Lipoxygenase-Catalyzed Oxidation of N-6 and N-3 Polyunsaturated Fatty Acids: Relevance to and Activity in Fish Tissue

Lipid peroxidation is an important process responsible for the flavor deterioration of many plant and animal foods. In order to understand possible mechanisms of initiation, a soybean lipoxygenase-polyunsaturated fatty acid model system was studied. The rate of enzyme-initiated oxidation was monitored by both oxygen consumption and diene conjugation. The hydroperoxides from an n-6 fatty acid, i.e. arachidonic, and n-3 fatty acids, i.e. linolenic, eicosapentaenoic, and docosahexaenoic acids were reduced and analyzed by reverse-phase high pressure liquid chromatography and gas chromatography/mass spectrometry. The lipoxygenase specifically catalyzed oxygenation at the n-6 carbon of both n-3 and n-6 fatty acids. Lipoxygenase activity was demonstrated in skin homogenate from rainbow trout and its role in off-flavor development is discussed.     

应用遥测技术探讨台湾花莲地区土砂灾害集水区崩塌地的变迁

以1996年、2002年、2005年及2007年四期SPOT卫星影像为材料,配合相关图籍数字化台湾花莲地区寿丰溪集水区与秀姑峦溪集水区的崩塌地图层,透过植生回复率(VRR)、新增崩塌率(ICR)及崩塌地重心位移的计算,探讨这两个集水区崩塌地变迁情形,并分析其环境因子特性.研究结果显示:利用多期卫星影像数据可有效进行崩塌地长期监测,并获知其变动情形;另突发暴雨可使崩塌大量发生,显为事件直接影响因子;而VRR、ICR与重心位移的计算,可有效量化植生恢复情形及新增崩塌状况;至于地理环境特征方面,崩塌发生概率随高程增加而增加,也与坡度呈正相关,因此未来在开发上应特别留意.     

EVALUATION of DIE SWELL and VOLUMETRIC EXPANSION IN CORN MEAL EXTRUDATES1

A method to determine die swell in the presence of volumetric expansion due to moisture vaporization in extruded food products is proposed. the method is applied to twin screw extrusion of corn meal in a study to investigate the effects of extruder die parameter (exit capillary length and entrance cone angle), screw speed, and specific feeding load on die swell and volumetric expansion. the die swell results are compared with known effects for nonexpanded polymers. Die swell tended to decrease with increasing exit length, but had only a weak response to entrance angle. Increasing specific feeding load (SFL) increased die swell, where as increasing screw speed produced increases or decreases in die swell, depending on the SFL. Die swells ranged from approximately 1.2 to 1.7, accounted for approximately 10 to 22% of the total radial expansion, and for approximately 18 to 38% of the extrudate cross sectional area. Volumetric expansion increased with increasing die exit length, but was insensitive to entrance angle with a slight concave upward response. Increasing screw speed produced large increases in volumetric expansion, while increasing SFL produced only slight increases. Observations about die swell compare favorably with previous studies of nonexpanded polymers, suggesting that the proposed analysis method may be useful for food viscoelasticity evaluation studies.     

SPECIES SUBSTITUTION OF RESTAURANT FISH ENTREES

Fish species substitution has been a common problem in the retail markets. However, this problem has not been documented in restaurant-cooked fish entrees. This study investigated fish substitution in restaurant-cooked snapper and swordfish entrees from four major cities in the U.S. The species of 16 snappers including 13 red snapper and 21 swordfish samples were verified as presented on the menu using isoelectric focusing (IEF). Fish samples were cleaned and desalted by rinsing with distilled water before protein extraction. Protein separation was carried out in a polyacrylamide gel with a wide pH gradient range of 3.5–9.5. Distinctive IEF protein band patterns of unknown samples were compared with the authentic standards. Six out of 13 (46%) red snapper samples and two out of 21 (10%) swordfish samples were misrepresented. The method used in this study adequately and efficiently verified the species of restaurant-cooked snapper and swordfish samples.     

Analysis of Crabmeat Volatile Compounds

Boiled and pasteurized blue crab (Callinectes sapidus) meat samples were analyzed for volatile flavor components by dynamic headspace sampling, capillary column gas chromatography and mass spectrometry. Fifty-three compounds were identified including aldehydes, ketones, alcohols, aromatics, furans, sulfur-containing compounds, terpenes, alkanes, and miscellaneous compounds. Levels in both samples were compared and boiled crabmeat contained higher levels of most compounds.     

Isolation and Identification of Objectionable Volatile Flavor Compounds in Defatted Soybean Flour

The volatile flavor constituents of defatted soy flour were isolated by a specially designed apparatus. The isolated volatiles were fractionated by gas chromatography. The fractions with characteristic beany, grassy, and green odors were identified by infrared and mass spectrometry. A total of 25 compounds was identified, including nine alcohols, six aldehydes, nine ketones, and 2-pentyl furan. Among the identified compounds, 2-pentyl furan and ethyl vinyl ketone are probably the key compounds for the beany and grassy odors of the soy flour. All the compounds identified in this study can be postulated as autoxidative decomposition products of soy lipids. Therefore, the presence of these compounds in soy flour might be due to the incomplete removal of lipids in soy flour.     

Characterization of the Nonvolatile Minor Constituents Responsible for the Objectionable Taste of Defatted Soybean Flour

A scheme was developed for the separation of the nonvolatile minor constituents from soy flour which are responsible for the astringent an bitter tastes. The scheme involved solvent extraction, freeze drying, and fractional crystallization. Two fractions, collected by semipreparative HPLC, had the characteristic bitter and astringent tastes. Further fractionation by reverse phase HPLC produced three pure compounds which were identified by UV, NMR spectrometry and elemental analysis, as daidzein, glycitein 7-β-O glucoside, and genestin. Preliminary sensory evaluation showed that these isoflavones might contribute additively to the undesirable bitter and astringent tastes of soy protein products.     

大型荧幕作业下工作绩效与视觉不适之研究

伴随今日荧幕技术进步,大型荧幕已经成为一种流行趋势.本研究希望得知大型荧幕对视觉、工作绩效之影响,并了解肌肉不适之情形.比较四种荧幕尺寸(15、17、19和21英时)以主观评量、工作绩效、视觉压力、颈肩姿势与肌肉活动之影响.由主观评量得知,19时工作绩效是最好的,荧幕大小对视觉表面积的影响是显著的,在工作超过一小时候,眨眼率与视觉疲劳也大幅增加,颈肩姿势对荧幕大小无显著的,最后,荧幕大小对平均作业时间有显著的影响.结论,19 英时萤幕是我们推荐适用于长时间的作业平台.