Study on the Harvest Time, Drying Method of Saussurea sonchifolius Leaves and Their Effects on Biscuit Quality

Taking Saussurea sonchifolius leaves as the research object, four main growth stages （tender stage (May), growth period (July), mature stage (October), senescence period (November) and different drying methods（constant temperature hot air drying (40 ℃), natural drying, microwave drying (320 W), vacuum drying (60 ℃), vacuum freeze drying (−60 ℃)）of the leaves were discussed in order to obtain the best harvest time and drying method. And the effects of leaf powder addition on the quality of crisp biscuits were discussed.The results showed that with the growth of leaves, the contents of total flavonoids and chlorogenic acid increased first and then decreased, and reached the highest at the mature stage, which were 0.435 and 33.52 mg/g, respectively. Among the selected drying methods, vacuum freeze-drying (−60 ℃) was better, and the content of flavonoids and chlorogenic acid in the dried yacon leaves was higher. Adding leaf powder (0～20%) to crisp biscuits, the biscuits were green and had unique fruit leaf fragrance. With the increase of the addition amount, the moisture content of biscuits decreased gradually, and the hardness decreased first, then increased, and then decreased. Compared with ordinary biscuits, the flavor of Saussurea sonchifolius leaf biscuits was more abundant and had unique aroma components, which including 3.23% hydroxyacetone, 1.34% 2-methylpyrazine, 1.03% b-bourbon, etc. In conclusion, the content of total flavonoids and chlorogenic acid in the leaves of Saussurea sonchifolius was relatively optimal at the mature stage, which could be collected in October and dried by vacuum freeze-drying or constant temperature hot air drying. The obtained leaf powder could be used for the development of baked food and give the product unique flavor.