Method for improving browning of kiwi fruit can pulp

Abstract

The invention relates to the technical field of can processing, in particular to a method for improving pulp browning of canned kiwi fruits. The preparation method comprises the following steps: S1, cleaning, peeling and dicing kiwi fruits, soaking the kiwi fruits in a color protection solution, blanching the kiwi fruits, and cooling the kiwi fruits; s2, soaking the cooled blocky kiwi fruits in a D-erythorbic acid solution, and sequentially canning, injecting sweet water, sealing, sterilizing and cooling after soaking is finished; the color protection liquid in the step S1 comprises the following components: D-erythorbic acid, citric acid, calcium chloride and psicose. According to the method provided by the invention, browning of the kiwi fruit pulp can be remarkably inhibited, the fresh green color and complete form of the pulp can be kept, nutrition loss is reduced, the process is simple, the flow is standard, complex equipment is not needed, the method is suitable for industrial large-scale production, and the prepared can is long in shelf life, excellent in taste, safe and healthy.

Description

Technical Field

[0001] This invention relates to the field of canning technology, and in particular to a method for improving browning of canned kiwifruit flesh. Background Technology

[0002] Kiwifruit (scientific name: *Actinidia chinensis* Planch.), also known as Chinese gooseberry, is mostly oval in shape. Its skin is initially yellowish-brown, turning reddish-brown when ripe, and covered with dense fuzz. The flesh can be eaten directly. It is a tender, nutritious, and delicious fruit. Kiwifruit has a soft texture and a sweet and sour taste, and is often hailed as the "King of Fruits." Besides being rich in vitamins C, A, and E, as well as potassium, magnesium, and fiber, it is also rich in nutrients less common in other fruits—folic acid, carotene, calcium, lutein, amino acids, and natural inositol. Its nutritional value far exceeds that of other common fruits: its calcium content is 2.6 times that of grapefruit, 17 times that of apples, and 4 times that of bananas; its vitamin C content is twice that of oranges.

[0003] However, ripe kiwifruit has high cell activity, and prolonged refrigeration can cause it to become sour and overly soft. At room temperature, it typically only lasts 3-5 days before overripening and spoiling. To achieve long-term preservation of kiwifruit and extend its shelf life, processing it into canned goods has become the most common industrial method.

[0004] However, because kiwifruit pulp contains abundant polyphenols, these substances are prone to browning during canning, resulting in a dark color and poor taste in the finished canned fruit, which seriously affects the sensory quality of the product. Therefore, how to improve the browning problem of kiwifruit pulp during the canning process and enhance the quality stability of the finished canned fruit has become a key technical problem that urgently needs to be solved in the current kiwifruit canning industry. Summary of the Invention

[0005] The purpose of this invention is to provide a method for improving the browning of kiwifruit flesh in canned fruit production, thereby addressing the problem of browning in the flesh during the canning process.

[0006] To achieve the above objectives, the present invention provides a method for improving browning of canned kiwifruit pulp, comprising the following steps: S1. Wash, peel, and cut the kiwifruit into pieces, then soak them in the color-protecting solution, followed by blanching and cooling. S2. After cooling, place the kiwifruit pieces in a D-isoascorbic acid solution for soaking. After soaking, proceed with canning, adding sugar water, sealing, sterilization, and cooling in sequence. The color-protecting liquid described in S1 contains the following components: D-isoascorbic acid, citric acid, calcium chloride, and allulose.

[0007] In this invention, the kiwifruit mentioned in S1 is a fresh kiwifruit with no external damage.

[0008] In this invention, the cleaning process described in S1 includes: washing fresh kiwifruit with no external damage using water, immersing it in a sodium bicarbonate solution with a mass concentration of 10%-12% for 2-3 minutes at a temperature of 100-105°C, rinsing it with water to remove the sodium bicarbonate solution, and then peeling it.

[0009] In this invention, the components of the color-protecting liquid described in S1, based on 100% by mass, include: 0.3%-0.5% D-isoascorbic acid, 0.2%-0.4% citric acid, 0.1%-0.2% calcium chloride, 0.1%-0.2% allulose, and the remainder is water.

