Glass Transition of Extruded Wheat,Corn and Rice Starch

Commercial wheat, corn and rice starch were extrusion cooked under a specific mechanical energy input (SME) ranging from 81 to 365 Wh/kg (288 to 1314 kJ/kg). Extrusion cooking at low and high SME resulted in products having significant differences in molecular weight distribution and having crystalline structures of the V‐ and E‐type, as determined by gel permeation chromatography and X‐ray diffraction analysis. Differential scanning calorimetry revealed that the glass transition temperature (T_g) of the extruded starches was independent of the botanical source, the degree of extrusion‐induced molecular fragmentation and the formation of the V‐ and E‐type crystalline structures. The obtained master curve, defined by the relationship between water content and T_g of the amorphous starch, may be used as a predictive tool in modelling the extrusion process of starch or starch containing blends, especially with regard to the formation of the morphological structure and texture attributes of directly expanded products.     

Nixtamalization Process Affects Resistant Starch Formation and Glycemic Index of Tamales

Tamales were prepared with 3 nixtamalization processes (traditional, ecological, and classic) and evaluated for chemical composition, starch properties, and glycemic index. Resistant starch (RS) in tamales increased 1.6 to 3.7 times compared to raw maize. This increment was due to the starch retrogradation (RS3) and amylose–lipid complexes (RS5) formation. Tamales elaborated with classic and ecological nixtamalization processes exhibited the highest total, soluble and insoluble dietary fiber content, and the highest RS content and lower in vivo glycemic index compared to tamales elaborated with traditional nixtamalization process. Thermal properties of tamales showed 3 endotherms: amylopectin retrogradation (42.7 to 66.6 °C), melting of amylose lipid complex type I (78.8 to 105.4), and melting of amylose–lipid complex type II (110.7 to 129.7). Raw maize exhibited X‐ray diffraction pattern type A, after nixtamalization and cooking of tamales it changed to V‐type polymorph structure, due to amylose–lipid complexes formation. Tamales from ecological nixtamalization processes could represent potential health benefits associated with the reduction on blood glucose response after consumption.     

高直链玉米淀粉添加对挤压荞麦面条结构、蒸煮品质及消化特性的影响

制备挤压荞麦面条,研究不同添加量（10%、20%、25%、30%）的高直链玉米淀粉（m/m,基于全粉）对挤压荞麦面条结构、蒸煮品质及消化特性的影响。结果表明,随着高直链玉米淀粉添加量的增加,挤压面条直径减小,糊化度降低。X射线衍射结果表明添加高直链玉米淀粉后,面条除了V型结晶峰外还存在未完全糊化的直链淀粉的典型B型峰。热力学性质结果也表明直链淀粉发生部分糊化。添加高直链玉米淀粉后,面条色泽变浅变亮,最佳蒸煮时间缩短,蒸煮损失率由9.90%增加到12.43%。当高直链玉米淀粉添加量为25%时,面条开始出现断条。面条硬度由2 105.709 g显著增加至3 680.401 g,弹性由0.961降低至0.866。扫描电镜结果表明,随着高直链玉米淀粉添加量的增加,致密的面条结构逐渐出现裂纹,且面条截面有较多未完全糊化的淀粉颗粒。淀粉体外消化实验表明,随着高直链玉米淀粉添加量的增加,淀粉水解率逐渐下降,预计血糖指数减小,抗性淀粉含量增加。当高直链玉米淀粉添加量为30%时,挤压荞麦面条的预计血糖指数从74.28降至66.31,抗性淀粉含量从34.43%增加至47.86%。     

Effect of maize type and extrusion‐cooking conditions on starch digestibility profiles

This study aimed at evaluating the influence of screw speed (250–600 rpm), barrel temperature (100–160 °C) and water content (16.4–22.5%) on rapidly digestible (RDS), slowly digestible (SDS) and resistant (RS) starch levels of waxy, normal and high‐amylose maize starches. In native starches, an increase in amylose content was correlated with lower SDS content. After extrusion, this trend was reversed. Both waxy and normal maize starches became rapidly digested. However, for normal maize starch, some SDS fraction remained. In contrast, the high‐amylose maize starch showed a significant increase in digestibility and an increase in SDS content from 20.4% in the native starch up to 27.5% after extrusion. This high level of SDS may be attributed to the presence of some remaining granular structures and formation of crystalline orders, which have slow digestion properties.     

