A preparation method and application of Chinese yam slices

Abstract

The present invention belongs to the technical field of food processing, and particularly relates to a preparation method and application of yam slices. A preparation method of yam slices comprises the following steps: (1) The yam tubers are subjected to ultra-high pressure treatment to obtain ultra-high pressure-treated yam tubers; (2) The yam tubers obtained in step (1) are sliced, placed in a color protection solution, subjected to pulsed vacuum treatment, and dried to obtain yam slices. The present invention prepares yam slices by using a method of combining ultra-high pressure treatment with pulsed vacuum-assisted color protection. The yam slices prepared by this preparation method have good color, high integrity rate, high retention rate of nutrients, simple process, high production efficiency, do not use any food additives, and are green and safe.

Description

Technical Field

[0001] The present invention belongs to the technical field of food processing, and particularly relates to a preparation method and application of yam slices. Background Art

[0002] Fresh yam is prone to microbial infection due to its high water content, large amounts of starch and mucus, and improper storage can cause mildew, spoilage and nutrient loss. Slicing the yam and then dehydrating it to make yam slices is one of the most common processing methods for yam at present. Against the background of traditional yam slices pursuing external sensory quality, color and integrity of the yam slices are still important indicators for evaluating their quality. Therefore, during the processing of yam slices, blanching, sulfur fumigation or other combined color protection solutions are often used for color protection. However, blanching for color protection will cause starch gelatinization on the surface of the yam, affecting the color of the yam slices. Sulfur fumigation or combined color protection solution for color protection generally takes a long time, 2 - 4 hours, which is not conducive to improving production efficiency, and there are many broken yam slices with poor integrity. At the same time, food additives are usually added to the combined color protection solution, which does not meet people's demand for green and additive-free products. In addition, during the final drying of traditional preparation methods for yam slices, the required drying time is relatively long, which also reduces production efficiency. At present, there is no research report on improving the integrity and nutritional functional quality of dehydrated yam slices through ultra-high pressure treatment.

[0003] Therefore, there is an urgent need to provide a preparation method for yam slices, which has good integrity, good color, high retention rate of nutrients, simple process, high production efficiency, does not use any food additives, and is green and safe. Summary of the Invention

[0004] The present invention aims to solve one or more technical problems existing in the prior art, and at least provides a beneficial choice or creation condition. The present invention provides a preparation method for yam slices, which has good integrity, good color, high retention rate of nutrients, simple process, high production efficiency, does not use any food additives, and is green and safe.

[0005] Inventive concept of the present invention: The present invention uses a method of ultra-high pressure treatment combined with pulsed vacuum-assisted color protection to prepare yam slices. Ultra-high pressure treatment can not only inactivate enzymes, effectively reducing the degradation of functional substances such as polyphenols and diosgenin caused by enzymatic reactions during the drying and dehydration process of yam slices; it can also change the tissue structure of fresh yam, improve the texture, which is beneficial to reducing the fragmentation of yam slices during slicing and the cracking caused by volume shrinkage during drying. Finally, the prepared yam slices have the characteristics of good integrity rate and high retention rate of nutrients. At the same time, during the color protection process, pulsed vacuum treatment will effectively enhance the mass transfer effect between the color protection liquid and the yam chips, shorten the color protection soaking time, generally only about 14 minutes is required to complete the color protection operation, improve production efficiency, and has strong operability and good application value. In addition, after ultra-high pressure and pulsed vacuum treatment, it helps to open the pore network for water transfer, shorten the drying time, and improve production efficiency.

[0006] Therefore, in the first aspect of the present invention, a method for preparing yam slices is provided.

[0007] Specifically, a method for preparing yam slices includes the following steps:

[0008] A method for preparing yam slices includes the following steps:

[0009] (1) The yam tubers are subjected to ultra-high pressure treatment to obtain ultra-high pressure-treated yam tubers;

[0010] (2) The yam tubers obtained in step (1) are sliced, placed in a color protection liquid, subjected to pulsed vacuum treatment, and dried to obtain yam slices;

[0011] In step (1), the pressure of the ultra-high pressure treatment is 180 - 550 MPa.

[0012] Preferably, in step (1), the yam tubers are first cut into sections and then subjected to ultra-high pressure treatment.

