Fresh-keeping method for prolonging shelf life of chive and application of fresh-keeping method

Abstract

The invention relates to a preservation method for prolonging the shelf life of chive by using a modified atmosphere packaging technology of low-temperature storage (4 DEG C) and nylon packaging. The method comprises the following steps: picking, cleaning, grading and airing allium fistulosum, putting 30-35 g of leaves with the width of 5-8 cm into a nylon packaging bag (22 * 32 cm), filling nitrogen into the packaging bag to exhaust air in the bag, sealing with a heat sealing machine, putting the packaged allium fistulosum into a carton, storing in a refrigerated cabinet at 4 DEG C, and carrying out comprehensive comparison and evaluation according to sensory indexes such as chromaticity, texture, water content and flavor. According to the method, the color change of the chive is effectively slowed down within 40 days, and the water content is maintained at 87%-90%; meanwhile, the characteristics of hardness, brittleness and special flavor of the chive are effectively reserved. According to the method, a more scientific and effective solution can be provided for fresh keeping of the chive, and the progress of a storage and circulation technology of fruits and vegetables with special flavors such as the chive and other perishable big-leaf vegetables is promoted.

Description

Technical Field

[0003] The invention relates to the field of green vegetable preservation, and in particular to a novel preservation method for extending the shelf life of shallots. Background Art

[0005] Allium victorialis L., also known as chives, mountain onions, and deer-ear onions, is a perennial herbaceous plant of the Liliaceae family and the genus Allium L. It is distributed in the Northeast China and many provinces such as Shanxi, Inner Mongolia, Shaanxi, and Gansu (eastern China) in my country. It grows on shady and moist hillsides, under forests, and along grassland ditches, but its number is small and its distribution is sparse. In Heilongjiang Province, it is mainly concentrated in Heihe, Yichun, and the eastern region. Allium victorialis is edible and is a rare wild vegetable with rich nutrition and unique flavor. It is a pollution-free natural green food and is also widely used as a precious medicinal material. According to ancient Chinese medicine books, allium victorialis is spicy, slightly warm, and non-toxic. It can be used to treat warm and heat accumulation in the body, clear damp heat, and eliminate miasma, especially in the abdominal digestive system. Studies in various countries have found that the chemical composition of allium is very rich, including sulfur-containing substances, flavonoids, alkaloids, steroidal saponins, carbohydrates and rich vitamin C, and has certain pharmacologically active functions, including protecting the central nervous system and cardiovascular and cerebrovascular systems, anti-tumor, anti-inflammatory, antibacterial and enhancing the body's immunity.

[0006] With the improvement of global health awareness, consumers tend to choose natural, healthy and fresh functional foods. As a nutritious wild vegetable, winter onion has great development value and economic potential. However, fresh fruits and vegetables are prone to water loss, deterioration and rot during storage due to water transfer, metabolism and microbial infection. Winter onion has large leaves and high water content, so it is easier to lose water. In recent years, Japan and South Korea have imported a large number of winter onions from my country. In order to facilitate preservation, reduce transportation losses and maintain the nutritional value of winter onions, fresh winter onions are generally salted and packaged for export. However, the flavor and nutritional quality of winter onions after salting will not only change, but also cause certain damage to the environment. In this case, extending the shelf life of winter onions and ensuring that their nutritional value and flavor are not lost have become the primary research direction and main problem for the development of the winter onion industry. Scientific and low-cost preservation technology can help improve the economic benefits of farmers, promote the market competitiveness of winter onions, and provide consumers with better quality products over a longer period of time.

[0007] Adjusting the storage temperature and optimizing modified atmosphere packaging are two important technical means in the field of fruit and vegetable preservation, which have a significant impact on extending the shelf life of fruits and vegetables and maintaining their sensory and nutritional quality.

[0008] Temperature is one of the key factors affecting the physiological and biochemical processes of fruits and vegetables after harvest. Low temperature can effectively slow down water migration and molecular movement, thereby reducing respiratory metabolic intensity and other physiological metabolic rates. This process helps to delay the aging and decay of fruits and vegetables, thereby extending their storage period and maintaining good quality and nutritional value. Modified atmosphere packaging is widely used in food preservation and antiseptic treatment to extend the shelf life of food and maintain its sensory and nutritional quality. The core of modified atmosphere packaging includes two aspects: the choice of packaging method and the preparation of gas composition inside the packaging.

[0009] Modified atmosphere packaging takes into account both sealing and air permeability. These packages can effectively isolate the impact of the external environment on food, while regulating the internal environmental conditions. High-quality packaging materials can prevent excessive exchange of moisture and oxygen, inhibit the growth of microorganisms, reduce water evaporation, prevent mechanical damage caused by squeezing and collision during transportation and storage of winter onions, and maintain the freshness and flavor of food. And by using labels and standardized packaging forms, merchants and consumers can more easily identify products. Therefore, appropriate packaging plays a vital role in the storage and transportation of winter onions.

