Effect of hydroxypropylation on physical and rheological properties of sweet potato starch

Sweet potato starches (SPS) were hydroxypropylated to evaluate the effect of molar substitution (MS, 0.042-0.153) on the rheological properties, thermal properties, freeze-thaw stability, paste clarity, and gel strength of hydroxypropylated sweet potato starches (HPSPS). The swelling power and solubility values of HPSPS were higher than those of native sweet potato starch (SPS) and increased with an increase in MS. The transition temperatures (T_o, T_p, and T_c), and enthalpy (ΔH) of gelatinization of HPSPS were lower than those of native SPS, and significantly decreased with an increase in MS.Rheological properties of HPSPS pastes were measured under the conditions of steady and dynamic shear. Their consistency index (K), apparent viscosity (η_a,100), Casson yield stress (σ_oc), complex viscosity (η*), and dynamic moduli (G′ and G″) values decreased with an increase in MS, while their flow behavior index (n) and tan δ (ratio of G″/G′) values increased. The dependence of apparent viscosity on temperature followed the Arrhenius model for all samples. The paste clarity of HPSPS paste was more pronounced with increasing MS of hydroxypropyl groups. The HPSPS gels showed lower gel strength and also better freeze-thaw stability with a significant decrease in syneresis (g/100 g) compared to native SPS.     

紫薯-小麦混合粉的性质及在面条上的应用

紫薯全粉保留了鲜薯的色泽和营养,是极好的食品加工原料,能够弥补小麦粉营养结构单一的缺点。将紫薯粉添加到小麦粉中,对混合粉的特性及在面条上的应用进行了研究,结果表明：随着紫薯粉的添加量由0%增加到30%,混合粉的糊化温度由66.31℃上升至67.73℃;糊化黏度、崩解值和回生值均减小;面团稳定时间由18min下降至7.8min;紫薯面条煮沸损失率由7.2%上升至11.8%;最大拉伸应力、剪切应力及硬度均减小;面条色度变暗,色泽向紫红色渐变。紫薯粉最佳添加量为15%。     

Steady and dynamic shear rheology of glutinous rice flour dispersions

The steady and dynamic shear rheological properties of Korean glutinous rice flour dispersions were evaluated at different concentrations (4, 5, 6, 7 and 8%). Glutinous rice flour dispersions at 25 °C showed a shear‐thinning behaviour (n = 0.487–0.522) with low magnitudes of Casson yield stresses (σ_oc = 0.056–0.339 Pa). The magnitudes of σ_oc, consistency index (K) and apparent viscosity (η_a,100) increased with the increase in concentration. The power law model was found to be more suitable than the exponential model in expressing the relationship between concentration and apparent viscosity. The apparent viscosity over the temperature range of 25–70 °C obeyed the Arrhenius temperature relationship, with high determination coefficients (R² = 0.982–0.998), indicating that the magnitudes of activation energies (E_a) were in the range of 9.05–11.89 kJ mol^?1. A single equation, combining the effects of temperature and concentration on η_a,100, was used to describe the flow behaviour of glutinous rice flour dispersions. Magnitudes of storage (G′) and loss (G′′) moduli increased with the increase in concentration and frequency. Magnitudes of G′ were higher than those of G′′ over most of the frequency range.     

Peeling,drying temperatures,and sulphite-treatment affect physicochemical properties and nutritional quality of sweet potato flour

The effects of peeling, drying temperature (55–65 °C) and pretreatment on the physicochemical properties and nutritional quality of sweet potato flour were investigated. The flours were prepared from peeled and unpeeled sweet potatoes dipped in 0.5% sodium hydrogen sulphite (NaHSO₃). There were significant differences (p < 0.05) in ΔE values and browning index between flours from peeled and unpeeled sweet potatoes without sulphite-treatment (PF and UF). On the other hand, flours from peeled and unpeeled sweet potatoes with sulphite-treatment (PSF and USF) had higher L∗, a∗, and b∗ values, swelling capacity, ascorbic acid, and total phenolics than PF and UF. However, USF and UF had higher β-carotene content than PSF and PF. β-Carotene and ascorbic acid contents decreased with increasing drying temperature for all flours, whereas total phenolics increased for PSF and USF. Therefore, the best quality product was obtained when samples were pretreated with sulphite before drying at any temperature.     

甘薯全粉生产过程中护色工艺研究

主要研究甘薯全粉生产工艺环节中护色剂、护色时间、及高温处理对甘薯护色效果,利用回归正交得到最佳复合护色剂,即0.58%柠檬酸和0.5%亚硫酸钠。通过单因素试验,得出复合护色剂最佳浸泡时间为45min;经护色处理后甘薯多酚氧化酶(PPO)活性为0.083,其抑制率达87.52%。     

Physicochemical properties of sweet potato starch

Tropical root crops, of which the sweet potato is an important representative, constitute an under exploited resource of developing countries. They can be used as food for both human and animal consumption and their starch is a source of industrial raw material. This review will consider recent reports on sweet potatoes, the physicochemical properties of their starches in comparison with other starches, and the possible causes of variation in these characteristics.     

