A method for preparing fresh pickled crisp radish by pulse electric field assisted fermentation

Abstract

The invention discloses a method for preparing fresh pickled crisp radish by pulse electric field assisted fermentation. Through two pulse electric field treatments, the pulse electric field input energy is accurately controlled to reduce the free water content and convert it into non-flowing water, thereby increasing the Ca 2+ The diffusion rate is increased, and the fresh pickled radish is obtained by assisting the directional fermentation of lactic acid bacteria, thereby effectively improving the crispness and taste of the radish during fermentation and storage, and having a significant effect on delaying the softening and deterioration of the fresh pickled radish, extending the shelf life of the fresh pickled radish, and the crispness change rate is small. The crispness retention rate of the radish pickled vegetable product is above 90% after being stored at room temperature for 30 days. It is easy to store and circulate in the market, and is suitable for industrial production.

Description

Technical field:

[0001] The invention relates to the technical field of food processing, and in particular to a method for preparing fresh soaked crisp radish by pulse electric field assisted fermentation. Background technology:

[0002] Kimchi is a traditional fermented vegetable product in China. Its unique processing method and fresh, crisp and refreshing taste have led to the rapid development of the kimchi industry. Currently, kimchi is mostly pickled kimchi and seasoned kimchi. The high-salinity pre-treatment process is used to remove moisture and inhibit the microbial fermentation of the vegetables themselves. As people's awareness of nutrition and health increases, fresh kimchi prepared by medium-salt or low-salt lactic acid fermentation has attracted more and more attention. However, fresh kimchi is easy to soften during storage, the taste deteriorates seriously after high-temperature sterilization, the shelf life is short, and cold chain transportation is required, resulting in high production costs and difficulty in large-scale production.

[0003] The softening of kimchi is mainly due to the decomposition of pectin substances, which often exist in the form of protopectin, pectin and pectic acid. Protopectin is insoluble in water, but it can be hydrolyzed into water-soluble pectin under the action of chemical reagents such as acid, alkali, salt and enzymes. As the fermentation and storage time of kimchi increases, the content of water-soluble pectin gradually increases, and the taste becomes softer. The water content in the cells is also positively correlated with the crispness, but too much free water content can easily cause the fruits and vegetables to rot and deteriorate, so salting, drying and other methods are often used to reduce the water content and lose a certain degree of crispness to extend the shelf life.

[0004] At present, fresh pickled cabbage is often made by blanching, adding pectin methylesterase and other means, and the insoluble pectate is formed after combining with metal ions to improve the crispness of pickled cabbage. For example, Chinese patent CN202311122862.7 discloses a kind of instant radish pickled cabbage and its preparation method, which adopts vacuum freezing cooling after blanching at 55-60℃, and fermentation to prepare instant radish; Chinese patent CN201710892245.3 discloses a crispness preservation process of white radish pickled cabbage, which adopts blanching at 55℃ combined with the addition of exogenous pectinase. Although the above methods all improve the crispness of white radish pickled cabbage, on the one hand, the amount of metal salt used during blanching is large, and the content of calcium pectinate cannot be accurately controlled; on the other hand, the moisture content of radish is not effectively controlled before fermentation, and the crispness decays significantly during fermentation. Summary of the invention:

[0005] The invention aims to provide a method for preparing fresh pickled crisp radish by pulse electric field assisted fermentation, which solves the problem that fresh pickled crisp radish is easy to soften in a short time and has a short shelf life.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing fresh pickled crisp radish by pulse electric field assisted fermentation, the method comprising the following steps:

[0008] (1) Select fresh white radish, rinse it, and cut it into long strips of 1-2 cm in width and height by 1-2 cm for later use;

[0009] (2) Spreading the long strips of radish obtained in step (1) in a pulsed electric field treatment chamber, setting the treatment parameters as follows: field strength 0.5-0.8 kV / cm, pulse width 5-10 μs, frequency 50-100 Hz, treatment 1-2 min, and drying the treated radish strips in an oven at 40-45° C. to 65-70% of the weight of fresh radish for later use;

