Comparative study of the retrogradation of intermediate water content waxy maize, wheat, and potato starches

The retrogradation of extruded starches from three different botanical sources was studied in concentrated conditions (34 +/- 1% water) at 25 degrees C using differential scanning calorimetry (DSC) and isothermal calorimetry, Fourier transform infrared spectroscopy (FTIR), and wide-angle X-ray scattering. Potato starch showed the highest rate of retrogradation (approximately 0.17 h(-1)) followed by waxy maize (approximately 0.12 h(-1)), while the retrogradation of wheat starch was the slowest (approximately 0.05 h(-1)). In addition to the kinetics, the extent of molecular order in the retrograded samples was studied in detail in terms of "short-range" (helical) and "long-range" (crystalline) distance scales. The amylopectin crystallinity indices were essentially the same (approximately 47-51% amylopectin basis) for the three starches. However, significant differences were found in the enthalpy of melting measured by DSC after "full" retrogradation (potato, 11.6 +/- 0.7; waxy maize, 9.0 +/- 0.5; and wheat, 6.1 +/- 0.3 J/g of amylopectin). The degree of short-range molecular order in the retrograded state determined by FTIR was waxy maize > potato > wheat. The effect of amylopectin average chain length and the polymorphism of the crystalline phase were taken into account to explain the differences in the retrogradation enthalpies.     

Consequence of Starch Damage on Rheological Properties of Maize Starch Pastes

Waxy and normal maize starches were damaged to different extents by ball milling, with waxy starch notably more susceptible to damage. Starch damage caused substantial decreases in shear stress or apparent viscosity in both waxy and normal maize starch pastes at a wide range of shear rates (5.6 to 400 1/sec). Shear stress or apparent viscosity decreases were more evident in waxy than in normal maize starch pastes at the same ball milling times. Values of storage moduli were much higher than values of loss moduli, and storage moduli decreased with increase in starch damage in both waxy and normal maize starches, indicating decrease in elastic property. The study showed that starch damage causes substantial rheological changes in gelatinized pastes and that waxy starch undergoes more pronounced changes than normal starch. These results can be used to understand the general behavior of damaged normal and waxy starches in processed foods.     

Properties of Some Starch Blends

Normal corn, high-amylose corn, waxy corn (waxy maize), wheat, rice, potato, cassava (tapioca), and a modified waxy corn starch were blended in various combinations and ratios. Pasting behavior, paste and thermal properties, and retrogradation tendency were determined. Differential scanning calorimetry (DSC) traces of the mixtures did not resemble those of either of the two components, nor did any DSC trace have two peaks suggestive of a mixture of two distinct starches. Amylograph data suggested that some mixtures behaved like a chemically modified starch. Observations from light microscopy suggested that intermolecular, molecular-supermolecular, and intersupermolecular interactions may be responsible for this behavior.     

Effects of Heat-Moisture Treatment and Lipids on Gelatinization and Retrogradation of Maize and Potato Starches

Effects of heat-moisture treatment (HMT) and lipids on the structure and gelatinization of maize and potato starches were studied, and the retrogradation process of 20% HMT starch gels was also investigated. Maize starch was physically modified by HMT or by defatting. Potato starch was physically modified by HMT or by adding monoglycerides. The X-ray pattern of the HMT maize starch was assigned to a combination of A and V patterns, which indicated that HMT formed crystallized amylose complexes and recrystallized amylose in maize starch granules. However, the X-ray pattern of defatted maize starch did not change for HMT, so the lipids originally existing in starch granules were important to the formation of new crystallites during this treatment. Differential scanning calorimetry (DSC) results suggested that weaker structures in amylopectin crystallites were more susceptible to degradation after HMT, while crystallized amylose complexes developed thermal stability after treatment. The amylose contents increased with increasing degree of HMT, which suggested that the newly created amylose arose from exterior linear chains of amylopectin degraded by the treatment. Investigation of retrogradation process showed that HMT significantly promoted retrogradation of starch gels, especially the initiation of recrystallization.     

