阅读说明：本技术 盒式包装鲜玉米常温保鲜方法 (Box type package fresh corn normal temperature fresh-keeping method ) 是由 李喜宏 贾晓昱 杜美军 于 2019-07-26 设计创作，主要内容包括：本发明涉及一种盒式包装鲜玉米常温保鲜方法,步骤如下：玉米经剥皮机剥皮处理清洗杀菌；微波协同护色剂钝酶处理、风干后涂膜、表面活性剂抗菌、抗氧化、抗老化涂膜处理、将风干后的玉米装入耐高温高压聚丙烯包装盒、反压灭菌。本发明采用纳米水离子和臭氧微纳米气泡发生协同循环灭菌锅梯度升温升压、恒温恒压杀菌、梯度降温降压灭菌工艺,降低爆袋率,纳米雾化水可以将水分子激发形成结合能力非常强的羟基负离子和氢正离子,因为纳米的小尺寸效应,比表面积大大增强,杀菌抑菌性能更加优越。可以增加灭菌锅内热水、蒸汽等杀菌介质的穿透能力,提高杀菌效果。(The invention relates to a box-type packaged fresh corn normal-temperature fresh-keeping method, which comprises the following steps: peeling, cleaning and sterilizing the corns by a peeling machine; performing enzyme inactivation treatment by microwave synergistic color fixative, air-drying, coating, performing antibacterial, antioxidant and anti-aging coating treatment by surfactant, packaging the air-dried corn in a high-temperature and high-pressure resistant polypropylene packaging box, and sterilizing under back pressure. According to the invention, the sterilization process of gradient temperature rise and pressure rise, constant-temperature and constant-pressure sterilization and gradient temperature reduction and pressure reduction of the sterilization pot by using the synergistic circulation of nanometer water ions and ozone micro-nano bubbles is adopted, the bag explosion rate is reduced, nanometer atomized water can excite water molecules to form hydroxyl negative ions and hydrogen positive ions with very strong binding capacity, the specific surface area is greatly enhanced due to the nanometer small-size effect, and the sterilization and bacteriostasis performance is more excellent. Can increase the penetration capability of sterilization media such as hot water, steam and the like in the sterilization pot and improve the sterilization effect.)

1. A box-type packaged fresh corn normal-temperature fresh-keeping method is characterized in that: the method comprises the following steps:

(1) peeling the corn by a peeling machine or manually peeling, removing the stigma, cleaning by using a corn rolling rod cleaning machine in cooperation with ultrasonic waves, cleaning and sterilizing;

(2) carrying out enzyme inactivation treatment by microwave synergistic color fixative, blanching, adding ultrasonic treatment in the blanching process, controlling the blanching temperature to be 90-95 ℃, blanching for 3min, and adding color fixative with microwave power of 200W in the blanching process, wherein the formula of the color fixative is as follows: 0.4Citric acid g/kg, sodium erythorbate 1.0g/kgD g, CaCl 0.1g/kg₂；

(3) The blanched corn enters an ice water cooling machine, the center temperature of the blanched corn is reduced to be below 10 ℃, and then the blanched corn enters an air drying machine, and after air drying, a film is coated;

(4) coating with surfactant for resisting bacteria, oxidation and aging, wherein the air-dried corn is coated with 2-2.5% of sucrose, 3-5% of phospholipid, 0.3-0.5% of konjac glucomannan or glycoside, 0.6-0.8% of polydextrose-delta-lactone, 0.2-0.4% of sodium carboxymethylcellulose and 1.0-1.2% of β -glucan, and the coating is air-dried;

(5) the air-dried corn is put into a high-temperature and high-pressure resistant polypropylene packaging box, the high-temperature resistant packaging box is prepared by using a modified PP material, the thickness of the packaging box is 1-2mm, and the specification of the box is as follows: length x width x height 220mm x 80mm x 6 mm; the packaging box is sealed after nitrogen is filled into the box;

(7) back pressure sterilization:

the sterilization adopts ozone micro-nano bubble water, the ozone treatment concentration is 2mg/L, the treatment time is 8min, and the passing air volume is 0.15m³Min; the temperature control program of the counter pressure sterilization process is as follows:

