阅读说明：本技术 一种龙眼鲜果货架期间优化护色方法 (Method for optimizing color protection of fresh longan fruits during shelf period ) 是由 韩冬梅 吴振先 罗焘 李建光 郭晓萌 郭栋梁 黄石连 王静 于 2021-09-10 设计创作，主要内容包括：本发明涉及水果保鲜技术领域,具体为一种龙眼果实采后货架期间果皮优化护色的方法,可有效延长货架寿命。本发明所述龙眼鲜果货架期间优化护色方法,在自主开发的龙眼保鲜纸的基础上,进一步采用“中温预冷+中温反应+免纸贮运+货架色度优化保护”的方式,实现了更为简便、安全的保鲜护色应用技术,且能够优化保持果实货架期间的外观色度,抑制褐变,大幅延长果实货架寿命,具有操作简便、安全、流程少、环境和设施条件要求较低、效果突出、易于被消费者接受等优势特点,成本低,易于推广的优势,具有良好的应用前景。(The invention relates to the technical field of fruit preservation, in particular to a method for optimizing the color protection of longan fruit peels during the shelf life after the longan fruits are picked, which can effectively prolong the shelf life. The method for optimizing and protecting the color of the fresh longan fruits during the shelf life further adopts a mode of medium-temperature precooling, medium-temperature reaction, paper-free storage and transportation and shelf color optimization protection on the basis of the self-developed fresh longan paper, realizes a simpler and safer application technology for fresh-keeping and color protection, can optimize and maintain the appearance color of the fruits during the shelf life, inhibits browning, greatly prolongs the shelf life of the fruits, and has the advantages of simplicity and convenience in operation, safety, less flow, lower requirements on environment and facility conditions, outstanding effect, easiness in acceptance by consumers and the like, and has the advantages of low cost, easiness in popularization and good application prospect.)

1. An optimized color protection method for fresh longan fruits during a shelf period is characterized by comprising the following steps:

(1) selecting mature longan fruits, quickly transferring to a shady and cool place after picking, radiating, conveying back to a treatment workshop, controlling the temperature in the treatment workshop to be about 25 +/-1 ℃, and performing ear arrangement, fruit selection and boxing treatment;

(2) keeping the surface of a fruit pile in an open state, placing the packaged fruit box in a refrigeration house at 20-25 ℃ for air-blowing precooling treatment, then laying longan preservative paper on the upper surface of the fruit pile, and then sealing the packaging bag with the inner lining;

(3) transferring the packaged fruit box to a refrigeration house with the temperature of 15-20 ℃ for continuous cooling treatment, and releasing SO from the longan preservative paper₂Gas, preserving the fruits;

(4) after the continuous cooling is finished, removing the longan preservative paper, keeping the fruit surface open, carrying out air blowing treatment, then covering water absorption paper on the surface of the fruit pile, sealing under the continuous cooling treatment condition, and entering the conventional logistics storage and transportation process;

(5) and after the logistics storage and transportation are finished, opening the package, removing the absorbent paper, emitting the smell in the sealed fruit box, finishing the fruit ears, packaging and putting on the shelf.

2. The method for optimizing color protection during shelf life of fresh longan fruits as claimed in claim 1, wherein in the step (2), the time of the air-blowing pre-cooling treatment step is 0.5-1.5 h.

3. The method for optimizing the color protection of fresh longan fruits during the shelf life according to claim 1 or 2, wherein the continuous cooling treatment time in the step (3) is 30-40 h.

4. The method for optimizing color protection of fresh longan fruits during the shelf life according to any one of claims 1 to 3, wherein the step (1) further comprises the step of spraying ears on trees with a conventional bactericide 1 to 3 days before the longan fruits are harvested.

5. The method for optimizing color protection of fresh longan fruits during shelf life according to any one of claims 1 to 4, wherein in the step (1), the ear-arrangement and fruit-selection step is to eliminate bad fruits such as diseases, insects, injuries, over-ripening and abnormal development and the like, and short fruit branches with the length of 10-25cm or single fruits with branches are reserved.

6. The method for optimizing the color protection during the shelf life of fresh longan fruits as claimed in any one of claims 1-5, wherein in the step (1), the step of packing is performed by using a plastic basket or a foam box, a Polyethylene (PE) bag with a thickness of 0.025mm is lined, and 1-2 pieces of absorbent paper or absorbent pads with a thickness of 1-3mm are placed at the bottom of the bag, and then the finished fruits are placed.

7. The method for optimizing color protection during the shelf life of fresh longan fruits according to any one of claims 1-6, wherein in the step (2), the fruit boxes in the refrigeration house are required to be layered or stacked in a delta shape in the air blowing and pre-cooling treatment step, and an air duct is left between the stacks along the air outlet direction so that cold air can smoothly pass through the fruit boxes to ensure the cooling effect.

8. The method for optimizing longan fresh fruit shelf life according to any one of claims 1-7, wherein in the step (4), the time of the air blowing treatment step is 15-30 min.

9. The method for optimizing color protection during the shelf life of fresh longan fruits as claimed in any one of claims 1-8, wherein in the step (5), the step of packaging on shelf comprises storing in a room with six-sided air-permeable packaging boxes, or storing at 5 ℃ after packaging with film bags.

