CHARACTERIZATION AND INHIBITION OF POLYPHENOL OXIDASE FROM PEARS (PYRUS COMMUNIS L. CV. BOSC AND RED)

Red pears had higher PPO activity, total phenolics and chlorogenic acid concentration than Bosc pears. PPO activity and phenolics both decreased in fruits held at room temperature. pH and temperature optima for Bosc and Red pears PPOs were 5.0 and 5.5, and 20 and 23C, respectively. 4-Methylcatechol, catechol and dopamine were good substrates for PPO from both pear cultivars; however, no activity was observed with any of the mono-hydroxy substrates studied. Higher K_m and lower V_max values were observed for Bosc pear PPO. Heating at 75C for 30 min completely inactivated the enzyme from both cultivars. Heating at 55 and 65C for the same duration resulted in partial inactivation (45–60%) of this enzyme. Ascorbic acid, L-cysteine, sodium metabisulfite and thiourea effectively inhibited browning due to pear PPOs.     

Light and temperature effects on shoot fruitfulness in Vitis vinifera L. cv. Sultana: Influence of trellis type and grafting

Fruit bud initiation in Sultana is more sensitive to climatic factors than fruit bud initiation in other cultivars. This paper considers historical findings regarding the influence of light and temperature on fruit bud initiation and fruitfulness in view of modern Sultana vineyard management practices.
Past results were reviewed and confirmed by experiments in which variability in vine size and structure was introduced by grafting and modifications of trellis design. Ramsey-grafted vines were consistently less fruitful than own-rooted Sultana, possibly because of a more shaded canopy interior due to greater vegetative growth of vines grafted to Ramsey rootstock. Carbohydrate reserves of node and internode tissue in late winter between node 2 and 18 followed a similar trend along the cane as fruitfulness in the following spring.     

EFFECT OF HOT WATER IMMERSION ON PEEL COLOR OF PEARS AND ON WHITE ROT CAUSED BY BOTRYOSPHAERIA BERENGERIANA

Abstract The effectiveness of hot water immersion (HWI) on peel color and the control of white rot caused by Botryosphaeria berengeriana on wound-inoculated European pears, cv. La-France, were investigated. After HWI at 40, 45, 48, 50, 52 and 54C for varying immersion periods, the pears were held at 20C, ≥ 90% RH (simulated retail conditions). The peel color (L*, a*, b*) was determined before and after HWI treatment. The dominant role of L* suggested that peel darkening was the major factor in color change of the HWI treated pears. The L* value of 54 was judged as the border line for acceptability and less than 51 resulted in browning. Similarly the critical points for a*, b*, chroma, hue and ΔE* were found to be −6, 34, 35, 100, and 8, respectively. Disease incidence recorded 7 days after treatment revealed that High Temperature Short Time (HTST) treatment of 54C for 3 min reduced incidence about 85% with good retention of color. Both temperature and immersion period are to be carefully selected to prolong shelf-life and retain the peel color quality of 'La-France'pears.     

BROWNING OF SAGO (METROXYLON SAGU) PITH SLURRY AS INFLUENCED BY HOLDING TIME, pH AND TEMPERATURE

The effect of holding time, pH and temperature of sago pith slurry on its browning was evaluated. Holding time of sago pith slurry, which browning took place, proved to be an important factor in determining the amount of soluble phenolic compounds that were oxidized. This subsequently led to the development of color. The amount of (+)-catechin and (-)-epicatechin that was oxidized increased with pH particularly above pH 4.5. This resulted in simultaneous development of color in the sago pith slurry. The oxidation of phenolic compounds in acidic conditions was suggested to be caused by latent polyphenol oxidase (LPPO) as it is activated by acidic pH. The amount (+)-catechin and (-)-epicatechin oxidized also increased with increase in temperature particularly above 30C.     