Lactic acid assisted wet fractionation of field pea (Pisum sativum L.) flour

The use of lactic acid (LA) in the isolation of starch from field pea (Pisum sativum L.) flour was investigated. The yield, purity, morphology, and the physicochemical properties (color, swelling, pasting and gelatinization characteristics, X‐ray diffraction pattern, and crystallinity) of the starches isolated with and without LA were determined. When compared to the control (0% LA), addition of LA at concentrations ranged from 0.5 to 7.0% v/v significantly increased the purity of the isolated starches up to 4% w/w and reduced the residual protein content by 6% w/w. The resistant starch and apparent amylose contents of the isolated starches using LA were significantly higher (up to 25 and 42.5%, w/w, respectively). Furthermore, the starches produced by LA assisted extraction showed significantly lower swelling factor and pasting viscosities, but generally insignificant changes were observed in the gelatinization parameters as compared to that of control. Marginal differences were observed in the X‐ray diffractograms between control and the LA processed starches. However, the relative crystallinity of LA processed starches was significantly higher than the control. The present study revealed that the use of LA in pea starch extraction show benefits in terms of starch purity, brightness, resistance to amylolysis, and apparent amylose content.     

Effect of soy flour addition and heat-processing method on nutritional quality and consumer acceptability of cassava complementary porridges

BACKGROUND: The nutritional quality of cassava complementary porridge was improved through extrusion cooking and compositing with either defatted or full fat soy flour (65:35 w/w), and product acceptability by mothers with children of the target population was evaluated. RESULTS: The protein digestibility‐corrected amino acid score (PDCAAS) of extrusion‐ and conventionally cooked composite porridges was within the recommendations for complementary foods. The kinetics of starch digestibility showed that all porridges had a rapid rate of starch digestibility, but the rate was lower when defatted soy flour was added and lowest when full fat soy flour was added. The formation of amylase‐lipid complexes as shown by X‐ray diffraction and differential scanning calorimetry can be attributed to the lower digestibility of extrusion‐cooked porridge with full fat soy flour. If fed thrice per day, extrusion‐cooked porridge with defatted or full fat soy flour would meet the energy, protein and available lysine requirements of a child aged 6–8 months receiving low or average nutrients from breast milk. All porridges were well received by Mozambican mothers who use cassava as a staple food. The mean scores for sensory liking of all porridges were 3 and above on a five‐point hedonic scale. CONCLUSION: Extrusion‐cooked cassava/soy flour porridges have good potential for use as high‐energy/high‐protein complementary foods and have acceptable sensory properties. Copyright © 2012 Society of Chemical Industry     

玉米淀粉的挤压研究──淀粉在挤压过程中降解机理的研究（Ⅱ＿b）

利用ＳｅｐｈａｄｅｘＧ－２００凝胶过滤层折，碘吸附值，碘络合物吸收光谱，Ｘ－射线衍射光谱等方法对挤压淀粉进行了研究。结果表明，玉米淀粉在挤压过程中，其直链级分未发生显著变化，支链级分的降解位置位于其分子内部，挤压施加于淀粉聚合物的剪应力是挤压淀粉中直链淀粉脂肪络合物的Ｖ型结构向Ｅ型结构转换的根本原因。依据淀粉的聚集态结构，从理论上阐述了淀粉在挤压过程中降解的力化学过程，并提出淀粉降解可能为自由基过程的机理。     

