JP2005278596A - Method for producing processed product of leaf and stem of sweet potato - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing processed products of leaves and stems of sweet potato, which products have high polyphenol contents and/or antioxidative activity. <P>SOLUTION: In the method for producing processed products of leaves and stems of sweet potato, having high polyphenol contents and/or antioxidative activities, the method includes heat-treating the leaves and stems of sweet potato at ≥pH5.6. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a processed sweet potato stover. More specifically, the present invention relates to a method for producing a processed sweet potato stover with a high polyphenol content and / or antioxidant activity.

  Sweet potato stems and leaves are known to contain health-effective ingredients such as vitamins and minerals, and are used as food materials (Patent Document 1). For example, Patent Document 1 describes a potassium-containing food in which sweet potato stems and leaves are immersed and boiled in water, the eluate is concentrated, and the resulting extract is applied to laver. In Patent Document 2, as a method for treating sweet potato stalks and leaves, when washing sweet potato stalks and leaves, it is washed with spray water, dried and powdered so that active ingredients such as vitamins and minerals contained therein do not flow out. Has been described.

  In recent years, it has become clear that this sweet potato stem and leaf further contains polyphenols as active ingredients other than vitamins and minerals. Polyphenols are contained in various plants, such as purple sweet potato and koganesengan (for example, Non-Patent Documents 1 and 2), and have various in vivo activities such as antioxidant activity. Patent Document 3 describes that a food composition containing proanthocyanidins, which are one of polyphenols, and glutathione has a synergistic whitening effect.

However, an active ingredient having an antioxidative action such as polyphenol is generally easily decomposed and lost due to oxidation. Since the amount and speed of such loss vary depending on the type of plant, plant part, treatment method, etc., various studies are necessary when focusing on an active ingredient having an antioxidant effect. . As for sweet potato stems and leaves, it has not yet been examined to treat polyphenol or antioxidant activity.
JP 7-11878 A JP-A-6-62783 Japanese Patent No. 30409992 Ikuo Suda et al. Measurement of radical scavenging ability of colored agricultural products and foods by DPPH spectroscopy, Kyushu Agricultural Research, Vol. 61, p. 32, 1999 Oki et al. Radical scavenging activity of chips made from purple sweet potato, food industry, Vol. 48, No. 12, 926-932, 2001

  Accordingly, a method for producing a processed sweet potato stem and leaf product having a high polyphenol content or an antioxidant activity is desired.

  The method for producing a processed product of sweet potato stover with high polyphenol content and / or antioxidant activity of the present invention includes a step of heat-treating sweet potato stover with a pH of 5.6 or more.

  In a preferred embodiment, the heat treatment is performed at a temperature higher than 80 ° C.

  According to the production method of the present invention, a processed sweet potato foliage product having a high polyphenol content and / or high antioxidant activity can be obtained. This processed sweet potato stover is excellent in stability such as the color inherent in the sweet potato stover, has little bitterness and pungent taste, and is excellent in palatability, so that it can be combined with various foods to form a composition. .

(Sweet potato leaves)
The sweet potato used in the present invention is a plant belonging to the convolvulaceae family generally called sweet potato. Examples of the varieties include koganesengan, shiroyutaka, sweet potato, ayamurasaki, and suiou.

  In this specification, a sweet potato stem and leaf means the above-ground site | part at the time of cultivation of the said sweet potato. In particular, sweet potato foliage that has grown from the ground by 5 cm or more, preferably 10 cm or more, more preferably 20 cm or more is preferably used. Furthermore, it is preferable to use sweet potato stalks and leaves that retain green color.

  Sweet potato stover is usually washed with water after harvesting to remove attached mud. The sweet potato stover is cut into an appropriate length (for example, the major axis is about 10 to 30 cm) as necessary.

(Heat treatment process)
The sweet potato stover is heat-treated at pH 5.6 or higher. Specifically, the sweet potato stover is immersed in an aqueous solution adjusted to a predetermined pH by adding a pH adjuster, or heat-treated, or the aqueous solution is sprayed onto the sweet potato stover and then heat-treated. From the viewpoint of maintaining a high component effective for antioxidant activity such as polyphenol, the pH is preferably 5.6 or more and less than 8.4, more preferably 5.6 to 8.0, and even more preferably 6.6 to 8. Heat treatment is performed at 0, most preferably from 7.0 to 8.0. By this heat treatment, a sweet potato stalk-and-leaves product with enhanced antioxidant activity is obtained. When the pH is less than 5.6, the amount of polyphenol in the processed sweet potato leaves is reduced, and the antioxidant activity is also reduced. When pH exceeds 8.4, since polyphenol may be decomposed | disassembled, attention is required.

