Freeze-thaw resistance-imparting agent for fruits and vegetables

Abstract

The present invention addresses the problem of providing a novel means for producing frozen fruits and vegetables that are similar in texture to fresh fruits and vegetables even after the fruits and vegetables have been frozen and thawed, and can be tastily consumed. Said problem is solved by providing: a freeze-thaw resistance-imparting agent for fruits and vegetables comprising pullulan; and frozen vegetables and fruits that comprise pullulan. In order to solve this problem, the present invention also provides a method for producing frozen vegetables and fruits, the method comprising: a step for immersing vegetables and fruits in an immersion liquid comprising pullulan; and a step for freezing the fruits and vegetables after removing the fruits and vegetables from the immersion liquid. According to the freeze–thaw resistance-imparting agent, the frozen fruits and vegetables, and / or the production method according to one aspect of the present invention, it is possible to obtain frozen fruits and vegetables which are similar in texture to fresh fruits and vegetables before freezing, and which can be tastily consumed.

Description

Cold-thaw resistance enhancer for fresh produce

[0001] The present disclosure relates to a cold-thaw resistance imparting agent for fruits and vegetables.

[0002] In recent years, the market for frozen produce, which is obtained by freezing fruits, vegetables, and other fresh produce, has been expanding. Frozen produce is less likely to spoil, can be supplied even off-season, regardless of the season, and retains its nutritional value better than non-frozen produce. Furthermore, frozen produce has the advantage of being less damaged during transportation, allowing for rough transportation.

[0003] On the other hand, the texture of fresh produce is easily damaged during the manufacturing process of frozen produce, and it is extremely difficult to obtain frozen produce that retains the same texture as before freezing, even after thawing. In particular, it is known that the crystallization of water in fresh produce and the growth of ice crystals during the freezing and thawing processes significantly damage the texture of fresh produce. When ice crystals form and grow in fresh produce, the ice crystals destroy the tissue of the fresh produce, and when thawed, water leaks out from the tissue, significantly reducing the texture of the fresh produce. It is also known that the concentration during the freezing process and the temperature increase during the thawing process promote enzymatic reactions, damaging the color and flavor of the fresh produce.

[0004] Blanching is known as a method for avoiding such problems. Blanching is a process in which vegetables are heated with hot water or steam before being frozen. Blanching softens the vegetable tissue, thereby preventing tissue destruction by ice crystals and helping to maintain the texture of the vegetables. Furthermore, blanching inactivates the enzymes contained in the vegetables, thereby preventing changes in color and flavor over time due to the action of the enzymes. Most frozen vegetables currently on the market are produced through blanching.

[0005] However, as can be seen from the fact that the blanching process includes a heat treatment step, it is difficult to maintain the texture of the raw vegetables before freezing in frozen vegetables produced through the blanching process. Therefore, frozen vegetables produced through the blanching process are basically warm vegetables for cooking with heat, such as simmered or stir-fried dishes, and there are no known frozen vegetables for eating raw without cooking with heat, such as for salads. Furthermore, compared to vegetables, fruits are more likely to lose their aroma and texture through the blanching process, making it even more difficult to apply the blanching process to them. Most frozen fruits currently on the market are limited to those intended for cooking with heat, such as for jams or baked goods, or those intended for eating without worrying about texture, such as for smoothies.

[0006] Therefore, rapid freezing has attracted attention as a freezing technique that aims to suppress the growth of ice crystals during the freezing process of fresh produce and improve the quality of frozen produce. Rapid freezing is a freezing technique that suppresses the formation and growth of ice crystals by rapidly passing through the maximum ice crystal formation temperature range (-1°C to -5°C), known as the temperature range where ice crystals are likely to form. Methods such as air blast freezing, in which extremely cold air is blown onto an object to freeze it, and brine freezing, in which an object is immersed in cryogenically cooled brine to freeze it, are known and are used in the production of various frozen products. However, even with rapid freezing, it is extremely difficult to maintain the original texture of raw vegetables and fruits. This is demonstrated, for example, in the experimental examples described below.

[0007] There is a strong demand for frozen fruits and vegetables that have a texture similar to that of fresh vegetables and fruits even after thawing and that can be eaten deliciously, and various methods for producing frozen fruits and vegetables have been proposed. For example, Patent Document 1 discloses frozen vegetables that have been subjected to a predetermined dry heat treatment before freezing, and that have a drip rate and a bulk density fluctuation rate within a predetermined range when thawed naturally, and that the frozen vegetables have excellent volume, reduced dripping, are not watery, and exhibit a firm texture.

[0008] Furthermore, Patent Document 2 discloses a method for producing frozen fruits or vegetables, which includes a step of rapidly freezing the fruits or vegetables and then freeze-drying them to remove 1 to 10% of the water content. It is said that this method makes it possible to produce frozen fruits and vegetables that can be stored frozen for long periods of time while maintaining a texture close to that of fresh fruit.

[0009] On the other hand, pullulan is a water-soluble polysaccharide produced by a microorganism belonging to Aureobasidium pullulans, a type of fungus, and is known to be used, for example, as a coating material, an edible film, a binder, etc. (For example, Patent Documents 3, 4, and 5.) However, to the best of the inventors' knowledge, nothing is known about the effect of pullulan on the texture of frozen fruits and vegetables.

[0010] International Publication No. 2018 / 159585 Japanese Patent Application Laid-Open No. 2021-158964 International Publication No. 2011 / 158936 International Publication No. 2018 / 212118 Japanese Patent Application Laid-Open No. 2019-115269

[0011] As described above, there is a strong demand for a method for producing frozen fruits and vegetables that have a texture similar to that of fresh vegetables and fruits even after thawing, but the means for achieving this are limited. Furthermore, the methods described in the above patent documents are complicated, including a drying step that requires strict control, and place a heavy burden on the production process. It would be extremely useful if there was a means for providing frozen fruits and vegetables with a more preferable texture more easily. The present invention has been made in view of the above-mentioned problems with the prior art, and in one aspect, it is an object of the present invention to provide a new means for producing frozen fruits and vegetables that have a texture similar to that of fresh fruits and vegetables before freezing even after thawing, and that can be eaten deliciously.

[0012] In the course of extensive research efforts to solve the above problems, the present inventors surprisingly discovered that frozen fruits and vegetables prepared by immersing the fruits and vegetables in an immersion solution containing pullulan and then freezing the fruits and vegetables have a desirable texture even after thawing that is closer to the texture of raw fruits and vegetables.

[0013] That is, in one aspect, the present invention solves the above-mentioned problems by providing a pullulan-containing agent for imparting cold-thaw resistance to fruits and vegetables.

[0014] In another aspect, the present invention solves the above-mentioned problems by providing a method for imparting cold-thawing resistance to fresh produce, which method comprises the step of immersing fresh produce in an immersion liquid containing pullulan.

[0015] In another aspect, the present invention solves the above-mentioned problems by providing a method for producing frozen fruits and vegetables, the method comprising the steps of immersing fruits and vegetables in an immersion liquid containing pullulan, and freezing the fruits and vegetables after removing them from the immersion liquid.

