桃金娘中可水解丹宁的分离与结构

利用Diaion HP-20、Toyopearl HW-40及MCI gel CHP-20P等反复柱层析,从桃金娘(Rhodomyrtus tomentosa(Ait)Hassk)叶及根中分得4种可水解丹宁,其中3种为C-甙可水解丹宁。经化学方法和波谱分析,分别确定为:pedunculagin(Rt-2),casuariin(Rt-3),castalagin(Rt-9)和一新的C-甙可水解丹宁(Rt-8),命名为山稔甲素(tomentosin),这些化合物均为首次从该植物中得到。     

天然C19—二萜生物碱的核磁共振谱（Ⅱ）

本文将迄今为止已发表的230余个天然C_(19)二萜生物碱,按其结构和核磁共振波谱特征分为8个类型,着重叙述了每个类型的结构和核磁共振波谱,并对某些立体构型与~(13)C-NMR化学位移的关系进行了讨论。最后以表格的形式报导了每个天然C_(19)-二萜生物碱的结构及其主要植物来源,并将其中170余个生物碱的~(13)C-NMR化学位移数据分门别类,整理成表,有助于C_(19)-二萜生物碱的结构鉴定。这是本文的第二部分,包括二氧亚甲基型,氨缩醛型,C-18甲基型。C_(18)型不饱和型和内脂型等六个类型的结构特征及其核磁共振波谱。     

大曲来源淀粉利用型乳酸菌的筛选及其淀粉利用特性

【背景】乳酸菌是面包、馒头等发酵食品中的重要功能微生物,对改善质地和风味均具有重要作用。淀粉利用能力高的乳酸菌,因其能够在生面粉中更好地定殖而具有重要的应用价值。【目的】筛选获得淀粉水解型乳酸菌并研究其淀粉利用特性。【方法】以浓香型白酒大曲为筛选源,采用淀粉基质碳源对大曲中乳酸菌进行定向富集,结合淀粉发酵能力筛选高淀粉利用能力菌株,并对筛选得到的优良菌株展开淀粉酶表达及其酶活力研究。【结果】以贮存3-6个月的大曲为优秀筛选源,以生面糊传代富集方法可较快筛选出具有良好淀粉利用能力的乳杆菌,主要物种为植物乳杆菌和类食品乳杆菌。对其中一株具有淀粉利用能力的类食品乳杆菌LBM12001的淀粉水解特征和淀粉酶活力展开研究,该菌株淀粉水解能力达10 g/L,并且其在面糊中具有良好的定殖能力;酶活力测定表明,其α-淀粉酶和麦芽糖淀粉酶为胞外酶;麦芽糖淀粉酶水解淀粉的最适pH值为3.5,比酶活为1 240 U/mg。【结论】建立起从我国传统白酒发酵大曲中高效筛选淀粉水解型乳酸菌的富集筛选方法,以及菌株的水解能力评价方法,获得的胞外麦芽糖淀粉酶分泌型乳杆菌在酸面团、馒头等需进行生面粉发酵食品的生产中具有重要应用前景。     

综合利用薯芋淀粉生产肌苷的研究

本文报道综合利用野生薯芋属植物盾叶薯芋(Dioscorea zingibensisC.H.wright)和穿龙薯芋(Dioscorea nipponica Makino)中的淀粉生产肌苷(Inosine)的方法。将薯芋原料带水磨碎,在水中筛分得到皂甙淀粉浆,用稀酸水解该物质使淀粉糖化,分离后得到糖液和糖渣。糖液加氮源和无机盐,发酵生产肌苷。糖渣再水解提取薯芋皂甙元。     

