Serpentinite Applications: Effects of Surface-Ions-Modified Natural Silicate Minerals on Cultivation of Magnesium–Manganese-Enriched Garlics

Abstract

Serpentinite refers to a group of hydrated magnesium-rich natural silicate rocks. Because serpentinite contains metallic elements and has a layered structure, it can release magnesium ions when immersed in water. Garlic is a widely cultivated crop characterized by a rich chemical composition and many health benefits. Magnesium and manganese are essential nutrients for the human body. In garlic, magnesium stabilizes allicin and prevents its decomposition and release, and manganese promotes polysaccharide metabolism. In this study, serpentinite powder was modified using immersion plating and sintering to improve its crystallinity and ion release capability and enable the cultivation of magnesium–manganese-enriched garlic. An experimental analysis of growth characteristics confirmed the layered structure of serpentinite powder, with sintering effectively reducing impurities and enhancing the powder’s crystallinity and ion release capability. An evaluation of the powder’s specific surface area and ion release capability after surface treatment revealed that Mg-Si-Mn-O sintered at 400 °C for 1 h was the optimal powder for preparing magnesium–manganese ion water. Magnesium–manganese garlic grown with this water contained magnesium and manganese at concentrations of 38–43 and 11–17 mg/L, respectively, and had a higher concentration of allicin and sulfur compounds relative to garlic grown with distilled water. After natural drying, the allicin in the magnesium–manganese-enriched garlic remained stable, and the garlic was found to have a high moisture content. These findings jointly demonstrate the high nutritional value and antioxidant properties of garlic in applications involving serpentinite technology.

1. Research Background and Objectives

1.1. Growth Characteristics of Garlic

Garlic is widely consumed worldwide; it is easy to cultivate and is regarded as an essential perennial crop. In commercial cultivation, garlic is grown in an annual cycle with a growing period of approximately 10 months [1]. Its growth primarily requires abundant sunlight and water. At suitable temperatures, garlic grows well and produces many cloves. Its growth rate depends on the fertility of the soil, which should be loose and rich in organic matter, as well as the availability of sufficient water. High temperatures accelerate the growth of garlic [2]. Once mature, garlic is typically dug up and dried to prevent spoilage and to prepare it for storage and consumption.

1.2. Varieties and Flavors of Garlic

Garlic is grown across the globe. Its varieties differ by country, depending primarily on the climate, soil, and cultivation conditions. The following is an overview of garlic varieties from several key countries [3]:

• China: China is the world’s largest producer of garlic. It grows several types of garlic, including red, white, and green garlic. Red garlic is one of the most prominent varieties of garlic and is known for its strong, spicy flavor and firm texture. White garlic is another common variety with a milder taste and softer texture. Green garlic comprises tender stalks that are harvested at an early stage; it is highly nutritious and offers a fresh taste.
• France: French garlic is best represented by Rose de Lautrec, a variety distinguished by its strong fragrance. Rose de Lautrec is mainly grown in certain regions in southern France, where the climate and soil are particularly well suited for garlic growth.
• Spain: The most famous variety in Spain is Provence Wight, a white garlic known for its intense spiciness and aroma.

1.3. Chemical Composition and Health Benefits of Garlic [4,5,6]

Garlic is valued for its nutritional and medicinal properties, which stem from its chemical constituents. For example, allicin, also known as garlic essence, has strong antioxidant properties that effectively alleviate damage caused by free radicals. Allicin has antibacterial, antiviral, and cholesterol-lowering effects. It reduces blood pressure and promotes cardiovascular health. Garlic is also rich in sulfur compounds, such as diallyl trisulfide and diallyl disulfide, which have both anticancer and antioxidant effects. These compounds mitigate the risk of cancer by inhibiting the growth and spread of cancer cells. They also promote collagen production, facilitating the repair and regeneration of skin and connective tissues. Additionally, garlic is rich in polysaccharides, such as inulin and galactose, which promote immune function.

Garlic is a convenient source of vitamin C and essential minerals such as calcium, copper, iron, magnesium, manganese, and selenium. Vitamin C, a water-soluble vitamin, aids in the synthesis of collagen and enhances skin and vascular elasticity. Calcium is crucial for maintaining bone health and strength. Copper helps the body absorb iron and vitamin C, supporting the production of red blood cells. Iron is a key component of red blood cells. Magnesium facilitates the absorption and utilization of calcium and the maintenance of normal heart and muscle function. Manganese promotes lipid and carbohydrate metabolism, thereby contributing to bone and connective tissue health. Selenium is a key trace element with strong antioxidant and anticancer properties.

