Polyacrylamide对菠萝蛋白酶活力的稳定作用

行了提高菠萝蛋白酶活力稳定性的技术开发研究。以Polyacrylamide(PAAM)作为菠萝蛋白酶的稳定剂,采用桂Q/ws-1-326-84的方法测定菠萝蛋白酶的活力;在Perkin-Elmer公司的差示扫描量热仪(DSC)上,测定菠萝蛋白酶(每样5~10mg)在30~130 ℃之间的热效应。研究结果表明,PAAM可使菠萝蛋白酶的变性温度提高5.7℃;在25℃下贮存时,加PAAM稳定剂的酶的失活率常数K1为1.33×10-4/h和纯酶的失活速率常数K2为2.65×10-4/h,半衰期由109d提高到217d;在液体酶的情况下,PAAM同样显著提高了酶液的稳定性     

差示扫描量热法在大豆蛋白产品品质检测中的应用

差示扫描量热分析仪(DSC仪)因其使用方便,精确度高等特点,多年来备受青睐.综述了近20年来DSC分析仪在大豆蛋白产品品质测定中的典型应用,涉及试验条件的选择及因试验条件不同导致的试验结果的差异.主要包括升温速率、保护气体、样品量、液体样品的溶剂等条件对样品热稳定性的影响.     

Rheological and Thermal Properties of Potato Starch

<正>Particle size, rheological and thermal properties of potato starch from Yunnan province of China was investigated. The particle size ranges from 0.429-102.3 μm determined by laser light-scatter. The major flow type of 6 w/v% potato starch was shear-thinning fluid even the shear rate up to 800·s-1, and the gel formed by 6 w/v% potato starch fell to weak gel for its little difference between G′ and G′′, high dependence on frequency and low value of G′(Pa). The hardness and cohesiveness of potato starch gel were 31.3 g and 131.9 g·s, respectively. The thermal properties of potato starch were also determined by DSC at the starch∶ water = 3∶ 1. The To, Tp, and △H of potato starch were 62.23℃, 67.31℃, and 2.22 J·g-1.     

差示扫描量热法(DSC)在油脂分析中的应用

介绍差示扫描量热法(DSC)在测定油脂的组分、结晶与融化、氧化及氧化动力学和油脂掺假等方面的应用，以及热分析法在油脂的科学理论研究和实际生产中的应用前景。     

Novel mechanochemical approach for wheat starch-LPC complex formation

Amylose-LPC inclusion complexes are acquired by a novel mechanochemical method and by hydrothermal method. The new synthetic method includes mechanical milling of suspension of LPC and starch under controlled conditions. Both methods applied resulted in similar microstructure of the complexes, studied by x-ray diffraction (XRD). Furthermore, Solid-state ¹³C NMR spectroscopy and differential scanning calorimetry (DSC) also confirm the efficient complexation by the new approach.     

A Continuous Measurement of Swelling of Rice Starch During Heating

The changes in size distribution of rice starch granules during heating have been determined continuously using a polarised light microscope in combination with a hot stage and an image analysis system. The size of starch granules increased slightly as the temperature was raised from 35°C to 55°C, with a 3·9% increase in average area; however, a dramatic increase in size of starch granules occurred at 65°C. The swelling of the starch granules reached a maximum 54·7% increase in average area at 75°C which is coincidental with the peak temperature (T_p) of DSC thermograms. Starch granules proceeded to disrupt/dissolve above 75°C. Loss of birefringence occurred at a lower temperature than granule rupture.T_pappeared to be the critical point in the phase change between the stages of swelling and disruption/dissolution of rice starch granules during heating.     

