing step, and the rest are the same.

[0070] Comparative Example 4: The difference compared with Example 1 is that the acidic penetration solution prepared in step (2) does not contain low molecular weight chitosan, and the concentrations of other components and all process steps are the same.

[0071] Comparative Example 5: The difference compared with Example 1 is that after completing the vacuum pulse penetration treatment of step (3), the pH-responsive trigger in-situ crosslinking step of step (4) is omitted and directly enters the low-temperature curing of step (5), and the rest are the same.

[0072] Test Example 1: 1. Experimental method: The purpose of this test example is to verify the effectiveness of the expected changes in the internal microenvironment pH value of guava tissue in the method of the present application with key process steps. The experimental samples are divided into three groups: Group A is fresh guava pieces; Group B is guava pieces after completing the vacuum pulse penetration treatment of step (3) according to the method of Example 1; Group C is guava pieces after completing the pH-responsive trigger in-situ crosslinking treatment of step (4) according to the method of Example 1.

[0073] The specific determination steps are as follows: (1) Sampling: randomly sample from the treated guava pieces of each group, and accurately weigh 20.0 grams.

[0074] (2) Homogenization: place the weighed sample in a tissue crusher, add 40 milliliters of boiled and cooled deionized water (to exclude the interference of carbon dioxide), and homogenize at high speed for 2 minutes to prepare a uniform tissue homogenate.

[0075] (3) Determination: use a precision pH meter calibrated with three-point standard buffers of potassium hydrogen phthalate (pH 4.01), mixed phosphate (pH 6.86), and borax (pH 9.18), insert the electrode into the prepared tissue homogenate, gently stir and stand, and record the pH value when the reading is stable.

[0076] (4) Replicates: Three replicates were performed for each sample set, and the results were averaged.

[0077] 2. Experimental Results The results of pH determination of guava tissue homogenate at each treatment stage are shown in Table 1.

[0078] Table 1. Results of pH determination of guava tissue homogenate at each treatment stage. .

[0079] The test data in Table 1 clearly confirm the effectiveness of the pH-responsive trigger mechanism designed in the present application. The endogenous pH of fresh guava tissue is weakly acidic (average 5.31). After treatment with the acidic penetrating solution (set pH 4.2), the internal pH of the tissue is significantly reduced to 4.38, indicating that the functional components in the acidic penetrating solution have effectively entered the tissue and established an acidic microenvironment. Subsequently, after treatment with the cross-linking trigger buffer (set pH 5.8), the internal pH of the tissue quickly rises to 5.68. This rapid change in pH drives the electrostatic interaction and ionic bonding between the pre-penetrated chitosan cations, calcium ions, and the carboxyl groups of the endogenous pectin in the tissue, thereby constructing a support network in situ within the tissue. Therefore, this test example verifies from the chemical principle level that the technical concept of achieving the step-by-step action of structural strengthening components in fruit and vegetable tissues by precisely regulating pH is feasible.

[0080] Test Example 2: 1. Experimental Method This test example aims to quantitatively characterize the fixation efficiency of key structural strengthening components (calcium ions and low molecular weight chitosan) in guava tissue after process treatment. The experiment is based on the principle of mass balance, by measuring the change in component concentration in the working solution before and after treatment, to calculate the net fixation amount in guava tissue.

[0081] The experimental steps are as follows: (1) Solution preparation and initial concentration determination: Prepare the acidic penetrating solution (treatment solution A) and cross-linking trigger buffer (treatment solution B) according to the method of Example 1. Take samples and measure the initial concentrations of calcium ions and low molecular weight chitosan in treatment solution A. Treatment solution B does not contain these two components.

[0082] (2) Sample treatment and solution collection: Process the guava samples according to the complete process of Example 1. After treatment, collect the used treatment solution A (denoted as A') and treatment solution B (denoted as B').

[0083] (3) Final concentration determination: The concentrations of calcium ions and chitosan in solution A' and the concentrations of calcium ions and chitosan eluted from the tissue in solution B' were determined. The concentration of calcium ions was determined by EDTA complexometric titration; the concentration of low molecular weight chitosan was determined by the indantrione colorimetric method by determining the content of amino groups.

[0084] 2. Experimental results The results of the determination of the fixation rate of the structural reinforcement components in guava tissue are shown in Table 2.

[0085] Table 2 shows the results of the determination of the fixation rate of the structural reinforcement components in guava tissue. .

