Multidimensional ecological preservation technology for sweet potatoes

Abstract

The present invention relates to a multidimensional ecological preservation technology for sweet potatoes, including the following steps: collecting mature tuberous roots in proper time; and performing BTH soak cleaning to promote callus, and performing callus treatment as follows: pretreatment before storage, disinfection in a cellar, sand storage, tent air conditioning, and performing secondary cobalt ray irradiation at an irradiation dose of 0.1-0.5 kGy before the end of storage and marketing, thereby achieving dual guarantee of storage period and shelf life. In the present invention, the traditional sand is replaced with a sandy material (having a particle size of 1-3 mm), and the sandy material is lightweight, breathable, and high in water absorbing and retaining property, thermal insulation and heat preservation.

Claims

1. A cellar sand storage preservation method for sweet potatoes, comprising the following specific operating steps: (1) collecting mature tuberous roots, removing damaged, incomplete and diseased sweet potato pieces, and trimming to remove root hair and vines; (2) performing BTH (Benzothiadiazole) soaking and cleaning on sweet potatoes to promote formation of a callus on an outer surface of the sweet potatoes, wherein a concentration is 100 mg/L, and soaking time is 3-5 min; (3) performing ultrasonication on cleaned sweet potato potatoes under a high temperature of 25-33° C. and high humidity of 90-95% for 2-3 days so as to form a wound healing periderm, wherein ultrasonic power is 100-300 W, and a frequency is 15 kHz; (4) uniformly spraying a hydrophobic nano silica solution on sweet potato surfaces, wherein a concentration of the solution is 1-4 wt %; and then performing .sup.60Co y ray irradiation on the sweet potatoes at an irradiation dose of 0.1-0.5 kGy; (5) uniformly spraying a potassium permanganate solution having a mass fraction of 1-1.5 wt % on each part of a cellar, and performing synergistic ultrasonication during oxidation on the each part of the cellar, wherein ultrasonic power is 100 W, a frequency is 20-25 kHz, and time is 20-30 min; (6) alternately laying multiple layers of sweet potatoes and multiple layers of sand when a temperature in the cellar is reduced to 13° C., wherein sand layer thickness is appropriate when the sweet potatoes are not seen; covering sandy particles of 5-8 cm thick on a last layer; and uniformly mixing microencapsulated preservation particles in the sandy particles, wherein a ratio of the microencapsulated preservation particles accounting for the sandy material is 5-15 wt %; (7) building a frame to cover with a membrane tent outside sand storage heaps, wherein the membrane tent is a PE (Poly Ethylene) film of 0.04-0.06 mm thick, and concentrations of O.sub.2 and CO.sub.2 in the storage environment are respectively maintained in ranges of 7-8% and <10%; and (8) performing secondary .sup.60Co y ray irradiation at an irradiation dose of 0.1-0.5 kGy on the sweet potatoes after being removed from the sand.