  For example, when the pH adjuster is adjusted to basic, sodium hydroxide, sodium bicarbonate, calcium carbonate (eg eggshell calcium, scallop shell calcium, coral calcium, etc.), calcium oxide obtained by firing the calcium carbonate, or the like is used. It is done. Moreover, you may use directly as aqueous solution which adjusted alkali ion water etc. to predetermined | prescribed pH. In the case of adjusting the acidity, organic acids such as acetic acid, citric acid, ascorbic acid, tartaric acid, malic acid, fumaric acid and the like are used.

  The amount of the aqueous solution adjusted to a predetermined pH is not particularly limited. When spraying on sweet potato stalks and leaves, it is preferable to make sufficient contact.

  The heat treatment temperature is not particularly limited, but is preferably a temperature higher than 80 ° C, more preferably 90 ° C or higher, and further preferably 90 ° C to 97 ° C. What is necessary is just to set a heating time suitably with the magnitude | size of a sweet potato stalk, and heating temperature. It is preferably less than 5 minutes, more preferably 3 minutes or less, still more preferably about 10 seconds to 3 minutes, particularly preferably about 10 seconds to 2 minutes, and most preferably about 10 seconds to 1 minute.

  Examples of the heat treatment method include blanching treatment (blanching), dry heat treatment, microwave treatment, infrared or far infrared treatment, and steam treatment. Among these, blanching treatment and steam treatment are preferably used.

  In particular, the heat treatment is preferably carried out by immersing the sweet potato foliage in an aqueous solution adjusted to pH 7.0 to 8.0 and blanching at 90 ° C. to 97 ° C. for 10 seconds to 1 minute. By treating under the above conditions, the green color of sweet potato stems and leaves is maintained without reducing the pigment chlorophyll, the flavor and nutrients are not impaired, and the physiological activity (especially antioxidant activity) of active ingredients such as polyphenols Can be obtained.

  Before heat treatment, from the viewpoint of improving the flavor, 0.01 to 5% by mass, preferably 0.2 to 3% by mass of sodium chloride may be added to the aqueous solution in advance. By adding salt, it is possible to obtain a processed sweet potato foliage that has a brighter green color, good flavor, and excellent palatability.

  It is preferable to cool immediately after the heat treatment in order to maintain the green color and flavor of the sweet potato leaves. The cooling method is not particularly limited, and a cooling means usually used by those skilled in the art can be used. For example, a method of immersing the sweet potato stems and leaves after the treatment in cooling water or bringing cold air into contact therewith can be mentioned. Cooling is preferably performed at a lower temperature because the green color of the sweet potato stems and leaves is excellent in appearance. The cooling time is an arbitrary time according to the processing amount of sweet potato foliage, but it is preferable to carry out until the sweet potato foliage itself becomes equal to the cooling temperature.

  When immersed in cooling water, the cooling water is preferably 30 ° C. or lower, and more preferably 20 ° C. or lower.

(Processed sweet potato stems and leaves)
The processed sweet potato foliage obtained by the present invention contains polyphenols in a high proportion. Preferably, it contains 0.5 to 2 times, more preferably 0.5 to 1.5 times, and even more preferably 1 to 1.5 times the polyphenol, compared to the sweet potato stems and leaves before treatment. .

  The processed sweet potato foliage contains, in particular, a high proportion of polyphenols derived from sweet potato foliage that is excellent in physiological activity among polyphenols. Examples of such polyphenols derived from sweet potato foliage include caffeic acid, caffeoylquinic acid in which caffeic acid and quinic acid are combined, and the like. Specifically, caffeoylquinic acid is a chlorogenic acid to which one molecule of caffeic acid is bonded to one molecule of quinic acid, and dicaffeoylquinic acid to which two molecules of caffeic acid are bonded (3,4-dicarboxylic acid). Caffeoylquinic acid, 3,5-dicaffeoylquinic acid, 4,5-dicaffeoylquinic acid, etc.) Tricaffeoylquinic acid (3,4,5-tricaffeoyl oil) to which three molecules of caffeic acid are bound Quinic acid and the like) and derivatives thereof. Such characteristic polyphenols not only exhibit high antioxidant activity, but also have various physiological activities such as an anti-HIV effect.