[0016] In another aspect, the present invention solves the above-mentioned problems by providing frozen fruits and vegetables containing pullulan.

[0017] According to the present invention, frozen fruits and vegetables can be provided that, even after thawing, have a texture similar to that of the raw fruits and vegetables before freezing.

[0018]

[0033] Figure 1 shows the breaking loads of cut apples stored in a refrigerator (Control 1-1), cut apples cold-thawed without immersion in an immersion solution (Comparative Example 1-1), cut apples cold-thawed after immersion in an immersion solution not containing pullulan (Comparative Example 1-2), and cut apples cold-thawed after immersion in an immersion solution containing pullulan (Example 1-1). Figure 2 shows the breaking loads of cut apples cold-thawed after immersion in an immersion solution containing 0.3% by mass of pullulan (Example 2-1), and cut apples cold-thawed after immersion in an immersion solution containing 1.0% by mass of pullulan (Example 2-2). Figure 3 shows the breaking loads of cut apples cold-thawed after immersion in an immersion solution containing calcium lactate (Comparative Example 3-1), and cut apples cold-thawed after immersion in an immersion solution containing calcium lactate and pullulan (Example 3-1).

[0033] Figure 1 shows the breaking load of cut apples (Examples 4-1 to 4-5) that were immersed in an immersion solution containing 0% to 1.0% calcium lactate in addition to pullulan and then cold-thawed.

[0034] Figure 1 shows representative micrographs showing the tissue state of sections obtained from refrigerated cut apples (Control 1-1), cut apples that were immersed in an immersion solution containing no pullulan and then cold-thawed (Comparative Example 5-1), cut apples that were immersed in an immersion solution containing pullulan and then cold-thawed (Example 5-1), and cut apples that were immersed in an immersion solution containing pullulan and calcium lactate and then cold-thawed (Example 5-2).

[0035] Figure 1 shows the breaking load of cut apples (Comparative Examples 6-2 to 6-4) that were immersed in an immersion solution containing carboxymethylcellulose instead of pullulan and then cold-thawed.

[0036] Figure 1 shows chromatograms obtained by ion-exchange chromatography of cut apples (Example 7-2) that were immersed in an immersion solution containing 0.5% pullulan and then cold-thawed, either without pullulanase treatment or after pullulanase treatment.

[0019] <Agent for Imparting Cold-Thawing Resistance> In one aspect, the present invention provides an agent for imparting cold-thawing resistance to fruits and vegetables, which contains pullulan.

[0020] As used herein, "cold-thaw resistance" refers to the property of maintaining the quality of fresh produce before freezing after the fresh produce has been frozen and thawed. "Imparting" cold-thaw resistance means imparting cold-thaw resistance and / or enhancing cold-thaw resistance.

[0021] The quality of fruits and vegetables that can be maintained by the cold-thaw resistance imparted by the cold-thaw resistance imparting agent according to one aspect of the present invention can preferably be the texture of the fruits and vegetables. The texture of the fruits and vegetables can preferably be the texture of raw fruits and vegetables, and more preferably the texture of raw fruits and vegetables that have not been cooked, salted (salted), sugared (sugared), or the like. Such raw fruit and vegetable textures include the crisp, crunchy, or crisp texture of fresh, raw fruits and vegetables before freezing. Typically, when fruits and vegetables are subjected to a cold-thawing process, the water contained in the fruits and vegetables crystallizes and the resulting ice crystals grow, destroying the fruit and vegetable tissue and causing excessive water leakage during thawing, etc. As a result, the frozen fruits and vegetables after thawing appear limp and have a softer texture than the fruits and vegetables before freezing. In contrast, as shown in the experimental examples described below, the cold-thaw resistance imparting agent according to one aspect of the present invention makes it possible to prepare frozen fruits and vegetables that have a desirable texture similar to that of fresh fruits and vegetables before freezing, even after thawing.

[0022] The texture of fruits and vegetables can be evaluated by any suitable method, for example, using a creep meter, as shown in the experimental examples described below. Specifically, a creep meter equipped with a plunger of an appropriate shape is used to apply a load to the fruits and vegetables to be evaluated, and the load at which the fruits and vegetables break (i.e., the breaking load) is evaluated. However, the method for evaluating the texture of fruits and vegetables is not limited to the above method. For example, the texture may be evaluated by sensory evaluation by trained panelists.

[0023] Meanwhile, in this specification, "frozen fruits and vegetables" means fruits and vegetables in a frozen state, and unless otherwise specified, can include both those that are to be eaten as is after thawing and those that are to be cooked and eaten after thawing. As shown in the experimental examples described below, frozen fruits and vegetables obtained using the cold-thawing resistance imparting agent according to one aspect of the present invention have a desirable texture similar to that of raw fruits and vegetables even when eaten raw after thawing. Therefore, the cold-thawing resistance imparting agent according to one aspect of the present invention can be particularly suitably used for producing frozen fruits and vegetables that are to be eaten as is after thawing. Frozen fruits and vegetables that are to be eaten as is after thawing can include, for example, frozen fruits and vegetables for salads and frozen fruits and vegetables for condiments.

[0024] As used herein, the term "fruit and vegetables" includes both vegetables and fruits. Vegetables may be root vegetables, leafy vegetables, fruit vegetables, or spicy vegetables. Examples of root vegetables include, but are not limited to, turnips, burdock, taro, sweet potatoes, potatoes, radishes, carrots, beets, mountain yams, Chinese yams, and lotus roots. Examples of leafy vegetables include, but are not limited to, asparagus, cauliflower, Japanese mustard spinach, chrysanthemums, celery, onions, bok choy, Chinese cabbage, spinach, chives, garlic, garlic sprouts, leeks, butterbur, broccoli, mizuna, mitsuba, and lettuce. Examples of fruit vegetables include, but are not limited to, edamame, pumpkin, cucumber, green peas, snow peas, broad beans, corn, tomatoes, eggplant, paprika, bell peppers, green beans, etc. Examples of spicy vegetables include, but are not limited to, ginger.

[0025] Meanwhile, there is no particular limitation on the type of fruit for which the cold-thaw resistance imparting agent according to one aspect of the present invention can be used, and examples include, but are not limited to, figs, oranges, persimmons, kiwi, grapefruit, cherries, plums, pears, pineapples, loquats, grapes, mandarin oranges, peaches, apples, pears, etc. In the present specification, the term "fruit" also includes fruit-like vegetables such as strawberries, watermelons, and melons, unless otherwise specified.

[0026] The fruits and vegetables for which the cold-thaw resistance imparting agent according to one aspect of the present invention can be used may be cut into appropriate sizes. There are no particular limitations on the cutting method, and the cutting method may be, for example, wedges, thin slices, round slices, cubes, thin strips, strips, or irregular cuts.