Physicochemical properties of the starchy flour extracted from sweet potato tubers through lactic acid fermentation

The efficiency of starch extraction from sweet potato tubers was improved by lactic acid fermentation using a mixed culture inoculum. Study of the properties of the starchy flour showed that there was a significant reduction in the starch content and consequently the soluble and apparent amylose contents of fermented samples from all six varieties used. A fall in peak viscosity and viscosity breakdown was observed for fermented samples, while the pasting temperature was enhanced significantly. The fermented flour showed greater solubility and reduced swelling. Differential scanning calorimetry studies indicated a delay in gelatinisation and a fall in enthalpy of gelatinisation of the starch on fermentation. Unlike cassava, all the properties of the starch from sweet potato tubers, ie viscosity, swelling, solubility, gelatinisation temperature, amylose content and starch content, were affected by fermentation, and variation was also observed among cultivars. Copyright © 2005 Society of Chemical Industry     

Effects of cross‐linking on the rheological and thermal properties of sweet potato starch

Sweet potato starches were modified with three different concentrations of phosphorus oxychloride (POCl₃) (0.01, 0.02, and 0.03%, based on dry weight of starch) as a cross‐linking agent. The effects of crosslinking on rheological and thermal properties of sweet potato starch (SPS) pastes were evaluated. Cross‐linking considerably reduced the swelling power, consistency index (K), apparent viscosity (η_a), and yield stress (σ_oc) values of SPS, which significantly decreased with increase in POCl₃ concentration. The gelatinization temperature (T_p) and enthalpy (ΔH) values of the cross‐linked SPS, which were determined using differential scanning calorimetry, were higher than those of native SPS. Storage modulus (G′), loss modulus (G″), and complex viscosity (η*) of the cross‐linked SPS pastes determined using small deformation oscillatory rheometry, were higher than native starch, and they also decreased with increase in POCl₃ concentration from 0.01 to 0.03%. The tan δ (ratio of G″/G′) values (0.15–0.19) of the cross‐linked SPS samples were much lower than that (0.37) of the native SPS, indicating that the elastic properties of the SPS pastes were strongly influenced by modifications from cross‐linking. Finally, Cox–Merz plots showed that η* was much higher than η_a for the cross‐linked SPS pastes.     

Effect of high hydrostatic pressure to sweet potato flour on dough properties and characteristics of sweet potato‐wheat bread

The effect of high hydrostatic pressure (HHP, 100–400 MPa) for 20 min at 25 °C to sweet potato flour (SPF) on dough properties and characteristics of sweet potato‐wheat bread was investigated. The particle size of SPF after HHP was decreased significantly. The obvious rupture was observed in granules of SPF after HHP at 300 and 400 MPa by scanning electron microscopy (SEM). After HHP, significant differences on endothermic peak temperatures (T_P) of SPF were observed by differential scanning calorimetric (DSC), of which the enthalpy change (ΔH) had a slight increase, expect that at 200 MPa. Gas retention of dough with SPF after HHP increased markedly from 1199 (0.1 MPa) to 1246 ml (100 MPa). Specific loaf volume of bread with SPF at 400 MPa was increased significantly, while the hardness and chewiness were reduced. Thus, SPF treated with HHP at 400 MPa could be potentially used in wheat bread production.     

Effect of temperature on dynamic and steady-state shear rheological properties of siriguela (Spondias purpurea L.) pulp

The present work has evaluated the dynamic and steady-state shear rheological properties of siriguela (Spondias purpurea) pulp as function of temperature (0-80 °C), as well as the applicability of the Cox-Merz rule. The product flow behavior could be well described by the Herschel-Bulkley’s model (R² > 0.98), whose parameters were modeled as function of temperature (R² > 0.91). The product has shown a weak gel behavior, with storage modulus higher than loss modulus in the evaluated frequency range. The storage and loss modules could be well described by a power function of the oscillatory frequency (R² > 0.93), whose parameters were modeled as function of temperature (R² > 0.97). Moreover, a power modified Cox-Merz rule could describe the rheological properties of S. purpurea pulp (R² > 0.96). The obtained data are potentially useful for future studies on food properties and process design.     

Storage conditions affect quality of noodles with added soy flour and sweet potato

Summary Noodles were prepared from a formulation in which a portion of the flour was replaced with 10% defatted soy flour and sweet potato as 10% flour or 15% puree. Dried noodles were packaged in plastic bags under partial vacuum or air and stored at 4.4 °C or 22–30 °C for 6 months. Colour, β-carotene and sensory characteristics were analyzed at 2-month intervals. Packaging atmosphere had minor effects on colour. Stored noodles became lighter and yellower, and β-carotene decreased, with all changes being greater at 22–30 °C. Storage conditions influenced acceptability scores minimally. Noodles were stored successfully under air with greater quality retention with 4.4 °C storage.     

