黄花菜抗氧化性研究.doc

Introduction Daylily flowers have been used as a vegetable and medicinal herb for a long history in China. Both fresh and dried daylily flowers are widely consumed. Daylilies have been reported to possess antidepressant properties, reduce inflammation, and promote digestion. Pharmacological studies have shown that daylilies can facilitate neurological changes in sleeping mice and impact motor activity in rats as a result of alteration to the normal levels of several central nervous system neurotransmitters. (黄花菜4) Research shows ascorbic acid、b-carotene and phenolic compounds attribute to daylily flowers possessing of the antioxidant properties. Daylily flower development and senescence was categorised into seven stages, each separated by one day. Flower respiration was only relatively constant through Stage I to III.(Flower senescene in daylily) Thus fresh daylily flowers are difficult to store and are subject to deterioration after harvest. Dried daylily flowers are available the whole year and can be stored, which makes them the conventional and stable form of daylily flower products. Various drying methods such as freeze-drying and hot-air drying have been applied to daylily flower processing. Hot-air drying is relatively cheap and is the most widely used method for food production. Major problems concerned with air dehydration are considerable shtinkage caused by cell collapse following the loss of water,poor rehydration characteristics of the dried product and unfavorable changes in colour,texture,flavour and nutritive value caused by drying. Freeze-drying gives high product quality but at a relatively high production cost. The effect of various drying treatments on the carotenoid stability in the daylily flowers has also been studied. Application of infrared drying to food drying is recently of special interest because of the progress in radiator construction.Studies show that infrared radiation method is quicker than convection-based methods. The