Retrogradation of Starches from Different Botanical Sources

Retrogradation in 2% pastes prepared from unmodified commercial starches by cooking at 98–100°C under low shear, then held at 4°C for 56 days, was examined by turbidometric analysis and light microscopy. Turbidometric analysis revealed that retrogradation rates followed the order of wheat, common corn > rice, tapioca, potato ≫ waxy maize. Microstructures of stored pastes were examined both before and after centrifugation. Granule remnant morphologies and fresh and stored paste microstructures were unique to each starch examined. Fresh pastes from amylose-containing starches were dominated by networked amylose that condensed into higher density aggregates upon storage. Unique phenomena seen in some stored pastes included interactions of granular remnants with aggregated amylose, composite networks of co-associated amylopectin and amylose, and slight birefringence regained by granule remnants. Microstructural changes in stored pastes could be related to changes in turbidity and to the results of other methods used to quantitate retrogradation.     

鲜食糯玉米籽粒理化特性的基因型差异

以糯玉米国家区域试验14个品种为材料,研究其鲜食期籽粒理化特性的基因型差异。结果表明,鲜食糯玉米籽粒理化特性存在显著的基因型差异,淀粉和蛋白质含量变幅分别在48.7%~72.2%和7.4%~8.9%之间,但其含量高低对籽粒理化特性无显著影响。籽粒淀粉最大吸收波长变幅在531.6~559.4nm之间,但总体上变异较小,且均表现出典型的糯性特征。碘结合力和微量元素含量均存在显著的基因型差异。差示扫描量热仪(DSC)和快速黏度分析仪(RVA)研究表明,供试品种中淮科糯3号和禾盛糯1512黏度特征值较优,适合作鲜穗食用;禾盛糯1512和沈糯062回生值较低,在速冻玉米上具有独特优势。相关分析表明,碘结合力与回生值显著负相关,与回复值显著正相关。微量元素中,Cu、Fe、Ca、Na元素含量与热力学特征值和糊化特征值无显著相关性,Mn、Zn、S和P元素含量与峰值黏度和崩解值显著负相关,K与崩解值显著正相关,S与糊化温度显著正相关。     

Increasing Slowly Digestible Starch Content of Normal and Waxy Maize Starches and Properties of Starch Products

Changes in the digestibility and the properties of the starch isolated from normal and waxy maize kernels after heat‐moisture treatment (HMT) followed by different temperature cycling (TC) or isothermal holding (IH) conditions were investigated. Moist maize kernels were heated at 80°C for 2 hr. The HMT maize kernels were subjected to various conditions designed to accelerate retrogradation of the starch within endosperm cells. Two methods were used to accelerate crystallization: TC with a low temperature of –24°C for 1 hr and a high temperature of 20, 30, or 50°C for 2, 4, or 24 hr for 1, 2, or 4 cycles, and IH at 4, 20, 30, or 50°C for 24 hr. The starch granules were then isolated from the treated kernels. The starch isolated from HMT normal maize kernels treated by TC using –24°C for 1 hr and 30°C for 2 hr for 2 cycles gave the greatest SDS content (24%) and starch yield (54%). The starch isolated from HMT waxy maize kernels treated by TC using –24°C for 1 hr and 30°C for 24 hr for 1 cycle had an SDS content of 19% and starch yield of 43%. The results suggest that TC after HMT changes the internal structure of maize starch granules in a way that results in the formation of SDS (and RS). They also suggest that thermal treatment of maize kernels is more effective in producing SDS than is the same treatment of isolated starch. All starch samples isolated from treated normal maize kernels exhibited lower peak viscosities, breakdown, and final viscosities and higher pasting temperatures than did the control (untreated normal maize starch). Although peak viscosities and breakdown of the starch isolated from treated waxy maize kernels were similar to those of the control (untreated waxy maize starch), their pasting temperatures were higher. The starch isolated from treated normal and waxy maize kernels with the highest SDS contents (described above) were further examined by DSC, X‐ray diffraction, and polarized light microscopy. Onset and peak temperatures of gelatinization of both samples were higher than those of the controls. Both retained the typical A‐type diffraction pattern of the parent starches. The relative crystallinity of the starch from the treated normal maize kernels was higher than that of the control, while the relative crystallinity of the starch from the treated waxy maize kernels was not significantly different from that of the control. Both treated starches exhibited birefringence, but the granule sizes of both starches, when placed in water, were slightly larger than those of the controls.     