海枣曲霉β-半乳糖苷酶的催化性质

 通过测定海枣曲霉β-半乳糖苷酶的底物特异性,表明该酶水解对-硝基酚基β-半乳糖苷(PNP-β-gal)的活力最高。该酶水解PNP-β-gal,乳糖和对-硝基酚基β-D-岩藻糖苷(PNP-β-fuc)的相对活力为100,63.1,10.3。不同测定方法的结果均表明,这一PNP-β-fuc水解活性来自β-半乳糖苷酶本身。Hg~(2+)、D-半乳糖和D-半乳糖-r-内酯对该酶有强烈的抑制作用,Ag~+和4mol/l脲也有较强的抑制作用。该酶水解PNP-β-gal和乳糖的Km值分别为1.3及36.2mmol/l,Vmax则分别为478和189μmol.min~(-1).mg~(-1)。Lineweaver-Burk作图法及Dixon作图法均表明D-半乳糖和D-半乳糖酸-γ-内酯对该酶显示竞争性抑制作用,其Ki分别为4和0.9mmol/l。     

产碱菌麦芽四糖淀粉酶水解淀粉的特性

产碱菌麦芽四糖淀粉酶水解不同来源淀粉的产物组成有差异:G4占81.5％～98.8％,G_3占0％～9.6％,G_2占0％～5.9％。不同淀粉的水解速度在4170～9036mgGlch~-(1)·mg~(-1)之间。对可溶性淀粉的水解产物为6-型。麦芽四糖淀粉酶能被小麦、玉米及马铃薯的生淀粉吸附,其吸附率分别为60.2％、50.0％及52.2％,相对水解率分别为4.5％、2.7％及0％,水解生淀粉的主要产物为G_4。     

植物叶片暂时淀粉分解途径研究进展

植物叶片暂时淀粉主要分解途径包括如下过程:叶绿体中半结晶状淀粉粒在葡聚糖-水双激酶(GWD)和磷酸葡聚糖-水双激酶(PWD)作用下磷酸化,使淀粉粒结构松散;异淀粉酶(ISA3)作用于松散淀粉粒而释放出磷酸葡聚糖,再经磷酸葡聚糖磷酸酶(SEX4)水解去除磷酸而生成可溶性线性葡聚糖;葡聚糖在β-淀粉酶(BAM3)催化下水解生成麦芽糖后,再通过麦芽糖载体(MEX1)转运至细胞质.该文主要综述了以上转化过程中涉及的底物、生成物和催化酶类的研究进展情况,同时简述了植物叶片暂时淀粉分解的次要途径和抗逆性相关途径,并提出了该领域目前存在的问题和今后研究方向.     

淀粉含量不同的玉米自交系籽粒淀粉积累及其关键酶活性

以2个高淀粉和2个低淀粉玉米自交系为材料,分析了玉米籽粒淀粉的动态积累规律,同时对高低淀粉玉米籽粒灌浆过程中淀粉生物合成关键酶活性的动态变化及其与淀粉积累动态的相关性进行讨论分析。研究结果表明:灌浆过程中4个自交系淀粉含量变化趋势均呈sigmoid型曲线。灌浆过程中ADPG-PPase(腺苷二磷酸葡萄糖焦磷酸化酶)、SSS(可溶性淀粉合成酶)、GBSS(颗粒结合淀粉合成酶)活性均呈单峰曲线变化,峰值都出现在20～30DAP(授粉后天数)。2个高淀粉自交系的Q酶(淀粉分支酶)活性也呈单峰曲线变化,峰值也出现在20DAP,而2个低淀粉自交系的Q酶活性则呈双峰曲线变化,2个峰值分别出现在15～20DAP和30～35DAP。4个自交系籽粒淀粉的积累速率与各自交系ADPG-PPase、SSS和GBSS的活性变化呈极显著正相关。各自交系关键酶活性之间,ADPG-PPase、SSS和GBSS三者间活性变化呈极显著正相关,这3种酶活性变化与Q酶活性变化也呈不同程度的正相关。     

黑曲霉突变株葡萄糖淀粉酶的底物特异性

黑曲霉(Aspergillus niger)突变株T-21葡萄糖淀粉酶(GAI)仅能水解多种淀粉及麦芽低聚糖生成唯一产物β-葡萄糖,其水解麦芽糖及麦芽三糖的速度分别为200和570mg葡萄糖·h^(-1)·mg^(-1).GAI水解α-1,4键的速度比水解α-1.6键快100多倍.除了马铃薯淀粉外,对其它淀粉及麦芽低聚糖几乎都能100%地水解,但不能水解环状糊精,其水解各麦芽低聚糖的最先产物都比原底物少一个葡萄糖单位,说明GAI为一外切型淀粉酶.GAI对麦芽糖、麦芽三糖、可溶性淀粉、糯米淀粉、糊精及糖原的Km值分别1.92mmol/L、0.38mmol/L、0.053%、0.045%、0.059%、及0.076%,V_(max)分别为590、1370、1270、1520、1120和1220mg葡萄糖·h^(-1)·mg^(-1).D-葡萄糖酸-δ-内酯及麦芽糖醇对此酶分别具有反竞争性抑制和混合性抑制.     