Garlic is associated with enhanced sexual function. Both allicin and sulfur compounds enhance circulation and increase blood flow, which can in turn alleviate erectile dysfunction. These compounds can also induce the secretion of sex hormones, such as testosterone, thereby enhancing sexual performance, stamina, and endurance.

1.4. Preservation and Consumption of Garlic [7]

Garlic is often dried in commercial applications. Fresh and dried garlic differ in several characteristics. First, dried garlic is easier to store and use; it can be stored for several years, whereas fresh garlic can be stored for only a few weeks. In addition, dried garlic can be easily ground into powder or chopped for use in cooking. Second, dried garlic retains the rich flavor of fresh garlic for seasoning, and certain components are broken down and released during the drying process such that the human body can more easily digest and absorb them. Finally, the duration and temperature at which dried garlic is stored can affect its allicin and antioxidant content.

1.5. Importance of Magnesium and Manganese to the Human Body [8,9]

Magnesium is an essential nutrient for the human body. It is involved in more than 300 chemical reactions, including protein synthesis, bone formation, and DNA synthesis. The Health Promotion Administration of the Ministry of Health and Welfare of Taiwan recommends that adults consume approximately 400 mg of magnesium daily because of its crucial role in protein digestion and vitamin D metabolism.

A magnesium deficiency can lead to symptoms such as muscle twitching, cramps, or spasm; fatigue, irritability, and depression; frequent headaches and soreness; and premature aging. Such a deficiency often occurs early in the aging process, with its risk increasing with aging. Notably, calcium and magnesium are antagonistic; in other words, excessive intake of calcium can deplete magnesium levels, potentially leading to health risks such as kidney stones, cardiovascular disease, and cancer.

Manganese is an essential trace element involved in various metabolic processes and physiological functions. A manganese deficiency may lead to symptoms such as fatigue, high blood cholesterol levels, abnormal fat metabolism, poor bone development, and muscle spasms. The World Health Organization recommends that adults consume 2–3 mg of manganese daily. Among the functions of manganese in the human body are (1) improving bone and connective tissue health; (2) mitigating the risk of disease through its antioxidant properties; (3) regulating blood sugar levels by improving lipid and carbohydrate metabolism and reducing inflammation; (4) alleviating symptoms of premenstrual syndrome when combined with calcium; (5) enhancing thyroid function and preventing weight gain and hormonal imbalances; and (6) promoting collagen formation in skin cells, thereby aiding in wound healing. Increasing the concentration of magnesium in garlic enables the formation of magnesium–sulfur compounds, which stabilize allicin and prevent its decomposition and release. Additionally, increasing the concentration of manganese in garlic can promote the metabolism of polysaccharides. Therefore, magnesium and manganese optimize the stability of garlic’s chemical composition, reducing the degradation of allicin and antioxidants during the drying process and enhancing the overall nutritional benefits of garlic.

1.6. Characteristics of Natural Serpentinite Materials [10,11,12,13,14,15,16,17,18,19]

Serpentinite is a term that refers to metamorphic, hydrated, magnesium-rich silicate minerals. These minerals have the chemical formula Mg₃Si₂O₅(OH)₄. Each of these minerals has a unique degree of metamorphism. Serpentinite is composed of both major minerals, such as serpentine minerals (e.g., antigorite and chrysotile), and minor minerals (e.g., olivine, pyroxene, dolomite, calcite and magnetite).Natural serpentinite is typically dark green in color, with a texture similar to that of snake skin. Because of its hardness and glossy surface, natural serpentinite is widely used in construction materials. Serpentinite often contains minerals such as plagioclase, amphibole, and olivine, along with compounds such as silicon dioxide and iron oxide. Serpentinite also contains many metallic elements and is conductive. When immersed in water, it releases magnesium ions; hence, it is suitable for cultivating magnesium-rich crops. In Japan, serpentinite-rich rice has been successfully grown and used to produce serpentinite-rich sake. This study focused on serpentinite obtained from Hualien County, Taiwan.

