Effect of repeated heating and cooling cycles on the pasting properties of starch

The properties of starch and starch–lipid pastes have been explored using a novel extended Rapid Visco Analyser (RVA) profile, in which the heating and cooling cycles are repeated five times. Starches from four wheat varieties with amylose content ranging from 23 to 27%, and waxy starches of wheat, rice and maize were tested, alone and in mixtures with lauric acid and monopalmitin (glyceryl-1-monopalmitin). Gels of all of the starches formed and melted reproducibly during repeated heating and cooling in the RVA. The addition of lauric acid to the waxy starches had no effect on the multiple RVA profile. Monopalmitin caused an increase in viscosity during the heating stage of the second to the fifth cycles with the waxy starches, which was attributed to the presence of monopalmitin aggregates. Changes in the multiple cycle viscosity traces observed when monopalmitin or lauric acid was added to the amylose-containing starches were complex. It was concluded that RVA paste viscosities were determined by starch–lipid interactions, as well as by free lipid in the starch mixtures. The water solubility of the lipid and association of proteins with starch granules influence these interactions.     

Hydrothermal modification of wheat starch. Part 2. Thermal characteristics of pasting and rheological properties of pastes

Water suspensions of starch (with the concentration of 8 g/100 g) were prepared in a measuring vessel of a Brabender viscograph and heated to temperatures of 74, 76.5, 79, 81.5, 84, 86.5, 89, 91.5 or 94 °C under continuous stirring. The resultant solution was cooled and frozen, and then defrosted. Thermal characteristics of re-pasting, rheological properties of produced pastes, starch solubility in water and swelling power were determined.The heating and freezing of the wheat starch suspension induced changes in its properties, with tendency and extent of these changes depending on temperature of pre-heating. The thermal characteristics of the analyzed starches revealed three peaks that corresponded to transitions proceeding during solubilization of retrograded amylopectin and retrograded amylose and solubilization of amylose–lipid complexes. Retrogradation of amylose induced by starch pre-heating followed by its freezing affected also the consistency coefficient and yield stress of the pastes formed by the analyzed starches. Values of these rheological parameters were higher at higher temperatures of pre-heating, compared to the pastes prepared from native starch, and were changing accordingly to the determined second order polynomial function. Amylose retrogradation occurring during the production of starch preparations diminished their solubility in water and increased their swelling power compared to native starch.     

Hydrothermal modification of wheat starch part 1. Effect of particle size on the viscosity of formed pastes

Aqueous starch suspensions (8 g/100 g) were prepared in a measuring flask of a Brabender viscograph and heated to temperatures of 74.0, 76.5, 79.0, 81.5, 84.0, 86.5, 89.0, 91.5 or 94.0 °C under continuous stirring. The resultant solution was cooled and frozen, and then defrosted and subjected to re-pasting in the Brabender viscograph.The heating and freezing of wheat starch suspension evoked changes in its properties, with the tendency and extent of these changes dependent on the pre-heating temperature. During re-pasting of the produced starch preparations in a Brabender viscograph, an increase occurred in particle size of the granules—and 8-fold increase in paste viscosity—compared with pastes produced from native starch. The viscosity of pastes was positively correlated with the size of formed gel sacks determined using a laser particle size analyzer. This was also found to depend on pre-heating temperature and changed according to a determined quadratic function. The strength of produced gels, measured with the oscillating–rotating viscometer, was higher than that of the gel produced from native starch and depended on the pre-heating temperature; however, these changes followed a determined quadratic function.     

干热变性莲子淀粉特性的研究

从淀粉的颗粒特性、淀粉糊特性及淀粉糊化后的成膜特性等方面对干热变性莲子淀粉特性进行系统的研究，以期为干热变性莲子淀粉的进一步研究开发利用提供理论基础。结果表明：添加海藻酸钠对莲子淀粉干热处理后，淀粉颗粒多数呈椭圆形，少部分淀粉颗粒表面有细微裂纹，颗粒彼此粘连，淀粉颗粒表面有粘连物；溶解度升高，膨胀度降低，淀粉糊透明度降低。干热变性处理对提高莲子淀粉糊冻融稳定性的作用不明显；布拉班德黏度曲线显示，添加海藻酸钠进行干热变性后莲子淀粉起糊温度明显降低，终值黏度降低，热稳定性降低，冷稳定性增强，凝沉性减弱。添加海藻酸钠进行干热变性可以提高莲子淀粉膜的机械性能和阻水性，降低膜的溶解度。     

Properties of starch-palmitic acid complexes prepared by high pressure homogenization

