SUSCEPTIBILITY TO AMYLOLYSIS OF GAMMA-IRRADIATED WHEAT

SUMMARY– Initial reducing sugars and diastatic activity, expressed as "maltose value," are increased in irradiated wheat and are functions of dose levels in the range 20—200 Krad. Both alpha-and beta-amylases retain their activities in irradiated wheat, but the sensitivities of starch to amylolysis are increased with radiation dose levels. Latent beta-amylase present in resting seeds, is also radioresistant. Susceptibility of starch to radiation treatment is more pronounced with moist than dry grain.     

Effect of Gamma Irradiation on Molecular Structure and Physicochemical Properties of Corn Starch

ABSTRACT:  Carboxyl content and amylose leaching of gamma-irradiated corn starch increased and swelling factor decreased with increasing radiation dose. The apparent amylose content decreased gradually from 28.7% for native starch to 20.9% for 50 kGy irradiated starch. The proportion of short amylopectin branch chains (DP 6 to 12) increased, while the proportion of longer branch chains (DP ≥ 37) decreased with increasing radiation dose. The relative crystallinity and the degree of granule surface order decreased from 28.5% and 0.631 in native starch to 26.9% and 0.605 in 50 kGy irradiated starch, respectively. Pasting viscosity and gelatinization temperatures decreased with an increase in radiation dose. At a high dose (50 kGy), melting of amylose–lipid complex in DSC thermogram was not observed. The rapidly digestible starch (RDS) content slightly decreased up to 10 kGy but increased at 50 kGy. The resistant starch (RS) content slightly decreased at 2 kGy and then increased up to 50 kGy. The slowly digestible starch (SDS) content showed the opposite trend to RS content. Slower irradiation dose rate reduced carboxyl content, swelling factor, and amylose leaching. The apparent amylose content and amylopectin chain length distribution were not significantly affected by dose rate of gamma irradiation. However, the relative crystallinity and gelatinization enthalpy increased with slower dose rate. Slower dose rate decreased RDS and SDS contents, and increased RS content.     

Variation in maltose in sweet wort from barley malt and rice adjuncts with differences in amylose structure

Starch from malt and solid adjuncts provides the majority of fermentable sugars for fermentation. However, there is no current data on the variation in starch structure (particularly long chained amylose) and its impact on the final wort composition of fermentable sugars, specifically maltose. This is the first study to report variation in amylose structure from barley malt and rice used as an adjunct and how this impacts the production of maltose. We compared four commercial malts with two rice adjuncts mashes, in solid and liquid additions, with an all‐malt mash used as a control. All combinations of malt and rice adjuncts were tested under two grist‐to‐liquor (G:L) ratios (1:3 and 1:4) in a 65°C ramped mash. After mashing, the wort original gravity and maltose concentration were measured. The commercial malts had different malt quality but very similar gelatinisation temperatures (~65°C). The malts varied in starch and amylose contents but had only minor variations in average amylose chain lengths. The two rice adjuncts also had similar average amylose chains lengths, but quite different amylose contents, and hence different gelatinisation temperatures. The results showed that liquid adjunct mashes had higher original gravity and maltose concentration for both G:L ratios. However, there was no consistent result in original gravity or maltose between G:L ratio or adjunct type, suggesting interactions between each malt and rice adjunct. Knowing amylose chain length could improve understanding of the potential maltose levels of the sweet wort prior to fermentation. © 2018 The Institute of Brewing & Distilling     

Effects of cross-linking and low molecular amylose on pasting characteristics of waxy corn starch

The action of amylose within the granule of normal corn starch is investigated by changes in pasting characteristics of waxy corn starch in a Rapid Visco Analyzer (RVA), using addition of soluble amylose (DP = 18) and cross-linking with epichlorohydrin. Although waxy corn starch, containing no amylose, did not show an effect of addition of amylose on pasting characteristics, by cross-linking with epichlorohydrin, the pasting peak viscosity and breakdown were greatly enhanced and set-back (viscosity increased in the cooling process after gelatinization) was generated. The cross-linking depressed the disintegration of starch granules in the swelling process, with amylose interaction, resulting in RVA pasting characteristics similar to those seen with normal corn starch containing amylose. Set-back was essentially caused by rearrangement among modified amylopectins. Addition of sodium dodecyl sulfate (SDS) to the RVA more efficiently enhanced the effect. This indicated that amylose in normal corn starch interacts with amylopectin through locally strong linkages.     