Effect of Cooking Time,Steeping and Lime Concentration on Starch Gelatinization of Corn During Nixtamalization

White dent corn was nixtamalized under different conditions to evaluate thermal properties using differential scanning calorimetry (DSC), swelling power and solubility. Cooking time was the factor that had the major influence on the behavior of the evaluated parameters as indicated by the analysis of variance. Onset and peak temperatures of gelatinization increased with increasing cooking time while gelatinization enthalpies decreased, indicating that more starch granules were gelatinized. A decrease in the swelling power was also observed at increasing cooking times, but solubility was significantly inhibited only if steeping was allowed. Considering these results, it was assumed that amylose‐lipid complexes are being formed during cooking and reorganized during steeping. X‐ray studies confirmed the presence of amylose‐lipid complexes. Steeping also caused an increment in the peak temperature that seemed to support the hypothesis of recrystallization or annealing occurring during this nixtamalization step. Temperature ranges indicated that in general, lime acted as a factor for structural disorganization.     

Crystallinity and Pasting Properties of Freeze‐Thawed High Amylose Maize Starch

Native and defatted high amylose (about 70%) maize starch gels were freeze‐dried or repeatedly freeze‐thawed, and the effects of the treatments on the crystallinity, pasting viscosity, and resistance to digestive enzymes of the dried starch were examined. Both native and defatted starches showed a B‐type crystal structure in the X‐ray diffractogram, but the crystallinity was decreased by repeating the freeze‐thawing cycle. In the DSC thermogram, the freeze‐thawed starches exhibited two endothermic transitions in the temperature ranges of 90—110 °C and 130—160 °C, representing amyloselipid complexes and amylose‐amylose double helix crystals, respectively. By defatting, the melting enthalpy for the amylose double helices was increased, indicating that the residual lipids inhibited the amylose crystal formation. Ice crystals in the starch gel matrix became smaller and the ice cell membrane became thinner as freeze‐thawing was repeated. The freeze‐dried or freeze‐thawed starch powders swelled to a paste by heating in water as did typical granular starch, but the setback by cooling was significantly high due to the rapid retrogradation of leached amylose. By the treatments, the resistance of the starch to digestive enzymes was also raised. The defatted starches displayed greater paste viscosity and resistance to digestive enzymes than the native starches. But the overall viscosity was decreased as the number of freeze‐thawing cycles increased.     

Physicochemical Characterization and Application of Yam (Dioscorea cayenensis‐rotundata) Starch as a Pharmaceutical Excipient

Yam starch from Dioscorea cayenensis‐rotundata complex was isolated and characterized by scanning electron microscopy (SEM), particle size analysis, X‐ray diffraction, differential scanning calorimetry (DSC), compaction and rheology, and compared to maize (Zea mays) and potato (Solanum tuberosum) starches. Yam starch exhibited a log‐normal distribution of flattened ovoid shaped granules with a mean particle size of 25 µm. X‐ray diffraction showed a C‐type crystalline pattern with the degree of relative crystallinity estimated to be 34%. DSC analysis suggests that the crystalline regions in yam starch are thermally and structurally more stable as in maize and potato. Irrespective of the relative humidity (39, 67, 78% R.H.) yam starch exhibited higher moisture uptakes than maize starch and lower than potato. Intermediate values of swelling power and amylose leaching were obtained for yam as compared to maize and potato. Compaction properties of yam and potato starches were similar. However, compacts from yam presented a relatively lower tensile strength. Aqueous starch systems (4%) of yam and maize starches showed analogous shear‐thinning (pseudo‐plastic) behavior suitably described by the power‐law model. These results support the potential use of yam starch as excipient comparable to potato starch in pharmaceutical solid forms and as thickening agent similar to maize in pharmaceutical applications.     

