Application of microbial metabolism compound in preservation of picked strawberries

Abstract

The invention relates to the technical field of microorganisms, and discloses an application of a microbial metabolism compound in preservation of harvested strawberries, the volatility of 2-methylbutyl acetate is utilized, the 2-methylbutyl acetate is used as a fumigant to carry out closed fumigation treatment on the strawberries, and then the strawberries are preserved. The 2-methylbutyl acetate is applied to the preservation of the picked strawberries for the first time, and the 2-methylbutyl acetate is proved to have a remarkable antibacterial effect, can effectively inhibit the growth of botrytis cinerea, and can effectively reduce the rotting rate of the strawberries, maintain the hardness of the strawberries, reduce the loss of nutritional ingredients and prolong the shelf life of the picked strawberries; and the fresh-keeping effect is good.

Description

Technical Field

[0001] The present invention relates to the field of microbial technology, and in particular to an application of a microbial metabolic compound in the post-harvest preservation of strawberries, specifically to a Bacillus jemiella W51 ( Paenibacillus jamilae ) is used in the post-harvest preservation of strawberries. Background Art

[0002] Strawberry is a fruit that is loved by the public. It has bright color, delicious taste and is rich in various nutrients, such as vitamin C and cellulose. However, strawberries are very prone to rot and deterioration after being picked. This is mainly because strawberry fruits are soft and juicy, and the skin lacks an effective protective structure. After picking, they have vigorous respiration, lose water quickly, and are also very susceptible to microbial infection. From a physiological point of view, gases such as ethylene produced by the respiratory metabolism of strawberries after picking will accelerate the ripening and aging process of the fruit. At the same time, its high water content causes water to evaporate, causing the fruit to shrink and shrunken, affecting its appearance and taste. During the post-harvest storage and transportation process, bacteria, molds and other microorganisms on the surface of strawberries will multiply rapidly under suitable temperature and humidity conditions, causing the fruit to mildew and rot.

[0003] Traditional strawberry preservation methods, such as low-temperature refrigeration, can slow down the deterioration of strawberries to a certain extent, but they have limitations. For example, low temperatures may cause chilling damage to strawberries, affecting their quality. Although controlled atmosphere preservation can adjust the gas composition in the storage environment, the equipment cost is high and the operation is relatively complicated. The use of chemical preservatives faces problems such as food safety and consumer acceptance. Therefore, the development of an efficient, safe and economical strawberry post-harvest preservation technology has important practical significance, which is also the technical background for the emergence of many patented strawberry post-harvest preservation technologies.

[0004] The compound 2-methylbutyl acetate is a Paenibacillus jamilae )Exocrine compounds produced by W51 bacterial liquid, colorless liquid, with fruity aroma, soluble in organic solvents such as alcohols and ethers, insoluble in water. It belongs to the food additives in GB1886.153-2015. It is a food additive commonly used as a flavoring ingredient in the food industry and has strong volatility. Volatile substances inhibit bacteria by destroying the cell membrane structure of microorganisms, inhibiting the activity of key metabolic enzymes, affecting DNA and protein synthesis, and thus hindering the normal growth of microorganisms. In order to reduce the economic losses caused by pathogenic bacteria in the transportation and storage of fruits and vegetables after harvest, researchers have actively explored the application of accessible and practical volatile organic compounds as natural preservatives in the post-harvest preservation of fruits and vegetables in recent years. Summary of the invention

[0005] Purpose of the invention: In view of the problems existing in the prior art, the present invention provides an application of a microbial metabolic compound in the post-harvest preservation of strawberries. The present invention uses a conventional food additive, 2-methylbutyl acetate, for the post-harvest preservation of strawberries. The compound is easy to obtain and can significantly improve the post-harvest preservation effect of strawberries.

[0006] Technical solution: The present invention provides an application of a microbial metabolic compound in the preservation of strawberries after harvest, which utilizes the volatility of the compound to preserve the strawberries, and the compound does not come into direct contact with the strawberries; the compound is 2-methylbutyl acetate, with a molecular formula of C7H 14 O2, CAS number: 624-41-9.

[0007] Furthermore, the 2-methylbutyl acetate is used to perform a closed fumigation treatment on strawberries, thereby preserving the strawberries after harvest.

[0008] Furthermore, the fumigation concentration of the 2-methylbutyl acetate is 20-25 μL / L.

[0009] Further, the specific steps are: S1. Pick fresh strawberries and pre-cool them with natural air; S2. Choose a fresh-keeping box with a drain compartment and disinfect it; S3. Evenly spread sterile absorbent paper under the disinfected fresh-keeping box interlayer in S2, and quantitatively inject 2-methylbutyl acetate on the absorbent paper; then place the strawberries in S1 on the fresh-keeping box interlayer and cover the fresh-keeping box tightly.