Glucose Oligomers as Models to Elucidate the Starch Radiolysis Mechanism

A comparative study of gamma irradiated glucose and glucose oligomers has been carried out in order to find a suitable model to understand the mechanism of starch radiolysis. Measurements of malonaldehyde and formic acid, produced by irradiation, showed that the quantitative comparison of radiolytic products was not significant for our purpose, which was also confirmed by a literature survey. However, an electron spin resonance kinetic study of several oligomers, irradiated in the powder state, showed that maltopentaose, and to a lesser extent, maltotriose, may be used as models in the radiolysis of starch.     

Modification of bean starch by γ-irradiation: Effect on functional and morphological properties

Starches isolated from Red, White, Yellow and Black Kidney beans were treated by γ-irradiation doses of 5, 10 and 20 kGy. Physicochemical, morphological and pasting properties of irradiated bean starches were investigated. Microscopic observation under scanning electron microscope (SEM) showed that some of the bean starch granules were destroyed by γ-irradiation and the breakage was greater at a higher dose (20 kGy). Physicochemical properties differed significantly and showed strong dose-dependent relationship. Carboxyl content, solubility, water absorption capacity and transmittance increased, whereas swelling power, apparent amylose content, syneresis and pasting properties decreased upon the irradiation of kidney bean starch. Radiation doses were positively correlated with water absorption capacity and solubility index and negatively correlated with swelling index, peak viscosity, trough viscosity, breakdown and final viscosity. There were high positive correlations between pasting properties. X-ray diffraction pattern remained same upon irradiation but a decrease in crystallinity was observed with increasing irradiation dose.     

Retrogradation of Rice Starches Studied by Differential Scanning Calorimetry and Influence of Sugars, NaCl and Lipids

In waxy and nonwaxy rice starch gels the retrogradation process was a function of time. The enthalpy for rice starch gel with high amylose content was higher than those for low amylose content or for waxy starch samples. In all rice starch gels, samples stored under 25°C had lower enthalpy and higher endothermic onset temperature. In presence of sucrose, extent of retrogradation increased, while in presence of NaCl, it decreased. Effects of maltose, glucose and lipids were dependent on rice starch gel and storage temperature.     

不同植物来源淀粉之间的理化性质的比较

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

Effect of High Doses of Gamma Rays on Corn Grains. Part II. Influence on Some Physical and Chemical Properties of Starch and Its Fractions

Solubility, swelling power, viscosity, alkali number and ferricyanide number were estimated in the starch isolated from both irradiated air-dried and moist corn grains. An increase in solubility, alkali number and ferricyanide number and decrease in relative viscosity were found in starch isolated from irradiated air-dried as well as moist corn grains as the dose level was raised. The swelling power increased up to 2 megarad, then decreased rapidly. Infrared analysis revealed an additional absorption band which arises from a new methylene group at 5 megarad. An increase in amylose percentage concomitant with a decrease in amylopectin percentage was found as the radiation dose was increased up to 2 megarad. Above 2 megarad, the opposite was found. The chain length of amylose and amylopectin showed a progressive decrease as the irradiation dosage was raised.     

Analytical screening studies on irradiated food packaging

Foods may be irradiated in their final packaging and this process may affect the composition of the packaging and in turn affect the migration of substances into food. Headspace and liquid injection GC-MS and HPLC with time-of-flight MS have been used to identify and estimate levels of radiolytic products in irradiated finished plastic packaging materials. Fifteen retail packaging materials were studied. Investigations were carried out into the effect of different irradiation types (gamma and electron beam), irradiation doses (1, 3, 7 and 10 kGy) and dose rates (5 kGy s^–1 for electron beam and 0.4 and 1.85 kGy h^–1 for gamma) on the radiolytic products. Any differences seen in comparing the two ionising radiation types were attributed largely to the very different dose rates; for electron beam a 10 kGy dose was delivered in just 2 s whereas using gamma it took 5.4 h. Differences were also seen when comparing the same samples irradiated at different doses. Some substances were not affected by irradiation, others decreased in concentration and others were formed upon increasing doses of irradiation. These results confirm that irradiation-induced changes do occur in substances with the potential to migrate and that the safety of the finished packaging material following irradiation should be assessed.     

Labeling of Starch Granules by Bombardment with Tritium Atoms

Starch granules were labeled by exposure to tritium atoms produced by thermal dissociation of tritium gas at a tungsten filament. Activity was shown by α-amylase etching experiments to be confined to the surface of the granule. Dextrins and low molecular weight compounds could be partially resolved on Sephadex G-75. The dextrin produced during tritiation had an elution volume corresponding to dextrin of 20–35 glucose units and was hydrolyzeable by α-amylase. Labeled starch was hydrolyzed first with ß-amylase and the limit dextrin hydrolyzed further with α-amylase. A comparison of the specific activities of the maltoses produced by the two enzymes demonstrated that labeling was more heavily concentrated in outer brunches than in inner branches. Amylose obtained from labeled potato starch was purified by crystallization and on DEAE-Sephadex columns. The ion-exchange purified potato amylose was hydrolyzed with ß-amylase with 50% of the activity retained in maltose. Tritium was found to be concentrated at the nonreducing ends of the amylose molecules. These results suggest that starch molecules are organized in granules with nonreducing ends oriented to the surface.     