  The processed sweet potato stem and leaf product further exhibits the original vivid green color of the sweet potato stem and leaf even when stored for a long period of time (for example, 1 month or longer) compared to the unprocessed sweet potato stem and leaf. . Furthermore, it is excellent in palatability.

  The processed sweet potato foliage is processed into various forms such as paste, liquid, and powder, and can be used as a food raw material to form a food composition.

  The paste is obtained by performing crushing means commonly used by those skilled in the art, such as a food processor and a mass collider. From the viewpoint of facilitating the crushing, it is preferable to crush it roughly with a food processor or the like and then crush it more finely using a mass collider or the like.

  The liquid material can be obtained, for example, by squeezing the processed sweet potato leaves with a press or by removing the solid content of the paste by a separation means usually used by those skilled in the art such as filtration. This liquid material can be used as a beverage as it is. When a liquid material is used as a food material, it is preferably used after heat sterilization at 80 ° C to 130 ° C.

  The powder can be obtained, for example, by drying and pulverizing the processed sweet potato foliage, or by drying the paste or liquid thereof and, if necessary, pulverizing.

  As a drying method when the processed sweet potato foliage product or paste thereof is pulverized, a hot air dryer, a high-pressure steam dryer, an electromagnetic wave dryer, a freeze dryer, a direct-fired heater, a rotary dryer, or the like can be used. From the viewpoint of production cost and drying efficiency, a hot air dryer, a direct-fired heater, and a rotary dryer are preferable. In addition, it is preferable to perform drying temperature at about 60 to 150 degreeC from the point which obtains the powder of the sweet potato foliage processed product with good flavor and a bright color.

  In the case of using a rotary dryer, the paste, which is preferably crushed roughly with a food processor or the like, and then further finely crushed with a mass collider or the like, is preferably 100 ° C to 150 ° C, more preferably 110 ° C to By putting it in a rotating drum at a heating temperature of 130 ° C., a sweet potato leaf powder having a water content of 5% by weight or less can be obtained. Since the heating temperature is high, sterilization can be performed at the same time. In addition, since there exists a possibility that a sweet potato foliage may discolor in this case, it is preferable to set it as about 30 second-2 minutes.

  When using a hot air dryer, drying may be performed in one stage until the water content of the green leaves reaches 5% by weight, but it is preferable to perform two-stage drying. In the two-stage drying, after the primary drying at a temperature of 60 to 80 ° C. until the water content becomes 25% by weight or less, the temperature higher than the primary drying until the water content of the primary dried green leaves becomes 5% by weight or less. Secondary drying is preferable. When the drying temperature is less than 60 ° C., the drying rate is slow, and when the drying temperature exceeds 100 ° C., burns may occur. Therefore, by adjusting the primary drying temperature to around 80 ° C., a colorful sweet potato stalk having a high polyphenol content can be obtained as a powder. By performing this two-stage drying, the drying time is shortened, and at the same time, the green color and flavor of the sweet potato leaves are maintained. The temperature difference between the primary drying and the secondary drying is preferably about 5 to 15 ° C, and more preferably about 10 ° C. Moreover, by setting the temperature difference within a certain range as described above, water management of the green leaves in the drying process is facilitated, and drying is performed efficiently.

  The dried sweet potato foliage treatment product can be made into a fine powder of the sweet potato foliage treatment product by pulverization, if necessary. Sweet potato stems and leaves have different sizes and hardnesses such as stems, leaves, and petiole. Therefore, from the viewpoint of facilitating pulverization, it is preferable to perform the fine pulverization after the coarse pulverization.

  The coarse pulverization treatment is performed by using any machine or tool commonly used by those skilled in the art, such as a cutter, a slicer, and a dicer. As for the size of the coarsely pulverized product, the major axis is 20 mm or less, preferably 0.1 to 10 mm.