[0010] Furthermore, in S1, the specific conditions for precooling are: spreading the picked strawberries evenly and placing them in an environment with a temperature of 20°C for 6 hours to fully dissipate the field heat.

[0011] Furthermore, in S2, the specific steps of disinfection are: first disinfect the surface with 70-80% alcohol, and then irradiate with ultraviolet light for 25-35 minutes.

[0012] Beneficial effects: Compared with the prior art, the present invention has the following specific beneficial effects: The present invention utilizes the volatility of 2-methylbutyl acetate, uses 2-methylbutyl acetate as a fumigant to perform closed fumigation treatment on strawberries, and then preserves the strawberries. The present invention provides an application of a microbial metabolite compound in post-harvest preservation of strawberries, and the 2-methylbutyl acetate used has not yet been reported for application on strawberries. Treatment with 2-methylbutyl acetate can effectively reduce the decay rate of strawberries during post-harvest storage, thereby extending their shelf life. By measuring key quality indicators such as the decay rate, hardness, ascorbic acid content, soluble solids and total phenol content of the treated strawberries, the results show that the strawberries treated with 2-methylbutyl acetate have a significant preservation effect. At the same time, the treatment can effectively maintain the hardness, nutritional components and sensory quality of the fruit. The present invention applies 2-methylbutyl acetate to post-harvest preservation of strawberries for the first time, confirming that 2-methylbutyl acetate has a significant antibacterial effect and can effectively inhibit the growth of Botrytis cinerea. At the same time, 2-methylbutyl acetate is easy to obtain, has the advantages of significant preservation effect, high safety, green environmental protection and simple operation. And it is safe and reliable to use within the specified range. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 The inhibitory effect of 2-methylbutyl acetate at different concentrations on Botrytis cinerea. Figure 2 The effect of different concentrations of 2-methylbutyl acetate on the colony diameter and inhibition rate of Botrytis cinerea; Figure 3 The appearance changes of strawberries in different treatment groups during storage; Figure 4 The effect of 2-methylbutyl acetate treatment on the decay rate and weight loss rate of strawberries; Figure 5 This is the effect of 2-methylbutyl acetate treatment on relevant quality indicators of strawberry. DETAILED DESCRIPTION

[0014] The present invention is described in detail below in conjunction with the embodiments.

[0015] In the present invention, the 2-methylbutyl acetate used was purchased from Shanghai MacLean Biochemical Technology Co., Ltd., project number: M813666, CAS: 624-41-9, specification: 99%.

[0016] The preparation method of the potato dextrose agar (PDA) medium used is as follows: 200 g of peeled potatoes are cut into small pieces, added to water and boiled for 20-30 min, then filtered with double-layer gauze, the filtrate is taken and water is added to 1000 mL. 20 g of glucose and 15 g of agar are added and stirred until completely dissolved. The pH is adjusted to 6.5 with hydrochloric acid or sodium hydroxide. The mixture is packaged and sterilized for later use.

[0017] The activation method of Botrytis cinerea used is as follows: the Botrytis cinerea strain provided by the laboratory was activated on PDA medium, cultured at a constant temperature of 25 ºC for 72 h, and then transferred to a new, sterile PDA plate for culture and standby use.

[0018] Embodiment 1: Antibacterial effect of 2-methylbutyl acetate on Botrytis cinerea: The culture dishes were buckled. Strawberry gray mold is mainly a fungal disease caused by Botrytis cinerea. Under the clean bench, the activated Botrytis cinerea plate was punched out with a puncher to produce a cake of uniform diameter, and the cake was inoculated in the center of a new PDA medium plate; the pre-sterilized and dried filter paper was placed in the center of the culture dish cover, and 2-methylbutyl acetate with treatment concentrations of 24, 48, 72, 96, and 120 μL / L was injected into the filter paper with a micro-syringe. After the culture dishes were buckled immediately, the edges of the culture dishes were sealed with Parafilm sealing film to prevent the volatilization of the compounds. The control group was inoculated with only Botrytis cinerea cake, and each treatment was repeated 3 times. The treated culture dishes were inverted in a 25 ℃ constant temperature incubator for 3 days. The colony diameter was determined by the cross method on the third day, and the inhibition rate was calculated. The calculation formula for the inhibition rate is as follows: Inhibition rate (%) = (colony diameter of control group - colony diameter of treatment group) / colony diameter of control group × 100.

