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1.
The influence of an antistaling α‐amylase on bread crumb and on wheat starch gels was investigated taking into account different levels of structural hierarchy. Bread was prepared by a conventional baking procedure. Starch gels were produced by heating a concentrated starch dispersion in closed molds. Bread and starch gels were characterized by compression tests, light microscopy (LM), differential scanning calorimetry, and X‐ray measurements. The α‐amylase enhanced the initial firmness of starch gels and reduced the firming rate of bread and starch gels on aging. LM revealed that amylose and amylopectin phase‐separated within the starch granules and that freshly baked control bread and starch gels showed weak birefringence which became more intense during aging. Amylase‐containing bread and starch gels exhibited strong birefringence in the amylose rich region of the granules directly after baking which did not significantly increase during aging. The enzyme hindered the retrogradation of amylopectin as detected by differential scanning calorimetry, whereas X‐ray diffraction indicated that the enzyme induced low levels of starch crystallinity which did not change during aging. It is hypothesized that the antistaling effect of the amylase is based on the capacity to partially degrade amylopectin and, by this, to hinder its recrystallization. On the other hand, the enzyme slightly degrades amylose by an endo‐mechanism which, in turn, promotes the rapid formation of a partly crystalline amylose network in fresh bread and hinders amylose rearrangements during aging.  相似文献   

2.
During the digestion of starch in foods, starch is mixed with bile in the duodenum. Because fatty acids and some kinds of polyphenols could bind to starch, it was postulated that bile salts might also bind to starch. The purpose of this paper is to study the effects of bile and bile salts on starch/iodine complex formation and pancreatin-induced starch digestion. Bile suppressed starch/iodine complex formation and inhibited pancreatin-induced starch digestion slightly in control buckwheat starch, but did so significantly in buckwheat starch from which fatty acids and polyphenols had been extracted. Such significant suppression and inhibition by bile were also observed in a reagent soluble starch. The effects of cholate and taurocholate on the starch/iodine complex formation and the pancreatin-induced starch digestion were essentially the same as those of bile. Bile, cholate, and taurocholate suppressed amylose/iodine complex formation more significantly than amylopectin/iodine complex formation and inhibited pancreatin-induced amylose digestion more effectively than the digestion of amylopectin. It is concluded from the results that bile salts could bind to starch, especially amylose, the helical structures of which were not occupied by other molecules such as fatty acids and polyphenols, and that the binding resulted in the inhibition of starch digestion by pancreatin. The conclusion suggests that the function of bile salts can be discussed from the point of not only lipid digestion but also starch digestion.  相似文献   

3.
The present investigation aims at understanding the mechanism of bread firming during staling. Changes in the starch fraction due to the addition of amylases and their influence on the texture of bread crumb were studied during aging and after rebaking of stale bread. Pan bread was prepared by a conventional baking procedure. The influence of three different starch‐degrading enzymes, a conventional α‐amylase, a maltogenic α‐amylase, and a β‐amylase were investigated. The mechanical properties of bread were followed by uniaxial compression measurements. The microstructure was investigated by light microscopy, and starch transformations were assessed by differential scanning calorimetry (DSC) and wide‐angle X‐ray powder diffraction. Firming of bread crumb and crystallization of starch are not necessarily in agreement in systems with added amylases. Reorganization of both starch fractions, amylopectin and amylose, and the increase of starch network rigidity due to increase of polymer order are important during aging. Starch‐degrading enzymes act by decreasing the structural strength of the starch phase; for instance, by preventing the recrystallization of amylopectin or by reducing the connectivity between crystalline starch phases. On the other hand, starch‐degrading enzymes may also promote the formation of a partly crystalline amylose network and, by this, contribute to a kinetic stabilization of the starch network. Based on the results, a model for bread staling is proposed, taking into account the biphasic nature of starch and the changes in both the amylose and amylopectin fraction.  相似文献   

