Mulberry leaf exhibiting reduced accumulation of calcium oxalate monohydrate crystal with complete yellowing

Abstract

To develop a cultivation technique that enables provision of mulberry leaves sufficiently reducing the content of calcium oxalate monohydrate crystals which are associated with food poisoning concerns, from the perspective of provision of safe and reliable food; and to enable complete yellowing of mulberry leaves and enhance the content of a flavonoid pigment.SOLUTION: Since mulberry is a C3 plant and its photosynthetic activity is particularly susceptible to photoinhibition, light receiving posture, such as a leaf angle, has a significant impact on the photosynthetic capacity of the plant community. Therefore, establishment of a cultivation environment (e.g., pruning, planting density) that account for leaf blade inclination angle, regulation of a photosynthetic amount through appropriate shading control, and use reduction of lime to an upper limit for soil management, are actively examined.SELECTED DRAWING: Figure 1, Figure 6

Description

Technical Field

[0001] The present invention relates to the discovery that by a new soil and fertilizer management method, it is possible to almost completely suppress the accumulation of calcium oxalate monohydrate crystals in the leaves of mulberry trees used for sericulture and tea raw materials. At the same time, it relates to the discovery that when the leaves of mulberry trees are yellowed based on a new soil and fertilizer management method, the whole leaf turns yellow and the color density of the leaf is increased to the color density of ginkgo leaves.

Background Art

[0002] Leaves collected from mulberry (Morus alba L.) are not only used in the sericulture industry, but also contain flavonoids (morusin, kuwanon A) and triterpenes (α-amyrin acetate), and have been highly regarded in traditional Chinese medicine and have been said to have antipyretic, antitussive, and thirst-improving effects for diabetes. In recent years, it has been reported that mulberry leaf extract suppresses the formation of β-amyloid and suppresses hippocampal neuron death induced by β-amyloid, and the flavonoids released from mulberry leaves have been confirmed to have an effect of suppressing β-amyloid formation (Non-Patent Document 1). Furthermore, the α-glucosidase inhibitory action of 1-deoxynojirimycin (DNJ) contained in mulberry sap (Non-Patent Document 1) has attracted attention, and products made from mulberry leaves, including from the perspective of so-called "weight loss drugs", are penetrating not only among health-conscious elderly people but also among young people. Regarding the thermal stability of DNJ, there are reports of about 100°C - 121°C (Non-Patent Documents 2 and 3), and it is considered that DNJ can be used without being altered when making tea from mulberry leaves. In addition to DNJ, the blood pressure-lowering action of γ-aminobutyric acid released from mulberry leaves (Non-Patent Document 4) and the fatigue-reducing action of arginine (Non-Patent Document 5) have attracted attention.

[0003] When paying attention to the metabolism of mulberry, there are characteristics not seen in other plants. That is, as it grows, it accumulates calcium carbonate in the giant cells on the upper surface layer of the leaves (Non-Patent Document 6). On the other hand, since photosynthesis occurs in the leaves, ascorbic acid is synthesized from the saccharides produced by photosynthesis via the D-mannose / L-galactose pathway (Non-Patent Document 7). Ascorbic acid is decomposed into oxalic acid and threonine. Also, glycolic acid produced by photosynthesis also becomes oxalic acid (Non-Patent Documents 8 and 9). Therefore, in the case of mulberry, calcium ions transported from the roots to the leaves are accumulated as calcium carbonate in the giant cells, and in addition, they combine with oxalic acid generated from photosynthesis to produce calcium oxalate, which is then accumulated in the leaves. Calcium oxalate has actually been detected in mulberry leaves (Non-Patent Document 10). The crystals of calcium oxalate monohydrate are stored as needle-like crystals in the living tissue of the leaves (Non-Patent Document 11).

