Does Higher Temperature Speed Up Drying? Does Medicinal Herb Slice Retain Its Efficacy After High-Temperature Drying?

During the drying validation process of medicinal herb slices, we discovered that the maximum temperature these slices can tolerate is significantly lower than the temperature allowed by factory processes. In such cases, the loss of various medicinal components in the herb slices can reach 60% to 70%. Identifying the main factors that affect the loss of these components and the drying quality of the slices is an important issue.

In validations using Trillium, Paeonia lactiflora, and Mulberry bark, the drying air velocity was 1.1 m/s, with component loss of 100%, 60%, and an increase of 14.9%, respectively. For Licorice, Angelica, and Madder root, the velocity was 1 m/s, with losses of 24.2%, 29.1%, and 2.7%, respectively. Atractylodes, Magnolia bark, and others were dried at 0.5 m/s, with losses of 25.3%, 2.8%, and 0%, respectively. These data indicate that internal oven air velocity is not a factor in the loss of medicinal properties of the slices.

Trillium, Angelica, and Citrus peel all had an initial moisture content of 75%, but the losses were 100%, 29.12%, and 1.4%, respectively, indicating that initial moisture content is also not a primary factor in component loss.

In experiments, the temperature of the slices was just 3°C over the allowable limit for Atractylodes, 1°C below for Angelica, and lower for the rest, yet there were still losses in active components, some up to 100%. This suggests that if the experimental temperature exceeds the maximum allowable temperature, the loss of medicinal properties could be even greater. This is why many herbs can only be air-dried; for example, mint can only be air-dried because if dried at low temperatures, it turns into dry grass with all its fragrance lost.

Different constant and variable temperature schemes were tested with hay. The results show that the layer thickness should be around 30mm, the initial moisture content of the test medicine was 44%, and the heating method was hot air circulation at 1 m/s. The results were as follows: 40°C constant temperature took 70 minutes, 50°C took 61 minutes, and 70°C took 48 minutes, demonstrating that higher air temperatures speed up the drying process.

But does the herb slice retain its medicinal efficacy after high-temperature drying? Most plant-based medicinal materials lose a significant amount of efficacy when dried at high temperatures, and some must be processed at high temperatures to achieve the desired effects.

This doesn’t require much explanation; it is basic knowledge that the thicker the pile, the more product there is, and the slower the heat transfer process, resulting in slower drying.

These five factors are the main factors affecting the hot air circulation drying of medicinal herb slices and lay the foundation for further research using infrared radiation heating. We will continue to share in the future how effective it is to dry medicinal herb slices using carbon fiber heater elements as an infrared radiation source.

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