[0010] In practical applications, temperature control and modified atmosphere packaging are not isolated technologies, but can be combined to achieve synergistic effects. Reasonable storage temperature can enhance the effect of modified atmosphere packaging, while modified atmosphere packaging can alleviate the impact of temperature fluctuations on the quality of winter onions to a certain extent. Therefore, the preservation strategy of winter onions should comprehensively consider the synergistic effect of temperature control and modified atmosphere packaging, so as to significantly extend the shelf life without losing sensory quality. This research can not only provide a more scientific and effective solution for the preservation of winter onions, but also help promote the storage and circulation technology of special flavor fruits and vegetables such as winter onions and other perishable large-leaf vegetables, and contribute to food safety and sustainable development. Summary of the invention

[0012] In view of this, the purpose of this experiment is to overcome the problems of fresh vegetables being easy to wilt, dry and rot, extend the shelf life of winter onions, and provide an excellent preservation method for leafy vegetables with special flavors such as winter onions.

[0013] In this experiment, onion plants grown by the Horticulture Branch of Heilongjiang Academy of Agricultural Sciences were used to compare the sensory quality of packaged and stored onions with that of fresh onion leaves after a certain period of storage. The experiment was also verified in other varieties of onion to evaluate the effect of the preservation method on the quality of onion and to screen for a preservation method that can extend the shelf life of fresh onion.

[0014] The research significance lies in:

[0015] 1. The normal shelf life of fresh shallot is only 2-3 days. The present invention can effectively extend the shelf life of fresh shallot to 30-40 days, thus overcoming the problem of short shelf life of fresh shallot.

[0016] 2. While extending the shelf life, the color, texture, flavor, moisture content, etc. of the onion leaves are guaranteed to be closer to fresh leaves.

[0017] Based on the above purpose, the present invention sets different storage conditions for winter onions, and screens out the best storage method for extending the shelf life of winter onions based on the evaluation results of appearance indicators, color, texture, water content, flavor and other indicators. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Comparison of the preservation effect of shallots exposed to air (unpackaged) and packed in nylon fresh-keeping bags at room temperature

[0020] Figure 2 Effects of storing scallions in nylon fresh-keeping bags, nitrogen-filled bags and vacuum-packed bags at different temperatures (room temperature, 4°C and -20°C) for different periods of time (comparison of the same packaging treatment at different temperatures)

[0021] Figure 3 Effects of storing scallions in nylon fresh-keeping bags, nitrogen-filled bags and vacuum-packed bags at different temperatures (room temperature, 4°C and -20°C) for different periods of time (comparison of different packaging treatments at the same temperature)

[0022] Figure 4 Color difference of winter onions stored at different temperatures and packaging conditions after 20 days of storage (a: strain A; b: strain B), color difference of winter onions stored at 4°C for 40 days in ordinary packaging and nitrogen packaging (c: strain A; d: strain B)

[0023] Figure 5 The hardness values ​​of shallots stored at different temperatures and packaging conditions after 20 days of storage (a: strain A; b: strain B), the hardness values ​​of shallots in ordinary packaging and nitrogen packaging after 40 days of storage at 4°C (c: strain A; d: strain B), ACK is the fresh shallot control

[0024] Figure 6 Leaf crispness values ​​of shallots stored at different temperatures and packaging conditions after 20 days of storage (a: strain A; b: strain B), leaf crispness values ​​of shallots stored at 4°C for 40 days in ordinary packaging and nitrogen packaging (c: strain A; d: strain B), ACK is the fresh shallot control

[0025] Figure 7Leaf water content of shallots (line A) stored at different temperatures and packaging conditions after 20 days of storage (a), leaf water content of shallots in ordinary packaging and nitrogen packaging after 40 days of storage at 4℃ (b), ACK is the fresh shallot control

[0026] Figure 8 Radar graph (a) and principal component analysis graph (b) of electronic nose analysis of shallot (strain A) stored at different temperatures and packaging conditions at 20 days, radar graph (c) and principal component analysis graph (d) of electronic nose analysis of shallot in ordinary packaging and nitrogen packaging at 4°C for 40 days, ACK is the fresh shallot control

[0027] Fig. 9 Electronic tongue analysis radar chart (a) and principal component analysis chart (b) of shallot (strain A) stored at different temperatures and packaging conditions after 20 days of storage, electronic tongue analysis radar chart (c) and principal component analysis chart (d) of shallot in ordinary packaging and nitrogen packaging after 40 days of storage at 4℃, ACK is the fresh shallot control

[0028] Fig.10 Radar graph (a) and principal component analysis graph (b) of electronic nose analysis of shallot (strain B) stored at different temperatures and packaging conditions at 20 days, radar graph (c) and principal component analysis graph (d) of electronic nose analysis of shallot in ordinary packaging and nitrogen packaging at 4°C for 40 days, ACK is the fresh shallot control

