WO2021023295A1

WO2021023295A1 - Zizyphus jujube slice drying method using cold plasma activated water

Info

Publication number: WO2021023295A1
Application number: PCT/CN2020/107754
Authority: WO
Inventors: 陈卫; 鲍涛
Original assignee: 浙江大学
Priority date: 2019-08-08
Filing date: 2020-08-07
Publication date: 2021-02-11
Also published as: CN110447705B; CN110447705A

Abstract

A zizyphus jujube slice drying method using cold plasma activated water. The method comprises the following steps: preparing cold plasma activated water; using the cold plasma activated water to carry out an immersion treatment on fresh zizyphus jujube slices; and performing a hot air drying treatment on the pretreated fresh zizyphus jujube slices to obtain dried zizyphus jujube slices.

Description

Method for drying red date slices by using cold plasma to activate water

Technical field

The invention relates to the technical field of agricultural products processing, in particular to a method for drying red jujube slices using cold plasma to activate water.

Background technique

Zizyphus jujube, also known as jujube, belongs to the phylum Angiosperm, Dicotyledon, Rhamnaria, Rhamnaceae, and Jujube. Red dates are rich in sugars, amino acids, vitamin C and organic acids. In addition, red dates also contain a variety of biologically active substances, such as phenolic compounds, red date polysaccharides, cyclic adenylate, and triterpenoids. Chinese medicine believes that red dates are sweet and warm in nature, soothing the nerves, helping sleep, protecting the spleen and stomach, nourishing qi and blood, and delaying aging. Studies have shown that phenolic compounds in red dates have biological activities such as antioxidant, anti-tumor, and antibacterial. Because of the high water content of the red jujube, it is difficult to store and transport, which causes great waste, so it needs to be processed in time after picking. At present, the most commonly used method of processing and storage aims to reduce the moisture content in food to a safe level, at which level it will minimize microbial spoilage and moisture-mediated deterioration reactions. Dried jujube slices are a traditional processed product of red dates in my country, as well as an important product of my country's current red date processing. Hot air drying method processing is currently one of the most widely used methods, but hot air drying is a high-energy-consuming unit operation.

Plasma is the fourth state of matter after solid, liquid and gaseous states. When the applied voltage reaches the breakdown voltage, gas molecules are ionized to produce a mixture of electrons, ions, atoms and atomic groups. Cold plasma refers to a plasma with a lower overall temperature generated under atmospheric pressure (normal pressure) conditions. Due to the advantages of being able to generate under normal pressure, low gas temperature (close to or slightly higher than room temperature), high content of active components, no pollution, no waste, etc., cold plasma is used in food processing, medicine and health, environmental protection, biological Many fields such as medicine have shown broad application prospects. As an emerging non-thermal food processing technology, cold plasma technology has received widespread attention. The application of cold plasma technology in food processing includes the killing of harmful microorganisms in food, the processing of packaging materials, the functional modification of food ingredients, the improvement of seed germination, the improvement of the physical and chemical properties of grains, and the degradation of pesticide residues. However, cold plasma treatment of fatty foods and other sensitive foods may induce chemical changes. In addition, the efficiency of cold plasma treatment is largely affected by the surface morphology of the sample. Therefore, the cold plasma jet system can be used to generate plasma discharge on the water surface or directly in the water to prepare cold plasma activated water, and the cold plasma activated water is used for sample pretreatment. When preparing cold plasma activated water, a chemical reaction occurs to form active oxygen species and active nitrogen species. Studies have shown that cold plasma activated water can be used as an alternative to microbial disinfection to promote seed germination and plant growth (Thirumdas R, Kothakota A, Annapure U, et al. Plasma activated water (PAW): chemistry, physico-chemical properties, applications in food and agriculture[J].Trends in Food Science&Technology,2018,77:21-31.). However, how to effectively apply plasma activated water to the field of food drying pretreatment has not been reported yet.

Summary of the invention

The invention discloses a drying pretreatment method for jujube slices, which adopts cold plasma activated water to pretreat fresh jujube slices, thereby reducing the hot air drying time of the jujube slices, improving drying efficiency, reducing drying energy consumption, and increasing the content of biological active components of the jujube slices. The pretreatment process can increase the water diffusion efficiency, reduce the hot air drying time, effectively reduce the hot air drying time of the red date slices, and at the same time reduce the degradation of phenolic substances, thereby increasing the total phenol content in the dried red date slices. The technical scheme of the present invention is as follows:

The embodiment of the invention discloses a method for drying jujube slices using cold plasma activated water, which specifically includes the following steps:

(1) The cold plasma equipment body is used to pretreat water to prepare cold plasma activated water; the output power of the cold plasma equipment is 600-900W, the flow rate of the cold plasma gas flow is 100-300L/min, and the pretreatment time is 5-40min.