10. The method for optimizing color preservation of fresh longan fruits during shelf life according to any one of claims 1 to 9, wherein the fresh longan fruit-preserving paper comprises a base material, a coating layer and SO sequentially from top to bottom₂The release agent and the sealing material are packaged, wherein the base material and the sealing material are both made of air-permeable and water-permeable materials, and the application layer is a safe and nontoxic adhesive; the SO₂The release agent is prepared from a main release agent and a release promoting agent in a ratio of 1: 0.10-0.25 by mass ratio.

Technical Field

The invention relates to the technical field of fruit preservation, in particular to a method for optimizing the color protection of longan fruit peels during the shelf life after the longan fruits are picked, which can effectively prolong the shelf life.

Background

Longan (Dimocarpus Longan Long Lour.) is one of the famous and special fruits in tropical and subtropical regions in south China, is also one of the four major fruits in Guangdong province, and occupies a great position in the agricultural and economic composition of major producing areas. However, it is known that longan fruits are extremely weak to storage after harvesting, and in particular have a shorter shelf life after harvesting or after storage. Generally, after fresh longan fruits are exposed at room temperature (30-35 ℃) for 8-10 hours, the color of the fruits is obviously dark to light brown, and the fruits can be deeply browned in the next day, so that the commodity value is lost; browning is started when the outdoor stall is placed from the morning to the afternoon (6-8h) under the temperature of 33-37 ℃; if the fruit is left bare in the air-conditioning environment of a supermarket, the fruit loses water more quickly, browning begins after about 4-6 hours, but the fruit flesh is kept intact. For the fruits stored for a period of time in the early stage, if the fruits are taken out of the warehouse and then put on a shelf, the browning speed of the peels is higher, and the shelf life is only about 0.5-1 d. Therefore, in addition to SO, the current market of fresh longan fruits at home and abroad₂Except for Thai longan subjected to gas fumigation treatment, the native longan fresh fruit which is not subjected to sulfur treatment is basically harvested and sold immediately, and basically no product is sold on the market after long-term storage. Therefore, compared with the fruit peel browning during the storage and transportation of the longan, the browning problem during the shelf life is more serious, is the biggest obstacle to the increase of the market benefits after the longan is picked, and is urgently needed to be solved in the research of longan preservation technologyAnd (5) problems are solved.

Research shows that rapid water loss of the pericarp is the main reason of severe browning of fresh longan fruits during the shelf life, and the rapid water loss is related to poor water retention capacity caused by loose tissue structure characteristics of longan pericarp. At present, longan exported in Thailand in foreign markets is combusted by sulfur to generate SO₂The gas fumigation technology not only can obviously prolong the storage and transportation life of the fruits, but also can greatly improve the color of the fruit peel and basically keep the color unchanged. However, SO₂The implementation of the gas fumigation technology needs large-area infrastructure, and the technology has low practicability and low utilization rate for the production situation manufactured in China for one year, which is the main reason that the technology cannot be popularized in China. In China, the conventional sterilization and antistaling agent or the fresh-keeping storage and transportation means such as medium-temperature and low-temperature cold chains mainly improve the anti-browning capability of fruits packaged in a closed environment in the storage and transportation process, but have little effect on removing the browning problem of fresh longan fruits placed on a goods shelf after packaging, and no technology capable of really and effectively improving the anti-browning capability of the goods shelf of fresh longan fruits exists in production. Therefore, the shelf browning is still the biggest problem for the current sale situation of fresh longan fruits in China, and no feasible solution is available.

In the prior art, the utilization of self-made SO has been reported for many times₂The technology of treating the longan fruits stored at low temperature by the slow release agent not only improves the preservative and fresh-keeping effects of the fruits during the cold storage period, but also can improve the color of the pericarp and prolong the shelf life by 2-3 days. However, in view of the loose structure and storage characteristics of longan pericarp and the control requirement of residual sulfur amount, SO is determined₂The gas action form is a high-concentration short-time treatment process, and an improper formulation and packaging form cannot play a role in preservation, and can also aggravate the phenomena of pericarp browning and pulp autolysis. Because the longan pericarp cells contain a large amount of phenolic substances, the phenolic substances are main substrates of browning reaction, and the SO with low concentration₂Gas can destroy cell wall and cell membrane structure in SO₂In the case where the gas concentration is insufficient to kill the relevant catalytic enzyme, the substrate in the cell is in unhindered contact with the catalytic enzyme and oxygen, but rather the occurrence of enzymatic browning reaction is accelerated, so that only a high concentration is usedSO of (A)₂The gas can destroy the cell structure and simultaneously kill the browning catalytic enzyme, so that the effects of color protection and freshness preservation can be really played. Research shows that slow-release SO is utilized₂The release agent is packaged, and the treatment effect is unstable or short-term. Moreover, the fruit absorbs SO due to the use of the bagged release agent₂Uneven gas, SO in fruit at different positions in the heap₂The residual quantity is unlikely to be uniform, the higher the residual sulfur content of fruits close to the antistaling agent is, the longer the residual sulfur content of fruits close to the antistaling agent is, the lower the residual sulfur content of fruits is, the absorption is slow, the browning is fast, the refreshing effect is poor, and even the control is not as good as possible. Many years of research have demonstrated that SO is rapidly produced using a releasing agent such as sodium metabisulfite₂The packaging form of the planar gas preservative is suitable for preserving longan.