Starch Structure and Digestibility of Rice High in Resistant Starch

Starch digestibility and starch structure of a high‐resistant starch (RS) rice (RS111) was compared to that of a wild rice type (R7954). RS111 exhibited high RS content and incomplete starch hydrolysis in both cooked rice and retrograded rice flour. High RS rice RS111 had a higher λ_max of absorbance and blue value of iodine‐binding starch complex and contained a higher percentage of intermediate chains of amylopectin than R/954. X‐ray diffraction pattern of RS isolated from cooked high RS rice displayed a mixture of B‐ and V‐type that was more resistant to starch hydrolysis by alpha‐amylase. Resistant starch in RS111 is composed mainly of linear amylose and some low‐molecular‐weight amylopectin.     

A Study of Some Physicochemical Properties of High‐Crystalline Tapioca Starch

Tapioca starch was partially hydrolyzed in hydrochloric acid solution at room temperature for various lengths of time to obtain high‐crystalline starches. RVA viscoamylograms of acid‐modified starches demonstrated a very low viscosity as compared to that of native tapioca starch. The relative crystallinity of native and acid‐modified tapioca starches were measured by X‐ray diffraction ranging from 39.53% to 57.75%. The native and acid‐modified tapioca starches were compressed into tablets using various compression forces. The % relative crystallinity of starch increased with the increase in hydrolysis time and the crushing strength of the tablet was also increased in line with the crystallinity while the amylose content decreased when the crystallinity increased. These results suggested that the erosion of amylose might cause the rearrangement of starch structure into a new more tightly packed form, which provided the higher crushing strength for the tablets.     

脱胚玉米在加酶挤压过程中化学成分的变化

为了研究添加酶制剂的脱胚玉米在挤压机内部化学性质的变化情况,将正常工作的挤压机急停,迅速左右分开套筒,沿螺杆分段采集样品,分析挤压物的化学组成及降解特性。脱胚玉米在螺纹推送下由松散状态逐渐被压实,在螺杆前端发生塑性形变进而熔融。挤压脱胚玉米和挤压添加酶制剂脱胚玉米中的淀粉、直链淀粉和脂肪含量沿物料输送方向降低,而糊化度、还原糖和抗性淀粉含量逐渐增加。添加酶制剂的挤压脱胚玉米与挤压脱胚玉米相比较,在相同取料部位,淀粉、直链淀粉、抗性淀粉含量和糊化度降低,而还原糖含量增加。挤压改变了脱胚玉米成分的含量以及淀粉糊化和水解特性,酶制剂在挤压过程提升了淀粉的水解特性,但缺降低了糊化度。然而由于挤压剪切的破坏,酶活性沿物料输送方向降低。通过对脱胚玉米挤压机理的研究,可以更好地为脱胚玉米挤压蒸煮系统的设计和参数选择提供科学依据和理论基础。     

Physicochemical Properties of Starch Isolated from Bracken (Pteridium aquilinim) Rhizome

Bracken (Pteridium aquilinum) is an important wild plant starch resource worldwide. In this work, starch was separated from bracken rhizome, and the physicochemical properties of this starch were systematically investigated and compared with 2 other common starches, that is, starches from waxy maize and potato. There were significant differences in shape, birefringence patterns, size distribution, and amylose content between bracken and the 2 other starches. X‐ray diffraction analysis revealed that bracken starch exhibited a typical C‐type crystalline structure. Bracken starch presented, respectively, lower and higher relative degree of crystallinity than waxy maize and potato starches. Ordered structures in particle surface differed among these 3 starches. The swelling power tendency of bracken starch in different temperature intervals was very similar to that of potato starch. The viscosity parameters during gelatinization were the lowest in waxy maize, followed by bracken and potato starches. The contents of 3 nutritional components, that is, rapidly digestible, slowly digestible, and resistant starches in native, gelatinized, and retrograded starch from bracken rhizome presented more similarities with potato starch than waxy maize starch. These finding indicated that physicochemical properties of bracken starch showed more similarities with potato starch than waxy maize starch.     