[0004] When consuming foods containing crystals of calcium oxalate monohydrate, the crystals of calcium oxalate monohydrate are needle-shaped (there is a risk of piercing the inner membrane of the digestive tract), and also show water solubility (8.8 ppm (25 °C), 11.8 ppm (100 °C)) (Non-Patent Document 12). Since the pH of gastric acid is a strong acid showing 1 (Non-Patent Document 13), calcium oxalate may be decomposed in the stomach to become oxalic acid. Therefore, when consuming foods containing a large amount of crystals of calcium oxalate monohydrate, there is a risk of developing poisoning. Actually, on the homepage of the Food Safety Commission of the Cabinet Office (Non-Patent Document 14), a food poisoning case (September 20, 2016) suspected of being related to calcium oxalate crystals by the Centre for Health Protection of the Department of Health of Hong Kong has been published.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 6

Non-Patent Document 7

Non-Patent Document 8

Non-Patent Document 9

Non-Patent Document 10

Non-Patent Document 11

Non-Patent Document 12

Non-Patent Document 13

Non-Patent Document 14

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the cultivation of mulberry soil, in the conventional cultivation method of spraying, for example, 1-2 kg of calcined magnesia lime per mulberry tree (about 10 square meters) every autumn evening, there is a concern about the accumulation of excessive calcium oxalate monohydrate crystals on the mulberry leaves. When making tea using mulberry leaves with a large amount of calcium oxalate monohydrate crystals accumulated, there is a risk that the calcium oxalate monohydrate crystals will be released from the leaf tissue and exposed on the surface of the tissue during the kneading process, or that the calcium oxalate monohydrate crystals will dissolve in water and regenerate needle-like crystals on the surface of the tissue. On the other hand, in the leaves of the tea plant (Camellia sinensis) that has been consumed for a long time, significant calcium transport such as that occurring in mulberry leaves does not occur, so the formation of calcium oxalate monohydrate crystals is hardly observed. From the perspective of providing safe and secure food, in order to utilize mulberry leaves as food, the development of cultivation techniques to suppress the accumulation of calcium oxalate monohydrate crystals in mulberry leaves is desired.

Means for Solving the Problems

[0007] Mulberry is a C3 plant, and since photosynthesis is particularly susceptible to light inhibition, the light-receiving posture such as the leaf angle has a significant impact on the photosynthetic ability of the plant community. Therefore, as a result of earnestly studying the preparation of the cultivation environment (pruning, planting density, etc.) considering the leaf inclination angle, the adjustment of the photosynthetic amount by appropriate shading management, and the reduction of the use of lime for soil management to the limit, the present invention has been achieved.