EFFECT OF REDUCTION CONDITIONS ON THE ACTIVITY OF Ni/γAl2O3 CATALYST FOR METHANATION REACTION

The effect of reduction conditions, mainly reduction temperature and duration time on the activity of Ni/γAl₂O₃ catalyst were studied for a methanation reaction in a gradientless Berty reactor. The methanation reaction was investigated using a feed containing CO (6.7 mole%), H₂ (26 mole%) and the balance being nitrogen at a pressure of 30 psig and a fixed temperature of 350°C. The reduction temperature was varying from 250 to 500°C, in order to investigate its effect on the methanation reaction. The methanation activity of the catalyst increased to a maximum by increasing the reduction temperature up to a maximum at 300-350°C and showed a slight negative decline afterward. The second parameter investigated was reduction duration time which was varied from 2 to 16 hours. It was observed that the methanation reaction activity increased by increasing the reduction duration time up to 6 hours. After six hours, there was no increase in activity. Based on the finding of this investigation, a recommended set of reduction conditions is given: reduction temperature of 300°C and a duration time of six hours.     

Al-Ti-B-RE细化剂对Al-7．0Si-0．55Mg合金显微组织和力学性能的影响

研究添加Al-5Ti-lB-RE细化剂对Al-7．0Si-0．55Mg（A357）合金的显微组织和力学性能的影响。先利用真空熔炼技术制各Al-7．0Si-0．55Mg合金,然后在Al-7．0Si-0．55Mg合金中加入不同成分的Al-5Ti-1B-RE中间合金。通过X射线衍射仪（XRD）、金相显微镜（OM）和扫描电子显微镜（SEM）对显微组织和拉伸试样的断口形貌进行观察。在室温下对合金的力学性能进行测试。观察Al-5Ti-1B-RE细化剂的形态以及内部结构,可以发现以TiB,为异质形核核心的TiAl3／Ti2Al20RE的壳层结构相。在Al-7．0Si-0．55Mg合金中加入Al-5Ti-1B-3．0RE细化剂后,抗拉强度会有明显提升,直到0．2％添加量时,抗拉强度会达到峰值。     

平纹机织玄武岩纤维/环氧树脂复合材料冲击拉伸行为

以常规机织工艺生产织物增强体,以真空辅助树脂转移模塑法(VARTM)制备成型复合材料,研究单层平纹玄武岩长丝增强环氧树脂复合材料在准静态和高应变率加载下的拉伸性能。准静态和高应变率拉伸试验分别在MTS-810.23试验仪和分离式霍普金森拉杆(SHTB)测试系统上完成。试验结果表明该材料的力学性能具有应变率依赖性:随着应变速率的增加,拉伸模量和拉伸强度单调增加,失效应变单调减小,弹性能先增加后减小。材料的失效破坏特征也呈现明显的应变率效应:准静态拉伸时,材料断口整齐,树脂的破碎少,几乎没有纤维的抽拔和经纬向纤维束间的滑移;高应变率拉伸时,材料断口参差错乱,树脂完全破碎,纤维束抽拔严重、相互崩裂和滑移,织物增强体结构的整体性破坏严重。     

微生物白云岩形成机制研究进展与存在问题

近年来,有关微生物白云岩沉淀作用机制的研究拓宽了沉积学中"白云岩问题"研究的视角。硫酸盐还原反应、产甲烷作用、有机分子水解等一系列可促进沉淀白云石的微生物代谢机制的发现,延伸了微生物白云石(岩)形成模式;有关可溶解硫化物催化白云石沉淀的研究,不但强调了硫酸盐还原反应机制,也为重新认识硫酸盐还原反应促进白云石沉淀机理提供了新线索。在现代环境中,微生物席内的原生白云石沉淀的发现,将微生物过程引入地表环境原生白云石沉淀作用和机理的研究,可能为寻找地层记录中的微生物白云石提供了更多有益的工作手段和思考途径。然而更加复杂的白云岩地层记录说明,运用微生物白云石去解释复杂的地质记录还存在着较多的局限性。