A postharvest green in vivo fresh-keeping method for sweet dragon bamboo shoots

Abstract

The present invention provides a post-harvest green in-vivo preservation method for sweet dragon bamboo shoots, which relates to the technical field of bamboo shoot preservation. The preservation method mainly includes pre-cooling the sweet dragon bamboo shoots at a temperature of 4-10°C in a cold storage for 8-14 hours after harvest, soaking them in a preservative, wrapping them with a plastic wrap, and refrigerating them at 4°C. Chitosan, lysozyme, the fermentation extract of sweet dragon bamboo shoot shells, tea polyphenols, antioxidants, etc. are used as the preservative. The fermentation extract of sweet dragon bamboo shoot shells is obtained by steaming and grinding the sweet dragon bamboo shoot shells and the remaining bamboo shoot trimming residues, fermenting them with Saccharomyces cerevisiae, and then sterilizing and filtering. The present invention overcomes the deficiencies of the prior art, effectively extends the shelf life of sweet dragon bamboo shoots, prevents the loss of bamboo shoot nutrients and browning, and comprehensively improves the economic value of sweet dragon bamboo shoots.

Description

Technical Field

[0001] The present invention relates to the technical field of bamboo shoot preservation, and particularly relates to a post-harvest green in-vivo preservation method for Tianlong bamboo shoots. Background Art

[0002] Tianlong bamboo shoots, also known as sweet bamboo shoots, are extremely robust in appearance and are good fresh edible bamboo shoot varieties. Tianlong bamboo shoots are rich in nutrition, have a refreshing taste, and have high market value. Now, artificial cultivation of Tianlong bamboo for bamboo shoot production is gradually carried out.

[0003] Since the shooting period of Tianlong bamboo is mostly in summer and the shooting period is during the high-temperature season, Tianlong bamboo shoots need to be eaten as soon as possible after harvesting. Otherwise, the bamboo shoots will gradually age or deteriorate, the nutritional components will be lost, and the whole will turn brown, seriously affecting the edible value and economic value of the bamboo shoots. Based on this, how to carry out in-vivo preservation of Tianlong bamboo shoots after harvesting to extend their shelf life is crucial.

[0004] In the literature "Effects of Three Biological Preservatives on the Lignification of Post-harvest Bolina Tianlong Bamboo Shoots" published by Zhang Xiongfeng et al., a preservative was prepared by using nisin, lysozyme, and chitosan solution to treat fresh Bolina Tianlong bamboo shoots, which could effectively extend the shelf life of Bolina Tianlong bamboo shoots and prevent discoloration and lignification. However, in this document, the preservation effect of Bolina Tianlong bamboo shoots was for 8 days, which is relatively short for the production and sales of Tianlong bamboo shoots. Therefore, how to further extend the shelf life of Tianlong bamboo shoots is an important research direction at the present stage. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a post-harvest green in-vivo preservation method for Tianlong bamboo shoots, which can effectively extend the shelf life of Tianlong bamboo shoots, prevent the loss of bamboo shoot nutrition and browning, and comprehensively improve the economic value of Tianlong bamboo shoots.

[0006] To achieve the above object, the technical solution of the present invention is realized through the following technical solutions:

[0007] A post-harvest green in-vivo preservation method for Tianlong bamboo shoots, the preservation method comprising the following steps:

[0008] S1. Bamboo shoot precooling treatment: Take fresh Tianlong bamboo shoots, peel off the outer bamboo shoot sheaths, trim and shape them, then wash them clean, and place them at a temperature of 4-10°C for precooling treatment; or place them at a temperature of 4-10°C for precooling after harvesting, and then peel the sheaths, trim and shape them, and wash them.

[0009] S2. Prepare the preservative according to the following contents: chitosan 10 - 20 g / L + lysozyme 0.5 - 0.8 g / L + fermented extract of sweet dragon bamboo shoot shell 120 - 180 mL / L + tea polyphenols 20 - 40 mg / L + antioxidant 15 - 20 mg / L, and the rest is distilled water; the fermented extract of sweet dragon bamboo shoot shell is obtained by steaming the sweet dragon bamboo shoot shell and the remaining bamboo shoot trimming residues, mixing them with Saccharomyces cerevisiae for fermentation, and then sterilizing and filtering;

[0010] S3. Preservative treatment: Soak the pre-cooled bamboo shoots in the preservative for 30 - 60 s, and then take them out and let them stand at 10 °C to drain the excess preservative;

[0011] S4. Long-term storage: Wrap the above-mentioned standing bamboo shoots with plastic wrap and store them at 4 °C for a long time.