2. The cellar sand storage preservation method for sweet potatoes according to claim 1, wherein a formula of the sandy particles comprises the following raw materials in percentage by mass: TABLE-US-00005 modified diatomite 30%-60% modified expanded perlite 30%-60% polymerizer-acrylic acid 3%-5% Initiator-potassium persulfate 1%-3% cross-linking agent-polyacrylamide 1%-3% dispersing agent-polyvinyl alcohol  0.1-2%% preparation method of the sandy particles is as follows: (1) weighing diatomite in a container, treating the container under microwave power of 300-320 W for 10-15 min, and placing the container in a thermostatic water bath; dropwise adding a sulfuric acid solution having a mass fraction of 3-5 wt % while stirring at low speed of 300 r/min, wherein a ratio of mass g of the diatomite to volume mL of the sulfuric acid solution is 1:3; then, regulating the rotation speed to 600 r/min, and stirring for 5-6 h; and washing the solution to be neutral with 1 wt % of NaOH solution after cooling, and drying under a condition of 100-110° C. for 3 h, thereby obtaining the modified diatomite; (2) preheating and stirring perlite particles at 110° C. for 10 min, wherein a stirring rate is 800 r/min; adding a performance additive ammonium hydroxide accounting for 1-5 wt % of the weight of perlite to regulate a surface potential of the perlite, and promoting bonding between a coupling agent and the surface of the perlite; adding a silane coupling agent accounting for 2 wt % of the weight of the perlite; and performing surface modification at 160-180° C. for 40-50 min, and filtering to obtain modified perlite powder; (3) adding potassium persulfate and polyacrylamide into an acrylic solution having a concentration of 30% in sequence according to a mass ratio, stirring by a high-speed stirrer at a rate of 600 r/min, and adding polyvinyl alcohol within 5 min after dispersing; and performing, ultrasonic mixed dispersion for 20 min under ultrasonic power of 300 W so as to obtain a polymerization solution; (4) performing ultrafine grinding on the modified diatomite and expanded perlite to 800 meshes, adding the ground powder into the polymerization solution, heating and reacting under a temperature condition of 50-60° C. for 4-6 h, raising the temperature to 70-80° C., and carrying out a reaction for 2 h so as to obtain a gel-like sandy material; and (5) drying the gel-like sandy material under a high-temperature condition of 110° C. until water content is up to 5-8 wt %, and performing mechanical pulverization to 0.08-2 mm, thereby obtaining final sandy particles.

3. The cellar sand storage preservation method for sweet potatoes according to claim 1, wherein the microencapsulated preservation particles comprise: 1-3 parts of jasmonic acid methyl ester, 1-3 parts of CaO.sub.2, 5-10 parts of beta-cyclodextrin, 5-15 parts of chitosan, 4-8 parts of sodium alginate, 0.3-0.5 part of Tween-80 and 100 parts of sterile water.

4. The cellar sand storage preservation method for sweet potatoes according to claim 3, wherein a preparation method of the microencapsulated preservation particles comprises the following steps: adding the beta-cyclodextrin and sterile water into a triangular flask according to a preset weight ratio, and stirring at a rotation speed of 800-1500 r/min; then, heating to a temperature of 60-80° C. to completely dissolve the beta-cyclodextrin; continuously stirring, and gradually cooling the solution to 35-45° C.; adding the jasmonic acid methyl ester and CaO.sub.2 to be uniformly dispersed in the solution; slowly reducing the temperature to room temperature so as to form single-wall double-core beta-cyclodextrin-jasmonic acid methyl ester-CaO.sub.2 microcapsules, and adding a second layer of mixed wall material composed of chitosan and sodium alginate on the basis, wherein a weight ratio of the chitosan to sodium alginate is 3:1 to 2:3; treating a homogeneous emulsifier Tween-80 and a mixed solution by a high-shear emulsification instrument for 5-10 min; finally forming double-walled double-core microcapsule preservative emulsion which takes chitosan/sodium alginate and beta-cyclodextrin as the wall material and takes the jasmonic acid methyl ester and CaO.sub.2 as the core material; performing suction filtration and, washing; and performing vacuum drying at 25° C. for 48 h, thereby obtaining powdered particles.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a photo of a sandy material (having a particle size of 0.08-2 mm).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(2) The present invention will be further described below in detail in combination with drawings and through specific embodiments. The following embodiments are descriptive only, rather than restrictive, and shall not be used to limit the protection scope of the present invention.

(3) A multidimensional ecological preservation technology for sweet potatoes includes the following specific operating steps:

(4) (1) collecting mature tuberous roots in proper time, removing damaged, incomplete and diseased potato pieces, and trimming to remove root hair and vines;

(5) (2) performing BTH soak cleaning to promote callus, wherein a concentration is 100 mg/L, and soaking time is 3-5 min;

(6) (3) callus treatment: performing callus treatment on cleaned sweet potato tubers under ultrasonication of a high temperature of 25-33° C. and high humidity of 90-95% for 2-3 days so as to form wound periderm, wherein ultrasonic power is 100-300 W, and a frequency is 15 kHz;

