Method for prolonging preservation time of longan by using wood chips

Abstract

The invention provides a method for prolonging the preservation time of longan by using wood chips, which comprises the following steps of: burying fresh longan in sterilized dry wood chips, filling in a foam box, not sealing the box, and storing at indoor room temperature. The method can effectively delay deterioration of longan fruits, reduces fruit disease infection and water loss, has an excellent fresh-keeping effect on the collected longan, and effectively improves the fruit quality and economic benefits of the collected longan during storage and transportation.

Description

Technical Field

[0001] The invention belongs to the field of post-harvest fruit preservation, and in particular relates to a method for prolonging the preservation of longan by utilizing sawdust. Background Art

[0002] Longan (Dimocarpus longan Lour.), also known as "longan", is widely planted in tropical and subtropical areas in southern my country (such as Guangdong, Guangxi, Fujian and Taiwan). Longan has a unique flavor and good taste, and contains high levels of glucose, sucrose, vitamin C, vitamin B1, vitamin B2, potassium, etc. In addition, longan has many functions and effects such as relieving fatigue, promoting sleep, nourishing the body, nourishing the heart and spleen, nourishing blood and calming the nerves. Longan fruit matures in the high temperature season, and its physiological metabolism is vigorous. It is very easy to have browning of the peel, ulceration of the flesh, and infection by pathogens. It is not resistant to storage and transportation, which seriously affects the nutritional value and economic value of longan.

[0003] At present, the storage and preservation of longan mainly relies on refrigeration, preservatives, radiation, gas conditioning, sulfur treatment, natural preservatives and comprehensive technology applications. In recent years, the application of radiation, heat treatment and biological control technology in the research of longan preservation has also developed. However, the current research on the application of comprehensive technology for storage and preservation of longan is relatively lagging, and chemical preservatives and drug residues have potential threats to the environment and human health. In addition, the dangers of radiation preservation and microbial agents to human toxicity, carcinogenesis, teratogenesis and physiological diseases need further research. Therefore, the development of new, low-toxic, environmentally friendly and low-cost preservatives to improve the preservation effect of longan, extend the preservation time, maintain the nutritional value of longan and improve its economic value is of great significance to the development of the longan industry. Summary of the invention

[0004] The invention provides a method for prolonging the freshness of longan by utilizing sawdust. By burying the longan in sterilized dry sawdust and storing the longan in a box without sealing the box, the degree of fruit lesions and the water loss rate of the harvested longan can be effectively reduced, and the fruit quality of the harvested litchi during storage and transportation can be improved, thereby improving the economic benefits.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for extending the freshness of longan by using sawdust comprises the following steps: burying fresh longan in sterilized dry sawdust, packing the fresh longan in a box without sealing it, and storing it at room temperature (25-27°C).

[0007] Preferably, the box is a foam box.

[0008] Preferably, the moisture content of the dry sawdust is 15-20%.

[0009] Preferably, the dry sawdust is dry sawdust of poplar and / or pine.

[0010] The dry wood chips have uneven particle sizes. Preferably, the dry wood chips are dry sawdust.

[0011] Preferably, the sterilization method is high-pressure steam sterilization at 121° C. for 30 min.

[0012] Preferably, the density of longan packed in the box is 15-30Kg / m 3 .

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1. The present invention provides a method for extending the freshness of longan by using sawdust, wherein the longan is buried in sterilized dry sawdust and placed in a foam box without sealing, and the disease susceptibility index and water loss rate of the longan stored at room temperature for 6 days are 15.51% and 12.09% respectively; while the longan is not buried in dry sawdust and is directly placed in a foam box without sealing and stored at room temperature, and the disease susceptibility index and water loss rate of the longan on the 6th day of storage are 25.45% and 15.42% respectively; this indicates that the method of the present invention can effectively reduce the disease susceptibility index and water loss rate of longan. The longan was buried in sterilized dry sawdust and packed in a foam box without sealing. The contents of soluble sugar, malondialdehyde and titratable acid in the longan stored at room temperature for 6 days were 442.80 mg / g, 1.70 nmol / g and 0.153 g / 100 mL respectively, while the contents of soluble sugar, malondialdehyde and titratable acid in the longan without any treatment on day 0 were 442.81 mg / g, 1.58 nmol / g and 0.150 g / 100 mL respectively; this shows that the method of the present invention can effectively delay the deterioration of longan and maintain the quality of longan.