[0019] The results are as follows Figure 1 and Figure 2 As shown in the figure, the colony diameter after 2-methylbutyl acetate treatment was significantly smaller than that of the control group. With the increase of the concentration, the colony diameter decreased significantly. On the third day, there was a significant positive correlation between the treatment concentration of 2-methylbutyl acetate and the inhibition rate. When the initial concentration of 2-methylbutyl acetate was 24 μL / L, the inhibition rate was 3.62%, which was at a low level. As the concentration gradually increased to 48 μL / L and 72 μL / L, the inhibition rate increased relatively slowly. When the concentration of 2-methylbutyl acetate increased to 120 μL / L, the inhibition rate reached 63.52%. It can be seen that 2-methylbutyl acetate can significantly inhibit the growth of strawberry gray mold hyphae without direct contact with the hyphae through its volatile characteristics, indicating its potential application value in the antibacterial mechanism of volatile compounds.

[0020] Embodiment 2: Effect of 2-methylbutyl acetate treatment on postharvest strawberries: Fresh strawberries were picked from Huai'an Chaimihe Agricultural Science and Technology Co., Ltd. and transported back to the laboratory on the same day. Fruits with no lesions, no mechanical damage, and basically the same size, color, and maturity were selected. The picked strawberries were evenly spread on a table covered with newspapers in advance and placed at a temperature of 20 ℃ for 6 hours to fully dissipate the field heat. They were treated with 2-methylbutyl acetate on the same day. A polypropylene fresh-keeping box with a drainage layer was taken, and the surface was first disinfected with 75% alcohol. After irradiation with ultraviolet light for 30 minutes, sterile absorbent paper was evenly spread on the bottom as a carrier of 2-methylbutyl acetate. 2-methylbutyl acetate with a fumigation concentration of 24 μL / L was injected into the absorbent paper with a pipette. The polypropylene fresh-keeping box without any treatment was used as the control group. The selected strawberries were quickly placed on the top of the fresh-keeping box compartment and the fresh-keeping box lid was tightly closed. The fresh-keeping box containing strawberries was stored at 25±1 ℃ for 4 days. The rot rate and weight loss rate of the strawberries were counted on the 2nd, 3rd, and 4th days respectively. Each treatment group contained 80 fruits and was repeated three times.

[0021] Rot rate (%) = ∑ (rot level × number of fruits at that level) / (highest rot level × total number of fruits) × 100 Rot level: Level 0: no decay, no wrinkling on the surface; Level 1: rot area <25%; Level 2: rot area 25%-50%; Level 3: rot area 50%-75%; Level 4: rot area >75%.

[0022] Weight loss rate (%) = (original weight of strawberry - weight of strawberry when weighed) / original weight of strawberry × 100 The results are as follows Figure 3 As shown in the figure: Appearance change is one of the most important and intuitive indicators to measure the quality change of fruits during storage. In this study, mycelial growth was observed on the second day of storage in the control group of strawberry fruits, and on the fourth day, the surface of the strawberry fruits showed signs of corruption and deterioration. In contrast, after treatment with 2-methylbutyl acetate at a concentration of 24 μL / L, no obvious signs of microbial infection were observed in the strawberry fruits in the first three days of storage, and only a small amount of decay occurred on the fourth day. This result shows that 2-methylbutyl acetate treatment can significantly delay the microbial infection process of strawberry fruits and prolong their storage period, providing an effective technical means for the preservation of strawberries after harvest.

[0023] like Figure 4As shown in the figure: On the 3rd and 4th days of strawberry storage, the rot rate of strawberry fruits treated with 2-methylbutyl acetate was 46.19% and 60.17%, which was significantly lower than 61.67% and 80.21% of the control group. This result shows that 2-methylbutyl acetate treatment can significantly reduce the rot rate of strawberry fruits during storage and delay the occurrence of postharvest diseases. However, compared with the control group, the weight loss rate of strawberry fruits treated with 2-methylbutyl acetate increased during the entire storage period. This may be related to the volatility of 2-methylbutyl acetate, which enhances fruit transpiration and water loss. Moderate water loss helps to reduce the surface humidity of the fruit, thereby inhibiting the growth of microorganisms.