Through research and improvement for many years, the applicant develops longan preservative paper suitable for longan preservation (see the Chinese patent CN105804796B in detail), and guarantees transportation and storage of longan based on a mode of precooling in a refrigeration house at 5 ℃ and carrying the preservative paper for storage and transportation. However, practical application finds that the method still has certain limitations, which are specifically shown in the following steps: the precooling temperature is too low, a refrigeration house facility is required to be equipped, for most small production units integrating production and marketing, no special refrigeration house facility is generally provided, the popularization and application of the technology are limited, the packaging process after fruit precooling is also required to be completed under the condition of low temperature of 5 ℃, the environment temperature is too low, and the production operation difficulty is larger. In addition, SO₂The releasing agent reacts chemically by combining with moisture and oxygen to release SO₂The gas is absorbed by the fruits to play a role in keeping fresh. Theoretically, the lower the temperature and the lower the respiration intensity of the fruit after precooling, the less the moisture is released, which is not favorable for releasing high-concentration gas as soon as possible, SO that enough SO can be released for a long time only when the fruit is stored with paper during storage and transportation₂Gas, but lower concentration SO for a long period of time₂The gas environment may cause fruit damage and browning, reduce the preservation effect, and in addition, the long-term accumulation can bring SO₂The residue is higher. Therefore, a low temperature of 5 ℃ is not a suitable pre-cooling temperature. Further, the webs are stored and transportedIn such a way that the smell in the packaging box is heavy and the SO in the fruit is heavy₂The residue may be too high, affecting the consumer's intuitive experience.

More importantly, the fruit is expressed in commercial rate or good fruit rate during the shelf life, and the characteristic requirement is that the fruit has no browning and mildew symptoms. Although the preservative paper can improve the phenomena of mildew and rot of longan in the storage life, the preservative paper has the color protection effect on fresh longan fruits, except that the epicarp chromaticity data shows that the preservative paper has the effects of improving the surface color of the fruits and improving the commodity property when the fruits are unpacked or delivered from a warehouse, the preservative paper has no support data to prove that the preservative paper has the effects of improving the fruit color of the fresh longan fruits, keeping the optimized fruit color basically unchanged and obviously prolonging the commodity life of the longan fruits on a shelf. Therefore, a higher requirement is provided for the browning and color protection requirements of fresh longan fruits in shelf life.

Disclosure of Invention

Therefore, the technical problem to be solved by the invention is to provide an optimized color protection method for fresh longan fruits during a shelf life so as to solve the problems of short shelf life and easy browning of fresh longan fruits.

In order to solve the technical problems, the method for optimizing color protection during the shelf life of the fresh longan fruits comprises the following steps:

(1) selecting mature longan fruits, quickly transferring to a shady and cool place after picking, radiating, conveying back to a treatment workshop, controlling the temperature in the treatment workshop to be about 25 +/-1 ℃, and performing ear arrangement, fruit selection and boxing treatment;

(2) keeping the surface of a fruit pile in an open state, placing the packaged fruit box in a refrigeration house at 20-25 ℃ for air-blowing precooling treatment, then laying longan preservative paper on the upper surface of the fruit pile, and sealing the packaging bag with the inner lining;

(3) transferring the packaged fruit box to a refrigeration house with the temperature of 15-20 ℃ for continuous cooling treatment, and releasing SO from the longan preservative paper₂Gas, preserving the fruits;

(4) after the continuous cooling is finished, removing the longan preservative paper, keeping the fruit surface open, carrying out air blowing treatment, then covering water absorption paper on the surface of the fruit pile, sealing under the continuous cooling treatment condition, and entering the conventional logistics storage and transportation process;

(5) and after the logistics storage and transportation are finished, opening the package, removing the absorbent paper, emitting the smell in the sealed fruit box, finishing the fruit ears, packaging and putting on the shelf.

Specifically, in the step (2), the time of the air-blowing pre-cooling step is 0.5-1.5h, and the time of the step can be properly adjusted within the above range according to the wind power.

Specifically, in the step (3), the time of the continuous cooling treatment is 30-40 h.

In the method, the temperature (25 +/-1 ℃) of the harvested pretreatment environment needs a larger air-conditioning workshop, when the condition is not met, fruits can directly enter the 20-25 ℃ air-conditioning room for air-blowing precooling under the condition of higher fruit temperature, and the precooling time can be properly prolonged according to the condition, so that the method also belongs to the reasonable adjustment of the technical scheme.

Specifically, the step (1) further comprises the step of spraying the fruit clusters on the trees by using a conventional bactericide 1-3 days before the longan fruits are harvested.

Specifically, in the step (1), the ear-tidying and fruit-selecting step is to remove bad fruits such as disease-free fruits, insects, injuries, over-ripening fruits, abnormal development and the like, and keep short fruit branches fruits with the length of 10-25cm or single fruits with branches.