[0013] Specifically, in step (1), mature yam tubers are selected, the bad, diseased, and pest-infested tubers are removed, washed clean, and then cut into sections.

[0014] Preferably, the length of the yam tubers after cutting into sections is 30 - 50 cm.

[0015] Preferably, in step (1), the pressure of the ultra-high pressure treatment is 200 - 500 MPa.

[0016] Preferably, in step (1), the time of the ultra-high pressure treatment is 4.5 - 22 min; more preferably, the time of the ultra-high pressure treatment is 5 - 20 min.

[0017] Preferably, in step (1), the ultra-high pressure treatment is carried out in an ultra-high pressure treatment chamber. The cut Chinese yam is placed in the ultra-high pressure chamber under the temperature condition of 20-30°C.

[0018] Preferably, in step (2), the Chinese yam is peeled before slicing.

[0019] Specifically, manual peeling or mechanical peeling is adopted.

[0020] Specifically, manual slicing or mechanical slicing is adopted for slicing.

[0021] Preferably, in step (2), the slicing angle of the Chinese yam during slicing is 25-75°, and the thickness after slicing is 3.5-9 mm.

[0022] Further preferably, the slicing angle of the Chinese yam during slicing is 30-70°, and the thickness after slicing is 4-8 mm.

[0023] Specifically, the angle is the angle between the cutting knife and the length direction of the Chinese yam.

[0024] Preferably, in step (2), the color protection liquid is vinegar, and the concentration of the vinegar is 0.18-0.55%.

[0025] Further preferably, the concentration of the vinegar is 0.2-0.5%.

[0026] Preferably, the mass ratio of the Chinese yam slices obtained after slicing the Chinese yam segments to the vinegar is 1:1.8-5.5.

[0027] Further preferably, the mass ratio of the Chinese yam slices obtained after slicing the Chinese yam segments to the vinegar is 1:2-5.

[0028] Preferably, in step (2), the pulse vacuum treatment includes a vacuum holding stage and a post-vacuum release holding stage.

[0029] Preferably, the pressure in the vacuum holding stage is 0.01-0.06 MPa, and the holding time in the vacuum holding stage is 27-130 s; the holding time in the post-vacuum release holding stage is 27-130 s.

[0030] Further preferably, the pressure in the vacuum holding stage is 0.01-0.05 MPa, and the holding time in the vacuum holding stage is 30-120 s; the holding time in the post-vacuum release holding stage is 30-120 s.

[0031] Preferably, the vacuum holding stage and the post-vacuum release holding stage are one cycle of pulse treatment, and the number of pulse treatments is 2-6 times.

[0032] Specifically, the pressure during the holding stage after releasing the vacuum is normal pressure.

[0033] Specifically, in step (2), under the temperature condition of 20 - 30°C, after the yam chips are placed in the color protection liquid, they are put into a pulsed vacuum chamber for pulsed vacuum treatment.

[0034] Preferably, in step (2), the drying is carried out by hot air drying, the temperature of the hot air drying is 50 - 80°C, the time of the hot air drying is 4 - 6 h, and the wind speed of the hot air drying is 0.45 - 3.3 m / s.

[0035] More preferably, the drying is carried out by hot air drying, the temperature of the hot air drying is 55 - 75°C, the time of the hot air drying is 4.5 - 5.5 h, and the wind speed of the hot air drying is 0.5 - 3.0 m / s.

[0036] Preferably, in step (2), the moisture content of the yam slices ≤ 12%.

[0037] Specifically, after the yam slices are dried, they also include the process of naturally cooling to room temperature, and then being classified according to size and integrity rate and then packaged.

[0038] The second aspect of the present invention provides an application of the method for preparing the yam slices described in the first aspect of the present invention in the field of food processing.

[0039] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows:

[0040] (1) The present invention uses ultra-high pressure treatment combined with pulsed vacuum-assisted color protection to prepare yam slices. This preparation method can improve the integrity and nutritional quality of dehydrated yam slices, and has a simple process, high production efficiency, does not use any food additives, and is green and safe.