[0029] Fig.11 Electronic tongue analysis radar chart (a) and principal component analysis chart (b) of shallot (strain B) stored at different temperatures and packaging conditions at 20 days, electronic tongue analysis radar chart (c) and principal component analysis chart (d) of shallot in ordinary packaging and nitrogen packaging at 4℃ for 40 days, ACK is the fresh shallot control DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. The following embodiments are only for illustrating the present invention, and are not intended to limit the scope of the present invention in any way. Based on the embodiments in the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention. The experimental methods used in the present invention are conventional methods unless otherwise specified. The materials, reagents, etc. used in the present invention, unless otherwise specified, can be obtained from commercial channels. In addition, other terms used in the present invention, unless otherwise specified, generally have the meanings commonly understood by those of ordinary skill in the art.

[0032] Example 1: Study on the shelf life of shallots at room temperature

[0033] Experimental materials: Onion leaves (variety A Raohe) with a width of 5-8 cm, free of disease, good texture and no mechanical damage were selected for the experiment.

[0034] After washing and drying the onion leaves, place them directly in a room temperature environment. The room temperature measured by a thermometer is 24℃~26℃. Samples are taken and photographed every 2 days.

[0035] The result is as follows Figure 1 As shown, from Figure 1 It can be clearly seen that some of the fresh onion leaves had turned yellow and the smell had weakened on the third day. On the sixth day, they had almost completely turned yellow and shriveled, and the smell had almost completely disappeared. This shows that the quality of onions without any preservation treatment began to decline on the third day, and completely lost its use value on the sixth day. The shelf life is extremely short, which is not conducive to the transportation and sales of onions.

[0036] Example 2: Research on the effect of packaging on the preservation of shallots

[0037] Put an appropriate amount of shallots into the packaging bag. Pay attention to the integrity of the shallot leaves when bagging. Try to avoid mechanical damage to the shallots during bagging. Seal the bag after packaging. Put the well-packaged shallot samples into a carton, protect them from light, and store them at room temperature. Take samples every 3 days. The experimental results are shown in the figure below. Figure 1 As shown in the figure, the unpackaged winter onions had completely dried up and turned yellow on the 6th day and lost their edible value, while the packaged winter onions showed no obvious changes on the 6th day, and some local rot appeared on the 12th day. It can be concluded that this packaging can extend the shelf life of winter onions to a certain extent.

[0038] Example 3: Analysis of the preservation effect of shallots under different temperature and aeration conditions

[0039] Appropriate amount of 30-35 g of onion (strain A Raohe) was packed into the packaging bag. When packing, attention was paid to the integrity of the onion leaves, and mechanical damage to the onion was avoided as much as possible. Different inflation treatments were carried out: Treatment group 1: nitrogen was slowly filled into the packaged onion to discharge the remaining air in the bag, and the bag was immediately sealed after filling. There was no obvious deformation after gentle squeezing; Treatment group 2: the air in the bag was extracted and sealed by a vacuum sealer; Treatment 3: After the onion was placed in the packaging bag, it was directly sealed with a heat sealer, leaving a little air in the bag. The packaged onions were placed in cartons and placed in a refrigerator (temperature range 2-6℃) and a freezer (-20℃), and samples were taken at intervals for appearance evaluation; samples were taken every 20 days to test color difference, texture, water content, flavor and other indicators, and fresh onions were used as the control group for comparative analysis.

[0040] 3.1 Evaluation of the effect of different temperatures and aeration conditions on the appearance of postharvest preservation of winter onions

[0041] Appearance is the simplest and most intuitive indicator for evaluating the freshness of vegetables, and it is the primary indicator for consumers when selecting and evaluating vegetables. Therefore, we constructed a matrix diagram of the changes in appearance of different modified atmosphere packaging methods or different fresh-keeping temperatures that affect the fresh-keeping effect, in order to explore the changes in the appearance of winter onions under different packaging methods or different temperature conditions.

[0042] 3.1.1 Different preservation temperatures under the same modified atmosphere packaging method affect the preservation effect and appearance changes

[0043] In order to facilitate the comparison of the changes in the leaves of Allium sibiricum under different treatment methods, we will arrange the pictures in chronological order into a matrix according to the method of single factor variables. Figure 2 This is a matrix diagram of the changes in appearance of the effects of different fresh-keeping temperatures under the same modified atmosphere packaging method. The ordinary packaging treatment is to put the cold onion into the packaging bag and seal it without other treatment. It can be seen that at room temperature, the shelf life of the cold onion is short, and the vegetables are obviously rotten on the 12th day. After opening the packaging bag, a distinct odor can be smelled, accompanied by juice exudation. These phenomena indicate that microbial growth and physiological deterioration have occurred, which in turn affects its sensory quality and safety. The cold onion stored at 4℃ performed well. On the 40th day, the bag was opened for inspection and there was still no rot. Most of the cold onion leaves were intact and there was no obvious color change by naked eye observation. The quality was similar to that of fresh cold onions. There were a small amount of water droplets on the surface, which should be a low-temperature condensation phenomenon. A small amount of water accumulated in some bags. After the cold onion stored at -20℃ was taken out, it should be placed in warm water (37-40℃) for slow freezing immediately, and the leaves of the cold onion were taken out and photographed. After slow freezing, the onions are darker in color and have softer leaves. They are easily broken during slow freezing and handling, resulting in a poor appearance.

