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黄花菜抗氧化性研究.doc

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1、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

2、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 dayl

3、ily 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

4、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 fl

5、ower 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 unfavorab

6、le 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 dryi

7、ng 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 effect of hot-air drying and freeze-drying on antioxidant activities of daylily flowers have been compared and

8、studied. However, infrared drying of daylily flowers and its effect on antioxidant activities are rarely reported. The objective of the study is to compare hot-air drying and infrared drying of daylily flowers and the effect of infrared drying on antioxidant performance of daylily flowers was also s

9、tudied.(黄花菜抗氧化)Materials and methods1、 Chemicals and reagent2、 Daylily flowers Fresh daylily flower (Hemerocallis Citrine Baroni cv. Mengzihua) buds were harvested in June, 2012, from a farm in Qidong County, Hunan Province, China, air- expressed to our lab in a modified atmosphere (MAP) bag, and th

10、en stored at 2-3oC in a refrigerator. The average moisture content of daylily samples was about 91.010.17% (wb, wet basis), which was determined in a vacuum drying oven in 13.3 kPa at 70 oC until the constant weight of sample reached (AOAC, 1990). The daylily flower buds could roughly be considered

11、as cylindrical vegetables with diameter of about 7.50.6 mm and length of about 82.79.7 mm. 3、Hot-air dryer set-up 4、IR dryer set-up 5、Drying processThree drying temperatures (50,60 and 70) were tested in both hot-air dryer and IR dryer. Two levels of power (225 and 450W) of the IR dryer were also te

12、sted at the same time. An approximate mass of 100 g of daylily flower samples was chosen for each batch. Three batches were put on mental wire containers and three marked containers were put in the dryer at the same place each time. During the drying course, one container was removed at a specific t

13、ime and used for measuring weight loss. Time required for each weighting was about 10 s. Drying stopped when the sample moisture (wb) reached about 151%(wb). Thereafter color ,quantity of ascorbic acid 、- carotene and phenolic compounds and antioxidant activity were analyzed accordingly.6、 Determina

14、tion of drying rate and diffusion coefficient The moisture ratio(MR) of samples was calculated using the following equation:where Me is equilibrium moisture content of sample(g water/g dry solid). The value of Me is relatively small compared with Mt or Mo, especially for IR drying(Diamante&Munro,199

15、3). Therefore, Me was assumed to be zero in this study. The overall drying rate(DR)(Kar&Gupta,2003 ) was calculated using the equation: where DR is overall drying rate(g water/ g dry solid min-1); Mo is moisture content of daylily at time0(g water /g dry solid); and Mt is moisture content of daylily

16、 at time t(g water/g dry solid). According to Ficks second law equation for non steady-state, when the material of cylindrical shape is isotropic with regard to mass transfer the diffusion of moisture (M, kg water/kg dry matter) in the cylinder is expressed as follows (Crank, 1975): (5)where Deff is the effective diffusivity of moisture (m2/s), r is the cylinder radius (m), z is