Granule Integrity and Starch Solubility During Slow,Extended Pasting of Maize Starch — the Second Viscosity Peak

Maize starch granule integrity and starch solubilisation at specific intervals during a relatively long pasting profile—which is known to exhibit biphasic peak viscosity character—was studied by microscopy and high‐performance size‐exclusion chromatography, respectively. Maize starch granules, although swelling and leaching components, remained mainly intact until the second viscosity peak when they lost integrity and formed a relatively homogenous paste. The second viscosity peak coincided with a decrease in starch content in solution and amylose going out of solution was mainly responsible for this decrease. It is suggested that the loss of granule integrity during the second viscosity peak increases the potential for amylose to form complexes with lipids at this stage. It is further suggested that the second viscosity peak is due to the formation and breakdown of superstructures of amylose‐lipid complexes.     

直链淀粉含量对玉米淀粉/瓜尔胶复配体系糊化和流变特性的影响

为考察直链淀粉含量对淀粉/瓜尔胶复配体系性质的影响,以不同直链淀粉含量的玉米淀粉(蜡质玉米淀粉、普通玉米淀粉和高直链玉米淀粉)为原料,加入瓜尔胶,研究复配体系的糊化、流变及凝胶特性。结果表明:瓜尔胶与直链淀粉之间的相互作用是引起淀粉复配体系黏度和稠度系数增加、成糊温度和流体指数降低的主要原因。动态流变实验结果表明淀粉中直链淀粉含量不同对复配体系的动态模量的影响也不同。在糊化过程中,随着直链淀粉含量增加,直链淀粉分子与瓜尔胶间的相互作用增强,阻碍了直链淀粉分子间的聚集重排,使得复配体系硬度值减小,3种玉米淀粉形成了质地更为柔软的凝胶。     

Study on Solid Acid Catalyzed Hydrolysis of Maltose and Related Polysaccharides

Within a study on combined hydrolysis and oxidation of starch toward D -gluconic acid the solid acid catalyzed hydrolysis of maltose as model compound was investigated. Acid zeolites and ion-exchange resins in the H*-form as well as amorphous silica-aluminas were used as the catalysts. The optimal conditions found for maltose were applied in the hydrolysis of amylose and starch. It is shown that the catalysis by zeolites and alumino-silicates involves homogeneous as well as heterogeneous catalysis.     

Effect of Amylose Content on Gelatinization,Retrogradation and Pasting Properties of Flours from Different Cultivars of Thai Rice

Presently, rice cultivars are categorized according to amylose content into three groups: low, medium and high amylose content cultivars. The correlation of amylose content with gelatinization properties, retrogradation, and pasting properties of eleven cultivars of Thai rice were investigated. Rice flour was prepared from milled rice by the wet grinding process. Onset (T_o), peak (T_p) and conclusion (T_c) temperatures of gelatinization, (determined by DSC) were found to be highly positively correlated with amylose levels. This correlation could be used for prediction of amylose content of rice flour. Low amylose starch could also be characterized by low degree of retrogradation (%R). The data obtained from RVA‐viscograms (peak viscosity, breakdown, setback, and pasting temperature) can be used only for characterization of the group of low amylose starches (waxy rice). It was demonstrated that low amylose rice starch provided the highest peak viscosity and breakdown and the lowest setback and pasting temperature among the groups investigated.     

Effect of γ-ray irradiation on starch granule structure and physicochemical properties of rice

Irradiation, an effective method to change starch structure and its functionalities, was carried out before traditional air-drying. Effect of irradiation on the structural and physicochemical properties of rice starch and contrast with that of non-irradiated and traditional air-dried rice was studied in this research. Micrology observation of microstructure of starch, at outer and inner layer rice endosperm, showed that the starch granules would be destroyed by gamma irradiation, and the breakage was increased with increasing dose. Effect of gamma irradiation on microstructures of inner endosperm was greater than that of outer endosperm. Chemistry examination and RVA rice viscosity analysis were carried out on the air-dried rice. Apparent amylose content, gel consistency and gelatinisation temperature were all affected by irradiation pre-treatment. Apparent amylose content was decreased, and gel consistency and gelatinisation temperature were increased with increasing dose. These affects generally related to the changes of starch structure. With the analysis of RVA, six major parameters of starch pasting properties, peak viscosity (PKV), hot pasting viscosity (HPV), cool pasting viscosity (CPV), setback (CPV minus PKV), breakdown (PKV minus HPV), and peak time (PKT), were significant decreased with the increasing dose by different velocity. There were high correlation coefficient between dose and individual major parameters of starch pasting properties (range from 0.961 to 0.998). These changes of pasting properties were also due to the breakage of starch granules caused by gamma irradiation.     