(7) (4) pretreatment before storage: uniformly spraying a hydrophobic nano silica solution on sweet potato surfaces wherein a concentration of the solution is 1-4 wt %; and then performing .sup.60Co γ ray irradiation on the sweet potatoes at an irradiation dose of 0.1-0.5 kGy;

(8) (5) cellar disinfection: uniformly spraying a potassium permanganate solution having a mass fraction of 1-1.5 wt % on each part of a cellar, and performing synergistic ultrasonication during oxidation, wherein ultrasonic power is 100 W, a frequency is 20-25 kHz, and time is 20-30 min;

(9) (6) sand storage: performing sand storage when a temperature in the cellar is reduced to 13° C., and laying sand by adopting an interlayer heaping method, wherein sand thickness is appropriate when the sweet potatoes are not seen; covering sandy particles of 5-8 cm thick on the last layer; and uniformly mixing microencapsulated preservation particles in the sandy particles, wherein a ratio of the microencapsulated preservation particles accounting for the sandy material is 5-15 wt %, and the sandy particles may be repeatedly used;

(10) (7) tent air-conditioning: building a frame to cover a membrane tent outside sand storage heaps, wherein the membrane tent is a PE film of 0.04-0.06 min thick, an automatic air-conditioning effect of the sweet potatoes is achieved, and concentrations of O.sub.2 and CO.sub.2 in the storage environment are respectively maintained in ranges of 7-8% and <10%; and

(11) (8) performing secondary .sup.60Co γ ray irradiation at an irradiation dose of 0.1-0.5 kGy before storage is ended and the sweet potatoes appear on the market, thereby achieving dual guarantee of storage period and shelf life.

(12) II. The formula of the used sandy particles includes the following raw materials in percentage by mass:

(13) TABLE-US-00003 modified diatomite (a main component is silica) 30-60%  modified expanded perlite (lightweight, thermal insulation and 30-60%  heat preservation) polymerizer-acrylic acid (a vinyl monomer having a quite high 3-5% polymerization speed) initiator-potassium persulfate (promoting polymerization) 1-3% cross-linking agent-polyacrylamide (increasing gel strength of 1-3% a high absorbent water-retaining agent) dispersing agent-polyvinyl alcohol 0.1-2%. 

(14) Preparation methods are as follows:

(15) (1) Diatomite modification: weighing a certain amount of diatomite in a container, treating the container tinder microwave power of 300-320 W for 10-15 min, and then placing the container in a thermostatic water bath; dropwise adding a sulfuric acid solution having a mass fraction of 3-5 wt % while stirring at low speed of 300 r/min wherein a ratio of mass (g) of the diatomite to volume (mL) of the sulfuric acid solution is 1:3; regulating the rotation speed to 600 r/min, and stirring for 5-6 h; and washing the solution to be neutral with 1 wt % of NaOH solution after cooling, and drying under a condition of 100-110° C. for 3 h, thereby obtaining the modified diatomite.

(16) Modification instructions: the diatomite is modified by combining microwaves with acid treatment. On one hand, the microwave treatment may remove partial water in the diatomite, increase porosity and specific surface area of the diatomite and increase an adsorbing effect; and on the other hand, impurities on the surfaces of diatomite particles are removed by virtue of etching of a strong acid, the purity of the diatomite is increased, density of the diatomite is decreased, the diatomite becomes light weight, the pore volume and specific surface area of the diatomite are increased, a pore structure of the diatomite is obviously improved, and adsorptive property of the diatomite is further improved. Through the above modification treatment, the specific surface area is increased by 56%, and the adsorption rate is increased by 41%.

(17) (2) Expanded perlite modification: preheating and stirring perlite particles at 110° C. for 10 mm, wherein a stirring rate is 800 r/min; adding a performance additive ammonium hydroxide (a ratio of ammonium hydroxide to water is 1:2) accounting for 1-5 wt % of the weight of perlite to regulate a surface potential of the perlite, and promoting bonding between a coupling agent and the surface of the perlite; then, adding a silane coupling agent (KH550) accounting for 2 wt % of the weight of the perlite (the silane coupling agent is diluted in advance until a concentration is 50 wt %, and a solvent is absolute ethyl alcohol); and performing surface modification at 160-180° C. for 40-50 min, and filtering to obtain modified perlite powder.