① heating in gradient manner, placing nitrogen-filled packaged semen Maydis in a tray of a sterilizing pot, putting into the pot, introducing cold water, heating with steam to 115 deg.C, maintaining the pressure at 0.16MPa for 18min, maintaining the temperature at 115 deg.C for 3min, slowly heating to 121 deg.C for 1-2min, and totally consuming for 22-24 min;

② sterilizing at constant temperature and pressure at 121 deg.C for 30min under 0.23 MPa;

③ gradient cooling, introducing cold air and small amount of cold water to slowly reduce the temperature and pressure in the pan from 121 deg.C to 110 deg.C, keeping the pressure constant at 0.23Mpa for 7min, slowly reducing the temperature from 110 deg.C to 90 deg.C, reducing the pressure to 0.20Mpa at a rate of 0.002-0.003 Mpa/min for 8min, maintaining for 2min, slowly reducing the temperature from 90 deg.C to 60 deg.C for 9min, slowly reducing the temperature from 60 deg.C to 40 deg.C for 10min, slowly reducing the temperature from 40 deg.C to 24-25 deg.C for 6min, and totally reducing the temperature for 42 min.

2. The method for preserving fresh boxed corn at normal temperature according to claim 1, which is characterized in that: the cleaning process in the step (1) is as follows: using a corn rolling rod cleaning machine to clean in cooperation with ultrasonic waves, cleaning and sterilizing: ultrasonic cleaning and ozone water cleaning are combined, the ultrasonic power is 50W, the frequency is 35kHz, the catalytic reaction time is 10-15 min, the ozone gas input amount is 2-3 mg/L, the ozone gas is dissolved in water in a micro-nano bubble mode through a high-pressure micro-nano bubble nozzle, the particle size is 200 nm-4 um, the contact area of ozone and water is increased, and efficient impurity removal and sterilization are realized.

3. The method for preserving fresh boxed corn at normal temperature according to claim 1, which is characterized in that: the preparation steps of the high-temperature and high-pressure resistant polypropylene packaging box are as follows:

1) monomer HDDA graft modified polypropylene, which uses dicumyl peroxide as an initiator, styrene as an auxiliary agent, bifunctional monomer HDDA as a grafting monomer, β crystal form nucleating agent, is prepared by loading pimelic acid to nano-CaCO₃Reacting to generate and modify nano-SiO₂Preparing a grafted product having high melt strength;

2) modified nano-SiO₂Preparation: firstly nano-SiO₂Mixing the particles with an ethanol solution of a silane coupling agent for surface treatment, oscillating for 60min by ultrasonic at 40 ℃, removing the solvent, and drying for later use;

3) the raw materials comprise PP, HDDA, DCP, St, β crystal form nucleating agent and modified nano-SiO₂100: 2.8: 0.02: 0.02: 0.4: 2, accurately weighing PP, a monomer, an initiator, an auxiliary agent and a nucleating agent according to an experimental proportion, and uniformly mixing; accurately measured monomer HDDA and initiator DCP are placed in a certain amount of acetone, are dripped into the PP powder which is uniformly mixed after being dissolved, are uniformly mixed again and are placed in a fume hood overnight; performing double-screw extrusion granulation, wherein the screw extrusion conditions are as follows: the rotating speed is 185 r/min; temperature: the first zone was 195 ℃ and the second to fifth zones were maintained at 220 ℃ and 215 ℃ respectively, 215 ℃ and 220 ℃.

4. The method for preserving fresh boxed corn at normal temperature according to claim 1, which is characterized in that: the sealing film is prepared by selecting seven layers of co-extruded films: polyethylene/adhesive resin/polyamide/ethylene-vinyl alcohol copolymer/polyamide/adhesive resin/polyethylene-polyvinyl acetate copolymer, 12 filaments in thickness, oxygen permeability < 30cm³/m²D.bar, water vapor transmission rate < 5g/cm²·d。

5. The method for preserving fresh boxed corn at normal temperature according to claim 1, which is characterized in that: the nanometer atomized water adopts about 10% of water ions with the particle size range of about 80nm, and the passing air quantity is 0.2m³And/min, mixing ozone bubbles and nano atomized water in a ratio of 3: 4.

Technical Field

The invention belongs to the technical field of preservation, and particularly relates to a box-type packaged fresh corn normal-temperature preservation method.