[0027] On the other hand, the "pullulan" contained in the cold-thaw resistance imparting agent according to one aspect of the present invention is a water-soluble polysaccharide having a structure in which a basic unit is a maltotriose structure in which three glucose molecules are linked together via α-1,4 bonds, and in which these basic units are linked together via α-1,6 bonds, as represented by the following formula (1):

[0028]

[0029] Pullulan is typically produced by culturing a microorganism capable of producing pullulan in a medium containing a carbon source such as sucrose, glucose, maltose, etc., and isolating and purifying pullulan from the resulting culture. Aureobasidium pullulans, a type of filamentous fungus, is known as a microorganism capable of producing pullulan, and a method for producing pullulan using Aureobasidium pullulans is described, for example, in International Publication No. 2011 / 158936.

[0030] Although there are no particular limitations on the average molecular weight of pullulan that can be used in the cold-thaw resistance imparting agent according to one aspect of the present invention, the average molecular weight may be, for example, 5,000 to 500,000 daltons, more preferably 50,000 to 400,000 daltons. In this specification, when a numerical range is indicated using "to" as "A to B," etc., this means a numerical range that includes the upper limit (B) and the lower limit (A), unless otherwise specified.

[0031] Although there are no particular limitations on the origin or production method of the pullulan contained in the cold-thaw resistance imparting agent according to one aspect of the present invention, commercially available pullulan can be suitably used from the viewpoints of availability and quality. As commercially available pullulan, for example, food additive-grade pullulan (trade name "Pullulan") manufactured and sold by Nagase Vita Co., Ltd. can be suitably used, but is not limited thereto.

[0032] The content of pullulan in the cold-thawing resistance imparting agent according to one aspect of the present invention is not particularly limited, but may be, for example, 0.1 to 100% by mass, preferably 0.2 to 50% by mass, more preferably 0.3 to 40% by mass, and even more preferably 0.4 to 35% by mass, based on the total solids content of the cold-thawing resistance imparting agent. As described below, the cold-thawing resistance imparting agent according to one aspect of the present invention typically imparts cold-thawing resistance to fresh produce by immersing the fresh produce in an immersion solution containing the cold-thawing resistance imparting agent. A suitable content of pullulan in the immersion solution is as described below. The content of pullulan in the cold-thawing resistance imparting agent according to one aspect of the present invention can be appropriately adjusted so that when the immersion solution for immersing fresh produce is prepared by dissolving or diluting the cold-thawing resistance imparting agent in an appropriate solvent, the content of pullulan in the immersion solution falls within the specified range described below. However, taking into consideration the relationship with other components that may be contained in the cold-thawing resistance imparting agent, the pullulan content is preferably adjusted to the above-mentioned content.

[0033] In a preferred embodiment, the cold-thawing resistance imparting agent according to one aspect of the present invention may further contain a sugar. The type of sugar that may be contained in the cold-thawing resistance imparting agent according to one aspect of the present invention is not particularly limited, and may be, for example, a monosaccharide such as galactose, glucose, or fructose; a disaccharide such as sucrose, trehalose, maltose, or lactose; or a sugar alcohol such as sorbitol, mannitol, or maltitol, more preferably glucose, fructose, sucrose, sorbitol, trehalose, or maltose. The sugar that may be contained in the cold-thawing resistance imparting agent according to one aspect of the present invention may be a mixture containing one or more of the above sugars, and such a mixture may be, for example, starch syrup or reduced starch syrup, but is not limited to these.

[0034] The sugar content of the cold-thaw resistance imparting agent according to one aspect of the present invention is not particularly limited, but may be, for example, 1 to 99% by mass, preferably 5 to 98% by mass, more preferably 10 to 97% by mass, and even more preferably 25 to 95% by mass, based on the total solids of the cold-thaw resistance imparting agent. To reiterate, the cold-thaw resistance imparting agent according to one aspect of the present invention typically imparts cold-thaw resistance to fruits and vegetables by immersing them in an immersion solution containing the cold-thaw resistance imparting agent. The sugar content of fruits and vegetables is typically about 1 to 25%, depending on the type. If the sugar content of the immersion solution in which the fruits and vegetables are immersed is lower than that of the fruits and vegetables to be immersed, sugars and the like may be lost from the fruits and vegetables during immersion, and moisture may transfer to the fruits and vegetables. On the other hand, if the sugar content of the immersion solution is higher than that of the fruits and vegetables to be immersed, moisture may transfer from the fruits and vegetables to the immersion solution during immersion, resulting in dehydration of the fruits and vegetables. The content of sugars in the cold-thawing resistance imparting agent according to one aspect of the present invention can be appropriately adjusted so that when an immersion solution for immersing fruits and vegetables is prepared by dissolving the cold-thawing resistance imparting agent in an appropriate solvent or diluting it with an appropriate solvent, the sugar content of the immersion solution becomes approximately the same as the sugar content of the fruits and vegetables. However, taking into consideration the relationship with other components that may be contained in the cold-thawing resistance imparting agent, it is preferable that the sugars be blended in the above-mentioned content.

[0035] In a preferred embodiment, the cold-thawing resistance imparting agent according to one aspect of the present invention may further contain a calcium salt. There are no particular limitations on the type of calcium salt that may be contained in the cold-thawing resistance imparting agent according to one aspect of the present invention, and the calcium salt may be, for example, calcium chloride, calcium citrate, calcium gluconate, calcium carbonate, calcium lactate, calcium sulfate, calcium acetate, calcium hydroxide, etc., but as shown in the experimental examples described below, calcium lactate is particularly preferred. Calcium salts form cross-linked structures with pectin, which is contained in many fruits and vegetables, to strengthen the texture of the fruits and vegetables and protect the texture of the fruits and vegetables from ice crystals, thereby contributing to maintaining the texture of the fruits and vegetables after cold thawing. Therefore, when the cold-thawing resistance imparting agent according to one aspect of the present invention contains a calcium salt, it may be particularly suitable for use with pectin-containing fruits and vegetables, such as apples and carrots.

[0036] When the cold-thaw resistance imparting agent according to one aspect of the present invention contains a calcium salt, the content thereof is not particularly limited, and may be, for example, 0.1 to 20% by mass, preferably 0.5 to 10% by mass, and more preferably 1 to 5% by mass, based on the total solid content of the cold-thaw resistance imparting agent.

[0037] The cold-thaw resistance imparting agent according to one aspect of the present invention may further contain any component used in the art. Such components may preferably be components effective in improving or maintaining the texture, appearance, taste, aroma, etc. of frozen fruits and vegetables, and may be, for example, salt or an antioxidant. The type of antioxidant that may be contained in the cold-thaw resistance imparting agent according to one aspect of the present invention is not particularly limited, and may be, for example, ascorbic acids such as L-ascorbic acid, sodium L-ascorbate, calcium L-ascorbate, L-ascorbyl palmitate, L-ascorbyl stearate, and L-ascorbic acid 2-glucoside; tocopherols such as dl-α-tocopherol, d-α-tocopherol, d-γ-tocopherol, and d-δ-tocopherol; or polyphenols such as catechin, quercetin, ferulic acid, and gallic acid. The antioxidant and salt may contribute to maintaining the color, taste, and aroma of frozen fruits and vegetables. However, the components that can be contained in the cold-thaw resistance imparting agent according to one aspect of the present invention are not limited to the above, and may also contain, for example, an acidulant, a pH adjuster, a preservative, a colorant, a color former, a thickener, a seasoning, a solvent, etc.