(18) Modification instructions: mass water absorption of the expanded perlite may be up to 4-9 times, while a heat conductivity coefficient of water is 24 times higher than that of air, so that thermal insulation and heat preservation effects of the expanded perlite are seriously influenced. After hydrophobic modification is performed, water may be prevented from entering an inner cavity of the expanded perlite. The silane coupling agent and the perlite micro powder are bonded in the form, of hydrogen bonds and a monomolecular coating which achieves a condensation effect; bonding is firm, and hydrophobic nature is enhanced.

(19) (3) Polymerization solution preparation: adding potassium persulfate and polyacrylamide into an acrylic solution having a concentration of 30% in sequence according to a mass ratio, stirring by a high-speed stirrer at a rate of 600 r/min, and adding polyvinyl alcohol within 5 min after dispersing; and performing ultrasonic mixed dispersion for 20 min under ultrasonic power of 300 W so as to obtain a polymerization solution.

(20) (4) Polymerization reaction: performing ultrafine grinding on the modified diatomite and the expanded perlite to 800 meshes, adding the ground powder into the polymerization solution, heating and reacting under a temperature condition of 50-60° C. for 4-6 h, raising the temperature to 70-80° C., and carrying out a reaction for 2 h so as to obtain a gel-like sandy material.

(21) (5) Drying the gel-like sandy material under a high-temperature condition of 110° C. until water content is up to 5-8 wt %, and performing mechanical pulverization to 0.08-2 mm, thereby obtaining final sandy, particles.

(22) III. A formula of the used microencapsulated preservation particles includes the following components (in parts by weight): 1-3 parts of jasmonic acid methyl ester, 1-3 parts of CaO.sub.2, 5-10 parts of beta-cyclodextrin, 5-15 parts of chitosan, 4-8 parts of sodium alginate, 0.3-0.5 part of Tween-80 and 100 parts of sterile water.

(23) The preparation method includes the steps: adding the beta-cyclodextrin and sterile water into a triangular flask according to a preset weight ratio, and stirring at a rotation speed of 800-1500 r/min; then, heating to a temperature of 60-80° C. to completely dissolve the beta-cyclodextrin; continuously stirring, and gradually cooling the solution to 35-45° C.; adding the jasmonic acid methyl ester and CaO.sub.2 to be uniformly dispersed in the solution; slowly reducing the temperature to room temperature so as to form single-wall double-core beta-cyclodextrin-jasmonic acid methyl ester-CaO.sub.2 microcapsules, and adding a second layer of mixed wall material composed of chitosan and sodium alginate on the basis, wherein a weight ratio of the chitosan to sodium alginate is 3:1 to 2:3; treating a homogeneous emulsifier Tween-80 and a mixed solution by a high-shear emulsification instrument for 5-10 min; finally forming double-walled double-core microcapsule preservative emulsion which takes chitosan/sodium alginate and beta-cyclodextrin as the wall material and takes the jasmonic acid methyl ester and CaO.sub.2 as the core material; performing suction filtration and washing; and performing vacuum drying at 25° C. for 48 h, thereby obtaining the powdered particles.

(24) IV. Measured Data

(25) In the present invention, the sandy material is combined with the microencapsulated preservation particles. Efficient rapid callus before storage is matched, and a unique storage manner is matched. By controlling the humidifier, ventilation in the cellar, automatic tent air-conditioning, own thermal insulation and water retention of the sandy material and gas regulation, the conditions are maintained as follows: the storage temperature is 10-14° C., the humidity is 85-90%, the O.sub.2 concentration is 7-8%, and the CO.sub.2 concentration is less than 10%, so that the sweet potatoes are stored for an extra long time up to 8-10 months, the water retention rate is up to 94-97%, and a healthy fruit rate is up to 95-98%. The sweet potatoes do not sprout during the storage period and after appearing on the market, and are safe and residue-free.