(2) Soak the fresh red date slices in cold plasma activated water for pre-drying; the thickness of the red date slices is 2-10 mm, and the fresh red date slices are completely immersed in the cold plasma activated water for 0.5-5 min.

(3) The pretreated fresh red date slices are dried with hot air to obtain dried red date slices.

The cold plasma activated water used in the step (2) is the cold plasma activated water obtained in step (1) that has not been immersed and used, or the cold plasma that has been immersed and used in step (2) one or more times. Activated water. The cold plasma activated water is repeatedly used no more than 3 times, and it is more preferable to use it repeatedly only once.

Under the conditions of step (1) of the present invention, according to the content of the water to be treated, about 10-50L cold plasma activated water that meets the pretreatment requirements and has a better implementation effect can be prepared. Preferably, in step (1), the output power of the cold plasma equipment is 600-800 W, the flow rate of the cold plasma gas flow is 100-200 L/min, and the pretreatment time is 5-20 min.

Preferably, in step (1), the cold plasma activated water is kept in an ice water bath during preparation. The ice water bath can prevent the water temperature from rising too high during the preparation process.

Preferably, in step (2), the fresh red dates are washed and then cored and sliced, and the thickness of the red date slices is 4-8 mm.

Preferably, in step (2), the fresh red date slices are completely immersed in cold plasma activated water, and the immersion time is 0.5-2 min. The soaking temperature has no significant influence on the soaking effect. It can be carried out at room temperature, or it can be carried out in a wider temperature range (such as 0-50°C) according to the actual production environment and production conditions.

Preferably, in step (2), take it out after soaking, and use absorbent paper to dry the surface moisture.

Preferably, in step (3), the hot air drying temperature is 50-70° C., and the wind speed is 1-2 m/s.

Preferably, in step (3), at the end of hot air drying, the moisture content of the red date slices is controlled to not exceed 5% on a wet basis.

Compared with the prior art, the present invention has the following advantages:

The invention adopts cold plasma activated water to pretreat the jujube slices, which is green and pollution-free. The jujube slices treated with cold plasma activated water have no hidden food safety hazards, and the cold plasma activated water has a sterilization function to a certain extent; the present invention optimizes the treatment time and treatment methods of the cold plasma activated water.

The invention adopts cold plasma activated water to pretreat the jujube slices. Compared with the direct treatment with cold plasma, the processing capacity of the jujube slices per unit time is larger and the processing efficiency is higher; the direct treatment with the cold plasma requires attention to the jujube slices and cold plasma The distance and the positional relationship between the plasma treatment technology require high process. If the process is not properly controlled, the pretreatment effect will be unsatisfactory, and it will also cause nutritional damage to the red jujube slices, which makes the cold plasma direct pretreatment process less efficient , Poor operability. Tests have confirmed that the cold plasma activated water in the process of the present invention can be reused many times, and it still has a good pretreatment effect (in the case of repeated 1-3 times, all have a good pretreatment effect), This greatly reduces the use cost of cold plasma equipment and improves the efficiency of pretreatment. Compared with cold plasma direct treatment, cold plasma activated water treatment can reduce the drying time by up to 20% (as shown in Figure 5), and can significantly increase the polyphenols of dried jujube slices (as shown in Figure 6, up to 16%) ), flavonoids (as shown in Figure 7, up to 29%) and procyanidins (as shown in Figure 8, up to 31%). In addition, the experimental results show that direct cold plasma treatment will cause the destruction of vitamin C in the jujube slices. Compared with the untreated group, the vitamin C content is reduced by up to 50% (as shown in Figure 9).