Background

The water content of sweet corn grains reaches 65-80%, the water-soluble sugar content reaches 25-40%, the grain skin is soft and tender, compared with common fresh corn and waxy corn, the amylase activity is extremely strong, the quality is rapidly deteriorated after 5 hours at normal temperature, the optimum edible period at normal temperature is only 8-10 hours, even under the ideal condition of 0 ℃, only 20-26 hours, and the industrialized out-of-season sale is difficult. At present, quick freezing and vacuum packaging sterilization are main fresh-keeping means.

The technical mode of vacuum packaging high-temperature steaming enzyme and bacterium killing and fresh keeping is that after fresh sweet corn is harvested, leaves are removed, the fresh sweet corn is cleaned, quick frozen at the temperature of-40 ℃, frozen and stored at the temperature of-18 ℃, and transported at the temperature of-18 ℃ for sale, and the fresh sweet corn is steamed and eaten at high temperature under the freezing condition.

In the storage process of gelatinized starch, starch molecules generate self-assembly phenomenon, amylose and straight line parts of the amylose tend to be arranged in parallel and return to a crystal state from an amorphous state, so that the viscosity of the starch is reduced, the flexibility of the molecules is weakened, the transparency is reduced, the solution is coagulated, phase separation is carried out or the hardness of precipitated gel is increased, and the like, thereby causing starch aging problems.

According to the search, the patent literature related to the present application discloses and evaluates the following:

(1) the patent No. ZL201410175986.6 of the fresh-keeping processing technology of the sweet waxy corn has the key technologies of 2016 year, 6 month and 1 day, the period of raw material collection → soaking color protection → precooling → blanching → cooling → quick freezing → packaging → sterilization → freezing storage and the like, the patent has the advantages that ① color protection agent selects citric acid, isoascorbic acid, sodium sulfite, sodium polyphosphate and salt composite liquid, the patent has the defects of high energy consumption of ① quick freezing, large equipment investment, large energy consumption and high cost, particularly, the cold chain ring breaking in China often occurs thawing or repeated thawing and sugar Maillard reaction generates aldehyde fishy smell during transportation and sale, the low-temperature freezing of ② causes starch denaturation and texture deterioration

(2) A method for biologically preserving fresh corn includes such steps as providing ① corn pollen polyose, lysozyme, chitosan, tea polyphenol, sorbitol, span-80, tween-80 and edible soybean oil as coating antistaling agent, preparing coating antistaling agent by immersing them in the solution of sodium chloride, immersing in antistaling agent, draining and cold storage, preserving fresh corn in ① for 65 days, and sterilizing the surface of corn in ② by immersing in chemical antiseptic, resulting in poor effect and short preservation period.

(3) A method for antistaling fresh sweet corn at ordinary temp includes such steps as vacuumizing the interior of ①, filling N in two bags, and sterilizing under negative pressure₂N in the outer bag₂The corn fresh-keeping bag has buffering and protecting effects, but the inner bag is still in a vacuum state, and the texture, color and quality of the corn fresh-keeping bag are difficult to maintain for a long time.

According to the defects of the prior art and related patents, the method is researched and developed in a targeted mode, and the box-type packaged fresh corn normal-temperature preservation method with better effect is obtained.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a box-type packaged fresh corn normal-temperature fresh-keeping method which has good fresh-keeping performance and does not discolor in the fresh-keeping process.

The technical problem to be solved by the invention is realized by adopting the following technical scheme:

a normal-temperature preservation method for box-type packaged fresh corn comprises the following steps:

(1) peeling the corn by a peeling machine or manually peeling, removing the stigma, cleaning by using a corn rolling rod cleaning machine in cooperation with ultrasonic waves, cleaning and sterilizing;

(2) carrying out enzyme inactivation treatment by microwave synergistic color fixative, blanching, adding ultrasonic treatment in the blanching process, controlling the blanching temperature to be 90-95 ℃, blanching for 3min, and adding color fixative with microwave power of 200W in the blanching process, wherein the formula of the color fixative is as follows: 0.4g/kg citric acid, 1.0g/kg D-sodium erythorbate, 0.1g/kg CaCl₂；

(3) The blanched corn enters an ice water cooling machine, the center temperature of the blanched corn is reduced to be below 10 ℃, and then the blanched corn enters an air drying machine, and after air drying, a film is coated;

