On Crystallinity in Cereal and Tuber Starches

The size and shape of the crystalline regions of wheat and potato starch were analyzed by X-ray line broadening. It was found that wheat A- and B-granules contained almost identical roughly spherical crystallites, about 100Å in size. Potato starch crystallites showed about the same dimensions in the different directions, but were somewhat smaller than wheat starch. The crystallite size agreed well with literature values of the radial length of the amylopectin cluster.     

Effects of Na2CO3 and NaOH on Pasting Properties of Selected Native Cereal Starches

ABSTRACT: Using a Rapid Visco Analyzer (RVA), it was revealed that 2 alkalizing agents (Na2CO3 and NaOH) had a far larger effect on pasting properties of nonwaxy starches (wheat, corn, rice) compared with their effect on waxy starches (waxy corn and waxy rice). It was hypothesized that the alkalizing agents have a greater propensity to attack the amorphous regions of the nonwaxy starch granules, thereby causing increased leaching of amylose molecules and possibly also some hydrolysis of starch chains. As a result, the RVA pasting profile of a nonwaxy starch, in the presence of alkali, was drastically altered to one that more closely resembled that of its waxy counterpart without added alkali.     

几种不同品种淀粉及羟丙基产物糊液性质比较研究

以薯类淀粉(木薯,马铃薯)及禾谷类淀粉(普通玉米、蜡质玉米、高直链玉米及糯米)为原料,以环氧丙烷为醚化剂。制备了羟丙基变性淀粉。反应条件:淀粉乳质量分数40%、反应温度40℃、无水Na_2SO_4添加量12%(以淀粉干基计)、NaOH添加量1.2%、环氧丙烷添加量12%、反应时间18h。分别对原淀粉及在相同的反应条件下制备的羟丙基变性淀粉糊性质做了对比研究。不同品种淀粉糊性质存在很大差别。经过羟丙基改性。淀粉糊液粘度性质、冻融稳定性、透光率、都有不同程度的改善,但凝沉性质不能准确反映羟丙基化对蜡质玉米淀粉和糯米淀粉糊液性质的改善。     

糯米淀粉的晶体性质和糊化特性

以不同产地、品种的糯米为原料,探讨糯米淀粉晶体性质和糊化特性的差异,并进行相关性分析,以期为糯米食品加工的原料选择提供参考。试验结果表明,糯米淀粉的结晶度为16.4%~25.3%,糊化温度为71.1~87.2℃,且结晶度和糊化温度均以珍珠糯最高,禾胜糯1次之,扬丰糯最低。其中,结晶性质主要取决于品种,受产地影响相对较小,而产地、品种的差异极大地影响糯米淀粉的糊化性质。相关性分析表明,糯米淀粉的碘蓝值、结晶度与糊化温度三者之间呈极显著正相关关系。因此,品种和产地对糯米淀粉的结晶性质和糊化特性均有较大影响。     

Pasting and Thermal Properties of Potato and Bean Starches

Starches from potato (Mainechip, ND651-9 and Commercial) and Navy and Pinto bean were isolated and the pasting and thermal properties examined. Analysis by Rapid Visco-Analyzer (RVA) showed potato starches had lower pasting temperatures, higher peak viscosity, and lower setback than bean starches. High intrinsic viscosity values obtained for the potato starch indicated higher average molecular weight for the potato starches compared to the bean starches. Characterization of thermal (gelatinization and retrogradation) properties of starches by Differential Scanning Calorimetry (DSC) showed that potato starches had sharp, well-defined gelatinization thermograms, while bean starches had broad, shallow thermograms with higher peak temperature (Tp). Potato starches required higher gelatinization enthalpies than bean starches. In comparison with gelatinization, the retrogradation thermograms of starches stored at three different temperatures (23,4 and −10°C) were broader and occurred at the lower temperatures. Compared to potato starches, Navy and pinto bean starches showed a higher retrogradation enthalpy at 4 and 23°C storage temperatures, but a lower enthalpy at −10°C.     