After the plasma activated water pretreatment, the compact fiber structure on the surface of the red date slices opens, forming more uniform holes or pores, so that the quality of the final dried red date slices is more stable and uniform, which can effectively reduce the hot air drying time; while the plasma direct treatment Later, the red date slices have uneven surface holes, and some of the surfaces are burnt, resulting in shrinkage; this makes the quality of dried shiitake mushroom products obtained in the subsequent hot air drying stage unstable; for dry red date slices with unsatisfactory quality, they often need to be selected for further drying or Processing of defective products. In the cold plasma activated water pretreatment stage, the jujube slices are evenly immersed in the activated water during the pretreatment stage. Therefore, the jujube slices are relatively uniform before entering the hot air drying, and it is easy to obtain dry red date slices with stable quality.

The present invention finds for the first time that cold plasma activated water pretreatment can effectively increase the content of phenolic substances in hot-air dried red date slices and improve the quality of dried red date slices. The cold plasma activated water is rich in reactive oxygen species (ROS) and reactive nitrogen molecules (RNS). ROS and RNS have a peroxidation effect, which can destroy the membrane lipids of the jujube slice cells, cause the cell membrane to rupture, and release the jujube slice cell sap, thereby enhancing Drying rate. Cold plasma activated water pretreatment can significantly increase the active substance content of dried jujube slices. On the one hand, cold plasma activated water pretreatment can increase the hot air drying rate of red jujube slices, thereby reducing the thermal degradation of active substances; on the other hand, The cold plasma activated water pretreatment can oxidize part of the active substances on the surface of the jujube slices to form an anti-oxidation protective film. The formation of this film can reduce the oxidative degradation of the active substances in the jujube slices during the drying process.

The invention provides a new food processing application for cold plasma activated water and expands a new application field.

Description of the drawings

Figure 1 is a comparison diagram of the drying time of the jujube slices of Comparative Example 1-3 and Example 1-3;

Figure 2 is a comparison diagram of the total phenol content of jujube tablets of Comparative Example 1-3 and Example 1-3;

Figure 3 is a comparison diagram of flavonoid content of jujube tablets of Comparative Example 1-3 and Example 1-3;

4 is a comparison diagram of the proanthocyanidin content of jujube slices of Comparative Example 1-3 and Example 1-3;

Figure 5 is a comparison diagram of the drying time of the jujube slices of Comparative Examples 4-6 and Examples 1-3;

Figure 6 is a comparison diagram of the total phenol content of jujube tablets of Comparative Examples 4-6 and Examples 1-3;

Figure 7 is a comparison diagram of the flavonoid content of the jujube tablets of Comparative Examples 4-6 and Examples 1-3;

Fig. 8 is a comparison diagram of proanthocyanidin content of jujube slices of Comparative Examples 4-6 and Examples 1-3;

Figure 9 is a comparison diagram of the vitamin C content of the jujube tablets of Comparative Example 1-6 and Example 1-3.

detailed description

The present invention will be further described below in conjunction with comparative examples and specific embodiments. The following are only specific embodiments of the present invention, but the protection scope of the present invention is not limited to this:

Comparative example 1

The fresh red dates are washed and then cored and sliced. The thickness of the red dates is 6mm. For fresh red date slices without pretreatment, preheat the temperature of the hot air dryer to 50℃, put the red date slices in for hot air drying at a wind speed of 1.0m/s, and measure the water content of the red date slices every 30 minutes. When the water content of the red date slices is lower than Stop drying at 5% (based on wet basis) to obtain dried red date flakes.

The drying time is 1050min, the polyphenol content in dried red date tablets is 13.56mg/g DW (dry basis), the flavonoid content in dried red date tablets is 3.26mg/g DW (dry basis), and the proanthocyanidin content in dried red date tablets is 2.56 mg/g DW (dry basis), the vitamin C content in dried red jujube tablets is 1.38mg/g DW (dry basis).

Comparative example 2

The fresh red dates are washed and then cored and sliced. The thickness of the red dates is 6mm. The fresh red date slices are not pre-treated, the hot air dryer temperature is preheated to 60℃, and the red date slices are put in for hot air drying at a wind speed of 1.0m/s. The water content of the red date slices is measured every 30 minutes. When the water content of the red date slices is lower than Stop drying at 5% (based on wet basis) to obtain dried red date flakes.

The drying time is 630 minutes, the polyphenol content in the dried red jujube tablets is 14.26mg/g DW (dry basis), the flavonoid content in the dried jujube tablets is 4.01mg/g DW (dry basis), and the proanthocyanidin content in the dried red jujube tablets is 2.58 The vitamin C content in mg/g DW (dry basis) dried red jujube tablets is 1.62mg/g DW (dry basis).

