Preparation method and application of composite jam of Korla fragrant pear

Abstract

This invention provides a method for preparing Korla fragrant pear compound jam and its application. The steps are as follows: Fresh Korla fragrant pears are selected, washed, cut, treated for color protection, and pulped with water to obtain Korla fragrant pear pulp; casein powder and calcium chloride are added to the pulp and mixed well, then rennet is added for coagulation treatment to obtain pretreated pulp; the pretreated pulp is heated and concentrated, and compound modified fragrant pear peel dietary fiber, pectin, erythritol and citric acid are added for adjustment, followed by cooking, filling and sterilization to obtain the final product. This invention utilizes casein coagulation, compound modified fragrant pear peel dietary fiber, and pectin to synergistically construct a stable three-dimensional gel network, effectively inhibiting water migration and sugar release during the processing and storage of low-sugar jam, giving the jam good spreadability and anti-water separation properties, while retaining the natural active ingredients of fragrant pears; at the same time, the compound modified fragrant pear peel dietary fiber is obtained from pear peel, a by-product of Korla fragrant pear processing, through extraction and compound modification, realizing high-value utilization of resources.

Description

Technical Field

[0001] This invention belongs to the field of food processing technology, specifically relating to a method for preparing Korla fragrant pear compound jam and its application. Background Technology

[0002] Jam is a product loved by consumers worldwide. Currently, most jam products on the market have a sugar content of over 60%, and some even reach 75%. Although high sugar content promotes the gelation of high-methoxyl pectin, helping jam form a thick texture and inhibiting microbial growth, it also results in jam containing a large amount of calories, which contradicts modern healthy eating concepts. Therefore, low-sugar jams are becoming increasingly popular with consumers, and developing reduced-sugar and low-sugar jams has become the main trend in jam product development at present.

[0003] Reduced-sugar jams are required to have a sugar content reduced by more than 25% compared to reference foods. Common jam products typically have a sugar content of over 60%, so products with a sugar content below 45% can be called reduced-sugar jams. However, due to their lower sugar content, low-sugar jams have weaker water-holding capacity and lower osmotic pressure, making them prone to water separation. They are also susceptible to browning during storage, leading to jam runnyness and a decline in edible quality, severely impacting sensory quality and shelf life. Currently, there are two main approaches to developing reduced-sugar jams: one is to add hydrocolloids for thickening to reduce sucrose addition, and the other is to add sweeteners to compensate for the lack of sweetness resulting from low sucrose. Although hydrocolloids are a green and safe food additive, typically composed of long-chain polymers with numerous hydrophilic groups such as hydroxyl and carboxyl groups attached to the polysaccharide backbone, they are relatively easy to dissolve in water and rapidly swell to form a three-dimensional network structure, transforming aqueous solutions into a viscous, gel-like, semi-fluid state. However, the use of hydrocolloids also has certain limitations. For example, low-sugar jams with added low-methoxyl pectin still experience water leaching during storage; sodium alginate, due to its inherent fishy odor, negatively impacts the sensory quality of jams; and while agar can provide good viscosity for low-sugar jams, it is easily decomposed under acidic conditions upon heating. Therefore, although current development of low-sugar jams often uses hydrocolloid thickeners or sweetener substitutions, these methods still have significant shortcomings in terms of water retention, flavor quality, and storage stability. There is an urgent need to develop a new high-quality low-sugar jam preparation technology to meet consumers' pressing demand for healthy, natural, and high-quality jam products. Summary of the Invention

[0004] Technical Problem to be Solved: To address the aforementioned technical problems, the present invention aims to provide a method for preparing Korla fragrant pear compound jam and its application. The steps are as follows: Fresh Korla fragrant pears are selected, washed, cut, treated for color protection, and pulped with water to obtain Korla fragrant pear pulp; casein powder and calcium chloride are added to the pulp and mixed well, then rennet is added for coagulation treatment to obtain pretreated pulp; the pretreated pulp is heated and concentrated, and compound modified fragrant pear peel dietary fiber, pectin, erythritol, and citric acid are added for adjustment; the mixture is then boiled, bottled, and sterilized to obtain the final product. This invention effectively solves the quality problems of traditional low-sugar jams, such as easy water separation, dispersion, poor spreadability, and rough texture caused by reduced sugar content.

[0005] Technical solution: A method for preparing Korla fragrant pear compound jam, comprising the following steps: Step 1. Select fresh, high-quality, mold-free Korla fragrant pears, wash them clean, peel and core them, and cut them into chunks to obtain fragrant pear pieces; Step 2. After treating the pear pieces for color protection, add water to make pulp and adjust the pH to 5.0-5.5 to obtain Korla pear pulp; Step 3. Add casein powder and calcium chloride to the Korla fragrant pear pulp and mix well. Then add rennet to perform coagulation treatment to obtain pretreated Korla fragrant pear pulp. Step 4. The pre-treated Korla fragrant pear pulp is heated and concentrated, then mixed with compound modified fragrant pear peel dietary fiber, pectin, erythritol and citric acid, and boiled until the soluble solids content is 35-45%. After filling and sterilization, Korla fragrant pear compound jam is obtained.

[0006] Preferably, in step 2, the color protection treatment involves immersing the pear pieces in D-isoascorbic acid at a mass fraction of 0.1-0.25%; the ratio of pear pieces to water in the pulping process is 1g:(0.5-2)mL.