Effects of gamma irradiation on starch granule structure and physicochemical properties of brown rice starch

In the present research effects of gamma irradiation (5–20 kGy) on the physicochemical, antioxidant and thermal properties of brown rice starch were studied. Scanning electron microscopy displayed mostly polyhedral shapes with no surface fractures. XRD displayed characteristic A type pattern and decrease in per cent crystallinity (22.53–20.41%) was observed as the dose increased from 5 to 20 kGy. DPPH % inhibition and FRAP values were increased in a dose dependent manner. Pasting properties (peak, final and setback viscosity) decreased with irradiation. Pasting temperature also significantly decreased with irradiation for all the irradiated starches. The transition temperatures, enthalpy of gelatinization, pH and apparent amylose content of starch decreased significantly with increase in irradiation dose.     

Preparation of starch-based polyurethane films and their mechanical properties

In this study, polyurethane films were prepared using starch as the main polyol component, and the mechanical properties of these films were investigated. The starch content of the polyols was 30–50 wt%. To confirm the formation of a urethane linkage between the −OH of starch and −NCO of toluene 2,4-diisocyanate, Fourier transform infrared (FT-IR) spectroscopic analysis was performed. Differential scanning calorimetry (DSC) thermograms of the polyurethanes resulted in two endothermic peaks, which shifted to higher temperatures with increasing starch content and −NCO/−OH molar ratio. Due to the melting behavior of polyurethane, films could be prepared by hot pressing at an appropriate temperature. Polyurethane films were prepared with various polyol starch content and −NCO/−OH molar ratios. Tensile testing indicated that the breaking stress and elastic modulus increased significantly with starch content and −NCO/−OH molar ratio. In addition, bending tests indicated an increase in breaking stress and bending modulus with starch content and −NCO/−OH molar ratio and decreased breaking strain. The strain rate in both tensile and bending tests had a significant effect on the mechanical properties.     

Glass transition temperature of starches with different amylose/amylopectin ratios

The glass transition temperatures (T_g) of starch with different amylose/amylopectin ratios were systematically studied by a high-speed DSC. The cornstarches with different amylose contents (waxy 0; maize 23, G50 50 and G80 80) were used as model materials. The high heating speed (up to 300 °C/min) allows the weak T_g of starch to be visible and the true T_g was calculated by applying linear regression to the results from different heating rates. It is confirmed for the first time, that the higher the amylose content is, the higher the T_g is for the same kind of starch. The sequence of true T_g of cornstarch is G80 > G50 > maize > waxy when samples contain the same moisture content, which corresponds to their amylose/amylopectin ratio. It was found that T_g was increased from about 52 to 60 °C with increasing amylose content from 0 to 80 for the samples containing about 13% moisture. The microstructure and phase transition were used to explain this phenomenon, in particular the multiphase transitions that occur in high-amylose starches at higher temperatures, and the gel-ball structure of gelatinized amylopectin.     

Effect of thermal processing and storage on digestibility of starch in whole wheat grains

Gelatinisation and retrogradation of starch in wheat flour systems and whole wheat grains were studied using DSC and the impact of these events on starch digestibility was investigated. Gelatinisation of starch was possible in wheat flours with more than 60% moisture content (dwb) and gelatinised samples had higher digestibility values. Retrogradation of starch was studied with partially and fully cooked (boiled at 100 °C for 12 min and 32 min, respectively) wheat grains that were subjected to storage at 22 °C for 48 h. Stored samples had lower digestibility values when compared to the freshly cooked counterparts. The effect of moisture on retrogradation was studied with fully cooked wheat grains that were dried to a range of moisture contents (14.6–35.9%, wwb) and stored at 20 °C for 24 h. Retrogradation enthalpy increased with increasing moisture content; however, digestibility values did not reflect the changes in retrogradation enthalpy. The possibility of estimating the degree of retrogradation in fully cooked grains (32 min cooking) was investigated using a wheat flour-water system. The retrogradation enthalpy of fully cooked grains was slightly higher than the wheat flour-water system (at a moisture content of 49%, wwb) during the course of storage at 22 °C.     

