A processing method for extending the storage time of wild rice stem

Abstract

The present invention provides a processing method for extending the storage time of wild rice stems, and belongs to the technical field of fruit and vegetable preservation. The processing method for extending the storage time of wild rice stems comprises: dipping fresh wild rice stems in bamboo shoot protein Pickering emulsion for 20 to 30 seconds, and drying in an environment of 25 to 40°C after dipping; sealing the fresh wild rice stems dipped in bamboo shoot protein Pickering emulsion separately; and storing them in an environment of 0 to 2°C and a low-voltage electrostatic field with an output voltage of ≤2500V and an output current of ≤0.2mA. The method of the present invention can significantly reduce the decay rate and browning of wild rice stems during storage, reduce the senescence of wild rice stem cells, and reduce the loss of wild rice stems.

Description

Technical Field

[0001] The invention belongs to the technical field of fruit and vegetable preservation, and particularly relates to a processing method for prolonging the storage time of wild rice stem. Background Art

[0002] Zizania latifolia Griseb., also known as wild rice, wild rice shoots, and wild rice melon, is a perennial shallow-water herb of the genus Zizania in the Poaceae family. Wild rice is a unique aquatic vegetable in my country, with a wide cultivation area, becoming the second largest aquatic vegetable after lotus root. The largest planting area is in Zhejiang Province, which has reached 20,000 hm2. 2 The above. The texture of wild rice is crisp and tender, rich in nutrients, rich in dietary fiber, protein, polysaccharides and other nutrients, which can promote the intestinal health of the human body. Due to the high water content of wild rice and the vigorous respiration after harvest, it is very easy to turn yellow, rot, and fibrosis during the storage period, resulting in a short sales cycle and a small sales radius for wild rice, which seriously restricts the development of the wild rice industry and affects the economic income of wild rice farmers. Therefore, studying post-harvest preservation methods to extend the storage period of wild rice and improve storage quality is of great significance to the development of the wild rice industry in various parts of my country.

[0003] At present, low-temperature refrigeration is a commonly used method for storing fruit and vegetable raw materials. With the continuous improvement of refrigeration infrastructure and cold chain logistics platforms, the post-harvest loss rate of fruits and vegetables in my country has dropped significantly, and the storage time has also been extended. However, relying solely on low-temperature refrigeration methods cannot keep fruits and vegetables in good taste and flavor during long-term storage. Therefore, multiple preservation methods synergistically extend the shelf life of fruits and vegetables and improve their quality during storage, which has gradually become a hot topic for researchers.

[0004] Low-voltage electrostatic field is a safe electrostatic field that can be used by humans and can purify the air to prevent airborne diseases. This technology is an emerging high-tech technology that has a very significant effect on the regulation of the storage environment of fruits and vegetables. Its principle is to create a specific frequency electric field environment at low temperature, aggregate and migrate water vapor under the action of electric field ions, induce water molecules to resonate at the same frequency, attach to the anode and become liquid water, thereby reducing the humidity in the air. Therefore, environmental factors such as temperature and humidity can be changed to inhibit the growth and reproduction of bacteria. At the same time, applying additional electric field treatment to fruit and vegetable raw materials can change the physiological and biochemical characteristics of fruits and vegetables, help improve the storage performance of fruits and vegetables, and improve the quality of fruits and vegetables during storage. This technology is applied to the storage of fruits and vegetables, which can achieve an ultra-long preservation effect. In recent years, research on the application of low-voltage electrostatic fields at home and abroad has mainly focused on the effects of low-voltage electrostatic fields on plant growth and development.

[0005] my country is rich in bamboo shoot resources. As the world's largest producer and consumer of bamboo shoots, China produces 5 to 6 million tons of bamboo shoots annually. Since the bamboo shoot production period is highly seasonal and relatively concentrated, fresh bamboo shoots are prone to browning and lignification, resulting in a short shelf life. Therefore, a large number of primary processing methods such as drying, pickling, quick freezing and canning are widely used to make dried bamboo shoots, pickled bamboo shoots, quick frozen bamboo shoots and canned bamboo shoots. During the processing of bamboo shoots, a large number of processing by-products such as bamboo shoot skins, bamboo shoot residues and bamboo shoot heads are produced, which can reach about 15% to 20% of the total weight of the bamboo shoot raw materials. Bamboo shoot proteins and polysaccharides have special reactions to electrostatic fields and can be prepared into film-forming materials.