[0010] In this invention, the soaking temperature in S1 is 18-30°C and the soaking time is 30-60 min.

[0011] In this invention, the rinsing temperature in S1 is 90-100℃, and the rinsing time is 2-4 minutes.

[0012] In this invention, the cooling method described in S1 is as follows: the blanched kiwifruit is placed in a cooling tank and rinsed with water for 1-2 minutes; the temperature of the water is 10-15℃.

[0013] In this invention, the mass concentration of the D-isoascorbic acid solution in S2 is 0.5‰-1‰; the soaking temperature is 1-5℃, and the soaking time is 15-20min.

[0014] In this invention, the sugar water in S2 comprises, by mass percentage: 30%-35% white sugar, 0.2%-0.4% citric acid, 0.01%-0.02% D-isoascorbic acid, and the remainder is water.

[0015] In this invention, the mass ratio of the blocky kiwifruit to the sugar water in S2 is 1:4-8.

[0016] In this invention, the sterilization temperature is 90-100℃ and the sterilization time is 10-20 minutes.

[0017] In this invention, the target cooling temperature in S2 is 35-40°C.

[0018] The present invention has the following beneficial effects: This invention provides a method for improving browning of kiwifruit flesh in canned fruit, comprising the following steps: S1, washing, peeling, and cutting the kiwifruit into pieces, then soaking them in a color-protecting solution, followed by blanching and cooling; S2, soaking the cooled kiwifruit pieces in a D-isoascorbic acid solution, and after soaking, sequentially canning, adding sugar water, sealing, sterilizing, and cooling; the color-protecting solution in S1 comprises: D-isoascorbic acid, citric acid, calcium chloride, and allulose.

[0019] This invention involves soaking chunks of kiwifruit in a color-protecting solution before blanching, which can improve the browning phenomenon that occurs in the kiwifruit flesh during the blanching process. The D-isoascorbic acid in the color-protecting solution can quickly remove reactive oxygen species in the fruit pulp, inhibit the activity of polyphenol oxidase, and block the oxidation of polyphenols into brown substances. Citric acid can adjust the pH of the color-protecting solution to acidic, further inhibiting the activity of polyphenol oxidase and enhancing the antioxidant and color-protecting effect of D-isoascorbic acid. On the other hand, it can neutralize alkaline substances in the fruit pulp, reducing the occurrence of non-enzymatic browning (such as Maillard reaction). Calcium chloride can bind with pectin in the cell walls of the fruit pulp, enhancing the rigidity and stability of the cell walls, reducing the exposure of browning substrates caused by cell rupture during blanching, and reducing the problems of softening and deformation of the fruit pulp in subsequent processing, maintaining the integrity of the fruit pulp, and indirectly reducing local browning caused by fruit pulp damage. Allulose itself has certain antioxidant properties, which can synergistically enhance the anti-browning effect with D-isoascorbic acid. It is also chemically stable and not easily decomposed during subsequent blanching, and can play a long-term auxiliary color-protecting role.

[0020] This invention involves cooling the fruit after blanching in S1, which can quickly lower the temperature of the fruit pulp and avoid the problem of "secondary browning" caused by residual heat from blanching. At the same time, it reduces the loss of nutrients caused by high temperature, achieving the dual effect of color protection and preservation of fruit pulp nutrients.

[0021] In the present invention S2, the cooled kiwifruit blocks are soaked in D-isoascorbic acid solution, which can form an antioxidant protective film on the surface of the fruit pulp. During subsequent canning, sugar water injection and sealing, the oxidation reaction when the fruit pulp comes into contact with air and sugar water can be reduced, and local browning of the fruit pulp surface can be avoided.

[0022] The present invention further specifies that the soaking temperature in S2 is 1-5℃ and the soaking time is 15-20min. Under these temperature and time conditions, the self-oxidation and inactivation of D-isoascorbic acid can be avoided, and the further loss of heat-sensitive nutrients such as vitamin C and polyphenols in the pulp can be reduced.