Effect of steaming on the rheological characteristics of wheat flour dough

 The effect of steaming on the various rheological characteristics of wheat flour dough was studied. Steaming of flours at atmospheric pressure for 15 min completely denatured the gluten and reduced the water absorption capacity from 58.4% to 45.0%. Even steaming for just 5 min increased the resistance to extension considerably from 500 BU (Brabender Units) to 1000 BU and the ratio figure (resistance to extension/extensibility) from 4.2 to 27.4, indicating stiffening of the dough. The dough made from steamed flour had a higher hardness value of 91.1 N than the dough made from raw wheat flour which had a value of 51.1 N. The pasting characteristics of flour steamed for 15 min measured in a Rapid Visco Analyser showed increased peak viscosity from 218 rapid visco units (RVU) to 257 RVU as well as increased cold paste viscosity from 175 RVU to 200 RVU and increased hot paste viscosity from 94 RVU to 108 RVU for flour steamed for 15 min. Received: 4 August 1998 / Revised version: 23 October 1998     

甘薯生物活性成分功能特性研究进展

甘薯是重要的粮食作物,在世界范围内被广泛种植。随着全球不可再生资源的加剧匮乏,材料学和生命科学的快速兴起,甘薯的研究、应用领域也得到了进一步的拓展和深化。近年来,甘薯生物活性成分的功能特性成为研究的热点。本文对近年来国内外学者对从甘薯中提取的纤维素、甘薯多糖、糖蛋白、酚类、醛类、醇类等生物活性成分在抗氧化和诱发糖尿病、高血糖、高血脂以及肿瘤等体内外实验中所取得的研究进展和成果进行综述。通过对这些最新研究成果的梳理,可为相关院校、科研院所和企业单位提供相应参考。     

不同干燥方式对紫薯全粉品质的影响

紫甘薯具有很高的营养价值,紫薯全粉的开发研究有利于其加工的扩大化和优质化。以紫薯为原料,通过鼓风干燥、真空冷冻干燥、真空干燥三种干燥方法对紫薯全粉的制备进行研究,探讨三种方式对于紫薯全粉基本化学成分、色差、碘蓝值、持水性和持油性、总花青素含量等品质的影响。通过对比实验得出结论,真空冷冻干燥对于紫薯全粉的基本化学成分、色差、碘蓝值、持水性和持油性、总花青素含量等品质的综合影响最小,真空干燥紧随其后。因此,为了保持紫薯全粉的完整性,同时考虑生产成本,在加工紫薯全粉过程中以真空干燥方法为最佳。     

The relationship between entanglement concentration and physicochemical properties of potato and sweet potato starch dispersions

Entanglement concentration (c_e) is defined as the onset of overlap and interpenetration of random‐coil chains in a polymer solution and is important in determining rheological, dynamic and fracture properties. However, few studies have reported in detail how c_e influences physicochemical properties of starch dispersions. So, the effects of c_e on the physicochemical properties of the potato and sweet potato starch dilute and semi‐dilute dispersions were investigated. The results showed that for the two starch dispersions with concentrations ≥c_e, the gelatinisation temperature increased more significantly with increasing concentrations, and storage modulus increased faster than loss modulus with increasing frequency. The potato starch dispersion with concentrations ≥c_e possessed higher entanglement density of the chain segments. The two starch dispersions with concentrations >c_e exhibited shear thinning with increasing frequency. The two starches could only form film at concentrations ≥c_e. So, c_e will be a suitable concentration for regulating the concentration of starch dispersions to obtain the expected physicochemical properties.     

Changes in characteristics of sweet potato flour prepared by different drying techniques

The changes occurring in the characteristics of sweet potato flour as a result of processing were investigated. Pasting behaviour of drum dried and hot air-dried sweet potato flour was determined using Rapid Visco-Analyser. The pasting characteristics decreased due to gelatinization of starch during processing. The degradation of starch by amylases during hot air drying further lowered the water binding capacity/viscosity and total amylose and increased the digestibility compared to those of drum dried and native flour. Swelling power and solubility of the flours increased as a result of processing which subsequently increased with increase in temperature. Scanning electron micrographs of starch granules showed tendency of clustering, especially in drum dried samples. X-ray diffraction patterns showed alteration from Ca-type to V-type with a marked reduction in crystallinity index as a result of processing. The ¹³C NMR spectra of processed starches showed reduced peak intensities and line widths due to depolymerizing effects, and also pointing to their change in crystallinity.     

香菇粉对小麦面团热机械学和动态流变学特性的影响研究

本试验通过测定不同比例的香菇粉和小麦粉混合粉的热机械学和动态流变学特性,研究香菇粉对小麦面团特性的影响。结果表明,香菇粉的添加使小麦面团的吸水率增大,面团的形成时间和稳定时间先下降后上升,相应的蛋白质弱化度先升高后降低。香菇粉的添加使小麦面团的峰值黏度和回生值均显著降低。动态流变学试验显示:香菇粉的添加使得小麦面团的黏弹特性发生了显著的变化,储能模量(G')与损失模量(G")均呈现先降低后升高的趋势。而tanδ随香菇粉比例的增大呈现了先略微升高后明显降低的趋势,表明了混合体系中分子交联的程度有所增加,弹性比例增大。