金星蕨科16种植物叶表皮特征的研究

利用光学显微镜对金星蕨科(Thelypteridaceae)8属16种植物的叶表皮形态进行了观察和研究,为金星蕨科植物的系统演化及分类提供科学依据。结果表明:(1)16种金星蕨科植物的叶片表皮细胞为不规则型,表皮细胞垂周壁大多呈深波状。(2)气孔为下生型,多呈椭圆形;共观察到6种气孔器类型(极细胞型、腋下细胞型、聚合极细胞型、聚腋下细胞型、不规则型和聚围绕细胞型),每种植物具2~5种不同类型的气孔器。(3)金星蕨科8属植物在表皮细胞大小、垂周壁形状、气孔大小和形状、气孔密度、气孔指数和气孔器类型上存在一定的属间差异。     

Effect of annealing and pressure on microstructure of cornstarches with different amylose/amylopectin ratios

This work focuses on the effect of annealing and pressure on microstructures of starch, in particular the crystal structure and crystallinity to further explore the mechanisms of annealing and pressure treatment. Cornstarches with different amylose/amylopectin ratios were used as model materials. Since the samples covered both A-type (high amylopectin starch: waxy and maize) and B-type (high amylose starch: G50 and G80) crystals, the results can be used to clarify some previous confusion. The effect of annealing and pressure on the crystallinity and double helices were investigated by X-ray diffraction (XRD) and ¹³C CP/MAS NMR spectroscopy. The crystal form of various starches remained unchanged after annealing and pressure treatment. XRD detection showed that the relative crystallinity (RC) of high amylopectin starches was increased slightly after annealing, while the RC of high amylose-rich starches remained unchanged. NMR measurement supported the XRD results. The increase can be explained by the chain relaxation. XRD results also indicated that some of the fixed region in crystallinity was susceptible to outside forces. The effect of annealing and pressure on starch gelatinization temperature and enthalpy are used to explore the mechanisms.     

Amylopectin molecular structure reflected in macromolecular organization of granular starch

For lintners with negligible amylose retrogradation, crystallinity related inversely to starch amylose content and, irrespective of starch source, incomplete removal of amorphous material was shown. The latter was more pronounced for B-type than for A-type starches. The two predominant lintner populations, with modal degrees of polymerization (DP) of 13-15 and 23-27, were best resolved for amylose-deficient and A-type starches. Results indicate a more specific hydrolysis of amorphous lamellae in such starches. Small-angle X-ray scattering showed a more intense 9-nm scattering peak for native amylose-deficient A-type starches than for their regular or B-type analogues. The experimental evidence indicates a lower contrasting density within the "crystalline" shells of the latter starches. A higher density in the amorphous lamellae, envisaged by the lamellar helical model, explains the relative acid resistance of linear amylopectin chains with DP > 20, observed in lintners of B-type starches. Because amylopectin chain length distributions were similar for regular and amylose-deficient starches of the same crystal type, we deduce that the more dense (and ordered) packing of double helices into lamellar structures in amylose-deficient starches is due to a different amylopectin branching pattern.     

Study on the granular characteristics of starches separated from Chinese rice cultivars

Granule size distribution, the relative crystallinity, morphology and thermal degradation of starches from 10 different non-waxy rice cultivars were measured in present study. The relationships between granular structure and thermogravimetric parameters of tested starches were evaluated using Pearson correlation analysis. The range of median size for rice starches was 6.23-7.81 μm. The relative crystallinity of 10 non-waxy rice starches ranged from 20.4% to 33.4%. The range of activation energy from different rice starches was between 155.6 and 201.5 kJ/mol. The Pearson correlation results showed that the relative crystallinity was positively correlated (r = 0.6750, p < 0.05) with the percentage of branch chains with DP12-23. Furthermore, the activation energy of the rice starches showed a positive correlation (r = 0.7903, p < 0.01) with relative crystallinity.     