4.
The effect of partial gelatinization with and without lipid addition on the granular structure and on α‐amylolysis of large barley starch granules was studied. The extent of hydrolysis was monitored by measuring the amount of soluble carbohydrates and the amount of total and free amylose and lipids in the insoluble residue. Similarly to the α‐amylolysis of native large barley starch granules, lipid‐complexed amylose (LAM) appeared to be more resistant than free amylose and amylopectin. Partial gelatinization changed the hydrolysis pattern of large barley starch granules; the pinholes typical of α‐amylase‐treated large barley starch granules could not be seen. Lipid addition during partial gelatinization decreased the formation of soluble carbohydrates during α‐amylolysis. Also free amylose remained in the granule residues and mostly amylopectin hydrolyzed into soluble carbohydrates. These findings indicate that lysophospholipid (LPL) complexation with amylose occurred either during pretreatment or after hydrolysis, and free amylose was now part of otherwise complexed molecules instead of being separate molecules. Partial gelatinization caused the granules to swell somewhat less during heating 2% starch‐water suspensions up to 90°C, and lipid addition prevented the swelling completely. α‐Amylolysis changed the microstructure of heated suspensions. No typical twisting of the granules was seen, although the extent of swelling appeared to be similar to the reference starch. The granules with added LPL were partly fragmented after hydrolysis.  相似文献   

5.
Effects of α‐amylase modification on dough and tortilla properties were determined to establish the role of starch in tortilla staling and elucidate the antistaling mechanism of this enzyme. Control and amylase‐treated tortillas were prepared using a standard bake test procedure, stored at 22°C, and evaluated over four weeks. Amylase improved shelf‐stability of tortillas. The enzyme also produced a significant amount of dextrins and sugars, decreased loss of amylose solubility, and weakened starch granules. Amylopectin crystallinity increased with time, but was similar for the control and treated tortillas. Staling of tortillas appears to mainly involve the starch in the amorphous phase. As such, amylase activity does not significantly interfere with amylopectin crystallization. It is proposed that amylase partially hydrolyzed the dispersed starch (i.e., mostly amylose), starch bridging the crystalline region, and protruding amylopectin branches. Starch hydrolysis decreases the rigid structure and plasticized polymers during storage. The flexibility of tortillas results from the combined functionalities of the amylose gel and amylopectin solidifying the starch granules during storage. Protein functionality may also be involved in tortilla staling, but this needs further research.  相似文献   

6.
Maize starches of the endosperm mutants waxy (wx), dull:waxy (duwx), and amylose‐extender:dull:waxy (aeduwx) from inbred line Ia453 lack amylose. However, in addition to high molecular weight (HMW) amylopectin, the duwx and aeduwx starches contained 40 and 80%, respectively, intermediate branched material of low molecular weight (LMW). As gelatinized, the amylopectin of the wx starch was easily hydrolyzed into small dextrins by the α‐amylase of B. amyloliquefaciens, but components of duwx and aeduwx possessed partial resistance to amylolytic attack. Residual material of intermediate size obtained by a 4‐hr α‐amylolysis could not be separated from LMW dextrins by fractional precipitation in methanol. It is suggested that this material possessed a more regularly branched structure, in which the d ‐glucosyl chain segments were too short to allow α‐amylase action. The granular starches of duwx and aeduwx genotypes were initially considerably more resistant than the wx sample to α‐amylase attack. This was possibly due to an altered structure in the amylopectin component or the high content of intermediate material in the former granules.  相似文献   