Production of Resistant Starch by Extrusion Cooking of Acid-Modified Normal-Maize Starch

ABSTRACT:  The objective of this study was to utilize extrusion cooking and hydrothermal treatment to produce resistant starch (RS) as an economical alternative to a batch-cooking process. A hydrothermal treatment (110 °C, 3 d) of batch-cooked and extruded starch samples facilitated propagation of heat-stable starch crystallites and increased the RS contents from 2.1% to 7.7% up to 17.4% determined using AOAC Method 991.43 for total dietary fiber. When starch samples were batch cooked and hydrothermally treated at a moisture content below 70%, acid-modified normal-maize starch (AMMS) produced a greater RS content than did native normal-maize starch (NMS). This was attributed to the partially hydrolyzed, smaller molecules in the AMMS, which had greater mobility and freedom than the larger molecules in the NMS. The RS contents of the batch-cooked and extruded AMMS products after the hydrothermal treatment were similar. A freezing treatment of the AMMS samples at −20 °C prior to the hydrothermal treatment did not increase the RS content. The DSC thermograms and the X-ray diffractograms showed that retrograded amylose and crystalline starch–lipid complex, which had melting temperatures above 100 °C, accounted for the RS contents.     

Physicochemical Properties of Pin Oak (Quercus palustris Muenchh.) Acorn Starch

Physicochemical properties of acorn (Quercus palustris) starch were studied. Acorn starch granules were spherical or ovoid, with diameters ranging from 3–17 μm. Acorn starch exhibited A‐type X‐ray diffraction pattern, an apparent amylose content of 43.4% and absolute amylose content of 31.4%. Relative to other A‐type starches, acorn amylopectin had a comparable weight‐average molar mass (3.9×10⁸ g/mol), gyration radius (288 nm) and density (16.3 g mol⁻¹nm⁻³). Average amylopectin branch chain‐length corresponded to DP 25.5. Onset gelatinization temperature was 65.0°C and peak gelatinization temperature was considerably higher (73.7°C). The enthalpy change of gelatinization was very high compared to non‐mutant starches (20.8 J/g). An amylose‐lipid thermal transition was not observed. Starch retrograded for 7 d at 4°C had very high peak melting temperature (54.2°C) relative to other A‐type starches. Final (260 RVU) and setback (138 RVU) viscosity of an 8% acorn starch paste was high relative to other starches and pasting temperature was 71.5°C.     

Starch‐Soybean Oil Composites With High Oil: Starch Ratios Prepared By Steam Jet Cooking

Aqueous mixtures of soybean oil and starch were jet cooked at oil: starch ratios ranging from 0.5:1 to 4:1 to yield dispersions of micron‐sized oil droplets that were coated with a thin layer of starch at the oil‐water interface. The jet cooked dispersions were then centrifuged at 2060 and 10,800×g, the buoyant, high‐oil fractions that rose to the surface were isolated, and the size distributions of the oil droplets were determined. Experiments were conducted with normal dent, waxy, and high‐amylose corn starches; and oleic acid was added during jet cooking to form helical inclusion complexes with amylose. With normal dent and waxy corn starches, nearly all of the oil was recovered in the buoyant layers, and only small amounts of oil were found in the aqueous mid layers and settled solids. Oil droplet diameters in the buoyant layers obtained with normal dent and waxy corn starch ranged from under 5 µm to over 50 µm. Centrifugation at high versus low relative centrifugal force produced only minor differences in the droplet size distributions. With high‐amylose starch, microscopy showed that most of the oil droplets were entrapped within aggregates of sub‐micron particles that were apparently formed from amylose‐oleic acid inclusion complexes when the dispersions were cooled. Droplet sizes increased with an increase in the oil: starch ratio, and decreased when oleic acid was added during jet cooking.     