Aqueous mixtures of defatted corn starch and palmitic acid were heated and high pressure homogenized in order to form amylose inclusion complexes. The effects of homogenization pressure (0–120 MPa) and palmitic acid concentration (0.5–8% based on starch content) on starch-palmitic acid complex formation as well as on complex index, X-ray diffraction, thermal properties, viscosity and particle size were investigated. Complex index increased with an increase in the amount of palmitic acid and homogenization pressure, and reached a maximum value (about 60%) when the fatty acid content was 4% and the homogenization pressure was 100 MPa. X-ray diffraction patterns indicated the formation of V-helical complexes between starch and palmitic acid. This technology could prospectively be used in prepared starch-lipid complexes.     

The Null-4A Allele at the Waxy Locus in Durum Wheat affects Pasta Cooking Quality

Granule-bound starch synthase, also known as the waxy protein catalyses the synthesis of amylose in wheat endosperm starch. In durum wheats, the genes encoding GBSS are present at the two Wx loci on chromosome 7A and 4A (a segment of 7B that has been translocated). Several null Wx-B1 (missing GBSS protein from chromosome 4A) durum lines were produced from crosses with null-4A bread wheats backcrossed to durum wheats. Semolina milled from 4 normal and 7 null-4A durum wheat lines grown over two seasons (1999 and 2000) in South Australia were analysed for amylose content, starch pasting properties as measured by the Rapid Viscoanalyzer (RVA), swelling power and starch damage, protein content and electrophoretic protein analysis. Spaghetti was prepared with a micro-scale extruder and the cooked pasta evaluated for cooking loss, firmness, stickiness and water absorption. The null-4A lines had significantly lower (ca. 5%) amylose content, higher starch peak viscosities and semolina swelling power. The pasta derived from the null-4A lines had lower cooking loss and in 1999 was more adhesive than the non-waxy lines. Cooking loss was correlated with amylose content, peak starch viscosity, swelling power of semolina and cooked pasta adhesiveness. Semolina swelling power was highly correlated with RVA peak viscosity. Waxy durum wheats appear to have an advantage over the normal types in terms of lower cooking loss, widely used as an indicator of pasta cooking quality.     

The impact of heating and cooling on the physico-chemical properties of wheat gluten–water suspensions

The rapid visco analysis (RVA) system was used to measure rheological behaviour in 20% (w/v) gluten-in-water suspensions upon applying temperature profiles. The temperature profiles included a linear temperature increase, a holding step, a cooling step with a linear temperature decrease to 50 °C, and a final holding step at 50 °C. Temperature and duration of the holding phase both affected RVA viscosity and protein extractability. Size-exclusion and reversed-phase HPLC showed that increasing the temperature (up to 95 °C) mainly decreased glutenin extractability. Holding at 95 °C resulted in polymerisation of both gliadin and glutenin. Above 80 °C, the RVA viscosity steadily increased with longer holding times while the gliadin and glutenin extractabilities decreased. Their reduced extractability in 60% ethanol showed that γ-gliadins were more affected after heating than α-gliadins and ω-gliadins. Enrichment of wheat gluten in either gliadin or glutenin showed that both gliadin and glutenin are necessary for the initial viscosity in the RVA profile. The formation of polymers through disulphide bonding caused a viscosity rise in the RVA profile. The amounts of free sulphydryl groups markedly decreased between 70 and 80 °C and when holding the temperature at 95 °C.     

扬麦系列品种的淀粉糊化特性及Wx蛋白缺失分析

为了明确扬麦系列品种(系)的淀粉品质特点,为生产应用和淀粉品质的改良提供依据,测定了扬麦系列品种(系)及国内部分其他小麦品种(系)的RVA参数,并分析了它们的Wx蛋白缺失情况及其对RVA参数的影响.结果表明,扬麦系列品种(系)的峰值粘度和稀懈值极显著高于供试的北方小麦;低谷粘度和最终粘度显著高于北方小麦和南方小麦;反弹值显著高于南方小麦.扬麦系列品种(系)的Wx-B1缺失比例较高,为18.18%.Wx-B1缺失的扬麦系列品种的峰值粘度和稀懈值显著高于不缺失Wx-B1的扬麦系列品种, 而其它RVA参数差异不显著,但部分Wx-B1不缺失的扬麦系列品种(系)也具有较好的淀粉糊化品质.     