7.
Wheat starch is considered to have a low paste viscosity relative to other starches. Consequently, wheat starch is not preferred for many applications as compared to other high paste viscosity starches. Increasing the viscosity of wheat starch is expected to increase the functionality of a range of wheat flour-based products in which the texture is an important aspect of consumer acceptance (e.g., pasta, and instant and yellow alkaline noodles). To understand the molecular basis of starch viscosity, we have undertaken a comprehensive structural and rheological analysis of starches from a genetically diverse set of wheat genotypes, which revealed significant variation in starch traits including starch granule protein content, starch-associated lipid content and composition, phosphate content, and the structures of the amylose and amylopectin fractions. Statistical analysis highlighted the association between amylopectin chains of 18-25 glucose residues and starch pasting properties. Principal component analysis also identified an association between monoesterified phosphate and starch pasting properties in wheat despite the low starch-phosphate level in wheat as compared to tuber starches. We also found a strong negative correlation between the phosphate ester content and the starch content in flour. Previously observed associations between internal starch granule fatty acids and the swelling peak time and pasting temperature have been confirmed. This study has highlighted a range of parameters associated with increased starch viscosity that could be used in prebreeding/breeding programs to modify wheat starch pasting properties.  相似文献   

8.
Waxy wheat (Triticum aestivum L.) contains endosperm starch lacking in amylose. To realize the full potential of waxy wheat, the pasting properties of hard waxy wheat flours as well as factors governing the pasting properties were investigated and compared with normal and partial waxy wheat flours. Starches isolated from six hard waxy wheat flours had similar pasting properties, yet their corresponding flours had very different pasting properties. The differences in pasting properties were narrowed after endogenous α‐amylase activity in waxy wheat flours was inhibited by silver nitrate. Upon treatment with protease, the extent of protein digestibility influenced the viscosity profile in waxy wheat flours. Waxy wheat starch granules swelled extensively when heated in water and exhibited a high peak viscosity, but they fragmented at high temperatures, resulting in more rapid breakdown in viscosity. The extensively swelled and fragmented waxy wheat starch granules were more susceptible to α‐amylase degradation than normal wheat starch. A combination of endogenous α‐amylase activity and protein matrix contributed to a large variation in pasting properties of waxy wheat flours.  相似文献   

9.
Previous attempts have been made to obtain gluten‐free bread of acceptable quality for bread specific volume and crumb texture. Rice bread is a good alternative to celiac patients, but it has a very rapid staling during storage. Rice starch is more prone to retrograde during storage than wheat starch, and the special hydrophobic nature of the rice proteins requires specific enzymes to be used in the rice bread process. To retard rice bread staling, two different starch hydrolyzing enzymes (α‐amylase of intermediate thermostability and cyclodextrin glycoxyl transferase [CGTase]) have been tested and their effect on fresh bread quality and staling during storage has been evaluated. The addition of α‐amylase improved bread specific volume and crumb firmness but very sticky textures were obtained. The addition of CGTase produced even higher specific volume and similar crumb firmness with better texture. Both enzymes decreased the ability of amylopectin to retrograde during storage. The firming kinetic was lowered by the α‐amylase but not the limiting firmness, while the rice crumb from CGTase firmed quickly with a very short range of firmness increase. Results revealed that the starch hydrolysis brought about by the α‐amylase was not sufficient to retard staling. CGTase was considered a better antistaling agent because of its starch hydrolyzing and cyclizing activity.  相似文献   

10.
Triticale is a high‐yielding cereal crop with potential to increase grain production for human consumption over the coming decades. Minimal targeted selection has been conducted to produce cultivars with α‐amylase, amylose, and nonstarch polysaccharide (NSP) content appropriate for a milling market. Nevertheless, genotypic variability exists. Standard quality screening methods used for wheat, including pasting properties, falling number, and quantification of α‐amylase activity were employed to assess the environmental and genotypic variability among modern triticale cultivars and to investigate the suitability of these tests for triticale. Samples of 11 triticale lines from four environments were compared with five wheat cultivars bred for various end uses. Triticale exhibited a greater range than wheat for most tested variables, and the ranges usually overlapped. Triticale exhibited higher NSP content, generally equivalent pasting properties, higher α‐amylase activity, and lower falling number on average compared with wheat checks. However, low falling number was not indicative of high α‐amylase activity; the relationship with NSP level and other factors is discussed, and caution is recommended for interpretation of previous research. Three cultivars with equivalent α‐amylase activity to wheat and two with partially waxy starch were identified. These findings have great significance for research and the emerging triticale milling market.  相似文献   