[0044] The nitrogen treatment is to fill the packaging bag with nitrogen to exhaust the air and then seal it. The appearance change trend is similar to that of the packaging only treatment group. Under room temperature, there is obvious yellowing on the 12th day; under 4℃, there is no obvious color change, and there are a few water drops on the surface, which should be low-temperature condensation; the appearance of the cold onion under -20℃ is similar to that of the packaging only group. The appearance does not change significantly over time, and there is damage.

[0045] The vacuum treatment is to use a vacuum packaging machine to remove all air and seal the bag after putting it into the packaging bag. Under room temperature, the cold onion began to rot on the 6th day, with a noticeable odor after opening the bag. It was completely soft and rotten on the 12th day; under 4℃, the color gradually darkened with time, and the leaves showed obvious water release. After opening the bag, some leaves became soft and the taste changed; at -20℃, the integrity of the leaves was better than that of the other two groups, and the appearance changes were similar to those of the other two groups.

[0046] 3.1.2 Changes in the appearance of different modified atmosphere packaging methods at the same fresh-keeping temperature

[0047] Figure 3 This is a matrix diagram of the changes in appearance of different modified atmosphere packaging methods at the same fresh-keeping temperature. Room temperature treatment is three groups of different modified atmosphere packaging methods stored at room temperature. It can be seen intuitively that the vacuum treatment group rots earlier and has a shorter shelf life; 4℃ is three groups of different modified atmosphere packaging methods stored at 4℃. It can be seen that the vacuum group has a darker color at 4℃, and the other two groups have no significant changes; stored at -20℃, the three groups have basically the same changes. The leaves frozen at -20℃ show higher brittleness and are prone to breakage. Due to the relatively large space in the bags of the nitrogen group and the packaging group, the leaves are prone to shaking during storage and use, resulting in more serious breakage. This physical damage significantly affects the appearance and sensory quality of the leaves. In contrast, the leaves in the vacuum group are more complete, because the vacuum-treated samples are packaged more flat and more stable during storage, but storage at -20℃ causes the rupture and damage of the leaf cells of the onion. Compared with the leaves stored at 4℃, its flexibility is reduced to a certain extent. This not only affects the physical properties of the leaves, but also has a negative impact on their sensory qualities, which in turn may affect consumer acceptance.

[0048] Based on the above appearance evaluation, we found that the best indicators for maintaining the quality of winter onions are: temperature index: 4℃ refrigerated storage; packaging: the nitrogen-filled treatment group and the packaging-only treatment group were basically the same in appearance evaluation, and both effectively extended the shelf life of winter onions. Based on the above appearance evaluation, we found that the methods to maintain the sensory quality of winter onions include: in terms of temperature control, 4℃ refrigerated conditions can effectively extend its shelf life. At the same time, in terms of packaging, the nitrogen-filled treatment group and the packaging-only treatment group showed basically the same effect in appearance evaluation, and both effectively extended the shelf life of winter onions.

[0049] 3.2 Effects of different temperatures and aeration conditions on the postharvest preservation effect and color of winter onions

[0050] Chroma is one of the important indicators that reflect the freshness of plants. Fresh plants have bright colors, and as the storage time increases and the quality decreases, the color of the plants tends to change. Therefore, chroma can be used as an important basis for evaluating the freshness and quality of green plants. Experimental method: Randomly select onion samples from different treatment groups, with a sampling interval of 20 days. Use a colorimeter for testing, measure each group three times, read the L, a, and b values, and use the L, a, and b values ​​of fresh onions as controls, recorded as L0, a0, and b0, and calculate the color difference value ∆E. ∆E represents the size of the color difference. The color difference value is obtained and a one-way analysis of variance is performed. P < 0.05 is considered significant. The formula is as follows:

[0051]

[0052] Figure 4 (a) is a comparison chart of the color difference values ​​of the winter onion variety A under different treatments at 20 days. At 20 days, the color difference values ​​of the 4℃ packaging group and the 4℃ nitrogen group were significantly lower than those of the other treatment groups, and there was no significant difference between the two groups. The packaging group and the other groups were significantly different, while the nitrogen group and the vacuum group were not significantly different, indicating that the color difference value of the packaging group was the lowest, which was closer to the color of fresh winter onion, followed by the nitrogen group. Since the preservation effect of the group treated at -20℃ and the group under vacuum conditions was not ideal at 20 days, they were not tested at 40 days. Combined with the appearance evaluation results in Example 3.1 and the color difference value data at 20 days, the 4℃ packaging group and the 4℃ nitrogen group were selected to measure the leaf chromaticity at 40 days. Figure 4 (c) is a comparison chart of the color difference values ​​of the two treatment groups at 40 days, among which the color difference value of the 4℃ packaging group is slightly lower than that of the 4℃ nitrogen-filled group.