Molecular Distribution and Pasting Properties of UV-Irradiated Corn Starches

Suspension (30 %, w/w) of corn starch (25 % amylose) in water was irradiated by UV-light with wavelength greater than 250 nm at 25°C, under a stream of nitrogen or air, for time intervals ranging from 5 to 25 h. Effects of the irradiation on the transition enthalpy and temperature for melting, and the pasting viscosity profile of the irradiated starch were examined. Weight-average molecular weight (M_w) and radius of gyration (R_g) of the irradiated starch molecules were measured by high performance size exclusion chromatography coupled with multiangle laser light scattering and differential refractive index detectors (HPSEC-MALLS-RI). In the case of starch irradiated under nitrogen, the transition enthalpy (ΔH) decreased with increasing irradiation time whereas the melting temperature was not changed. Similarly, the peak paste viscosity (P_v) decreased from 97 to 56 RVU by 25 h irradiation. Average M_w and R_g of amylopectin and amylose fractions, which were 93 × 10⁶ and 144 nm, and 2.0 × 10⁶ and 104 nm, respectively, were decreased by irradiation to 32.2 × 10⁶ and 93.7 nm, and 0.7 × 10⁶ and 83.6 nm by the irradiation for 15 h under nitrogen, respectively. When the starch was irradiated with aeration, sharp drops of all measured parameters were observed in 5 h of irradiation (ΔH 11.4 J/g, P_v 53.2 RVU, amylopectin M_w 50 × 10⁶). After 15 h under air, however, all measured values increased (ΔH 16.8 J/g, P_v 65.5 RVU, amylopectin M_w 63.1 × 10⁶). Molecular size distribution profiles confirmed oxidative the photodegradation in the early stage (up to 5 h), and cross-linking reactions in the late stage (5—15 h) of irradiation under aeration.     

Morphology of Cereal Starches Grafted with Polyacrylonitrile

Morphological aspects of six cereal starches and their graft copolymers with polyacrylonitriles (PAN) prepared from granular as well as geletinized starches are reported. Scanning electron microscopy showed that grafting is not uniform on the surface but has also occurred in the interior of the granules. The graft copolymers prepared from gelatinized starches maintained the individuality but no resemblance with original shape of the granules.     

Pasting Properties of Various Retrograded Starches Isolated with Ethanol

The pasting properties of various retrograded starches were studied by means of RVA. Most retrograded starch pastes showed a low‐temperature peak which did not appear in the viscograms of any raw starch sample: for wheat and rice starches, both a high‐temperature peak shown in the viscogram of their raw samples and a low‐temperature peak appeared, while for other cereal starches and potato starch, only a low‐temperature peak was detected in the retrograded paste. The low‐temperature peak began to appear, when the degree of gelatinization decreased below 60—70%. The viscosity of both peaks tended to increase to a maximum value and then decrease during storage.     

谷朊粉对不同淀粉糊化特性和质构特性的影响

研究了谷朊粉对马铃薯淀粉、红薯淀粉、玉米淀粉、绿豆淀粉、小麦淀粉、大米淀粉、大米粉的糊化特性、质构特性及回生性的影响。通过RVA数据分析表明,谷朊粉添加量为0%～25%时,淀粉的糊化温度没有显著变化,峰值黏度、低谷黏度、最终黏度、衰减值和回生值均随谷朊粉添加量的增加而升高。通过TPA分析,淀粉凝胶的弹性无显著变化,硬度均呈现下降,马铃薯淀粉、红薯淀粉、玉米淀粉、绿豆淀粉、大米淀粉、大米粉的硬度分别下降了50.45%、6.58%、5.71%、54.97%、78.26%、59.90%。添加了谷朊粉后,随着贮藏时间的延长,淀粉样品的硬度增加,回生性升高,其中绿豆淀粉、马铃薯淀粉、大米淀粉和大米粉的回生性显著升高。     

Chemical and Enzymatic Modifications of the Pasting Properties of Legume Starches