Specifically, in the step (1), a plastic basket or a foam box is used as the boxing step, a Polyethylene (PE) bag with the thickness of 0.025mm is lined in the plastic basket or the foam box, 1-2 pieces of water-absorbing paper or water-absorbing pads with the thickness of 1-3mm are placed at the bottom of the bag, and then the finished fruits are placed.

The method of the invention mainly serves as a normal-temperature storage and transportation form of 'foam box + ice bag', and the technology is also applicable to longan fruits which are stored and transported for a short time by a refrigerator car without using the packaging and transportation form, and can change the heat-preservation type foam box into a non-heat-preservation plastic basket or carton and other packaging materials.

Specifically, in the step (2), in the air-blowing pre-cooling treatment step, the fruit boxes in the refrigeration house are required to be layered or stacked in a delta shape, and an air duct is reserved between the stacks along the air outlet direction, so that cold air can smoothly pass through the fruit boxes, and the cooling effect is ensured.

Specifically, in the step (4), the time of the air blowing treatment step is 15-30 min.

Specifically, in the step (5), the step of packaging and shelving comprises placing six-sided breathable packaging boxes in a room at normal temperature for storage, or placing the six-sided breathable packaging boxes in a 5 ℃ package for storage after packaging by using a film bag.

Specifically, the longan preservative paper is a previous research result of the applicant, and the specific implementation scheme is described in chinese patent CN 105904796B. No alternative SO for longan preservative paper₂The preservative substance of the releasing agent, but other safer and more efficient SO with the same effect can be found in the future₂Releasing the agent. The application technical parameter combination and the technical process of the 'substitute preservative paper' obtained in the technical thought range both belong to the improvement and adjustment scope of the technical scheme.

Specifically, the longan preservative paper sequentially comprises a base material, a coating layer and SO from top to bottom₂The release agent and the sealing material are packaged, wherein the base material and the sealing material are both made of air-permeable and water-permeable materials, and the application layer is a safe and nontoxic adhesive; the SO₂The release agent is prepared from a main release agent and a release promoting agent in a ratio of 1: 0.10-0.25 by mass ratio.

The method for optimizing and protecting the color of the fresh longan fruits during the shelf life further adopts the modes of medium-temperature precooling, medium-temperature reaction, paper-free storage and transportation and shelf color optimization protection on the basis of the developed fresh longan paper, realizes a simpler and safer application technology for fresh-keeping and color protection, can optimize and maintain the appearance color of the fruits during the shelf life, inhibits browning, greatly prolongs the shelf life of the fruits, and has the advantages of simplicity and convenience in operation, safety, less flow, lower requirements on environment and facility conditions, outstanding effect, easiness in acceptance by consumers, low cost and easiness in popularization, and has a good application prospect.

The method for optimizing color protection during shelf life of fresh longan fruits adopts the treatment modes of medium-temperature pre-cooling and continuous cooling, so that the pre-cooling temperature is increased, and the operating environment condition is improvedThe medium fruit temperature is kept, so that the fruit temperature can be properly reduced, a large amount of field heat is emitted, and the strong metabolism physiology of the fruits is reduced; can maintain relatively high respiration intensity, release enough water and promote the preservative paper to quickly release a large amount of SO₂The gas plays an effective fresh-keeping role.

The method for optimizing color protection during shelf life of fresh longan fruits adopts the modes of pre-cooling treatment and continuous cooling treatment in a medium-temperature environment, realizes paper-free storage and transportation in the transportation process, can meet the safety of consumers, and can avoid continuous SO₂The release results in excessive SO accumulation in the fruit₂The gas brings about the problem of over-standard residual quantity; the shelf condition of low air humidity or other unprotected measures in a supermarket can be met, the preservative paper is not required to be hermetically packaged for treating the fruits, the improved fruit color after the optimization of the shelf period of the fruits can be kept, the shelf life of the fruits is remarkably prolonged to 4-6d, and the benefit increment of a market end is promoted.

The method for optimizing color protection during shelf life of fresh longan fruits adopts the previously researched longan preservative paper in the continuous cooling treatment process, and has the advantages of replacing and optimizing the conventional SO generated by burning sulfur₂The longan fresh-keeping technology has strong operability, the using amount of the fresh-keeping agent is controllable, and special burning civil engineering facilities and large-area factory processing space are not needed; the flat fresh-keeping paper is beneficial to the fruits at each part in the fruit pile to absorb SO as uniformly as possible₂Gas, the preservation effect is guaranteed to have uniformity. Particularly, the optimization method of the invention carries out pre-cooling and continuous cooling treatment on longan preservative paper which is pre-cooled in a low-temperature (5 ℃) environment originally in a medium-temperature environment, not only improves the treatment effect of the preservative paper, but also improves the operability of the pre-cooling technology and the environmental conditions of pre-cooling and subsequent packaging treatment, and can finish the treatment work in an air-conditioned room or a high-temperature cold storage (15-25 ℃), reduce the energy consumption cost and improve the working efficiency and the environmental comfort.