[0023] This invention further specifies that the sugar syrup in S2 comprises, by mass percentage: 30%-35% white sugar, 0.2%-0.4% citric acid, 0.01%-0.02% D-isoascorbic acid, and the remainder being water. The 30%-35% white sugar creates a high osmotic pressure environment within the can, inhibiting the growth of bacteria and extending the shelf life of the canned goods. Simultaneously, it neutralizes the sour taste of the kiwifruit pulp, enhancing the overall flavor of the canned goods. D-isoascorbic acid continuously removes reactive oxygen species from the sugar syrup and fruit surface, blocking oxidation reactions after contact between the fruit and the sugar syrup, reducing browning of the fruit during long-term storage, and ensuring color stability during canned storage. Citric acid adjusts the pH of the sugar syrup to an acidic range, enhancing the stability and antioxidant activity of D-isoascorbic acid, strengthening the color-protecting effect. Simultaneously, the acidic environment further inhibits the growth of bacteria, assisting the white sugar in achieving dual antibacterial effects.

[0024] The present invention provides a method for improving browning of canned kiwifruit flesh. The process is simple, the raw materials are readily available, no complicated equipment is required, and it is convenient for industrial mass production.

[0025] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0026] Figure 1 This is a comparison chart of the color difference (ΔE) values ​​of canned kiwifruit prepared in the embodiments and comparative examples of the present invention after being stored in an environment of 25°C and 65% relative humidity for 30 days. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should be understood in their ordinary sense by those skilled in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.

[0028] Example 1 S1. Wash fresh kiwifruit with water to remove any surface damage. Place the kiwifruit in a 10% sodium bicarbonate solution at 105°C for 2 minutes. Rinse with water to remove the sodium bicarbonate solution. Peel and cut the kiwifruit into 1.2cm thick pieces. Place the pieces in a color-protecting solution (color-protecting solution components: D-isoascorbic acid 0.3%, citric acid 0.4%, calcium chloride 0.2%, allulose 0.1%, water 99%) at 18°C ​​for 60 minutes. Then blanch the kiwifruit at 100°C for 2 minutes. Place the blanched kiwifruit in a cooling tank and rinse with 15°C water for 2 minutes to cool. S2. Place the cooled kiwifruit chunks in a 0.5‰ D-isoascorbic acid solution and soak them at 5°C for 20 minutes. After soaking, pack them into cans, add sugar syrup (sugar syrup composition: 30% white sugar, 0.2% citric acid, 0.01% D-isoascorbic acid, 69.79% water, with a mass ratio of 1:5 between the kiwifruit chunks and the sugar syrup), seal them, and then sterilize them at 100°C for 10 minutes and cool them to 35°C.

[0029] Example 2 S1. Wash fresh kiwifruit with water to remove any surface damage. Place the kiwifruit in a 10% sodium bicarbonate solution and soak at 100°C for 3 minutes. Rinse with water to remove the sodium bicarbonate solution. Peel and cut the kiwifruit into 1.2cm thick pieces. Place the pieces in a color-protecting solution (color-protecting solution components: D-isoascorbic acid 0.5%, citric acid 0.2%, calcium chloride 0.1%, allulose 0.2%, water 99%) and soak at 25°C for 45 minutes. Then blanch the kiwifruit at 95°C for 2 minutes. Place the blanched kiwifruit in a cooling tank and rinse with 10°C water for 1 minute to cool. S2. Place the cooled kiwifruit chunks in a D-isoascorbic acid solution with a mass concentration of 0.8‰ and soak at 3°C ​​for 18 minutes. After soaking, pack the kiwifruit chunks into cans, add sugar syrup (sugar syrup composition: 35% white sugar, 0.4% citric acid, 0.02% D-isoascorbic acid, 64.58% water, with a mass ratio of 1:8 between the kiwifruit chunks and the sugar syrup), seal, and then sterilize at 95°C for 15 minutes and cool to 40°C.