[0041] (2) Ultra-high pressure treatment can not only inactivate enzymes, effectively reduce the degradation of functional substances such as polyphenols and diosgenin caused by enzymatic reactions during the drying and dehydration process of yam slices; but also change the tissue structure of fresh yam, improve the texture, facilitate reducing the fragmentation of yam slices caused during the slicing process and the rupture caused by volume shrinkage during the drying process, and finally make the prepared yam slices have the characteristics of good integrity rate and high retention rate of nutrients.

[0042] (3) The present invention effectively improves the mass transfer effect between vinegar and yam slices through pulsed vacuum treatment, shortens the color protection soaking time, improves the production efficiency, has strong operability, and has good application value. In addition, after ultra-high pressure and pulsed vacuum treatment, it helps to open the pore network for water transfer, shortens the drying time, and improves the production efficiency. Specific embodiments

[0043] To make the technical solution of the present invention clearer and more understandable to those skilled in the art, the following embodiments are listed for illustration. It should be noted that the following embodiments do not limit the scope of protection required by the present invention.

[0044] Unless otherwise specified, the raw materials, reagents or devices used in the following embodiments can be obtained from conventional commercial channels or can be obtained by existing known methods.

[0045] The raw materials used in Examples 1-3 and Comparative Examples 1-5 are all "Caojiang Huai Mountain Yams" freshly harvested from Gaozhou, Maoming.

[0046] Example 1

[0047] A method for preparing yam slices, comprising the following steps:

[0048] (1) Select yam tubers, remove damaged, diseased and pest-infested tubers, wash the selected yam tubers, cut them into 40 cm long sections, put them into an ultra-high pressure treatment chamber for ultra-high pressure treatment, control the temperature at 20 °C, the pressure at 300 MPa, and the pressure holding time at 15 min to obtain ultra-high pressure treated yam tubers;

[0049] (2) Manually peel the ultra-high pressure treated yam tubers obtained in step (1), cut them into 6 mm thick yam slices at a 45° angle, put the yam slices into a 0.4% acetic acid solution, and place them in a pulsed vacuum chamber at 20 °C for pulsed vacuum treatment, with a pressure of 0.02 MPa, a vacuum holding time of 120 s, a vacuum release time of 90 s, and 4 pulsed treatment times to obtain color-protected yam slices;

[0050] (3) Drain the water from the color-protected yam slices obtained in step (2), and hot air dry them at a temperature of 60 °C and a wind speed of 2 m / s until the moisture content ≤ 12% to obtain dehydrated yam slices;

[0051] (4) Naturally cool the dehydrated yam slices obtained in step (3) to room temperature, and classify and package them according to size and integrity rate.

[0052] Example 2

[0053] A method for preparing yam slices, comprising the following steps:

[0054] (1) Select yam tubers, remove damaged, diseased and pest-infested tubers, wash the selected yam tubers, cut them into 40 cm long sections, put them into an ultra-high pressure treatment chamber for ultra-high pressure treatment, control the temperature at 20 °C, the pressure at 500 MPa, and the pressure holding time at 5 min to obtain ultra-high pressure treated yam tubers;

[0055] (2) Manually peel the Dioscorea opposita Thunb. tubers obtained in step (1), cut them into Dioscorea opposita Thunb. slices with a thickness of 6 mm at a 45° angle, place the Dioscorea opposita Thunb. slices into a 0.4% acetic acid solution, and conduct pulsed vacuum treatment in a pulsed vacuum chamber at 20°C. The pressure is 0.02 MPa, the vacuum holding time is 120 s, the vacuum release time is 90 s, and the number of pulsed treatments is 4 times to obtain Dioscorea opposita Thunb. slices with color protection treatment;

[0056] (3) Drain the water from the Dioscorea opposita Thunb. slices with color protection treatment obtained in step (2), and then conduct hot air drying at a temperature of 60°C and a wind speed of 2 m / s until the moisture content ≤ 12% to obtain dehydrated Dioscorea opposita Thunb. slices;

[0057] (4) Naturally cool the dehydrated Dioscorea opposita Thunb. slices obtained in step (3) to room temperature, and then classify and package them according to size and integrity.