[0024] Embodiment 3: Effects of 2-methylbutyl acetate treatment on relevant quality indicators of postharvest strawberries: Hardness, soluble solids content and ascorbic acid content are important indicators for directly measuring fruit maturity and storage quality. Therefore, the quality indicators of experimental strawberries were measured on the 0th, 2nd, 3rd and 4th days of storage. The hardness of strawberries was measured by GY-3 pointer-type fruit hardness tester; the soluble solids content of strawberries was measured by portable sugar meter; the ascorbic acid content was measured by iodine titration; the total phenol content was measured by Flin-Ciocalteu method with gallic acid as standard and slightly modified. 0.25 g of frozen strawberry sample was ground into pulp with a small amount of anhydrous ethanol solution under ice bath conditions and transferred to a 25 ml volumetric flask. Rinse the mortar with anhydrous ethanol, transfer it to the volumetric flask, dilute to the mark, mix well, extract at 4 ℃ in the dark for 20 min, shake several times during the period, and centrifuge at 8000 rpm, 4 ℃ for 20 min. Take 0.4 ml of strawberry sample supernatant, 2 ml of distilled water, 0.4 ml of Folin phenol reagent, shake well and let stand for 3 min, then add 1.2 ml of sodium carbonate solution, keep away from light for 40 min, and measure the absorbance at 765 nm. Repeat the experiment three times.

[0025] The results are as follows Figure 5 As shown in the figure: On the third day of storage, the hardness of strawberry fruits treated with 2-methylbutyl acetate was 2.9 times that of the control group, which was much higher than that of the control group. On the fourth day of storage, the hardness of the treated group was 1.97 kg / cm 2 The control group had a large area of ​​decay and a hardness of only 0.57 kg / cm 2. On the 2nd, 3rd and 4th days of storage, the soluble solids of the strawberries in the treatment group were 1.46 times, 1.53 times and 1.58 times that of the control group, respectively, and the total phenolic content of the strawberries in the treatment group was 1.49 times, 1.46 times and 1.21 times that of the control group, respectively. On the 2nd day of storage, the ascorbic acid content of the treatment group was 14.78 mg / 100g, while that of the control group was only 11.20 mg / 100g. On the 3rd and 4th days of storage, the ascorbic acid content of the treatment group was 1.43 times and 1.25 times that of the control group, respectively. The above results show that the treatment with 2-methylbutyl acetate at a concentration of 24 μL / L can significantly increase the firmness, soluble solids, total phenolic content and ascorbic acid content of strawberries. Compared with the control group, the treatment with 2-methylbutyl acetate has a good effect in delaying the deterioration of postharvest quality of strawberries and maintaining the nutritional value of fruits.

[0026] In summary, the present invention relates to the application of a microbial metabolite compound, 2-methylbutyl acetate, in the preservation of strawberries, and provides a novel and effective strawberry post-harvest preservation technology. As a food additive, 2-methylbutyl acetate has been used for the first time in the field of post-harvest preservation of strawberries, with significant effects. The experimental results show that treating strawberries with 2-methylbutyl acetate at a treatment concentration of 24 μL / L can effectively inhibit the decay of strawberries and maintain their quality. During storage, the hardness, soluble solids, total phenol content and ascorbic acid content of the strawberries in the treatment group were significantly higher than those in the control group, indicating that 2-methylbutyl acetate treatment can effectively delay the deterioration of the quality of strawberries after harvest and extend the shelf life.

[0027] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. An application of a microbial metabolic compound in post-harvest preservation of strawberries, characterized in that: The compound does not come into direct contact with the strawberries when preserving them after harvest, and its volatility is used to preserve the strawberries after harvest; the compound is 2-methylbutyl acetate, with a molecular formula of C7H 14 O2, CAS number: 624-41-9.

2. The use of the microbial metabolite compound according to claim 1 in preserving strawberries after harvest, characterized in that: The 2-methylbutyl acetate is used to perform a closed fumigation treatment on strawberries, thereby preserving the strawberries after harvest.

3. The use of the microbial metabolite compound according to claim 2 in post-harvest strawberry preservation, characterized in that: The fumigation concentration of the 2-methylbutyl acetate is 20-25 μL / L.

4. The use of the microbial metabolite compound according to any one of claims 1 to 3 in the post-harvest preservation of strawberries, characterized in that: The specific steps are: S1. Pick fresh strawberries and pre-cool them with natural air; S2. Choose a fresh-keeping box with a drain compartment and disinfect it; S3. Evenly spread sterile absorbent paper under the disinfected fresh-keeping box interlayer in S2, and quantitatively inject 2-methylbutyl acetate on the absorbent paper; then place the strawberries in S1 on the fresh-keeping box interlayer and cover the fresh-keeping box tightly.

5. The use of the microbial metabolite compound according to claim 4 in the post-harvest preservation of strawberries, characterized in that: In S1, the specific conditions of the precooling are: spreading the picked strawberries evenly and placing them in an environment with a temperature of 20°C for 6 hours to fully dissipate the field heat.

6. The use of the microbial metabolite compound according to claim 4 in the post-harvest preservation of strawberries, characterized in that: In S2, the specific steps of disinfection are: first disinfect the surface with 70-80% alcohol, and then irradiate with ultraviolet light for 25-35 minutes.

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