[0053] 3.3 Effects of different temperatures and aeration conditions on the postharvest preservation, hardness and brittleness of shallots

[0054] Hardness and brittleness are important indicators for evaluating the freshness and quality of shallots, which are of great significance for ensuring their competitiveness in the market and consumer satisfaction. Onion samples from different treatment groups were randomly selected, and a texture analyzer with a P / 2 mm probe was used to perform a puncture test on the leaves of shallots to obtain the hardness and brittleness indicators and conduct statistical analysis. P < 0.05 was considered significant.

[0055] Figure 5 (a) is a comparison of the hardness of the leaves of shallots at different temperatures and packaging conditions on the 20th day. ACK represents fresh A-series shallots (ACK in the following figures has this meaning). The data show that there is no significant difference between the three treatment groups stored at 4°C and ACK. Among the samples stored at -20°C, there is no significant difference between the nitrogen group and ACK, and the hardness of the other two groups is significantly lower than that of fresh shallots. Combined with the appearance evaluation and color index, the 4°C vacuum group had problems such as water seepage, juice flow, blackening, and poor taste at 20 days. The -20°C nitrogen group had higher leaf toughness, but due to the low-temperature freezing, the plant cells were broken, the leaf shape was poor, and it was very easy to break, so it was not involved in the further exploration of the preservation time. Finally, the 4°C packaging group and the 4°C nitrogen group were selected to measure the hardness at 40 days. Figure 5 (c) is a comparison of the hardness of onion leaves under different temperatures and packaging conditions on the 40th day. The 4℃ packaging only group and the 4℃ nitrogen group still had no significant difference from ACK at 40 days. This result is consistent with the results in Examples 3.1 and 3.2.

[0056] Figure 6(a) Comparison of the brittleness of shallot leaves under different temperatures and packaging conditions on the 20th day. At -20℃, only the packaged group showed significant difference from the fresh shallot, while there was no significant difference between the other groups. Figure 6 (c) is a comparison of the crispness of shallots under different temperatures and packaging conditions on the 40th day. At 40 days, the crispness of the 4°C packaging group and the 4°C nitrogen group was significantly lower than that of fresh shallots, but there was no significant difference between the two groups.

[0057] 3.4 Effects of different temperatures and aeration conditions on the moisture content of postharvest cold onions

[0058] Water content is an important factor affecting the preservation of shallots. By controlling and monitoring the water content of shallots, its shelf life can be effectively extended and its quality and nutritional value can be maintained. The experimental method was determined according to GB 5009.3-2016, and the water content index was obtained and statistically analyzed. P < 0.05 was considered significant. Figure 7 As shown in (a), after 20 days of storage, the water content of the three groups of winter onions treated at 4°C was not significantly different from that of fresh winter onions. The water contents of the nitrogen packaging group and the ordinary packaging group were 89.95 ± 0.73% and 89.17 ± 2.14%, respectively. The nitrogen-filled group at -20°C was not significantly different from fresh winter onions, with a water content of 87.88 ± 0.24%. On the 20th day, the water content of the 4°C nitrogen packaging was slightly higher and closer to that of fresh winter onions. Figure 7 In (c), there was no significant difference between the two groups of treatments of shallots stored for 40 days, but there was a significant decrease compared with fresh shallots, which were 87.48 ± 0.80% and 87.82 ± 1.87%, respectively.

[0059] 3.5 Effects of different temperatures and aeration conditions on the postharvest preservation and flavor of shallots

[0060] Flavor index is an important index for judging the freshness of vegetables. Chives are a spicy vegetable with a special smell. As can be seen from the phenomenon in Example 1, when the appearance quality of chives deteriorates, the smell will gradually disappear. Therefore, it is necessary to detect the flavor of chives to evaluate the preservation effect of chives. Chive flavor index is measured by electronic nose and electronic tongue. The electronic nose measures the smell of chives, and the electronic tongue measures the taste of chives. According to the appearance evaluation results in Examples 3.1-3.2, the 4°C vacuum group has already produced color and taste changes in 20 days, so there is no need to participate in electronic nose and electronic tongue measurement.

[0061] Experimental method: Using PEN3.5 electronic nose, cut up an appropriate amount of sample and put it into the headspace bottle, cover it tightly, and balance the headspace for 30 minutes. Electronic tongue measurement: Mix 20 g sample with 40 mL deionized water, stir, stir for 30 minutes, and then filter. Collect 50 mL of the filtrate for E-tongue analysis.