[0007] Preferably, in step 3, the amount of casein powder added is 3.5-6%, the amount of calcium chloride added is 0.1-0.25%, and the amount of rennet added is 0.01-0.06%, all based on the volume of Korla fragrant pear pulp.

[0008] Preferably, the conditions for the curdling process in step 3 are a curdling temperature of 40-55℃ and a curdling time of 15-25 min.

[0009] Preferably, in step 4, the amount of added compound modified pear peel dietary fiber is 0.5-3%, the amount of added pectin is 0.3-0.8%, the amount of added erythritol is 3.5-6.5%, and the amount of added citric acid is 0.15-0.28%, all based on the volume of Korla pear pulp.

[0010] Preferably, the preparation method of the composite modified pear peel dietary fiber in step 4 includes the following steps: S1. The peel of Korla fragrant pear is dried, pulverized and made into fragrant pear peel powder. The fragrant pear peel powder is mixed with choline chloride-glycerol eutectic solvent, and then xylanase is added for enzymatic hydrolysis. After separation, concentration and drying, Korla fragrant pear peel dietary fiber is obtained. S2. Disperse Korla fragrant pear dietary fiber and sodium tripolyphosphate in water at a mass ratio of (5-10):1 and adjust the pH to 6.5-7.5. React at 70-85℃ for 2-4 hours. After cooling to 35-45℃ and adjusting the pH to 5.2-6.5, add ferulic acid and tyrosinase for 2-5 hours. Then, obtain the composite modified fragrant pear peel dietary fiber by alcohol precipitation, washing and drying.

[0011] Preferably, in S1, the molar ratio of choline chloride to glycerol in the eutectic solvent is 1:(1-3), and the water content is 30-45%; the amount of xylanase added is 0.5-2% based on the mass of pear peel powder; the conditions for xylanase enzymatic hydrolysis are a temperature of 45-55℃, a pH of 4.5-6.0, and a time of 1.5-3h.

[0012] Preferably, the amount of ferulic acid added in S2 is 0.5-2%, and the amount of tyrosinase added is 100-500 U / g, both based on the dietary fiber weight of Korla fragrant pear peel.

[0013] Korla fragrant pear compound jam prepared by any of the methods described above.

[0014] Beneficial effects: 1. This invention adds casein powder and calcium ions to Korla fragrant pear pulp and treats it with rennet. Casein powder is used to replace the sugar content reduction in low-sugar Korla fragrant pear compound jam. Rennet specifically cleaves κ-casein in the casein powder to generate casein macropeptides, thereby disrupting the spatial stability of casein micelles. Under the bridging effect of calcium ions, the casein micelles are promoted to form a dense three-dimensional gel network, which traps fruit pulp particles, soluble sugars and water in Korla fragrant pear pulp. At the same time, by controlling the degree of coagulation, the coagulation is ensured to be moderate and the texture is uniform and delicate, while the rough taste caused by excessive coagulation is solved. Thus, a solid textural foundation is laid for the spreadability and stability of low-sugar Korla fragrant pear compound jam.

[0015] 2. This invention first extracts dietary fiber from the pear peel residue produced during the preparation of Korla fragrant pear compound jam. After phosphorylation and phenolic acid compound modification, it is added to the Korla fragrant pear compound jam. The phosphate ester groups of the compound modified fragrant pear peel dietary fiber are attracted by electrostatics and bridged by calcium ions, while the phenolic acid groups are dispersed in the gel network of casein curd through hydrophobic association. At the same time, the compound modified fragrant pear peel dietary fiber and pectin form a jam gel network through multiple hydrogen bonds. This network can firmly lock in the pulp particles, water, and active ingredients of Korla fragrant pear during cooking and processing, effectively inhibiting water migration, sugar precipitation, and pulp sedimentation during cooking and storage, giving it good spreadability and water resistance. In addition, the stable composite gel network formed by the compound modified fragrant pear peel dietary fiber, pectin, and casein curd can reduce the degree of decomposition of the active ingredients contained in Korla fragrant pear under acid and heat processing conditions, avoiding the deterioration of the jam's nutritional quality due to degradation, and improving the quality of Korla fragrant pear compound jam.

[0016] 3. The Korla fragrant pear compound jam prepared by this invention still has good spreadability and jam stability under low sugar conditions. It has a natural color, pure aroma, delicate and uniform taste, and a moderate sweet and sour flavor. It solves the problems of easy water separation, dispersion, and rough jam texture caused by reducing the sugar content in traditional low sugar jams in order to achieve the purpose of low sugar. In addition, the Korla fragrant pear compound jam has more active ingredients and higher nutritional value, realizes the resource utilization of Korla fragrant pear processing by-products, provides a theoretical basis for the development of functional fragrant pear jam, and can also provide a theoretical reference for the product development and industrial production of sugar-free fragrant pear jam. Attached Figure Description

[0017] Figure 1 The sensory quality changes during storage for Examples 9 and Comparative Examples 6-13; Figure 2 The changes in browning index during storage for Examples 9 and Comparative Examples 6-13; Figure 3 The changes in water content during storage for Examples 9 and Comparative Examples 6-13; Figure 4 The changes in total bacterial count during storage for Examples 9 and Comparative Examples 6-13 are shown. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments. These embodiments are illustrative of the present invention, but the present invention is not limited to these embodiments: Example 1