拔节期追氮对春播和秋播糯玉米淀粉胶凝和回生特性的影响

以垦粘1号、苏玉糯1号和苏玉糯5号为材料,研究了拔节期追氮量(N 01、50和300 kg/hm2)对春播和秋播糯玉米淀粉胶凝和回生特性的影响,试验于扬州大学实验农牧场进行。结果看出,播期、品种和拔节期追氮量单因素及其互作对淀粉胶凝和回生主要特征值存在显著影响。糯玉米淀粉胶凝和回生特征值在拔节期追氮150 kg/hm2时和秋播条件下较优,即原淀粉具有较低的峰值温度、较高的热焓值,回生淀粉具有较低的回生值,且以垦粘1号表现较好。糯玉米淀粉胶凝和回生特征值之间存在一定的相关性。回生值分别与回生淀粉的热焓值、原淀粉的终值温度显著正相关,相关系数分别为0.82(P0.01)和0.47(P0.05);原淀粉的热焓值与峰值指数显著正相关,相关系数为0.53(P0.05),与原淀粉峰值温度、回生淀粉的终值温度显著负相关,相关系数分别为-0.53(P0.05)和-0.52(P0.05);回生淀粉的热焓值分别与回生淀粉起始温度、终值指数显著正相关,相关系数分别为0.46(P0.05)和0.66(P0.01)。综合考虑淀粉胶凝和回生特性在不同处理下的变化趋势,以秋播糯玉米淀粉在拔节期追N 150 kg/hm2处理下较优。     

Structures of Four Waxy Rice Starches in Relation to Thermal,Pasting, and Textural Properties

Waxy rice starches from three japonica cultivars (Taichung Waxy 1 [TCW1], Taichung Waxy 70 [TCW70], Tachimemochi) and one indica cultivar (Tainung Sen Waxy 2 [TNSW2]) were characterized for chemical and physicochemical properties. The amylopectin structures were different for the four waxy rice starches in terms of degree of polymerization (DP), average chain length (CL), exterior chain lengths (ECL), and distribution of chains, indicating the existence of varietal differences. The order of swelling power was TCW1 > TCW70 > TNSW2 > Tachimemochi; the order of water solubility index was TCW70 > TNSW2 > Tachimemochi > TCW1. The low water solubility index of TCW1 might be ascribed to a high DP. All starches shared similar gelatinization temperatures and enthalpies but showed distinct retrogradation patterns. TNSW2 showed the highest retrogradation rate, followed by TCW2, Tachimemochi, and TCW70. TCW70 exhibited the highest overall pasting viscosity, followed by TNSW2, TCW1, and Tachimemochi. The hardness of waxy rice starch pastes from a Brabender amyloviscograph increased rapidly after storage at 5°C for one day and remained the same or slightly increased after seven days of storage, whereas the opposite trend was observed for adhesiveness. The lower degree of retrogradation of TCW70 was probably a result of a larger amount of A chain and a shorter ECL. The changes in hardness correlated with the amount of A and B1 chains. The texture attributes of waxy rice starch pastes were significantly affected by amylopectin retrogradation during storage.     

玉米淀粉糊的流变学特性分析

利用生物显微镜分析系统观察玉米淀粉颗粒的外形及结构,并利用旋转黏度计研究了不同玉米淀粉乳制备淀粉糊的流变性能,根据其流变性能数据非线性回归得到淀粉糊在不同温度下的流变模型.研究结果表明:在试验中所设的剪切速率范围内,淀粉糊的剪切应力均是随着剪切速率的增加而增大;且在同一剪切速率同一温度下,淀粉与水的比值越大,淀粉糊所受的剪切应力就越大;相同比例淀粉乳形成的淀粉糊在同一剪切速率下,随着温度的升高而剪切应力减小;玉米淀粉糊属于屈服-假塑性流体,模型的拟合相关系数γ2在0.990～1.000之间,说明屈服-假塑性流体模犁能有效地表征玉米淀粉糊的流变性能.淀粉糊的流变学特性研究为进一步淀粉胶黏剂的开发及利用提供了理论和试验依据.     

