促进玉米直链淀粉回生的甘薯淀粉晶种的筛选及表征

通过向四次回生的玉米直链淀粉中添加草酸侵蚀的四次回生的甘薯淀粉、甘薯直链和甘薯支链淀粉晶种(质量分数:1%),研究甘薯淀粉晶种对玉米直链淀粉回生的影响。结果表明,甘薯淀粉晶种明显促进了玉米直链淀粉回生长晶,其中甘薯直链淀粉晶种使得玉米直链淀粉回生率达到59.5%,比不添加晶种提高了19.3%。可见吸收光谱研究表明,甘薯淀粉晶种及长晶后的玉米直链淀粉均保持了双螺旋结构。X-射线研究表明草酸侵蚀后甘薯淀粉、甘薯直链淀粉、甘薯支链淀粉均为A+B型。将其分别添加到玉米直链淀粉中并长晶后的样品,结构均为B型。DSC研究表明,甘薯支链淀粉晶种具有最高的吸热焓,说明其晶体含量最高。三种晶种分别促进玉米直链淀粉长晶后的结构较为相似,晶体含量也较相近。该研究为提高淀粉的回生率、研究回生淀粉结晶结构提供良好的技术支持。     

酵母菌发酵生淀粉提高马铃薯淀粉回生率机理研究

以马铃薯淀粉为原料,淀粉回生率为考察指标,研究酵母菌发酵对马铃薯淀粉回生率的影响。通过对比发酵前后马铃薯回生淀粉的可见和红外吸收曲线,分析了酵母菌发酵提高马铃薯淀粉回生率的机理。结果表明,纤细酵母菌发酵马铃薯淀粉可使马铃薯淀粉回生率由12%提高到39.4%,提高了2.28倍。发酵后马铃薯回生淀粉中直链淀粉的最大可见吸收波长为587.8 nm,大于发酵前的569.6 nm。酵母菌发酵马铃薯淀粉提高其回生率的原因有两方面:一是发酵过程产生的酶使马铃薯支链淀粉脱支生成直链淀粉,增加了参与回生直链淀粉的量;二是发酵过程使马铃薯淀粉中醛基部分转变为伯醇基,进而生成糖苷键,增加直链淀粉链长,有利于淀粉回生过程晶体长大。     

原花青素抑制玉米淀粉回生作用的研究

目的研究原花青素(OPCs)对高直链玉米淀粉、普通玉米淀粉和高支链玉米淀粉回生的影响。方法采用差示扫描量热仪(DSC)、傅立叶红外光谱仪(FTIR)、核磁共振光谱仪(NMR)测定与分析原花青素与淀粉间的相互作用;同时测定原花青素对淀粉体外消化性的影响。结果结果表明,随着OPCs含量的增加,高直链玉米淀粉回生程度降低;当OPCs添加量为5%时,原花青素对普通玉米淀粉和高支链玉米淀粉回生抑制效果较好。高直链玉米淀粉中慢消化淀粉(SDS)含量随OPCs增加而增加,普通淀粉中SDS含量在添加5%OPCs时较高,而高支链玉米淀粉的快消化淀粉(RDS)含量在5%时较高;NMR结果表明OPCs分子与直链和支链淀粉之间均存在分子间相互作用。结论添加5%原花青素对三种玉米淀粉回生抑制效果较好;原花青素对直链和支链淀粉的结合方式和结合能力不同。     

甘薯淀粉动力学特性及其回生机理探讨

采用流变仪和差示扫描量热仪考察了甘薯淀粉在不同保持时间下的回生过程,发现甘薯淀粉糊化后,在4℃下,支链淀粉结晶、直链淀粉-脂肪复合结晶物和纯直链淀粉结晶的形成和完善是一个动态变化的过程,其动力学模型可用Avrami方程表达.短期回生以直链淀粉结晶为主体,长期回生以支链淀粉结晶为主体,并伴随着直链淀粉链结晶的进一步完善和稳定.     