[0058] Example 3

[0059] A method for preparing Dioscorea opposita Thunb. slices, comprising the following steps:

[0060] (1) Select Dioscorea opposita Thunb. tubers, remove the bad, diseased, and pest-infested tubers, wash the selected Dioscorea opposita Thunb. tubers clean, cut them into 40 cm long segments, place them in a high-pressure treatment chamber for high-pressure treatment, control the temperature at 20°C, the pressure at 300 MPa, and the pressure holding time at 15 min to obtain high-pressure treated Dioscorea opposita Thunb. tubers;

[0061] (2) Manually peel the high-pressure treated Dioscorea opposita Thunb. tubers obtained in step (1), cut them into Dioscorea opposita Thunb. slices with a thickness of 6 mm at a 45° angle, place the Dioscorea opposita Thunb. slices into a 0.2% acetic acid solution, and conduct pulsed vacuum treatment in a pulsed vacuum chamber at 20°C. The pressure is 0.05 MPa, the vacuum holding time is 90 s, the vacuum release time is 60 s, and the number of pulsed treatments is 2 times to obtain Dioscorea opposita Thunb. slices with color protection treatment;

[0062] (3) Drain the water from the Dioscorea opposita Thunb. slices with color protection treatment obtained in step (2), and then conduct hot air drying at a temperature of 60°C and a wind speed of 2 m / s until the moisture content ≤ 12% to obtain dehydrated Dioscorea opposita Thunb. slices;

[0063] (4) Naturally cool the dehydrated Dioscorea opposita Thunb. slices obtained in step (3) to room temperature, and then classify and package them according to size and integrity.

[0064] Comparative Example 1

[0065] Comparative Example 1 is the commonly used blanching method in the prior art.

[0066] A method for preparing Dioscorea opposita Thunb. slices, comprising the following steps:

[0067] (1) Select Chinese yams, remove the damaged, diseased, and pest-infested yams. After cleaning the selected Chinese yams, peel them manually. Cut the Chinese yams into slices 6 mm thick at a 45° angle, and place the yam slices in hot water preheated to 95°C for blanching for 2 minutes;

[0068] (2) Drain the water from the blanched yam slices, and then dry them in hot air at 60°C and a wind speed of 2 m / s until the moisture content ≤ 12%, obtaining dehydrated yam slices;

[0069] (3) Naturally cool the dehydrated yam slices obtained in step (2) to room temperature, and then classify and package them according to size and integrity.

[0070] Comparative Example 2

[0071] Comparative Example 2 is a commonly used mixed color protection method in the prior art.

[0072] A method for preparing yam slices, comprising the following steps:

[0073] (1) Select Chinese yams, remove the damaged, diseased, and pest-infested yams. After cleaning the selected Chinese yams, peel them manually. Cut the Chinese yams into slices 6 mm thick at a 45° angle, and place the yam slices in a mixed color protection solution prepared from 0.02 g / 100 mL L-cysteine, 1.4 g / 100 mL citric acid, and 0.016 g / 100 mL VC for color protection for 60 minutes;

[0074] (2) Drain the water from the color-protected yam slices, and then dry them in hot air at 60°C and a wind speed of 2 m / s until the moisture content ≤ 12%, obtaining dehydrated yam slices;

[0075] (3) Naturally cool the dehydrated yam slices obtained in step (2) to room temperature, and then classify and package them according to size and integrity.

[0076] Comparative Example 3

[0077] Comparative Example 3 is a commonly used vacuum freeze-drying method in the prior art.

[0078] A method for preparing yam slices, comprising the following steps:

[0079] (1) Select Chinese yams, remove the damaged, diseased, and pest-infested yams. After cleaning the selected Chinese yams, peel them manually. Cut the Chinese yams into slices 6 mm thick at a 45° angle, and place the yam slices in a refrigerator at -35°C for pre-freezing for 24 hours;

[0080] (2) Put the pre-frozen yam slices into a vacuum freeze dryer, set the pressure to 32 Pa, the cold trap temperature to -55°C, the temperature of the heating plate during the sublimation stage to 20°C, and the temperature during the desorption stage to 35°C until freeze-drying is completed, obtaining dehydrated yam slices;

[0081] (3) Naturally cool the dehydrated yam slices obtained in step (2) to room temperature, and then classify and package them according to size and integrity rate.