Heat Stress at Different Grain Filling Stages Affects Fresh Waxy Maize Grain Yield and Quality

The effects of heat stress (mean day/night temperatures were 29/18 and 35/18°C for control and heat stress treatments, respectively) at 1–10 or 11–20 days after pollination (DAP) on grain yield and quality of two waxy maize varieties, Suyunuo5 and Yunuo7, were studied. The decrease in grain number and fresh grain yield was more severe when heat stress was introduced early. The responses of grain weight and its components to heat stress were dependent on the variety and heat stress stage. Heat stress increased the starch granule size and volume percentage of diameter larger than 17 μm in both varieties. Crystallinity, iodine binding capacity, and pasting and gelatinization temperatures were increased in both varieties under heat stress at 11–20 DAP; however, the response to early‐stage heat stress was variety dependent. Peak viscosity and retrogradation percentage were increased by heat stress at either stage. These results suggest that heat stress decreases fresh grain yield and accelerates grain filling rate; it increases starch content, starch granule size, crystallinity, and iodine binding capacity as well as decreases the protein content in Yunuo7, thus making the grain less tender and prone to retrogradation. Warm conditions should shorten the time to harvest in fresh waxy maize production.     

Effect of Sugars on Retrogradation of Waxy Maize Starch‐Sugar Extrudates

The effect of sucrose, fructose, and xylose on the retrogradation of waxy maize starch extrudates at relatively low moisture contents (20–50 g of water/ 100 g of dry solid) at 277–353 K was investigated using X‐ray diffraction and ¹H nuclear magnetic resonance (NMR) relaxometry. The role of the sugar depended on the type of sugar and its concentration, but most importantly on the retrogradation conditions (water content and storage temperature). For the isothermal retrogradation at 313 K, fructose considerably increased the rate of retrogradation over the range of water contents investigated, and the increase was proportional to the sugar concentration. The behavior of xylose and sucrose was more complex. At 10% sugar content, both sugars enhanced starch retrogradation, while at 30% sugar content, xylose accelerated the process at <35% (mc, dsb) but decreased the rate constant when more water was present. This crossover took place at 42% mc for sucrose. Sugars enhanced the transformation of the A‐type polymorph to a so‐called pseudo‐B with an X‐ray diffractogram similar to that of B‐type starch, with the exception of the 1.6‐nm peak which was considerably depressed. The effects of these sugars on the retrogradation kinetics in variable storage temperature conditions mirrored those obtained when isothermal retrogradation was examined in the water content domain.     

Effects of Ice Structuring Proteins on Freeze‐Thaw Stability of Corn and Wheat Starch Gels

The effect of ice structuring proteins (ISP, 0.5%, starch weight basis) on the freeze‐thaw stability of corn and wheat starch gels (CS and WS, respectively) was studied. Syneresis measurement, hardness, thermal properties using differential scanning calorimetry (DSC), X‐ray diffractions, and scanning electron microscopy (SEM) were determined with starch gels (SG) subjected up to nine freeze‐thaw cycles (FTC). The gelatinized SG were stored at –20°C for 22 hr and thawed at 30°C for 2 hr. As the number of FTC increased, syneresis was increased; however, ISP significantly (P < 0.05) reduced the syneresis for all FTC except at FTC 1. Hardness was increased up to FTC 4, then decreased for both SG. ISP significantly lowered the hardness of both SG. The ice melting enthalpy (ΔH_{ice sample}) of SG increased as FTC increased but SG with ISP had significantly lower enthalpy. The retrogradation ratio (RR) from DSC was significantly increased as the number of FTC increased. ISP reduced RR but most of RR was not significantly different for the corresponding FTC. The X‐ray diffraction patterns showed less recrystallization of WS with addition of ISP. The microstructures from SEM showed that the addition of ISP reduced the size of ice cell cavities.     

