Fresh-keeping method for prolonging shelf life of southern red pears after refrigeration

Abstract

The invention discloses a fresh-keeping method for prolonging shelf life of Nanhong pears after refrigeration, which comprises the following steps: picking Nanhong pears in an optimal coloring period, selecting Nanhong pear fruits with a fruit surface coloring rate of more than 80% and a single fruit weight of 85-100g, loading the Nanhong pear fruits into a packaging box with a shockproof effect, putting one 1-MCP fresh-keeping bag into the packaging box, sleeving the packaging box with a microporous bag, tying the packaging box, and mailing the packaging box from a base to a destination. After differential pressure precooling, storing in a refrigeration house, taking out the packaging box filled with the southern red pears from the refrigeration house within 6 months, placing at normal temperature for 2-4 hours, opening the microporous bag for commercial packaging, directly selling, and enabling the shelf life to be more than 14 days; when the southern red pears are stored for 7-10 months, the southern red pears which are delivered from the warehouse need to be recovered to the room temperature, the southern red pears are soaked in a composite preservative solution for 2-3 minutes and then blow-dried, the southern red pears are sold after commercialized packaging, and the shelf life is 7 days or The Nanhong pears treated by the method disclosed by the invention are red in fruit, good in quality and capable of meeting the requirements of consumers.

Description

Technical Field

[0001] The present invention belongs to the technical field of agricultural product storage and preservation, and particularly relates to a green preservation method for the harvesting time of Nanhong pears, shockproof packaging, 1-MCP treatment, differential pressure precooling, low-temperature storage, and the development of a composite preservative. Background Art

[0002] Nanguo pears are a variety of Ussurian pears with distinct local characteristics in Liaoning Province. The cultivation area in Anshan alone exceeds 800,000 mu. Their pulp is soft, sweet and sour, with a strong aroma, and the quality is excellent. After the Nanguo pear fruit matures, it is generally yellow. In recent years, a bud mutation of Nanguo pears has been discovered in cultivation and named Nanhong pears after approval. The peel of Nanhong pears begins to turn red in the later stage of fruit development and shows a yellowish-red color after maturity, which is deeply loved by consumers. Now, the price of Nanhong pears in the market is 2 to 3 times higher than that of ordinary Nanguo pears. However, due to the large yield of Nanhong pears and the concentrated harvesting period, the harvested Nanhong pears cannot be sold in time and need to be stored or the shelf life needs to be extended to relieve the sales pressure. Therefore, it is of great significance to study a preservation method to delay or extend its storage or shelf life.

[0003] 1-Methylcyclopropene (1-MCP) is an ethylene receptor inhibitor that delays the senescence of fruits and vegetables and enhances the resistance to physiological or infectious diseases. It is widely used because of its low cost, safety, non-toxicity, and low usage amount to achieve the purpose of extending the storage period and maintaining the fruit quality. Differential pressure precooling uses the suction of a fan to generate a pressure difference in the fruit and vegetable tent, forcing cold air to flow through the entire device system from bottom to top, taking away the heat on the surface of the fruits and vegetables, thereby achieving precooling and temperature reduction. The efficiency of differential pressure precooling is 2 to 3 times that of static precooling. Natamycin is a natural preservative, and the most popular reason is that it has no odor and color. After a comprehensive evaluation by the World Health Organization (WHO), the European Food Safety Authority (EFSA), and the US Food and Drug Administration (FDA), it is listed as Generally Recognized as Safe (GRAS), and the European Union regards it as a natural preservative. L-Aspartic acid has excellent flavor enhancement and preservation effects and is widely used as a flavor enhancer and preservative in the food industry. Seaweed oligosaccharide is an eco-friendly water-soluble non-toxic plant biostimulant that can accelerate plant development and prevent plant diseases, and has a potential protective effect during fruit storage, enhancing the plant's resistance to abiotic stress, stimulating the plant's resistance to diseases, and extending the plant's shelf life. By treating with 1-MCP, differential pressure precooling, and low-temperature storage to improve the quality of Nanhong pears during the storage period, combined with the use of a composite preservative after cold storage, it is expected to extend the shelf life of Nanhong pears after cold storage. Summary of the Invention

[0004] The objective of the present invention is to fill the gaps in previous research and provide a fresh-keeping method for extending the shelf life of Nanhong pears after cold storage. The present invention provides a green fresh-keeping method involving the harvesting time of Nanhong pears, shock-proof packaging, 1-MCP treatment, differential pressure precooling, low-temperature storage, and the development of a composite fresh-keeping agent.