[0062] Figure 8 The electronic nose data of onions with different treatments are shown in Figure 2. Figure 8 (a) is the radar chart of electronic nose data. It can be seen from the figure that the odor profiles of the different treatments of winter onions stored for 20 days have changed from fresh winter onions. The odor profiles of the three groups treated at -20℃ are similar, but they are quite different from the odor profile of fresh winter onions. The odor profiles of the 4℃ nitrogen group and the 4℃ packaging group are similar to those of fresh winter onions. Figure 8 (b) The principal component analysis diagram shows that the cumulative contribution rate of PC1 and PC2 is 83.6%, indicating that PCA can better reflect the multi-index information of each group. The onions treated with different treatments are clearly distinguished in the PCA diagram. The onions treated with -20℃ form a new group, and the 4℃ nitrogen group, the 4℃ packaging group and the fresh onion CK form a new group, indicating that the 4℃ nitrogen group and the 4℃ packaging group have no significant difference in flavor and are closer to fresh onions. Figure 8 (c) is the radar and PCA diagram of the electronic nose data of the 4℃ nitrogen group and the 4℃ packaging group on the 40th day. The odor profile of the scallions stored at 4℃ for 40 days and the fresh scallions has obvious changes. Figure 8 (d) The principal component analysis showed that the 4℃ ordinary packaging group was closer to fresh shallots. Fig. 9 (a) is the radar chart of electronic tongue data, which shows that the nitrogen packaging group and the ordinary packaging group treated at 4℃ have profiles close to those of fresh shallots, and the profiles of the three groups stored at -20℃ are basically the same. Fig. 9 (b) is the principal component analysis of the electronic tongue data. The cumulative contribution rate of PC1 and PC2 is 97.5%, indicating that PCA can better reflect the multi-index information of each group. Unlike the principal component analysis of the electronic nose, the fresh shallots are clearly distinguished from the other groups. The 4℃ nitrogen packaging group and the 4℃ ordinary packaging group formed a new group. Compared with the three groups treated at -20℃, the two groups at 4℃ are closer to the fresh shallot group. Fig. 9 (c) is the radar chart of the electronic tongue data at 40 days. The contours of the 4℃ nitrogen packaging group and the 4℃ ordinary packaging group are basically the same, and there is a slight difference with the contour of ACK. Fig. 9 (d) The principal component analysis showed that although the two treatments were significantly separated from ACK, the difference between the two groups was not significant. In summary, in terms of flavor analysis, it was found that the 20-day-stored winter onions had different degrees of difference from the fresh winter onions, and the 4℃ ordinary packaging group and the 4℃ nitrogen packaging group were more similar to the fresh winter onions in flavor.

[0063] Based on the experimental results of Examples 1-3, the storage conditions that can better store winter onions and extend the shelf life of winter onions are the 4°C nitrogen packaging group and the 4°C ordinary packaging group. The results of the two groups in various indicators are similar and close to the indicators of fresh winter onions.

[0064] Example 4: Verification and analysis of the preservation effect of cold onion of strain B (Yichun) under different temperature and aeration conditions

[0065] Put an appropriate amount of 30-35 g of shallot (variety B) into the packaging bag and repeat the same treatment method as above. The specific test plan is the same as Example 3. The color, texture, water content and flavor indexes of the differently treated shallots are measured, and a verification experiment is carried out to analyze whether the optimal preservation method is consistent with the preservation method of variety A shallots.

[0066] 4.1 Verification of the effects of different temperatures and aeration conditions on the postharvest preservation effect and chromaticity of winter onions

[0067] The specific experimental method is the same as that in Example 3.2. Fig.10 This is the color difference ∆E value diagram of the cold onion of strain B. Figure 4 (b) shows the onions stored under different treatments for 20 days. The results in the figure show that the color difference values ​​of the 4℃ ordinary packaging and 4℃ nitrogen packaging groups are significantly lower than those of the other groups, and there is no significant difference between the two groups. Figure 4 (d) is a comparison of the ∆E values ​​of the nitrogen-filled group and the packaging-only group stored at 4°C for 40 days. The color difference value of the nitrogen packaging group is slightly lower than that of the ordinary packaging group, but the difference between the two is not significant.

[0068] 4.2 Verification of the effects of different temperatures and aeration conditions on the postharvest preservation of onions, hardness and brittleness

[0069] The specific experimental method is the same as the determination method in Example 3.3, and the results are as follows Fig.11 As shown, Figure 5 (b) is a comparison chart of the hardness of shallots treated with different methods at 20 days. In the figure, the 4℃ vacuum group, 4℃ nitrogen group, 4℃ packaging group and -20℃ vacuum group have no significant difference in hardness compared with fresh shallots. The 4℃ nitrogen packaging group and 4℃ ordinary packaging group are closer to the hardness of BCK. Different from the results in Example 3.3, the vacuum group showed higher hardness in this experiment. Figure 5 (d) is a comparison chart of the hardness of the 4℃ nitrogen packaging group and the 4℃ ordinary packaging group at 40 days. There is no significant difference between the 4℃ ordinary packaging group and BCK.