[0015] 2. The present invention uses sawdust as a fresh-keeping material, turning waste sawdust into treasure, and improving the use value of waste sawdust. The method of the present invention has simple operation steps and can be promoted for the preservation of other fruits. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the disease susceptibility index of longan of Example 1 and Comparative Examples 1-5 at 0, 3, 6 and 9 days.

[0017] Figure 2 The water loss rates of longan in Example 1 and Comparative Examples 1-5 at 0, 3, 6 and 9 days.

[0018] Figure 3 The longan pulp quality changes of Example 1 and Comparative Examples 1-5 at 0, 6 and 9 days.

[0019] Figure 4 The soluble sugar content of longan pulp of Example 1 and Comparative Examples 1-5 at 0, 6 and 9 days.

[0020] Figure 5 The titratable acid content of longan pulp of Example 1 and Comparative Examples 1-5 at 0, 6 and 9 days.

[0021] Figure 6 The changes of malondialdehyde content in longan pulp of Example 1 and Comparative Examples 1-5 at 0, 6 and 9 days. DETAILED DESCRIPTION

[0022] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Example 1

[0024] A method for prolonging the freshness of longan by using sawdust, comprising the following steps:

[0025] S1. Fresh longan is buried in dry sawdust sterilized by high pressure steam at 121℃ for 30min, and then packed in foam box without sealing. The density of longan in the foam box is 15Kg / m 3 The dry wood chips are dry sawdust of poplar and pine, with a moisture content of 15%;

[0026] S2. Store at room temperature (25-27°C).

[0027] The water loss rate and disease susceptibility index of longan were tested every 3 days (on days 0, 3, 6 and 9).

[0028] Water loss rate: Weigh the longan on an electronic balance and record the weight to calculate the water loss rate. Formula: Water loss rate (%) = (m0-m1) / m0×100%; where m0 is the initial mass of the longan before treatment (g); m1 is the mass of the longan after being buried in dry sawdust and placed in a foam box for several days (g).

[0029] Fruit susceptibility index: According to the size of the lesions on the fruit surface, it is graded as follows: 0: no susceptibility; 1: slight susceptibility; 2: 20% < lesion area < 25%; 3: 25% < lesion area < 50%; 4: lesion area ≥ 50%. Formula: susceptibility index = ∑ (number of diseased fruit grades × number of fruits in this grade) × 100% / (total number of fruits × highest grade number).

[0030] The pulp quality was observed on days 0, 6 and 9, and the contents of soluble sugar, malondialdehyde and titratable acid in the pulp were tested. The longan on day 0 was used as the control group.

[0031] Soluble sugar and malondialdehyde contents were detected according to the instructions of the plant soluble sugar content detection kit (PYFA4-M96) and the malondialdehyde content detection kit (PYHA4-M96) (Mofan Biotechnology), respectively.

[0032] Titratable acid content detection: Crush the longan pulp, centrifuge at 5000rpm for 5min, take the supernatant extract, transfer 20.0mL of the extract into a conical flask, add 2 drops of 1% phenolphthalein indicator, and titrate with a calibrated sodium hydroxide solution. Titrate until the solution begins to turn pink and does not fade within 0.5min, record the amount of sodium hydroxide titrant, and repeat three times. Then titrate with distilled water instead of the supernatant as a blank control.

[0033] According to the consumption of NaOH titration solution, the titratable acid content in longan pulp is calculated. Calculation formula:

[0034] Titratable acid content = V × c × (V1-V0) × 0.064 × 100% / Vs

[0035] V is the total volume of sample extract, mL;

[0036] Vs is the volume of the extract taken during titration, mL;

[0037] c is the concentration of NaOH titration solution, mol / L;

[0038] V1 is the volume of NaOH solution consumed in titrating the extract, mL;

[0039] V0 is the volume of NaOH solution consumed in titrating distilled water, mL;

[0040] 0.064 is the number of grams of citric acid equivalent to 1mL of 0.1mol / LNaOH solution.