[0038] As described above, the cold-thawing resistance imparting agent according to one aspect of the present invention may be in the form of a composition containing not only pullulan but also other components. That is, in a preferred embodiment, the cold-thawing resistance imparting agent according to one aspect of the present invention may be a composition containing pullulan for imparting cold-thawing resistance to fruits and vegetables.

[0039] The form of the cold-thaw resistance imparting agent according to one aspect of the present invention is not particularly limited, and may be, for example, a solid, semi-solid, or liquid. The solid form may be, for example, a powder, granule, or tablet form, but is not limited thereto. The semi-solid form may be, for example, a gel or cream form, but is not limited thereto. The liquid form may be, for example, an aqueous solution form, but is not limited thereto.

[0040] Furthermore, the cold-thaw resistance imparting agent according to one aspect of the present invention may be in the form of a concentrate that is dissolved or diluted with an appropriate solvent before use, or may be in the form of a pre-prepared formulation that can be used as is.

[0041] <Method for imparting cold-thawing resistance> In another aspect, the present invention provides a method for imparting cold-thawing resistance to vegetables and fruits.

[0042] A method for imparting cold-thawing resistance according to one aspect of the present invention includes a step of immersing fruits and vegetables in an immersion solution containing pullulan. As shown in the experimental examples described below, immersion of fruits and vegetables in an immersion solution containing pullulan imparts cold-thawing resistance to the fruits and vegetables.

[0043] The immersion liquid containing pullulan is a solution containing pullulan, and can be prepared, for example, by diluting or dissolving the cold-thaw resistance imparting agent according to one aspect of the present invention described above with an appropriate solvent. As described above, the cold-thaw resistance imparting agent according to one aspect of the present invention may be provided in the form of a pre-prepared formulation that can be used as is, i.e., in the form of an immersion liquid itself. In this case, the cold-thaw resistance imparting agent according to one aspect of the present invention can be used as is as the immersion liquid.

[0044] The soaking liquid containing pullulan may preferably be an aqueous solution containing pullulan, and the water constituting the aqueous solution may be, for example, tap water, natural water, mineral water, distilled water, ion-exchanged water, etc., but is not limited to these.

[0045] The pullulan content in the soaking solution is not particularly limited, but is preferably 0.01 to 1.0% by mass, more preferably 0.05 to 0.8% by mass, even more preferably 0.1 to 0.5% by mass, and even more preferably 0.2 to 0.4% by mass. According to the findings of the present inventors, the pullulan contained in the soaking solution permeates into fruits and vegetables and inhibits the formation and growth of ice crystals, thereby imparting cold-thawing resistance. If the pullulan content in the soaking solution exceeds 1.0% by mass, the viscosity of the soaking solution containing pullulan increases, reducing the permeability of pullulan into fruits and vegetables, potentially making it difficult to impart sufficient cold-thawing resistance. On the other hand, if the pullulan content is less than 0.01% by mass, the amount of pullulan contained in the soaking solution decreases, potentially making it difficult to impart sufficient cold-thawing resistance.

[0046] The pullulan-containing immersion solution may further contain other components, which are as described in the description of the cold-thaw resistance imparting agent according to one aspect of the present invention, and therefore will not be described in detail here.

[0047] When the soaking solution containing pullulan further contains sugars, the sugar content in the soaking solution is preferably 1 to 25% by mass, although this depends on the type of fruit or vegetable being soaked. As described above, the sugar content of fruit or vegetable is usually about 1 to 25%. If the sugar content of the soaking solution in which the fruit or vegetable is soaked is lower than that of the fruit or vegetable being soaked, sugars and other substances may be lost from the fruit or vegetable during soaking, and moisture may transfer to the fruit or vegetable. On the other hand, if the sugar content of the soaking solution is higher than that of the fruit or vegetable being soaked, moisture may transfer from the fruit or vegetable to the soaking solution during soaking, resulting in dehydration of the fruit or vegetable. From these perspectives, it is preferable that the soaking solution contain sugars at a content similar to the sugar content of the fruit or vegetable being soaked.

[0048] Furthermore, when the soaking solution containing pullulan further contains a calcium salt, the content thereof is not particularly limited, and may be, for example, 0.01 to 3 mass %, preferably 0.05 to 2 mass %, more preferably 0.1 to 1 mass %, even more preferably 0.1 to 0.5 mass %, and still more preferably 0.3 to 0.5 mass %. Soaking solutions containing a calcium salt in addition to pullulan are particularly suitable for imparting cold-thawing resistance to pectin-containing fruits and vegetables, such as apples and carrots.

[0049] The immersion time for immersing fruits and vegetables in an immersion solution containing pullulan can be appropriately set depending on the type, shape, size, etc. of the fruits and vegetables. From the viewpoint of allowing pullulan to sufficiently penetrate the fruits and vegetables, the immersion time may be, for example, 3 hours or more, preferably 12 hours or more, more preferably 24 hours or more, even more preferably 48 hours or more, and even more preferably 72 hours or more.

[0050] There are no particular limitations on the temperature of the soaking solution containing pullulan, but from the viewpoint of the shelf life of fruits and vegetables, it is preferably 10° C. or less, more preferably 8° C. or less, even more preferably 5° C. or less, and even more preferably 4° C. or less. There are no particular limitations on the specific method for adjusting the temperature of the soaking solution, but for example, the soaking step may be carried out in a space such as a refrigerator whose temperature is adjusted to a predetermined temperature.

[0051] As will be shown in the experimental examples described later, fruits and vegetables immersed in a soaking solution containing pullulan are endowed with cold-thawing resistance, and therefore, the fruits and vegetables immersed in the soaking solution can be suitably used in the production of frozen fruits and vegetables.

[0052] <Method for producing frozen fruits and vegetables> In another aspect, the present invention provides a method for producing frozen fruits and vegetables. The method for producing frozen fruits and vegetables according to one aspect of the present invention includes the steps of immersing fruits and vegetables in an immersion liquid containing pullulan, and freezing the fruits and vegetables after removing them from the immersion liquid.

[0053] In the method for producing frozen vegetables and fruits according to one aspect of the present invention, the vegetables and fruits, pullulan, the soaking liquid containing pullulan, and the step of soaking the vegetables and fruits in the soaking liquid containing pullulan are as already described.

[0054] In a method for producing frozen vegetables and fruits according to one aspect of the present invention, the vegetables and fruits soaked in a soaking liquid containing pullulan are removed from the soaking liquid and then frozen.

[0055] In the method for producing frozen fruits and vegetables according to one aspect of the present invention, there are no particular limitations on the specific method for freezing the fruits and vegetables. However, from the perspective of suppressing crystallization and crystal growth of water contained in the fruits and vegetables and obtaining frozen fruits and vegetables that have an excellent texture even after thawing, it is preferable to rapidly freeze the fruits and vegetables (also referred to as "rapid freezing"). Here, rapid freezing refers to a freezing method in which the core temperature of the fruits and vegetables passes through a temperature range of -1°C to -5°C, the temperature range for maximum ice crystal formation, within 30 minutes. There are no particular limitations on the specific means for rapid freezing, and those skilled in the art can adopt an appropriate rapid freezing method. Examples of rapid freezing methods that can be used include an air blast method in which cold air is blown onto the object, a brine method in which the object is immersed in alcohol brine and frozen, a liquefied gas method using liquefied nitrogen or liquefied carbon dioxide, and a contact method in which the object is sandwiched between cooled metal plates and frozen.