(4) coating with surfactant for resisting bacteria, oxidation and aging, wherein the air-dried corn is coated with 2-2.5% of sucrose, 3-5% of phospholipid, 0.3-0.5% of konjac glucomannan or glycoside, 0.6-0.8% of polydextrose-delta-lactone, 0.2-0.4% of sodium carboxymethylcellulose and 1.0-1.2% of β -glucan, and the coating is air-dried;

(5) the air-dried corn is put into a high-temperature and high-pressure resistant polypropylene packaging box, the high-temperature resistant packaging box is prepared by using a modified PP material, the thickness of the packaging box is 1-2mm, and the specification of the box is as follows: length x width x height 220mm x 80mm x 6 mm; the packaging box is sealed after nitrogen is filled into the box;

(7) back pressure sterilization:

the sterilization adopts ozone micro-nano bubble water, the ozone treatment concentration is 2mg/L, the treatment time is 8min, and the passing air volume is 0.15m³Min; the temperature control program of the counter pressure sterilization process is as follows:

① heating in gradient manner, placing nitrogen-filled packaged semen Maydis in a tray of a sterilizing pot, putting into the pot, introducing cold water, heating with steam to 115 deg.C, maintaining the pressure at 0.16MPa for 18min, maintaining the temperature at 115 deg.C for 3min, slowly heating to 121 deg.C for 1-2min, and totally consuming for 22-24 min;

② sterilizing at constant temperature and pressure at 121 deg.C for 30min under 0.23 MPa;

③ gradient cooling, introducing cold air and small amount of cold water to slowly reduce the temperature and pressure in the pan from 121 deg.C to 110 deg.C, keeping the pressure constant at 0.23Mpa for 7min, slowly reducing the temperature from 110 deg.C to 90 deg.C, reducing the pressure to 0.20Mpa at a rate of 0.002-0.003 Mpa/min for 8min, maintaining for 2min, slowly reducing the temperature from 90 deg.C to 60 deg.C for 9min, slowly reducing the temperature from 60 deg.C to 40 deg.C for 10min, slowly reducing the temperature from 40 deg.C to 24-25 deg.C for 6min, and totally reducing the temperature for 42 min.

Moreover, the step (1) cleaning process is as follows: using a corn rolling rod cleaning machine to clean in cooperation with ultrasonic waves, cleaning and sterilizing: ultrasonic cleaning and ozone water cleaning are combined, the ultrasonic power is 50W, the frequency is 35kHz, the catalytic reaction time is 10-15 min, the ozone gas input amount is 2-3 mg/L, the ozone gas is dissolved in water in a micro-nano bubble mode through a high-pressure micro-nano bubble nozzle, the particle size is 200 nm-4 um, the contact area of ozone and water is increased, and efficient impurity removal and sterilization are realized.

Moreover, the preparation steps of the high-temperature and high-pressure resistant polypropylene packaging box are as follows:

1) monomer HDDA graft modified polypropylene, which uses dicumyl peroxide as an initiator, styrene as an auxiliary agent, bifunctional monomer HDDA as a grafting monomer, β crystal form nucleating agent, is prepared by loading pimelic acid to nano-CaCO₃Reacting to generate and modify nano-SiO₂Preparing a grafted product having high melt strength;

2) modified nano-SiO₂Preparation: firstly nano-SiO₂Mixing the particles with an ethanol solution of a silane coupling agent for surface treatment, oscillating for 60min by ultrasonic at 40 ℃, removing the solvent, and drying for later use;

3) the raw materials comprise PP, HDDA, DCP, St, β crystal form nucleating agent and modified nano-SiO₂100: 2.8: 0.02: 0.02: 0.4: 2, accurately weighing PP, a monomer, an initiator, an auxiliary agent and a nucleating agent according to an experimental proportion, and uniformly mixing; accurately measured monomer HDDA and initiator DCP are placed in a certain amount of acetone, are dripped into the PP powder which is uniformly mixed after being dissolved, are uniformly mixed again and are placed in a fume hood overnight; performing double-screw extrusion granulation, wherein the screw extrusion conditions are as follows: the rotating speed is 185 r/min; temperature: the first zone was 195 ℃ and the second to fifth zones were maintained at 220 ℃ and 215 ℃ respectively, 215 ℃ and 220 ℃.