[0010] (3) soaking the radish strips obtained in step (2) in a liquid with a solid-liquid ratio of 1:1.5-1.8, and performing a second pulse electric field treatment, wherein the treatment parameters are: field strength 1-2 kV / cm, pulse width 5-10 μs, frequency 50-100 Hz, and treatment 1-1.5 min;

[0011] (4) adding 0.08-0.12 g / kg of lactic acid bacteria to the radish liquid obtained in step (3), and fermenting in a closed environment at a constant temperature of 27-28° C. for 48-50 h, wherein the acidity (in terms of lactic acid) is 3.5-4.5 g / L, and filtering the mixture to separate the fermented liquid into radish and lactic acid bacteria;

[0012] (5) placing the radish obtained in step (4) in a liquid with a solid-liquid ratio of 1:1-1.5, and sterilizing at 68-72° C. for 5-8 min to obtain a finished product.

[0013] Preferably, the fresh white radish in step (1) has a diameter of 5-7 cm.

[0014] The liquid ingredients in step (3) are: 835-870 g / kg of drinking water, 110-130 g / kg of white sugar, 20-30 g / kg of salt, and 3-5 g / kg of calcium lactate.

[0015] Preferably, the CFU of lactic acid bacteria in step (4) is 1.0×10 9 .

[0016] Preferably, the liquid ingredients in step (5) are: 800-860 g / kg of drinking water, 60-80 g / kg of lactic acid bacteria fermentation broth, 30-50 g / kg of white sugar, 5-10 g / kg of salt, 2.6-5 g / kg of calcium lactate, 40-60 g / kg of chili pepper, 0.08-0.12 g / kg of sulfur dioxide, and 0.32-0.6 g / kg of potassium sorbate.

[0017] The present invention achieves precise control of pulse electric field input energy by controlling the pulse treatment intensity and the number of pulse treatments, thereby achieving dehydration and rehydration of radish cells. The first pulse electric field treatment: applying a low-intensity pulse electric field of 0.5-0.8 kV / cm, radish cells are under a weak electric field strength, under the electrical parameter conditions that do not destroy the integrity of cells with a diameter in the range of 50-200 μm, due to the fluidity of living cells and the continuous attack of multiple pulses, under the continuous effect of "electroporation", a short "perforation" is formed on the cell membrane surface, opening the mass transfer channel of small molecular water molecules, which can enhance mass transfer and promote the outflow of free water from the radish cell fluid, while large molecules such as pectin cannot be dissolved. Pectin molecules can form a tighter cell wall structure in a low-water environment, and the cells have a better rehydration ability than direct drying. The second pulse electric field treatment is to soak the radish after the first pulse electric field treatment in a liquid with a material-liquid ratio of 1:1.5-1.8, and apply a high-intensity pulse electric field of 1-2kV / cm. Under the action of this pulse electric field, the electric field can promote the charged ions, and the directional application of the electric field can significantly increase the Ca 2+ The diffusion rate is increased, and the formation of calcium pectinate is promoted, forming a dense and orderly gel network structure in the radish tissue structure, making the radish tissue firmer and more crisp. The method prepares fresh pickled crisp radish by assisted lactic acid bacteria fermentation through two pulse electric field treatments, which effectively improves the crispness and taste of the radish during fermentation and storage, and has a significant effect on delaying the softening and deterioration of the fresh pickled radish, achieving a crispness retention rate of more than 90% for radish pickled vegetables stored at room temperature for 30 days. The relevant fermentation form can also be applied to other fermented vegetables such as cucumbers, etc., and has broad market application prospects for solving the problems of fresh pickled vegetables being easily softened in a short time and having a short shelf life.

