The drying process of honeysuckle flower tea is a crucial step affecting the retention of its active substances, with chlorogenic acid being the core component. Its stability directly determines the quality and efficacy of the flower tea. Different drying methods, through differences in temperature, time, and mechanisms of action, significantly impact the retention of chlorogenic acid and other active substances, requiring a comprehensive analysis considering both the process principles and the characteristics of the components.
The ortho-phenolic hydroxyl group in the chlorogenic acid molecule makes it susceptible to oxidative condensation under the catalysis of polyphenol oxidase, forming a high-molecular-weight colored substance. This characteristic necessitates strict control of temperature and time during the drying process: slow drying at low temperatures increases polyphenol oxidase activity with rising temperature, accelerating the oxidative decomposition of chlorogenic acid; rapid drying at high temperatures inhibits the oxidation reaction by quickly inactivating enzyme activity, but excessively high temperatures may directly damage the chlorogenic acid molecular structure, causing it to decompose into smaller molecules. Therefore, the drying process must strike a balance between enzyme inactivation and preventing thermal decomposition.
Natural sun-drying relies on ambient temperature and ventilation conditions, has a long drying cycle, and involves continuous action of polyphenol oxidase during this period, resulting in significant chlorogenic acid oxidative condensation and a decrease in its content. Meanwhile, prolonged exposure to air makes the product susceptible to ultraviolet radiation and oxygen, further exacerbating the loss of active substances. While this method is inexpensive, the finished product has a dull color and a low retention rate of medicinal components, making it suitable only for small-scale home production.
Air drying slows down the drying process by controlling environmental humidity and temperature, reducing the stage of enhanced chlorophenol oxidase activity. However, in humid southern regions, excessive humidity can easily lead to mold growth, causing chlorogenic acid to degrade into inactive substances and potentially producing harmful microbial metabolites. This method requires stringent environmental conditions and must be used in conjunction with dehumidification equipment; otherwise, quality stability cannot be guaranteed.
Hot air drying accelerates moisture evaporation and shortens drying time through circulating hot air. A staged heating strategy (e.g., preheating to 35℃ followed by gradual temperature increases) can effectively inhibit polyphenol oxidase activity, preventing early oxidation of chlorogenic acid. However, when the temperature exceeds 60℃, the risk of thermal decomposition of chlorogenic acid increases, requiring strict control of the final drying temperature and time. This method is highly efficient and suitable for industrial production, but precise parameter control is necessary to balance efficiency and component retention.
Microwave drying utilizes high-frequency electromagnetic waves to rapidly heat and vaporize the internal moisture of materials, achieving simultaneous internal and external drying. Its unique advantage lies in the rapid inactivation of polyphenol oxidase, while simultaneously disrupting cell structure through non-thermal effects, promoting the dissolution of chlorogenic acid. Studies have shown that microwave-dried honeysuckle has a significantly higher chlorogenic acid content than sun-dried, hot-air-dried, and vacuum-dried honeysuckle, with a lower total bacterial count and extended shelf life. However, attention must be paid to the number of stacking layers and heating time to avoid localized overheating that could lead to discoloration and component loss.
Steam blanching combines high-temperature steam treatment with low-temperature drying. Steam instantly inactivates polyphenol oxidase, fixing the petal shape, followed by hot-air drying to complete dehydration. This method retains over 82% of the medicinal components, and the finished product has a bright color and rich aroma. Excessive steaming time can cause the petals to soften and rot; therefore, air circulation must be ensured during the drying stage to prevent moisture retention and mold growth. This method is suitable for large-scale production, but requires high-level equipment and process control.
The impact of different drying processes on the retention of active substances in honeysuckle flower tea is essentially a trade-off between temperature, time, and the mechanism of action. Natural sun-drying and air-drying methods, due to their long cycles and difficulty in environmental control, result in severe oxidative decomposition of chlorogenic acid; hot air drying requires precise temperature control to avoid thermal decomposition; microwave drying and steam fixation methods achieve efficient retention of components by rapidly inactivating enzyme activity and destroying cell structure. In actual production, it is necessary to select appropriate processes based on the scale of raw materials, equipment conditions, and quality requirements, and optimize parameters to maximize the retention of active substances, providing consumers with high-quality honeysuckle flower tea products.