[0006] This study used fresh wild rice stem in shell as raw material to investigate the effects of low-voltage electrostatic field and combined treatment on the storage quality and lignification process of fresh wild rice stem in shell under low-temperature storage conditions, in order to provide a theoretical basis for extending the storage and preservation of fresh wild rice stem in shell and improving its storage quality. Summary of the invention

[0007] In order to prolong the fresh-keeping time of wild rice stem and reduce the rotting and deterioration of wild rice stem during storage, the present invention provides a processing method for prolonging the storage time of wild rice stem, which specifically comprises the following steps:

[0008] ① Soak fresh wild rice stems in bamboo shoot protein Pickering emulsion for 20 to 30 seconds, and then quickly blow dry in an environment of 25 to 40°C;

[0009] ② Seal the fresh wild rice stem soaked in bamboo shoot protein Pickering emulsion separately;

[0010] ③Store in a low-voltage electrostatic field environment with a temperature of 0-2°C and an output voltage ≤2500V and an output current ≤0.2mA.

[0011] Wherein, the separate sealing process is a sealing process of packaging with a PE fresh-keeping bag.

[0012] The preparation method of the bamboo shoot protein Pickering emulsion is as follows:

[0013] The collected fresh bamboo shoot residues were crushed and homogenized, and the pH was adjusted to 9.0±0.2 with NaOH solution (1.0M), and then stirred and centrifuged at 60±5°C, and the supernatant was collected, and the pH was adjusted to 7.0±0.2; after being completely dispersed, the powder was dialyzed, freeze-dried, crushed and sieved to obtain the treated bamboo shoot residue powder;

[0014] The treated bamboo shoot residue powder is dispersed in deionized water, the pH is adjusted to 4.2±0.2, and after being completely dispersed by stirring, it is treated at 120±5°C for 15-30 minutes; after cooling to room temperature, it is centrifuged, and the obtained wet precipitate is dispersed again in deionized water, the pH is adjusted to 7.5±0.2, and it is completely dispersed by stirring; dialyzing and freeze-drying are performed to obtain bamboo shoot residue protein powder;

[0015] Accurately weigh the dried bamboo shoot protein powder sample and disperse it in a phosphate buffer, then add sodium azide, stir and fully hydrate overnight; obtain bamboo shoot protein nanoparticles after shearing and ultrasonic treatment;

[0016] The bamboo shoot protein solution and D-galactose solution were mixed evenly in equal volumes, and the pH of the mixture was adjusted to pH 7.0±0.2, sealed and stirred in a water bath at 60±5°C for 10-15h, and immediately transferred to an ice bath for cooling after the reaction was completed, and dialyzed to obtain glycosylated bamboo shoot protein;

[0017] The glycosylated bamboo shoot protein nanoparticles are dispersed in distilled water to obtain a glycosylated bamboo shoot protein nanoparticle suspension, and the glycosylated bamboo shoot protein nanoparticle suspension is mixed with camellia oil and then subjected to ultrasonic emulsification to obtain a bamboo shoot protein Pickering emulsion.

[0018] Wherein, the shearing treatment is carried out at a rotation speed of 3000 to 8000 rpm for 2 to 10 minutes.

[0019] The ultrasonic treatment is carried out for 15 to 30 minutes at a power of 750 W and 25 kHz; during the ultrasonic treatment, the ultrasonic amplitude is 54%, and ultrasonic pulses are used to suppress the temperature rise of the sample, and the temperature of the sample is controlled not to be higher than 25°C.

[0020] The mixture of the glycosylated bamboo shoot protein nanoparticle suspension and camellia oil is dispersed by an ultrasonic-assisted method, and the mixing ratio of the glycosylated bamboo shoot protein nanoparticle suspension and camellia oil is 4 to 2:1.