[0018] Beneficial effects of the present invention:

[0019] (1) The present invention firstly controls the pulse electric field strength at 0.5-0.8 kV / cm, effectively dissolves water, and reduces the drying time by more than 45%, while large molecules such as pectin cannot be dissolved. Pectin molecules can form a tighter cell wall structure in a low-moisture environment, and the cells have a better rehydration ability than direct drying.

[0020] (2) The second pulse electric field is used to control the pulse electric field strength to a high-intensity pulse electric field of 1-2 kV / cm, thereby assisting fermentation to extract calcium ion content, increasing the pectin calcium content from 130 ug / g to 190 ug / g, increasing the diffusion rate, and reducing the amount of calcium lactate used.

[0021] (3) Two pulsed electric field treatments were used to assist lactic acid bacteria fermentation to prepare fresh pickled crispy radish, which effectively improved the crispness and taste of the radish during fermentation and storage. It had a significant effect on delaying the softening and deterioration of the fresh pickled radish, extending the shelf life of the fresh pickled radish, and reducing the change rate of crispness. The crispness retention rate of the pickled radish product was above 90% after 30 days of storage at room temperature.

[0022] (4) Optimize the fermentation substrate and introduce lactic acid bacteria fermentation. The fermentation process is stable and easy to control. The fermentation time is further shortened by optimizing the selection of bacteria, which improves the crispness of the radish and the edible quality. The entire preparation process is simple, easy to store and circulate in the market, and suitable for industrial production.

[0023] In summary, the present invention uses two pulse electric field treatments to accurately control the pulse electric field input energy, reduce the free water content, convert it into non-flowing water, and increase the Ca 2+ The diffusion rate is increased, and the fresh pickled radish is obtained by assisting the directional fermentation of lactic acid bacteria, thereby effectively improving the crispness and taste of the radish during fermentation and storage, and having a significant effect on delaying the softening and deterioration of the fresh pickled radish, extending the shelf life of the fresh pickled radish, and the crispness change rate is small. The crispness retention rate of the radish pickled vegetable product is above 90% after being stored at room temperature for 30 days. It is easy to store and circulate in the market, and is suitable for industrial production. Specific implementation method:

[0024] The following is a further description of the present invention, rather than a limitation of the present invention.

[0025] Embodiment 1:

[0026] Select fresh white jade radish with a diameter of 6 cm and a weight of 750 g, rinse it and prepare long strips of radish with a width and height of 1 cm×1 cm, totaling 2000 g; lay the long strips of radish flat in a pulse electric field treatment chamber, with a field strength of 0.8 kV / cm, a pulse width of 10 us, and a frequency of 100 Hz for 1 min, and then place it in a 45°C oven to dry to 70% of the weight of the fresh radish for use. The drying time is 2 hours.

[0027] The treated radish strips were soaked in a liquid with a material-liquid ratio of 1:1.5, with the liquid ratio of 855g / kg drinking water, 120g / kg white sugar, 20g / kg salt, and 5g / kg calcium lactate, and then subjected to the second pulse electric field treatment. The treatment parameters were: field strength 1.5kV / cm, pulse width 10us, frequency 100Hz, and treatment for 1min. After being taken out, 0.1g / kg lactic acid bacteria were added, and the fermentation was closed at 27℃ for 48h. The acidity (in terms of lactic acid) was 4.1g / L. After filtration, it was divided into radish and lactic acid bacteria fermentation liquid. The absorbance was measured by atomic absorption spectrophotometer and the calcium pectinate content was calculated to be 185ug / g according to the standard curve. The texture analyzer (Shanghai Ruiying Intelligent Technology Co., Ltd., TA.XTPlus) measured the crispness of 115N.

[0028] The treated radish was soaked in a liquid with a material-liquid ratio of 1:1, with the liquid ratio being 837g / kg drinking water, 60g / kg lactic acid bacteria fermentation liquid, 30g / kg white sugar, 10g / kg salt, 3g / kg calcium lactate, 60g / kg chili pepper, 0.08g / kg sulfur dioxide, and 0.6g / kg potassium sorbate. The finished product was sterilized at 70℃ for 5min and had a shelf life of 30d at 30℃. The calcium pectate content was 175ug / g and the crispness was 103N.