[0086] The data in Table 2 show that the fixation rates of calcium ions and low molecular weight chitosan in guava tissue reached 95.8% and 97.2%, respectively. In the pH response triggering step, only a small amount of components (less than 5%) were eluted from the tissue into buffer B. This result indicates that the two structural reinforcement components are not present in the tissue in a simple physical adsorption or concentration equilibrium manner. If it were physical adsorption, significant ion migration and desorption would occur when the tissue enters buffer B with a change in the ionic environment. The actual low elution amount proves that after the pH value increases, the calcium ions and chitosan that penetrate into the tissue rapidly undergo chemical conversion and are fixed in the tissue matrix through electrostatic interaction and ionic crosslinking, forming a stable, water-insoluble network structure. Therefore, this test example quantitatively confirms that the technical solution of the present application can achieve efficient in-situ fixation of structural reinforcement components in plant tissue.

[0087] Test Example 3: 1. Experimental method This test example aims to quantitatively characterize and compare the key physical properties of the final products obtained in the examples and comparative examples through instrumental analysis. The evaluation indicators include texture parameters (hardness and brittleness), dry shrinkage rate, and rehydration.

[0088] (1) Texture analysis: A texture analyzer (Texture Analyser) was used, and a P / 2 type cylindrical probe was configured to perform compression testing on the samples. The test parameters were set as follows: pre-test speed 2.0 mm / s, test speed 1.0 mm / s, post-test speed 2.0 mm / s, trigger force 5.0 g, and compression strain 50%. The maximum peak force in the force-time curve was taken as the hardness of the sample, and the peak force of the first significant breaking peak appearing on the curve was taken as the brittleness of the sample. Ten samples were randomly selected from each sample group for determination, and the results were averaged.

[0089] (2) Drying shrinkage: The initial volume of guava pieces before drying was measured using a digital vernier caliper, and the final volume after drying to constant weight was also measured. Ten samples were randomly selected from each sample group, and the results were averaged.

[0090] (3) Rehydration: About 2.0 g of dried sample was accurately weighed and placed in 100 mL of 50°C constant-temperature deionized water, and soaked for 30 minutes. After the sample was taken out, the surface adhering water was absorbed with filter paper, and immediately weighed. Each sample group was measured in triplicate, and the results were averaged.

[0091] 2. Experimental results The physical property test results of the products of each example and comparative example are shown in Table 3.

[0092] Table 3 Physical property test results of products of each example and comparative example .

[0093] The data in Table 3 quantifies the effect of the technical solution of the present application from multiple physical dimensions.

[0094] The hardness value of the products obtained in Examples 1, 2, and 3 is significantly lower than that of all comparative examples, and the brittleness value is much higher than that of all comparative examples. This indicates that the product prepared by the method of the present application forms a crispy texture, rather than a hard or tough texture. Comparative Example 1 (traditional drying) has the highest hardness and extremely low brittleness, showing typical characteristics of severe tissue collapse. The texture parameters of the remaining comparative examples (2-5) have improved, but still have a huge gap compared to the examples, which respectively confirm the necessity of high-efficiency penetration of vacuum pulses, step-by-step triggering of pH, and the decisive role of chitosan and in-situ cross-linking reaction on the formation of the final texture.

[0095] In terms of volume shrinkage, the shrinkage of the products of the examples is maintained at a low level (22.5%-26.8%), while all the comparative examples show severe volume shrinkage (48.9%-78.6%). This result directly proves that the present application effectively resists the capillary contraction force caused by water migration during the drying process by constructing a micro support network inside the tissue, thereby maintaining the original form of the product and forming a porous structure.

[0096] The test results of the rehydration ratio are highly correlated with the shrinkage data. The products of the examples exhibit excellent rehydration performance (rehydration ratio > 3.3) due to their porous structure, while the products of the comparative examples have a dense internal structure, making it difficult for water to penetrate, resulting in generally low rehydration ratios.

[0097] In summary, the physical property test data confirm that the technical solution adopted by the present application successfully builds an internal support structure capable of resisting dry stress through efficient introduction of functional components and in-situ cross-linking in response to pH, which is the key to obtaining low-shrinkage, high-porosity, and crispy-texture guavas products.

[0098] Test Example 4: Comprehensive evaluation of product flavor and sensory quality 1. Experimental method This test example combines instrumental analysis and artificial sensory evaluation to comprehensively evaluate the flavor retention effect and overall acceptability of each group of products.

[0099] (1) Main aroma component retention rate determination: Headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) technology was used for analysis. 2.0 grams of crushed sample was accurately weighed into a 20-milliliter headspace bottle and equilibrated at 60°C for 30 minutes. A DVB / CAR / PDMS extraction head was used to adsorb the headspace at the same temperature for 30 minutes. After injection, GC-MS analysis was performed. The total peak area of characteristic aroma substances ((Z)-3-hexenyl acetate, ethyl hexanoate) in fresh guava raw materials was taken as the reference (100%), and the relative retention rate of the total peak area of these substances in each dried sample was calculated.