[0019] A method for preparing composite modified pear peel dietary fiber includes the following steps: S1. Mix choline chloride and glycerol in a molar ratio of 1:1, add water until the water content of the system is 30%, and stir at 80°C to obtain a choline chloride-glycerol eutectic solvent. S2. Take 200g of peeled Korla fragrant pear peel, dry it, pulverize it and pass it through a 60-mesh sieve to obtain fragrant pear peel powder; mix 100g of fragrant pear peel powder with 500mL of choline chloride-glycerol eutectic solvent, add 0.5g of xylanase to adjust the pH to 4.5, enzymatically hydrolyze it in a 45℃ water bath for 1.5h, after inactivating the enzyme, centrifuge at 4000rpm for 15min to separate the supernatant, concentrate it to 1 / 3 of the original volume by rotary evaporation at 50℃, and then freeze-dry it to obtain Korla fragrant pear peel dietary fiber; S3. Weigh 20g of Korla fragrant pear peel dietary fiber and 2g of sodium tripolyphosphate, disperse them in 200mL of deionized water, adjust the pH to 6.5, and react at 70℃ for 2h. After the reaction, cool the system to 35℃ and adjust the pH to 5.2. Then add 0.1g of ferulic acid and 100U / g of tyrosinase and stir at 35℃ for 2h. Add 600mL of 95% ethanol to the reaction solution and let it stand for 2h to precipitate. Centrifuge to collect the precipitate, wash it three times with 200mL of water, and vacuum dry it at 40℃ to obtain the composite modified fragrant pear peel dietary fiber. Example 2

[0020] A method for preparing composite modified pear peel dietary fiber includes the following steps: S1. Mix choline chloride and glycerol in a molar ratio of 1:2, add water until the water content of the system is 35%, and stir at 80°C to obtain a choline chloride-glycerol eutectic solvent. S2. Take 200g of peeled Korla fragrant pear peel, dry it, pulverize it and pass it through a 60-mesh sieve to obtain fragrant pear peel powder; mix 100g of fragrant pear peel powder with 550mL of choline chloride-glycerol eutectic solvent, add 1.0g of xylanase to adjust the pH to 5.0, enzymatically hydrolyze it in a 50℃ water bath for 2h, after inactivating the enzyme, centrifuge at 4000rpm for 15min to separate the supernatant, concentrate it to 1 / 3 of the original volume by rotary evaporation at 50℃, and then freeze-dry it to obtain Korla fragrant pear peel dietary fiber; S3. Weigh 20g of Korla fragrant pear peel dietary fiber and 2.5g of sodium tripolyphosphate, disperse them in 200mL of deionized water, adjust the pH to 7.0, and react at 75℃ for 2h. After the reaction, cool the system to 40℃ and adjust the pH to 5.8. Then add 0.2g of ferulic acid and 300U / g of tyrosinase and stir at 40℃ for 3.5h. Add 600mL of 95% ethanol to the reaction solution and let it stand for 2h to precipitate. Centrifuge to collect the precipitate, wash it three times with 200mL of water, and vacuum dry it at 40℃ to obtain the composite modified fragrant pear peel dietary fiber. Example 3

[0021] A method for preparing composite modified pear peel dietary fiber includes the following steps: S1. Mix choline chloride and glycerol in a molar ratio of 1:3, add water until the water content of the system is 40%, and stir at 80°C to obtain a choline chloride-glycerol eutectic solvent. S2. Take 200g of peeled Korla fragrant pear peel, dry it, pulverize it and pass it through a 60-mesh sieve to obtain fragrant pear peel powder; mix 100g of fragrant pear peel powder with 600mL of choline chloride-glycerol eutectic solvent, add 1.5g of xylanase to adjust the pH to 5.0, enzymatically hydrolyze it in a 55℃ water bath for 2h, after inactivating the enzyme, centrifuge at 4000rpm for 15min to separate the supernatant, concentrate it to 1 / 4 of the original volume by rotary evaporation at 50℃, and then freeze-dry it to obtain Korla fragrant pear peel dietary fiber; S3. Weigh 20g of Korla fragrant pear peel dietary fiber and 2g of sodium tripolyphosphate, disperse them in 200mL of deionized water, adjust the pH to 7.5, and react at 85℃ for 2h. After the reaction, cool the system to 45℃ and adjust the pH to 6.5. Then add 0.3g of ferulic acid and 400U / g of tyrosinase and stir at 45℃ for 2h. Add 600mL of 95% ethanol to the reaction solution and let it stand for 2h to precipitate. Centrifuge to collect the precipitate, wash it three times with 200mL of water, and vacuum dry it at 40℃ to obtain the composite modified fragrant pear peel dietary fiber. Example 4

[0022] A method for preparing composite modified pear peel dietary fiber includes the following steps: S1. Mix choline chloride and glycerol in a molar ratio of 1:1.5, add water until the water content of the system is 45%, and stir at 80°C to obtain a choline chloride-glycerol eutectic solvent. S2. Take 200g of peeled Korla fragrant pear peel, dry it, pulverize it and pass it through a 60-mesh sieve to obtain fragrant pear peel powder; mix 100g of fragrant pear peel powder with 500mL of choline chloride-glycerol eutectic solvent, add 2.0g of xylanase to adjust the pH to 6.0, enzymatically hydrolyze it in a 50℃ water bath for 3h, after inactivating the enzyme, centrifuge at 4000rpm for 15min to separate the supernatant, concentrate it to 1 / 3 of the original volume by rotary evaporation at 50℃, and then freeze-dry it to obtain Korla fragrant pear peel dietary fiber; S3. Weigh 20g of Korla fragrant pear peel dietary fiber and 3.3g of sodium tripolyphosphate, disperse them in 200mL of deionized water, adjust the pH to 7.2, and react at 75℃ for 2.5h. After the reaction, cool the system to 40℃ and adjust the pH to 6.0. Then add 0.4g of ferulic acid and 500U / g tyrosinase and stir at 40℃ for 4h. Add 600mL of 95% ethanol to the reaction solution and let it stand for 2h to precipitate. Centrifuge to collect the precipitate, wash it three times with 200mL of water, and vacuum dry it at 40℃ to obtain the composite modified fragrant pear peel dietary fiber. Example 5