Comparative example 3

The fresh red dates are washed and then cored and sliced. The thickness of the red dates is 6mm. Without pretreatment, the hot air dryer temperature is preheated to 70℃, and the red date slices are put in for hot air drying at a wind speed of 1.0m/s. The water content of the red date slices is measured every 30 minutes. When the water content of the red date slices is lower than Stop drying at 5% (based on wet basis) to obtain dried red date flakes.

The drying time is 540min, the polyphenol content in dried red date tablets is 14.33mg/g DW (dry basis), the flavonoid content in dried red date tablets is 3.48mg/g DW (dry basis), and the proanthocyanidin content in dried red date tablets is 2.18 The vitamin C content in mg/g DW (dry basis) dried red jujube tablets is 1.44mg/g DW (dry basis).

Example 1

The output power of the cold plasma equipment was adjusted to 600W, the flow rate of the cold plasma gas flow was 200L/min, and the water was pretreated for 20 minutes (the water was kept in an ice water bath during the entire treatment process) to prepare 25L of cold plasma activated water. The fresh red dates are washed and then cored and sliced. The thickness of the red dates is 6mm. The fresh red date slices are completely immersed in cold plasma activated water for 2 minutes, and then taken out after soaking, and the surface water is wiped off with absorbent paper. Preheat the temperature of the hot air dryer to 50℃, put the pretreated red date slices into hot air drying at a wind speed of 1.0m/s, and measure the water content of the red date slices every 30 minutes. When the water content of the red date slices is less than 5% (to Drying was stopped at the time of wet basis, and dried red date slices were obtained.

The drying time is 930 minutes, the content of polyphenols in dried red date tablets is 15.26mg/g DW (dry basis), the content of flavonoids in dried red date tablets is 4.95 mg/g DW (dry basis), and the content of proanthocyanidins in dried red date tablets is 3.38 mg/g DW (dry basis), the vitamin C content in dried red jujube tablets is 1.37mg/g DW (dry basis).

Comparative example 4

The fresh red dates are washed and then cored and sliced. The thickness of the red dates is 6mm. Direct cold plasma treatment is adopted, the output power of the cold plasma equipment is adjusted to 600W, the flow rate of the cold plasma gas flow is 200L/min, the cold plasma probe is 15cm away from the surface of the jujube slice, and the pretreatment is 5min.

Preheat the temperature of the hot air dryer to 50℃, put the pretreated red date slices into hot air drying at a wind speed of 1.0m/s, and measure the water content of the red date slices every 30 minutes. When the water content of the red date slices is less than 5% (to Drying was stopped at the time of wet basis, and dried red date slices were obtained. Figure 5-9 shows the active ingredient content of hot air drying and dried red jujube tablets.

The drying time is 1020 minutes, the polyphenol content in the dried red date tablets is 14.28mg/g DW (dry basis), the flavonoid content in the dried red date tablets is 3.85 mg/g DW (dry basis), and the proanthocyanidin content in the dried red date tablets is 2.59 mg/g DW (dry basis), the vitamin C content in dried red jujube tablets is 0.69mg/g DW (dry basis).

Example 2

The output power of the cold plasma equipment was adjusted to 800W, the flow rate of the cold plasma gas flow was 150L/min, and the water was pretreated for 5 minutes (keeping in an ice water bath) to prepare 10L of cold plasma activated water. The fresh red dates are washed and then cored and sliced. The thickness of the red dates is 6mm. The fresh red date slices are completely immersed in cold plasma activated water for 0.5 min. After soaking, they are taken out, and the surface water is wiped off with absorbent paper. Preheat the temperature of the hot air dryer to 60℃, put the pretreated red date slices into hot air drying at a wind speed of 1.0m/s, and measure the water content of the red date slices every 30 minutes. When the water content of the red date slices is less than 5% (to Drying was stopped at the time of wet basis, and dried red date slices were obtained.

The drying time is 510 minutes, the content of polyphenols in dried red date tablets is 16.29mg/g DW (dry basis), the content of flavonoids in dried red date tablets is 4.39mg/g DW (dry basis), and the content of proanthocyanidins in dried red date tablets is 2.99 The vitamin C content in mg/g DW (dry basis) dried red jujube tablets is 1.72mg/g DW (dry basis).