Effects of the Invention

[0008] As shown in Example 1, when exploring for calcium oxalate monohydrate crystals in mulberry leaves at the time when the sericulture work in mid-October is completed and at the stage before yellowing of the leaves, as shown in Figure 1, almost no diffraction peaks of calcium oxalate monohydrate crystals could be confirmed. Even at the stage in mid-November when the leaves were yellowed, as shown in Figure 2, the maximum diffraction peak intensity (arrow a) of the observed calcium oxalate monohydrate crystals was only 15% = (100 × a / b) compared to the maximum peak intensity (arrow b) of the mesophyll tissue where the diffraction peak occurred, which was extremely small. X-ray diffraction measurements of mulberry leaves grown under conventional cultivation methods in mid-October (as shown in Figure 3 of Comparative Example 1) revealed significant diffraction peaks of calcium oxalate monohydrate crystals. When mulberry leaves with these properties are processed into tea, the evaporation of water and the drying and shrinkage of the leaves during the tea-making process result in the liberation and concentration of organic and inorganic substances contained in the leaves. Focusing on calcium oxalate monohydrate crystals, there is a risk that calcium oxalate monohydrate crystals may be liberated from the leaf tissue during the rolling process and adhere to the surface of the finished tea leaves, or that calcium oxalate monohydrate crystals may dissolve in water and regenerate needle-like crystals on the surface of the finished tea leaves. X-ray diffraction measurements of commercially available mulberry tea leaves revealed a significant increase in the diffraction peak of calcium oxalate monohydrate crystals, indicating a significant increase in the concentration of calcium oxalate monohydrate crystals, corresponding to the component concentration effect during the tea-making process (as shown in Figure 4 of Comparative Example 2). When the commercially available mulberry leaf tea used in Comparative Example 2 was strained and drunk, chemical mediators such as histamine were secreted from the blood vessels about two hours after drinking, causing an itchy rash to appear all over the body, and a fever, as shown in Figure 5 of Comparative Example 3. The patient then sought emergency medical attention. This was thought to be food poisoning, possibly related to calcium oxalate crystals. Since the mulberry leaves of the present invention contain almost no calcium oxalate monohydrate crystals before they turn yellow, even if mulberry leaves picked when they are green are made into tea and served as tea, it is possible to at least avoid the occurrence of food poisoning associated with calcium oxalate monohydrate crystals. On the other hand, when mulberry leaves were yellowed using the cultivation method of the present invention, the color intensity of the leaves was comparable to that of fully yellowed ginkgo leaves, as shown in Figure 6 of Example 3. Since the wavelengths of light at which the color intensity peaks are generated are different, it is clear that there are differences in the structure and composition of the pigments that cause the coloration. However, it is speculated that the content of flavonoid pigments in the mulberry leaves of the present invention may be comparable to that of ginkgo leaves, and it is expected that products utilizing these flavonoid pigments will be provided. [Brief explanation of the drawings]

[0009]

Figure 1

Figure 2

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Figure 6

Mode for Carrying Out the Invention

Example

[0010] Leaves of the variety "Hayatezakari" of the Colocasia esculenta var. antiquorum grown based on a new cultivation method were collected on October 17, 2023, refrigerated, and on October 19, 2023, wide-angle X-ray diffraction measurements were performed on the vein part and mesophyll part of the leaves. As a result, the diffraction intensity curves shown in Fig. 1 were observed for each part. Diffraction peaks corresponding to the crystal peaks of calcium oxalate monohydrate were hardly observable at a trace level.

Example

[0011] Leaves of the variety "Hayatezakari" of the Colocasia esculenta var. antiquorum that grew based on a new cultivation method and had yellowed leaves were collected on November 12, 2023, refrigerated, and on November 21, 2023, wide-angle X-ray diffraction measurements were performed on the vein part and mesophyll part of the leaves. As a result, the diffraction intensity curves shown in Fig. 2 were observed for each part. Diffraction peaks corresponding to the crystal peaks of calcium oxalate monohydrate were observed in the mesophyll part. However, the ratio of the maximum peak intensity (arrow a) of the calcium oxalate monohydrate crystal to the peak intensity (arrow b) of the mesophyll tissue was 15.0% (= 100 × a / b). Comparative Example 1

[0012] Leaves of the variety "Ichinose" of the Colocasia esculenta var. antiquorum grown based on a conventional cultivation method were collected on October 6, 2023, refrigerated, and on October 11, 2023, wide-angle X-ray diffraction measurements were performed on the vein part and mesophyll part of the leaves. As a result, the diffraction intensity curves shown in Fig. 3 were observed for each part. Diffraction peaks corresponding to the crystal peaks of calcium oxalate monohydrate were significantly observed in the vein part. The ratio of the maximum peak intensity (arrow a) of the calcium oxalate monohydrate crystal to the peak intensity (arrow b) of the vein tissue was 31.4% (= 100 × a / b). Comparative Example 2

[0013] Regarding commercially available mulberry leaf tea (100% mulberry leaves), when wide-angle X-ray diffraction measurements were performed on the vein part and the mesophyll part, the diffraction intensity curves shown in Fig. 4 were observed for each part. Diffraction peaks corresponding to the crystal peaks of calcium oxalate monohydrate were confirmed in both parts, but were particularly prominent in the vein part. The ratio of the maximum peak intensity of calcium oxalate monohydrate crystals (arrow a) to the peak intensity of the vein tissue (arrow b) was 75.6% (= 100 × a / b). Comparative Example 3