11.
Native and processed high‐amylose maize starch (HAMS) is an important source of resistant starch (RS). The objectives of this work were to use an in vitro procedure to estimate the RS content of native granules from a series of ae‐containing HAMS genotypes, and to examine the nature of the α‐amylase resistant starch (ARS). By the method of Englyst et al (1992), RS for ae V, ae VII, ae su2, and ae du were estimated to be 66.0, 69.5, 69.5, and 40.6%, respectively. By transmission electron microscopy, most of the residual granules from ae V, ae VII, and ae su2 showed little evidence of digestion. Partially digested granules had a radial digestion pattern in the interior and an enzyme‐resistant layer near the surface. Size and chain‐length profile of constituents of ARS were similar to those of the native HAMS (unlike type 3 RS), consistent with complete hydrolysis in susceptible granule regions. Between crossed polarizers, many iodine‐stained native and residual HAMS granules had blue centers and pink exteriors, which may be due to a difference in orientation of the amylose‐iodine complexes in the exterior. Four granule color types were observed for ae du, differing in enzyme resistance. The high‐enzyme resistance of native HAMS granules may result from altered granule organization, which appears to vary among and within granules from ae‐containing genotypes.  相似文献   

12.
Manipulation of starch composition in cereals and particularly in wheat is receiving increasing attention due to recognition of its important role in food and nonfood applications. The amylose/ amylopectin ratio influences the physicochemical properties of starches and nutritional value of derived end products. Identification of the key enzymes involved in the starch biosynthetic pathway has opened new avenues for altering the amylose and amylopectin content in durum and bread wheat. The granule bound starch synthases (GBSSI), or waxy proteins, are the enzymes responsible for amylose synthesis in storage tissues; amylopectin is produced by the concerted action of different enzymes, including starch synthases (SS), branching (SBE), and debranching enzymes (DBE). By altering the level of key enzymes involved in the regulation of starch synthesis, it is possible to generate novel starches with unique functional properties. In this respect, both low and high amylose starches are particularly interesting because they are associated with industrial and processing properties as well as with human health and nutrition. So far, major attention has addressed the manipulation of starch composition in bread wheat, whereas durum wheat has been investigated to a much lesser extent. Approaches currently available to alter amylose/amylopectin ratio and tailor starch composition in durum wheat are presented.  相似文献   

13.
Starch structures from an extrusion process were stored at different temperatures to allow for molecular rearrangement (retrogradation); their thermal characteristics (DSC) and resistance to amylase digestion were measured and compared. The structure of four native and processed starches containing different amylose/amylopectin compositions (3.5, 30.8, 32, and 80% amylose content, respectively) before and after digestion was studied with small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD). Rearrangement of the amylose molecules was observed for each storage condition as measured by the DSC endotherm at around 145 degrees C. The crystalline organization of the starches after processing and storage was qualitatively different to that of the native starches. However, there was no direct correlation between the initial crystallinity and the amount of enzyme-resistant starch (ERS) measured after in vitro digestion, and only in the case of high-amylose starch did the postprocess conditioning used lead to a small increase in the amount of starch remaining after the enzymatic treatment. From the results obtained, it can be concluded that retrograded amylose is not directly correlated with ERS and alternative mechanisms must be responsible for ERS formation.  相似文献   