Comparative example 5

The fresh red dates are washed and then cored and sliced. The thickness of the red dates is 6mm. Direct cold plasma processing is adopted, the output power of the cold plasma equipment is adjusted to 800W, the flow rate of the cold plasma gas flow is 150L/min, the cold plasma probe is 5cm away from the surface of the jujube slice, and the pretreatment is 3min.

Preheat the temperature of the hot air dryer to 60℃, put the pretreated red date slices into hot air drying at a wind speed of 1.0m/s, and measure the water content of the red date slices every 30 minutes. When the water content of the red date slices is less than 5% (to Drying was stopped at the time of wet basis, and dried red date slices were obtained. Figure 5-9 shows the active ingredient content of hot air drying and dried red jujube tablets.

The drying time is 580min, the polyphenol content in dried red date tablets is 14.04mg/g DW (dry basis), the flavonoid content in dried red date tablets is 3.94mg/g DW (dry basis), and the proanthocyanidin content in dried red date tablets is 2.66 mg/g DW (dry basis), the vitamin C content in dried red jujube tablets is 1.35mg/g DW (dry basis).

Example 3

The output power of the cold plasma equipment was adjusted to 700W, the flow rate of the cold plasma gas flow was 100L/min, and the water was pretreated for 10 minutes (keeping in an ice water bath) to prepare 15L of cold plasma activated water. The fresh red dates are washed and then cored and sliced. The thickness of the red dates is 6mm. The fresh red date slices are completely immersed in cold plasma activated water for 1 min. After soaking, they are taken out, and the surface water is wiped off with absorbent paper. Preheat the temperature of the hot air dryer to 70℃, put the pre-treated red date slices into hot air drying at a wind speed of 1.0m/s, and measure the water content of the red date slices every 30 minutes. When the water content of the red date slices is less than 5% (to Drying was stopped at the time of wet basis, and dried red date slices were obtained.

The drying time is 360 minutes, the content of polyphenols in dried red date tablets is 15.37mg/g DW (dry basis), the content of flavonoids in dried red date tablets is 4.15 mg/g DW (dry basis), and the content of proanthocyanidins in dried red date tablets is 2.74 mg/g DW (dry basis), the vitamin C content in dried red jujube tablets is 1.40mg/g DW (dry basis).

Comparative example 6

The fresh red dates are washed and then cored and sliced. The thickness of the red dates is 6mm. Direct treatment with cold plasma is adopted, the output power of the cold plasma equipment is adjusted to 700W, the flow rate of the cold plasma gas flow is 100L/min, the cold plasma probe is 10cm away from the surface of the jujube slice, and the pretreatment is 6min.

Preheat the temperature of the hot air dryer to 70℃, put the pre-treated red date slices into hot air drying at a wind speed of 1.0m/s, and measure the water content of the red date slices every 30 minutes. When the water content of the red date slices is less than 5% (to Drying was stopped at the time of wet basis, and dried red date slices were obtained. Figure 5-9 shows the active ingredient content of hot air drying and dried red jujube tablets.

The drying time is 450min, the polyphenol content in dried red date tablets is 14.13mg/g DW (dry basis), the flavonoid content in dried red date tablets is 3.43mg/g DW (dry basis), and the proanthocyanidin content in dried red dates tablets is 2.22 mg/g DW (dry basis), the vitamin C content in dried red jujube tablets is 0.77mg/g DW (dry basis).

Example 4

The output power of the cold plasma equipment was adjusted to 900W, the flow rate of the cold plasma gas flow was 300L/min, and the water was pretreated for 40min (keeping in an ice water bath) to prepare 50L of cold plasma activated water. The fresh red dates are washed and then cored and sliced. The thickness of the red dates is 10mm. The fresh red date slices are completely immersed in cold plasma activated water for 5 minutes, and then taken out after soaking, and the surface water is wiped dry with absorbent paper. Preheat the temperature of the hot air dryer to 55℃, put the pretreated red date slices into hot air drying at a wind speed of 1.5m/s, and measure the water content of the red date slices every 30 minutes. When the water content of the red date slices is less than 5% (to Drying was stopped at the time of wet basis, and dried red date slices were obtained.

The drying time is 630 minutes, the polyphenol content in the dried red date tablets is 15.26mg/g DW (dry basis), the flavonoid content in the dried red date tablets is 4.35 mg/g DW (dry basis), and the proanthocyanidin content in the dried red date tablets is 3.08 mg/g DW (dry basis), the vitamin C content in dried red jujube tablets is 1.45mg/g DW (dry basis).