[0021] Beneficial Effects

[0022] The present invention adopts bamboo shoot protein Pickering emulsion to impregnate wild rice stem, and after impregnation, combined with the treatment of low-voltage electrostatic field, a layer of mobile water-retaining and preservative film is formed on the surface of wild rice stem, and this "preservative film" is a kind of emulsion, containing camellia oil and bamboo shoot protein, and has a certain effect of preventing a small amount of external oxygen from oxidizing wild rice stem, and has a certain water-retaining effect, so that bamboo shoots will not lose water and oxidize during storage. After bamboo shoot protein and camellia oil are mixed, under the action of low-voltage electrostatic field, bamboo shoot protein contains a certain amount of antimicrobial peptides, which are evenly distributed on the surface of wild rice stem, and can effectively prevent the reproduction of microorganisms, and achieve the purpose of inhibiting harmful strains. The bamboo shoot protein Pickering emulsion prepared by the present invention is a natural product, and it has the characteristics of high stability, and bamboo shoot protein can be evenly attached to the surface of wild rice stem to form uniform antibacterial protection, thereby effectively extending the storage time of wild rice stem, and reducing the browning inside wild rice stem.

[0023] The storage method of the invention is simple, has low storage cost, does not add any antibacterial agent or other storage auxiliary reagents, is efficient and safe, and has good market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 : Effect diagram of the blank group, low-voltage electrostatic field group, bamboo shoot protein treatment group and composite treatment group stored for 60 days. DETAILED DESCRIPTION

[0025] In all the embodiments of the present invention, the fresh shelled wild rice stem is provided by the Minyi Wild Rice Stalk Professional Cooperative of Yuexi County, and the bamboo shoot residue is a by-product of processing fresh bamboo shoots in Huangshan area.

[0026] Preparation of bamboo shoot protein Pickering emulsion:

[0027] 1. Pretreatment of bamboo shoots residue

[0028] The collected fresh bamboo shoots were crushed, homogenized with deionized water at a ratio of 1:3 (W:W), adjusted to pH = 9.0 ± 0.2 with NaOH solution (1.0M), and then placed in a 60 ± 5 ℃ water bath and stirred at 500 rpm for 115 to 30 minutes (calibrate the pH value every 12 to 10 minutes); centrifuged at 4000g for 15 minutes, collected the supernatant, and adjusted the pH to 7.0 ± 0.2. After complete dispersion, put it into a dialysis bag prepared in advance and dialyzed at 4 ℃ for 48 hours, changing the water every 12 hours, and freeze-dried after dialysis. Finally, crush and pass through a 120-mesh sieve for use.

[0029] 2 Preparation of bamboo shoot protein

[0030] The treated bamboo shoot residue powder was dispersed again with deionized water at a ratio of 1:5 (w / w), the pH was adjusted to 4.2±0.2, and after being completely dispersed by stirring, it was placed in a high-pressure steam sterilizer at 120±5°C for 15-30 minutes. After cooling to room temperature, centrifuged at 7000g for 12-10 minutes. Then, the wet precipitate of this step was dispersed again with deionized water at a ratio of 1:5 (w / w), the pH was adjusted to 7.5, and it was completely dispersed by stirring. The powder was bagged and dialyzed for 72 hours, the water was changed every 12 hours, and finally freeze-dried to obtain bamboo shoot residue protein, with a bamboo shoot protein content of 79.63%.

[0031] 3. Preparation of bamboo shoot protein nanoparticles

[0032] Accurately weigh the dried bamboo shoot protein powder sample and disperse it in phosphate buffer (5mM, pH=7.0±0.2) (concentration is 2.0wt%), add 0.02wt% sodium azide, stir magnetically for 4h, and fully hydrate at 4°C overnight. After hydration overnight, shear treatment is performed at a speed of 3000-8000rpm for 2-10min, and then the dispersion is ultrasonically treated at a power of 750W and 25kHz for 15-30min to obtain bamboo shoot protein nanoparticles. During the ultrasonic treatment, the ultrasonic amplitude is set to 54%, and a pulse of three seconds on / three seconds off is used to suppress the temperature rise of the sample. At the same time, the sample is immersed in an ice water bath to absorb the heat generated by the ultrasonic process, and the temperature of the sample is controlled not to be higher than 25°C.