[0056] It is preferable to remove moisture adhering to the surface of the fruit and vegetables after they have been removed from the soaking liquid and before they are frozen. That is, in a preferred embodiment, the method for producing frozen fruit and vegetables according to one aspect of the present invention can further include a step of removing moisture adhering to the surface of the fruit and vegetables after they have been removed from the soaking liquid. There are no particular limitations on the specific method for removing moisture, and the fluid may be drained using an appropriate draining table, a stainless steel or plastic sieve, or a draining device, but it is preferable to contact the fruit and vegetables with a paper towel or the like and absorb or wipe off the moisture adhering to the surface of the fruit and vegetables. By removing moisture adhering to the surface of the fruit and vegetables after they have been removed from the soaking liquid, frozen fruit and vegetables with an even better texture after thawing can be obtained.

[0057] The frozen fruits and vegetables obtained as described above are thawed by an appropriate method before eating. There are no particular limitations on the method for thawing the frozen fruits and vegetables, but for example, thawing at 8° C. or below, preferably 5° C. or below, more preferably 4° C. or below is preferred. For example, the frozen fruits and vegetables may be thawed by leaving them to stand in a refrigerator adjusted to a predetermined temperature.

[0058] As will be shown in the experimental examples described below, the frozen fruits and vegetables obtained by the above-described production method, which includes the steps of immersing fruits and vegetables in an immersion solution containing pullulan and freezing the fruits and vegetables after removing them from the immersion solution, have a desirable texture even after thawing that is closer to the texture of the fruits and vegetables before freezing.

[0059] <Frozen Fruits and Vegetables> According to another aspect, the present invention provides frozen fruits and vegetables containing pullulan.

[0060] As will be shown in the experimental examples described below, the inventors have found that pullulan that has penetrated into the tissues of fruits and vegetables inhibits the formation and growth of ice crystals during the freezing and thawing process, thereby reducing damage to the tissues of the fruits and vegetables. In other words, the frozen fruits and vegetables containing pullulan according to one aspect of the present invention are frozen fruits and vegetables that are less susceptible to the formation and growth of ice crystals during the freezing and thawing process, and that have a desirable texture after thawing that is similar to the texture of the fruits and vegetables before freezing.

[0061] The pullulan content in the frozen fruits and vegetables according to one aspect of the present invention may be, for example, but is not limited to, 10 μg / g to 2000 μg / g, preferably 50 μg / g to 1500 μg / g, more preferably 100 μg / g to 1000 μg / g, and even more preferably 100 μg / g to 400 μg / g. For example, as shown in the experimental examples described below, the pullulan content may be 112 μg / g to 738 μg / g, 112 μg / g to 390 μg / g, or 390 μg to 738 μg / g.

[0062] The amount of pullulan contained in frozen fruits and vegetables can be quantified by an appropriate method. As described above, pullulan is a polysaccharide having a structure in which maltotrioses are linked via α-1,6 bonds, and maltotriose is produced when pulled by the action of pullulanase (EC 3.2.1.41) on it. Therefore, for example, the amount of pullulan contained in frozen fruits and vegetables can be quantified based on the amount of maltotriose detected when pullulanase is applied to frozen fruits and vegetables according to one aspect of the present invention. More specifically, for example, as shown in the experimental examples described below, after thawing frozen fruits and vegetables, pullulanase is applied to the thawed frozen fruits and vegetables, and the presence and / or content of maltotriose in the resulting product is quantified by an appropriate method such as a chromatography method such as ion exchange chromatography or mass spectrometry, and the amount of pullulan contained in the frozen fruits and vegetables can be quantified based on the amount of maltotriose detected. As a non-limiting example, the measurement conditions for ion exchange chromatography are as follows: Column: CK04SS (inner diameter 10 mm x length 200 mm, volume 15.7 ml, manufactured by Mitsubishi Chemical Corporation) two columns connected together Column temperature: 80°C Mobile phase: ultrapure water Flow rate: 0.4 mL / min Detector: differential refractometer

[0063] From the viewpoint of the efficiency of the action of pullulanase, it is preferable that the frozen fruits and vegetables are pulverized before the action of pullulanase. Needless to say, the resultant product obtained by the action of pullulanase on thawed frozen fruits and vegetables may be purified and concentrated before analyzing the amount of maltotriose produced by ion exchange chromatography or the like.

[0064] Furthermore, when frozen fruits and vegetables contain maltotriose and / or a source of maltotriose other than pullulan, the production of maltotriose from pullulan by the action of pullulanase may be confirmed by comparing the amount of maltotriose detected when pullulanase is acted on and the amount of maltotriose detected when pullulanase is not acted on. For example, if the amount of maltotriose detected in the product obtained by thawing frozen fruits and vegetables and acting pullulanase on the thawed frozen fruits and vegetables is increased compared to when pullulanase is not acted on, the increase can be determined to be the amount of maltotriose produced from the pullulan contained in the frozen fruits and vegetables by the action of pullulanase.

[0065] In a preferred embodiment, the frozen fruits and vegetables according to one aspect of the present invention are preferably produced by the production method according to one aspect of the present invention. The production method according to one aspect of the present invention has already been described, and therefore a detailed description thereof will be omitted here.

[0066] <Experimental Examples> The present invention will be specifically described below based on experimental examples, but the present invention is not limited to these experimental examples.

[0067] <Experiment 1: Effect of pullulan on cold-thawing resistance> The effect of pullulan on the cold-thawing resistance of cut apples was examined.

[0068] The prepared fresh apples of Example 1-1 were cut into eight equal wedges, and the resulting cut apples were immersed entirely in an immersion solution having the composition shown in the "Example 1-1" column of Table 1. The immersed cut apples were stored in a refrigerator at 4°C for 3 days. After removing the cut apples from the immersion solution, the moisture on the surfaces of the removed cut apples was wiped off with a paper towel. The cut apples were then rapidly frozen by air blast freezing at -40°C for 30 minutes using a commercially available quick freezer (product name "HBC-6A3", manufactured by Hoshizaki Corporation). The frozen cut apples were stored in a freezer at -20°C. The apples thawed in the refrigerator at 4°C were designated as Example 1-1.

[0069] The prepared raw apples of Comparative Example 1-1 were cut into eight equal wedges, and the resulting cut apples were quickly frozen by air blast freezing at −40°C for 30 minutes using a commercially available quick freezer (product name "HBC-6A3", manufactured by Hoshizaki Corporation). The frozen cut apples were stored in a freezer at −20°C. The apples thawed in a refrigerator at 4°C were used as Comparative Example 1-1.

[0070] Preparation of Comparative Example 1-2 Comparative Example 1-2 was obtained in the same manner as in Example 1-1, except that the immersion liquid had the composition shown in the "Comparative Example 1-2" column in Table 1.