[0082] Comparative Example 4

[0083] The difference between Comparative Example 4 and Example 1 is that the color protection process with pulsed vacuum treatment is not included in step (2) of Comparative Example 4, that is, after the yam is treated by ultra-high pressure, peeled and sliced, it is directly dried by hot air, and the others are the same as in Example 1.

[0084] Comparative Example 5

[0085] The difference between Comparative Example 5 and Example 1 is that the process of ultra-high pressure treatment is not included in step (1) of Comparative Example 5, and the others are the same as in Example 1.

[0086] Performance test

[0087] 1. Appearance evaluation

[0088] Place the yam slices prepared in Examples 1-3 and Comparative Examples 1-5 on a clean black porcelain plate, and directly observe the color, shape with the naked eye by sensory evaluation method, and smell their odor. The appearance measurement results are shown in Table 1.

[0089] 2. Integrity rate measurement

[0090] The number of fresh yam slices in each batch of Examples 1-3 and Comparative Examples 1-5 is N. Record the number of intact yam slices after dehydration and drying as N1. The integrity rate R of the yam slices = N1 / N×100%. The integrity rate measurement results are shown in Table 1.

[0091] 3. Determination of moisture content of yam slices:

[0092] Adopt the method specified in the national standard GB / T 8858-1988 "Methods for Determining Dry Matter and Moisture Content in Fruit and Vegetable Products" to measure the moisture content in the yam slices prepared in Examples 1-3 and Comparative Examples 1-5. The moisture content measurement results are shown in Table 1.

[0093] 4. Measurement of brightness

[0094] Adopt a color difference meter to measure the color of the yam slices prepared in Examples 1-3 and Comparative Examples 1-5, and use the L value to represent the brightness of the measured sample. The brightness values are shown in Table 1.

[0095] 5. Preparation time measurement

[0096] Use a timer to time the time used in the process of preparing yam slices in Examples 1-3 and Comparative Examples 1-5, and calculate the time consumed from the pretreatment stage to the finished product stage.

[0097] Among them, the pretreatment stage of Examples 1-3 refers to the ultra-high pressure treatment stage; the pretreatment stage of Comparative Examples 1-2 refers to the blanching and conventional color protection stages, the pretreatment stage of Comparative Example 3 refers to the pre-freezing stage; the pretreatment stage of Comparative Example 4 refers to the ultra-high pressure treatment stage; the pretreatment stage of Comparative Example 5 refers to the color protection stage.

[0098] 6. Determination of total phenols

[0099] The total phenols in the Dioscorea opposita slices prepared in Examples 1-3 and Comparative Examples 1-5 were determined with reference to the method in the national standard GB / T 8313-2008 "Detection Methods for the Contents of Tea Polyphenols and Catechins in Tea". The results are shown in Table 1.

[0100] The specific determination method is as follows: The dried Dioscorea opposita slices are powdered, passed through an 80-mesh sieve, 1.0 g of the sample is accurately weighed and placed in a 25-mL centrifuge tube. 8 mL of 80% (volume fraction) methanol is added, and ultrasonic extraction is carried out for 30 min at a frequency of 40 KHz and a power of 200 W. After centrifuging at 8000 r / min for 10 min, the supernatant is taken. Ultrasonic extraction and centrifugation are repeated once, and the supernatants are combined and made up to 20 mL with a volumetric flask to obtain an extract; 0.2 mL of the extract diluted by a certain multiple is taken and placed in a test tube, distilled water is added to make up to 2 mL, 1 mL of 10% (mass fraction) Folin-Ciocalteu phenol is added, vortexed and mixed well, and then left standing for 6 min. Subsequently, 2 mL of 7.5% (mass fraction) Na2CO3 solution is added, vortexed and mixed well, and made up to 10 mL with a volumetric flask, and reacted at 75 °C for 10 min. An 80% methanol solution is used as a blank control, and its absorbance is measured at a wavelength of 765 nm. A standard curve is drawn with gallic acid as the standard substance, and the results are expressed as the equivalent of gallic acid (GAE) per unit mass of dry matter, with the unit of mg / g dry basis.

[0101] 7. Determination of allantoin

[0102] The allantoin in the Dioscorea opposita slices prepared in Examples 1-3 and Comparative Examples 1-5 was determined. The results are shown in Table 1.