[0023] A method for preparing composite modified pear peel dietary fiber includes the following steps: S1. Mix choline chloride and glycerol in a molar ratio of 1:2.5, add water until the water content of the system is 38%, and stir at 80°C to obtain a choline chloride-glycerol eutectic solvent; S2. Take 200g of peeled Korla fragrant pear peel, dry it, pulverize it and pass it through a 60-mesh sieve to obtain fragrant pear peel powder; mix 100g of fragrant pear peel powder with 500mL of choline chloride-glycerol eutectic solvent, add 2g of xylanase to adjust the pH to 5.5, enzymatically hydrolyze it in a 50℃ water bath for 2.5h, after inactivating the enzyme, centrifuge at 4000rpm for 15min to separate the supernatant, concentrate it to 1 / 3 of the original volume by rotary evaporation at 50℃, and then freeze-dry it to obtain Korla fragrant pear peel dietary fiber; S3. Weigh 20g of Korla fragrant pear peel dietary fiber and 2.2g of sodium tripolyphosphate, disperse them in 200mL of deionized water, adjust the pH to 6.8, and react at 80℃ for 3h. After the reaction, cool the system to 40℃ and adjust the pH to 6.0. Then add 0.24g of ferulic acid and 250U / g of tyrosinase and stir at 42℃ for 3h. Add 600mL of 95% ethanol to the reaction solution and let it stand for 2h to precipitate. Centrifuge to collect the precipitate, wash it three times with 200mL of water, and vacuum dry it at 40℃ to obtain the composite modified fragrant pear peel dietary fiber. Comparative Example 1

[0024] The difference between this comparative example and Example 3 is that the eutectic solvent of choline chloride-glycerol is replaced with water; the remaining operations are the same as in Example 3. Comparative Example 2

[0025] The difference between this comparative example and Example 3 is that xylanase is not added; the remaining operations are the same as in Example 3. Comparative Example 3

[0026] The difference between this comparative example and Example 3 is that sodium tripolyphosphate is not added; the remaining operations are the same as in Example 3. Comparative Example 4

[0027] The difference between this comparative example and Example 3 is that ferulic acid and tyrosinase are not added; the remaining operations are the same as in Example 3. Comparative Example 5

[0028] The difference between this comparative example and Example 3 is that phenolic acid modification is performed first, followed by phosphorylation modification. The remaining operations are the same as in Example 3. Performance testing

[0029] (1) Dietary fiber yield The dietary fiber extracted from the peel of Korla fragrant pear obtained by the above preparation method S1 is weighed (denoted as M0). The yield is calculated according to the yield calculation formula: dietary fiber yield (%) = M0 / M × 100%, where M represents the mass of fragrant pear peel powder used in the extraction of dietary fiber from Korla fragrant pear peel.

[0030] (2) Water holding capacity Take 20g of the composite modified pear peel dietary fiber and place it in a 50mL centrifuge tube. Record the total weight of the sample and the centrifuge tube as m1. Add 20mL of deionized water and stir overnight at room temperature. Then centrifuge at 4500rpm for 10min. Carefully pour out the supernatant and remove the water droplets adhering to the inner wall of the tube. Weigh the sample and record the weight of the precipitate and the centrifuge tube as m. The formula for calculating water holding capacity is WHC (g / g) = (m-m1) / m2, where m2 represents the mass of the composite modified pear peel dietary fiber sample.

[0031] (3) Swelling force Accurately weigh 0.5g of sample (denoted as m), place it in a 10mL graduated cylinder, gently shake the sample surface to level it, and read the initial sample volume V0. Add 10mL of distilled water to the graduated cylinder and shake to ensure that the sample is completely wetted. Then let it stand at room temperature for 24h and read the hydrated sample volume V in the graduated cylinder. The formula for calculating the swelling force is SC (mL / g) = (V-V0) / m.

[0032] Table 1. Dietary fiber yield, water-holding capacity, and swelling capacity of Examples 1-5 and Comparative Examples 1-5

[0033] Note: - indicates that no measurement will be performed.