[0071] Preparation of Control 1-1: A fresh apple was cut into eight equal wedges, and the resulting cut apples were stored in a refrigerator at 4°C to prepare Control 1-1.

[0072]

[0073] The details of the materials used in the above procedure are as follows: Trehalose (trade name "Treha", manufactured by Nagasevita Co., Ltd.) Ascorbic acid (vitamin C) (trade name "L-ascorbic acid", manufactured by Marugo Corporation) Pullulan (trade name "Pullulan", manufactured by Nagasevita Co., Ltd.)

[0074] Breaking Load Measurement: The breaking load of cut apples was measured as an index of their texture. Breaking load measurements were performed using a creep meter (product number "RE2-33005C," manufactured by Yamaden Co., Ltd.) and a wedge-shaped plunger (product number "No. 64," 13 mm wide x 10 mm deep x 30°, 1 mm wide flat wedge at the tip, manufactured by Yamaden Co., Ltd.). To measure the breaking load, as shown in Figure 1, each cut apple obtained using the procedure described above was cut perpendicularly to the longitudinal direction of the cut apple at approximately its center, and 10 mm thick apple slices were cut out. The plunger was pressed against the approximate center of the cut surface of each apple slice, and the load (breaking load) at which the apple slice broke was measured. The results are shown in Figure 1.

[0075] As shown in Figure 1, the breaking load of Control 1-1, which was cut apples stored in a refrigerator without being subjected to a cold-thawing treatment, was 18.23 N, whereas the breaking load of Comparative Example 1-1, which was cut apples that were cold-thawed without being immersed in an immersion solution, was 8.36 N, meaning that the breaking load of Comparative Example 1-1 was reduced to about 46% of that of Control 1-1. This result indicates that the cut apples of Comparative Example 1-1 were significantly softer than those of Control 1-1. It can be seen that even if frozen apples were prepared by freezing cut apples using quick freezing (air blast freezing), which is thought to prevent ice crystal growth, the texture after thawing was significantly inferior to the original texture of fresh cut apples before freezing.

[0076] In contrast, the breaking load of Example 1-1, which was cut apples that had been immersed in an immersion solution containing 0.3% by mass of pullulan and then cold-thawed, was 12.59 N. This breaking load was significantly higher than that of Comparative Example 1-1, which was cut apples that had been cold-thawed without immersion in an immersion solution, and was closer to the breaking load of Control 1-1, which was cut apples that had not been cold-thawed and had been stored in a refrigerator. This result indicates that the cut apples of Example 1-1 have a texture closer to that of Control 1-1 than the cut apples of Comparative Example 1-1, and it is clear that by immersing in an immersion solution containing pullulan and then performing quick freezing (air-blast freezing), frozen apples can be obtained that have a texture closer to that of fresh cut apples even after thawing.

[0077] On the other hand, the breaking load of Comparative Example 1-2, which was cut apples that had been immersed in an immersion solution of the same composition as the immersion solution used in the preparation of Example 1-1 but without pullulan and then subjected to a cold-thawing treatment, was 8.36 N. The breaking load of Comparative Example 1-2 was clearly smaller than that of Example 1-1 and was not different from that of Control 1-1, which was cut apples that had been cold-thawed without immersion in an immersion solution. These results demonstrate that immersion in an immersion solution containing pullulan before freezing is important for obtaining frozen cut apples with an excellent texture, and that immersion in an immersion solution containing pullulan confers cold-thawing resistance to cut apples.

[0078] <Experiment 2: Investigation of pullulan concentration> The influence of the pullulan content in the soaking solution on the cold-thaw resistance imparting effect was investigated.

[0079] Preparation of Examples 2-1 and 2-2: Fresh apples were cut into eight equal wedges, and the resulting cut apples were immersed entirely in the immersion solution having the composition shown in the "Example 2-1" or "Example 2-2" column of Table 2. The immersed cut apples were stored in a refrigerator at 4°C for 3 days. After removing the cut apples from the immersion solution, the moisture on the surfaces of the removed cut apples was wiped off with a paper towel. The cut apples were then rapidly frozen by air blast freezing at -40°C for 30 minutes using a commercially available quick freezer (product name "HBC-6A3", manufactured by Hoshizaki Corporation). The frozen cut apples were stored in a freezer at -20°C. The apples thawed in the refrigerator at 4°C were used as Examples 2-1 and 2-2. The materials used in the preparation of Examples 2-1 and 2-2 were the same as those used in Experiment 1.

[0080]

[0081] Measurement of Breaking Load The measurement of breaking load was carried out in the same manner as in Experiment 1. The results are shown in Figure 2. The results in Figure 2 represent the average and standard deviation of the measured values ​​obtained from three independent samples.

[0082] As shown in Figure 2, the breaking load of Example 2-1, which was cut apples immersed in an immersion solution containing 0.3% by weight of pullulan and then subjected to a cold-thawing treatment, was 12.9 N, while the breaking load of Example 2-2, which was cut apples immersed in an immersion solution containing 1% by weight of pullulan and then subjected to a cold-thawing treatment, was 9.2 N. Thus, the breaking load of Example 2-1, which was cut apples immersed in an immersion solution containing 0.3% by weight of pullulan and then subjected to a cold-thawing treatment, was greater. These results demonstrate that the pullulan content in the immersion solution affects the cold-thawing resistance-imparting effect. It is believed that the pullulan content in the immersion solution is preferably 0.01 to 1.0% by weight, more preferably 0.05 to 0.8% by weight, more preferably 0.1 to 0.5% by weight, and even more preferably 0.2 to 0.4% by weight.

[0083] <Experiment 3: Combined Use of Pullulan and Calcium Lactate> The effect of combining pullulan and calcium lactate on imparting cold-thaw resistance was examined.

[0084] The prepared fresh apples of Example 3-1 were cut into eight equal wedges, and the resulting cut apples were immersed entirely in an immersion solution having the composition shown in the "Example 3-1" column of Table 3. The immersed cut apples were stored in a refrigerator at 4°C for 3 days. After removing the cut apples from the immersion solution, the moisture on the surfaces of the removed cut apples was wiped off with a paper towel. The cut apples were then rapidly frozen by air blast freezing at -40°C for 30 minutes using a commercially available quick freezer (product name "HBC-6A3", manufactured by Hoshizaki Corporation). The frozen cut apples were stored in a freezer at -20°C. The apples thawed in the refrigerator at 4°C were designated as Example 3-1.

[0085] Preparation of Comparative Example 3-1 Comparative Example 3-1 was obtained in the same manner as in Example 4, except that the immersion liquid had the composition shown in the "Comparative Example 3-1" column in Table 3.

[0086]

[0087] The materials used in the preparation of Example 3-1 and Comparative Example 3-1 are as follows: Reduced starch syrup (trade name "HS-10", sold by Nagase Vita Co., Ltd.) Calcium lactate (trade name "Calcium Lactate", manufactured by Happo Shokai Co., Ltd.) Table salt (trade name "Table Salt", manufactured by the Salt Industry Center, Public Interest Incorporated Foundation) Ascorbic acid (vitamin C) (trade name "L-ascorbic acid", manufactured by Marugo Corporation) Pullulan (trade name "Pullulan", manufactured by Nagase Vita Co., Ltd.)