Effect of γ-irradiation on pasting and emulsification properties of octenyl succinylated rice starches

Octenylsuccinylated (OS) starches from waxy rice or high-amylose rice (28.1% amylose) (DS 0.023 and 0.025, respectively) were gamma-irradiated at 10, 30, or 50kGy and their pasting and thermal properties, crystallinity, and emulsification property were examined. When the OS starches were irradiated, the degrees of substitution gradually decreased as irradiation dose increased. A significant decrease in pasting viscosity was observed with an increase in irradiation dose, indicating the presence of chain degradation induced by the radiation. The melting temperature and enthalpy determined by differential scanning calorimetry increased slightly by irradiating at 10 or 30kGy. Little change in crystallinity was observed in the X-ray diffraction analysis for the OS high-amylose rice starch regardless of irradiation doses, whereas a decrease in crystallinity was observed with the OS waxy starch irradiated at 50kGy. Chain degradation induced by irradiation occurred mainly in the amorphous regions, but some loss of crystallinity occurred when the irradiation was excessive. The OS starches showed greater emulsion capacity and stability than the native counterparts due to their amphipathic nature. The irradiation further improved the emulsification properties of OS starches. The irradiation at 10kGy was optimal, and treating at higher doses decreased the emulsion capacity and stability of the OS starches.     

Physicochemical properties and structure of large, medium and small granule starches in fractions of normal barley endosperm

Normal barley grain was milled to flour with a machine used to polish brewers' rice from the surface layer to the center. Large (18.4 microm, median size), medium (12.3 microm) and small (2.2 microm) granule starches were isolated from classified flours. Their physicochemical properties and fine structure were investigated. The percentage (w%) of large granules decreased from the surface layer to the center, while the amounts of medium and small granules increased. Although all the starch granules were an A-type crystal, the relative crystallinity varied from 22.0 to 27.4%. The DPn of the amyloses was around 1600 and similar for all the samples. But the amylose content of the starches varied from 21.9 to 26.4%. Also, the amylopectins showed differences in DPn (around 5700-7900) and chain-length distribution between granule size or fractions. The transition temperature ranges and the enthalpy values of the starch granules differed with granule size. The gelatinization properties showed no correlation with any of the parameters, except the enthalpy value and relative crystallinity (gamma = +0.73). The findings suggested that the structural characteristics of the starches in classified flours of normal barley differed essentially from those of waxy barley.     

Effect of heat–moisture treatment on the structure and physicochemical properties of tuber and root starches

Starch from tubers potato (Solanum tuberosum), taro (Alocassia indica), new cocoyam (Xanthosoma sagitifolium), true yam (Dioscorea alata), and root cassava, (Manihot esculenta) crops was isolated and its morphology, composition and physicochemical properties were investigated before and after heat–moisture treatment (HMT) (100 °C, for 10 h at a moisture content of 30%). Native starch granules were round to oval to polygonal with smooth surfaces. The granule size (diameter) ranged from 3.0 to 110 μm.The total amylose content ranged from 22.4 to 29.3%, of which 10.1–15.5% was complexed by native lipid. The phosphorus content ranged from 0.01 to 0.1%. The X-ray pattern of potato and true yam was of the ‘B’-type. Whereas, that of new cocoyam and taro was of the ‘A’-type. Cassava exhibited a mixed ‘A+B’-type X-ray pattern. The relative crystallinity, swelling factor (SF), amylose leaching (AML), gelatinization temperature range and the enthalpy of gelatinization of the native starches ranged from 30 to 46, 22 to 54, 5 to 23%, 13 to 19 °C and 12 to 18 J/g, respectively. Susceptibility of native starches towards hydrolysis by 2.2N HCl and porcine pancreatic -amylase were 60–86% (after 12 days), and 4–62% (after 72 h), respectively. Retrogradation was most pronounced in the B-type starches. Granule morphology remained unchanged after HMT. The X-ray pattern of the B-type starches was altered (B→A+B) on HMT. However, that of the other starches remained unchanged. HMT decreased SF, AML, gelatinization enthalpy and susceptibility towards acid hydrolysis, but increased gelatinization temperatures and enzyme susceptibility. Extent of retrogradation and relative crystallinity decreased on HMT of true yam and potato starches, but remained unchanged in the other starches. The foregoing data showed that changes in physicochemical properties on HMT are influenced by the interplay of crystallite disruption, starch chain associations and disruption of double helices in the amorphous regions.     