Physicochemical and Functional Properties of Tetraploid and Hexaploid Waxy Wheat Starch

Waxy wheats possess unique starch functional properties that may be useful in specific end‐uses. To assess the physicochemical, thermal, and pasting properties, starches from seven waxy genotypes originating from two wheat classes, tetraploid durum and hexaploid hard red spring (HRS), were evaluated and compared with their counterpart non‐waxy wild types. The amylose content ranged from 2.3% to 2.6% in waxy durum lines, compared to 29.2% in normal durum control, and 2.1% to 2.4% in waxy HRS, compared with 26.0% in normal HRS control. Significant differences in the degree of crystallinity were observed between the waxy and control starches, despite similar A‐type X‐ray patterns, although differences between the two wheat classes were non‐significant. Both, control and waxy starches displayed an X‐ray peak corresponding to the amylose‐lipid complex, but the intensity of the peak was markedly lower in the waxy starches. The waxy durum starches exhibited the highest transition temperatures as measured by Differential Scanning Calorimetry (DSC), whereas, the enthalpy of gelatinization of most waxy genotypes was statistically higher than that of the controls. All waxy starches displayed high peak viscosity, high breakdown, and low setback profile as measured by the Rapid Visco Analyser (RVA). Texture analysis of RVA gels revealed significant differences between waxy and non‐waxy wheats, as well as between waxy tetraploid and hexaploid wheats, confirming that the nature and class of wheat starch would play a significant role when using waxy wheat blends in different wheat‐based products.     

Study of starch-lipid complexes in model system and real food produced using extrusion-cooking technology

The formation of starch-lipid complexes during extrusion of model system (rice starch added with oleic acid) and real food (rice starch added with pistachio nut flour) was evaluated. Both formulas were extruded at the same processing conditions (temperature profiles, screw speed and water feed content).The formation of starch-lipid complexes in real food, is strongly dependent on water feed content. In fact, at barrel temperature of 128 °C, the highest melting enthalpy of real food (6.7 J/g) was obtained only at 21% of water feed content whereas in the model system it was obtained both at 16 and 21%.These results point out the importance to consider all components present in the extruded food in order to study biopolymers modifications that occur during processing.

Industrial relevance

Additions of lipids alter the physical and chemical properties of starchy foods. The changes brought about by them in starchy foods have been attributed to the formation of complexes between amylose and lipids. These changes in the functionality of starch are of interest to the food industry and for human nutrition. Lipid complexation with starch is a very important reaction in extrusion cooking that affects structure formation and texture of the extruded products. Most studies on the starch-lipid complex formation during extrusion of model systems like starch and free fatty acids have been carried out, instead very little is known about starch-lipid complex formation during extrusion of flour blends containing fatty meal. This paper points out the importance to consider all components present in the food extruded in order to study biopolymers modifications that occur during processing. For this reason it is very important to use model systems that are not very different to real food and anyhow it would be advisable to verify the obtained results on real food, above all when a relation between macromolecular modifications and quality characteristics of extruded products would be studied.     

Study of the Thermoplastic Wheat Starch Cationisation Reaction under Molten Condition

This paper deals with the functionalization of thermoplastic wheat starch with cationic groups under the action of thermo‐mechanical energy. Two reagents, leading to the same reactive species, are used: 3‐chloro‐2‐hydroxypropyltrimethylammonium chloride and 2‐epoxypropyltrimethylammonium chloride. An experimental study and a theoretical approach for reactive extrusion operations were carried out in a bench‐top twin‐screw microcompounder. The theoretical model developed is in satisfactory agreement with the experimental results obtained in the molten state, with low water content. Reaction kinetic studies, performed at different temperatures between 100 and 140°C, show that starch cationisation follows a second order reaction, with rate constants following the Arrhenius law. The obtained results allow calculation of the values of activation energy. The analysis of the thermoplastic unmodified and modified cationic starches by size exclusion chromatography (SEC) shows a decrease of the excluded fraction, which is attributed to the effect of the thermo‐mechanical melting process. The X‐ray diffraction spectra typical of molten starches were obtained.