The invention relates to an optimized color protection method for fresh longan fruits during shelf life, which is mainly applied to longan fruits stored and transported at normal temperature. Although the normal temperature storage time of the fruits is short, the ambient temperature and the relative humidity in the package are highThe condition of mildewing is easy to occur, SO for the preservative paper, higher reaction temperature and longer reaction time are required to reach higher concentration of SO₂The gas plays the effects of fully inhibiting fruit respiration, reducing colored substances and killing fruit surface germs as far as possible, so that the problems of optimizing color protection of fruits, reducing physiological metabolism and inhibiting postharvest mildew and rot are balanced and unified, and the fruits are promoted to have extremely strong shelf chromaticity and internal quality retention capability.

According to the method for optimizing color protection of fresh longan fruits during the shelf life, the processed fruit color is better than the fruit color during collection, is brighter and cleaner than the fruit color during collection, and the optimized fruit color is basically kept unchanged during the shelf life; when the fruit is stored on the shelf 1d, the contrast begins to be browned completely, the commodity value is lost, and when the fruit is stored on the shelf 6d, the commodity rate can be kept more than 90%, and the contrast shows absolute superiority.

Drawings

In order that the present disclosure may be more readily and clearly understood, the following detailed description of the present disclosure is provided in connection with specific embodiments thereof and the accompanying drawings, in which,

FIG. 1 is a graph showing the comparison of browning indexes of endocarps after opening of different types of treated Shixia fruits in example 2;

FIG. 2 is a graph showing the commercial score of fruits treated in example 2 in the shelf life (7d) after storage at room temperature;

FIG. 3 shows the fruit pulp SO after storage at room temperature of the fruits treated differently in example 2₂Comparing the contents;

FIG. 4 is the comparison result of the fruit colors of the Shixia fruit shelf 4d for the medium-temperature precooling preservative paper free-from-paper normal-temperature storage in example 2;

FIG. 5 is a comparison of the results of the processing of example 3 in the evaluation of the product rate (control value: good fruit rate, product rate of 0) in the shelf life of the fruits after storage at room temperature;

FIG. 6 is a comparison of the difference between the color at shelf 6d and the color at harvest 0d of the fruits stored at room temperature in example 3;

FIG. 7 shows SO in the pulp of the fruits treated in different ways in example 3 after storage at room temperature₂Comparing the contents;

FIG. 8 is an average value of the margin estimates for different levels of each test factor in example 3;

FIG. 9 shows the comparison of the fruit colors of the medium-temperature precooled preservative paper of example 3 during the paper-free normal-temperature storage of Shixia fruits for picking, unpacking and shelf life.

Detailed Description

Example 1

The method for optimizing color protection during shelf life of fresh longan fruits comprises the following steps:

(1) 1-3 days before fruit harvest, spraying fruit ears on trees by using conventional low-toxicity and safe bactericides such as prochloraz (500-; during picking, selecting longan fruits with the maturity of 85-95%, quickly transferring to a shady and cool place for heat dissipation after picking, quickly transporting back to a treatment plant after basket loading, and setting the air-conditioning temperature in the treatment plant to be about 25 +/-1 ℃; the step is the first step of precooling treatment, namely, the temperature is reduced to 25 +/-1 ℃ from 30-35 ℃ during picking, and meanwhile, the conventional treatment processes of ear arrangement, fruit selection, box packing and the like are carried out in an air conditioning workshop, and the whole process is about 1 h;

in the process of fruit cluster arrangement, inferior fruits without diseases, insects, injuries, overripening, abnormal development and the like need to be removed, short fruit branches or single fruits with branches with the length of 10-25cm are reserved, and the short fruit clusters or the single fruits with branches are beneficial to forming air-permeable channels in fruit stacks to promote SO released by preservative paper₂The gas can be rapidly and uniformly diffused to each position of the fruit heap;

in the packing process, a plastic basket or a foam box is preferably used, a Polyethylene (PE) bag with the thickness of 0.025mm is lined in the plastic basket or the foam box, 1-2 pieces of water absorption paper with the thickness of 1-3mm are placed at the bottom of the bag, then the finished fruit clusters or single fruits with branches are placed, the surface of a fruit pile needs to be kept in an open state after the fruit is packaged, and the subsequent treatment is carried out;

(2) the packaged open fruit box is firstly moved to a refrigeration house or an air-conditioning house with the temperature of 20-25 ℃, meanwhile, equipment such as a fan and the like is used for blowing the fruits for 0.5-1.5h (precooling process), then 1 piece of preservative paper is laid on the upper surface of the fruit pile according to the scheme of the longan preservative paper and the dosage proportion of the preservative paper release agent recorded in Chinese patent CN105904796B, the release surface is downward, and the film bag mouth of the liner is tightly sealed;

during the whole precooling period, the fruit boxes in the refrigeration house are required to be layered or stacked in a shape like a Chinese character 'pin'; an air duct is reserved between the stacks along the air outlet direction, so that cold air can smoothly pass through the fruit box, and the cooling effect is ensured;

(3) then the fruit box is transferred to a 15 ℃ refrigeration house or an air-conditioned room for continuous storage, and the preservative paper is subjected to chemical reaction with moisture and oxygen in the packaging bag to release SO₂Gas is used for keeping fruits fresh, and the process lasts for more than 30-40h (continuous cooling reaction process);