[0005] To achieve the above objective, the present invention discloses the following technical content: A fresh-keeping method for extending the shelf life of Nanhong pears after cold storage, characterized by the following steps: Step 1: Harvest Nanhong pears at the optimal coloring stage, and select Nanhong pear fruits with a fruit surface coloring rate of 80% and a single fruit weight of 85 - 100 g. Step 2: Pack the selected Nanhong pears into a shock-proof packaging box, with each box containing 2.2 - 2.4 kg of fruits. After placing 1 bag of 1-MCP fresh-keeping package and covering it with a microporous bag and tying the mouth, mail it from the base to the destination, and then put it into the cold storage after differential pressure precooling. Step 3: After 6 months of cold storage, take out the packaging box containing Nanhong pears from the cold storage. After placing it at room temperature for 2 - 3 hours, open the microporous bag, conduct commercial packaging, and then directly sell it. The shelf life is more than 14 days. Step 4: When storing for 7 - 10 months, after restoring the Nanhong pears taken out of the cold storage to room temperature, soak them in the composite fresh-keeping agent solution for 2 - 3 minutes and then dry them, conduct commercial packaging, and then sell them. The shelf life is more than 7 days. The formula of the composite fresh-keeping agent is: 0.85 g / L natamycin + 2 g / L L-aspartic acid calcium + seaweed oligosaccharide diluted 850 times.

[0006] Among them, for the 1-MCP treatment time and treatment method, it is recommended that the 1-MCP treatment be completed within 3 days after the harvest of Nanhong pears. Regarding the treatment method, note that it needs to be wetted in pure water before putting the 1-MCP fresh-keeping package to facilitate the volatilization of 1-MCP. The material of the microporous bag is PE, with a thickness of 16 - 20 μm, an average pore diameter of 10 - 15 μm, and a pore density of 25 - 36 pores / mm 2 。

[0007] For the differential pressure precooling described in the present invention, the wind speed is 1.0 - 2.0 m / s, and the differential pressure precooling time is 8 - 10 h. During differential pressure precooling, the temperature drops from 25 - 30 °C to -1 - 0 °C. Additionally, the temperature of the cold storage is controlled at -1 - 0 °C.

[0008] It should be noted that: After taking out the Nanhong pears from the cold storage, the microporous bag cannot be directly opened to avoid the appearance of water droplets on the surface of the Nanhong pear fruits due to the temperature difference. It is recommended to determine the placement time based on the temperature difference. Generally, the higher the temperature, the longer the placement time. Usually, in an environment of 20 - 25 °C, the placement time is about 3 hours.

[0009] The present invention further discloses the application of a fresh-keeping method for extending the shelf life of Nanhong pears after cold storage in improving the fruit quality and commercial value of Nanhong pears; the improvement of the fruit quality of Nanhong pears refers to inhibiting the browning, softening, and rotting phenomena of the fruits during the shelf life after cold storage of Nanhong pears. The experimental results show that: the Nanhong pear fruits treated by the method of the present invention have a red charm, and there is no browning phenomenon of the fruits after cold storage. The hardness of the fruits can also be effectively maintained. The normal temperature shelf life of Nanhong pears within 10 months of cold storage is more than 7 days, effectively maintaining the quality of Nanhong pear fruits and improving the commercial value.

[0010] The present invention mainly solves the problems that Nanhong pears are prone to browning, softening, and rotting during the shelf life after cold storage, and focuses on investigating the dual-control fresh-keeping method of controlling physiology with 1-MCP after harvest and inhibiting diseases after cold storage. The main difficulty lies in determining the treatment time of 1-MCP and the compound fresh-keeping agent formula.

[0011] The positive effects of a fresh-keeping method for extending the shelf life of Nanhong pears after cold storage disclosed by the present invention compared with the prior art are as follows: (1) The compound fresh-keeping agent formula obtained in this patent is based on single factors, with the peel browning index as an indicator, and combined with the comparison of sensory quality. Through response surface experiments and multiple verification experiments, the compound fresh-keeping agent formula is screened out, and all are composed of safe and green reagents. Compared with the existing fresh-keeping agents, the shelf life after 6 months of cold storage is extended to more than 14 days.

