Tomato preservation method

Abstract

To provide a method for preserving tomatoes for a long period by a simple method.SOLUTION: A tomato preservation method includes the steps of: washing a tomato fully ripened on a vine with hypochlorous acid water to obtain a hypochlorous acid water-washed tomato; washing the hypochlorous acid water-washed tomato with water to obtain a water-washed tomato; and preserving the water-washed tomato in nitrogen, and thereby even fully-ripened tomato can be eaten for 3 to 5 weeks like a fresh tomato without any change. Further, after about 3 to 4 weeks, the tomato has a higher sugar content and a lower acidity than those of the tomato fully ripened on the vine, and can be sold and eaten as a sweet tomato.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for preserving tomatoes, and more particularly to a preservation method that can produce sweet tomatoes with higher sugar content and sugar-acid balance even when the tomatoes are harvested after being fully ripened on the tree. [Background technology]

[0002] To preserve tomatoes, green tomatoes should be stored at 10℃~15℃ to ripen. This ripening process takes about 3~5 days, and they can be eaten fresh for about a week after that. If stored in the refrigerator, they can be preserved for about 10 days when ripe and red. They can also be preserved for about two months if frozen.

[0003] On the other hand, at a direct tomato sales point, consumers want to purchase red ripe tomatoes, so sellers try to sell ripe tomatoes at the point of sale.

[0004] This would allow tomatoes harvested while still green to be transported to a sales outlet for a period of ripening and then sold after they have ripened, making it possible to sell tomatoes up to about two weeks after harvest.

[0005] In addition, tomatoes that have been allowed to ripen on the tree are sweeter and more delicious, making them more valuable as a product. However, because there is no further ripening period, their shelf life is shorter.

[0006] Therefore, if the shelf life of tomatoes could be extended, there would be more time to adjust inventory between the time of arrival and the time of sale, which would be beneficial for producers and sellers. For this reason, methods of preserving tomatoes without losing their freshness or texture have been studied.

[0007] Patent Document 1 discloses a method for preserving fresh edible agricultural products which comprises initially placing the fresh edible agricultural products in a gaseous atmosphere containing 10-100% nitric oxide or argon or a mixture thereof and 0-50% oxygen, the remainder being an inert gas, if present, under a pressure of 0.5-3 x 10^5 Pa at a cooling temperature for a period of one hour or more.

[0008] Patent Document 2 also discloses a method for producing frozen vegetables, including a step S101 of washing vegetables, a step S103 of blanching the washed vegetables and setting the surface temperature to a range of 40°C to 90°C, and a step S105 of rapidly freezing the blanched vegetables from the freezing start temperature to a freezing end temperature at an average cooling rate of 0.9°C / min or more, using this surface temperature as the freezing start temperature. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 03-206873 [Patent Document 2] JP 2019-135973 A [Non-patent literature]

[0010] [Non-Patent Document 1] "Theory and Practice of Cleaning and Sterilization Using Sodium Hypochlorite" Satoshi Fukusaki, Cooking Food and Technology Vol,16 No,1 (2010) Summary of the Invention [Problem to be solved by the invention]

[0011] In Patent Document 1, detailed adjustments are required, such as first creating an oxygen-free atmosphere and then creating an oxygen-containing atmosphere, and it cannot be said that it is easy to implement. In addition, Patent Document 2 is basically a method for producing frozen vegetables, and does not disclose a method for long-term storage of unfrozen tomatoes. [Means for solving the problem]

[0012] The present invention is intended to solve the above problems and enables long-term storage of tomatoes in a simple manner. Specifically, the method for storing tomatoes according to the present invention comprises the following steps: A step of washing the tomatoes that have ripened on the tree with hypochlorous acid water to obtain hypochlorous acid water washed tomatoes; A step of washing the hypochlorous acid water-washed tomatoes with water to obtain water-washed tomatoes; The method further comprises a step of storing the water-washed tomatoes in nitrogen. Effect of the Invention

[0013] The method for preserving tomatoes according to the present invention is a simple method that involves washing tomatoes with hypochlorous acid water and sealing them with nitrogen, and can extend the storage period of tomatoes by several weeks. This makes it possible to suppress deterioration of tomatoes during transportation from harvest to sales.