(4) after the continuous cooling process is finished, removing the preservative paper, opening the fruit surface, blowing air for 15-30min, covering 1-2 pieces of absorbent paper on the surface of the fruit pile, sealing the fruit pile or packaging the fruit pile under the condition of a continuous cooling cold store, adopting a conventional foam box ice-adding packaging method, sealing the fruit pile and then entering a normal-temperature logistics storage and transportation process for about 24-72 h;

(5) after the logistics or storage and transportation process is finished, the package is opened, the absorbent paper is removed, and the odor in the sealed fruit box is emitted and is contained by the residual SO in the box₂CO produced by gas, respiration₂Acetaldehyde, ethanol and esters; then the clusters are arranged, single clusters or small clusters with short fruit branches are cut, the small clusters are placed in a six-face breathable packaging box and placed in a supermarket or a shelf in a spread way and a room temperature room for storage, and the small clusters can also be placed in a 5 ℃ room for continuous storage after being packaged by using a film bag.

Example 2

In this example, in 2018, a fresh-keeping effect of longan fruits stored and transported in a normal-temperature paper-free manner is studied by combining medium-temperature precooling with fresh-keeping paper treatment.

The material and the method are as follows: the gorge of the variety is about 90-95% of maturity.

After the fruits are harvested, the fruits are immediately transported back to a cold storage hall in a laboratory, and after diseases, insects, injuries, brown stains and rotten fruits are removed at the air conditioning temperature of 25 +/-1 ℃, subsequent related pretreatment and packaging are directly carried out.

The test uses L₉(4×3²) The orthogonal design of (1) takes 'precooling temperature, precooling time, reaction time and continuous cooling time' as test factors, and designs factor combinations of different levels, wherein the total number of the factor combinations is 12. Another is provided with a pairAnd according to the experiment, RCK0 is used as a blank control of the experiment, precooling is carried out for 1h in a refrigerator at the temperature of 5 ℃, preservative paper is not added, and the product is taken out of the refrigerator after sealing and stored in a constant temperature room at the temperature of (25 +/-1). Wherein RCK1-3 is used as test control, RCK1 is used as non-precooling, fresh-keeping paper is directly added, and the paper is removed for sealing after continuous cooling for 31 hours in a cold storage at 5 ℃; RCK2 is precooled for 1.5 hours in a cold storage at 5 ℃, and then the paper is removed and the box is sealed after the fresh-keeping paper is added and subsequently cooled for 31 hours; RCK3 is pre-cooled for 3 hours in a cold storage at 5 ℃ and stored for 31 hours, and then the paper is removed and boxed.

In each experimental group, fruit branches with the length of 15-20cm are cut and reserved on clusters, the clusters are packaged in 2.5kg foam boxes, each box is filled with 2.5kg of fruits, a liner is 0.02mm of PE microporous membrane bags, all experimental treatments are uncovered bare fruit treatments, after the fruits are subjected to open precooling for a period of time in a refrigeration house with corresponding precooling temperature, one piece of preservative paper is laid on the surface of each fruit pile according to the dosage proportion of a preservative paper release agent in patent CN105904796B, the release surface of each fruit pile faces downwards, the fruits are sealed and reacted for a period of time, then the fruits are placed in the refrigeration house with the temperature of (5 +/-0.5) DEG C for storage, and the reaction and continuous cooling processes are completed at different temperatures, wherein the reaction temperature is the same as the precooling temperature, and the continuous cooling temperature is 5 +/-1 ℃. The design table of the horizontal combination of the orthogonal test factors is shown in table 1.

TABLE 1 test factors in combination with levels

And when the continuous cooling time is up, removing the preservative paper, ventilating for 15min, adding the ice bag, sealing, placing in a constant temperature chamber of (25 +/-1) DEG C for storage, and opening the box after 70 h. After the fruit is pre-cooled and continuously cooled, removing the preservative paper, transferring the preservative paper to a cold storage at 5 ℃ for storage for 50 days, and then taking the preservative paper out of the cold storage. Selecting good fruits, observing on a shelf, using transparent plastic preservation boxes with six-sided holes for containing, wherein each box contains about 500g of fruits, and storing in a constant temperature room at (25 +/-1) DEG C for 4 times. Observing shelf performance every day, calculating shelf commodity rate, rotten fruit rate and mildewed fruit rate, and analyzing the shelf period of fruits by using a factor analysis method in SPSS softwareThe commodity rate and the mildew rate are comprehensively scored, and SO in the pulp is measured by referring to the pararosaniline hydrochloride method (parafuchsin method) in the national standard GB/T5009.34-2003₂Residual sulfur content.

The results of the tests are shown in FIGS. 1-4 and Table 2, respectively.

As shown in FIG. 1, the browning index of the blank control was 0 when the box was opened, and in 3 of the test controls, the browning index increased as the precooling time was increased. Among the 12 orthogonal combinations, the non-precooled browning indexes of R1, R4, R7 and R10 are all lower and are similar to RCK1, and the longer the precooling time is, the browning indexes tend to increase. However, the browning indexes of the orthogonal treatment combination with higher precooling temperature are almost lower than those of the corresponding control, which shows that the browning degree of the fruits precooled at medium temperature can be reduced more than that of the fruits precooled at low temperature in the preservative paper treatment.