The impact of heating and cooling on the physico-chemical properties of wheat gluten–water suspensions

The rapid visco analysis (RVA) system was used to measure rheological behaviour in 20% (w/v) gluten-in-water suspensions upon applying temperature profiles. The temperature profiles included a linear temperature increase, a holding step, a cooling step with a linear temperature decrease to 50 °C, and a final holding step at 50 °C. Temperature and duration of the holding phase both affected RVA viscosity and protein extractability. Size-exclusion and reversed-phase HPLC showed that increasing the temperature (up to 95 °C) mainly decreased glutenin extractability. Holding at 95 °C resulted in polymerisation of both gliadin and glutenin. Above 80 °C, the RVA viscosity steadily increased with longer holding times while the gliadin and glutenin extractabilities decreased. Their reduced extractability in 60% ethanol showed that γ-gliadins were more affected after heating than α-gliadins and ω-gliadins. Enrichment of wheat gluten in either gliadin or glutenin showed that both gliadin and glutenin are necessary for the initial viscosity in the RVA profile. The formation of polymers through disulphide bonding caused a viscosity rise in the RVA profile. The amounts of free sulphydryl groups markedly decreased between 70 and 80 °C and when holding the temperature at 95 °C.     

Maize Starch Biphasic Pasting Curves

The pasting of commercial maize starches was found to be a biphasic phenomenon, exhibiting an expected first viscosity peak as well as an unexpected, relatively large second viscosity peak under specific cooking conditions when using a Rapid Visco Analyser (RVA). The second peak formed at long holding times (between 32 and 45 min), holding temperatures within the range of 82 to 95 °C, starch concentrations from 8 to 13% with a wide range of initial heating rates (0·5–10 °C/min) and shear conditions (150–500 rev/min). The second pasting peak is attributed to the formation of complexes between amylose and low levels of lipid present in maize starch. When lipid was partially removed by extraction with methanol-chloroform (1 : 3 v/v), the second pasting peak disappeared. When, however, the starch sample was treated with solvent and the solvent removed by evaporation, the second peak remained, but formed earlier. Increasing the holding temperature gave a slightly higher first viscosity peak, slightly earlier, and led to a decrease in the area and height of the second viscosity peak. Increasing heating rate also led to an earlier, slightly higher first peak and earlier but lower second viscosity peak. Increasing starch concentration led to an increase in height and area of both the first and second peaks and their later occurrence. Increasing shear led to a decrease in height and area of both the first and second peaks and their later appearance.     

The Rapid Visco Analyzer (RVA) as a tool for differentiating potato cultivars on the basis of flour pasting properties

Potatoes of two cultivars representing extremes in potato texture, Russet Burbank (mealy) and IdaRose (waxy), were lyophilized, ground into flour, and analyzed with a Rapid Visco Analyzer (RVA) to identify flour pasting characteristics unique to each cultivar. A factorial experiment, which included multiple levels of heating rate, peak temperature, and flour concentration, was employed to assess RVA run parameter association with flour pasting behaviors and the potential to differentiate cultivars according to the responses. Pasting profiles of the potato flour provided a unique functional finger-print for each cultivar flour, which embodies structural and molecular components of the native potato tissue. Pasting profile viscosity attributes were influenced by variable levels of heating rate, peak temperature, and flour concentration. At increasing flour concentrations, RVA viscosity attributes increased in magnitude, but possessed similar pasting curves. A variable heating rate primarily affected events occurring early within the pasting profile (time to gelatinization, time to peak viscosity, peak viscosity), while changes in peak temperature influenced viscosity attributes (trough viscosity, breakdown, final viscosity, total setback) associated with the latter portion of the viscosity curve. A high peak temperature generally resulted in increased breakdown and total setback and decreased trough and final viscosities. RVA viscosity attributes, time to gelatinization, peak viscosity, breakdown, and final viscosity were identified as potential characteristics for cultivar differentiation. Discrimination of the cultivar extremes was affected by RVA run parameters, and was maximized at moderate heating rates (4 to 6 C min^-1), moderate to high levels of peak temperature (85 to 90 C), and intermediate flour concentrations.     