[0041] Comparative Example 1

[0042] Referring to Example 1, the difference is that the fresh longan is not buried in the sterilized dry sawdust, but is directly placed in a foam box without sealing it and stored at room temperature. The other steps are the same as in Example 1.

[0043] Comparative Example 2

[0044] Referring to Example 1, the difference is that the fresh longan is not buried in the sterilized dry sawdust, but is directly placed in a foam box, sealed, and stored at room temperature. The other steps are the same as in Example 1.

[0045] Comparative Example 3

[0046] Referring to Example 1, the difference is that the fresh longan is buried in sterilized dry sawdust, and then placed in a foam box, sealed, and stored at room temperature. The other steps are the same as in Example 1.

[0047] Comparative Example 4

[0048] Refer to Example 1, except that fresh longan is buried in sterilized wet sawdust (sawdust: sterile water = 1 kg: 500 mL), and packed in a foam box, not sealed, and stored at room temperature. Other steps are the same as in Example 1.

[0049] Comparative Example 5

[0050] Refer to Example 1, except that the fresh longan is buried in sterilized wet sawdust (sawdust: sterile water = 1 kg: 500 mL), packed in a foam box, sealed, and stored at room temperature. Other steps are the same as in Example 1.

[0051] The results of the water loss rate, disease susceptibility index, pulp quality, and soluble sugar, malondialdehyde, and titratable acid content in longan in Example 1 and Comparative Examples 1-5 are shown in Figure 1-6 .

[0052] Depend on Figure 2 It can be seen that after 6 days of storage at room temperature, the water loss rate of longan treated with Comparative Example 2 (longan was not buried in dry sawdust and was directly placed in a foam box, and stored in a sealed box), Comparative Example 3 (longan was buried in dry sawdust and stored in a foam box, and stored in a sealed box), Comparative Example 4 (longan was buried in wet sawdust and stored in a foam box, and stored in an unsealed box) and Comparative Example 5 (longan was buried in wet sawdust and stored in a foam box, and stored in a sealed box) was less than 10%. The water loss rate of longan treated with Comparative Example 4 was less than 1%, and Comparative Example 5 was even a negative number. This may be because the wet sawdust made the longan epidermis moist, and the moisture was not easy to evaporate. In addition, there was a little sawdust on the longan, which made the water loss rate of the longan too low. Comparative Examples 2 and 3 were sealed in boxes, so the moisture on the longan epidermis evaporated in the foam box, making the storage environment high in moisture and the longan low in water loss. In addition, Figure 3 As shown, due to the high moisture content in the storage environment of the longan in Comparative Examples 2, 3, 4 and 5, the longan skin was moist and easy to break. The water loss rates of the longan treated in Comparative Example 1 (the longan was not buried in dry sawdust and directly placed in a foam box without sealing the box) and Example 1 (the longan was buried in dry sawdust and placed in a foam box without sealing the box) after 9 days of storage were 20.89% and 17.78% respectively. In addition, Figure 3 As shown, the longan skin of Example 1 is not dry and not easy to break. This shows that longan buried in dry sawdust and packed in foam boxes without sealing the box can effectively maintain the moisture of the longan skin and will not make the skin too wet and easy to break.

[0053] Depend on Figure 1It can be seen that after 6 days of storage at room temperature, the disease susceptibility index of the longan treated by Comparative Examples 2, 3, 4 and 5 is greater than 70%, and the disease susceptibility index of the longan treated by these comparative examples is greater than 90% after 9 days of storage, especially the disease susceptibility index of the longan treated by Comparative Example 2 reaches 100%. This may be because the storage environment of the longan treated by these comparative examples has high moisture, which is conducive to the growth of microorganisms on the longan epidermis. The disease susceptibility index of the longan treated by Comparative Example 1 and Example 1 after 9 days of storage is 42.71% and 30.21% respectively. This shows that the longan buried in dry sawdust and packed in a foam box without sealing the box can effectively reduce the contact with microorganisms in the air and keep the storage environment of the longan dry, thereby reducing the disease susceptibility index of the longan.