酶法修饰抑制小麦淀粉回生工艺优化及机理的探讨

糊化后的淀粉很容易回生,大大影响了淀粉制品的品质。采用β-淀粉酶处理对小麦淀粉进行酶法修饰,利用响应面分析法优化酶处理工艺条件,以获得最佳的抑制小麦淀粉回生参数。结果表明,β-淀粉酶修饰的最佳条件为:酶浓度为34.33 U,酶作用温度为56.5℃,酶作用时间32.2 min。在此工艺条件下制得的小麦淀粉凝胶,相对于未经酶处理的小麦淀粉凝胶,凝胶硬度降低了66.15%。通过对酶处理前后小麦淀粉的直链淀粉和还原糖含量以及支链淀粉平均侧链长度的测定,发现β-淀粉酶抑制小麦淀粉回生主要是通过降低直链淀粉和支链淀粉分子质量及支链淀粉平均侧链长度,从而降低了直链淀粉与支链淀粉形成双螺旋的趋向,抑制淀粉的回生。     

差示扫描量热法分析麦谷蛋白抑制小麦淀粉回生的机理

为了深入探索麦谷蛋白抑制小麦淀粉回生的机理,以小麦谷蛋白、小麦原淀粉和小麦回生淀粉中分子量分布范围较窄的直链和支链淀粉为原料,对比淀粉混合蛋白回生前后热学性质的变化,分析小麦谷蛋白抑制小麦淀粉回生的机理。结果表明,小麦谷蛋白的添加在回生前使小麦原淀粉、直链淀粉的峰值温度升高,使小麦支链淀粉的峰值温度降低,使3种淀粉的熔化吸热焓从225.0、238.0、241.8 J/g分别降低为134.2、96.5和93.5 J/g。回生后含谷蛋白的直链淀粉峰值温度下降,回生过程使含有谷蛋白的3种淀粉的熔化吸热焓均明显升高。小麦谷蛋白的添加使3种小麦淀粉均出现第2个峰值温度(220~230℃),说明蛋白和淀粉混合相互作用形成了新物质,该物质的形成阻碍了淀粉分子相互作用,抑制了淀粉的回生。     

玉米直、支链淀粉回生对含羟基红曲红色素护色机理探讨

以测定残留红曲红色素方法研究了玉米直链淀粉、支链淀粉的回生和色素添加方式对含羟基红曲红色素护色的效果,并利用红外光谱、核磁共振和X-射线衍射分析了淀粉护色机理。结果表明,玉米直链和支链淀粉的回生对红曲红色素具有明显的护色作用,15h紫外光照可使红曲红色素的保留率由38.3%提高到70%以上。在淀粉回生的糊化、高压和老化三个阶段中,高压后添加色素所得回生淀粉护色效果最好。核磁、红外和X-射线结果表明,回生淀粉与色素在C1、C6上发生了结合;直链淀粉结合色素更多,所以护色效果更好。     

不同米淀粉精细结构对其回生特性的影响

选用4种不同的淀粉,通过考察回生特性,探究相对分子质量、链长分布、短程有序性、相对结晶度及半结晶层状结构等精细结构影响回生特性的机理。结果表明：与糯米淀粉和粳米淀粉相比,小米淀粉和黑米淀粉回生值、硬度和热焓值较大,糯米淀粉储藏前后硬度和回生后的热焓值均较小,具有较好的抗回生特性。研究发现,这是由于小米淀粉和黑米淀粉的直链质量分数较高(小米淀粉15.55%、黑米淀粉11.22%),支链淀粉峰M_w较大(小米淀粉M_w=2.12×10⁷ g/mol、黑米淀粉M_w=2.25×10⁷ g/mol)、半结晶层厚(小米淀粉d=6.978 4 nm、黑米淀粉d=6.698 6 nm),且中长链占比大(小米淀粉B1链占比40.91%),易形成稳定的双螺旋结构,具有更高的表面有序度(小米淀粉0.76、黑米淀粉0.70),回生后2种淀粉分子重排更有序稳定。     