[0012] Preferably, the pre-cooling treatment time in step S1 is 8 - 14 h, and the purpose is to finally reduce the central temperature of the bamboo shoots below 6 °C, and preferably 4 °C.

[0013] Preferably, the preparation method of the fermented extract of sweet dragon bamboo shoot shell in step S2 includes the following steps:

[0014] S2-1. Rinse the fresh bamboo shoot shells and the remaining bamboo shoot trimming residues, steam them at 110 - 120 °C for 30 min, collect the juice during steaming and mix it with the bamboo shoot shells, then add water to control the solid-liquid ratio to 1:2 - 3 and grind it into a slurry to obtain a mixed slurry for standby;

[0015] S2-2. Inoculate the mixed slurry with 0.1% - 0.2% of the total mass of Saccharomyces cerevisiae, and ferment for 30 - 40 h to obtain a fermented material for standby;

[0016] S2-3. Sterilize the above-mentioned fermented material and then press and filter it. The filtrate is the fermented extract of sweet dragon bamboo shoot shell.

[0017] Preferably, the viable count of Saccharomyces cerevisiae in step S2-2 is 1×10 9 -2×10 9 CFU / g.

[0018] Preferably, the sterilization method in step S2-3 is to raise the temperature to 115 °C, raise the pressure to 1.85 Mpa, and perform heat and pressure preservation sterilization for 15 min.

[0019] Preferably, the storage and use temperatures of the fermented extract of sweet dragon bamboo shoot shell and the prepared preservative are both controlled below 10 °C.

[0020] Preferably, the antioxidant in step S2 is citric acid.

[0021] Preferably, during the soaking treatment in step S3, the temperature of the preservative is controlled at 2-10°C.

[0022] Preferably, the standing time in step S3 is 1-2 h.

[0023] Preferably, the plastic wrap used in step S4 is PE plastic wrap.

[0024] The present invention provides a post-harvest green in-vivo preservation method for sweet dragon bamboo shoots. Compared with the prior art, the advantages are as follows:

[0025] The present invention adopts early low-temperature treatment followed by pre-cooling and then treatment with a mixed preservative for fresh sweet dragon bamboo shoots, effectively extending their shelf life. Moreover, the low-temperature and pre-cooling treatments can effectively inhibit the respiration of bamboo shoots, reduce the nutrient loss during subsequent low-temperature storage of bamboo shoots, and through the preservative prepared by compounding chitosan, lysozyme, the fermentation extract of sweet dragon bamboo shoot shells, tea polyphenols, and antioxidants, treating the bamboo shoots and then wrapping them with plastic wrap and refrigerating, it can effectively resist oxidation and prevent the browning of bamboo shoots, and further reduce the loss of total sugar during storage, reduce the generation of lignin, delay the lignification degree of bamboo shoots, and extend the shelf time to 35 d. Description of the Drawings

[0026] Figure 1 It is a schematic diagram of the surface browning of bamboo shoots stored for 10 d in Experimental Group 1 of the present invention;

[0027] Figure 2 It is a schematic diagram of the surface browning of bamboo shoots stored for 35 d in Experimental Group 1 of the present invention;

[0028] Figure 3 It is a schematic diagram of the surface browning of bamboo shoots stored for 10 d in Experimental Group 2 of the present invention;

[0029] Figure 4 It is a schematic diagram of the surface browning of bamboo shoots stored for 35 d in Experimental Group 2 of the present invention;

[0030] Figure 5 It is a schematic diagram of the surface browning of bamboo shoots stored for 10 d in Experimental Group 3 of the present invention;

[0031] Figure 6 It is a schematic diagram of the surface browning of bamboo shoots stored for 35 d in Experimental Group 3 of the present invention;

[0032] Figure 7 It is a schematic diagram of the surface browning of bamboo shoots stored for 10 d in Experimental Group 4 of the present invention;