月桂酸对小麦淀粉凝胶回生特性的影响

为了解月桂酸对小麦淀粉凝胶回生特性的影响,利用X射线衍射仪和差示扫描量热仪研究了月桂酸对小麦淀粉凝胶晶体结构和热特性的影响。结果表明,月桂酸与小麦淀粉结合形成了月桂酸-淀粉复合物。在短期回生过程中,淀粉含有V-型结晶结构和B-型结晶结构,淀粉凝胶中直链淀粉分子特征衍射峰减弱,月桂酸-淀粉复合物衍射峰增强;短期回生淀粉含有直链淀粉重结晶的熔融峰和淀粉-脂肪酸复合物的熔融峰,月桂酸-淀粉复合物熔融焓显著小于淀粉凝胶熔融焓;月桂酸对淀粉短期回生的抑制作用主要是对直链淀粉重结晶的抑制。长期回生过程中,随贮藏时间延长,支链淀粉分子发生了重结晶,淀粉凝胶的结晶度从15.37%增大至18.75%,而月桂酸-淀粉复合物结晶度从10.36%增大至13.23%;回生淀粉中支链淀粉重结晶的熔融焓增大,复合物重结晶的熔融焓减少。说明月桂酸与淀粉形成复合物能抑制小麦淀粉的短期回生和长期回生。     

长期定位施肥对不同筋力型小麦品质的影响

为了解长期施肥对小麦品质的作用,在33年长期定位施肥试验的基础上,分析了不同施肥条件下强筋小麦品种徐麦32和弱筋小麦品种宁麦13蛋白及淀粉相关品质特性。结果表明,有机肥、无机肥以及有机肥与品种的互作对小麦大部分蛋白和淀粉特性参数有显著或极显著影响。施肥对徐麦32和宁麦13蛋白质含量、干面筋含量、湿面筋含量、SDS沉淀值及面粉糊化特性参数影响基本一致。单施氮肥处理的蛋白质含量显著高于其他处理,单施有机肥处理显著低于其他处理,其他处理间无显著差异。干、湿面筋含量、SDS沉淀值与蛋白质含量呈较明显的正相关。施有机肥处理的峰值黏度、低谷黏度、最终黏度及峰值时间均显著高于不施有机肥处理,说明有机肥能显著改善小麦面粉的糊化特性;而无论施有机肥与否,施用无机肥不能显著改善面粉糊化特性。综上所述,长期有机、无机肥配合施用有利于弱筋小麦品质的改善,而对强筋小麦品质的改善不利。大田生产中应根据不同专用品种对品质的不同要求施用不同种类的肥料。     

面粉高白度小麦种质资源筛选及其品质分析

为了挖掘面粉白度高、品质优的小麦种质,对1 248份小麦种质资源进行了面粉白度测定,并对面粉白度值超过80的小麦种质的籽粒硬度、淀粉RVA糊化特性以及面团揉混特性等有关品质性状进行了分析。筛选出面粉白度值≥80的小麦种质195个,其籽粒硬度指数分布范围为15～77;淀粉RVA糊化特性参数峰值黏度范围为1 030～3 407cP,稀懈值范围为629～1 522cP,回生值范围为5～1 546cP,糊化温度范围为65.3～88.2℃,最终黏度范围为755～3 870cP;面团形成时间范围为1.3～4.2min,衰落角范围为3～35度,沉降值范围为21～58.7mL。研究结果还表明,面粉中类胡萝卜素含量低,则面粉白度就高,仅靠延长面粉储存时间不会大幅度提高面粉白度。筛选出的14个高白度优异小麦种质可用于培育中强筋面粉高白度小麦新品种。     

Structure and thermal stability of thermoplastic films based on wheat flour modified by monoglyceride

The effects of the incorporation of monoglyceride on the structure and thermal stability of extruded thermoplastic films based on modified wheat flour have been investigated using X-ray diffraction (XRD) and thermogravimetric method (TGA). Addition of the monoglyceride reduced the intensity and widened the peaks obtained by XRD indicating a reduction in crystal size. A significant decrease of apparent length of the crystals have been noticed when the quantity of monoglyceride increases. The thermal analysis proved that the thermal stability of the polymeric material decreases as a function of the monoglyceride content. Finally an attempt is made to correlate the thermal stability of the polymeric materials, with the degree of crystallinity.     

播期和密度对不同玉米品种淀粉糊化特性和子粒品质的影响

以农大108和青农105为材料,设置3个播期和6个密度处理,研究播期和密度对两个玉米品种淀粉糊化特性和子粒品质的影响。结果表明,品种间比较,淀粉峰值黏度、谷值黏度、崩解值、回复值、峰值时间、糊化温度差异显著;播期对糊化特征值及子粒淀粉、蛋白质含量的影响较大,密度的影响较小。晚播条件下,峰值黏度和谷值黏度显著升高,糊化温度显著降低;中播条件下,淀粉含量最低,蛋白质含量最高。因此,试验播期范围内,晚播有利于改良淀粉糊化特性,适期播种有利于改良子粒品质。     

Enhancement of the pasting properties of teff and maize starches through wet–heat processing with added stearic acid