1.7. Cultivation and Characteristics of Magnesium–Manganese-Enriched Garlic

In this study, magnesium–manganese-enriched garlic was cultivated. Powdered natural serpentinite rich in magnesium was soaked in a food-grade manganese citrate solution for a certain period before it was removed and sintered at high temperatures to produce serpentinite powder containing both magnesium and manganese (high-temperature baking was conducted to reduce the concentration of impurities). This powder was added to soil that was subsequently used to cultivate Chinese red garlic, and its growth characteristics were examined. After the chemical composition, including the magnesium and manganese content, of the enriched garlic was analyzed, its shelf life was determined. Finally, the enriched garlic was dried to measure its content of allicin and sulfur compounds.

2. Experimental Procedures and Methods

2.1. Preparation of Serpentinite Powder and Immersion Plating and Sintering

Before cultivation, serpentinite rocks were crushed into blocks, and these blocks were ground into a fine powder, with particle sizes ranging from 30 to 180 μm, by using a milling machine. This raw serpentinite powder is hereinafter referred to as magnesium silicate powder (Mg-Si-O). This raw powder was soaked in a food-grade manganese citrate solution (5 wt.%) for 1 h at 60 °C before it was air-dried. This process, referred to as immersion plating, enabled the raw powder to absorb manganese ions. Finally, the powder was baked and sintered in an oven at 400, 600, or 800 °C for 1 h, yielding three types of powder for comparison. This sintering process both eliminated impurities in the raw powder and enhanced its crystallinity by facilitating the crystallization of manganese ions. The resulting manganese-containing powder is hereinafter referred to as magnesium–manganese silicate powder (Mg-Si-Mn-O) [13].

Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to examine the powder’s microscopic characteristics and determine its composition. X-ray diffraction (XRD) was used to analyze the powder’s phase structure and crystallinity. Fourier transform infrared spectroscopy (FTIR) was used to examine the bonding characteristics of each powder sample. Raman spectroscopy was used to determine the powder’s compound structure. To calculate the concentration of the released ions, the powder’s specific surface area was measured, and elemental identification was performed using inductively coupled plasma mass spectrometry (ICP-MS).

2.2. Ion Release Test

An ion release test is a test that measures a powder’s ability to release ions into a liquid. This test is commonly used to evaluate material release performance, drug delivery systems, and biomaterials [14]. In this study, 5 g of the prepared powder was immersed in 100 mL of distilled water at 60 °C for 1 h and diluted to 1000 mL. Subsequently, the concentration of magnesium and manganese ions in the extracted solution was determined using ICP-MS. This solution containing magnesium and manganese ions is hereinafter referred to as magnesium–manganese water. By extension, the garlic grown with magnesium–manganese water (experimental group) and the garlic grown with distilled water (control group) are referred to as magnesium–manganese garlic and distilled water garlic, respectively.

2.3. Garlic Cultivation Test and Composition Analysis

Garlic was cultivated for both the experimental and control groups. For each group, a total of 25 garlic cloves were planted in potting soil at a depth of approximately 5 cm, with a spacing of approximately 10 cm between each clove. The cloves were watered every 2 days with magnesium–manganese water for the experimental group or with distilled water for the control group to maintain a soil moisture content of over 50%. They were also exposed to sunlight for half a day at room temperature for a period of 10 weeks. After harvesting, the composition of fresh garlic (also known as wet garlic) in each group was analyzed. Some of the harvested garlic in each group was subjected to natural air drying for 7 days, resulting in dried garlic, whose composition was analyzed. Liquid chromatography–mass spectrometry (LC-MS) was used to determine the concentrations of allicin and sulfur compounds per unit weight for each of the four groups (wet and dry experimental and control groups).

3. Results and Discussion

3.1. Characteristics of Serpentinite Powder and Surface Manganese Modification

Figure 1 depicts a photograph of raw serpentinite and its powder forms at each step of grinding. The raw serpentinite sample was dark green in color. SEM and EDX analyses were conducted to examine the powder’s characteristics and composition. The results indicated that the powder had a fragmented particle morphology with particle sizes ranging from 30 to 180 μm (Figure 2). Some particles had a loose surface structure. EDX analysis of multiple points on the particles’ surfaces confirmed that the primary components of the powder were magnesium, silicon, and oxygen. As outlined in [14], natural serpentinite is primarily composed of magnesium silicate, and it can release magnesium ions through dissolution. Surface roughness can increase surface area and thereby increase the rate of ion dissolution.