[0033] 4. Preparation of Glycosylated Bamboo Shoot Protein Nanoparticles

[0034] Prepare a bamboo shoot protein solution with a concentration of 2.0wt.% and a D-galactose solution with a concentration of 4.0wt.% respectively. Then, mix the two in equal volumes and adjust the pH of the mixture to pH 7.0 with 1M NaOH solution or HCl solution. Finally, stir the strictly sealed mixture in a 60±5℃ water bath for 10-15h. After the reaction is completed, transfer the solution to an ice bath to cool it down and dialyze it in parallel (to remove unreacted D-galactose). Obtain glycosylated bamboo shoot protein.

[0035] 5. Preparation of Pickering emulsion:

[0036] An appropriate amount of glycosylated bamboo shoot protein nanoparticles is dispersed in distilled water to obtain a suspension with a solid content of 2.0wt%. The glycosylated bamboo shoot protein nanoparticle suspension and camellia oil are mixed in a volume ratio of 4 to 2:1 and then subjected to ultrasonic emulsification treatment. An ultrasonic crusher with a power of 40W and a pulse of 50% is used to disperse the mixture of the suspension and camellia oil for 5 minutes, and the process is repeated 3 times. After the treatment, a bamboo shoot protein Pickering emulsion is obtained.

[0037] Example

[0038] A processing method for extending the storage time of wild rice stem is as follows:

[0039] Select fresh wild rice stems with suitable maturity, uniform size and no damage. Divide fresh wild rice stems with shells into four groups, namely, a blank group, a low-voltage electrostatic field group, a bamboo shoot protein treatment group, and a composite treatment group. The treatment methods and storage conditions are as follows:

[0040] ①Blank group: The wild rice stem samples were packed in PE fresh-keeping bags and sealed, and stored in a cold storage at 0-2℃ for 60 days, and then samples were taken for index determination.

[0041] ② Low-voltage electrostatic field group: The wild rice samples were packaged in PE fresh-keeping bags and sealed, and stored in a 0-2℃ cold storage for 60 days. During storage, a 2500V voltage and a 0.2mA low-voltage electrostatic field were applied. After storage, samples were taken for index measurement.

[0042] ③ Bamboo shoot protein treatment group: The wild rice samples were immersed in bamboo shoot protein Pickering emulsion for 20-30s, blown dry in a bellows at 25-40℃ or air-dried naturally, packaged and sealed in PE fresh-keeping bags, and stored in a cold storage at 0-2℃ for 60d. After storage, samples were taken for index determination.

[0043] ④Compound treatment group: The water bamboo samples were immersed in bamboo shoot protein Pickering emulsion for 20-30s, dried in a bellows at 25-40℃, packaged and sealed in PE fresh-keeping bags, and stored in a cold storage at 0-2℃ for 60d. During storage, a low-voltage electrostatic field with a voltage of ≤2500V and a current of ≤0.2mA was applied. After storage, samples were taken for index measurement.

[0044] Storage measurement indicators are as follows:

[0045] 1.Determination method of decay rate:

[0046] The weight of rotten wild rice stem / total weight of wild rice stem × 100%. The larger the value, the more serious the rot of the sample.

[0047] 2. L value of wild rice stem meat.

[0048] The color was measured using a handheld colorimeter. After the wild rice stems were shelled, the wild rice stems were cut longitudinally in the middle, and the L* value of the cross section was measured. Four wild rice stems were taken from each group for repeated measurement, and the average value was taken. The larger the value, the closer the color is to pure white.

[0049] 3. Hardness

[0050] The texture analyzer (probe diameter 6mm) was used for the measurement, and the measurement depth was 10mm. The hardness of the middle part of the cut surface of the wild rice stem was measured by taking the longitudinally cut wild rice stems. Four wild rice stems were taken from each group for repeated measurement, and the average value was taken. The larger the value, the firmer the texture of the wild rice stem stems and the better the quality.

[0051] 4. Malondialdehyde content

[0052] The MDA content was determined using a malondialdehyde assay kit, and the results were expressed in nmol / mg. The larger the value, the more serious the aging of the wild rice stem cells and the worse the quality.