Refined legume starches were evaluated for their Brabender Visco/Amylograph properties in their native form and after chemical and enzymatic pretreatment during incubation for 20 h at room temperature. Although exhibiting the characteristic restricted paste viscosities of legume starches, native lentil starch showed much higher viscosity parameters than navy bean starch while field pea starch had very low, stable viscosities. Pretreatments with mineral acids, alkali or enzymes failed to significantly alter the amylographs of the 8% slurries (w/v). Removal of surface lipids on the refined starch granules with propanol/water (3:1 v/v) or chloroform/methanol (2:1 v/v) increased paste viscosities substantially, as did the complexation of the starches with palmitic acid or glyceryl monopalmitate. None of the treatments resulted in complete dissolution of the starch granules and the modified starches showed no improvement in gel syneresis during storage.     

Behaviour of Oxidized Starches Towards Cyanoethylation

Starch of different molecular sizes brought about by oxidation of maize and rice starches were cyanoethylated under identical conditions. The degree of cyanoethylation, expressed as % N, was found to depend mainly on the molecular size of starch irrespective of its kind. As the molecular size decreases the degree of cyanoethylation increases. Cyanoethyl starches are water soluble and can be precipitated by ethanol. It was also found that the rheological properties are determined by the nitrogen content of cyanoethyl starch. When the latter acquires low nitrogen content, it exhibits non-Newtonian pseudoplastic behaviour. On the other hand, cyanoethyl starches with higher nitrogen content are characterized by non-Newtonian thixotropic. At constant rate of shear, the apparent viscosity of cyanoethyl starches is directly related to its molecular size. Storing of pastes prepared from these cyanoethyl starches for 7 d exerts considerable influence on rheological properties and apparent viscosity of these derivatives.     

Plastification Behaviour of Different Native Starches

Based on physical and thermal conservation laws a quantitative variable is introduced, which allows evaluation of the thermomechanical starch plastification much more independent of the transformation procedure. By that method, a comparison of plastification behaviour during extrusion of native potato, maize and wheat starch without any additives is realized for the first time. The complete energetical balance of the extrusion process supplemented by microscopical investigations leads to an essential better understanding of thermomechanical proceedings during extrusion of starch or compounding of other polymers. After optimization of extruder and screw configuration the resulting data for the energy needed for the plastification of starch, i.e. for the transformation of native starch granules into a thermoplastic melt by extrusion, have been measured under constant conditions. On these adequat extrusion conditions the native, laminated starch granules of all three used starches have been destroyed completely during its plastification by extrusion. The specific energy input needed for the plastification of potato starch was about 650 kJ/kg, for maize 380 and for wheat starch 435 kJ/kg. In comparison of these results the energy input for melting of polyethylene high density was about 585 kJ/kg under same conditions.     

Analysis of Cereal Starches by High-Performance Size Exclusion Chromatography

Starch has unique physicochemical characteristics among carbohydrates. Two important characteristics of starch are amylose/amylopectin ratio and molecular weight. The objective of this study was to develop a simple, one-step, and accurate method for the determination of amylose/amylopectin ratio and weight-averaged molecular weights of starch in whole meal cereal samples. This method would allow for the simultaneous measurement of these important properties without the time-consuming step of large-scale starch extraction. Starch from spring wheat, barley, oat, rye, buckwheat, rice, durum wheat, and corn was precipitated with ethanol and solubilized with potassium hydroxide and urea before analysis by a high-performance size exclusion chromatography (HPSEC) system with a refractive index detector. To verify peak identity, fractions were collected and then gas chromatography analysis of soluble starch and beta-glucan assays was performed. All HPSEC fractions contained only glucose and no beta-glucan was detected, indicating that there was no contamination from non-starch polysaccharides. Weight-averaged molecular weights were calculated using a series of gel permeation chromatography grade dextrans. The method described in this study can be used to determine amylose/amylopectin ratio and weight-averaged molecular weight of cereal starches using as low as 25 mg whole meal samples without large-scale starch extraction.     