[0014] Furthermore, the method for preserving tomatoes according to the present invention can improve the sugar-acid balance compared to tomatoes that are fully ripened on the vine, resulting in sweeter tomatoes. [Brief description of the drawings]

[0015] [Figure 1] 1 is a graph showing the time course of fructose in tomatoes subjected to a number of preservation methods including the tomato preservation method of the present invention. [Diagram 2] 1 is a graph showing the time course of glucose changes in tomatoes subjected to a number of preservation methods including the tomato preservation method of the present invention. [Diagram 3] 1 is a graph showing the change over time in the amount of citric acid in tomatoes subjected to a variety of preservation methods including the tomato preservation method of the present invention. [Figure 4] 1 is a graph showing the time course of changes in sugar and acid balance of tomatoes subjected to a variety of preservation methods including the tomato preservation method of the present invention. [Diagram 5] 1 is a graph showing the time course of changes in glutamic acid content in tomatoes subjected to a variety of preservation methods including the tomato preservation method of the present invention. [Figure 6]1 is a table showing the results of sensory tests on various tomatoes preserved by multiple methods, including the tomato preservation method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The tomato preservation method according to the present invention will be described below with reference to examples and drawings. Note that the following description illustrates one embodiment of the present invention and one example, and the present invention is not limited to the following description. The following description can be modified within the scope of the present invention. In addition, embodiments and examples obtained by appropriately combining the technical means disclosed in different embodiments and examples are also included in the technical scope of the present invention. In addition, all documents described in this specification are incorporated herein by reference. In this specification, when a numerical range is described as "A to B," the description intends "A or more and B or less."

[0017] The method for preserving tomatoes according to the present invention comprises the steps of: A step of washing the tomatoes that have ripened on the tree with hypochlorous acid water to obtain hypochlorous acid water washed tomatoes; A step of washing the hypochlorous acid water-washed tomatoes with water to obtain water-washed tomatoes; storing the water-washed tomatoes under nitrogen.

[0018] The tomato preservation method of the present invention is applicable to any type of tomato. However, it can be suitably used for medium to small tomatoes (cherry tomatoes). This is because medium to small tomatoes taste better when fully ripened on the tree than when harvested green and allowed to ripen further. Tomatoes that can be harvested in bunches are often fully ripened on the tree and can be suitably used. Examples of tomatoes that can be harvested in bunches include Kosuzu, Carol 7, Niagara Sweet, Rouge de Bordeaux, Jennalie, and Redley.

[0019] In addition, the method for preserving tomatoes according to the present invention is capable of increasing the flavor and sweetness of tomatoes that have ripened on the tree by preserving them. The stems can be left attached when washing with hypochlorous acid water.

[0020] It is desirable for the hypochlorous acid water to have a concentration of at least 10 ppm. It has also been confirmed that a concentration of around 100 ppm is sufficient, and that a concentration of 20 ppm to 40 ppm is sufficiently effective.

[0021] Washing with hypochlorous acid water can be done by soaking the tomatoes in the hypochlorous acid water without stirring them or wiping the surface of the tomatoes. Of course, stirring or scrubbing with a sponge, etc., can be done without scratching the surface of the tomatoes. The soaking time depends on the concentration of hypochlorous acid, but it should be between 30 seconds and 10 minutes.

[0022] Washing with hypochlorous acid water is thought to remove microorganisms attached to the skin and stem of tomatoes. Tomatoes washed with hypochlorous acid water are called hypochlorous acid washed tomatoes.

[0023] Next, the hypochlorous acid water tomatoes are washed with water. Although hypochlorous acid water is non-toxic and certified as edible, it is considered desirable not to leave it behind. The water is not particularly limited, and tap water can be used as long as it is drinkable. The hypochlorous acid water washed tomatoes are called water-washed tomatoes.

[0024] Next, the washed tomatoes are stored in nitrogen. Storing them in nitrogen reduces the respiration of the tomatoes. This operation causes an imbalance in the activity of the citric acid cycle, increasing the ratio of sugar content to glutamic acid, which is a tasty ingredient, resulting in tomatoes that taste better than when they are fully ripened on the vine.

[0025] In addition, the temperature may be lowered during this preservation process, because lowering the temperature can slow down biological activity itself. Examples will be described below. EXAMPLES

[0026] Cherry tomatoes that had ripened on the tree were divided into two groups: washed and unwashed. The washed group was immersed in 30 ppm hypochlorous acid water for one minute to obtain hypochlorous acid water-washed tomatoes. These hypochlorous acid water-washed tomatoes were then washed with running tap water for five minutes to obtain water-washed tomatoes.

[0027] The water-washed tomatoes were dried naturally at room temperature, and then divided into two groups: one with nitrogen sealed inside and one with air sealed inside. The nitrogen-sealed group was placed in a polyethylene bag, the inside of the bag was purged with nitrogen, and the opening was welded. The air-sealed group had air sealed inside and the opening welded.

[0028] The non-cleaned group was further divided into a nitrogen-filled group and an air-filled group. Each group was placed in a polyethylene bag, and the nitrogen-filled group had the bag purged with nitrogen and the inlet welded, while the air-filled group had air filled the bag and the inlet welded.