It is preferable to sterilize between coarse pulverization and fine pulverization. The processed sweet potato foliage product can be heated uniformly, the flavor of the processed sweet potato foliage product can be improved, and efficient sterilization can be performed. This sterilization treatment is performed at 110 ° C. or higher, and a high-pressure sterilizer, a heat sterilizer, a pressurized steam sterilizer, or the like can be used. For example, in the case of heat treatment by pressurized steam sterilization, the coarsely pulverized product is heat-treated with saturated steam at 110 to 200 ° C. for 2 to 10 seconds under a pressure of 0.5 to 10 kg / cm ² , for example.

  In the fine pulverization treatment, fine pulverization is performed so that 90% by weight of the obtained coarse pulverized product passes through the 200 mesh section. The pulverization is performed using any machine or tool normally used by those skilled in the art, such as, for example, a crusher, a mill, a blender, and a stone mill. The texture is improved by fine grinding. In particular, the texture is further improved by the order of the coarse pulverization process, the heat treatment, and the fine pulverization process.

  As a method of pulverizing the liquid product of the sweet potato stem and leaf processed product, for example, it is dried by a heat dryer, a vacuum concentrator or a freeze dryer, and then pulverized or directly using a spray dryer such as a spray dryer. Can be powdered. When spray drying is used, an excipient such as dextrin, cyclodextrin, starch or maltose is added as necessary to increase the recovery rate. Preferably dextrin is used. The ratio of liquid to dextrin is preferably 1:10 to 5: 1 by weight in order to facilitate powdering by adding dextrin.

(Composition containing processed sweet potato stems and leaves)
The processed sweet potato foliage product of the present invention can be made into a composition containing a processed sweet potato foliage as it is or, if necessary, by blending with various foods, additives and the like. The content of the processed sweet potato stover is not particularly limited.

  Examples of additives include excipients, extenders, binders, thickeners, emulsifiers, colorants, fragrances, food additives, seasonings, and the like. Examples of food additives include royal jelly, vitamins, proteins, calcium, chitosan, lecithin, sugar solution, seasonings and the like.

  Such a composition is used in a form usually used by those skilled in the art as needed, such as capsules such as hard capsules and soft capsules, tablets, pills, granules, tea bags, viscous liquids, and liquids. The Depending on the shape or preference, these may be eaten as they are, or may be drunk in water, hot water, milk or the like, or may be ingested with leached components.

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this Example is not intending limiting this invention.

(Example 1: Preparation of heat-treated sweet potato leaves)
Shiroyutaka seed buds were planted and cultivated, and the foliage grown to about 30 cm from the ground was cut and washed twice with water to obtain 2 kg of sweet potato foliage.

  100 g of the above sweet potato stover was immersed in hot water (97 ° C.) adjusted to pH 5.6 with acetic acid and / or sodium bicarbonate for 1 minute. Then, it was immediately immersed in water at 20 ° C. and cooled. The obtained sweet potato foliage heat-treated product was freeze-dried and pulverized using a micro hammer mill (KG IKA-Labortechnik, Janke & Kunkel Gmph & Co.) to obtain a dried powder of sweet potato foliage heat-treated product (powder 1) ).

  The total amount of polyphenols in the dried powder (powder 1) of the sweet potato foliage heat-treated product was measured as follows. First, 5 mL of an 80% by volume ethanol aqueous solution was added to 10 mg of powder 1 and extracted at 100 ° C. for 5 minutes. Thereafter, centrifugation was performed at 3000 rpm for 15 minutes, and the supernatant was collected. 25 μL of this supernatant was collected on a microplate and concentrated to dryness under reduced pressure, and then 25 μL of distilled water was added to prepare a sample for analysis. 25 μL of distilled water and 125 μL of 10% protein measurement phenol reagent (manufactured by Nacalai Tesque) were added to the sample for analysis and stirred for 3 minutes, and then 125 μL of 10% aqueous sodium carbonate solution was added to develop blue color. . After color development, absorbance at 600 nm was measured using a microplate reader. As a standard substance, commercially available chlorogenic acid (manufactured by Sigma-Aldrich Japan) was used. In the same manner as described above, the absorbance at 600 nm was measured to prepare a calibration curve, and using this, the total amount of polyphenol was calculated in terms of chlorogenic acid. Furthermore, the said operation was performed 3 times and the average value of the total polyphenol amount was calculated | required. The results are shown in Table 1.