(26) Characteristic Parameters of Sandy Material

(27) TABLE-US-00004 Sandy material in Parameter index Traditional sand the present invention Conclusion Density ρ (g/cm.sup.3) 1.6 1.3 Lightweight, density decreased by 18.8% Breathability (5 cm thick) 55 67 Breathability increased by 21.8% Hydrophobic property (5 cm Water seeping Durable Excellent hydrophobic property thick) within 6-8 h impermeability Water absorption (%) 9 11 Water absorption increased by 22.2% Porosity (%) 50 53 Increased by 6% Heat conductivity coefficient 0.27 0.22 Thermal insulation property (W/m .Math. K) increased by 18.5%

(28) VI. Other Correlation Descriptions:

(29) (1) BTH is a salicylic acid analogue, that is, a synthetic chemical inducer capable of inducing a plant production system to obtain, resistance. On one hand, the BTH may accelerate lignin deposition in the callus process of the sweet potato tubers so as to promote tissue callus; and on the other hand, the BTH may accelerate oxidative cross-linking of callus by inducing reactive oxygen production and antioxidase activity.

(30) (2) The CaO.sub.2 is low in price, and has characteristics of long oxygen release time, uniform release speed and the like. A reaction of the CaO.sub.2 in water or moist air is as follows: 2CaO.sub.2+2H.sub.2O.fwdarw.O.sub.2+2Ca(OH).sub.2+Q. Moreover, the produced calcium hydroxide may serve as the CO.sub.2 absorbent, thereby maintaining an appropriate gas concentration in the storage environment.

(31) (3) The polyacrylamide is a high water absorbing and retaining agent and has lots of amide and carboxyl hydrophilic groups. By utilizing an osmotic pressure produced by a concentration difference of ions and groups inside the resin and an aqueous solution and affinity between polyelectrolyte and water, a lot of water may be absorbed until the concentration difference disappears. The water retaining agent may absorb pure water that is hundreds of times heavier than the water retaining agent so as to enable the pure water to become hydrogel having a certain mechanical property. The hydrogel after absorbing water may slowly release the water and has a repeated water absorption function. The hydrogel is finally decomposed into carbon dioxide, water and ammonium nitrogen, and no residue exists.

(32) In the present invention, the sweet potatoes are preserved by adopting the following technology for the first time:

(33) Firstly, (1) the traditional sand is replaced with the modified sandy material, and the sandy material is lightweight, breathable, and high in water absorbing and retaining property, thermal insulation and heat preservation; and (2) the sandy material is combined with the microencapsulated preservation particles; efficient, rapid callus before storage is matched; and by controlling the humidifier, ventilation in the cellar, automatic tent air-conditioning, own thermal insulation and water retention of the sandy material and gas regulation, a stable and appropriate storage environment of the sweet potatoes is achieved.

(34) Secondly, (1) the nano silica spray collaborates with the secondary irradiation treatment, so that the sweet potatoes are prevented from sprouting; (2) the prepared microencapsulated antifreeze particles are uniformly dispersed in the sandy material, so that the damage of the reactive oxygen free radicals to plasma membranes is decreased so as to prevent the cold damage; and (3) the automatic tent air-conditioning and the characteristics of the sandy material such as light weight and breathability collaborate with the gas regulation, so that the storage gas conditions are appropriate.

(35) Thirdly, (1) the cellar is disinfected and sterilized with ultrasonically synergistic potassium permanganate, so that the effect is excellent, and the time is short; (2) by virtue of the BTH soaking capable of promoting the callus effect and synergistic ultrasonication capable of shortening the callus time, the sweet potato tubers form the callus so as to increase the own resistance; and (3) the automatic tent air-conditioning and the characteristics of the sandy material such as light weight and breathability collaborate with the gas regulation, so that the storage gas conditions are appropriate.