Abstract: In order to study the difference of different forms of tobacco stem after microwave coupling expansion, the long stem was divided into thick long stem and fine short stem. The optimum coupling expansion conditions were explored from three aspectsraw material moisture, expansion time and microwave power. Then the coupling expansion was carried out under the optimum technological conditions, and the relative contents of conventional chemical components and aroma components were determined respectively. The results show that, ①with the increase of raw material moisture, the expansion degree of coarse and short pedicel increased at first and then decreased, and tended to be the highest when the moisture content of raw material was 12%~14%. ②with the increase of expansion time, the expansion degree and color difference of coarse and short pedicels increased. After the expansion time exceeded 2 min, the expansion degree of coarse and long pedicels exceeded that of slender pedicels, and the difference became larger and larger. During the expansion time, the color difference of thin and short pedicels was higher than that of coarse and long pedicels. ③The best value of the microwave power of the coarse and short stems is about 700 and 600 W, respectively; ④The contents of total nitrogen, chlorine and potassium changed little after coupling expansion, but the contents of total sugar and reducing sugar decreased in varying degrees. The changes of total plant alkaloids before and after expansion were opposite; ⑤The change trend of alcohols, heterocycles, phenols, ketones, coarse and short pedicels was the same, while that of some acids, lipids, alkenes and alkenes was opposite after the coupling expansion of coarse and short pedicels.

Key words: tobacco stem, coupling expansion, thick long stem, short and fine stem