Myosin affects the structure and volatile flavour compounds binding of G-actin in grass carp

The effects of myosin (0, 0.2, 0.4, and 0.6 mg mL⁻¹) on the protein structure and volatiles adsorption capacity of G-actin from grass carp were investigated. The results showed that the myosin addition increased the surface hydrophobicity and sulfhydryl contents of G-actin. The Raman spectroscopy analysis showed that the α-helix and β-sheet of G-actin were converted into β-turn and random coil with 0.2 and 0.4 mg mL⁻¹ of myosin, while only the β-turn content increased with 0.6 mg mL⁻¹ of myosin. The GC-MS analysis indicated that with myosin addition, the adsorption capacities of G-actin on alcohols (1-pantanol, 1-hexanol, 1-octen-3-ol, and 1-octanol) and ketones (2-pentanone, 2-heptanone, 2-octanone, and 2-nonanone) were enhanced; meanwhile, the binding of G-actin to aldehydes (pentanal, hexanal, octanal, and nonanal) was weakened. It was probably due to the formation of actomyosin, and also the excess myosin when treated with high concentrations (0.4 and 0.6 mg mL⁻¹) of myosin.     

盐渍土盐胀对低层建筑的危害及其防治

通过对硫酸盐渍土盐胀的主要影响因素和典型工程实例的综合分析,提出了低层建筑防治盐胀的若干途径和措施。     

Nitrogen nutrition and flavour compounds of carrots (Daucus carota L) cultivated in Mitscherlich pots

Carrots (Daucus carota L) of the cultivar ‘Nanthya’ F₁ were grown in Mitscherlich pots containing quartz sand with inorganic nitrogen fertilisation (five levels, four replications) and time‐controlled drip irrigation. The effect of different nitrogen uptake on the yield and on the amount and composition of essential oils, sugars and organic acids was investigated. Sucrose, glucose and fructose were extracted and analysed by HPLC; L ‐malic acid and citric acid were measured with an enzymatic test. Medium‐ and higher‐boiling flavour components were isolated as essential oils by simultaneous watersteam distillation and pentane extraction (SDE) and separated gas chromatographically (HRGC–FID). Thirteen essential oil components were identified by mass spectrometry as well as by comparison of retention times and quantified by external standards. The higher the supply of nitrogen, the higher was its uptake and as a consequence the higher were the nitrogen and nitrate contents of the leaves as well as the roots of the carrots. Carrots with lower nitrogen application had higher amounts of sucrose and essential oils but lower amounts of glucose and fructose. Fertilisation with nitrogen affected not only the total content but also the composition of the essential oils. A correlation between nitrogen nutrition and organic acids could not be found. © 2000 Society of Chemical Industry     

Kinetics of flavour and aroma changes in thermally processed cupuaçu (Theobroma grandiflorum) pulp

Changes in ‘fresh’ and ‘cooked‐notes’ during thermal treatment of cupuaçu (Theobroma grandiflorum) pulp were evaluated and modelled. Isothermal experiments in the temperature range of 70–98 °C were carried out and a non‐linear regression was performed to all data to estimate kinetic parameters. ‘Fresh’ and ‘cooked‐notes’ change followed simple first‐order (Ea = 78–82 kJ·mol⁻¹, z = 30–31 °C) and reversible first order (Ea = 80–85 kJ·mol⁻¹) kinetics, respectively. Although ‘cooked‐notes’ were linearly correlated with ‘fresh‐notes’ (R² = 0.99), the former was a better indicator for quality degradation. These results are useful to design pasteurisation processes while minimising sensory changes. © 2000 Society of Chemical Industry     

Sensory quality of ethylene‐exposed carrots (Daucus carota L,cv ‘Yukon’) related to the contents of 6‐methoxymellein,terpenes and sugars

Carrots were analysed for taste and odour and for contents of terpenes, 6‐methoxymellein and sugars during 3 weeks storage at 15 °C in an atmosphere containing ethylene (1 µl l⁻¹). The ethylene treatment caused an increase in 6‐methoxymellein and the conversion of higher amounts of sucrose to fructose and glucose compared to control carrots stored in air. This corresponded to higher sensory scores for bitterness and terpene flavour and a lower score for sweetness, as measured by an expert taste panel. Principal component analysis showed a more expressed bitter taste, earthy flavour, green flavour, terpene flavour and aftertaste in the ethylene‐treated carrots. Correlations were found between sweet taste and the content of sucrose (r = 0.91, p < 0.005) and between the contents of various terpenes (particularly γ‐terpinene, limonene and caryophyllene) and terpene flavour, green flavour, aftertaste and bitter taste (r ≥ 0.72, p < 0.05). In the air‐stored carrots these off‐flavours seemed to be masked by a high sucrose content. © 2000 Society of Chemical Industry     