[0029] As described above, a group was formed in which the tomatoes were washed with hypochlorous acid water and nitrogen was sealed inside (hereafter simply referred to as "hyponitrous"); a group was washed with hypochlorous acid water and air was sealed inside (hereafter simply referred to as "hyponitrous air"); a group was not washed but nitrogen was sealed inside (hereafter simply referred to as "nitrogen"); and four groups were not washed but air was sealed inside (hereafter simply referred to as "air"). Each group contained 10 tomatoes. At least six bags were prepared for each group.

[0030] The above samples were stored in a cold room maintained at 4°C for 2, 3, 4, and 5 weeks. The day of sealing was designated as the zero-day sample. The samples after 2, 3, 4, and 5 weeks are called the 2-week sample, 3-week sample, 4-week sample, and 5-week sample, respectively.

[0031] Sample preparation for measurement Samples after each time period were prepared as follows to be used as measurement samples. (1) After the specified time had elapsed, the bags were taken out from the four groups, crushed in a food processor, and freeze-dried. These are called the dried samples. (2) The dried sample was further crushed into small pieces and 0.1 g was weighed out. (3) 10 mL of 80% ethanol solution was added and heated in a block heater at 80° C. for 10 minutes. (4) The mixture was centrifuged using a high-speed refrigerated centrifuge (4°C, 6000g, 10 min), and the supernatant was filtered. (5) The steps from (3) to (4) were repeated three times on the residue. (6) The obtained filtrate was concentrated to dryness under reduced pressure using a rotary evaporator and redissolved in 5 mL of milliQ. (7) The solution was filtered again through a 0.45 μm membrane filter to prepare the measurement solution.

[0032] A charged aerosol detector (CAD) was used to measure the sugar components. The column used was an Asahipak NH2P-50 4E (4.6 x 250 mm). The mobile phase was (A) water, (B) acetonitrile 75% B (0-10 min), 75-50% B (10-30 min). The flow rate was 1 mL / min, the column temperature was room temperature, and the sample injection volume was 20 μL.

[0033] In addition, a TSQ Endura was used for citrate / glutamate analysis (LC-ESI-MS / MS). The ion source was ESI (negative). The column used was a YMC Triart PFP (2.0×150 mm, 3 μm). The mobile phase was 0.5% formic acid, and the flow rate was 200 μL / min. The column temperature and vaporizer temperature were both 40°C. The sample injection volume was 5 μL.

[0034] The selected ions are m / z 148.1→84.1 at 14.6 eV for glutamic acid and m / z 190.9→85.1 at 16.7 eV for citric acid.

[0035] The results are shown in Figures 1 to 5. Please refer to Figures 1 and 2. Figure 1 is a graph showing the change over time in sugar content (fructose), and Figure 2 is a graph showing the change over time in sugar content (glucose). The level of sugar content can be said to be an indicator of sweetness. In both graphs, the horizontal axis shows the number of days elapsed, and the vertical axis shows the amount of sugar (μg / mL). It can be seen that both fructose and glucose tend to increase as the number of days elapsed increases. However, hyponitrous acid values ​​were highest after three weeks (21 days) for both fructose and glucose.

[0036] Figure 3 is a graph showing the change in citric acid content over time. The amount of citric acid is an index of sourness. The horizontal axis is the number of days that have passed, and the vertical axis is the amount of citric acid (μg / mL). The amount of citric acid generally tends to decrease with the number of days that have passed. At the third week (21 days after the start of the experiment), hyponitrous acid was at its lowest.

[0037] Figure 4 is a graph showing the change in sugar-acid balance over time. Sugar-acid balance is the ratio of "(fructose amount + glucose amount) / citric acid amount." This ratio is the ratio of sweetness to sourness, and it is thought that if this ratio is high enough, it will be possible to create a sweetness with just the right amount of sourness. In Figure 4, the horizontal axis is the number of days elapsed, and the vertical axis is the ratio (unitless). Sugar-acid balance also generally shows a tendency to increase with the number of days elapsed. At 3 weeks (21 days after the start of the experiment), the sugar-acid balance of hyponitrous acid reached its highest value. This is because sugar (fructose amount and glucose amount) reached its highest value (see Figures 1 and 2), while citric acid amount reached its lowest value (see Figure 3).

[0038] Figure 5 is a graph showing the change in glutamic acid content over time. Glutamic acid is known as an umami component. The horizontal axis shows the number of days that have passed, and the vertical axis shows the amount of glutamic acid (μg / mL). There was generally no change in glutamic acid up to the third week (21 days after the test), but from the fourth week (28 days after the test), the amount of glutamic acid showed an increasing trend in the samples washed with hypochlorous acid water, while the amount of glutamic acid showed a decreasing trend in the samples that were not washed with hypochlorous acid water. Furthermore, the amount of glutamic acid in the "hyponitrous acid" sample washed with hypochlorous acid water and then filled with nitrogen increased significantly from the fourth week (28 days after the test) to the fifth week (35 days after the test).