预处理对豆类淀粉性质的影响及在低GI食品中的应用

预处理方式影响豆类淀粉的性质,进而影响豆类产品的应用。本文综述了不同预处理方式对豆类淀粉的颗粒形态、分子结构、溶解度、糊化特性、抗性淀粉含量等性质的影响,分析这些预处理方法对豆类在低GI食品开发中应用的影响。一定条件下的湿热、超高压、干热、辐照、超声波和酶法处理可使豆类淀粉中抗性淀粉或直链淀粉的含量有所增加,有利于豆类在低GI食品开发中的应用。此外,本文综述了不同预处理的豆类产品在低GI食品开发中的应用现状,并对应用前景进行了展望。     

Changes in the structural and physicochemical characterization of pea starch modified by Bacillus-produced α-amylase

In this study, changes in structural and physicochemical properties of pea starch treated with Bacillus-produced α-amylase were determined. The results showed that enzymatically modified pea starch had lower amylose content and granule size but higher branching degree and relative crystallinity. After enzyme hydrolysis, the distribution of A and B1 chains slightly decreased, while the distribution of B2 and B3 chains increased lightly. Enzymatic hydrolysis preferentially occurred in the amorphous region and cannot change the crystalline structure of pea starch. Moreover, pea starch showed lower light transmittance, peak viscosity, breakdown viscosity, pasting temperature, shear viscosity, storage modulus and loss modulus, while the oil adsorption capacity and gelatinization enthalpy significantly increased with increasing α-amylase hydrolysis time. Correlation analysis indicated that α-amylase hydrolysis had different effects on different pea varieties. This research could provide ideas for exploring new applications for enzymatically modified pea starch in food industry.Industrial relevanceThis study found that Bacillus-produced α-amylase significantly changed the amylose content, granule size and viscosity of pea starch, which was helpful to further investigate the modified starch. This technology is expected to widen the applications of pea starch modified by Bacillus-produced α-amylase in food industry, for example as thickener, stabilizer and beverage, to improve the texture, stability and shelf-life of various food products.     

Chlorination of Cake Flour and Its Effect on Starch Gelatinization

The influence of a defined chlorination on the gelatinization behaviour of different cake flours in sucrose solutions (30–60% w/w) was investigated. Besides microscopic examinations, methods were developed for the estimation of hot paste viscosity and “amylose”

1 “Amylose” will throughout this paper mean linear polymers of glucose long enough to give a blue colour with iodine, but not necessarily native amylose as exists within the starch granule.

exudation from starch granules. The findings have shown that the amount of “amylose” which is exuded from starch granules during heating, as well as paste viscosity, increases with the chlorination of flour. High positive correlations were obtained between “amylose” exudation, hot paste viscosity and cake crumb firmness. It is proposed that this increased “amylose” exudation is, via an increase of gel strength, to a large extent responsible for the prevention of high ratio cake collapse. Besides reducing “amylose” exudation the high sucrose concentrations prevailing in cake batters were also found to inhibit greatly starch breakdown by malt and fungal amylase activity.     

Perspectives on the history of research on starch

Starch has been used over several millennia for a number of different applications. However, research on understanding this substance only spans about three centuries starting with Leeuwenhoek who observed it in 1716. This story of discovery of the molecular structure and architectural makeup of starch is chronicled in a series of six essays of which this is the third with a focus on contemporary terminologies used in the 19th and early 20th centuries and its impact on advances in starch. Following the discovery of diastase, researchers focused on understanding the action of diastase on “transforming” starch into sugar. Besides maltose, they found that the products consisted of a range of dextrins with different abilities to complex with iodine. However, the nomenclature of the products that were obtained under a myriad of experimental conditions gave rise to confusions and misinterpretations, which transpired for over 30 years. Researchers also attempted to understand starch structure through systematic analyses of the different stages of starch breakdown. A new era of confusion in both nomenclature and structural interpretation started in the early 20th century with the discovery of cyclodextrins that were obtained from starch using the microorganism B. macerans. This gave rise to the school of “the low molecular elementary unit hypothesis” for starch structure, which lasted for about 25 years.