[0033] Figure 8 It is a schematic diagram of the surface browning of bamboo shoots stored for 35 d in Experimental Group 4 of the present invention;

[0034] Figure 9Schematic diagram of the surface browning of bamboo shoots stored for 10 days in Experimental Group 5 of the present invention;

[0035] Figure 10 Schematic diagram of the surface browning of bamboo shoots stored for 35 days in Experimental Group 5 of the present invention;

[0036] Figure 11 Schematic diagram of the surface browning of bamboo shoots stored for 10 days in Experimental Group 6 of the present invention;

[0037] Figure 12 Schematic diagram of the surface browning of bamboo shoots stored for 35 days in Experimental Group 6 of the present invention;

[0038] Figure 13 Schematic diagram of the surface browning of bamboo shoots stored for 10 days in the control group of the present invention;

[0039] Figure 14 Schematic diagram of the surface browning of bamboo shoots stored for 35 days in the control group of the present invention. Detailed implementation manners

[0040] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] The Saccharomyces cerevisiae used below is commercially available, with a viable count of 1×10 9 CFU / g, and the preservation number of this Saccharomyces cerevisiae is CCTCC NO: M2014019; the antioxidant is citric acid. Example 1:

[0042] Raw material preparation:

[0043] 1. Raw material preparation:

[0044] 1.1 Select the same batch of mature Tianlong bamboo shoots, remove the bad ones, and reserve them as experimental materials;

[0045] 1.2 Preparation of the preservative:

[0046] Preservative 1: Chitosan 10 g / L + Lysozyme 0.5 g / L + Extract A 1200 mL / L + Tea polyphenols 20 mg / L + Antioxidant 15 mg / L, and the rest is distilled water;

[0047] Preservative 2: Chitosan 20 g / L + Lysozyme 0.8 g / L + Extract A 180 mL / L + Tea polyphenols 40 mg / L + Antioxidant 20 mg / L, the rest is distilled water;

[0048] Preservative 3: Chitosan 10 g / L + Lysozyme 0.5 g / L + Extract B 120 mL / L + Tea polyphenols 20 mg / L + Antioxidant 15 mg / L, the rest is distilled water;

[0049] Preservative 4: Chitosan 10 g / L + Lysozyme 0.5 g / L + Extract C 120 mL / L + Antioxidant 15 mg / L, the rest is distilled water;

[0050] 1.2 - 1. Preparation method of Extract A:

[0051] (1) Rinse the fresh bamboo shoot sheaths (including the residues remaining after bamboo shoot trimming) thoroughly, then steam them for 30 min. Collect the juice during steaming and mix it with the bamboo shoot sheaths, add water to control the solid - liquid ratio to 1:2, and then grind it into a slurry to obtain a mixed slurry;

[0052] (2) Inoculate the mixed slurry with Saccharomyces cerevisiae accounting for 0.2% of the total mass of the mixed slurry, and ferment for 35 h to obtain a fermented material;

[0053] (3) Heat the above - mentioned fermented material to 115 °C, increase the pressure to 1.85 Mpa, sterilize for 15 min, then press - filter. The filtrate is Extract A.

[0054] 1.2 - 2. Preparation method of Extract B:

[0055] (1) Rinse the fresh bamboo shoot sheaths (including the residues remaining after bamboo shoot trimming) thoroughly, then steam them for 30 min. Collect the juice during steaming and mix it with the bamboo shoot sheaths, add water to control the solid - liquid ratio to 1:2, and then grind it into a slurry to obtain a mixed slurry;

[0056] (2) Heat the mixed slurry to 115 °C, increase the pressure to 1.85 Mpa, sterilize for 15 min, then press - filter. The filtrate is Extract B.

[0057] 1.2 - 3. Preparation method of Extract C:

[0058] (1) Inoculate 0.2% of Saccharomyces cerevisiae into YPD liquid medium, and culture it under suitable conditions for 35 h to obtain a fermented material;

[0059] (2) Heat the above - mentioned fermented material to 115 °C, increase the pressure to 1.85 Mpa, sterilize for 15 min, then press - filter. The filtrate is Extract C.