[0030] Example 3 S1. Wash fresh kiwifruit with water to remove any surface damage. Place the kiwifruit in a 10% sodium bicarbonate solution and soak at 100°C for 3 minutes. Rinse with water to remove the sodium bicarbonate solution. Peel and cut the kiwifruit into 1.2cm thick pieces. Place the pieces in a color-protecting solution (color-protecting solution components: D-isoascorbic acid 0.4%, citric acid 0.3%, calcium chloride 0.1%, allulose 0.2%, water 99%) and soak at 30°C for 50 minutes. Then blanch the kiwifruit at 90°C for 4 minutes. Place the blanched kiwifruit in a cooling tank and rinse with 10°C water for 1 minute to cool. S2. Place the cooled kiwifruit chunks in a D-isoascorbic acid solution with a mass concentration of 1‰ and soak at 1°C for 15 minutes. After soaking, pack the kiwifruit chunks into cans, add sugar syrup (sugar syrup composition: 33% white sugar, 0.3% citric acid, 0.02% D-isoascorbic acid, 66.68% water, with a mass ratio of 1:4 between the kiwifruit chunks and the sugar syrup), seal, and then sterilize at 100°C for 10 minutes and cool to 35°C.

[0031] Example 4 S1. Wash fresh kiwifruit with water to remove any surface damage. Place the kiwifruit in a 12% sodium bicarbonate solution and soak at 100°C for 3 minutes. Rinse with water to remove the sodium bicarbonate solution. Peel and cut the kiwifruit into 1.2cm thick pieces. Place the pieces in a color-protecting solution (color-protecting solution components: D-isoascorbic acid 0.5%, citric acid 0.2%, calcium chloride 0.1%, allulose 0.2%, water 99%) and soak at 30°C for 30 minutes. Then blanch the kiwifruit at 95°C for 2 minutes. Place the blanched kiwifruit in a cooling tank and rinse with 10°C water for 1 minute to cool. S2. Place the cooled kiwifruit chunks in a D-isoascorbic acid solution with a mass concentration of 1‰ and soak at 2°C for 18 minutes. After soaking, pack the kiwifruit chunks into cans, add sugar syrup (sugar syrup composition: 35% white sugar, 0.3% citric acid, 0.02% D-isoascorbic acid, 64.68% water, with a mass ratio of 1:6 between the kiwifruit chunks and the sugar syrup), seal, and then sterilize at 90°C for 20 minutes, and cool to 35°C.

[0032] Comparative Example 1 This method is basically the same as the one provided in Example 1 for improving browning of canned kiwifruit flesh, except that the color-protecting solution soaking treatment is not performed in S1.

[0033] Comparative Example 2 This method is essentially the same as the one provided in Example 1 for improving browning of canned kiwifruit flesh, except that cooling in S1 is not performed.

[0034] Comparative Example 3 This method is essentially the same as the one provided in Example 1 for improving browning of canned kiwifruit flesh, except that it does not involve soaking in the D-isoascorbic acid solution in S2.

[0035] Comparative Example 4 This method is basically the same as the one provided in Example 1 for improving browning of canned kiwi fruit flesh, except that the sugar water in S2 is not used and the composition is 30% white sugar and 70% water.

[0036] Color measurement: The canned kiwifruit obtained in the above examples and comparative examples were stored at 25°C and 65% relative humidity for 30 days. The L, a, b values ​​and color difference value ΔE of the canned kiwifruit pulp were measured using a colorimeter. The results are shown in Table 1.

[0037] L represents brightness (lightness). The larger the L value, the brighter the fruit flesh; the smaller the L value, the less bright the fruit flesh. a represents redness / greenness. The smaller the a value, the more the color leans towards green (positive value indicates redness, negative value indicates greenness). b represents yellowness / blueness. The larger the b value, the more the color leans towards yellow (positive value indicates yellowness, negative value indicates blueness). ΔE is the color difference value.

[0038] Table 1 Results of color measurement

[0039] As shown in Table 1, after 30 days of storage, the a values ​​of Examples 1-4 were all negative, the b values ​​were all positive, the L values ​​were high, and the ΔE values ​​were small. This indicates that the kiwifruit preserves prepared by the method provided by this invention have a bright green flesh color, high brightness, stable color, and low browning degree. In contrast, for the comparative examples, the a value of Comparative Example 1 (without soaking in S1 color-protecting solution) was positive (3.26), the b value increased significantly, the L value decreased significantly, and the ΔE value increased significantly, indicating that the flesh underwent severe browning and showed a distinct brown color. Although the a values ​​of Comparative Example 2 (without S1 cooling), Comparative Example 3 (without S2 soaking), and Comparative Example 4 (sugar water without citric acid and D-isoascorbic acid) were negative, their absolute values ​​were much smaller than those of the examples, and their ΔE values ​​were significantly larger than those of the examples. This indicates that the absence of any process step or component would lead to a decrease in the color-protecting effect and different degrees of browning in the flesh.