This study determined the effects of stearic acid on the functional properties of teff starch, a compound granule starch in comparison to maize, a simple type granule starch. Stearic acid was incorporated into teff and maize starches and pasted (held for 5 or 120 min at 91 °C) with an RVA (Rapid Visco Analyser). Teff starch with added stearic acid (0.25 and 1.5% starch basis) did not produce a pasting peak viscosity within short holding time (5 min) compared to maize starch. The paste viscosity of both teff and maize starches with stearic acid increased by about three times with long pasting (120 min). This increase in paste viscosity occurred earlier for teff starch than maize starch. Teff starch with stearic acid was more viscous and was non-gelling. Confocal laser scanning microscopy showed that stearic acid did not diffuse in teff starch granules, but seemed to coat them. However, stearic acid diffused inside maize starch granules through channels. This microstructural difference may explain the different pasting behavior. The early high paste viscosity and non-gelling properties of the teff starch modified with stearic acid could have promising applications in foods, for example better mouthfeel with lower starch concentration.     

施氮量对糯小麦和非糯小麦籽粒淀粉组分与理化特性的影响

为探明氮肥对小麦籽粒淀粉组分和理化特性的影响,采用田间试验,分析了4个施氮量(0、100、200、300kg·hm~(-2))对糯小麦(农大糯50222)和非糯小麦(轮选987)籽粒淀粉组分与理化特性的影响。结果表明,随施氮量的增加,小麦籽粒淀粉含量降低,轮选987籽粒中B型淀粉粒的数目占比增加,而农大糯50222籽粒的B型淀粉粒数目占比呈减少趋势;增施氮肥能显著提高小麦籽粒淀粉的峰值黏度和谷值黏度。相同施氮量处理下,轮选987淀粉的被测糊化特征参数(除谷值黏度外)均大于农大糯50222。施氮量不同,2个品种籽粒淀粉X-衍射图谱中各峰的位置和相对强度明显不同。随施氮量的增加,轮选987淀粉的相对结晶度增大,而农大糯50222淀粉的相对结晶度减小。相关分析表明,小麦籽粒的直链淀粉含量和直支比与最终黏度、稀澥值、反弹值、糊化温度和峰值时间呈显著正相关,与谷值黏度和相对结晶度呈显著负相关;支链淀粉含量反之。小麦籽粒的B型淀粉粒数目占比与峰值黏度、稀澥值呈显著负相关。综上所述,施氮量可影响小麦籽粒的淀粉含量和粒度分布,进而改变其糊化特性和晶体特征。     

Effect of lauric acid on the V-amylose complex distribution and properties of swelled normal cornstarch granules

Starch–fatty acid complexes were prepared using swelled normal cornstarch (NC) and lauric acid (LA). Two different modes of adding LA to the starch slurry were employed; i.e. either adding the LA to the heated starch suspension (method I) or adding the LA to the starch suspension and then heating (method II). Effects of the modes of adding LA on the V-amylose complex distribution and digestibility were studied. Lipid content determination indicated that method I is favorable to the formation of V-amylose complex. Light and confocal laser scanning microscopic examination indicated that NC–LA complex prepared by method I seemed to be more swollen, and the V-amylose complex distributed throughout the granules, while NC–LA complex prepared by method II was mainly distributed on the surface of starch granules. The results of X-ray diffraction and thermal property demonstrated that method I was more beneficial to the formation of more crystalline structure than that of method II. The in vitro digestibility investigation showed that the addition of LA through method I had the ability of slowing the hydrolysis of starch.     

氮钾配施对济南17淀粉理化特性的影响

为给优质小麦的高产保质栽培提供借鉴,研究了氮钾配施对高产优质面包强筋小麦品种济南17籽粒淀粉理化特性的影响。结果表明,氮肥对济南17面粉直、支链淀粉和总淀粉含量均有一定的影响,氮肥水平提高,直、支链淀粉合成增加,淀粉总含量增加,但对淀粉化学特性的影响较小。后期施氮量提高,蛋白合成增加,直链淀粉合成能力相对减弱,但淀粉中直／支链淀粉比例相对稳定,峰值粘度没有明显变化。增施钾肥,面粉中直链淀粉含量下降,而支链淀粉和总淀粉含量显著上升,因此直／支链淀粉含量比例显著下降,但以中钾条件下支链淀粉和总淀粉含量最高。随着钾肥水平的提高,峰值粘度显著升高,但对膨胀势影响不显著。总之,氮肥处理对济南17面条品质的影响不大,但在合理的范围内增施钾肥可以显著改善淀粉理化特性,提高面条品质。