Thermal stability of soil organic matter pools and their δC values after C3-C4 vegetation change

Carbon isotopic composition of soils subjected to C₃-C₄ vegetation change is a suitable tool for the estimation of C turnover in soil organic matter (SOM) pools. We hypothesized that the biological availability of SOM pools is inversely proportional to their thermal stability. Soil samples from a field plot with 10.5 years of cultivation of the C₄ plant Miscanthus×gigantheus and from a reference plot under C₃ grassland vegetation were analysed by thermogravimetry coupled with differential scanning calorimetry (TG-DSC). According to differential weight losses (dTG) and energy release or consumption (DSC), five SOM pools with increasing thermal stability were distinguished: (I) 20-190 °C, (II) 190-310 °C, (III) 310-390 °C, (IV) 390-480 °C, and (V) 480-1000 °C. Their δ¹³C values were analysed by EA-IRMS. The weight losses in pool I were connected with water evaporation, since no significant C losses were measured and δ¹³C values remained unchanged. The δ¹³C of pools II and III in soil samples under Miscanthus were closer to the δ¹³C of the Miscanthus plant tissues (−11.8‰) compared to the thermally stable SOM pool V (−19.5‰). The portion of the Miscanthus-derived C₄-C in total SOM in 0-5 cm reached 55.4% in the 10.5 years. The C₄-C contribution in pool II was 60% and decreased down to 6% in pool V. The mean residence times (MRT) of SOM pools II, III, and IV were similar (11.6, 12.2, and 15.4 years, respectively), while pool V had a MRT of 163 years. Therefore, we concluded that the biological availability of thermal labile SOM pools (<480 °C) was higher, than that of the thermal stable pool decomposed above 480 °C. However, the increase of SOM stability with rising temperature was not gradual. Therefore, the applicability of the TG-DSC for the separation of SOM pools with different biological availability is limited.     

Primary structure and thermostability of bigeye tuna myoglobin in relation to those of other scombridae fish

ABSTRACT:   In the present study, the cDNA encoding myoglobin (Mb) of bigeye tuna Thunnus obesus was cloned and its amino acid sequence deduced in order to investigate the relationship between the primary structure and thermostability of scombridae fish Mb. An open reading frame of bigeye tuna Mb cDNA contained 444 nucleotides encoding 147 amino acids. The primary structure of bigeye tuna Mb was highly conserved when compared with those of bluefin tuna and yellowfin tuna Mb, the sequence identity being 95.2–100.0%. It also showed relatively high identity (82.3–89.1%) with the counterparts of scombridae fish. Myoglobin was then isolated from the dark muscle of four scombridae fish including bigeye tuna. Differential scanning calorimetry and circular dichroism measurements on these Mb revealed that the thermostability of bigeye tuna Mb was lowest and that of skipjack Katsuwonus pelamis Mb highest among the scombridae fish Mb examined. The α-helical contents of scombridae fish Mb at 10°C were in the range of 39.8–44.8%, clearly lower than that of horse Mb (55.3%), suggesting instability of fish Mb. The melting temperatures of these Mb fell in the range of 75.7–79.9°C, lower than that of horse Mb (84.2°C). These results strongly suggest the instability of fish Mb.     

麦秸与胶粘剂之间的热反应研究

用差示扫描量热法测定和分析了麦秸与异氰酸酯 ( MDI)、脲醛树脂 ( UF)、酚醛树脂 ( PF)之间的热反应特征 .结果表明 :MDI与干麦秸之间的反应有吸热和放热现象 ,而 MDI与湿麦秸之间的反应却只有吸热现象 .UF与麦秸混合物在加热过程中 ,两者之间的胶合热反应不明显 .与 UF相比 ,PF与麦秸之间的热反应更明显     

超氧化物歧化酶微胶囊的制备及微囊结构的表征

[目的]优化超氧化物歧化酶微胶囊的制备工艺,并对该微胶囊的结构进行初步的分析.[方法]采用水中干燥法制备超氧化物歧化酶微胶囊,并对其工艺进行优化.利用扫描电镜技术,分析超氧化物歧化酶微囊的表面形态及大小分布;并采用X射线光电子能谱和示差扫描热量技术,初步研究超氧化物歧化酶微囊的结构.[结果]在最佳工艺条件下,超氧化物歧化酶微囊形状规则,粒径分布均匀.超氧化物歧化酶微胶囊是由乙基纤维素包裹超氧化物歧化酶成囊的,乙基纤维素与超氧化物歧化酶呈囊后,乙基纤维素与超氧化物歧化酶分子间形成很强的分子间相互作用.[结论]超氧化物歧化酶微囊的结构分析,对进一步研究微胶囊的控制释放机制和改进微囊性能具有一定的意义.     

基于等温滴定微量热技术的植物脱落酸受体鉴定的方法

等温滴定微量热技术(ITC)是一种新发展的研究生物分子互作的方法,可获得生物分子相互作用的完整的热力学和动力参数等。为了探明ITC在植物激素受体筛选和鉴定方面的应用可靠性,以植物激素脱落酸(ABA)受体为例,通过等温滴定试验获得ABA受体PYR1和ABA结合的热力学信息,包括结合常数(Kd),反应的化学计量数(N)和焓(ΔH)等,开发植物激素受体筛选和鉴定的技术体系。ITC试验显示,受体蛋白PYR1和ABA结合Kd为67μmol/L,N为0.92,ΔH为19.78kJ/mol,表明他们结合具有特异性、饱和性和高亲和性等特征。等温滴定微量热技术可以应用于激素受体的筛选和鉴定。     

Starch properties, in vitro digestibility and sensory evaluation of fresh egg pasta produced from oat,teff and wheat flour