[0012] (2) Harvest time, shock-proof packaging, 1-MCP treatment, differential pressure rapid pre-cooling, low-temperature storage combined with compound fresh-keeping agent treatment after cold storage can maximize the guarantee of the red charm of Nanhong pear fruits, reduce the damage to the fruits caused by logistics, inhibit the respiration intensity and ethylene production rate, reduce the browning and disease occurrence of the fruits, and extend the normal temperature shelf life after cold storage. Description of the Drawings

[0013] Figure 1 Effects of different treatments on the peel color change index of Nanhong pears during cold storage; Figure 2 Effects of different treatments on the peel browning index and hardness of Nanhong pears during the shelf life after cold storage. Detailed Embodiments

[0014] The present invention will be described below through specific implementation examples. Unless otherwise specified, the technical means used in the present invention are all methods well-known to those skilled in the art. In addition, the implementation examples should be understood as illustrative and not limiting the scope of the present invention. The essence and scope of the present invention are only defined by the claims. For those skilled in the art, various changes or modifications made to the harvesting time, shock-proof packaging, 1-MCP treatment, microporous bag parameters, differential pressure precooling parameters, and compound preservative formula in these implementation examples without departing from the essence and scope of the present invention also fall within the protection scope of the present invention. The shock-proof packaging box, 1-MCP preservation package, microporous bag, natamycin, L-aspartic acid, and seaweed oligosaccharide used in the present invention are all commercially available. Example

[0015] Application comparison of 1-MCP treatment in the preservation of Yunnan Red Pear Harvest Yunnan Red Pears at the optimal coloring stage, and select Yunnan Red Pear fruits with a fruit surface coloring rate of over 80% and a single fruit weight of about 90 g; put the selected Yunnan Red Pears into a shock-proof packaging box (each box contains about 2.3 kg of fruits), put 1 bag of 1-MCP preservation package on the 3rd day after harvest, then put on a microporous bag and tie the mouth, mail from the base to the destination, the wind speed of differential pressure precooling is 1.0 m / s, the time of differential pressure precooling is 10 h, store in a -0.5 °C cold storage, and measure after standing at room temperature for 3 hours after 300 days of cold storage. Use no 1-MCP preservation package as the CK. From Figure 1 It can be seen that in the initial stage of cold storage, the surface colors of Yunnan Red Pears with different treatments are the same. As the cold storage time is postponed, the dark green on the fruit peel surface gradually turns to golden yellow. Among them, the conversion rate of the CK group is the fastest, showing an obvious increase at 180 days of cold storage, and the fruit peel color conversion index rises to 48%. By 300 days, it has reached 94%, and at this time, the fruit peels of most fruits have turned golden yellow; there is no obvious change in the fruit peel color of the 1-MCP treatment, indicating that 1-MCP can delay the fruit peel color conversion and ripening of Yunnan Red Pear. Example

[0016] Screening of compound preservative formula Harvest Yunnan Red Pears at the optimal coloring stage, and select Yunnan Red Pear fruits with a fruit surface coloring rate of over 80% and a single fruit weight of about 90 g; put the selected Yunnan Red Pears into a shock-proof packaging box (each box contains about 2.3 kg of fruits), mail from the base to the destination, perform differential pressure precooling on Yunnan Red Pears, the wind speed of differential pressure precooling is 2.0 m / s, the time of differential pressure precooling is 8 h, store in a -0.5 °C cold storage, take out after cold storage for different times, stand at room temperature for 2 hours, then soak in different preservatives for 2 minutes and air dry, and store at room temperature.

[0017] Single-factor experiment: After 30 days of storage, the experimental scheme is shown in Table 1; (2)Response surface optimization: After 60 days of storage, the experimental plan is shown in Table 2.

[0018]

[0019]

[0020] The results of single-factor experiments are shown in Table 3. According to the ranking results of the principal component scores, they are: natamycin, calcium L-aspartate, seaweed oligosaccharide, calcium chloride, ε-polylysine, melatonin, compound plant polypeptide, and salicylic acid. The three consecutive concentration treatment groups selected for the next round of experiments are: 0.8, 1.0, and 1.2 g / L of natamycin, 1.5, 2.0, and 2.5 g / L of calcium L-aspartate, and seaweed oligosaccharide diluted 500, 1000, and 1500 times.

[0021]

[0022] The preservative for Yunnan red pears was optimized by the Box-Behnken experimental design in the response surface method. Combinatorial experiments were carried out on natamycin, calcium L-aspartate, and seaweed oligosaccharide. The results had a significant effect on the browning degree of the peel of Yunnan red pears. The results of the 3-factor and 3-level response surface experiments are shown in Table 4.