[0100] 2. Experimental results The sensory evaluation scores and main aroma component retention rates of the products of each example and comparative example are shown in Table 4.

[0101] Table 4 Sensory evaluation and aroma retention rate of products of each example and comparative example .

[0102] The data in Table 4 clearly show that the products of Examples 1, 2, and 3 all obtained high scores in all sensory evaluation indicators, and their characteristic aroma substance retention rates were much higher than those of all comparative examples.

[0103] The instrumental analysis results show that the aroma retention rates of the products of Examples are all above 75%, which is attributed to two aspects: first, the low-temperature drying process of 50-60°C effectively reduces the degradation and volatilization of heat-sensitive aroma substances; second, D-xylose and L-cysteine in the permeate liquid protect the natural flavor substances of guavas by inhibiting the Maillard reaction and Strecker degradation under mild heating conditions.

[0104] The sensory evaluation results are highly consistent with the instrumental analysis results. The product of Example 1 has excellent aroma retention, natural color, and crispness due to the internal porous structure (which has been confirmed by Test Example 3). In contrast, Comparative Example 1 (traditional hot air drying) has almost complete loss of aroma due to high temperature, severe color browning, and the lowest product quality. The sensory scores and aroma retention rates of Comparative Examples 2 to 5 have improved to varying degrees, but there is still a significant gap compared to Example 1, which again confirms that the technologies of vacuum pulse penetration, pH step triggering, structure-enhancing components, and in-situ cross-linking are indispensable for the manufacture of high-quality guava products.

[0105] The comprehensive analysis shows that the technical scheme of the present application solves not only the physical structure problem of the product, but also achieves a decisive effect in the retention of flavor and sensory quality through the synergistic effect of multiple components and precise process control.

[0106] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements, and variations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A processing method for preserving the crispness and flavor of guava products, characterized in that, It includes the following steps: Step 1: Vacuum pulse permeation treatment is performed on guava fruit pieces using an acidic permeation composition containing trehalose, D-xylose, calcium lactate, L-cysteine ​​and low molecular weight chitosan. Step 2: Immerse the guava pieces treated in Step 1 in a buffer solution with a pH higher than that of the acidic osmotic composition to perform a pH response triggering treatment; Step 3: Perform low-temperature ripening treatment on the guava pieces that have been treated in Step 2; Step 4: Dry the guava pieces that have been treated in Step 3 with low-temperature hot air.

2. The processing method for preserving the crispness and flavor of guava products according to claim 1, characterized in that, In step one, the process parameters for vacuum pulse permeation treatment are: vacuum degree from -0.075MPa to -0.085MPa, vacuum holding time of 8-12 minutes, immersion time after restoring to normal pressure of 12-18 minutes, and repeated 2-3 times.

3. The processing method for preserving the crispness and flavor of guava products according to claim 1, characterized in that, In step two, the pH value of the buffer solution is 5.5-6.0, and the pH response triggering time is 3-5 minutes.

4. The processing method for preserving the crispness and flavor of guava products according to claim 1, characterized in that, In step three, the low-temperature curing temperature is 4-6℃ and the time is 4-6 hours; and / or, in step four, the low-temperature hot air drying temperature is 50-60℃.

5. The processing method for preserving the crispness and flavor of guava products according to claim 1, characterized in that, Before step one, there is also a pretreatment step of peeling and cutting the guava fruit into pieces.

6. An acidic penetrating composition for processing guava products, characterized in that, It is prepared from the following raw materials in the stated parts by weight: Trehalose: 18.0-22.0 parts; D-xylose: 1.5-2.5 parts; Calcium lactate: 0.6-1.0 parts; L-cysteine: 0.06-0.10 parts; Low molecular weight chitosan: 0.15-0.25 parts.

7. The acidic penetrating composition for processing guava products according to claim 6, characterized in that, The weight-average molecular weight of the low molecular weight chitosan is 5.0 × 10⁻⁶. 4 -1.5×10 5 Da has a degree of deacetylation of 85.0%-95.0%.

8. The acidic penetrating composition for processing guava products according to claim 6, characterized in that, The pH value of the composition is 4.0-4.

5.

9. An acidic penetrating composition for processing guava products according to claim 6, characterized in that, The weight ratio of trehalose, D-xylose, calcium lactate, L-cysteine ​​and low molecular weight chitosan is 20:2.0:0.8:0.08:0.

2.

10. Use of the acidic penetrating composition according to any one of claims 6-9, characterized in that, Used to enhance the crispness and flavor retention of guava products after processing.