(Examples 2 to 7)
Instead of hot water (97 ° C.) with the pH of Example 1 adjusted to 5.6, the pH was adjusted to 6.6, 7.0, 7.3, 7.6, 8.0, and 8.4. Except for using each of the six types of hot water (97 ° C.), dry powder of sweet potato stover was obtained (powder 2-7) in the same manner as in Example 1, and the total amount of polyphenols in each powder Was measured in the same manner as in Example 1 to obtain an average value. The results are also shown in Table 1.

(Comparative Examples 1 and 2)
Instead of hot water (97 ° C.) adjusted to pH 5.6 in Example 1, two types of hot water (97 ° C.) adjusted to pH 3.4 and 4.0 were used, respectively. In the same manner as in Example 1, dried powder of sweet potato foliage was obtained (powder 8 and 9), the total amount of polyphenol was measured, and the average value was obtained. The results are also shown in Table 1.

  From the results of Table 1, the powders (powder 1 to 7) subjected to heat treatment with hot water having a pH of 5.6 or more in Examples were subjected to heat treatment with hot water having a pH of less than 5.6 in the comparative example. Compared to the powders (powder 8 and 9), the total amount of polyphenols was higher. This indicates that a processed sweet potato foliage product having a high total amount of polyphenols can be obtained by the production method of the present invention.

(Example 8: Antioxidant activity)
Using the extracts of the four types of powders (powder 1, 2, 4, and 7) obtained in Examples 1, 2, 4, and 7, the radical scavenging activity was measured as an index for evaluating the antioxidant activity. did. The radical scavenging activity was measured with reference to the DPPH method (Non-patent Documents 1 and 2). First, each extract was diluted 3 times to obtain a test solution. Next, 75 μL of each test solution was placed in each well of the microplate, and 150 μL of an ethanol solution (pH 6.0) containing 0.1 M MES (2-morpholinoethanesulfonic acid monohydrate, manufactured by Wako Pure Chemical Industries, Ltd.) 75 μL of 0.16 mg / mL DPPH-containing ethanol solution (3.94 mg DPPH dissolved in 50% ethanol solution) was added and stirred for 2 minutes. After stirring, the absorbance at 520 nm was measured using a dual wavelength flying spot densitometer (manufactured by Shimadzu Corporation, CS9300). Trolox (manufactured by Sigma-Aldrich Japan) was used as a standard substance. A standard dilution solution (0.4 mM, 0.13 mM, 0.04 mM, and 0.01 mM) in which this Trolox was dissolved in an 80% ethanol aqueous solution was prepared and measured in the same manner as described above to prepare a calibration curve. In addition, 80% ethanol aqueous solution was used as a blank. Using this calibration curve, the amount of Trolox per gram of powder was calculated from the absorbance of each test solution. Furthermore, the said operation was performed 3 times and the average value of the amount of Trolox per 1g of powder was calculated | required. The results are shown in Table 2. In addition, it shows that radical scavenging activity is so high that the value of Trolox amount is large.

  From the results shown in Table 2, it can be seen that the powders (powder 1, 2, 4, and 7) subjected to heat treatment with hot water having a pH of 5.6 or more in Examples have antioxidant activity. In particular, powders 1, 2 and 4 (heat treatment at pH 5.6 to 7.3), preferably powder 4 (heat treatment at pH 7.3), had high antioxidant activity. In addition, these sweet potato stem-and-leaves treated products exhibited a vivid green color and were stably maintained even when left at room temperature for one month.

Example 9
100 g of sweet potato stover obtained in Example 1 was immersed in 1 L of hot water (70 ° C.) adjusted to pH 8.3 with sodium bicarbonate for 1 minute. Then, it was immediately immersed in water at 20 ° C. and cooled. The obtained sweet potato stover heat treatment product was freeze-dried and pulverized using a micro hammer mill (KG IKA-Labortechnik, Janke & Kunkel Gmph & Co.) to obtain a dry powder of sweet potato stover leaf heat treatment (powder 10) ). The total amount of polyphenols in the dry powder of this sweet potato foliage heat-treated product was measured in the same manner as in Example 1, and the radical scavenging activity was measured in the same manner as in Example 8. The average value of the values measured three times was obtained. The results are shown in Table 3.