Moreover, the sealing film is a seven-layer co-extrusion film: polyethylene/adhesive resin/polyamide/ethylene-vinyl alcohol copolymer/polyamide/adhesive resin/polyethylene-polyvinyl acetate copolymer, 12 filaments in thickness, oxygen permeability < 30cm³/m²D.bar, water vapor transmission rate < 5g/cm²·d。

Moreover, the nano atomized water adopts about 10 percent of particlesWater ions with diameter of about 80nm pass through the air volume of 0.2m³And/min, mixing ozone bubbles and nano atomized water in a ratio of 3: 4.

The invention has the advantages and positive effects that:

1. the invention adopts a nitrogen-filled box type package, and the new process of filling nitrogen in the box, ultrasonic cleaning, microwave cooperating with color fixative enzyme inactivation, gradient temperature and pressure raising, gradient temperature and pressure lowering is adopted, so that the corn color protection, sterilization and fixation and preservation are integrated, brown stain and peculiar smell are not caused like vacuum package, more nutrient components of the sweet corn can be kept, the defects of low-temperature frozen preservation of soluble solid matters of the fresh sweet corn, large energy consumption and the like can be prevented, the large-scale industrial production can be carried out, and the invention has the advantages of environmental protection and safety. In the box is filled with N₂The fresh corn is modified by air, so that the fresh corn has fresh and tender mouthfeel and beautiful color in the storage and preservation period, and the preservation period can reach 13 months at normal temperature.

2. The invention adopts box type modified atmosphere to package fresh sweet corn, and solves the problems of dark color, bitter taste and the like of vacuum-packaged corn.

3. The enzyme activity is inhibited by the enzyme inactivation treatment technology of the microwave synergistic color fixative, and the golden color of the sweet corn is kept.

4. The invention modifies the polypropylene packaging box material to solve the deformation problem, adds long branched chains on the polypropylene long chain by chemical modification modes such as grafting, crosslinking and the like to ensure that the polypropylene is subjected to crosslinking reaction to form a comb-shaped or net-shaped structure, the crosslinking modification of the polypropylene is an effective method for improving the thermal deformation temperature of the polypropylene, the mechanical property of the polypropylene can also be improved, the addition of β crystal form nucleating agent improves the transparency, tensile strength and the like of the material, and nano-SiO₂The particle size is small, the specific surface area is large, the rigidity, the thermal stability and the size stability are high, and the barrier property of the PP material can be improved.

5. According to the invention, the sterilization process of gradient temperature rise and pressure rise, constant-temperature and constant-pressure sterilization and gradient temperature reduction and pressure reduction of the sterilization pot by using the synergistic circulation of nanometer water ions and ozone micro-nano bubbles is adopted, the bag explosion rate is reduced, nanometer atomized water can excite water molecules to form hydroxyl negative ions and hydrogen positive ions with very strong binding capacity, the specific surface area is greatly enhanced due to the nanometer small-size effect, and the sterilization and bacteriostasis performance is more excellent. Can increase the penetration capability of sterilization media such as hot water, steam and the like in the sterilization pot and improve the sterilization effect.

Drawings

FIG. 1 is a schematic diagram of a device for generating and co-circulating ozone bubbles in nano water for a sterilization pot

FIG. 2 fresh-eating sweet corn produced in pilot scale of the invention

FIG. 3 shows fresh sweet corn produced by conventional vacuum packaging techniques.

Detailed Description

The present invention will be described in further detail with reference to the following embodiments, which are illustrative only and not limiting, and the scope of the present invention is not limited thereby.

A normal-temperature preservation method for box-type packaged fresh corn comprises the following steps:

(1) the corn is peeled by a peeling machine or is manually peeled, peeled and stigma-removed, and the corn is cleaned by a corn rolling rod cleaning machine in cooperation with ultrasonic waves, cleaned and sterilized: ultrasonic cleaning and ozone water cleaning are combined, the ultrasonic power is 50W, the frequency is 35kHz, the catalytic reaction time is 10-15 min, the ozone gas input amount is 2-3 mg/L, the ozone gas is dissolved in water in a micro-nano bubble mode through a high-pressure micro-nano bubble nozzle, the particle size is 200 nm-4 um, the contact area of ozone and water is increased, and efficient impurity removal and sterilization are realized.