[0034] As shown in Table 1, the dietary fiber yield of Examples 1-5 was significantly higher than that of Comparative Examples 1 and 2. This indicates that the extraction using choline chloride-glycerol eutectic solvent can effectively disrupt the cell wall structure of Korla pear peel, thereby improving the fiber dissolution efficiency. The addition of xylanase further promoted the extraction of dietary fiber. Furthermore, the water-holding capacity and swelling capacity of Examples 1-5 were superior to those of Comparative Examples 1-5. This indicates that the synergistic effect of phosphorylation-introduced phosphate ester groups and phenolic acid grafting can significantly enhance the spatial expansion capacity and water-holding capacity of dietary fiber. Therefore, the present invention uses eutectic solvent combined with enzyme-assisted extraction to significantly improve the yield, water-holding capacity, and swelling capacity of dietary fiber from Korla pear peel, providing a high-quality dietary fiber raw material for low-sugar Korla pear compound jam. Example 6

[0035] A method for preparing a Korla fragrant pear compound jam includes the following steps: Step 1. Select 1000g of fresh, high-quality, mold-free Korla fragrant pears, wash them clean, peel and core them, and cut them into 1.5cm long pieces; immerse 800g of fragrant pear pieces in 1L of 0.1% D-isoascorbic acid solution for 10min for color protection treatment, remove them and drain them, then add 400mL of water to make pulp and adjust the pH to 5.0 to obtain Korla fragrant pear pulp; Step 2. Add 35g casein powder and 1g calcium chloride to 1L of Korla fragrant pear pulp, mix well, then add 0.1g rennet and coagulate at 40℃ for 25min to obtain pretreated fragrant pear pulp; then simmer over low heat for 10min, then add 5g of the composite modified fragrant pear peel dietary fiber prepared in Example 3, 3g pectin, 35g erythritol and 1.5g citric acid, and continue to simmer until the soluble solids content is 35%, then can and seal, pasteurize at 85℃ for 15min, and cool to obtain Korla fragrant pear compound jam. Example 7

[0036] A method for preparing a Korla fragrant pear compound jam includes the following steps: Step 1. Select 1000g of fresh, high-quality, mold-free Korla fragrant pears, wash them clean, peel and core them, and cut them into 1.5cm long pieces; immerse 600g of fragrant pear pieces in 1L of 0.18% D-isoascorbic acid solution for 10min for color protection treatment, remove them and drain them, then add 750mL of water to make pulp and adjust the pH to 5.2 to obtain Korla fragrant pear pulp; Step 2. Add 50g casein powder and 1.8g calcium chloride to 1L of Korla fragrant pear pulp, mix well, then add 0.4g rennet and treat with curdling at 48℃ for 20min to obtain pretreated fragrant pear pulp; then simmer over low heat for 10min, then add 20g of the composite modified fragrant pear peel dietary fiber prepared in Example 3, 5.5g pectin, 50g erythritol, and 2.2g citric acid, and continue to simmer until the soluble solids content is 40%. After canning and sealing, pasteurize at 85℃ for 15min, and cool to obtain Korla fragrant pear compound jam. Example 8

[0037] A method for preparing a Korla fragrant pear compound jam includes the following steps: Step 1. Select 1000g of fresh, high-quality, mold-free Korla fragrant pears, wash them clean, peel and core them, and cut them into 1.5cm long pieces; immerse 800g of fragrant pear pieces in 1L of 0.25% D-isoascorbic acid solution for color protection treatment for 10min, remove them and drain them, then add 1600mL of water to make pulp and adjust the pH to 5.5 to obtain Korla fragrant pear pulp; Step 2. Add 60g casein powder and 2.5g calcium chloride to 1L of Korla fragrant pear pulp, mix well, then add 0.6g rennet and coagulate at 55℃ for 15min to obtain pretreated fragrant pear pulp; then simmer over low heat for 10min, then add 30g of the composite modified fragrant pear peel dietary fiber prepared in Example 3, 8g pectin, 65g erythritol, and 2.8g citric acid, and continue to simmer until the soluble solids content is 35%. After canning and sealing, pasteurize at 85℃ for 15min, and cool to obtain Korla fragrant pear compound jam. Example 9

[0038] A method for preparing a Korla fragrant pear compound jam includes the following steps: Step 1. Select 1000g of fresh, high-quality, mold-free Korla fragrant pears, wash them clean, peel and core them, and cut them into 1.5cm long pieces; immerse 800g of fragrant pear pieces in 1L of 0.15% D-isoascorbic acid solution for 10min for color protection treatment, remove them and drain them, then add 400mL of water to make pulp and adjust the pH to 5.0 to obtain Korla fragrant pear pulp; Step 2. Add 35g casein powder and 1g calcium chloride to 1L of Korla fragrant pear pulp, mix well, then add 0.1g rennet and coagulate at 40℃ for 25min to obtain pretreated fragrant pear pulp; then simmer over low heat for 10min, then add 20g of the composite modified fragrant pear peel dietary fiber prepared in Example 3, 4g pectin, 50g erythritol and 1.5g citric acid, and continue to simmer until the soluble solids content is 40%. After canning and sealing, pasteurize at 85℃ for 15min, and cool to obtain Korla fragrant pear compound jam. Example 10

[0039] A method for preparing a Korla fragrant pear compound jam includes the following steps: Step 1. Select 1000g of fresh, high-quality, mold-free Korla fragrant pears, wash them clean, peel and core them, and cut them into 1.5cm long pieces; immerse 600g of fragrant pear pieces in 1L of 0.25% D-isoascorbic acid solution for 10min for color protection treatment, remove them and drain them, then add 900mL of water to make pulp and adjust the pH to 5.4 to obtain Korla fragrant pear pulp; Step 2. Add 55g casein powder and 2.2g calcium chloride to 1L of Korla fragrant pear pulp, mix well, add 0.5g rennet, and coagulate at 52℃ for 20min to obtain pretreated fragrant pear pulp; then simmer over low heat for 10min, add 25g of the composite modified fragrant pear peel dietary fiber prepared in Example 3, 7g pectin, 40g erythritol, and 2.5g citric acid, and continue to simmer until the soluble solids content is 45%. After canning and sealing, pasteurize at 85℃ for 15min, and cool to obtain Korla fragrant pear compound jam. Comparative Example 6