[0060] 2. Fresh - keeping treatment of sweet dragon bamboo shoots:

[0061] (1)Peel the outer bamboo shoot sheaths from fresh Tianlong bamboo shoots, trim and shape them, then wash them clean. Place them at 4°C for 8 hours of pre-cooling treatment, and then take them out.

[0062] (2)Soak the pre-cooled bamboo shoots in a preservative at 5°C for 50 seconds, then take them out and let them stand at 10°C for 1.5 hours to drain the excess preservative. Then wrap them with PE plastic wrap and store them at 4°C.

[0063] Detection:

[0064] 1. Detect the preservation effects of different preservatives on Tianlong bamboo shoots:

[0065] Refer to the above preservation treatment method, and set up a total of 5 groups of preservation experiments (10 bamboo shoots in each group). Each group is treated with different preservatives according to Table 1 below, and detect the weight loss rate, total sugar content, lignin content, crude fiber content (the main component is cellulose, and also contains some hemicellulose, pentosan, nitrogenous substances), and vitamin C content of the bamboo shoots at 0d, 5d, 15d, and 35d of preservation.

[0066] Among them, the browning grade is divided into 0 - 5 levels, and the classification standard is: level 0 is no browning, level 1 is slight browning (browning area ≤ 10%), level 2 is mild browning (browning area 10% - 20%), level 3 is moderate browning (browning area 20% - 30%), level 4 is severe browning (browning area 30% - 40%), and level 5 is extreme browning (browning area > 50%);

[0067] Weight loss rate = (weight before storage - weight after storage) / weight before storage;

[0068] The total sugar content is determined by the direct titration method with Fehling's reagent.

[0069] The detection of lignin content is as follows: Cut 5g of bamboo shoots (M1), crush them, mix them with 10mL of 72% H2SO4 and stir evenly, then let them stand at a constant temperature of 20°C for 4 hours. Then dilute the H2SO4 to 3%, boil for 2 hours, then filter and wash until neutral, and then dry them in an oven at 105°C, cool and weigh and record as M2. Finally, the lignin content = M2 / M1;

[0070] The detection of crude fiber content is as follows: Refer to the method of GB / T 5009.10 - 2003 and use a Fibertc 8000 cellulose analyzer to determine.

[0071] The vitamin C content is determined by the 2,6 - dichlorophenolindophenol method.

[0072] The specific detection results are shown in Table 1 below:

[0073] Table 1

[0074]

[0075] As can be seen from the above table, the overall weight loss rate, lignin content, and crude fiber content of the bamboo shoots treated with preservative 1 and preservative 2 are lower after 35 days of storage, and the total sugar content and vitamin C content are higher. At the 5th day of storage, the total sugar content of experimental groups 1-4 and the control group increased. Subsequently, the total sugar content of the control group decreased significantly, while the total sugar content of experimental groups 1-4 decreased less, and the decrease amplitude of experimental groups 1-2 was the smallest. That is, treating bamboo shoots with preservative 1 and preservative 2 in experimental groups 1-2 has a better preservation effect.

[0076] 2. Use preservative 1 to preserve sweet dragon bamboo shoots, and set different preservation treatment methods according to the following experimental groups:

[0077] Experimental group 5:

[0078] (1) Peel the outer bamboo shoot sheaths of fresh sweet dragon bamboo shoots, trim and shape them, and then wash them clean;

[0079] (2) Soak the washed bamboo shoots in preservative 1 at 5°C for 50 s, then take them out and let them stand at 10°C for 1.5 h to drain the excess preservative, and then wrap them with PE plastic wrap and store them at 4°C.

[0080] Experimental group 6:

[0081] (1) Peel the outer bamboo shoot sheaths of fresh sweet dragon bamboo shoots, trim and shape them, wash them clean, and pre-cool them at 5°C for 8 h;

[0082] (2) Soak the pre-cooled bamboo shoots in preservative 1 at room temperature for 50 s, then take them out and let them stand at room temperature for 1.5 h to drain the excess preservative, and then wrap them with PE plastic wrap and store them at 4°C.

[0083] Detect the weight loss rate, total sugar content, lignin content, crude fiber content, and vitamin C content of the above experimental group 5 and experimental group 6 at 0 d, 5 d, 15 d, and 35 d of storage. The specific results are shown in Table 2 below

[0084] Table 2

[0085]

[0086] By comparing experimental groups 5-6 with the above experimental group 1, it can be seen that the differences in the weight loss rate, total sugar content, lignin content, crude fiber content, and vitamin C of experimental groups 5-6 and experimental group 1 during storage are small, but the overall flatness is slightly worse than that of experimental group 1.