14.
Starch granule composition and amylopectin structure affect starch digestibility, an important factor influencing wheat grain utilization for human food consumption. Six bread wheat cultivars with four belonging to the Canada Western Red Spring (CWRS) and two Canada Prairie Spring Red (CPSR) market classes were analyzed for the relationship between their grain constituents and in vitro enzymatic hydrolysis of starch. CPSR cultivars had higher starch and amylose concentrations compared with CWRS cultivars, which had a higher protein concentration. Starch granule size distribution did not differ among the genotypes, except AC Foremost, which had significantly (P < 0.05) higher volume percent of B‐type starch granules (≈15%) and lower volume percent of A‐type starch granules (≈9%) compared with other cultivars. Fluorophore‐assisted capillary electrophoresis revealed a lower content of R‐IV (DP 15–18, ≈6%) and a higher content of R‐VII (DP 37–45, ≈7%) chains in the CPSR cultivars compared with the CWRS cultivars. Starch in vitro enzymatic hydrolysis showed that compared with CWRS cultivars, the two CPSR cultivars had reduced amounts of readily digestible starch and higher amounts of slowly digestible starch and resistant starch. Consequently, the two CPSR cultivars also showed lower hydrolysis indexes in grain meal as well as extracted starch. CPSR cultivars, with higher starch and amylose concentrations, as well as a higher content of long chains of amylopectin, showed a reduced starch in vitro enzymatic hydrolysis rate.  相似文献   

15.
In this study, the functional properties of A‐ and B‐type wheat starch granules from two commercial wheat flours were investigated for digestibility in vitro, chemical composition (e.g., amylose, protein, and ash content), gelatinization, retrogradation, and pasting properties. The branch chain length and chain length distribution of these A‐ and B‐type wheat starch granules were also determined using high‐performance anion exchange chromatography (HPAEC). Wheat starches with different granular sizes not only had different degrees of enzymatic hydrolysis and thermal and pasting properties, but also different molecular characteristics. Different amylose content, protein content, and branch chain length of amylopectin in A‐ and B‐type wheat starch granules could also be the major factors besides granular size for different digestibility and other functional properties of starch. The data indicate that different wheat cultivars with different proportion of A‐ and B‐type granular starch could result in different digestibility in wheat products.  相似文献   

16.
The Waxy (Wx) gene in hexaploid wheat (Triticum aestivum L.) encodes granule‐bound starch synthase (GBSS1), which is involved in the synthesis of amylose, a mostly linear glucan polymer that makes up ∼25% of wheat starch. A null mutation of the Wx gene in each of the three genomes is associated with starch almost entirely consisting of the branched glucan polymer amylopectin (waxy starch), with corresponding changes in functionality. However, the rheological behavior of partially waxy starch remains unclear. The objective of this study was to characterize flour and baking quality in 16 near‐isogenic lines, null at the Wx locus on zero, one, two, or all three genomes, grown in four different environments. Across allelic groups, significant variations in amylose concentrations, flour paste viscosity, loaf structure and texture, dough stability, and proximate variables were observed. Because waxy wheat starch has greater water absorbance and resistance to retrogradation than normal starch, its inclusion in flour blends has been suggested as a means of improving the texture and appearance of bakery products and noodles. The results indicate that wheat encoding <3 functional homeologs of GBSS1 produces starch that has potential in the production of certain food items, such as Asian noodles. However, further research is necessary to determine the optimal amylose‐to‐amylopectin ratio to improve baking quality.  相似文献   

17.
Physical properties of resistant starch (RS) were examined in a range of barley genotypes to determine the contribution of starch and seed physical characteristics to the RS component. Thirty‐three barley genotypes were studied, which varied significantly in their RS, amylose, and starch contents and grain yield. From 33 genotypes, 13 exhibiting high RS were selected for detailed physicochemical analysis of starch. In high‐RS varieties, granule size and number were unimodal, compared with normal starches from a reference genotype, which showed a bimodal distribution. Principal component analysis (PCA) showed that a higher content of granules <15 µm was positively correlated with RS and amylose content, whereas the proportion of granules 15–45 µm was negatively correlated with the RS and amylose contents. Physical fractionation of starches by centrifugation into different population sizes demonstrated that size alone is not an accurate indicator of the population of A‐type and B‐type granules within a given genotype. PCA also showed that large 15–45 µm granules were positively correlated with seed thickness and that thousand grain weight was positively correlated with seed width. High‐RS and high‐amylose genotypes showed variation in overall yield and starch content, with some genotypes showing yield comparable to the reference genotype. Analysis of amylopectin chain length distribution showed that high amylose or RS content was not associated with a higher proportion of amylopectin long chains when compared with either waxy or reference (normal) barley genotypes. This study highlights useful markers for screening barley genotypes with favorable starch characteristics.  相似文献   

