Squash leaf glandular trichome volatiles: Identification and influence on behavior of female pickleworm moth [Diaphania nitidalis (Stoll.)] (Lepidoptera: Pyralidae)

Fourteen volatile compounds occurring in leaf trichomes of yellow squash (Cucurbita pepo L. cv. Early Prolific Straightneck) were identified. These compounds accounted for 83.5% of the volatile matrix. Ubiquitous constituents of the epidermis (myristic, palmitic, and stearic acids,n-tricosane, andn-pentacosane) accounted for 73.7%; these compounds were not bioassayed. The volatileso-,m-, andp-xylene, toluene, 2-heptanone, (R)-(+)- and (S)-(–)-limonene, and germacrene D were tested for their influence on attraction and oviposition by the pickleworm moth (Diaphania nitidalis Stoll.). No single compound, except germacrene D, was attractive. (R)-(+)-Limonene and 2-heptanone were weakly repellent. Mixtures of the highly volatile fractions were as attractive as volatiles emanating from whole, intact leaves. Oviposition levels on treated artificial sites corresponded with levels of visitation. Oviposition was significantly stimulated by whole-leaf volatiles, and (S)-(–)-limonene caused a slight but significant reduction.Mention of a trade name or proprietary product does not constitute a warranty or guarantee by the U.S. Department of Agriculture, nor does it imply exclusion of other products that may also be suitable.     

黄山贡菊多糖的微波浸提工艺和抑菌效果研究

利用响应面设计法和微波浸提法优化黄山贡菊的多糖提取工艺,多糖含量测定采用苯酚-硫酸法,并对多糖提取液进行了抑菌效果实验。结果表明：微波功率、浸提时间和pH因素对贡菊多糖提取率有显著影响,得出微波辅助提取贡菊多糖的最优工艺参数：微波功率为530W,提取时间为22min,液料比38：1,多糖浸提液pH为6.7,实际多糖得率为6.18%。抑菌实验表明：贡菊多糖的抑菌效果良好,贡菊多糖对大肠杆菌和苏云金芽孢杆菌的最小抑菌浓度为10mg·mL-1。     

Loss of ascorbic acid during storage of Conference pears in relation to the appearance of brown heart

To investigate the causes of brown heart (BH) in Conference pears, the contents of ascorbic acid (AA) and dehydroascorbic acid (DHAA) in fruits were studied during the first period of storage. AA was studied in 1999 and 2000, DHAA in 1999 only. Pears from normal and very late harvest stored immediately or after a delay in a controlled atmosphere with 2% O₂ and low (0.7%) or high (5%) CO₂ were compared. DHAA content did not change during storage in any treatment. AA decreased in storage according to an exponential model. The rate of AA loss was different in the two years and was higher in late‐harvest fruits and in those stored in 5% CO₂. BH appeared in different treatments when AA decreased below a threshold, which was about 2 mg kg^?1 fresh weight, corresponding to 5% of the AA content at harvest. The frequency and severity of symptoms depended linearly on the time spent by fruits in low‐ascorbate conditions. Advanced maturity at harvest and storage in high CO₂ determine the appearance of BH and increase the rate of AA loss, probably through a reduction in the turnover of antioxidants. © 2002 Society of Chemical Industry     

基于单片开关电源LinkSwitch的便携设备充电器设计

美国功率集成公司(Power Integrations Inc)最新推出的单片开关电源LinkSwitch适台制作高效、低成本3W以下的小型开关电源。本文以一个充电器的制作为例，介绍了其功能及电路设计要点。     

Identification of a volatile attractant forDiabrotica andAcalymma spp. from blossoms ofCucurbita maxima duchesne

Fractionation of headspace volatiles fromCucurbita maxima blossoms by high-performance liquid chromatography resulted in the isolation of a single component which was highly active in an electroantennogram bioassay onDiabrotica undecimpunctata howardi antennae. This compound was identified as indole by gas chromatography-mass spectrometry. Field-trapping bioassays were conducted which indicated that indole is a potent attractant of the western corn rootworm,D. virgifera virgifera, and the striped cucumber beetle,Acalymma vittatum. The southern corn rootworm,D. u. howardi, did not respond, despite its strong EAG response. The sex ratio ofD. v. virgifera found in indole-baited traps varied seasonally. Males were trapped in abundance in late July and later September, 1983, while females were more abundant August and early September. The effectiveness of indole as aD. v. virgifera attractant also varied seasonally. A prolonged period of depressed trap catches occurred in early August 1983, during the silking and tasseling period of the corn in the field where trapping was carried out.Coleoptera: Chrysomelidae.     

紫甘薯色素抗菌与抗氧化作用研究进展

主要就紫甘薯色素的抗菌与抗氧化活性研究进展进行了综述,涵盖紫甘薯色素的成分与特性、提取与纯化方法、抗菌与抗氧化机理及研究现状,以期为紫甘薯的综合利用拓展方向。     

南瓜中游离叶黄素的制备及抗氧化活性

为了探究南瓜提取物中叶黄素酯的皂化工艺条件和其体外抗氧化能力,在单因素试验基础上,以皂化液浓度、皂化温度和皂化时间为响应因子,采用Box-Behnken中心组合实验原理进行三因素三水平设计,优化南瓜叶黄素的皂化工艺;利用高效液相色谱（HPLC）和质谱（MS）分析检测皂化产物;经硅胶柱色谱分离得到纯化的南瓜叶黄素;采用分光光度法,通过比较DPPH·和·OH的清除能力评价南瓜中游离叶黄素的体外抗氧化活性。结果表明,南瓜提取物中叶黄素酯的最佳皂化工艺条件为皂化液质量浓度33 g/dL,温度33 ℃,时间5.5 h。在最优工艺条件下,南瓜提取物中游离叶黄素得率为0.4175%,与预测值相近,说明该优化工艺稳定可行。高效液相色谱（HPLC）和质谱（MS）分析检测表明皂化产物为叶黄素。硅胶柱色谱纯化后,游离叶黄素的纯度可提高到91.39%。南瓜中游离叶黄素清除DPPH·和·OH的半抑制质量浓度IC₅₀分别为0.021 4 mg/mL和0.038 3 mg/mL,抗氧化活性较高,可作为一种良好的天然抗氧化剂。