(Examples 10 to 12)
A powder of sweet potato foliage heat-treated product was obtained in the same manner as in Example 9 except that 80 ° C., 90 ° C., and 97 ° C. hot water was used instead of 70 ° C. hot water (powder 11 to 11). 13) The total polyphenol amount and radical scavenging activity were measured, and the average value of the values measured three times was determined. The results are also shown in Table 3.

  From the results of Table 3, when heat-treating sweet potato stems and leaves at a predetermined pH, a higher polyphenol content and anti-oxidation are particularly obtained by heat-treating at 70 ° C. or higher, preferably 80 ° C. or higher, more preferably 90 ° C. or higher. It can be seen that a heat-treated sweet potato stover is obtained.

(Example 13)
30 g of sweet potato stems and leaves of Example 1 were immersed in hot water (97 ° C.) adjusted to 1.5 L of pH 7.0 for 10 seconds. The heat-treated sweet potato stover was taken out, immediately immersed in water at 20 ° C., and cooled. The obtained sweet potato foliage heat-treated product was freeze-dried and pulverized using a micro hammer mill (KG IKA-Labortechnik, Janke & Kunkel Gmph & Co.) to obtain a dry powder of sweet potato foliage heat-treated product (powder 14) ). In the same manner as described above, dry powder of sweet potato foliage heat-treated products that had been subjected to heat treatment for 20, 30, 60, 120, 180, and 300 seconds were obtained. Let each powder be powder 15-20, respectively. Furthermore, a dry powder of sweet potato stems and leaves was obtained in the same manner as above except that no heat treatment was performed. This is designated as Powder 21. The total amount of polyphenols in powders 14 to 21 was measured in the same manner as in Example 1, and the average value was determined. Moreover, about the powder 17-19 which heat-processed for 60 second, 120 second, and 180 second, the amount of Trolox was further measured by the method similar to Example 1, the average value was calculated | required, and antioxidant activity was evaluated. . The results are shown in Table 4.

  From the results in Table 4, it can be seen that the powders (powder 14 to 20) subjected to the heat treatment at pH 5.6 or higher retain polyphenol. In particular, the powder (powder 14-17) subjected to heat treatment at pH 5.6 or higher for 10 seconds to 60 seconds increased the total amount of polyphenols compared to the powder not subjected to heat treatment (powder 21). Moreover, the total polyphenol amount of the powder (powder 20) subjected to the heat treatment for 300 seconds was 50% or less of the powder (powder 21) not subjected to the heat treatment. Regarding the antioxidant activity, all of the measured powders (powder 17 to 19) showed a high Trolox amount and excellent radical scavenging activity.

(Example 14)
Regarding the eight types of powders 1, 2, 4, 10-12, 18, and 19 obtained in the above examples, among polyphenols, caffeic acid (CFA), which is a characteristic component derived from sweet potato leaves, Chlorogenic acid (CHA), 3,4-dicaffeoylquinic acid (3,4-diCQA), 3,5-dicaffeoylquinic acid (3,5-diCQA), 4,5-dicaffeoylquinic acid ( 4,5-diCQA) and 3,4,5-tricaffeoylquinic acid (3,4,5-triCQA) were measured using HPLC under the following conditions. The results are shown in Table 5. In addition, after adding 8 mL of purified water to a 100 mg powder and mixing by vortex for several seconds, the sample was heated in boiling water for 10 minutes, and the supernatant was collected by centrifugation. A 2% ascorbic acid aqueous solution was added to the supernatant. Prepared by adding equal amounts.

(HPLC conditions)
Column: YMC-Pack ODS-AMAM-302
(4.6 mm ID × 150 mm)
Mobile phase A: 0.2% formic acid aqueous solution Mobile phase B: 0.2% formic acid methanol solution Volume ratio of mobile phase A and B: 0 to 5 minutes after sample injection, A: B = 98: 2. Thereafter, the gradient flow rate is 1 mL / min. So that it is 98: 2 to 55:45 over 15 to 50 minutes.
Column temperature: 40 ° C
Measurement wavelength: 326 nm
Standard substance: Chlorogenic acid (Wako Pure Chemical Industries, Ltd.)