[0088] Measurement of Breaking Load The measurement of breaking load was carried out in the same manner as in Experiment 1. The results are shown in Figure 3. Note that Figure 3 also shows the results of Control 1-1 and Comparative Example 1-1 obtained in Experiment 1.

[0089] As shown in Figure 3, the breaking load of Comparative Example 3-1, which was cut apples that had been immersed in an immersion solution containing 0.3% by mass of calcium lactate and then cold-thawed, was 15.41 N. This was closer to the breaking load of Control 1-1, which was cut apples that had been refrigerated without being cold-thawed, compared to the breaking load of Comparative Example 1-1, which was cut apples that had been cold-thawed without being immersed in an immersion solution. This result indicates that cut apples that had been cold-thawed after immersion in an immersion solution containing calcium lactate had a texture that was closer to that of cut apples that had been refrigerated without being cold-thawed. This is thought to be because the calcium contained in the calcium lactate formed a cross-linked structure with the pectin contained in the apple, strengthening the apple tissue.

[0090] On the other hand, the breaking load of Example 3-1, which was cut apples that had been immersed in an immersion solution containing 0.3% by mass of calcium lactate and then cold-thawed, was 18.22 N, a value comparable to the breaking load (18.23 N) of Control 1-1, which was cut apples that had not been cold-thawed and had been stored in a refrigerator. This result indicates that the combined use of pullulan and calcium lactate makes it possible to obtain frozen cut apples that have a texture very similar to that of fresh cut apples even after thawing.

[0091] <Experiment 4: Examination of the amount of calcium lactate used> The influence of the amount of calcium lactate used when pullulan and calcium lactate are used in combination on the cold-thaw resistance imparting effect was examined.

[0092] Preparation of Examples 4-1 to 4-5 Examples 4-1 to 4-5 were prepared in the same manner as Example 3-1 of Experiment 3, except that the immersion solutions had the compositions shown in the columns "Example 4-1" to "Example 4-5" in Table 4.

[0093]

[0094] Measurement of Breaking Load The measurement of breaking load was carried out in the same manner as in Experiment 1. The results obtained are shown in FIG.

[0095] 4, Examples 4-2 to 4-5, which are cut apples that were immersed in an immersion solution containing 0.3% by mass of pullulan and 0.1%, 0.3%, 0.5%, or 1.0% by mass of calcium lactate and then subjected to a cold-thawing treatment, all showed improved breaking loads compared to Example 4-1, which is cut apples that were immersed in an immersion solution containing 0.3% by mass of pullulan and then subjected to a cold-thawing treatment without calcium lactate. These results suggest that the effect of imparting cold-thawing resistance by the combined use of pullulan and calcium lactate can be achieved regardless of the concentration of calcium lactate.

[0096] <Experiment 5: Histological evaluation of the effect of pullulan on imparting cold-thawing resistance> The effect of pullulan on imparting cold-thawing resistance was examined from a histological perspective.

[0097] In Examples 5-1, 5-2, and Comparative Example 5-1, fresh apples were cut into eight equal wedges, and the resulting cut apples were immersed entirely in the immersion solution of the composition shown in Table 5. The immersed cut apples were stored in a refrigerator at 4°C for 3 days. After removing the cut apples from the immersion solution, the surface moisture of the removed cut apples was wiped off with a paper towel. The cut apples were then rapidly frozen by air blast freezing at -40°C for 30 minutes using a commercially available quick-freezer (product name "HBC-6A3," manufactured by Hoshizaki Corporation). The frozen cut apples were stored in a freezer at -20°C and used to prepare frozen sections. The materials used in Examples 5-1, 5-2, and Comparative Example 5-1 were the same as those used in Experiment 3.

[0098]

[0099] Section preparation: Sections for tissue observation were prepared according to standard procedures using a cryostat (trade name "CM3050S", manufactured by Leica Microsystems) and a sample freezing device (trade name "UT2000F", manufactured by Tokyo Rikakikai Co., Ltd.). Specifically, frozen cut apples prepared according to the procedure described above were cut vertically longitudinally using the cryostat and sample freezing device at a chamber temperature of -20°C and a sample stage temperature of -20°C, and 80 μm thick sections were obtained. The obtained sections were stained with toluidine blue according to standard procedures and subjected to observation under an optical microscope.

[0100] Observation of sections: Observation of sections was performed using an optical microscope (product name "BX50", Olympus Corporation) equipped with a microscope digital camera (product name "DP26", Olympus Corporation), and the images obtained were captured using microscope imaging software (product name "cellSens", Olympus Corporation). For each section, the tissue condition of the part close to the apple core (core side) and the part close to the skin (skin side) was observed. Representative images showing the tissue condition of the core side and skin side of each section are shown in Figure 5.

[0101] As shown in Figure 5, cell wall damage was observed on both the core and skin sides of Comparative Example 5-1, which was a cut apple immersed in an immersion solution containing no pullulan and then subjected to a cold-thawing treatment. This is believed to be due to the formation and growth of ice crystals caused by the freezing process. In contrast, no significant cell wall damage was observed in Example 5-1, which was a cut apple immersed in an immersion solution containing pullulan and then subjected to a cold-thawing treatment, and Example 5-2, which was a cut apple immersed in an immersion solution containing pullulan and calcium lactate and then subjected to a cold-thawing treatment. The tissue appearance was similar to that of Control 1-1, a cut apple that had not been subjected to a cold-thawing treatment. These results indicate that immersion in an immersion solution containing pullulan reduces cell wall damage caused by the cold-thawing treatment. Furthermore, this reduction in cell wall damage was observed not only on the surface of the tissue but also within the tissue, indicating that the pullulan in the immersion solution does not simply coat the surface of the cut apple but penetrates into the tissue, thereby reducing cell wall damage throughout the tissue.

[0102] <Experiment 6: Comparison with other polysaccharides> The specificity of the effect of pullulan in imparting cold-thaw resistance was examined in a comparative experiment using other polysaccharides.

[0103] Preparation of Comparative Examples 6-1 to 6-4 Comparative Examples 6-1 to 6-4 were prepared in the same manner as in Example 3-1 of Experiment 3, except that the compositions of the immersion solutions were changed to those shown in the columns "Comparative Example 6-1" to "Comparative Example 6-4" in Table 6. In this experiment, "FT-3" (manufactured by Nippon Paper Industries Co., Ltd.) was used as the carboxymethyl cellulose.

[0104]

[0105] The breaking load was measured in the same manner as in Experiment 1. The results are shown in FIG.

[0106] 6, Comparative Examples 6-2 to 6-4, which were cut apples that had been immersed in an immersion solution containing 0.3% by mass of calcium lactate and 0.1%, 0.3%, or 0.5% by mass of carboxymethylcellulose and then subjected to a cold-thawing treatment, all showed a lower breaking load than Comparative Example 6-1, which was cut apples that had been immersed in an immersion solution containing 0.3% by mass of calcium lactate and then subjected to a cold-thawing treatment without carboxymethylcellulose. This result indicates that the effect of pullulan on imparting cold-thawing resistance is specific to pullulan and cannot be obtained when other polysaccharides, such as carboxymethylcellulose, are used.