Briefly, 5 g of raw serpentinite powder was dissolved in 100 mL of food-grade manganese citrate solution (5 wt.%) at 60 °C for 1 h to enable the raw powder to absorb manganese ions. The powder was then filtered and subjected to atmospheric baking and sintering at 400, 600, or 800 °C for 1 h, yielding three manganese-containing powders. These magnesium–manganese silicate powders were labeled as Mg-Si-Mn-O-400, Mg-Si-Mn-O-600, and Mg-Si-Mn-O-800 [13]. Experimental analysis revealed that high-temperature baking and sintering enhanced the crystallinity of the powders. Figure 3 shows images of Mg-Si-Mn-O-400, revealing a substantial reduction in the looseness of the surface structure. The powder had a layered structure, with an average interlayer spacing of approximately 1 μm. This layered structure readily appeared after sintering, indicating that the process eliminated low-melting-point impurities and improved crystallinity. It also facilitated the release of magnesium ions and promoted the adsorption of manganese ions.

Figure 4 presents the characteristics of the Mg-Si-Mn-O-400 powder along with its chemical composition spectra obtained from multiple regions. The powder’s surface contained elemental magnesium, silicon, manganese, and oxygen, with a manganese content reaching 40–47 wt.%. These results indicated that the powder successfully absorbed manganese ions, which were subsequently integrated into the silicate surface lattice. Increasing the sintering temperature to 600 °C (Figure 5) reduced the surface manganese content to 3–35 wt.%, with substantial variability between samples. Further increasing the temperature (Mg-Si-Mn-O-800, Figure 6) substantially reduced the surface manganese content in all samples (<2 wt.%), suggesting that the manganese ions were volatilized at these high temperatures.

Because of the low concentration of manganese on the surface of the powder at 800 °C, further analyses were conducted only for the Mg-Si-Mn-O-400 and Mg-Si-Mn-O-600 powders. Figure 7 presents the XRD patterns of these powders and those of the unbaked powders. The results indicated that both baking and sintering improved phase crystallinity, with a manganese compound phase (MnO: JCPDS 18-0802) observed in the manganese-modified powders. The diffraction intensity was greater for the Mg-Si-Mn-O-400 powder than for the Mg-Si-Mn-O-600 powder, indicating that the volume fraction of manganese compounds was highest in the powder sintered at 400 °C for 1 h.

Figure 8 depicts the FTIR spectra of the Mg-Si-O, Mg-Si-Mn-O-400, and Mg-Si-Mn-O-600 powders. These spectra confirm that the structure of the serpentinite powders remained largely unchanged after baking and sintering (619, 660, 1018, 1108, 1420, 1641, 2853, 2928, 3410, and 3678 cm⁻¹). Overall, the Raman spectra of the powders (Figure 9) reveal slight differences between the Mg-Si-O and Mg-Si-Mn-O powders. These differences are primarily attributable to the increased stability of the powder compound phases resulting from sintering and the contribution of the magnesium–manganese compounds to the powder’s surface.

3.2. Cultivation and Growth Characteristics of Magnesium–Manganese Garlic

Ion release tests were conducted for the Mg-Si-O and Mg-Si-Mn-O powders. Briefly, 5 g of each powder was soaked in 100 mL of distilled water at 60 °C for 1 h. After the mixture was allowed to rest, samples were obtained, and the concentrations of magnesium and manganese ions were measured using ICP analysis. As shown in

Table 1. Ion release rates of raw and baked sintered powder at a water temperature of 60 °C.

mg/L	Mg-Si-O	Mg-Si-Mn-O-400	Mg-Si-Mn-O-600	Mg-Si-Mn-O-800
Mg ion	80.33	110.92	133.81	90.18
Mn ion	N/A	38.76	16.59	1.90

, immersion plating resulted in an increase in the concentration of the released magnesium ions. When the sintering temperature was increased, the concentration initially increased and then decreased. These results indicated that the high-temperature sintering process enhanced the crystallinity of the powder, but the layered structure of the powder became prone to collapse, affecting its ability to release magnesium ions. During the immersion plating process, manganese ions were adsorbed onto the surface of the powder. Sintering at 800 °C caused these ions to volatilize and be lost, thereby reducing the concentration of manganese on the surface and consequently decreasing the powder’s ion release capability.

Generally, the ion release capability of a powder is closely related to its specific surface area.

Table 2. Specific surface areas of raw and baked sintered powder.