[0040] The difference between this comparative example and Example 9 is that it uses the composite modified pear peel dietary fiber prepared in Comparative Example 1, while the remaining operations are the same as in Example 9. Comparative Example 7

[0041] The difference between this comparative example and Example 9 is that it uses the composite modified pear peel dietary fiber prepared in Comparative Example 2, while the remaining operations are the same as in Example 9. Comparative Example 8

[0042] The difference between this comparative example and Example 9 is that it uses the composite modified pear peel dietary fiber prepared in Comparative Example 3, while the remaining operations are the same as in Example 9. Comparative Example 9

[0043] The difference between this comparative example and Example 9 is that it uses the composite modified pear peel dietary fiber prepared in Comparative Example 4, while the remaining operations are the same as in Example 9. Comparative Example 10

[0044] The difference between this comparative example and Example 9 is that it uses the composite modified pear peel dietary fiber prepared in Comparative Example 5, while the remaining operations are the same as in Example 9. Comparative Example 11

[0045] The difference between this comparative example and Example 9 is that no curdling treatment is performed; the remaining operations are the same as in Example 9. Comparative Example 12

[0046] The difference between this comparative example and Example 9 is that the composite modified pear peel dietary fiber prepared in Example 3 is not added; the remaining operations are the same as in Example 9. Comparative Example 13

[0047] The difference between this comparative example and Example 9 is that no curdling treatment is performed and the composite modified pear peel dietary fiber prepared in Example 3 is not added. The remaining operations are the same as in Example 9.

[0048] Evaluation indicators (1) Sensory evaluation An evaluation panel of 15 professional judges with food tasting experience conducted sensory evaluations on four aspects: color (20 points), taste (30 points), texture (30 points), and aroma (20 points) (Table 2), with a total score of 100 points. The sensory evaluation criteria for Korla fragrant pear compound fruit jam are shown in Table 2. Evaluation method: Place a sample of fragrant pear jam in a white enamel dish and observe the color and texture of the jam with the naked eye under natural light; place it under the nose and gently fan it with your hand to smell the intensity of the fruit aroma; put it in your mouth to taste the sourness, sweetness, and smoothness of the jam; spread the sample on bread and observe the uniformity, gelling, and flow of the jam, and observe whether there is any water separation.

[0049] Table 2 Sensory Evaluation Criteria for Korla Fragrant Pear Compound Fruit Jam

[0050] (2) Total phenol content The total phenol content was determined by enzyme-linked immunosorbent assay (ELISA) using gallic acid as a standard. Under alkaline conditions, phenolic substances reduced tungsticotropic acid to produce a blue compound with a characteristic absorption peak at 765 nm. The total phenol content of the sample was obtained by measuring the absorbance at 765 nm. The standard curve for the total phenol content was y = 2.808x + 0.0012 (R²). 2 =0.9994).

[0051] The formula for calculating total phenol content is: Total phenol content (mg / g) = [(ΔA−0.0012) / 2.808]×V 样 / (V) 样 / V 样总 V × W) = [0.356 × (absorbance difference − 0.0012)] / W, where ΔA represents the absorbance difference, V 样总 V represents the volume of extract added (1 mL). 样 W represents the sample volume in the reaction (0.01 mL), and W represents the sample mass.

[0052] (3) Flavonoid content The flavonoid content was determined by enzyme-linked immunosorbent assay (ELISA) using rutin as a standard. In an alkaline nitrite solution, flavonoids and aluminum ions formed a red complex with a characteristic absorption peak at 510 nm. The flavonoid content of the sample was calculated by measuring the absorbance of the sample extract at 510 nm. The standard curve for flavonoid content was y = 2.0939x + 0.0183 (R²). 2 =0.9991).

[0053] The formula for calculating flavonoid content is: Flavonoid content (mg / g) = (ΔA - 0.0183) ÷ 2.0939 ÷ (W ÷ V) 样总 V = 0.4776 × (ΔA − 0.0183) ÷ W, where ΔA represents the absorbance difference, and V 样总 W represents the volume of extract added (1 mL), and W represents the sample mass.

[0054] (4) Sugar-acid ratio The sugar-acid ratio of the jam is calculated using the following formula: Sugar-acid ratio = Sugar content / Total acid content. The sugar content of the Korla fragrant pear compound jam was measured using a handheld refractometer, and the total acid content was determined according to GB 12456-2021 "National Food Safety Standard - Determination of Total Acid in Food". Measurement.

[0055] (5) Texture characteristics Texture properties were determined using a TA-XTPlus texture analyzer with a P0.5 probe. 20g of Korla pear-based compound jam was placed in a 50mL beaker, ensuring a smooth sample surface. The sample was equilibrated at 25°C for 2 hours before measurement. The TPA mode was used for measurement, with the following parameters: test speed 1mm / s, test distance 10mm, post-test speed 1mm / s, and trigger force 5g. (Hardness, viscosity, adhesiveness) Table 3 Sensory evaluation of the Korla fragrant pear jam prepared in Examples 6-10 and Comparative Examples 6-13

[0056] Table 4. Total phenols, flavonoids, sugar-acid ratio, and textural properties of the Korla fragrant pear jam prepared in Example 9 and Comparative Examples 6-13