[0029] Example 2

[0030] Select fresh white jade radish with a diameter of 7 cm and a weight of 800 g, rinse it and prepare long strips of radish with a width and height of 1 cm×1 cm for use, totaling 2000 g; lay the long strips of radish in a pulsed electric field treatment chamber, with a field strength of 0.6 kV / cm, a pulse width of 5 us, and a frequency of 80 Hz for 80 s, and then place it in a 40°C oven to dry to 70% of the weight of the fresh radish for use. The drying time is 2.2 hours.

[0031] The treated radish strips were soaked in a liquid with a material-liquid ratio of 1:1.6, with the liquid ratio of 860g / kg drinking water, 110g / kg white sugar, 25g / kg salt, and 5g / kg calcium lactate. The second pulse electric field treatment was carried out, and the treatment parameters were: field strength 1kV / cm, pulse width 5us, frequency 80Hz, and treatment 80s. After taking out, 0.08g / kg lactic acid bacteria were added, and the fermentation was closed at 27℃ for 48h, and the acidity (in terms of lactic acid) was 4.0g / L. After filtration, it was divided into radish and lactic acid bacteria fermentation liquid. The absorbance was measured by atomic absorption spectrophotometer and the calcium pectinate content was calculated to be 190ug / g according to the standard curve. The crispness was measured by texture analyzer and was 117N.

[0032] The treated radish was soaked in a liquid with a material-liquid ratio of 1:1.2, with the liquid ratio being 837g / kg drinking water, 80g / kg lactic acid bacteria fermentation liquid, 50g / kg white sugar, 8g / kg salt, 2.6g / kg calcium lactate, 50.4g / kg chili pepper, 0.1g / kg sulfur dioxide, and 0.4g / kg potassium sorbate. The finished product was sterilized at 72℃ for 6min and had a shelf life of 30d at 30℃. The calcium pectate content was 180ug / g and the crispness was 104N.

[0033] Example 3

[0034] Select fresh white jade radish with a diameter of 5 cm and a weight of 700 g, rinse it and prepare long strips of radish with a width and height of 1 cm×1 cm, totaling 2000 g; lay the long strips of radish in a pulsed electric field treatment chamber, with a field strength of 0.5 kV / cm, a pulse width of 10 us, and a frequency of 50 Hz for 2 min, and then place it in a 43°C oven to dry to 70% of the weight of the fresh radish for use. The drying time is 2.2 hours.

[0035] The treated radish strips were soaked in a liquid with a material-liquid ratio of 1:1.8, with the liquid ratio of 865g / kg drinking water, 130g / kg white sugar, 30g / kg salt, and 3g / kg calcium lactate. The second pulse electric field treatment was carried out, and the treatment parameters were: field strength 2kV / cm, pulse width 10us, frequency 50Hz, and treatment 1.5min. After taking out, 0.12g / kg lactic acid bacteria were added, and the fermentation was closed at 27℃ for 50h, and the acidity (in terms of lactic acid) was 4.3g / L. After filtration, it was divided into radish and lactic acid bacteria fermentation liquid. The absorbance was measured by atomic absorption spectrophotometer and the calcium pectinate content was calculated to be 180ug / g according to the standard curve. The crispness was measured by texture analyzer and was 119N.

[0036] The treated radish was soaked in a liquid with a material-liquid ratio of 1:1.5, with the liquid ratio being 837g / kg drinking water, 70g / kg lactic acid bacteria fermentation liquid, 40g / kg white sugar, 5g / kg salt, 5g / kg calcium lactate, 40g / kg chili pepper, 0.12g / kg sulfur dioxide, and 0.32g / kg potassium sorbate. The finished product was sterilized at 68℃ for 8min and had a shelf life of 30d at 30℃. The calcium pectate content was 175ug / g and the crispness was 93N.