Impact of guar and xanthan gums on proofing and calorimetric parameters of frozen bread dough

The influence of guar and xanthan gum and their combined use on dough proofing rate and its calorimetric properties was investigated. Fusion enthalpy, which is related to the amount of frozen water, was influenced by frozen dough formulation and storage time; specifically gum addition reduced the fusion enthalpy in comparison to control formulation, 76.9 J/g for formulation with both gums and 81.2 J/g for control, at 28th day. Other calorimetric parameters, such as T_g and freezable water amount, were also influenced by frozen storage time. For all formulations, proofing rate of dough after freezing, frozen storage time and thawing, decreased in comparison to non-frozen dough, indicating that the freezing process itself was more detrimental to the proofing rate than storage time. For all formulations, the mean value of proofing rate was 2.97 ± 0.24 cm³ min⁻¹ per 100 g of non-frozen dough and 2.22 ± 0.12 cm³ min⁻¹ per 100 g of frozen dough. Also the proofing rate of non-frozen dough with xanthan gum decreased significantly in relation to dough without gums and dough with only guar gum. Optical microscopy analyses showed that the gas cell production after frozen storage period was reduced, which is in agreement with the proofing rate results.     

Experimental studies on the physico-chemical properties of banana fibre from various varieties

Natural cellulosic fibres from various varieties of banana plants such as Red Banana, Nendran, Rasthaly, Morris and Poovan have been extracted manually and the physico-chemical properties of these fibres are investigated. The tensile strength of these fibres varies from 176 MPa to 525 MPa. The untreated fibres have more tensile strength than the treated one. The thermal properties of these fibres are studied by Differential Scanning Calorimetry (DSC). Two DSC thermal peaks, one is around 25°C to 180°C and the other is around 155°C to 240°C, are noticed. The tensile strengths have a direct correlation with the area of the lower thermal peak (enthalpy) and activation energy of the DSC, and also with the moisture absorption characteristics. The FTIR shows characteristic bands corresponds to cellulose. The reflections of the X-ray fibre diffraction pattern recorded for the banana fibre have been correlated with the mechanical strength.     

利用mRNA差别显示技术分离橡胶树死皮病相关cDNA

从中国热带农业科学院橡胶树早期预测试验地采集不同品系的橡胶树胶乳和树皮组织，分别提取纯化mRNA 合成cDNA第一链。通过4个简并锚定引物和10个随机引物进行PCR扩增，经6％变性聚丙烯酰胺凝胶电泳后发现了至少4个差异DNA片段只在健康树中表达而在死皮树中没有出现，这4个差异DNA片段分别命名为Hb1(725bp),Hb2,Hb3,Hb4。对Hb1进行了分离，纯化，经Northern杂交证实，Hb1在健康树胶乳中表达活跃，而在死皮树胶乳中表达受到强烈抑制，表明Hb1是与死皮病相关的cDNA片段，进一步将Hb1片段进行回收和克隆，并进行DNA序列分析，序列在GenBank中进行BLAST分析未发现相关同源片段，死皮病相关cDNA片段的获得，将分离全长死皮病相关基因，搞清该基因表达调控的机理提供条件，进而为从分子水平上阐明死皮病的致病机理打下了基础。     

Contribution of Major Ingredients during Baking of Biscuit Dough Systems

Nineteen dough systems were made of a combination of two to nine of the following ingredients: flour, water, fats (coconut and/or palm oils), sugars (sucrose, invert) and chemical leaveners (ammonium bicarbonate, sodium bicarbonate, citric acid and sodium acid pyrophosphate). Their thermal behaviour was studied over a large temperature scale (20 °C to 160 °C). Thermal analysis of baking by three different methods (DSC, DMTA and TGA) at the same heating rate (3 °C/min) provided information about phase transitions, volume and mass changes of doughs during heating. Temperature ranges over which all ingredients reacted were identified. Melting transitions of fats occurred between 10 °C and 50 °C. Sugars increase temperatures of starch transitions. Chemical leaveners decrease rise temperature, whereas fats and sugars have a delaying effect on their action. The texture of biscuits results from interactions between ingredients; complete dough cannot thus be considered as merely a simple addition of all components.