[0040] The comparison diagram of ΔE is as follows: Figure 1 As shown. From Figure 1 It can be more clearly seen that the color difference value of the canned kiwifruit prepared by the method of the present invention is lower than that of the comparative example, and the differences between the various examples are small, indicating that the preparation method of the present invention is stable.

[0041] The vitamin C content in the above-mentioned canned kiwifruit was determined according to GB 5009.86-2016, and the results are shown in Table 2.

[0042] Table 2. Test results of vitamin C content in canned kiwifruit

[0043] Table 2 shows that the vitamin C content in Examples 1-4 is at a high level, indicating that the method provided by this invention can effectively reduce the loss of vitamin C in kiwifruit pulp and fully retain its core nutritional value. Comparative Example 1 (without soaking in S1 color-protecting solution) has the lowest vitamin C content, indicating that soaking in S1 color-protecting solution not only inhibits browning but also effectively protects vitamin C from oxidation and loss. Comparative Example 2 (without S1 cooling) shows a significant decrease in vitamin C content due to further oxidation caused by residual heat from blanching. Comparative Example 3 (without S2 soaking) and Comparative Example 4 (sugar water without antioxidant components) also show significant vitamin C loss due to the lack of subsequent antioxidant protection.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for improving browning of canned kiwifruit flesh, characterized in that, Includes the following steps: S1. Wash, peel, and cut the kiwifruit into pieces, then soak them in the color-protecting solution, followed by blanching and cooling. S2. After cooling, place the kiwifruit pieces in a D-isoascorbic acid solution for soaking. After soaking, proceed with canning, adding sugar water, sealing, sterilization, and cooling in sequence. The color-protecting liquid described in S1 contains the following components: D-isoascorbic acid, citric acid, calcium chloride, and allulose.

2. The method for improving browning of canned kiwifruit pulp according to claim 1, characterized in that, The color-protecting liquid described in S1 comprises, by mass, 0.3%-0.5% D-isoascorbic acid, 0.2%-0.4% citric acid, 0.1%-0.2% calcium chloride, 0.1%-0.2% allulose, with the remainder being water.

3. The method for improving browning of canned kiwifruit pulp according to claim 1, characterized in that, The soaking temperature described in S1 is 18-30℃, and the soaking time is 30-60 minutes.

4. The method for improving browning of canned kiwifruit pulp according to claim 1, characterized in that, The rinsing temperature described in S1 is 90-100℃, and the rinsing time is 2-4 minutes.

5. The method for improving browning of canned kiwifruit pulp according to claim 1, characterized in that, The cooling method described in S1 is as follows: place the blanched kiwifruit in a cooling tank and rinse it with water for 1-2 minutes; the temperature of the water is 10-15℃.

6. The method for improving browning of canned kiwifruit pulp according to claim 1, characterized in that, The mass concentration of the D-isoascorbic acid solution in S2 is 0.5‰-1‰; The soaking temperature is 1-5℃, and the soaking time is 15-20 minutes.

7. The method for improving browning of canned kiwifruit pulp according to claim 1, characterized in that, The sugar solution in S2 contains, by mass percentage: 30%-35% white sugar, 0.2%-0.4% citric acid, 0.01%-0.02% D-isoascorbic acid, and the remainder is water.

8. The method for improving browning of canned kiwifruit pulp according to claim 1, characterized in that, The mass ratio of the kiwifruit chunks to the sugar water described in S2 is 1:4-8.

9. The method for improving browning of canned kiwifruit pulp according to claim 1, characterized in that, The sterilization temperature is 90-100℃, and the sterilization time is 10-20 minutes.

10. The method for improving browning of canned kiwifruit pulp according to claim 1, characterized in that, The target cooling temperature in S2 is 35-40℃.

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