[0054] The content of soluble sugar in plants is positively correlated with the resistance of plants. Figure 4 As shown, compared with the control group (longan without any treatment on day 0) (442.81 mg / g), the soluble sugar content of longan treated with Comparative Example 2 (330.3 and 299.7 mg / g), Comparative Example 4 (352.9 and 341.1 mg / g) and Comparative Example 5 (350.0 and 308.6 mg / g) decreased significantly after 6 and 9 days of storage at room temperature, indicating that longan packed in foam boxes, sealed boxes and buried in wet sawdust and stored in foam boxes all reduce the resistance of longan to the outside world. The soluble sugar content of longan treated with Comparative Example 1 (436.0 and 405.1 mg / g) and Example 1 (442.8 and 413.6 mg / g) only decreased slightly, especially Example 1. This shows that longan buried in dry sawdust and packed in foam boxes, and stored without sealed boxes can effectively delay the stress of the outside world on longan. The amount of MDA in plants indicates the degree of damage to the plant cell membrane. MDA content reflects the degree of peroxidation of plant cell membranes. High MDA content indicates that the degree of peroxidation of plant cell membranes is high and the cell membranes are seriously damaged. Titratable acid is related to the freshness, flavor quality and processing requirements of food. The higher the content of titratable acid, the greater the acidity of the solution. Figure 5 and Figure 6As shown, compared with the malondialdehyde content (1.58 nmol / g) and titratable acid (0.150 g / 100 mL) of longan in the control group, after storage at room temperature for 6 and 9 days, the malondialdehyde content (4.35 / 5.25 nmol / g, titratable acid: 0.445 / 0.515 g / 100 mL) of Comparative Example 2 and Comparative Example 3 (2.16 / 3.57 nmol / g, titratable acid) of longan in the control group increased significantly. : 0.172 / 0.265g / 100mL), Comparative Example 4 (malondialdehyde: 2.24 / 3.39nmol / g, titratable acid: 0.275 / 0.316g / 100mL) and Comparative Example 5 (malondialdehyde: 3.55 / 3.86nmol / g, titratable acid: 0.185 / 0.352g / 100mL) treated longan had significantly increased malondialdehyde content and titratable acidity. Figure 3 As shown, the pulp of the longan processed in these comparative examples is damaged and rotten. This may be because the storage method of longan buried in wet sawdust and sealed boxes makes longan easy to be infected by pathogens, which causes a high degree of damage to the cell membrane of longan. For this reason, the malondialdehyde content and titratable acidity are high, affecting the quality of longan. The malondialdehyde content and titratable acidity of the longan processed in Comparative Example 1 (malondialdehyde: 1.92 / 2.18nmol / g, titratable acid: 0.172 / 0.288g / 100mL) and Example 1 (malondialdehyde: 1.70 / 2.08nmol / g, titratable acid: 0.153 / 0.156g / 100mL) are only slightly improved, and the malondialdehyde content and titratable acidity of the longan processed in Example 1 are even lower. This shows that longan buried in dry sawdust and packed in foam boxes, and storage without sealed boxes can effectively delay the deterioration of longan and maintain its quality.

[0055] From the above results, it can be seen that burying longan in dry sawdust and storing it in foam boxes without sealing the boxes can effectively reduce the water loss rate and disease degree of longan fruit, delay the deterioration of longan and maintain its quality.

Claims

1. A method for prolonging the freshness of longan by using sawdust, characterized in that: The following steps are involved: Bury fresh longan in sterilized dry sawdust, put it in a box without sealing it, and store it at room temperature.

2. The method according to claim 1, characterized in that The box is a foam box.

3. The method according to claim 1, characterized in that The moisture content of the dry sawdust is 15-20%.

4. The method according to claim 1, characterized in that: The dry sawdust is dry sawdust of poplar and / or pine.

5. The method according to claim 1, 3 or 4, characterized in that: The dry wood chips are dry sawdust.

6. The method according to claim 1, characterized in that The sterilization method is high pressure steam sterilization at 121° C. for 30 min.

7. The method according to claim 1, characterized in that The density of longan packed in boxes is 15-30Kg / m 3 .

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