(2) Performing enzyme inactivation treatment by microwave in cooperation with a color fixative, and performing continuous bin type blanching production line, wherein a microwave generating device is arranged in a bin, the blanching temperature is controlled to be 90-95 ℃, blanching is performed for 3min, the microwave power is 200W, and the formula of a color fixative is as follows: 0.4g/kg citric acid, 1.0 g/kgD-sodium erythorbate, 0.1g/kg CaCl₂. (there are studies showing that Latore et al found that red beet was 90% inactivated in both PPO and POD after 5min treatment with 200W microwave power).

(3) And (3) the blanched corns enter an ice water cooling machine, the central temperature of the blanched corns is reduced to be below 10 ℃, and then the blanched corns enter an air drying machine to be dried and removed with water.

(4) The surface active agent is used for antibacterial, antioxidant and anti-aging film coating treatment, namely, 2 to 2.5 percent of cane sugar, 3 to 5 percent of phospholipid, 0.3 to 0.5 percent of konjak glucan, glycoside, 0.6 to 0.8 percent of polydextrose-delta-lactone, 0.2 to 0.4 percent of sodium carboxymethylcellulose (CMC) and 1.0 to 1.2 percent of β -glucan are added into air-dried corns by a film coating method, and the air-dried corns are subjected to film coating treatment and air-dried.

(5) And (3) carrying out crosslinking modification on the PP (polypropylene) plastic box material.

95% of the existing polypropylene materials are isotactic polypropylene, molecular chains of the isotactic polypropylene are of a linear structure, the molecular weight distribution is relatively narrow, the melt strength of the materials is low, the softening point of the materials is relatively close to the melting point, the melting range is relatively short, the strength and the viscosity of PP melts are rapidly reduced after the temperature is higher than the melting point in the thermoforming process, the toughness of products is poor, the products are easy to embrittle at low temperature, the thermal deformation temperature is low, secondary activity centers cannot be generated, the melt strength is low and the melt sag resistance is poor₂The particle size is small, the specific surface area is large, the rigidity, the thermal stability and the size stability are high, and the barrier property of the PP material can be improved.

Preparation procedure

1) The monomer HDDA graft modified polypropylene uses dicumyl peroxide (DCP) as an initiator, styrene (St) as an auxiliary agent, a bifunctional monomer HDDA (1, 6-hexanediol diacrylate) as a grafting monomer, and β crystal form nucleating agent (pimelic acid smart P crystal nucleating agent) by loading pimelic acid to nano-CaCO₃Reacting to generate and modify nano-SiO₂(average particle size of nano-silica is 20nm) to prepare a graft product having high melt strength.

2) Modified nano-SiO₂Preparation: firstly nano-SiO₂Mixing the particles with ethanol solution of silane coupling agent (KH-560) for surface treatment, ultrasonic oscillating at 40 deg.C for 60min, removing solvent, and oven drying.

3) The raw materials comprise PP, HDDA, DCP, St, β crystal form nucleating agent and modified nano-SiO₂100: 2.8: 0.02: 0.02: 0.4: and 2, accurately weighing PP, the monomer, the initiator, the auxiliary agent and the nucleating agent according to the experimental proportion, and uniformly mixing. Accurately measured monomer HDDA and initiator DCP are placed in a certain amount of acetone, and after being dissolved, the mixture is dripped on PP powder (added with 2% nano-SiO)₂) Mix again and leave in a fume hood overnight. Performing double-screw extrusion granulation, wherein the screw extrusion conditions are as follows: the rotating speed is 185 r/min; temperature: the first zone was 195 ℃ and the second to fifth zones were maintained at 220 ℃ and 215 ℃ respectively, 215 ℃ and 220 ℃.

4) The high-temperature-resistant packaging box is prepared by using the modified PP material, so that the problem of high-temperature deformation of the conventional PP box is solved. The thickness of the packing box is 1-2mm, and the specification of the box is as follows: length × width × height ═ 220mm × 80mm × 6 mm.

TABLE 1 high melt Strength Polypropylene Properties

(6) Nitrogen-filled package

The air-dried corn is put into a high-temperature and high-pressure resistant polypropylene (PP) packaging box, a full-automatic bin type modified atmosphere packaging machine is adopted for nitrogen-filled packaging, and the working principle is as follows: placing the corns into a box, vacuumizing a bin chamber at negative pressure, wherein the vacuum degree is 0.0006MPA to-0.001 Mpa, the vacuumizing time is 8-10s, the nitrogen charging time is 4-5s, and the nitrogen flow is 20m³The nitrogen purity is more than 99.999 percent. The packing box is sealed after nitrogen is filled into the box.