[0070] Figure 6 (b) is a comparison of the brittleness of the scallions treated with different methods at 20 days. In the figure, the 4℃ vacuum packaging group, 4℃ nitrogen packaging group, 4℃ ordinary packaging group and -20℃ packaging group have no significant difference in brittleness from the fresh scallions. At 40 days, the brittleness of the scallions in the two treatment groups is significantly different from that of the fresh scallions, but the difference between the two groups is not significant, which is similar to the results in Example 3.3.

[0071] 4.3 Verification of the effects of different temperatures and aeration conditions on the moisture content of postharvest preservation of winter onions

[0072] The specific experimental method is the same as the determination method in Example 3.4. Figure 7 (b) is a comparison chart of the moisture content of shallots treated with different methods at 20 days. There is no significant difference in moisture content between the 4℃ vacuum group, 4℃ nitrogen packaging group, 4℃ ordinary packaging group and fresh shallots. The moisture content of the 4℃ nitrogen packaging group is slightly higher at 91.19±0.50%. At 40 days, there is a significant difference between the 4℃ nitrogen packaging group and the 4℃ ordinary packaging group and fresh shallots, but there is no significant difference between the two, which is similar to the results in Example 3.4.

[0073] 4.4 Verification of the effects of different temperatures and aeration conditions on the post-harvest preservation and flavor of winter onions

[0074] The specific experimental method is the same as the determination method in Example 3.5. Fig.10 (a) is the radar chart of electronic nose data of onions stored for 20 days under different treatments. The odor profiles of -20℃ vacuum packaging group, -20℃ ordinary packaging group and -20℃ nitrogen packaging group are basically the same. The odor profile of 4℃ ordinary packaging group is basically the same as BCK, followed by 4℃ nitrogen group. Fig.10 (b) Similar results were also shown in the PCA graph, with the cumulative contribution rate of PC1 and PC2 being 86.7%, indicating that PCA can better reflect the multi-index information of each group. BCK, 4℃ nitrogen group and 4℃ packaging group formed new groups in the PCA graph, indicating that the 4℃ nitrogen packaging group and 4℃ ordinary packaging group performed better in flavor, and the overall flavor at -20℃ became weaker. Fig.10 (c) is the radar chart of the electronic nose data of onions stored for 40 days under different treatments. The odor profiles of the 4℃ nitrogen packaging group and the 4℃ ordinary packaging group are basically the same, but there is a significant difference with the onion odor profile at the W2S sensor. Fig.10 (d) is the principal component analysis of different treatments of winter onion stored for 40 days. The cumulative contribution rate of PC1 and PC2 is 79.5%, indicating that PCA can better reflect the multi-index information of each group. The winter onion after 40 days of storage is clearly separated from the fresh winter onion, but there is no significant difference between the 4℃ nitrogen packaging group and the 4℃ ordinary packaging group.

[0075] Fig.11 (a) is the radar chart of electronic tongue data of different treatments of winter onions stored for 20 days. The contours of each group of treatments are different from those of fresh winter onions. Fig.11 (b) Results in the PCA graph show that there was no significant difference between the 4℃ nitrogen group and the 4℃ packaging group, and there was no significant difference between the groups at -20℃, but each group was significantly separated from the fresh shallot, indicating that BCK was significantly different from each group. At 40 days, the 4℃ ordinary packaging and 4℃ nitrogen packaging had lower sourness and richness, higher saltiness, and were significantly different from CK.

[0076] In summary, we selected strain B winter onion to verify the winter onion preservation method again. The results showed that compared with the fresh winter onion control, the winter onions preserved in the 4°C nitrogen group were closer to the fresh winter onions in terms of appearance, texture, water content, flavor and other indicators. Both strains maintained good preservation performance and extended the storage period of winter onions.