[0039] Considering the above results, the sugar concentration (both glucose and fructose: see Figures 1 and 2) was high and showed similar trends in the "nitrogen sealed" samples ("nitrogen" and "hyponitrous acid") until around the third week, regardless of the hypochlorous acid cleaning.

[0040] The amount of citric acid (see Figure 3) was low in the samples that had been "washed with hypochlorous acid" ("hyponitrous acid" and "hypochlorous air") until around the third week, regardless of whether the enclosed gas was nitrogen or air, while the samples that had not been "washed" ("air" and "nitrogen") showed high values ​​and similar trends, regardless of the enclosed gas.

[0041] As the storage period became longer (after the third week), the amount of glutamic acid (see Figure 4) tended to increase in the samples that had been "washed with hypochlorous acid water" ("hyponitrous acid" and "hypochlorous air"), regardless of whether the enclosed gas was air or nitrogen, and tended to decrease in the samples that had not been "washed" ("nitrogen" and "air").

[0042] Therefore, the "hyponitrous" sample had high sugar and glutamic acid concentrations and low citric acid concentrations, resulting in a tomato with a taste that is more appealing to many people.

[0043] The cause of this is not yet clear. For example, in glycolysis, the reaction from sugar to pyruvate can occur even without oxygen. However, in the "nitrogen-sealed" sample, the metabolism of pyruvate → acetyl CoA → citric acid → ... → oxaloacetate, which takes place under aerobic conditions in the citric acid cycle, did not proceed smoothly, leading to the accumulation of pyruvate, which is thought to have caused sugar to remain at a high level.

[0044] On the other hand, it has been reported that hypochlorous acid water, not hypochlorite ions but non-ionized molecular hypochlorous acid, easily penetrates cell walls and cell membranes (Non-Patent Document 1). It is possible that some of the hypochlorous acid molecules that were absorbed into the tomato epidermis oxidized the cytoplasm and affected the citric acid cycle.

[0045] From the above results, the sample washed with hypochlorous acid water had the highest sugar acid balance in the third week, and the amount of glutamic acid also remained at a high level. Therefore, we actually conducted a sensory test on these samples.

[0046] The participants were five people in total, two from Ichinen Holdings and three from Kinki University. The participants were not informed of the sample conditions, but they tasted four types of samples at each elapsed time, summarized their impressions, and gave each person a score. At the end of the sensory test of the samples in the fifth week, the scores up to that point were totaled and ranked. The results are shown in Figure 6.

[0047] 6, the vertical axis indicates the type of sample, and the horizontal axis indicates the number of days (in weeks) that have passed. The final rightmost column indicates the ranking of the overall evaluation.

[0048] On the "same day" (day zero), there was no sensory difference between the samples. After two to three weeks, the "air" and "nitrogen" samples started to taste less fresh and more like spoilage. On the other hand, the "hyponitrogen air" and "hypochlorine" samples showed no deterioration in taste even after two to three weeks, and the "hyponitrogen" sample was the sweetest of the four samples. This coincides with the fact that the "hyponitrogen" sample had the highest sugar-acid balance at the third week.

[0049] After five weeks, the "air" sample had almost no change in appearance, but tasted almost spoiled (described as "disgusting"). Meanwhile, the "nitrogen" sample had lost the crisp texture that is unique to tomatoes when first chewed (described as "soft") and had a weaker flavor. The "hyponitrogen air" sample retained the unique texture that is unique to tomatoes when first chewed, but had a weaker flavor. Meanwhile, the "hyponitrogen" sample was still perfectly tasty, with only a slightly stronger sour taste.

[0050] As a result, the overall ranking for the five-week period was determined to be in the following order: hyponitrous acid sample, hyponitrous air sample, nitrogen sample, and air sample.

[0051] As described above, by employing the method for preserving tomatoes according to the present invention, even after tomatoes have fully ripened on the vine, the sugar-acid balance and the amount of glutamic acid can be further increased through preservation, and the sellable period from harvest can be extended. [Industrial Applicability]

[0052] The method for preserving tomatoes according to the present invention can be suitably used for preserving tomatoes, particularly cherry tomatoes or tomatoes that can be harvested in bunches.

Claims

1. A step of washing the tomatoes that have ripened on the tree with hypochlorous acid water to obtain hypochlorous acid water washed tomatoes; A step of washing the hypochlorous acid water-washed tomatoes with water to obtain water-washed tomatoes; A method for preserving tomatoes, comprising a step of preserving the water-washed tomatoes in nitrogen.

2. 2. The method for preserving tomatoes according to claim 1, wherein the step of preserving in nitrogen is at a temperature between 6°C and 0°C.

3. 2. The method for preserving tomatoes according to claim 1, wherein the tomatoes are cherry tomatoes or tomatoes harvested in bunches.

4. 4. The method for preserving tomatoes according to claim 1, wherein the preservation step is for a period of from 2 weeks to 5 weeks.

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