Specific dietary requirements, e.g. celiac disease, as well as increased consumer demand for products of high nutritional value, makes the production of pasta from alternative cereals interesting. Raw material characterisation showed that the utilisation of oat and teff flour is beneficial as these ingredients contain higher levels of fibre and mineral composition is superior to that of wheat. Starch properties significantly influence pasta quality and therefore damaged starch levels, amylase activity, pasting properties and gelatinisation temperatures of the flours were investigated. Fresh egg pasta based on wheat, oat and teff flour was produced. Sensory properties of oat spaghetti were found to be very close to that of wheat pasta but improvement of smoothness and aroma is necessary, while teff spaghetti showed reduced sensory quality. An in vitro enzymatic digestion was performed using a dialysis system to mimic the behaviour of pasta as eaten and make predictions on the glycemic index (GI). The predicted GI was highest for wheat pasta, followed by teff and oat. Ultra structure was studied using confocal laser scanning microscopy, allowing the visualisation of differences in starch granule size and shape as well as gelatinisation occurring during the cooking process.     

Variation in physicochemical properties and nutritional quality in chalky mutants derived from an indica rice

The physicochemical and nutritional quality of four chalky mutants (JM1-4) rice and their parent 93-11 were investigated. JM1 and JM4 are white-belly mutants, and JM2 is white-core mutant, while JM3 is floury mutant. JM2 is also a high amylose mutant with AAC of 29%. JM3 had the lipid content nearly three times of the parent, so it is also a high lipid mutant. JM1 had similar pasting viscosities with the parent, while JM2 and JM3 had smaller breakdown and setback than 93-11. JM2 had lower enthalpy of gelatinization, but higher enthalpy of retrogradation, so it had highest retrogradation percentage. JM3 had the highest accumulation of amino acids, fatty acids, and some major mineral elements such as P, K, Mg and Ca. The amino acids and fatty acids had negative correlation with PV, HPV and CPV. The pleiotropic effects caused by the mutations on starch and lipid metabolism deserve further investigation.     

纳米无机物对MF树脂耐磨性能的影响

用单一和复合的纳米无机物直接加入三聚氰胺甲醛(MF)树脂中,探讨其种类、用量、复合比例等对MF树脂耐磨性的影响。结果表明,纳米二氧化硅HTSi-03和纳米三氧化二铝HTAl-06以1:2的质量比复合,总用量为30g·m-2时,能显著提高MF树脂浸渍装饰纸层压板的耐磨性能,耐磨转数可达4300r,达到浸渍纸层压木质地板国家标准家用Ⅱ级的要求。用红外光谱和差示扫描量热法进一步分析了纳米无机物对提高MF树脂耐磨性的改性机理。     

大豆分离蛋白-玉米淀粉-谷朊粉共混体系热转变特性

【目的】蛋白质和淀粉的热转变特性对食品加工有重要的理论指导价值,系统研究蛋白质-淀粉共混体系的热转变特性,优化热加工参数,控制食品质量和节能。【方法】以大豆分离蛋白、玉米淀粉和小麦谷朊粉为研究对象,采用差式扫描量热技术,在20—130℃,水分含量为30%—70%,升温速率为10℃·min^-1条件下,测定大豆分离蛋白-玉米淀粉、大豆分离蛋白-谷朊粉、谷朊粉-玉米淀粉和大豆分离蛋白-玉米淀粉-谷朊粉混合体系在0—100%比例范围时的热转变特性。【结果】随着水分含量从30%增加至70%,大豆分离蛋白11 S亚基的热转变起始温度和峰值温度分别从105.17℃降至94.80℃,从113.75℃降至99.49℃;峰宽从20.72℃降低至10.59℃,焓变从2.79 J·g^-1增加至6.18 J·g^-1;玉米淀粉的热转变焓值从3.62 J·g^-1增至14.14 J·g^-1。谷朊粉则无热转变现象。增加水分含量促进了蛋白质和淀粉分子链的运动性是大豆蛋白热转变温度降低,焓值升高,玉米淀粉热转变焓值升高的主要原因。当物料含水率为50%,相对于单一体系,大豆分离蛋白-玉米淀粉混合体系中大豆蛋白11S亚基的热转变焓值显著降低,平均降低1.41 J·g^-1;混合体系中玉米淀粉的热转变起始温度和峰值温度显著升高,分别平均升高14℃和13℃。大豆分离蛋白-谷朊粉混合体系仅显示大豆分离蛋白的热转变,11S亚基热转变的焓值呈降低的趋势,与未添加谷朊粉相比,平均降低了2.40 J·g^-1。谷朊粉-玉米淀粉混合体系仅显示玉米淀粉的热转变,与未添加谷朊粉相比,玉米淀粉热转变的峰值温度和峰宽显著升高,平均增加12℃。大豆分离蛋白-玉米淀粉-谷朊粉混合体系中,当玉米淀粉和谷朊粉等比例增加时,大豆蛋白11S亚基与未添加玉米淀粉和谷朊粉相比,其热转变起始温度、峰值温度、焓值和峰宽均显著降低,分别平均降低4℃、5℃、1.64 J·g^-1和3℃。当固定大豆分离蛋白含量为40%,和添加40%谷朊粉相比,添加40%玉米淀粉的11S亚基热转变起始温度和峰值温度均显著降低了3℃。蛋白质与淀粉竞争水分可能是导致混合体系中淀粉热转变温度升高的主要原因,而玉米淀粉和谷朊粉分子的空间位阻是导致大豆蛋白11S亚基热转变焓值下降的主要原因。【结论】添加玉米淀粉或谷朊粉能降低大豆蛋白热转变焓,添加大豆分离蛋白或谷朊粉能增加玉米淀粉热转变温度。