As shown in FIG. 2, the longer the pre-cooling time, the lower the shelf commodity rate in the 3 trial controls. In 12 orthogonal treatments, the commodity rates of R4, R7 and R10 which are not precooled are higher than that of RCK1, and the good fruit rate is still more than 90% when the fruits are on a shelf 6 d; r2, R5, R8 and R11 are all higher than the control RCK2, and similarly R3, R6, R9 and R12 are all higher than the control RCK 3. It can be seen that the lower the pre-cooling temperature below 20 ℃, the lower the shelf commodity rate between bars with the same pre-cooling time.

As a result, SO in pulp was removed from the container at a precooling temperature of 25 ℃ as shown in FIG. 3₂Low content of SO at 20-5 deg.C and lower precooling temperature₂The content is higher; at 25 and 20 ℃ SO₂The content difference is not great; all treated pulps contained more SO2 than RCK0 but less than the national Standard limit (30 mg/kg).

The results shown in FIG. 4 show the comparison of the color of RCK0 when the paper is stored for 70h at room temperature and then stored on the shelf for 4d after the middle-temperature pre-cooling and fresh-keeping paper treatment: the control fruit is dark light brown to brown, while the treated fruit is bright dark yellow, so that the color of the fruit is kept unchanged when the box is opened, and the commodity rate of the goods shelf is remarkably improved. The fruit color of the RCK0 control was completely browned on the next day of the shelf, and although edible, it lost commercial value and could not be sold further.

TABLE 2 comparison of estimated marginal means of effective index at different levels for each test factor

Factors of the fact	Level of	Open box brown finger	Good fruit rate after opening box	Unpacking delta b	Unpacking Delta c	Shelf spoilage Rate Scoring	Shelf commodity rate scoring
								Pre-cooling temperature A	10℃	0.19	99.883	2.777	2.602	-0.28	-0.165
	15℃	0.08	99.527	4.178	3.941	-0.333	0.156
									20℃	0.049	99.733	4.35	4.196	-0.176	0.464
	25℃	0.08	99.49	4.635	4.493	-0.25	0.264
								B duration of precooling	0h	0.036	99.907	4.86	4.627	-0.123	0.426
	1.5h	0.077	99.626	3.921	3.797	-0.282	0.278
									3.0h	0.187	99.442	3.174	3	-0.373	-0.164
Length of C reaction	1.0h	0.058	99.562	4.381	4.15	-0.337	0.098
									2.5h	0.156	99.812	3.774	3.703	-0.054	0.084
	4.0h	0.086	99.601	3.799	3.571	-0.388	0.358
								Duration of continuous cooling	20h	0.181	100	4.129	3.887	-0.431	-0.204
	31h	0.061	99.437	4.034	3.83	0.399	0.374
									42h	0.058	99.522	3.791	3.707	-0.746	0.37

Table 2 shows the comparison results of the estimated marginal means at different levels for each factor of each effective index. For the precooling temperature, the precooling treatment at 20 ℃ ensures that the fruits obtain the lowest open-box browning index, the lowest shelf mildew rate, the highest shelf commodity rate and better open-box fruit color; the precooling time of 0h ensures that the fruits obtain the best open box fruit color and the highest commodity rate of a goods shelf; the reaction time of 4 hours ensures that the fruits obtain the highest commodity rate on a shelf; the continuous cooling time of 31h and 42h both obtain lower in-box quality loss rate and open-box browning index, and better shelf effect. In addition, all the treated fruits are sterilized and washed before entering the pre-cooling chamber and are aired in a cold storage at the temperature of about 25 ℃, and a slight pre-cooling process is actually carried out. In short, precooling at 20 ℃ for 0h, reacting at 20 ℃ for 4h, and precooling at 5 ℃ for 31-42h are reasonable combinations, and precooling fruits or fresh-keeping paper at a medium temperature has a reaction effect, so that the fruits can obtain better opening quality and shelf quality, the browning is less, and the commodity rate is high.

In addition, tests contrast with RCK2 and RCK3, namely the treatment method of the technical scheme of the longan preservative paper, namely low-temperature precooling and low-temperature cold-continuing reaction, and results show that the treatment effects of precooling and cold-continuing reaction under the low-temperature condition are obviously lower than those of medium-temperature precooling, medium-temperature reaction and low-temperature cold-continuing reaction, and the longer the precooling time at the low temperature is, the worse the effect is.

Example 3

In this embodiment, in 2020, a study is made on an optimized color protection effect of medium-temperature precooling combined with preservative paper treatment on a shelf period of normal-temperature paper-free storage and transportation of longan fruits.

The material and the method are as follows: the gorge of the variety is about 90-95% of maturity.