  From the results shown in Table 5, it can be seen that all the powders subjected to the heat treatment with hot water having a pH of 5.6 or more, that is, the measured powders contain a high proportion of characteristic polyphenols derived from sweet potato foliage. In particular, powders (1, 2, 4, 11, 12, 18, and 19) that have been heat-treated with hot water at pH 5.6 or higher and 80 ° C. or higher have pH 5.6 or higher and 70 ° C. Compared with powder (powder 10) heat-treated with hot water, the content of chlorogenic acid (II) (CHA) in the powder is high, and dicaffeoylquinic acid (III) (diCQA) and tricaffeoyl oil It can be seen that the total amount (III + IV) of quinic acid (IV) (triCQA) is high. The heat treatment conditions for containing a high proportion of the characteristic polyphenols of this sweet potato stover are pH 6.6 or more and less than 8.4 from the comparison of powders 1, 2, and 4, It can be seen that the temperature is 90 ° C. or higher from the comparison of powders 10 to 12, and the heat treatment time is preferably within 3 minutes, particularly within 2 minutes, from the comparison of powders 18 and 19.

(Example 15)
Shiroyutaka seed buds were planted and cultivated, and the foliage grown to about 30 cm from the ground was cut off and washed twice with water to obtain 5 kg of sweet potato foliage. 5 kg of this sweet potato stover was immersed in 2 L of hot water (97 ° C.) adjusted to pH 7.6 with sodium bicarbonate for 1 minute. Then, it was immediately immersed in water at 25 ° C. and cooled. The obtained sweet potato stover heat treatment product was pulverized using a food processor, and further pulverized using a mass collider to obtain a paste. This paste was heat-dried at 120 ° C. using a rotary dryer (drum dryer: JOHN-MILLDER research and development drum dryer tester, manufactured by Johnson Boiler Co., Ltd.), and the dried powder of sweet potato stalks and leaves was treated with 0. 5 kg was obtained.

(Example 16)
Stalks and leaves that grew to about 30 cm from the ground of Shiroyutaka were cut and washed twice with water to obtain 1.5 kg of sweet potato leaves. 1.5 kg of this sweet potato stover was immersed in 2 L of hot water (90 ° C.) adjusted to pH 7.3 for 1 minute. Then, it was immediately immersed in water at 25 ° C. and cooled. The resulting sweet potato foliage heat-treated product is centrifuged for 30 seconds and dehydrated to a certain extent, and then dried with warm air at 70 ° C. for 2 hours so that the water content of the sweet potato foliage heat-treated product is about 20% by weight (primary Dried). Next, warm air drying (secondary drying) was performed at 80 ° C. for 4 hours so that the final moisture content of the sweet potato foliage heat-treated product was 3% by weight. The dried product of the heat-treated sweet potato stover obtained was roughly pulverized (cut) to a size of about 5 mm using a cutter. Next, steam sterilization was performed using a saturated water vapor pressure of 150 ° C. for 3 seconds. Further, the coarsely pulverized product was dried, and then finely pulverized using a hammer mill so that 90% by weight passed through the 200 mesh section, thereby obtaining a fine powder of the sweet potato foliage heat-treated product. The powder of this sweet potato foliage heat-treated product had an excellent green color that could be used as a green juice when dissolved in water. This green juice had little bitterness and puffiness and had good palatability.

  The method of the present invention includes a step of heat-treating sweet potato foliage at a pH of 5.6 or higher, whereby a processed sweet potato foliage product having a high polyphenol content and / or antioxidant activity can be obtained. This processed sweet potato stem and leaf product is further excellent in the stability such as the color inherent in the sweet potato stem and leaf, has little bitterness and taste, and is excellent in palatability. The processed sweet potato stover obtained by this method is used as a food raw material (for example, green juice).

Claims (2)

A method for producing a processed sweet potato stover with a high polyphenol content and / or antioxidant activity,
A method comprising a step of heat-treating sweet potato stems and leaves at pH 5.6 or higher.   The method according to claim 1, wherein the heat treatment is performed at a temperature higher than 80 ° C.