单波长比色法测定甘薯直链淀粉含量

对单波长比色法测定甘薯直链淀粉含量的条件进行了优化和分析,并对部分甘薯资源进行了测定。结果表明:与马铃薯和玉米相比,甘薯直、支链淀粉-碘复合物吸收曲线存在一定的差异;在620 nm波长下,单波长比色法用于甘薯直链淀粉含量鉴定和评价的准确性和精密度较高;测定的35份甘薯资源直链淀粉质量分数的变幅为10.35%~20.72%,平均16.67%。这些结论可为探索更加准确、简便、快捷地测定甘薯直链淀粉含量的方法和甘薯淀粉品质改良提供参考。     

低GI淀粉原料的筛选及理化特性和体外消化特性的研究

以豌豆、马铃薯、玉米、木薯、大米、小麦、鹰嘴豆中的淀粉为研究对象,对其淀粉颗粒形貌、粒径分布、糊化特性、直链淀粉含量及淀粉组分进行探究,并采用体外消化试验分析7种淀粉的体外消化特性,计算其预测血糖生成指数(expected glycemic index,eGI)。结果表明:豌豆淀粉和鹰嘴豆淀粉粒度分布比较集中,大小较均匀;豌豆淀粉和鹰嘴豆淀粉的回生值较高,易于老化;豌豆淀粉和鹰嘴豆淀粉的直链淀粉含量较高,玉米淀粉中快消化淀粉含量最高,马铃薯淀粉慢消化淀粉含量最高,而鹰嘴豆淀粉的抗性淀粉含量最高。体外消化试验结果表明:鹰嘴豆淀粉体外消化率曲线增速最慢,7种淀粉的eGI值从低到高依次为:鹰嘴豆淀粉(48.9)小麦淀粉(57.7)豌豆淀粉(59.9)玉米淀粉(67.3)木薯淀粉(70.2)马铃薯淀粉(70.3)大米淀粉(76.3)。     

Retrogradation of sweet potato amylose and amylopectin with narrow molecular weight distribution

Retrogradation of sweet potato amylose and amylopectin with narrow molecular weight distribution at different temperatures was investigated by X-ray diffraction (XRD). Atomic force microscope (AFM), scanning electron microscope (SEM) and light microscopy were combined to study the morphology of the molecular assemblies during retrogradation. Avrami equation was used to the retrogradation kinetics the of above starches by determining the crystallinity and the ratio of peak area of two distinctive peaks. It was found that only the ratio of peak area/total area at 2θ = ~16.3° could represent the crystallinity of retrograded starch-containing amorphous regions. Considering the crystallinity as retrogradation rate, only the retrogradation kinetics of sweet potato amylose could be analysed by Avrami equation, but not the amylopectin’s. All Avrami exponents n of amyloses at any temperatures were less than 1.0, indicating instantaneous nucleation and rod-like growth. AFM results showed that the maximum heights of layered structure for sweet potato amylose, amylopectin and blending of both were approximately 4800, 180 and 200 nm, respectively. The height of the former two decreased during storage, but the height of blending remained unchanged. Amylose served as nuclei of amylopectin during starch retrogradation.     

不同植物来源淀粉之间的理化性质的比较

本研究比较了绿豆淀粉、马铃薯淀粉、红薯淀粉、大米淀粉及玉米淀粉的理化性质,结果如下：绿豆淀粉具有最高的直链淀粉渗滤和胶凝值,并且这两个指标均与表观和总直链淀粉含量呈高度的相关关系。尽管绿豆淀粉具有最高的直链淀粉含量,但它并不显示出热糊稳定性。红薯淀粉在加热过程中具有高的膨润力和峰值黏度、高的崩溃值以及低的离水率,这表明红薯淀粉颗粒在加热时能够自由膨胀,糊的热稳定性差,淀粉的老化速率较低,而大米淀粉则与红薯淀粉相反。五种淀粉具有不同的胶稠度,马铃薯淀粉最高,而大米淀粉最低。离水率与直链淀粉含量不呈现明显的相关关系,因此其值的大小可能受其他因素的影响。     