青海盐渍土对变电工程的危害与治理

本文通过对青海省盐渍土的分布类型和特性进行论述和探讨,阐述了盐渍土对变电工程地基与基础的危害及破坏机理,并对盐渍土地区变电工程建(构)筑物的地基处理方法等问题进行了分析和研究,对盐渍土地区输变电工程和建筑工程地基基础设计起到了很好的指导作用。     

鸭儿芹挥发性化学成分的研究

用水蒸气蒸溜法提取鸭儿芹挥发性化学成分,气相色谱法分离,质谱法鉴定结构并与计算机系统储存的已知物质的质谱进行比较,共鉴定出17个挥发性化合物,主要挥发性化学成分有:α 蒎烯、β 水芹烯、β 蒎烯、β 月桂烯、对伞花烃、枞油烯、γ 松油烯、β 石竹烯、(Z) β 金合欢烯、1 甲基 8 异丙基 5 亚甲基 1,6 环葵二烯、β 芹子烯、[2R (2α,4aα,8aβ)] 1,2,3,4,4a,5,6,8a 八氢 4a,8 二甲基 2 (1 甲基乙烯基)萘、β 红没药烯等。萜类化合物占总峰面积的82 37%。     

The influence of precultivation parameters on the catabolism of branched-chain amino acids by Staphylococcus xylosus and Staphylococcus carnosus

The influence of precultivation parameters on the ability of Staphylococcus xylosus and Staphylococcus carnosus to convert branched-chain amino acids—leucine, isoleucine and valine—into volatile flavour compounds was investigated using resting cells in a defined reaction medium. The studied precultivation parameters were: growth phase, temperature, NaCl concentration and the concentration of leucine, isoleucine and valine (only for S. xylosus). Flavour compounds were sampled by automatic static headspace collection and separated/quantified using gas chromatography/flame ionization detection (GC/FID).Main catabolic products from degradation of leucine, isoleucine and valine were the flavour intensive branched-chain acids: 2- and 3-methylbutanoic and 2-methylpropanoic acids. The precultivation parameters altered the production of the branched-chain acids significantly, but to various degrees for S. xylosus and S. carnosus.Production of branched-chain acids by S. carnosus was only influenced slightly by the growth phase and not by changing the NaCl concentration between 4.0% and 10.0% (w/w). Lowering the temperature from 28°C to 18°C significantly decreased S. carnosus’ generation of branched-chain acids. In contrast, S. xylosus was significantly influenced by all precultivation parameters, in particular by the growth phase. Cells taken from growing cultures had a much higher production of branched-chain acids compared to cells taken from stationary cultures. Addition of leucine and valine to the precultivation medium enhanced the production of branched-chain acids whereas addition of isoleucine had the opposite effect.     

CHANGES IN ACTIVITY OF SORGHUM LIPASE DURING MALTING AND MASHING

Lipase activity was monitored during malting and mashing of sorghum grains. All three sorghum varieties contained detectable lipase activity in the ungerminated form. Lipase activity changed only slightly during steeping for 24 hours but increased several fold in the course of germination. Between 24% and 60% of the lipase activity of the green malt was retained after kilning at 48°C but no activity was detected in the wort after mashing at 65°C. About 68% of the lipase activity of 72 hours old malt was detected in the plumule, while 29% and 3% were detected in the endosperm and radicle, respectively. Optimum activity was observed at pH 7.0.     

制曲微生物及蛋白质分解力的关系初探

通过对高温大曲入室发酵机理的探索,寻找高温大曲发酵过程中的各种微生物消长规律、微生物与蛋白质分解力的关系。结果表明,高温大曲在发酵初期微生物的数量、种类都最多,中后期芽孢菌占优势;而由于需满足微生物的生长及形成多种香味物质或其前驱物质,因而中期发酵大曲蛋白质分解力是最高的,可达16～19μg/g·min(酪氨酸计)。