Thermal and Pasting Properties of Acid‐treated Rice Starches

The physicochemical properties of acid‐treated rice starches were investigated. Rice starches were treated with hydrochloric acid at different acid concentrations and hydrolysis times. The pasting properties were tested using a Rapid Visco Analyser, and gelatinization and retrogradation properties using a differential scanning calorimeter. The results showed that acid concentration had a more pronounced effect on degree of polymerization (DP) and viscosity than hydrolysis time. The onset, peak and conclusion temperatures of gelatinization were increased significantly with hydrolysis time, while the gelatinization enthalpy (ΔH_G) was decreased. In addition, there was an increase in the gelatinization temperature range with longer hydrolysis time. After storing gelatinized starches at 4°C for 7 days, the transition temperature and enthalpy (ΔH_R) to melt retrograded amylopectin did not change significantly. Additionally, the temperature and enthalpy transition for melting amylose‐lipid complex of all gelatinized and retrograded starches were in the same range.     

On Ultrastructural and Nutritional Aspects of Some Tropical Tuber Starches

Type A starches (Manihot utilissima, Dioscorea dumetorum and Colocasia antiquorum) and type B starches (Canna edulis, Dioscorea alata and Dioscorea cayenensis) are investigated. Results show that the degradation of the pure tuber starch as compared with that of feeds made from a particular starch is more or less the same. However, type A starches are more rapidly degraded by bacterial α-amylase. The susceptibility to attack is compared to the nutritional efficiency of the feeds using axenic and holoxenic chickens. Comparison of the degree of degradation of the starch granules in the crop as well as in the feces (by in vitro and in vivo studies) is made by scanning electron microscopy. Type A starches show always a higher susceptibility to α-amylase attack. The feed efficiency tested on chicken and digestibility of tuber starches in the sheep rumen and in the chicken crop increase as their ease of degradation by bacterial α-amylase (in vitro) increases.     

Morphology of Some Legume and Tuber Starches Grafted with Polyacrylonitrile

Morphological aspects of three legumine and three tuber starches and their graft copolymers with polyacrylnitrile (PAN) prepared from granular and gelatinised states have been reported. Scanning electron microscopy revealed that grafting characteristics of legumine and tuber starches are quite different. In potato starch the hydrolysed S-g-PAN product showed that the grafting has occurred in the interior. In case of sweet potato starch a little grafting occurred on the surface of depression while normal grafting might have taken place in the interior through the depression. Little grafting seems to have occurred inside the tapioca starch granules. The grafting on legumine starches has mainly occurred on the surface of granules.     

低聚糖及用薯芋类淀粉生产低聚糖

本文对低聚糖的性能、应用作了概述。薯芋类是我国种植面积较大,产量高,种植区域广的农业经济 作物之一。利用薯芋类淀粉生产低聚糖,是淀粉深加工开发另一糖业——低聚糖的重要途径。薯芋类是可再生 绿色资源,不仅可以促进农业多种经营发展,对脱贫致富、保护环境,推动西部大开发,同样具有深远意义。     

Gelatinization of Sweet Potato,Tania and Yam Tuber Starches

Morphological changes that occur in starch granules of sweet potato, tania and yam tubers from native to cooked states, were studied both by electron microscopy and differential scanning calorimetry. In the first stages of heating, the same event was observed in all samples: a central cavity appeared at hilum level of the starch granules just before granule expansion started. Differences in gelatinization behaviour between these three starches were enhanced by mechanism by which amylose leached out. In the sweet potato starch granules, amylose was released through micropores formed in the starch granules during the phase of expansion whereas in tania starch granules, both micropores and pin-holes were observed. In yam starch granules, amylose escaped only by pin-holes formed across the starch granules. When cooking was achieved, spongy-like structures were observed in cooked sweet potato parenchyma cells while folded gelatinized granules remained in yam. In cooked tania tuber, both types of cell contents were observed. Sweet potato, tania and yam starches presented DSC endotherms at 72.7, 69.9 and 74.4°C with enthalpy change of 13.6, 12.9 and 20.9J/g, respectively.