Functional Properties and Retrogradation of Heat‐Moisture Treated Wheat and Potato Starches in the Presence of Hydroxypropyl β‐cyclodextrin

Some functional and retrogradation properties of native and heat‐moisture treated potato and wheat starches were examined in the presence of hydroxypropyl β‐cyclodextrin (HPβ‐CD). HPβ‐CD increased swelling factor, amylose leaching, and solubility of both native and heat‐moisture treated wheat starches but it had less impact on corresponding potato starches. Gelatinization enthalpy of native wheat starch was decreased in the presence of HPβ‐CD but was increased in potato starch with increasing concentration. Reduction of amylose‐lipid complex endotherm in both native and heat‐moisture treated wheat starch was observed in the presence of HPβ‐CD. Heat‐moisture treatment did not change the transition parameters of amylose‐lipid complex showing its resistance to hydrothermal treatment. HPβ‐CD greatly decreased the pasting temperature of wheat starch. Cold paste viscosity of both native and heat‐moisture treated wheat starch was increased by HPβ‐CD to a greater extent than corresponding potato starch. Amylopectin retrogradation of all the starches was unaffected in the presence of HPβ‐CD but heat‐moisture treatment slightly decreased retrogradation of potato starch. These results suggest that HPβ‐CD can disrupt the amylose‐lipid complex within the starch granule in both native and heat‐moisture treated wheat starch but has no influence on amylopectin retrogradation. However, greatly increased wheat starch setback with HPβ‐CD indicates its greater effect on wheat starch amylose retrogradation.     

Effect of retrogradation,pancreatin digestion and amylose/amylopectin ratio on the fermentation of starch by Clostridium butyricum (NCIMB 7423)

Using three different maize starches (maize, waxy maize and high amylose maize, containing 25%, 1% and 52% amylose, respectively) the influence of amylose/amylopectin content and of retrogradation on fermentation by the porcine caecal anaerobe Clostridium butyricum was assessed. Small intestine digestion was simulated using pancreatin before the starches were exposed to bacterial fermentation. It was found that retrogradation appeared to alter the extent of the fermentation and hence the amount of short-chain fatty acids produced, while pancreatin digestion appeared to alter the way in which the organism fermented the starch and hence the acetate/butyrate ratio. The amylose/amylopectin ratio seemed to have more influence on the way the starch was fermented by the bacteria after the starch had been subjected to digestion with pancreatic enzymes, but had less influence when the starch had been retrograded. © 1998 SCI.     

Molecular and physicochemical characterisation of starches from yam,cocoyam, cassava,sweet potato and ginger produced in the Ivory Coast

Granule sizes, macromolecular features and thermal and pasting properties of starches from seven tropical sources (Florido, Kponan and Esculenta yams, cocoyam, cassava, sweet potato and ginger) were compared with those of several well‐known cereal, legume and tuber starches. The aim of the study was to characterise some non‐conventional starches with a view to possibly marketing them. Amylose content varied from 148 mg g^?1 in Esculenta starch to 354 mg g^?1 in smooth pea starch. For total starches, weight‐average molar mass (M?_w) ranged between 0.94 × 10⁸ and 1.80 × 10⁸ g mol^?1 for potato and normal maize starches respectively. Gyration radius (R?_G) varied from 157 nm for ginger starch to 209 nm for normal maize starch. Gelatinisation enthalpy (ΔH) ranged between 9.8 and 20.7 J g^?1 for wheat and Florido starches respectively. Gelatinisation peak temperature (T_g) varied from 58.1 °C for wheat starch to 87.3 °C for ginger starch. Native starch granule mean diameter ranged between 5.1 and 44.5 µm for Esculenta and potato starches respectively. Cassava and potato starches had the highest swelling power and dispersed volume fraction at all treatment temperatures, while ginger starch had the lowest. Cocoyam starch had the highest and ginger starch the lowest solubility at 85 and 95 °C. Cassava starch was the most stable under cold storage conditions. Roots and tubers such as ginger and cassava produced in the Ivory Coast are new sources of starches with very interesting properties. Thus these starches could be isolated on an industrial level in order to market them. Copyright © 2007 Society of Chemical Industry     