Example 5

The output power of the cold plasma equipment was adjusted to 750W, the flow rate of the cold plasma gas flow was 250L/min, and the water was pretreated for 30min (keeping in an ice water bath) to prepare 35L of cold plasma activated water. The fresh red dates are washed and then cored and sliced. The thickness of the red dates is 2mm. The fresh red date slices are completely immersed in cold plasma activated water (the cold plasma activated water is used for the first time), and the immersion time is 3 minutes. After soaking, take it out, and use absorbent paper to dry the surface water. Preheat the temperature of the hot air dryer to 65℃, put the pre-treated red date slices into hot air drying at a wind speed of 2.0m/s, and measure the water content of the red date slices every 30 minutes. When the water content of the red date slices is less than 5% (to Drying was stopped at the time of wet basis, and dried red date slices were obtained.

The drying time is 450min, the polyphenol content in dried red date tablets is 15.66mg/g DW (dry basis), the flavonoid content in dried red date tablets is 4.01mg/g DW (dry basis), and the proanthocyanidin content in dried red date tablets is 2.63 mg/g DW (dry basis), the vitamin C content in dried red jujube tablets is 1.57mg/g DW (dry basis).

Example 6

The fresh red jujube slices were immersed and dried with hot air with the cold isocyanine in vitro activated water after the initial soaking in Example 5.

The second use of cold plasma activated water: completely soak the fresh red date slices in cold plasma activated water (the second use of cold plasma activated water), soaking time is 3 minutes, after soaking, take it out, use absorbent paper to dry the surface water . Preheat the temperature of the hot air dryer to 65℃, put the pre-treated red date slices into hot air drying at a wind speed of 2.0m/s, and measure the water content of the red date slices every 30 minutes. When the water content of the red date slices is less than 5% (to Drying was stopped at the time of wet basis, and dried red date slices were obtained.

The drying time is 460min, the content of polyphenols in dried red date tablets is 15.59mg/g DW (dry basis), the content of flavonoids in dried red date tablets is 4.01mg/g DW (dry basis), and the content of proanthocyanidins in dried red date tablets is 2.68 mg/g DW (dry basis), the vitamin C content in dried red jujube tablets is 1.52mg/g DW (dry basis).

Example 7

The fresh red jujube slices were immersed and dried with hot air with the cold plasma activated water after the second immersion used in Example 5 (cold plasma activated water was used for the third time).

The third use of cold plasma activated water: completely immerse the fresh red date slices in cold plasma activated water (the third use of cold plasma activated water), soaking time is 3min, after soaking, take it out, use absorbent paper to dry the surface water . Preheat the temperature of the hot air dryer to 65℃, put the pre-treated red date slices into hot air drying at a wind speed of 2.0m/s, and measure the water content of the red date slices every 30 minutes. When the water content of the red date slices is less than 5% (to Drying was stopped at the time of wet basis, and dried red date slices were obtained.

The drying time is 460min, the polyphenol content in dried red date tablets is 15.56mg/g DW (dry basis), the flavonoid content in dried red date tablets is 3.97 mg/g DW (dry basis), and the proanthocyanidin content in dried red date tablets is 2.56 mg/g DW (dry basis), the vitamin C content in dried red jujube tablets is 1.55mg/g DW (dry basis).

From the results of Examples 5-7, it can be seen that repeated use of cold plasma activated water has no significant effect on the drying time and active ingredient content of the jujube slices (not more than 3%). It can be seen that cold plasma activated water can still be used repeatedly. Maintain a better pretreatment effect.

From the above results and Figures 1-9, it can be seen that the cold plasma activated water pretreatment method of Example 1-3 of the present invention is compared with the non-pretreated Comparative Example 1-3 at the same hot air drying temperature and Under wind speed conditions, the drying time can be reduced by up to 33%, the polyphenol content in dried red date tablets can be increased by 14%, the flavonoid content in dried red date tablets can be increased by 52%, and the proanthocyanidin content in dried red date tablets can be increased by 32%. The cold plasma activated water is rich in reactive oxygen species (ROS) and reactive nitrogen molecules (RNS). ROS and RNS have a peroxidation effect, which can destroy the membrane lipids of the jujube slice cells, cause the cell membrane to rupture, and release the jujube slice cell sap, thereby enhancing Drying rate. Cold plasma activated water pretreatment can significantly increase the active substance content of dried jujube slices. On the one hand, cold plasma activated water pretreatment can increase the hot air drying rate of red jujube slices, thereby reducing the thermal degradation of active substances; on the other hand, The cold plasma activated water pretreatment can oxidize part of the active substances on the surface of the jujube slices to form an anti-oxidation protective film. The formation of this film can reduce the oxidative degradation of the active substances in the jujube slices during the drying process.