Structure and Functionality of Barley Starches

Amylose contents of prime starches from nonwaxy and high-amylose barley, determined by colorimetric method, were 24.6 and 48.7%, respectively, whereas waxy starch contained only a trace (0.04%) of amylose. There was little difference in isoamylase-debranched amylopectin between nonwaxy and high-amylose barley, whereas amylopectin from waxy barley had a significantly higher percentage of fraction with degree of polymerization < 15 (45%). The X-ray diffraction pattern of waxy starch differed from nonwaxy and high-amylose starches. Waxy starch had sharper peaks at 0.58, 0.51, 0.49, and 0.38 nm than nonwaxy and high-amylose starches. The d-spacing at 0.44 nm, characterizing the amylose-lipids complex, was most evident for high-amylose starch and was not observed in waxy starch. Differential scanning calorimetry (DSC) thermograms of prime starch from nonwaxy and high-amylose barley exhibited two prominent transition peaks: the first was >60°C and corresponded to starch gelatinization; the second was >100°C and corresponded to the amylose-lipid complex. Starch from waxy barley had only one endothermic gelatinization peak of amylopectin with an enthalpy value of 16.0 J/g. The retrogradation of gelatinized starch of three types of barley stored at 4°C showed that amylopectin recrystallization rates of nonwaxy and high-amylose barley were comparable when recrystallization enthalpy was calculated based on the percentage of amylopectin. No amylopectin recrystallization peak was observed in waxy barley. Storage time had a strong influence on recrystallization of amylopectin. The enthalpy value for nonwaxy barley increased from 1.93 J/g after 24 hr of storage to 3.74 J/g after 120 hr. When gel was rescanned every 24 hr, a significant decrease in enthalpy was recorded. A highly statistically significant correlation (r = 0.991) between DSC values of retrograded starch of nonwaxy barley and gel hardness was obtained. The correlation between starch enthalpy value and gel hardness of starch concentrate indicates that gel texture is due mainly to its starch structure and functionality. The relationship between the properties of starch and starch concentrate may favor the application of barley starch concentrate without the necessity of using the wet fractionation process.     

气流粉碎对玉米淀粉结构及理化性质的影响

为研究气流粉碎对玉米淀粉结构及理化性质的影响,该文以普通玉米淀粉为原料,通过流化床气流粉碎处理,采用扫描电子显微镜、偏光显微镜、粒度分析仪、X-射线衍射仪、红外光谱仪、差示扫描量热仪、快速黏度分析仪等分析手段研究经微细化处理前后玉米淀粉颗粒形貌、晶体结构、热力学特性、糊化特性、溶解度和膨胀度、冻融稳定性、持水能力等结构及性质的变化。结果表明,微细化处理后,淀粉颗粒形变的不规则,粒径明显减小,中位径(D50)由14.37μm减小到5.25μm,偏光十字减少,相对结晶度由33.43%降低至15.46%,淀粉颗粒结晶结构被破坏,由多晶态向无定形态转变,粉碎过程淀粉无新的基团产生;热焓值、糊化温度均降低,热糊稳定性好;溶解度、膨胀度均升高,持水能力增加,冻融稳定性好,产生较好的热糊稳定性和冷糊力学稳定性,该研究为玉米淀粉的深度加工与应用提供了理论依据及技术支撑。     

Morphological Changes of Granules of Different Starches by Surface Gelatinization with Calcium Chloride

Native starch granules of 11 selected cultivars (potato, waxy potato, sweet potato, normal maize, high‐amylose maize, waxy maize, wheat, normal barley, high‐amylose barley, waxy barley, and rice) were treated with a calcium chloride solution (4M) for surface gelatinization. The surface‐gelatinized starch granules were investigated using light microscopy and scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). In general, those starches with larger granule sizes required longer treatment time to complete the gelatinization. The salt solution treatment of starch was monitored by light microscopy and stopped when the outer layer of the granule was gelatinized. The surface gelatinized starch granules were studied using scanning electron microscopy. On the basis of the gelatinization pattern from calcium chloride treatments, the starches could be divided into three groups: 1) starches with evenly gelatinized granule surface, such as normal potato, waxy potato, sweet potato, maize, and high‐amylose maize; 2) starches with salt gelatinization concentrated on specific sites of the granule (i.e., equatorial groove), such as wheat, barley, and high‐amylose barley; and 3) starches that, after surface gelatinization, can no longer be separated to individual granules for SEM studies, such as waxy barley, waxy maize, and normal rice. The morphology of the surface gelatinized starch resembled that of enzyme‐hydrolyzed starch granules.     