Retrogradation Behavior of Wheat Starch Gels with Differing Molecular Profiles

Differing molecular profiles of starches were developed by acid treatment of native wheat starch. Molecular weight distribution, branching, and linear chain length distribution was characterized. Starches with fewer large size amylopectin fragments, increased smaller size amylopectin fragments, decreased branch points, decreased overall sizes, and narrower linear chain length distributions, had higher initial retrogradation rates. However, all aged starch gels had similar final crystalline enthalpy levels. Different retrogradation behaviors were due to smaller size amylopectin fragments, narrowed linear chain length distribution, and decreased branching. Retrogradation behavior was modeled using classical Avrami kinetics to allow comparison with other retrogradation studies.     

Properties of Cassava Starch Modified by Amylomaltase from Corynebacterium glutamicum

Amylomaltase (α‐1,4‐glucanotransferase, AM; EC 2.4.1.25) from Corynebacterium glutamicum expressed in Escherichia coli was used to prepare the enzyme‐modified cassava starch for food application. About 5% to 15% (w/v) of cassava starch slurries were incubated with 1, 3, or 5 units of amylomaltase/g starch. Apparent amylose, amylopectin chain length distribution, thermal properties, freeze–thaw stability, thermo‐reversibility, and gel strength of the obtained modified starches were measured. The apparent amylose content and retrogradation enthalpy were lower, whereas the retrogradation temperatures, freeze–thaw stability, and thermo‐reversibility were higher than those of the native cassava starch. However, when amylomaltase content was increased to 20 units of amylomaltase/g starch and for 24 h, the modified starch showed an improvement in the thermo‐reversibility property. When used in panna cotta, the gel strength of the sample using the 20 units/24 h modified cassava starch was similar to that of using gelatin.     

Physicochemical properties of potato and cassava starches and their mutants in relation to their structural properties

Physicochemical properties [swelling power (SP), pasting behaviour and retrogradation] of five wild type (wt), five amylose free (amf), four high-amylose (ha) potato starches (ps) and one wt and amf cassava starch (cs) were investigated. While swelling of wtps occurred in two phases, amfps showed a very fast swelling and no gel of swollen granules was observed at higher temperatures (>90 °C). Haps underwent only restricted swelling. SP of cassava starches were lower than those of potato starches. Wtps leached mainly amylose (AM) during heating at low temperatures. Molecules of higher molecular weight (MW) leached out at higher temperatures. Longer amylopectin (AP) chains [degree of polymerisation (DP) > 18] inhibited swelling while short chains (DP < 14) favoured swelling. Starch pasting behaviour of 5.0 and 8.0% starch suspensions was studied using Rapid Visco Analyser (RVA). For 5.0% suspensions, increased levels of high-MW AP and decreased levels of AM molecules led to higher peak viscosity. Longer AP chains (DP > 18) depressed peak viscosity, while short chains (DP < 14) increased peak viscosity for both concentrations. At 8.0%, peak viscosity increased with starch granule size. After 1 day of storage of gelatinised starch suspensions, wtps and especially amfps showed only limited AP retrogradation. In contrast, the high enthalpies of retrograded AP (ΔH_retro) and peak and conclusion temperatures of retrogradation (T_p,retro and T_c,retro) of haps suggested partial cocrystallisation between AM and AP. Chains with DP 18–25 seemed to be more liable to AP retrogradation. Wtcs and amfcs did not retrograde at room temperature.