Development and Physicochemical Characterization of New Resistant Citrate Starch from Different Corn Starches

Resistant starch has drawn broad interest for both potential health benefits and functional properties. In this study, a technology was developed to increase resistant starch content of corn starch using esterification with citric acid at elevated temperature. Waxy corn, normal corn and high‐amylose corn starches were used as model starches. Citric acid (40% of starch dry weight) was reacted with corn starch at different temperatures (120–150°C) for different reaction times (3–9 h). The effect of reaction conditions on resistant starch content in the citrate corn starch was investigated. When conducting the reaction at 140°C for 7 h, the highest resistant starch content was found in waxy corn citrate starch (87.5%) with the highest degree of substitution (DS, 0.16) of all starches. High‐amylose corn starch had 86.4% resistant starch content and 0.14 DS, and normal corn starch had 78.8% resistant starch and 0.12 DS. The physicochemical properties of these citrate starches were characterized using various analytical techniques. In the presence of excess water upon heating, citrate starch made from waxy corn starch had no peak in the DSC thermogram, and small peaks were found for normal corn starch (0.4 J/g) and Hylon VII starch (3.0 J/g) in the thermograms. This indicates that citrate substitution changes granule properties. There are no retrogradation peaks in the thermograms when starch was reheated after 2 weeks storage at 5°C. All the citrate starches showed no peaks in RVA pasting curves, indicating citrate substitution changes the pasting properties of corn starch as well. Moreover, citrate starch from waxy corn is more thermally stable than the other citrate starches.     

硫酸泵用钢的腐蚀行为研究

在温度为60℃、浓度为60％的H_2SO_4苛刻介质条件下,对7种铸造不锈钢进行了耐蚀试验。均匀腐蚀、晶间腐蚀和电化学腐蚀的试验结果表明,除316钢外,其余各试验钢均具有良好的抗硫酸腐蚀性能,可根据用户的要求选择使用。     

耐温抗盐共聚物AMPS／AM／AMC14S的合成

用引发聚合方法合成了ＡＭＰＳ／ ＡＭ／ ＡＭＣ１４Ｓ 三元共聚物。研究结果表明,在单体总浓度１０ ％ —１５ ％ ,ＡＭＣ１４Ｓ浓度０ ．１５ ％ ,ｐＨ值为中性时,在３０—４０℃反应８ ｈ 可以得到转化率９７％ 、特性粘数１０ —１７ ｄＬ／ｇ 的共聚物。通过红外光谱研究了共聚物的分子结构,并通过差热分析研究了共聚物的耐热性。     

阀门流道流场的数值模拟及阻力特性研究

本文用孔隙率定义流场空间,并采用了二维Ｋ－ε紊流模式和有限体积法对ＷＣＢ型阀门阀道流场进行了模拟。通过阀门阀道的体型优化,寻求到阻力系数和过水断面较小、合理的阀道体型。     

新型耐热级SMA/ABS工程塑料合金

介绍耐热级ＳＭＡ／ＡＢＳ工程塑料合金的制备和性能,研究了ＳＭＡ、ＡＢＳ配比、增韧剂对合金性能的影响。结果表明,ＳＭＡ的加入使冲击强度下降,但加入增韧剂可提高合金的冲击强度达到或超过ＡＢＳ水平,当ＳＭＡ∶增韧剂∶ＡＢＳ＝５０∶２５∶２５时,缺口冲击强度可达２００Ｊ／ｍ。已推出通用级Ｅ－２２０用于ＰＣ改性、耐热级Ｈ２５１用于耐热要求的家电、玻纤增强级２５１Ｇ用于汽车零部件     

润滑油中磨屑尺寸对滑动摩擦副咬死性能影响的试验研究

在ＭＨＫ－５００型环块式磨损试验机上,对含不同尺寸磨屑润滑油润滑的４５＾＃淬火屑试环,试块组成的滑动摩擦副进行了抗咬死性能试验研究,试验结果表明,润滑油中磨屑尺寸对滑劝摩擦副抗咬伤性能有很大的影响,改善润滑油清洁度的显著提高摩擦副的抗咬死承载能力,滑动摩擦副的抗咬死能力随润滑油中磨屑含量的增中减小很快,观察咬死后试件上的磨痕,表明滑动摩擦副的咬死是由于局部高温引起的接触区熔焊所致。     

抗性淀粉体外分析方法的优劣势比较及研究进展

抗性淀粉由于其潜在的健康益处和功能特性受到了广泛的关注。近年来,体外测定抗性淀粉的方法层出不穷,大都在初始方法的基础上不断补充、丰富、调整,使测定结果更加真实化、合理化,但这些调整都直接影响测定的抗性淀粉水平。食品原料中抗性淀粉的含量直接影响其在不同产品中应用的加工特性及其潜在的功能特性,因此对抗性淀粉含量测试方法研究进展的全面总结及分析是非常有必要的。【目的】本文对各种体外抗性淀粉测定方法的流程、原理进行了详细综述并针对其优劣势进行比较,旨在为抗性淀粉体外分析及加工应用提供一定的理论借鉴。     

