In the field of research and application of plant raw materials, spanning from traditional Chinese medicine to modern cosmetics, food, and biopharmaceutical industries, how to efficiently and accurately obtain the active ingredients from plants has always been the core issue that scientific researchers and industry practitioners are constantly exploring. The pretreatment process of plant raw materials, as the opening prelude of the entire process, is of self-evident importance. It is like a precise key that unlocks the door to the efficient utilization of plant raw materials.
I. Impurity Removal: The First Step to Ensure the Purity of Raw Materials
After being harvested, plant raw materials are like unpolished jade just out of nature, carrying natural traces and impurities. At this time, it is crucial to carry out the impurity-removal work quickly and meticulously. While the plant tissues are still intact, scientific researchers and technicians need to race against time to pick out the mixed dead branches, fallen leaves, weeds, and other impurities one by one, and then wash off the attached soil with clean water. This process is not just a simple cleaning; it is also laying a solid foundation for the subsequent extraction work at the source. After cleaning, according to the different requirements of storage, transportation, and subsequent processing, the fresh raw materials are cut into sections or slices to ensure the stable quality of the raw materials during the subsequent transfer process.
II. Drying: The Art of Balancing Preservation and Ingredient Retention
The drying stage is a key node in the pretreatment process of plant raw materials. It can not only extend the storage period of raw materials and facilitate transportation but also has a profound impact on the subsequent extraction of active ingredients. Different plant raw materials, due to the differences in their chemical compositions and properties, require different drying methods. For example, for raw materials such as Stephania tetrandra S. Moore, which are rich in alkaloids and sensitive to light, air-drying (drying in the shade) is a more ideal choice. Although the air-drying process causes relatively minor damage to the plant cell membrane, it can retain the active ingredients in the raw materials to the greatest extent. The sun-drying method, although it has a faster drying speed and causes greater damage to the cell membrane, which is beneficial for subsequent extraction, is significantly restricted by the local climate and weather conditions. If it encounters rainy weather during the sun-drying process, the raw materials are extremely prone to rot and mildew, resulting in ingredient loss and quality decline. In addition, for raw materials containing glycosides, it is necessary to inactivate the endogenous enzymes before drying. Because under suitable conditions, endogenous enzymes will promote the hydrolysis of glycosides, resulting in a large loss of active ingredients. Bitter almonds are a typical example in this regard.
III. Crushing: The Key Means to Improve Extraction Efficiency
The crushing process plays an important role in improving the extraction efficiency in the pretreatment of plant raw materials. By crushing the raw materials, the surface area of the raw materials can be significantly increased, thus greatly increasing the dissolution rate of active ingredients during the extraction process. However, the crushing particle size is not the smaller the better; it needs to be precisely controlled according to the type of raw materials. Generally speaking, the crushing particle size of root - and - grass-type raw materials can be relatively larger, while that of woody raw materials can be appropriately crushed finer. If the crushing particle size is too small, a series of problems will occur, such as the raw materials agglomerating and settling to the bottom, blocking the pipe holes and filters of the extraction equipment, etc. This will not only increase the difficulty of the extraction process but also may reduce the extraction efficiency and product quality.
IV. Fermentation and Hydrolysis: Opening up New Paths for Extraction
The application of fermentation and hydrolysis technologies has brought new breakthroughs and development opportunities to the field of plant raw material extraction. Using biological enzymes such as cellulase and pectinase can effectively break the structure of plant cell walls and cell membranes, thus increasing the dissolution rate of substances. This technology has shown significant advantages in the treatment of berry-type raw materials. The hydrolysis process can also convert saponin components into aglycones, improving their solubility in the extraction solvent. For example, in the extraction process of glycyrrhizic acid, the application of the hydrolysis process can significantly improve the extraction effect. More strikingly, through special fermentation processes with specific strains, the yield of target components can be greatly increased. Taking ginseng extract as an example, after special fermentation treatment, the content of rare saponins can be increased by nearly more than 500%, providing broad space for the in-depth development and utilization of plant raw materials.
V. Degreasing: A Necessary Treatment for Specific Raw Materials
For plant raw materials with a high content of oil and wax, degreasing is an essential pretreatment step. In the laboratory environment, a Soxhlet extractor is often used in combination with small - polar organic solvents such as petroleum ether for degreasing operations. In large - scale production, centrifugal degreasing and solvent degreasing (such as using petroleum ether, n - hexane, etc.) are more commonly used methods. These methods can effectively remove the oil and wax on the surface of plants or in seeds, avoiding their adverse effects on the subsequent extraction process and product quality. For example, in the extraction process of some plant oils, pre - degreasing can improve the purity and quality of the oil and reduce the damage of impurities to the extraction equipment at the same time.
VI. Special Treatment for Special Ingredients
For plant raw materials containing volatile oil components, due to the extremely easy loss of their volatile substances, the extraction operation needs to be carried out quickly in the fresh state to retain their unique aroma and active ingredients to the greatest extent. For components with biological activity such as proteins, enzymes, and nucleic acids, more careful care is required during the extraction process. The reasonable selection and application of the buffer system can maintain the normal dissociation state of the acid - base groups in the raw materials; the addition of protective agents can effectively protect the active centers of groups and enzymes; the use of inhibitors can inhibit the destruction of active ingredients by hydrolases. In addition, special conditions such as light - avoidance, anaerobic conditions, and strict temperature control are required. Every detail is closely related to the stability and effectiveness of biological active ingredients.
The pretreatment process of plant raw materials is a comprehensive technology that integrates the knowledge of multiple disciplines such as biology, chemistry, and engineering. It plays an irreplaceable and important role in various industries. From ensuring the stability of the efficacy of traditional Chinese medicine to improving the efficacy of cosmetics, from enriching the nutritional components of food to promoting the innovative development of the biopharmaceutical industry, every link is inseparable from these delicate and scientific pretreatment operations. With the continuous progress and innovation of science and technology, these processes will continue to be optimized and improved, bringing us more new methods and ideas for the efficient utilization of plant raw materials.
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