[0057] As shown in Tables 3 and 4, the sensory quality of the Korla fragrant pear compound jam prepared in Examples 6-10 is superior to that of Comparative Examples 6-13. In particular, the Korla fragrant pear compound jam prepared in Example 9 has a bright yellow color, a harmonious sweet and sour taste, a rich aroma, and a uniform, non-dispersible consistency, exhibiting the best overall sensory quality. Moreover, the total phenolic and flavonoid content and textural properties of Example 9 are superior to those of Comparative Examples 6-13. This indicates that the Korla fragrant pear compound jam retains abundant phenolic and flavonoid active ingredients. The rennet-induced casein curd provides the basic three-dimensional gel framework, while the composite modified fragrant pear peel dietary fiber is dispersed in the network through electrostatic attraction, calcium ion bridging, and hydrophobic association, while simultaneously forming multiple hydrogen bonds with pectin, thereby significantly enhancing gel strength and water-holding capacity.

[0058] (6) Total antioxidant capacity ① ABTS method for antioxidant activity determination Prepare 7.0 mmol / L ABTS solution and 2.45 mmol / L potassium persulfate solution, and mix 25 mL of each in equal proportion. Incubate in the dark for 15 h, then dilute the mixture with anhydrous ethanol to an absorbance of 0.7 ± 0.02. Mix 0.2 mL of the sample extract with 4 mL of ABTS solution for 6 min, using anhydrous ethanol as a blank control. Measure the absorbance at 734 nm. The experiment was conducted in the dark throughout. The scavenging rate was calculated as follows: ABTS free radical scavenging rate (%) = (1 - (A2 - A1) / A0) × 100%, where A0 is the absorbance after the reaction of 0.2 mL ethanol with 4 mL ABTS solution; A1 is the absorbance after the reaction of 0.2 mL of sample extract with 4 mL ethanol; and A2 is the absorbance after the reaction of 0.2 mL of sample extract with 4 mL ABTS solution.

[0059] The formula for calculating total antioxidant capacity based on sample weight is: Total antioxidant capacity (μmol Trolox / g fresh weight) = (ΔA − 0.0006) ÷ 0.55 × V 样 ÷ (V) 样 ÷V 样总 ×W) = 1.818 × (ΔA − 0.0006) ÷ W, where V 样总 V represents the volume of extract added (1 mL). 样 W represents the sample volume (10 μL) in the reaction, and W represents the sample mass.

[0060] ② DPPH method for antioxidant activity Accurately weigh 0.002 g of DPPH and dilute to 100 mL with anhydrous ethanol to prepare a DPPH solution with a concentration of 0.05 mL / L. Mix 2 mL of sample extract with 2 mL of DPPH solution for 30 min, using anhydrous ethanol as a blank control, and measure the absorbance at 517 nm. The experiment was conducted in the dark throughout. The scavenging rate was calculated using the formula: DPPH scavenging rate (%) = (1 − (A2 − A1)A0) × 100, where A0 is the absorbance after the reaction of 2 mL of ethanol with 2 mL of DPPH solution; A1 is the absorbance after the reaction of 2 mL of sample extract with 2 mL of ethanol; and A2 is the absorbance after the reaction of 2 mL of sample extract with 2 mL of DPPH solution.

[0061] Total antioxidant capacity (μmol Trolox / g fresh weight) = (ΔA + 0.0069) ÷ 0.5324 × V 样 ÷(V 样 ÷V 样总 ×W)=1.878×(ΔA+0.0069)÷W, where V 样总 V represents the volume of extract added (1 mL). 样 W represents the sample volume (20 μL) in the reaction, and W represents the sample mass.

[0062] ③Total antioxidant capacity using FRAP method Using Trolox as the standard, the standard curve is: y = 1.2994x − 0.002 (R²). 2 =1.0000), Total antioxidant capacity (μmol Trolox / g fresh weight) = (ΔA + 0.002) ÷ 1.2994 × V 样 ÷ (V) 样 ÷V 样总 ×W) = 0.7696 × (ΔA + 0.002) ÷ W, where V 样总 V represents the volume of extract added (1 mL). 样 W represents the sample volume (10 μL) in the reaction, and W represents the sample mass.

[0063] Table 5. Antioxidant properties of Korla pear jam prepared in Example 9 and Comparative Examples 6-13 (unit: μmolTrolox / g)

[0064] As shown in Table 5, Example 9 has better overall antioxidant performance than Comparative Examples 6-13 in terms of DPPH free radical, ABTS free radical, and iron ion reducing ability. This indicates that the synergistic effect of curdling treatment and composite modified pear peel dietary fiber in this invention forms a stable gel network, which effectively protects the natural antioxidant components such as phenols and flavonoids in Korla pears, thereby giving them good antioxidant activity.

[0065] (7) Storage test Korla fragrant pear compound jam was sealed and dispensed into several small bottles, sterilized, cooled, and then placed in a 4℃ incubator. One sample was taken every 10 days to analyze sensory quality, water content, browning index, and microbiological indicators. The experimental period was 60 days. The water content was determined by placing 5 mL of Korla fragrant pear compound jam in the center of absorbent paper using a syringe. After 30 minutes, the size of the water ring formed on the absorbent paper was observed (the smaller the water ring, the lower the water content of the jam). The browning index was determined by taking 10 g of jam, adding 20 mL of 95% ethanol, shaking, and extracting by oscillation for 60 minutes. Then, it was centrifuged at 4000 r / min for 20 minutes, and the absorbance of the supernatant was measured at 420 nm using a spectrophotometer. The total bacterial count was determined according to GB 4789.2-2022 National Food Safety Standard for Microbiological Examination of Food - Determination of Total Colony Count.