Effect of the Extent of Conversion and Retrogradation on the Digestibility of Potato Starch

The effect of starch conversion on the susceptibility of potato granules to α‐amylase was studied by direct sampling at different pasting times corresponding to different points on the RVA profile of a 6.4% (w/w) suspension of starch in distilled water. Native granules showed high resistance to α‐amylase with 8.6 ± 0.4% digestibility for a 6 h incubation period with the enzyme. When the suspension was heated to 60 °C, the digestibility increased to 53.5 ± 0.7% although, at this temperature, there was still no noticeable increase in the measured viscosity (≤0.040 Pa · s). The material sampled after a pasting time corresponding to the RVA peak viscosity showed a digestibility of 88.4 ± 0.5%. This suggested, owing to the expected retrogradation of amylose on cooling, the quasi‐total susceptibility of amylopectin to enzymatic digestion at this pasting stage. The effect of ions on the swelling of potato starch was used to assess whether the decrease of the swelling of the granules in the presence of NaCl was paralleled by an increase in resistance to α‐amylase. A small (∼6.1%) but significant decrease in the digestibility of pasted starch was observed in the presence of salt. Finally, the effect of the retrogradation of the amylopectin fraction on its digestibility was assessed in extruded potato starch ribbons containing 35% (w/w) water and stored at different temperatures. After 14 days of storage, the digestibility decreased from 77.0 ± 0.9% in the freshly extruded samples to between 28.0 ± 1.7% and 42.1 ± 0.3%, depending on the storage temperature. This suggested a measurable difference in the α‐amylase susceptibility between the A and B polymorphs of retrograded amylopectin.     

Resistant Starch Derived from Extruded Corn Starch and Guar Gum as Affected by Acid and Surfactants: Structural Characterization

Corn starches with and without guar gum [10% (w/w)] and 2% (w/w) of diacetyl tartaric acid ester of monoglyceride, sodium stearoyl‐2‐lactylate or citric acid, respectively, were extrusion‐cooked in a twin‐screw extruder at 18% moisture, 150 °C and 180 rpm screw speed. The content of resistant starch was determined by sequential enzymatic digestion. The formation of resistant starch in extruded corn starch was strongly affected by the addition of gum and the different food additives. X‐ray diffraction of the extruded starches gave a V diffraction pattern indicating the effect of extrusion cooking and amylose‐lipid complexes. Enzymatic digestion did not affect the V‐structure, which could apparently be attributed to extrusion cooking. Similarly, differential scanning calorimetric thermograms indicated that all isolated resistant starches exhibited endothermic transitions between 71—178 °C signifying a complex formation between amylose and the emulsifiers and possibly the melting of amylose crystallites in the resistant starch. Purification of the isolated resistant starches by size exclusion‐high performance liquid chromatography showed a dependence of molecular weight on the added additives. Results of differential scanning calorimetry and X‐ray diffraction suggest that amylose‐lipid complexes could also be involved in the formation of resistant starch in extruded cornstarch.     

Resistant Starch Content and Structural Changes in Maize (Zea mays) Tortillas During Storage

Storage of maize products such as tortillas may cause starch retrogradation and lead to resistant starch (RS) formation. This study was carried out to determine if storage of maize tortillas under refrigerated conditions enhanced RS content and/or modified RS structure. Improved Costeño variety maize grain was nixtamalized and processed into tortillas which were stored for five and ten days at 5°C. Total resistant starch (TRS) and retrograded resistant starch (RRS or RS3) contents were determined on raw and nixtamalized maize grain and tortillas stored for zero, five and ten days. Differential scanning calorimetry (DSC), X‐ray diffraction (XRD) and near‐infrared (NIR) spectroscopy were use to evaluate structural changes in retrograded resistant starch isolated from each sample type. Total starch content was 67 ± 1.5% for all samples, TRS ranged from 3.3% in the raw grain at 7.2% in tortillas stored for ten days, while RRS starch content ranged from 0% in the raw grain to 3.2% in tortillas stored for ten days. DSC showed endothermic transitions corresponding to amylopectin and amylose retrogradation, at 31.9 and 139.7°C in RRS from tortillas stored for five days, and at 47.9 and 146°C in RRS from tortillas stored for ten days. These values agreed with the higher total RS content recorded after prolonged storage. XRD revealed a starch crystallinity of 13.7% in tortillas stored for five days and 15.3% in those stored for ten days. NIR spectroscopy analysis showed evidence of structural changes in polymeric order that were more pronounced in RRS of tortillas stored for ten days, due to increase in crystalline region.