[0037] Embodiment 4:

[0038] Select fresh cucumbers with a diameter of 3 cm, rinse them and prepare long cucumber strips with a length, width and height of 5 cm × 2 cm × 1.5 cm, totaling 2000 g; lay the cucumber strips flat in a pulsed electric field treatment chamber, with a field strength of 0.8 kV / cm, a pulse width of 10 us, and a frequency of 100 Hz for 1 min, and then place them in a 45°C oven to dry to 70% of the weight of the fresh cucumbers for use. The drying time is 1.8 hours.

[0039] The treated cucumber strips were soaked in a liquid with a material-liquid ratio of 1:1.5, with the liquid ratio of 855g / kg drinking water, 120g / kg white sugar, 20g / kg salt, and 5g / kg calcium lactate. The second pulse electric field treatment was carried out, and the treatment parameters were: field strength 1.5kV / cm, pulse width 10us, frequency 100Hz, and treatment 1min. After taking out, 0.1g / kg lactic acid bacteria were added, and the fermentation was closed at 27℃ for 48h, and the acidity (in terms of lactic acid) was 4.2g / L. After filtration, it was divided into cucumber and lactic acid bacteria fermentation liquid. The atomic absorption spectrophotometer measured the absorbance and calculated the calcium pectinate content according to the standard curve to be 135ug / g, and the texture analyzer measured the crispness to be 90N.

[0040] The treated cucumbers were soaked in a liquid with a material-liquid ratio of 1:1, with the liquid ratio being 837g / kg drinking water, 60g / kg lactic acid bacteria fermentation liquid, 30g / kg white sugar, 10g / kg salt, 3g / kg calcium lactate, 60g / kg chili pepper, 0.08g / kg sulfur dioxide, and 0.6g / kg potassium sorbate. The finished product was sterilized at 70°C for 5 minutes and had a shelf life of 30 days at 30°C. The calcium pectinate content was 115ug / g and the crispness was 76N. Compared with the fresh pickled cucumbers prepared by natural fermentation without pulsed electric field under the same conditions, the crispness was increased by more than 50%.

[0041] Comparative Example 1

[0042] Select fresh white jade radish with a diameter of 5-7 cm and a weight of 700-800 g, rinse it and cut it into strips with a width and height of 1 cm × 1 cm for use, a total of 2000 g. Dry it in a 45°C oven until the weight of the fresh radish is 70% for use. The drying time is 3.5 hours.

[0043] The treated radish strips were soaked in a liquid with a material-liquid ratio of 1:1.5, with the liquid ratio being 855 g / kg drinking water, 120 g / kg white sugar, 20 g / kg salt, and 5 g / kg calcium lactate. The radish strips were fermented in a closed environment at a constant temperature of 27°C until the acidity (calculated as lactic acid) reached 4.1 g / L, and the fermentation time was 78 h. The absorbance was measured by an atomic absorption spectrophotometer and the calcium pectate content was calculated to be 145 ug / g according to the standard curve. The crispness was measured by a texture analyzer to be 45 N.

[0044] The treated radish was soaked in a liquid with a material-liquid ratio of 1:1, with the liquid ratio being 800-850g / kg of drinking water, 60g / kg of lactic acid bacteria fermentation liquid, 30g / kg of white sugar, 10g / kg of salt, 3g / kg of calcium lactate, 60g / kg of chili pepper, 0.08g / kg of sulfur dioxide, and 0.6g / kg of potassium sorbate. The finished product was obtained by sterilization at 70°C for 5 minutes. The natural fermentation system has a complex bacterial strain system and is difficult to sterilize effectively. The shelf life is 6 days at 30°C. The content of calcium pectinate is 102ug / g and the crispness is 35N.