[0066] Depend on Figure 1 , Figure 2 , Figure 3 and Figure 4It can be seen that with the extension of storage time, the sensory quality of the Korla fragrant pear compound jam prepared in Example 9 and Comparative Examples 6-13 deteriorated, and the browning index, water separation degree, and total bacterial count tended to increase, indicating that the overall quality of the Korla fragrant pear compound jam gradually deteriorated with the extension of storage time. However, the sensory quality, browning index, water separation degree, and total bacterial count of Example 9 were significantly better than those of Comparative Examples 6-13. This indicates that the present invention, through calcium ions combined with rennet, causes casein to undergo a coagulation reaction to initially form a uniform and stable protein gel network, effectively binding fruit pulp particles, sugars, and water in the pulp, thus solving the problem of low... The lack of sucrose in the sugar system leads to a loose texture and rough mouthfeel. At the same time, the composite modified pear peel dietary fiber, pectin and protein gel network further intertwine through multiple actions to form a denser and more stable composite gel skeleton, which enhances the overall structural strength of the jam. Therefore, this composite gel system can convert free water in the jam system into bound water. It can not only effectively inhibit water migration, pulp sedimentation and sugar precipitation during the production and processing stage, but also reduce the water activity of the jam during long-term storage at 4℃, significantly slow down the browning process, inhibit the growth and reproduction of microorganisms, and delay the deterioration of sensory quality.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the technical solutions of the present invention, shall still fall within the scope of protection of the present invention.

Claims

1. A method for preparing a Korla fragrant pear compound jam, characterized in that, Includes the following steps: Step 1. Select fresh, high-quality, mold-free Korla fragrant pears, wash them clean, peel and core them, and cut them into chunks to obtain fragrant pear pieces; Step 2. After treating the pear pieces for color protection, add water to make pulp and adjust the pH to 5.0-5.5 to obtain Korla pear pulp; Step 3. Add casein powder and calcium chloride to the Korla fragrant pear pulp and mix well. Then add rennet to perform coagulation treatment to obtain pretreated Korla fragrant pear pulp. Step 4. The pre-treated Korla fragrant pear pulp is heated and concentrated, then mixed with compound modified fragrant pear peel dietary fiber, pectin, erythritol and citric acid, and boiled until the soluble solids content is 35-45%. After filling and sterilization, Korla fragrant pear compound jam is obtained.

2. The method for preparing a Korla fragrant pear compound jam according to claim 1, characterized in that: In step 2, the color protection treatment involves immersing the pear pieces in D-isoascorbic acid at a mass fraction of 0.1-0.25%; the ratio of pear pieces to water in the pulping process is 1g:(0.5-2)mL.

3. The method for preparing a Korla fragrant pear compound jam according to claim 1, characterized in that: In step 3, the amount of casein powder added is 3.5-10%, the amount of calcium chloride added is 0.1-0.25%, and the amount of rennet added is 0.01-0.06%, all based on the volume of Korla fragrant pear pulp.

4. The method for preparing a Korla fragrant pear compound jam according to claim 1, characterized in that: The conditions for coagulation treatment in step 3 are a coagulation temperature of 40-55℃ and a coagulation time of 15-25 min.

5. The method for preparing a Korla fragrant pear compound jam according to claim 1, characterized in that: In step 4, the amount of dietary fiber added to the composite modified pear peel is 0.5-3%, the amount of pectin added is 0.3-0.8%, the amount of erythritol added is 3.5-6.5%, and the amount of citric acid added is 0.15-0.28%, all based on the volume of Korla pear pulp.

6. The method for preparing a Korla fragrant pear compound jam according to claim 1, characterized in that, The preparation method of the composite modified pear peel dietary fiber in step 4 includes the following steps: S1. The peel of Korla fragrant pear is dried, pulverized and made into fragrant pear peel powder. The fragrant pear peel powder is mixed with choline chloride-glycerol eutectic solvent, and then xylanase is added for enzymatic hydrolysis. After separation, concentration and drying, Korla fragrant pear peel dietary fiber is obtained. S2. Disperse Korla fragrant pear dietary fiber and tripolyphosphate in water at a mass ratio of (5-10):1 and adjust the pH to 6.5-7.

5. React at 70-85℃ for 2-4 hours, cool down to 35-45℃ and adjust the pH to 5.2-6.5, add ferulic acid and tyrosinase for 2-5 hours, and then obtain the composite modified fragrant pear peel dietary fiber by alcohol precipitation, washing and drying.

7. The method for preparing a Korla fragrant pear compound jam according to claim 6, characterized in that, In the S1 eutectic solvent, the molar ratio of choline chloride to glycerol is 1:(1-3), and the water content is 30-45%. The amount of xylanase added is 0.5-2% based on the mass of pear peel powder. The conditions for xylanase hydrolysis are a temperature of 45-55℃, a pH of 4.5-6.0, and a time of 1.5-3h.

8. The method for preparing a Korla fragrant pear compound jam according to claim 6, characterized in that, The amount of ferulic acid added in S2 is 0.5-2%, and the amount of tyrosinase added is 100-500 U / g, both based on the dietary fiber weight of Korla fragrant pear peel.

9. Korla fragrant pear compound jam prepared by the method according to any one of claims 1-8.

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