[0087] The browning conditions of the bamboo shoots in the above experimental groups 1-6 and the control group after being stored for 10 days and 35 days were graded (the average value was calculated by taking 3 bamboo shoots from each group), and the specific results are shown in Table 3 and the appendix Figures 1-14 As shown, the browning is divided into levels 0-5, and the grading standard for each level is as follows: level 0 is no browning, level 1 is slight browning (browning area ≤ 10%), level 2 is mild browning (browning area 10% - 20%), level 3 is moderate browning (browning area 20% - 30%), level 4 is severe browning (browning area 30% - 40%), and level 5 is extreme browning (browning area > 50%).

[0088] Table 3

[0089]

[0090] As can be seen from the above table, experimental groups 1-2 have lower browning grades and still have higher quality after being stored for 35 days, while experimental groups 5-6 have relatively higher browning degrees.

[0091] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A post-harvest green in-vivo preservation method for sweet dragon bamboo shoots, characterized in that, The preservation method includes the following steps: S1. Bamboo shoot precooling treatment: Take fresh Tianlong bamboo shoots, peel off the outer bamboo shoot sheaths, trim and shape them, then wash them clean, and place them at a temperature of 4 - 10°C for precooling treatment; or precool them at a temperature of 4 - 10°C after harvesting, and then peel the sheaths, trim and shape them, and wash them; S2. Prepare the preservative according to the following contents: chitosan 10 - 20 g / L + lysozyme 0.5 - 0.8 g / L + fermentation extract of Tianlong bamboo shoot sheaths 120 - 180 mL / L + tea polyphenols 20 - 40 mg / L + antioxidant 15 - 20 mg / L, and the rest is distilled water. The antioxidant is citric acid. The preparation method of the fermentation extract of Tianlong bamboo shoot sheaths includes the following steps: S2-1. Rinse the fresh bamboo shoot sheaths and the remaining bamboo shoot trimmings, then steam them at 110 - 120°C for 30 min, collect the juice during steaming and mix it with the bamboo shoot sheaths, then add water to control the solid - liquid ratio to 1∶2 - 3, and grind it into a slurry to obtain the mixed slurry for standby; S2-2. Inoculate the mixed slurry with 0.1% - 0.2% of the total mass of Saccharomyces cerevisiae, and ferment for 30 - 40 h to obtain the fermented material for standby; S2-3. Sterilize the above - mentioned fermented material, then press and filter it. The filtrate is the fermentation extract of Tianlong bamboo shoot sheaths; S3. Preservative treatment: Immerse the precooled bamboo shoots in the preservative for 30 - 60 s, then take them out and let them stand at a temperature of 10°C to drain the excess preservative; S4. Long - term storage: Wrap the above - mentioned standing bamboo shoots with a plastic wrap and store them at a temperature of 4°C for a long time.

2. The freshness preservation method according to claim 1, wherein: In step S1, the precooling treatment time is 8 - 14 h to make the final central temperature of the bamboo shoots drop below 6°C.

3. The freshness preservation method according to claim 1, wherein: The viable count of Saccharomyces cerevisiae in the step S2-2 is 1×10 9 -2×10 9 CFU / g.

4. The fresh-keeping method according to claim 1, wherein: The sterilization method in step S2-3 is to raise the temperature to 115°C, raise the pressure to 1.85 Mpa, and carry out heat - preservation and pressure - maintenance sterilization treatment for 15 min.

5. The freshness preservation method according to claim 1, characterized in that: The storage and use temperatures of the fermentation extract of Tianlong bamboo shoot sheaths and the prepared preservative are both controlled below 10°C.

6. The preservation method according to claim 1, wherein: During the immersion treatment in step S3, the temperature of the preservative is controlled at 2 - 10°C.

7. The freshness preservation method according to claim 1, characterized in that: The standing time in step S3 is 1 - 2 h.

8. The fresh-keeping method according to claim 1, characterized in that: The plastic wrap used in step S4 is PE plastic wrap.

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