[0045] Comparative Example 2

[0046] Referring to Example 1, the difference is that the radish sample is spread in the pulse electric field treatment chamber, the field intensity of the first pulse electric field treatment is the same as the field intensity of the second pulse electric field treatment, both are 1.5kV / cm, the pulse width is 10us, and the frequency is 100Hz. It is then placed in a 45°C oven and dried to 70% of the weight of the fresh radish for later use. The drying time is 1.6h. At this time, due to the high energy input of the first pulse electric field, the cell wall is broken, the dissolution of pectin substances is accelerated, and the drying is accelerated. After subsequent fermentation, the cells are further accelerated to break, and the brittleness is significantly reduced. The finished product has a calcium pectate content of 136ug / g and a brittleness of 60N.

[0047] Comparative Example 3

[0048] Referring to Example 1, the difference is that the field intensity of the second pulse electric field treatment is the same as that of the first pulse electric field treatment, both of which are 0.8 kV / cm, with a pulse width of 10 us, a frequency of 100 Hz, and a treatment of 1 min. The radish strips treated with a pulse electric field are immersed in a liquid with a solid-liquid ratio of 1:1.5, the liquid ratio is 855 g / kg of drinking water, 120 g / kg of white sugar, 20 g / kg of salt, and 5 g / kg of calcium lactate, at a field strength of 0.8 kV / cm, a pulse width of 10 us, and a frequency of 100 Hz, and the treatment is 1 min. At this time, because the field intensity of the pulse electric field is too small, it is impossible to promote the rapid exchange of calcium ions to form calcium pectate. The finished product has a calcium pectate content of 134 ug / g and a brittleness of 59N.

Claims

1. A method for preparing fresh pickled crisp radish by pulse electric field assisted fermentation, characterized in that: The method comprises the following steps: (1) Select fresh white radish, rinse it, and cut it into long strips of 1-2 cm in width and height by 1-2 cm for later use; (2) Spreading the long strips of radish obtained in step (1) in a pulsed electric field treatment chamber, setting the treatment parameters as follows: field strength 0.5-0.8 kV / cm, pulse width 5-10 μs, frequency 50-100 Hz, treatment 1-2 min, and drying the treated radish strips in an oven at 40-45° C. to 65-70% of the weight of fresh radish for later use; (3) soaking the radish strips obtained in step (2) in a liquid with a solid-liquid ratio of 1:1.5-1.8, and performing a second pulse electric field treatment, wherein the treatment parameters are: field strength 1-2 kV / cm, pulse width 5-10 μs, frequency 50-100 Hz, and treatment 1-1.5 min; (4) adding 0.08-0.12 g / kg lactic acid bacteria to the radish liquid obtained in step (3), and fermenting in a closed environment at a constant temperature of 27-28° C. for 48-50 h, wherein the acidity is 3.5-4.5 g / L in terms of lactic acid, and filtering the mixture to separate the fermented liquid into radish and lactic acid bacteria; (5) placing the radish obtained in step (4) in a liquid with a solid-liquid ratio of 1:1-1.5, and sterilizing at 68-72° C. for 5-8 min to obtain a finished product.

2. The method according to claim 1, characterized in that Step (1) Fresh white radish with a diameter of 5-7 cm.

3. The method according to claim 1, characterized in that The liquid ingredients in step (3) are: 835-870 g / kg of drinking water, 110-130 g / kg of white sugar, 20-30 g / kg of salt, and 3-5 g / kg of calcium lactate.

4. The method according to claim 1, characterized in that: The CFU of lactic acid bacteria in step (4) is 1.0×10 9 .

5. The method according to claim 1, characterized in that The liquid ingredients in step (5) are: 800-860 g / kg of drinking water, 60-80 g / kg of lactic acid bacteria fermentation liquid, 30-50 g / kg of white sugar, 5-10 g / kg of salt, 2.6-5 g / kg of calcium lactate, 40-60 g / kg of chili pepper, 0.08-0.12 g / kg of sulfur dioxide, and 0.32-0.6 g / kg of potassium sorbate.

6. The method according to claim 1, characterized in that Replace white radish with cucumber.