Microwave Drying Experiment of Chrysanthemum

Chrysanthemum tea is one of the top ten famous scented tea in China. Chrysanthemum tea is suitable for drinking all the year round and quite popular among people. Common drying equipment is difficult to meet its requirements, even if the drying requirements are met but output can not go up, so many enterprises choose industrial microwave drying machine for fast drying.

Mr. Yu, from hangzhou, zhejiang province, is the owner of a factory that makes deep processing of chrysanthemums. Hang baiju is planted in large quantities around the factory. Come to the season that chrysanthemum comes on the market in great quantities immediately, Mr. Yu brings sample to the factory to visit experiment. Customers brought fresh hangbaiju. Customer requirements to ensure that after drying chrysanthemum still has medicinal value, and still maintain a better color.

The fresh chrysanthemum water content is higher, among which the petal part water content is less, the organization is delicate, easy to dry. And flower head part of the water content is particularly large, up to 80%, and the organization is older, not easy to lose water, also chrysanthemum flower head is a very uneven medicinal material. Dried chrysanthemum is mostly used for tea drinking, with strong and sweet taste, original color, original sample characteristics, this requires drying after ripening, strong drying of flower head and weak drying of flower petal. At present, the traditional drying process of drying after steaming is not only dependent on the weather, but also causes excessive drying of the petals, petals fall off, the quality of the chrysanthemum after drying is not high.

The microwave oven used in this experiment has a maximum frequency of 2450 Hz and a maximum output power of 800 W, that is, 100% microwave frequency band. The microwave frequency band of fixed chrysanthemum was 55%, and the de-enzyming time was 3 min. The de-enzyming treatment of chrysanthemum was completed by changing the layer thickness (1, 2, 3, 4, 5 cm). Each group of experiments were repeated 3 times.

Effect of microwave frequency band on color: the layer thickness of fixed chrysanthemum was 1 cm, the de-enzyming time was 3 min, and the de-enzyming treatment of chrysanthemum was completed by changing the microwave frequency band of chrysanthemum (17%, 33%, 55%, 77%, 100%). The experiment was repeated three times in each group. On the basis of single factor test, the microwave frequency band, chrysanthemum layer thickness and de-enzyming time were selected as the main influencing factors, and the color difference of dry chrysanthemum was taken as the index to carry out orthogonal test, to determine the best technological conditions of microwave de-enzyming and drying of chrysanthemum. The color of chrysanthemum was compared with that of chrysanthemum at natural temperature. The chromatic aberration was measured by spectrophotometer. Among Δ E * (the size of the total color difference) value is smaller, says the closer to the contrast color, the better the drying quality [7, 14]. Color difference formula: Δ E * = (Δ L *) 2 + (Δ a *) 2 + (Δ b *), Δ L*= L* samples – L* contrast (lightness difference) Δ a * = a* sample – a* comparison (red green difference) Δ b= b* sample-b* contrast (yellow blue differences). Color is one of the important physical indexes to measure the quality of chrysanthemum. It also determines the market price of chrysanthemum to some extent. Since the color of natural dried chrysanthemum after de-enzyming is light yellow, and light yellow is the best color after drying, the color of naturally dried chrysanthemum is used as the control color in this experiment. According to the previous color calculation formula, with delta E* (total color difference size) to represent the different treatment of the sample color and contrast color difference value, the value of the smaller the better. When the de-enzyming time was 3 min, the color difference of chrysanthemum was the minimum.Therefore, the proper de-enzyming time is 3 min.

With the increase of chrysanthemum thickness, the color difference of chrysanthemum also increased trend of different degrees. When the thickness is 1 cm, the color difference value is the smallest, and when the thickness is 2~3 cm, the color difference value changes little.This is determined by the characteristics of microwave drying. When microwave de-enzyming, heat is transferred to the inside of the material, resulting in evaporation of water. When the thickness of the layer is smaller, the microwave penetration ability is stronger, which can make the chrysanthemum finish even de-enzyming;When the layer thickness increases, the microwave penetration and heat supply are limited under certain microwave frequency band, which is easy to cause uneven de-enzyming, thus affecting the color of chrysanthemum, resulting in large color difference. Therefore, the appropriate thickness of chrysanthemum layer was determined to be 1 cm.

In the process of microwave de-enzyming and drying, the primary and secondary order of the effect on the color difference of chrysanthemum were as follows: the de-enzyming time > microwave band > chrysanthemum layer thickness; The optimum technological conditions of microwave de-enzyming and drying chrysanthemum were: chrysanthemum layer thickness 1cm, 55% microwave frequency band, de-enzyming time 3 min.

To sum up, the best quality chrysanthemums were prepared by choosing 55% microwave frequency band, 1 cm thick chrysanthemum layer and 3 min de-enzyming time.

Microwave heating directly on the internal and external chrysanthemum, no need to preheat, can start processing instantly after opening, convenient and efficient.