[0023] The data in Table 4 were fitted by quadratic multiple regression using Design-Expert 13 software. Taking natamycin (A), calcium L-aspartate (B), and seaweed oligosaccharide (C) as independent variables and the browning index of the peel (R1) as the response value, a multiple quadratic regression equation was established. As shown in Table 5, the determination coefficient of the equation is R 2 = 0.90454, and the adjusted determination coefficient is R 2 Adj= 0.7818. The P value of the model is 0.0077, which is less than 0.01, indicating that the result is significant; at the same time, the P value of the lack-of-fit term is 0.9161, which is greater than 0.05, showing non-significance. Through data analysis, it can be seen that the established model is effective and highly reliable.

[0024] Table 4 Response surface plan and results Test serial number <![CDATA[Natamycin / (g·L -1 )]]> <![CDATA[Calcium L-aspartate / (g·L -1 )]]> Alginate oligosaccharide / dilution times R1 (peel browning index) 1 0.8 1.5 1000 16.7 2 1.2 1.5 1000 16.7 3 0.8 2.5 1000 16.7 4 1.2 2.5 1000 16.7 5 0.8 2 500 8.3 6 1.2 2 500 16.7 7 0.8 2 1500 25.0 8 1.2 2 1500 25.0 9 1 1.5 500 33.0 10 1 2.5 500 16.7 11 1 1.5 1500 25.0 12 1 2.5 1500 41.6 13 1 2 1000 16.7 14 1 2 1000 8.3 15 1 2 1000 8.3 16 1 2 1000 8.3 17 1 2 1000 0 Table 5 Model and variance analysis Source of variance Sum of squares Degree of freedom Mean square F value P value Model 0.1482 9 0.0165 7.37 0.0077** A - Natamycin 0.0009 1 0.0009 0.3946 0.5499 B - Calcium L - aspartate 1.125E-06 1 1.125E-06 0.0005 0.9827 C - Alginate oligosaccharide 0.0219 1 0.0219 9.82 0.0165* AB 0.0000 1 0.0000 0.0000 1.0000 AC 0.0018 1 0.0018 0.7891 0.4039 BC 0.0271 1 0.0271 12.11 0.0103* A² 0.0004 1 0.0004 0.1781 0.6856 B² 0.0368 1 0.0368 16.48 0.0048** C² 0.0547 1 0.0547 24.49 0.0017** Residual 0.0156 7 0.0022 Lack of fit 0.0017 3 0.0006 0.1629 0.9161 not significant Pure error 0.0139 4 0.0035 Total 0.1639 16 <![CDATA[R 2 > 0.90454 Note: * Significant difference ( P <0.05), ** extremely significant difference ( P <0.01).

[0025] The analysis of Design-Expert 13 software showed that the best combination of optimized anti-browning agent was 0.844 g / L natamycin, 2.046 g / L calcium L-aspartate, and 859.515 times dilution of seaweed oligosaccharide. Combined with the actual operation, each factor was adjusted to: 0.85 g / L natamycin, 2 g / L calcium L-aspartate, and 850 times dilution of seaweed oligosaccharide. At this time, the predicted value of browning index of the optimized preservative was 5.76%. Example

[0026] Application of MCP combined with compound preservatives in extending the shelf life of Nanhong pear Nanhong pears in the best coloring period were picked, and those with a coloring rate of more than 80% and a single fruit weight of about 90 g were selected; the selected Nanhong pears were packed into shockproof packaging boxes (each box weighed about 2.3 kg), put into a bag of 1-MCP fresh-keeping bag on the day after picking, and then put into a microporous bag and tied, and mailed from the base to the destination, with a differential pressure precooling wind speed of 1.5 m / s and a differential pressure precooling time of 9 h. The pears were put into a -0.5 ℃ cold storage, and after refrigeration for 180 days, they were allowed to stand at room temperature for 2 hours, and then immersed in a compound preservative (natamycin 0.85 g / L, L-aspartic acid calcium 2 g / L, seaweed oligosaccharide diluted 850 times) for 3 minutes, blown dry, and stored at room temperature.

[0027] from Figure 2 It can be seen that the peel browning index of CK (76.66%) was significantly higher than that of the compound preservative group (39.00%) on the shelf for 5 days. The peel browning index of the two groups increased with time, but the index difference between them gradually narrowed. There was no significant difference on the shelf for 20 days (CK was 96.66% and compound preservative was 93.33%). The peels of the 1-MCP and 1-MCP+compound preservative groups did not show browning in the early shelf life. In the late shelf life, the 1-MCP group (4.44%) showed slight browning on the shelf for 20 days, while the 1-MCP+compound preservative group still did not show browning.