18.
The objective of this study was to compare the structure and properties of flours and starches from whole, broken, and yellowed rice kernels that were broken or discolored in the laboratory. Physicochemical properties including pasting, gelling, thermal properties, and X‐ray diffraction patterns were determined. Structure was elucidated using high‐performance size‐exclusion chromatography (HPSEC) and high‐performance anion‐exchange chromatography with pulsed amperometric detection (HPAEC‐PAD). The yellowed rice kernels contained a slightly higher protein content and produced a significantly lower starch yield than did the whole or broken rice kernels. Flour from the yellowed rice kernels had a significantly higher pasting temperature, higher Brabender viscosities, increased damaged starch content, reduced amylose content, and increased gelatinization temperature and enthalpy compared with flours from the whole or the broken rice kernels. However, all starches showed similar pasting, gelling, thermal properties, and X‐ray diffraction patterns, and no structural differences could be detected among different starches by HPSEC and HPAEC‐PAD. α‐Amylase may be responsible for the decreased amylopectin fraction, decreased apparent amylose content, and increased amounts of low molecular weight saccharides in the yellowed rice flour. The increased amount of reducing sugars from starch hydrolysis promoted the interaction between starch and protein. The alkaline‐soluble fraction during starch isolation is presumed to contribute to the difference in pasting, gelling, and thermal properties among whole, broken, and yellowed rice flours.  相似文献   

19.
Flow field‐flow fractionation (flow FFF) with frit inlet and frit outlet mode (FIFO) was coupled online to multiangle light scattering (MALS) and refractive index (RI) detectors to investigate the molecular characteristics of normal and zero amylose barley starch polymers. Application of two different cross‐flows, 0.35 mL/min followed by 0.1 mL/min, and constant channel and frit flows of 0.1 and 1.0 mL/min, respectively, permitted a complete separation of amylose and amylopectin. The improved signals from the detectors due to application of the FIFO mode enabled the proper characterization of the small molecular weight species, as well as significantly enhanced the reproducibility of the measurements. The weight‐average molecular weight (Mw) and zaverage root‐mean‐square (RMS) radii of gyration (Rg) values for amylose and amylopectin in the normal starch samples were 2.3 × 106 and 280 × 106, and 107 and 260 nm, respectively. The Mw and Rg of amylopectin in the zero amylose starch samples were 360 × 106 and 267 nm, respectively. The slopes (α) obtained by plotting log Mw versus log Rg for amylose and amylopectin were 0.6 and 0.3, respectively. These results are in good agreement with the theoretical prediction of the molecular conformation of amylose and amylopectin.  相似文献   

20.
甘薯淀粉性质与其粉丝品质的关系   总被引：6，自引：2，他引：4  
为了弄清不同品种甘薯淀粉所制粉丝品质差异的原因,该研究通过对各种甘薯淀粉的理化性质、热力学特性、分子结构与甘薯粉丝品质的测定,并以绿豆淀粉做对照,对三者与其粉丝品质进行了相关性分析。结果表明：淀粉理化性质对粉丝品质影响较大,按相关系数大小依次是：膨润力＞溶解度＞表观直链淀粉含量＞蛋白质含量＞颗粒大小。回生对粉丝品质的影响远远大于糊化对其的影响。快速黏度分析参数与粉丝品质有显著的相关性,可作为预测其相应的粉丝品质的重要手段之一。淀粉分子结构对粉丝品质影响更大,按显著程度依次是：直链淀粉（A m ）含量＞支链淀粉（A P ）短链量＞AP长链量＞Am分支数＞AP短链长度＞Am链长＞AP长链长度。  相似文献   

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