	Mg-Si-O	Mg-Si-Mn-O-400	Mg-Si-Mn-O-600	Mg-Si-Mn-O-800
m2/g	42.82	61.50	60.92	56.47

lists the specific surface areas of the Mg-Si-O and Mg-Si-Mn-O powders. The values obtained for the Mg-Si-Mn-O powder were consistently higher than those obtained for the Mg-Si-O powder. As mentioned (Figure 3), the high-temperature sintering process transformed the loose powder into a more compact, block-like structure. This process not only enhanced the crystallinity of the powder but also strengthened its layered structure and increased its surface roughness. These effects increased the specific surface area of the powder, which in turn improved its ion release capability.

Among all three powders, Mg-Si-Mn-O-400 exhibited the greatest magnesium and manganese ion release capability. Therefore, it was used to prepare magnesium–manganese water, which was subsequently added to potting soil for garlic cultivation. This magnesium–manganese water was prepared by soaking 5 g of Mg-Si-Mn-O-400 powder in 100 mL of distilled water at 60 °C for 1 h, followed by dilution to 1000 mL. Objective findings on the ion transport effect were obtained through an analysis of the potting soil (solution chemistry of soil after immersion,

Table 3. Analysis results of potting soil composition (by ICP) and pH value.

	Na	P	K	Ca	Mg	Fe	Zn	Mn	pH
mg/g	10.2	35.4	158.2	111.7	0.5	1.6	0.8	0.0	7.2

). The results indicated that the potting soil was neutral (pH 7.2) and contained large amounts of potassium and calcium. However, the concentration of magnesium ions was very low (0.5 mg/g), with no manganese detected.

Experimental garlic was grown in the presence of magnesium–manganese water, whereas control garlic was grown in the presence of distilled water. Figure 10 depicts photographs of representative samples obtained from the two groups after harvesting. The results indicated that, compared with the control garlic, the experimental garlic had more roots and cloves. The moisture content of both the wet and dried garlic in the two groups was measured, and the concentrations of allicin and sulfur compounds were examined using LC-MS. The results are presented in

Table 4. Analysis of magnesium and manganese concentrations and composition in garlic.

	Mg Ion (mg/L)	Mn Ion (mg/L)	Allicin Content (mg/g)	Sulfur Compounds (mg/g)	Moisture Content (%)
Magnesium–manganese water–wet garlic	38.22	17.42	12.85	8.53	42.15
Distilled water–wet garlic	1.81	0	10.14	7.34	40.57
Magnesium–manganese water–dried garlic	42.92	11.72	11.40	8.04	26.00
Distilled water–dried garlic	0.46	0	5.70	6.01	24.28

. Both the wet and dried experimental garlic had considerably higher concentrations of magnesium and manganese compared with the control garlic; they also had slightly higher concentrations of allicin and sulfur compounds. Drying did not considerably reduce the concentration of allicin in the experimental garlic. In other words, the concentration of allicin slightly decreased from 12.85 mg/g in the wet garlic to 11.40 mg/g in the dried garlic. Finally, the moisture content of the experimental dried and wet garlic was higher than that of the corresponding control garlic, indicating that the magnesium–manganese garlic had stronger antioxidant properties.

4. Conclusions and Future Prospects

In this study, natural serpentinite was ground into a powder form and used to prepare natural magnesium–manganese ion water. This water was used to cultivate magnesium–manganese garlic, which has many health benefits. Additionally, the growth characteristics of this garlic were investigated. A heat-based surface modification was applied to enhance the crystallinity and ion release capability of the magnesium–manganese powder. The results indicated that the Mg-Si-Mn-O-400 powder retained its layered structure and had a high specific surface area, resulting in an excellent magnesium and manganese ion release capability. Compared with garlic grown in the presence of distilled water, garlic grown in the presence of magnesium–manganese ion water had stronger antioxidant properties and higher concentrations of allicin and sulfur compounds. This fortified garlic variant can be used as a dietary supplement to boost immunity and prevent diseases.

This study spans multiple fields, including mineral resource management, powder material engineering, agriculture, and biotechnology. It introduces a novel cultivation technique for magnesium–manganese-enriched garlic with anticancer properties. A certification for a trademark of magnesium-enriched agricultural products and a patent for magnesium–manganese ion water have already been obtained. In the future, this garlic fortification technique can be extended to garlic vinegar to enhance its accessibility and enable more people to enjoy its health benefits.