[0103] The specific determination method is: The dried Dioscorea opposita slices are powdered, 0.5 g of the Dioscorea opposita powder is accurately weighed, 20 mL of 20% ethanol is added to a 25-mL volumetric flask, and ultrasonic treatment is carried out for 30 min (power 350 W) at a temperature of 30 °C. After cooling, it is made up to the scale with 20% ethanol, shaken for 10 min, centrifuged at a speed of 4000 r / min for 10 min, and filtered through a 0.45-μm microporous filter membrane to obtain the supernatant. The content is determined by high performance liquid chromatography. The chromatographic column is an Agilent TC-C18 column (4.6 mm × 250 mm, 5 μm), the mobile phase is methanol: water (1:99), the flow rate is 0.5 mL / min, the injection volume is 10 μL, the detection wavelength is 224 nm, and the column temperature is 30 °C.

[0104] Table 1: Performance measurement results of the yam slices prepared in Examples 1-3 and Comparative Examples 1-5

[0105]

[0106]

[0107] As can be seen from Table 1, the yam slices prepared by the preparation method of the present invention are milky white or slightly yellowish in color, have a high integrity rate, have the fragrance of dried yam, and there are no cracks or very few products have cracks. Moreover, the preparation time is shortened, thus improving the production efficiency. In addition, the contents of total phenols and allantoin are relatively high, and the retention rate of nutrients is high.

[0108] Compared with Comparative Example 1, the surface of the yam slices prepared by the present invention has no ripening phenomenon, and the color is closer to the milky white after starch drying. At the same time, the edges of the yam slices are flat without curling. Compared with the yam slices prepared in Comparative Examples 2 and 3, the present invention greatly reduces the fragmentation of the yam slices caused by slicing cracks and volume shrinkage during dehydration. Compared with Comparative Example 4, the color of the yam slices prepared by the present invention is not significantly yellow and the total phenol content is slightly higher than that of Comparative Example 4. Compared with Comparative Example 5, the integrity rate of the yam slices prepared by the present invention is much higher than that of Comparative Example 5, and the contents of total phenols and allantoin are also slightly higher. Therefore, the preparation method of the present invention can significantly improve the appearance quality and nutrient retention rate of the yam slices, enhance the commercial value of the yam slices, and is conducive to popularization and application.

[0109] Color brightness / whiteness is an important factor for consumers to choose yam slices. As can be seen from Table 1, the L values of the yam slices prepared by the present invention are all above 91.5, which are comparable to the brightness values of the yam slices in Comparative Examples 2 and 3, and are significantly higher than the brightness values of the yam slices in Comparative Examples 1 and 4. The yam slices obtained by blanching treatment in Comparative Example 1 have a transparent edge and a slightly yellow surface after drying due to the surface gelatinization of yam starch. In Comparative Example 4, serious surface browning occurred during the drying process of the yam slices due to lack of color protection. Therefore, the color brightness / whiteness of the yam slices of the present invention more meets the selection criteria of consumers.

[0110] The time required for producing dehydrated Chinese yam slices by using the process of the present invention is 300 - 330 min. Compared with the preparation time of 360 min required in Comparative Example 1 and the time of 420 min required in Comparative Example 2, the preparation time is saved by at least 30 min. This is because, on the one hand, during the ultra-high pressure treatment, not only can enzymes be quickly inactivated, greatly reducing the browning reaction during the drying process of Chinese yam and retaining nutrients, but also the internal tissue structure of Chinese yam is destroyed, significantly improving the dehydration efficiency during the drying process of the material. On the other hand, during the vacuum pulse-assisted color protection process, multiple vacuum - vacuum release cycles are adopted. In addition to accelerating the interaction between the color protection liquid and the Chinese yam slices, it also helps to open the internal tissue structure of Chinese yam damaged by ultra-high pressure, forming an unobstructed mass transfer channel, greatly increasing the dehydration rate in the early stage, thereby significantly shortening the overall preparation time. In addition, the color protection time of the present invention is 5 - 14 min, and the color protection times of Comparative Example 1 and Comparative Example 2 are 2 min and 60 min respectively. Although the color protection time of Comparative Example 1 is shorter, the brightness and nutrient retention rate of the Chinese yam slices in Comparative Example 1 are both lower. Therefore, the preparation method of the present application can reduce the color protection time and shorten the preparation time on the basis of ensuring the quality, thereby improving the production efficiency and saving energy consumption.