Comparing Examples 1-3 with Comparative Examples 4-6, it can be seen that the cold plasma activated water treatment can reduce the drying time by up to 20% compared with the cold plasma direct treatment (as shown in Figure 5), and can significantly improve The content of dried jujube slices polyphenols (as shown in Fig. 6 up to 16%), flavonoids (as shown in Fig. 7 up to 29%) and proanthocyanidins (as shown in Fig. 8 up to 31%). In addition, the experimental results show that direct cold plasma treatment will cause the destruction of vitamin C in the jujube slices. Compared with the untreated group, the vitamin C content is reduced by up to 50% (as shown in Figure 9).

Therefore, compared to the hot-air drying method of jujube slices without pretreatment and the hot-air drying method using cold plasma in vitro direct pretreatment, the present invention adopts cold plasma activated water pretreatment to improve the hot-air drying rate and biological activity of jujube slices. The method of ingredient content can increase the drying rate of dried red date slices, reduce drying energy consumption, and improve the quality of dried red date slices.

Finally, the present invention can be summarized in other specific forms that do not violate the spirit and main features of the present invention. Therefore, no matter from which point of view, the above-mentioned embodiments of the present invention can only be regarded as descriptions of the present invention and cannot limit the present invention. The claims indicate the scope of the present invention, while the foregoing description does not indicate the scope of the present invention. Scope, therefore, any changes within the meaning and scope equivalent to the claims of the present invention shall be considered to be included in the scope of the claims.

Claims

A method for drying red date slices using cold plasma activated water, which is characterized in that it comprises the following steps:

(1) Use cold plasma equipment to pretreat water to prepare cold plasma activated water; the output power of cold plasma equipment is 600-900W, the flow rate of cold plasma gas flow is 100-300L/min, and the pretreatment time is 5-40min;

(2) Soak the fresh red date slices in cold plasma activated water for pre-treatment; the thickness of the red date slices is 2-10mm, and the fresh red date slices are completely immersed in cold plasma activated water for 0.5-5min;

(3) The pretreated fresh jujube slices are dried with hot air until the water content of the jujube slices meets the set requirements, and dried jujube slices are obtained.
The method for drying red jujube slices using cold plasma activated water according to claim 1, wherein the cold plasma activated water used in step (2) is the cold plasma activated water used in step (1) that is not soaked. The water may be cold plasma activated water that has been immersed in step (2) for one or more times.
The method for drying red jujube slices using cold plasma activated water according to claim 2, wherein the repeated use of cold plasma activated water is not more than 3 times.
The method for drying jujube slices using cold plasma activated water according to claim 1, wherein in step (1), the output power of the cold plasma equipment is 600-800W, and the flow rate of the cold plasma gas flow is 100-200L/min, The pretreatment time is 5-20min.
The method for drying red date slices using cold plasma activated water according to claim 1, wherein the water is kept in an ice water bath during the process of preparing cold plasma activated water in step (1).
The method for drying jujube slices using cold plasma activated water according to claim 1, wherein the fresh jujube slices in step (2) are prepared by washing the fresh jujube and then cored and sliced, and the thickness of the jujube slice is 4-8mm .
The method for drying red date slices using cold plasma activated water according to claim 1, wherein in step (2), the fresh red date slices are completely immersed in cold plasma activated water for a soaking time of 0.5-2 min.
The method for drying jujube slices using cold plasma activated water according to claim 1, characterized in that step (2) after soaking further comprises a step of wiping or absorbing moisture on the surface of the jujube slices.
The method for drying jujube slices using cold plasma activated water according to claim 1, characterized in that the specific operation method of step (3) hot air drying treatment is: hot air drying temperature is 50-70°C, wind speed is 1-2m/s .
The method for drying jujube slices using cold plasma activated water according to claim 1, characterized in that at the end of step (3) hot air drying, the moisture content of the jujube slices is required to be no more than 5% on a wet basis.