Preparation and characterization of new and improved soluble-starches, -amylose, and -amylopectin by reaction with benzaldehyde/zinc chloride

Seven different starches from potato, rice, maize, waxymaize, amylomaize-VII, shoti, and tapioca, and potato amylose and potato amylopectin have been reacted with benzaldehyde, catalyzed by ZnCl₂, to give new water-soluble starches and water soluble-amylose and soluble-amylopectin. In contrast to the native starches, aqueous solutions of the modified starches could not be precipitated with 2-, 3-, or 4-volumes of ethanol. β-Amylase gave no reaction with the modified starches, in contrast to the native starches, indicating that the modification occurred exclusively at the nonreducing-ends, giving 4,6-benzylidene-d-glucopyranose at the nonreducing-ends. Reactions of α-amylase with native and modified potato and rice starches gave a decrease in the triiodide blue color and an increase in the reducing-value that were similar for the native- and modified-starches, indicating the modified starches had not been significantly altered by the modification. The benzaldehyde-modified starches and benzaldehyde-modified potato amylose and potato amylopectin components, therefore, have a starch structure very much like their native counterparts, in contrast to the Lintner, Small, and the alcohol/acid-hydrolyzed soluble-starches that have undergone acid hydrolysis. The benzaldehyde-modified starches and starch components have significantly higher water solubility than their native counterparts even though the structures of the modified starches had only been slightly altered from the structures of their native counterparts. They all gave crystal-clear solutions that did not retrograde.     

New insights on the mechanism of acid degradation of pea starch

The degradation of pea starch granules by acid hydrolysis has been investigated using a range of chemical and structural methods, namely through measuring changes in amylose content by both the iodine binding and concanavalin A precipitation methods, along with small angle X-ray scattering (SAXS), wide angle X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The relative crystallinity, intensity of the lamellar peak and the low-q scattering increased during the initial stages of acid hydrolysis, indicating early degradation of the amorphous regions (growth rings and lamellae). In the first 2 days of hydrolysis, there was a rapid decline in amylose content, a concomitant loss of precipitability of amylopectin by concanavalin A, and damage to the surface and internal granular structures was evident. These observations are consistent with both amylose and amylopectin being located on the surface of the granules and attacked simultaneously in the early stages of acid hydrolysis. The results are also consistent with amylose being more concentrated at the core of the granules. More extensive hydrolysis resulted in the simultaneous disruption of amorphous and crystalline regions, which was indicated by a decrease in lamellar peak intensity, decrease in interhelix peak intensity and no further increase in crystallinity. These results provide new insights into the organization of starch granules.     

The effect of lintnerisation on wheat and potato starch granules

Wheat and potato starches were hydrolysed with 2·2 n hydrochloric acid at 35°C for a period of time up to 15 days. The residues (lintnerised starches) were washed and freeze dried, and studied by differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), small-angle light scattering (SALS), small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS). These techniques showed that profound changes took place in the first day of hydrolysis (during which time the extent of hydrolysis was 7·7% for potato starch and 12·5% for wheat starch). In particular, the gelatinisation enthalpy (ΔH) decreased, the X-ray crystallinity increased and the SANS and SAXS peaks (indicative of a regular spacing between crystalline and amorphous regions) virtually disappeared. The reduction in ΔH is surprising and is discussed at length. It was also shown that freeze drying results in a considerable lowering of the gelatinisation temperature of potato starch (and also of ΔH) while that of wheat starch is only slightly affected.