[0053] When stored for 60 days, the storage quality data of wild rice stem in low voltage electrostatic field and control group are shown in the following table:

[0054]

[0055] The experimental results show that after the low-voltage electrostatic field and bamboo shoot protein Pickering emulsion were combined, the decay rate of wild rice stems after 60 days of storage was significantly reduced, and its color after storage was also significantly whiter. Figure 1 As shown, Figure 1 From left to right, they are the compound treatment group, low-voltage electrostatic field group, bamboo shoot protein treatment group and blank group. Figure 1 It can be clearly seen that the whiteness of the water bamboo after the composite treatment is significantly higher than that of the other three groups. In terms of flatness, the composite treatment group has the best effect. The water bamboo after the blank group and the bamboo shoot protein Pickering emulsion treatment has obvious wrinkles, which is mainly a manifestation of cell aging and water loss. Similarly, in terms of hardness, the low-voltage electrostatic field group and the composite treatment group treated with low-voltage electrostatic field have greater hardness.

Claims

1. A method for prolonging the storage time of wild rice stem, characterized in that: The processing method comprises the following steps: ① Soak fresh wild rice stems in bamboo shoot protein Pickering emulsion for 20-30 seconds, and then blow dry in an environment of 25-40℃; ② Seal the fresh wild rice stem soaked in bamboo shoot protein Pickering emulsion separately; ③Store in a low-voltage electrostatic field environment at 0~2℃, voltage 2500V, current 0.2mA; Wherein, the preparation method of the bamboo shoot protein Pickering emulsion is as follows: The collected fresh bamboo shoot residues were crushed and homogenized, and the pH was adjusted to 9.0±0.2 with a 1.0M NaOH solution, and then stirred and centrifuged at 60±5°C, and the supernatant was collected and adjusted to pH 7.0±0.2; after being completely dispersed, the powder was dialyzed, freeze-dried, crushed and sieved to obtain the processed bamboo shoot residue powder; The treated bamboo shoot residue powder is dispersed in deionized water, the pH value is adjusted to 4.2±0.2, and after being completely dispersed by stirring, it is treated at 120±5℃ for 15-30 min; after cooling to room temperature, it is centrifuged, and the obtained wet precipitate is dispersed again in deionized water, the pH value is adjusted to 7.5, and it is completely dispersed by stirring; dialyzing and freeze-drying are performed to obtain bamboo shoot residue protein powder; Accurately weigh the dried bamboo shoot protein powder sample and disperse it in a phosphate buffer, then add sodium azide, stir and fully hydrate overnight; obtain bamboo shoot protein nanoparticles after shearing and ultrasonic treatment; The bamboo shoot residue protein nanoparticles were mixed with an equal volume of D-galactose solution, and the pH of the mixture was adjusted to pH 7.0, sealed and stirred in a water bath at 60±5°C for 10-15h, and immediately transferred to an ice bath for cooling after the reaction was completed, and dialyzed to obtain glycosylated bamboo shoot residue protein nanoparticles; The glycosylated bamboo shoot protein nanoparticles are dispersed in distilled water to obtain a glycosylated bamboo shoot protein nanoparticle suspension. The glycosylated bamboo shoot protein nanoparticle suspension is mixed with camellia oil and then subjected to ultrasonic emulsification to obtain a bamboo shoot protein Pickering emulsion.

2. The method for extending the storage time of wild rice stem according to claim 1, wherein: The individual sealing process is to use PE fresh-keeping bag packaging and sealing process.

3. The method for extending the storage time of wild rice stem according to claim 1, wherein: The shearing treatment is performed at a rotation speed of 3000-8000 rpm for 2-10 min.

4. The method for prolonging the storage time of wild rice stem according to claim 1, wherein: The ultrasonic treatment is carried out for 15 to 30 min at a power of 750 W and 25 kHz; during the ultrasonic treatment, the ultrasonic amplitude is 54%, and ultrasonic pulses are used to suppress the temperature rise of the sample, so that the temperature of the sample is controlled not to be higher than 25°C.

5. The method for prolonging the storage time of wild rice stem according to claim 1, characterized in that: The mixture of glycosylated bamboo shoot residue protein nanoparticle suspension and camellia oil was dispersed by ultrasound-assisted method.

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