[0014] The mulberry leaf tea (100% mulberry leaves) of Comparative Example 2 was purchased on June 24, 2023. Around 15:00 on the same day, about 3 g of the mulberry leaf tea was placed in a tea strainer and set in a teacup, and freshly boiled hot water was poured in. After nearly 1 minute, the tea strainer was removed and the tea was drunk (no snacks were eaten during drinking. The tea of mulberry leaves was drunk alone). Two hours after drinking, itching occurred on both hands, and then itching and rashes occurred on the knees, roots of the legs, inner sides of the elbows, back, and abdomen. On the next day, June 25, at 11:00, a fever was felt and the body temperature was measured to confirm 37.2°C. After that, a fever of about 37°C continued, and the rash became severe. Around 21:30 on the same day, a night clinic was visited at Kiryu General Hospital. After receiving a prescription of 60 mg of fexofenadine hydrochloride tablets, twice a day after breakfast and dinner, it was taken immediately after returning home. Note that fexofenadine hydrochloride tablets have the effect of suppressing the action of histamine and relieving itching and inflammation. It is prescribed for urticaria, eczema, dermatitis, etc. At around 2:00 am on June 26, it was confirmed that the swelling of the arms and abdomen had subsided slightly. On June 26, a general outpatient visit was made at Kiryu General Hospital, and a prescription of 60 mg of Allegra tablets, twice a day after breakfast and dinner for 14 days, was received and the intake was started, and eventually the skin returned to normal. Note that Allegra tablets have the effect of improving allergic rhinitis, urticaria, and itching. A photo of the back of the knee taken after 21:00, just before receiving night clinic at Kiryu General Hospital on June 25, is shown in Fig. 5. The rash and swelling on the back of the knee, especially on the back of the calf, are severe.

Example 3

[0015] Based on a new cultivation method, the leaves of the Karayamagwa variety "Hayatezakari" that had grown and turned yellow were collected on December 3, 2023, refrigerated, and the color density was measured on December 4, 2023. Also, on December 4, 2023, ginkgo leaves that had completely turned yellow and fallen were collected and the color density was measured. The measurement of the color density was carried out under the conditions of a D65 light source and a 10° field of view. The wavelength dependence of the color density K / S was obtained from the spectral reflectance curve and is shown in Figure 6. The conversion from the reflectance R at each light wavelength to the color density K / S was calculated using the Kubelka-Munk equation, that is, K / S = (1 - R) 2 / 2R. The wavelengths of the light that give the maximum color density K / S values for both are different, but the maximum values for both are almost the same.

Claims

Claim 1 Among the leaves of the mulberry tree of the genus Morus in the Moraceae family before yellowing, when measuring the X-ray diffraction of the leaf tissue, the leaf in which the maximum value of the diffraction peak intensity of the calcium oxalate monohydrate crystal observed is reduced to the trace level. Claim 2 Among the leaves according to Claim 1, even at the stage of yellowing, when measuring the X-ray diffraction of the leaf tissue, regarding the diffraction peak intensity of the calcium oxalate monohydrate crystal observed, the leaf in which the maximum value (a) of the diffraction peak intensity is 20% or less with respect to the maximum value (b) of the diffraction peak intensity of the leaf tissue where the peak is observed. Claim 3 Among the leaves according to Claim 1, the leaf in which the whole leaf has turned yellow and the average value of the color density K / S of the leaf is 9 or more. Claim 4 The leaves according to Claims 1 to 3 are the leaves of the mulberry tree of the genus Morus in the Moraceae family classified into the Karayama-magwa group. Claim 5 The leaves according to Claims 1 to 3 are the leaves of the variety "Hayate-sakari" of the mulberry tree of the genus Morus in the Moraceae family classified into the Karayama-magwa group.

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