[0107] <Experiment 7: Determination of pullulan content> The amount of pullulan in cut apples obtained by immersion in an immersion solution containing pullulan and then cold-thawing was determined by ion exchange chromatography.

[0108] Preparation of Examples 7-1 to 7-3: Fresh apples were cut into approximately 8 equal wedges so that each cut apple weighed 120 g. The resulting cut apples were immersed entirely in the immersion solution of the composition shown in Table 7. The immersed cut apples were stored in a refrigerator at 4°C for 3 days. After removing the cut apples from the immersion solution, the surface of the removed cut apples was wiped dry with a paper towel. The cut apples were then rapidly frozen by air blast freezing at -40°C for 30 minutes using a commercially available quick freezer (product name "HBC-6A3", manufactured by Hoshizaki Corporation). The frozen cut apples were stored in a freezer at -20°C and subjected to pullulan quantification. The materials used in sample preparation were the same as those in Experiment 3.

[0109]

[0110] An equal volume (120 g) of water was added to thawed cut apples and pulverized in a blender. The pulverized material was transferred to a centrifuge tube and subjected to ultrasonic extraction for 30 minutes. After ultrasonic extraction, the mixture was centrifuged (4000 rpm, 20 minutes) and the resulting supernatant was collected. 1 mL of the collected supernatant was mixed with 9 mL of 0.2 M phosphate buffer (pH 6.0) containing 2 U / mL pullulanase (product name "PULLULANASE", Nagasevita Co., Ltd.) and incubated at 35°C for 18 hours. After incubation, the mixture was centrifuged (4000 rpm, 10 minutes) and the resulting supernatant was collected. The collected supernatant was desalted according to standard methods, diluted 10-fold with water, and subjected to ion exchange chromatography. The measurement conditions for ion exchange chromatography are as follows: Column: CK04SS (inner diameter 10 mm x length 200 mm, volume 15.7 ml, manufactured by Mitsubishi Chemical Corporation), two columns connected together; Column temperature: 80°C; Mobile phase: ultrapure water; Flow rate: 0.4 mL / min; Detector: differential refractometer

[0111] The amount of maltotriose in the supernatant was quantified in a conventional manner based on the peak area of ​​the peak corresponding to maltotriose in the obtained chromatogram and a calibration curve prepared using a standard sample containing a predetermined amount of maltotriose, and the amount of pullulan in the cut apples was calculated based on the quantified amount of maltotriose in the supernatant.

[0112] As mentioned above, pullulan is a water-soluble polysaccharide whose basic unit is a maltotriose structure, and these basic units are linked together via α-1,6 bonds. Therefore, assuming that the molecular weight of maltotriose is 504.4 and that of water is 18, the molecular weight of pullulan, which is composed of n maltotriose units linked together, is expressed by the following formula: Note that when n is very large, it can be considered that 486.4n-18≒486.4n. Therefore, in this experiment, calculations were performed assuming that the molecular weight of pullulan was 486.4n, as expressed by the following formula:

[0113]

[0114] Next, assuming that the entire amount of pullulan in the cut apples is decomposed into maltotriose by the pullulanase treatment, the amount of pullulan in the cut apples can be calculated using the following formula based on the amount of maltotriose in the supernatant.

[0115]

[0116]

[0117] As a representative chromatogram obtained from cut apples soaked in a soaking solution containing pullulan, the chromatogram obtained by analyzing the cut apples of Example 7-2 by ion exchange chromatography is shown in Figure 7, and the quantitative results of pullulan in each sample are shown in Table 8. In addition, Figure 7 and Table 8 also show the analytical and quantitative results of a control sample prepared by the same procedure as above except that pullulanase was not applied (pullulanase treatment "-" in Figure 7 and Table 8).

[0118]

[0119] As shown in Figure 7, maltotriose was not detected in cut apples that had not been treated with pullulanase (Figure 7A), whereas maltotriose was detected in cut apples that had been treated with pullulanase (Figure 7B). These results indicate that cut apples prepared by immersion in a pullulan-containing soaking solution followed by cold thawing contain pullulan, and that the pullulan was degraded by pullulanase and detected by ion exchange chromatography. These results are also consistent with the finding that untreated apples that have not been immersed in a pullulan-containing soaking solution, i.e., normal apples, do not contain maltotriose.

[0120] As shown in Table 8, the amount of pullulan in the cut apples of Example 7-1, which were prepared by immersion in an immersion solution containing 0.3% by mass of pullulan followed by cold-thawing, was 112 μg / g; the amount of pullulan in the cut apples of Example 7-2, which were prepared by immersion in an immersion solution containing 0.5% by mass of pullulan followed by cold-thawing, was 390 μg / g; and the amount of pullulan in the cut apples of Example 7-3, which were prepared by immersion in an immersion solution containing 1.0% by mass of pullulan followed by cold-thawing, was 738 μg / g. It was confirmed that the cut apples prepared by immersion in an immersion solution containing pullulan followed by cold-thawing contained pullulan in an amount corresponding to the pullulan concentration in the immersion solution. It is presumed that the pullulan contained in the cut apples contributes to the cold-thawing resistance of the cut apples.

[0121] Although the demand for frozen fruits and vegetables that have excellent storage stability and distribution properties and can be supplied even during the off-season has been increasing in recent years, most of the frozen fruits and vegetables currently available on the market are blanched and intended for cooking, and there is a strong demand for frozen fruits and vegetables that have a texture similar to that of fresh fruits and vegetables even after thawing and that can be eaten deliciously as is. The present invention, which can provide frozen fruits and vegetables that have a texture similar to that of fresh fruits and vegetables before freezing even after thawing, has great industrial applicability.

Claims

1. A cold-thaw resistance imparting agent containing pullulan for fresh produce.

2. The cold-thaw resistance imparting agent according to claim 1, further comprising a sugar.

3. The cold-thaw resistance imparting agent according to claim 2, further comprising a calcium salt.

4. A method for imparting cold-thawing resistance to vegetables, comprising the step of immersing the vegetables in an immersion liquid containing the agent for imparting cold-thawing resistance according to any one of claims 1 to 3.

5. The method according to claim 4, wherein the pullulan content in the soaking liquid is 0.01 to 1.0% by mass.

6. A method for producing frozen vegetables and fruits, comprising the steps of: immersing vegetables and fruits in an immersion liquid containing the cold-thaw resistance imparting agent according to any one of claims 1 to 3; and freezing the vegetables and fruits after removing them from the immersion liquid.

7. The method according to claim 6, wherein the pullulan content in the soaking liquid is 0.01 to 1.0% by mass.

8. The method according to claim 7, wherein the step of freezing the fruits and vegetables comprises freezing the fruits and vegetables by quick freezing.

9. Frozen fruits and vegetables containing pullulan.

10. The frozen fruits and vegetables according to claim 9, having a pullulan content of 10 μg / g or more and 2000 μg / g or less.

Images