[0028] After 180 days of cold storage, the fruit hardness of the 1-MCP group was slightly higher than that of the CK group, but the difference between the two groups was small. After being taken out of the cold storage and stored at room temperature, the fruit hardness of the CK and compound preservative groups decreased compared with that when they left the warehouse after 5 days on the shelf, with 41.77% and 51.37% being the largest decreases during their respective shelf periods. As the shelf life continued to extend, the overall trend of the fruit hardness decline of the two groups remained similar throughout the shelf period, with no significant difference; the fruit hardness of the 1-MCP and 1-MCP+compound preservative groups remained at the level of leaving the warehouse during the entire shelf period, with no significant decrease.

[0029] Table 6 Comparison between the fresh-keeping method of this patent and the existing fresh-keeping agents in the fresh-keeping of Nanhong pears Note: "-" indicates no rot Conclusion: By using the fresh-keeping method for extending the shelf life of Nanhong pears after cold storage in this patent, the shelf life is > 14 days after 6 months of cold storage and > 7 days after 10 months of cold storage, and the fruit freshness is good. For the existing fresh-keeping method, the shelf life is < 5 days after 6 months of cold storage and < 1 day after 10 months of cold storage. It can be seen that the fresh-keeping method for extending the shelf life of Nanhong pears after cold storage in this patent can effectively inhibit the browning of the Nanhong pear peel and the softening of the fruit during the shelf life after cold storage, and can effectively extend the shelf life.

Claims

1. A method for preserving Nanhong pears for extending their shelf life after refrigeration, characterized in that Proceed as follows: Step 1: Pick Nanhong pears in the best coloring period, and select Nanhong pears with a fruit surface coloring rate of 80% and a single fruit weight of 85-100 g; Step 2: Put the selected Nanhong pears into shockproof packaging boxes, with each box weighing 2.2-2.4 kg, put in a bag of 1-MCP fresh-keeping bag, put in a microporous bag and tie the mouth, mail from the base to the destination, and put into the cold storage after differential pressure pre-cooling; Step 3: Storing in cold storage for 6 months. Take the box of Nanhong pears out of the cold storage, place it at room temperature for 2-3 hours, open the microporous bag, pack it into commercial packaging and sell it directly. The shelf life is more than 14 days. Step 4: When stored for 7 to 10 months, the Nanhong pears need to be restored to room temperature, soaked in a composite preservative solution for 2 to 3 minutes, blown dry, and sold after commercial packaging. The shelf life is more than 7 days; the composite preservative formula is: 0.85g / L natamycin + 2g / L L-calcium aspartate + 850-fold diluted seaweed oligosaccharides.

2. The method for prolonging the shelf life of Nanhong pear after refrigeration according to claim 1, characterized in that: The 1-MCP treatment should be completed within 3 days after the Nanhong pears are harvested. The pears need to be wetted in pure water before being placed in the 1-MCP preservation bag to facilitate the volatilization of 1-MCP.

3. The method for prolonging the shelf life of Nanhong pear after refrigeration according to claim 1, characterized in that: The microporous bag is made of PE, with a thickness of 16-20 μm, an average pore size of 10-15 μm, and a pore density of 25-36 pores / mm 2 .

4. The method for prolonging the shelf life of Nanhong pear after refrigeration according to claim 1, characterized in that: The wind speed of differential pressure precooling is 1.0~2.0 m / s, and the time of differential pressure precooling is 8~10 h; during differential pressure precooling, the temperature drops from 25~30 ℃ to -1~0℃, and the temperature of the cold storage is controlled at -1~0℃.

5. The method for preserving Nanhong pears for extending their shelf life after refrigeration according to claim 1, characterized in that: Nanhong pears are taken out of the cold storage and the storage time is determined according to the temperature difference. Usually, in an environment of 20-25 ℃, the storage time is 3 hours.

6. The use of the method for prolonging the shelf life of Nanhong pear after refrigeration as described in claim 1 for preserving the fruit to improve the quality and commercial value of Nanhong pear; the improvement of the quality of Nanhong pear fruit refers to: inhibiting the browning, softening and decay of the Nanhong pear fruit during the shelf life after refrigeration.

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