Effect of polysaccharides on the gelatinization properties of cornstarch dispersions

Konjac glucomannan (KG, neutral), carboxymethylcellulose (CMC, negatively charged), and chitosan (positively charged) were added to cornstarch dispersions to study the effect of polysaccharide-starch interactions on starch gelatinization properties. Pasting and retrogradation properties were measured with a rheometer and DSC. Swelling properties of the starch granules were determined by solubility index, swelling power, and particle size distribution. Depending on the nature of the different polysaccharides, viscosities of cornstarch dispersions were affected differently. The particle size distributions were not influenced by the addition of any of the polysaccharides. Swelling results showed that the KG and CMC molecules interacted with the released or partly released amylose in the cornstarch dispersions. This was correlated with the short-term retrogradation of the starch pastes being retarded by the additions of KG and CMC. However, the chitosan molecules appeared not to associate with the amylose, so the retrogradation of the chitosan-cornstarch dispersions was not retarded.     

挤压体系中可得然胶对小麦淀粉回生特性和冻融稳定性的影响

小麦淀粉的回生现象和较差的冻融稳定性是限制面制品加工的重要原因。为探索一种有效抑制小麦淀粉回生及改善其冻融稳定性的方法,该文研究了挤压体系中不同质量分数的可得然胶对小麦淀粉回生特性和冻融稳定性的影响,利用差示扫描量热仪、X-射线衍射和傅里叶红外光谱等技术表征了可得然胶-小麦淀粉复合物的分子结构,并结合化学试剂处理、质构仪和扫描电镜探讨了可得然胶与小麦淀粉的结合机制。结果表明：随着可得然胶浓度的增加,可得然胶-小麦淀粉复合物的回生值和析水率先降低后增加;与挤压小麦淀粉相比,添加质量分数0.6%的可得然胶能够显著提高小麦淀粉的糊化温度,并降低小麦淀粉的相对结晶度、短程有序性和碘结合力,抑制了直链淀粉的重结晶;挤压体系中可得然胶与小麦淀粉主要通过氢键和弱的静电相互作用结合,使小麦淀粉的结构更加致密,从而抑制小麦淀粉的回生并改善其冻融稳定性,该研究可为开发抗回生和低析水率的挤压小麦淀粉基食品提供参考。     

Utilization of Hydroxypropylated Waxy Rice and Corn Starches in Korean Waxy Rice Cake to Retard Retrogradation

A traditional waxy rice gel cake in Korea, Injulmi, was prepared with hydroxypropylated waxy rice and corn starches (molar substitutions 0.13 and 0.11, respectively), and the textural and retrogradation characteristics of the cake were compared with a conventional cake made of waxy rice flour. In the pasting viscogram, hydroxypropylated starches exhibited reduced pasting temperatures, but increased peak viscosities compared with the unmodified starches. Under differential scanning calorimetry, the T_g′ and ice melting enthalpy of the starch gel cakes were reduced by hydroxypropylation, which indicated that the modified starches had higher water‐holding capacity than the unmodified starches. The degree of retrogradation, as measured by the hardness of the gel cake and the melting enthalpy, was significantly reduced by hydroxypropylation and hydroxypropylated waxy rice starch was more effective in retarding the retrogradation than hydroxypropylated waxy corn starch     

Effect of alpha-amylases from different sources on the retrogradation and recrystallization of concentrated wheat starch gels: relationship to bread staling

Concentrated starch gels were supplemented with four alpha-amylases from different sources. The retrogradation and recrystallization of the gels were evaluated using differential scanning calorimetry (DSC) and X-ray crystallography. Correlations between the retrogradation data and the carbohydrate fractions extracted from these gels were determined. The thermostable (TBA) and intermediate temperature stability (ISBA) bacterial alpha-amylases were most effective in decreasing the rate of retrogradation of the starch in the gels. The cereal alpha-amylase at the high level (CAH) was also effective. Supplementation with the alpha-amylases increased the crystallinity of the gels. Gels supplemented with TBA or ISBA were most crystalline and retrograded to a lesser extent. The results indicated that DSC gives not only a measure of recrystallized amylopectin but also a measure of total order (recrystallized amylopectin and double-helical content). The maltooligosaccharides produced by the enzymes did not appear to be responsible for the reduced rates of retrogradation, but they appeared to be an expression of the degree of starch modification that was responsible for the inhibition of retrogradation. The crystallinity and retrogradation data were similar to results reported for bread and strongly suggest that bread staling is caused by the retrogradation of starch. The results also indicate that alpha-amylases decrease the rate and extent of retrogradation of starch gels by inhibiting the formation of double helices.