Drying Methods for Improving the Quality of Dried Herbs

Herbs are “any plant with leaves, seeds, or flowers used for seasoning, food, medicine, or perfume”. Herbs are considered to be extremely perishable foods thanks to their high moisture content and most herbs are chill-sensitive. They’re thus processed by drying to make shelf-stable product. Drying preserves the standard of herbs by reducing the moisture content that inhibits the expansion of microorganisms and chemical alterations throughout dried storage. Within the cooking sense, dried herbs are usually used as “flavouring” agents to feature their characteristic aromas to the foods. Aside from the cooking usages of herbs, their oil may be used as AN antimicrobial agent that’s effective against microorganism, yeast, and molds. Dried herbs even have several applications in alternative fields, like in medical and toiletry product and in fragrance producing. Herbs are identified to be a superb source of antioxidants. The standard characteristics thought of to be the most necessary for dried herbs could rely upon their usage. For example, the standard of medical dried herbs is defined by the content of bioactive compounds. Whereas the standard of culinary dried herbs is typically defined by their color and fresh-like characteristic aroma.

Dried culinary herbs are typically high in price, thus, the expectation of end user relating to the standard of the product are typically high. The quality specifications of dried herbs are listed largely to make sure the chemical and microbiological safety of the product, such as, moisture content, bulk density, foreign matter, and the content of excretory product, aflatoxins and heavy metals.

Essential oil is the main contribution of herb aroma though it’s present in little amounts. The international organization for Standardization (ISO) has defined the meaning of the term “essential oil” as a “product obtained from a natural material of plant origin, by steam distillation, by mechanical processes from the pericarp of citrus fruits, or by dry distillation, when separation of the liquid section — if any — by physical processes”. Essential oils are often utilized in many varieties of applications, like pharmaceutics, cosmetics, and therefore the medical and food industries. In fresh herbs, essential oils are keep on the surface of the leaves in specialised structures referred to as trichomes, that are uni- or multicellular appendages within the epidermal cells that develop outward from the surface of plant organs like leaves, roots or barks. Therefore, conserving trichome integrity or minimizing the harm to trichomes throughout drying may improve the yield of essential oils and therefore the aroma quality of dried herbs. Volatile compounds in herbs may be conjointly found in glycosidically-bound forms as they’re water soluble and may be accumulated within the plant tissues. 

Essential oils are composed of some or several chemical compounds, with some kinds of herbs containing over 100 chemical compounds. The chemical composition of the essential oils varies decided by the kind of herb, harvesting season, postharvest practices, age of the plant and storage conditions. Every compound contributes its specific flavor to the essential oil. This contribution depends on their specific odour threshold, which may be determined by the structure and volatility of the compound. The changes within the concentration of the essential oil chemical parts (either by chemical reactions or degradation), even with minor elements, could lead to drastic changes within the essential oil flavor.

The changes in volatile compounds throughout the drying method additionally rely on the biological factors of the herbs, as well as initial moisture content, the age of the plant, growth conditions and harvesting time. Storage conditions also have an effect on the content of volatiles of the dried product, particularly within the presence of light and oxygen. The reduction of some essential oil elements may be considered to be a profit, like the reduction of pulegone, a hepatotoxin in hedeoma pulegioides and mentha pulegium.

Pre-treatments before drying are process methods aimed toward achieving high-quality dried herbs; shorten the drying time, and reducing the energy consumption. Smart pre-treatments implementation should produce solely smallest modification to the drying method settings to reduce the follow-up prices from the modification. Many pre-treatments are reported to provide advantages for drying of herbs, like blanching, pulsed electric field, and ultrasonic treatment.

Drying technique is one among the main factors affecting the quality of dried herbs. Drying strategies applying extreme temperature would considerably decrease the number of aroma compounds, since aroma compounds are heat-sensitive substances and might be evaporated from plant tissues simply throughout drying.

Drying Methods used for herbs are classified below:

  • Sun drying
  • Shade drying
  • Solar-assisted drying
  • Hot-air drying
  • Freeze drying
  • Microwave drying
  • Microwave-vacuum drying
  • Heat-pump-assisted drying
  • Infrared drying
  • Fluidized bed drying
  • Supercritical CO2 drying (scCO2)
  • Radio-frequency drying
  • Hybrid drying methods

A number of pre-drying treatments and drying strategies, investigated in numerous herbs, are developed, showing an improvement in quality, better energy conservation, and higher method efficiency. Hybrid-drying techniques have shown promising results on the development of dried herbs quality as well as each color and aroma. In spite of those technological developments, obtaining high-quality dried herbs remains a difficulty as herbs are sensitive to completely different pre-drying and drying method conditions, primarily in regard to color and aroma. Moreover, the standard of dried herbs is incredibly sensitive to the kind of herb, harvesting season, postharvest practices, age of the plant and storage conditions.

We at KERONE have a team of experts to help you with your need for drying of herbs in various products range from our wide experience.

Scroll to Top