The sealing film is prepared from seven layers of co-extruded films of PE/TIE/PA/EVOH/PA/TIE/EVA: (polyethylene/binder resin/polyamide/ethylene-vinyl alcohol copolymer/polyamide/binder resin/polyethylene-polyvinyl acetate copolymer) 12 filaments thick, an oxygen permeability of < 30cm³/m²D.bar, water vapor transmission rate < 5g/cm²·d。

(7) Back pressure sterilization:

the existing sterilization pot is added with a device for generating the synergistic circulation of nano water ions and ozone micro-nano bubbles, a stainless steel circulating pipeline is arranged outside the pot, ozone and nano water ions in the pot are uniformly sprayed out through exhaust holes in a bottom pipeline, the ozone can react with double bonds of bacteria cell wall lipids to penetrate into thalli, and the ozone acts on protein and lipopolysaccharide to change the permeability of cells and also can act on nuclear substances in the cells, so that the bacteria are dead. The nano atomized water can excite water molecules to form hydroxyl negative ions and hydrogen positive ions with very strong binding capacity, and because of the nano small-size effect, the specific surface area is greatly enhanced, and the sterilization and bacteriostasis performance is more excellent. Can increase the penetration capability of sterilization media such as hot water, steam and the like in the sterilization pot and improve the sterilization effect.

The ozone micro-nano bubble water treatment concentration of the device is 2mg/L, the treatment time is 8min, and the passing air volume is 0.15m³And/min. The nanometer atomized water adopts about 10% of water ions with the particle size range of about 80nm, and the passing air quantity is 0.2m³And/min, mixing ozone bubbles and nano atomized water in a ratio of 3: 4.

The temperature control program of the counter pressure sterilization process is as follows:

① heating in gradient manner, placing nitrogen-filled packaged semen Maydis in a tray of a sterilizing pot, putting into the pot, introducing cold water, heating with steam to 115 deg.C, maintaining the pressure at 0.16MPa for 18min, maintaining the temperature at 115 deg.C for 3min, slowly heating to 121 deg.C for 1-2min, and totally consuming for 22-24 min.

② sterilizing at constant temperature and constant pressure at 121 deg.C for 30min under 0.23 MPa.

③ gradient cooling, after sterilization, introducing cold air and a small amount of cold water to slowly reduce the temperature and pressure in the pan from 121 ℃ to 110 ℃, keeping the pressure constant at 0.23MPa, slowly reducing the temperature from 110 ℃ to 90 ℃ in 7min, reducing the pressure to 0.20MPa at a speed of 0.002-0.003 MPa/min, slowly reducing the temperature from 90 ℃ to 60 ℃ in 2min, slowly reducing the temperature from 60 ℃ to 40 ℃ in 9min, slowly reducing the temperature from 40 ℃ to 24-25 ℃ in 10min, and totally reducing the temperature for 6min and 42 min.

And (3) detecting data:

the invention adopts a nitrogen-filled box type package, and the new process of filling nitrogen in the box, ultrasonic cleaning, microwave cooperating with color fixative enzyme inactivation, gradient temperature and pressure raising, gradient temperature and pressure lowering is adopted, so that the corn color protection, sterilization and fixation and preservation are integrated, brown stain and peculiar smell are not caused like vacuum package, more nutrient components of the sweet corn can be kept, the defects of low-temperature frozen preservation of soluble solid matters of the fresh sweet corn, large energy consumption and the like can be prevented, the large-scale industrial production can be carried out, and the invention has the advantages of environmental protection and safety. In the box is filled with N₂The fresh corn is modified by air, so that the fresh corn has fresh and tender mouthfeel and beautiful color in the storage and preservation period, and the preservation period can reach 13 months at normal temperature.

Taking waxy corn as an example, the fresh-keeping time of the waxy corn is 13 months, and various performance indexes are shown in tables 2, 3 and 4.

TABLE 2 comparison of nutrient content of maize after 13 months storage

TABLE 3 TPA test results for waxy maize stored for 13 months

TABLE 4 sensory evaluation results of waxy corn stored for 13 months