[0111] Allantoin is one of the main characteristic active substances in Chinese yam, and has functions such as anti-irritation, anesthetic analgesia, promoting epithelial growth, anti-inflammatory and antibacterial, and is commonly used to treat chapped hands and feet, ichthyosis, acne, chilblains and various keratotic skin diseases. The content of allantoin in Chinese yam slices is also an important standard for evaluating its quality. It can be seen from the results in Table 1 that the content of allantoin in the dehydrated Chinese yam slices prepared in Examples 1 - 3 of the present invention is not much different from that in the Chinese yam slices in Comparative Example 3, but is significantly higher than the content of allantoin in Comparative Examples 1 - 2. In addition, the content of polyphenols in the dehydrated Chinese yam slices prepared in Examples 1 - 3 of the present invention is not much different from that in the Chinese yam slices in Comparative Example 3, but is significantly higher than the content of polyphenols in Comparative Examples 1 - 2, and is higher than the content of polyphenols in the Chinese yam slices prepared without ultra-high pressure treatment in Comparative Example 5. It shows that the ultra-high pressure treatment adopted in the present invention has the effect of activating and releasing polyphenolic substances in Chinese yam, and the polyphenol content is still comparable to that of the freeze-dried sample in Comparative Example 3 even after 4 - 6 h of hot air dehydration.

[0112] In summary, compared with the yam slices in Comparative Example 1, the dehydrated yam slices prepared by the preparation method of the present invention have better appearance color and shape, and higher polyphenol and allantoin contents; compared with the yam slices color-protected with the mixed color-protecting solution in Comparative Example 2, they have a higher sample integrity rate, greatly improving the finished product rate of the dehydrated yam slices, and at the same time, the polyphenol and allantoin contents are also relatively higher; compared with the freeze-dried vacuum yam slices in Comparative Example 3, the preparation time of the yam slices is significantly shortened, the production efficiency is improved, and the integrity rate of the yam slices is also significantly higher; compared with Comparative Example 4, the surface browning of the yam slices caused by the lack of color protection treatment is significantly improved; compared with Comparative Example 5, the fragmentation of the yam slices caused by volume shrinkage during the drying process is significantly improved.

[0113] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A preparation method of Chinese yam slices, characterized in that, It includes the following steps: (1) The Dioscorea opposita thumb is subjected to ultra-high pressure treatment to obtain ultra-high pressure-treated Dioscorea opposita thumb; (2) The Dioscorea opposita thumb obtained in step (1) is sliced, placed in a color protection solution, subjected to pulsed vacuum treatment, and dried to obtain Dioscorea opposita thumb slices; In step (1), the pressure of the ultra-high pressure treatment is 180 - 550 MPa; In step (1), the time of the ultra-high pressure treatment is 4.5 - 22 min; In step (2), the color protection solution is vinegar, and the concentration of the vinegar is 0.18 - 0.55%; In step (2), the pulsed vacuum treatment includes a vacuum holding stage and a holding stage after vacuum release; The pressure of the vacuum holding stage is 0.01 - 0.06 MPa, and the holding time of the vacuum holding stage is 27 - 130 s; the holding time of the holding stage after vacuum release is 27 - 130 s; The vacuum holding stage and the holding stage after vacuum release are a cycle of pulsed treatment, and the number of pulsed treatments is 2 - 6 times.

2. The preparation method according to claim 1, wherein The mass ratio of the Dioscorea opposita thumb slices obtained after slicing the Dioscorea opposita thumb to the vinegar is 1:1.8 - 5.

5.

3. The preparation method according to claim 1, characterized in that, In step (2), the drying is carried out by hot air drying. The temperature of the hot air drying is 50 - 80 °C, the time of the hot air drying is 4 - 6 h, and the wind speed of the hot air drying is 0.45 - 3.3 m / s.

4. The preparation method according to claim 1, characterized in that, In step (2), the moisture content of the Dioscorea opposita thumb slices ≤ 12%.

5. Application of the preparation method according to any one of claims 1 - 4 in the field of food processing.

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