Claims

1. A preservation method for extending the storage period of Allium victorialis, characterized in that It does this by: (1) selecting fresh allium wilfordii leaves without mechanical damage, wilting, yellowing, or insect infestation, washing the allium wilfordii leaves twice, grading the allium wilfordii leaves, and air-drying them; (2) Put 30-35 g of onions with a leaf width of 5-8 cm into a packaging bag. Pay attention to the integrity of the onion leaves when bagging and try to avoid mechanical damage to the onions during bagging; (3) Nitrogen flushing packaging, vacuum packaging and ordinary packaging methods are used respectively. The specific process is as follows: Nitrogen filling packaging: slowly fill the packaged onions with nitrogen to expel the remaining air in the bag, seal it immediately after filling, and squeeze it gently without obvious deformation; Vacuum packaging method: use a vacuum sealer to extract the air from the bag and seal it directly; Common packaging method: Put the onions in the bag and seal it with a heat sealer, leaving a little air in the bag; (4) Place the packaged shallots in cartons and place them in a refrigerator (temperature range 2-6°C) and a freezer (-18--20°C); Control treatment: After washing, grading and drying the allium leaves, place them directly in a room temperature environment (24℃~26℃); (5) Take samples and take photos every 3 days to monitor their sensory quality; (6) Chromaticity determination of shallot: Onion samples from different treatment groups were randomly selected and tested using a colorimeter. Each group was measured three times, and the L*, a*, and b* values ​​were read. The L*, a*, and b* values ​​of fresh shallot were used as the control, recorded as L0, a0, and b0, and the color difference value ∆E was calculated. ∆E represents the size of the color difference. The color difference value was obtained and subjected to one-way analysis of variance. (7) Determination of hardness and brittleness of shallots: Onion samples from different treatment groups were randomly selected, and a texture analyzer with a P / 2 mm probe was used to perform a puncture test on the onion leaves to obtain the hardness and brittleness indexes; (8) Electronic nose measurement of onion odor: Using the PEN3.5 electronic nose, cut an appropriate amount of the sample into pieces and put them into a headspace bottle. Cover the bottle tightly and allow the headspace to equilibrate for 30 minutes. (9) Electronic tongue analysis of scallion flavor: 20 g scallion sample was mixed with 40 mL deionized water, crushed, stirred for 30 min, and then filtered. 50 mL of the filtrate was collected for E-tongue analysis.

2. The storage and preservation method according to claim 1, characterized in that: The onions are graded according to the width of their leaves. The grading standards are: Grade 1: width 5-8 cm, Grade 2: width 3-5 cm, Grade 3: width ≥8 cm. Grade 1 leaves are selected for subsequent operations.

3. The storage and preservation method according to claim 1, characterized in that: The packaging bag should be a nylon threaded vacuum bag with a size of 22*32 cm, and filled with an appropriate amount of shallots.

4. The storage and preservation method according to claim 1, characterized in that: The packaging method is heat sealing, and a sealing machine is used for sealing. The sealing time is 3-5 s. After sealing, squeeze and check for leaks.

5. The storage and preservation method according to claim 1, characterized in that: Adjust the temperature range of the refrigerator to 4±2℃, place the well-packaged shallot samples in cartons, protect them from light, and then store them in the refrigerator.

6. The storage and preservation method according to claim 1, characterized in that: The fresh shallots are those harvested 0 to 3 hours after harvest, and the above operations are all completed on the same day.

7. The storage and preservation method according to claim 1, characterized in that: Pay attention to the integrity of the onion leaves when bagging, and try to avoid mechanical damage to the onions during bagging.

8. The storage and preservation method according to claim 1, characterized in that: The results of the experiment to explore the shelf life of winter onions show that winter onions without any preservation treatment turned yellow on the third day, their smell weakened, and their quality showed a downward trend. On the sixth day, they had completely lost their commercial value. However, there was no obvious change in the packaged winter onions on the sixth day. This packaging can extend the shelf life of winter onions to a certain extent.

9. The storage and preservation method according to claim 1, characterized in that: The results of the color difference determination experiment showed that after 20 days of storage, the color difference values ​​of the 4℃ ordinary packaging group and the 4℃ nitrogen group were significantly different from those of the other treatment groups and were significantly lower than those of the other treatment groups. On the 40th day, the color difference values ​​of the 4℃ ordinary packaging group and the 4℃ nitrogen packaging group were still low, with ∆E values ​​between 4 and 6, and there were no significant differences (P<0.05).

10. The storage and preservation method according to claim 1, characterized in that: The results of the hardness and brittleness test showed that on the 20th day, there was no significant difference in the hardness and brittleness values ​​between 4℃ ordinary packaging, 4℃ nitrogen packaging and fresh shallots. On the 40th day, there was still no significant difference in the hardness values ​​between 4℃ ordinary packaging, 4℃ nitrogen packaging and fresh shallots, but the brittleness value was significantly reduced (P<0.05).

11. The storage and preservation method according to claim 1, characterized in that: The results of the moisture content determination experiment showed that after 20 days of storage, the moisture contents of the 4℃ nitrogen packaging group and the 4℃ ordinary packaging group were 89.95±0.73% and 89.17±2.14%, respectively, which were not significantly different from those of fresh shallots (P<0.05).

12. The storage and preservation method according to claim 1, characterized in that: The results of the electronic nose experiment on the smell of shallots showed that on the 20th day, principal component analysis showed that the 4℃ nitrogen packaging group and the 4℃ ordinary packaging group performed better in flavor and were closer to the flavor of fresh shallots.

13. The storage and preservation method according to claim 1, characterized in that: The results of the electronic tongue experiment on the taste of shallots showed that on the 20th day, principal component analysis showed that the 4℃ nitrogen packaging group and the 4℃ ordinary packaging group performed better in taste and were closer to the taste of the fresh shallot group.

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