Using an orthogonal table L₉(3³X 2) design run, 9 treatments in total, control CK, conventional pretreatment followed by direct binning (see table 3 below). After the fruits are harvested, the fruits are immediately transported back to a cold storage hall in a laboratory, and after diseases, insects, injuries, brown stains and rotten fruits are removed at the air conditioning temperature of 25 +/-1 ℃, subsequent related pretreatment and packaging are directly carried out. The using method of the fruit ear finishing, packaging and preservative paper is the same as the embodiment 1. The fruits to be treated were pre-cooled by "naked fruit + air blast" according to the design in table 3, and after pre-cooling, fresh-keeping paper was placed and then placed into each of themThe continuous refrigeration house continuously reacts and continuously cools the fruits; after finishing, removing the paper, blowing air for 15min, putting absorbent paper, and sealing the opening of the bag. Adding ice bag, sealing, storing in thermostatic chamber at 25 deg.C for 3d (72h), and opening.

The results are shown in Table 4 and FIGS. 5-9.

TABLE 3 test factor and level combination TABLE L₉₍3³×2)

As shown in the following Table 4, the comparison of the appearance of each treated fruit after unpacking after 3 days of paper-free storage at normal temperature shows that all the treated fruits have no rotten phenomenon, and the endocarp has no browning and is in a fresh state. The surface of the fruit treated by the preservative paper is bright yellow green and fresh, no water is accumulated on the surface and the bottom of the bag, and the fruit is slightly peculiar in smell and can be volatilized and dispersed quickly after being opened. Fresh, glittering and translucent and lustrous pulp and keeps the original color. The control fruit without preservative paper showed slightly dark yellow-green color and was relatively fresh. In a word, the fruit in the test is stored at normal temperature, and the control and the treatment show 100% of good fruit rate.

TABLE 4 appearance of opening box after storing fruit treated differently at room temperature for 3d

As shown in fig. 5, the comparison of the commodity rate (good fruit rate) comprehensive scores during the shelf period shows that the high and low orders of the good fruit rate are as follows: the commodity rate of RS5 RS7 RS3 RS4 RS1 RS2 RS1 RS8 RS9 RS6 RS5 RS7 treatment is obviously superior to that of fruits treated by contrast and other preservative paper, the commodity fruit rate is still more than 95% when the fruits are placed on a shelf 6d, and the commodity fruit rate is related to higher precooling temperature or shorter precooling time or longer continuous cooling reaction time, the levels of the factors are favorable for keeping relatively higher temperature of the fruits during the reaction of the preservative, and the treatment effect is better. The RSCK good fruit rate of the control is higher than RS6, RS8 and RS9, but the good fruit can be eaten after the control fruit is completely browned after 1d of a shelf, but the good fruit has no commercial value. The precooling temperature of RS6, RS8 and RS9 is the lowest (15 ℃), and the continuous cooling reaction time is the shortest, so the fresh-keeping effect is poor, and the good fruit rate is even lower than that of the control.

As shown in the results of fig. 6, the apparent shade of the fruit changes at shelf 6d, with line 0 representing the level of 5 shades on the day of harvest (0 d harvest). All treated and control fruit table a^*The values are similar and are slightly higher than a on the day of harvest^*The difference is mainly on the other 4 indexes. The control fruit further decreased in brightness and greenness to yellow, appearing as a near brown color, b^*Value of c^*The value is obviously lower than the colorimetric value on the day of harvest; while all the treatment results still maintain the higher saturation yellow chroma value (b)^*Value c^*Value and h deg.) and significantly exceeds the level at the time of unpacking, but the partial treatment is slightly less green (a)^*Slightly lower than the control) and appear bright yellow-green to dark yellow, particularly RS5 and RS7, the fruit color not only being optimized for harvest, but also being excellent in color protection during shelf life.

As a result, SO in pulp after unpacking was treated in all of the treatments as shown in FIG. 7₂Low content of SO in control pulp₂The background value is not more than 1.0mg/kg, and SO is generated in other treatments₂The content is between 2 and 6mg/kg and is far lower than the national standard value (30mg/kg), which indicates that the technology is very safe.

As shown in fig. 8, the comparison of the estimated marginal means for different levels of experimental factors obtains the most suitable combination of processing parameters for storing and transporting fruits at normal temperature: blowing and precooling at 20-25 ℃ for 1h +15 ℃ for a continuous cooling reaction for 30h, in practical application, properly adjusting the continuous cooling reaction time length according to the requirements of fruit warehousing precooling and storage and transportation time points, but more than 30h, and preferably between 30-40h because the SO in the pulp can be increased if the time is too long₂And (4) residual quantity.

As shown in FIG. 9, the fruit colors of Shixia fruits were compared during harvest, unpacking and shelf life of the mid-temperature precooled preservative paper without paper storage at normal temperature in 2020. The upper left is the original fruit color when the Shixia fruit is harvested, and the yellow green is brownish; the left middle part is a contrast fruit color after being stored and transported for 3 days at normal temperature, which is close to the harvesting time; the upper right part is the fruit color of the control fruit after 1d, and the control fruit is slightly browned compared with the whole brown stain when the box is opened and can be eaten, but has no commodity value of a stock shelf; the control fruit is placed on the shelf 6d in the middle right, and the browning is serious; the fruit color at the lower left and lower right of RS5 and RS7 treated shelf 6d maintained excellent bright yellow-green to dark yellow without any browning, showing excellent optimized color protection.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.