Application of an In‐line Viscometer to Determine the Shear Stress of Plasticised Wheat Starch

An in‐line viscometer was designed and constructed to enable determination of the shear stress of plasticised wheat starch during extrusion cooking. The viscometer was installed between the end of the barrel section and the extruder die plate so that the shear stress could be determined for the plasticised material, irrespective of the geometrical shape into which it was subsequently moulded by the extruder die. The extrusion conditions were described in terms of the process parameters, i. e. water content, barrel temperature, screw speed and screw configuration; and of the system parameters, which were the specific mechanical energy input (SME), product temperature (PT) and mean residence time (MRT). The parameters were measured and the results evaluated using statistical methods. Regression equations were used to describe functional relationships between the shear stress and the extrusion conditions on the one hand, and between the shear stress and the product characteristics of the extrudates on the other. The shear stress of plasticised wheat starch determined in‐line can be used to predict the morphological structure (volumetric expansion) and the functional properties (cold paste viscosity and cold water solubility) of extruded, directly expanded starch with a high degree of accuracy. The measurement technique used and the results of the extrusion tests undertaken for this project will therefore enable the shear stress of plasticised material in an extruder to be used as the principle parameter for controlling extruders on‐line.     

西农黑大穗小麦挤压膨化加工研究

以普冰9946小麦为对照,研究西农黑大穗挤压膨化过程中加工温度、物料含水量、喂料速度变化对挤压膨化的扭矩、4区压力、5区压力、单位机械能耗、产品比容、径向膨化率、脆度、硬度的影响。结果表明,在试验范围内,温度为T1时,西农黑大穗产品比容、径向膨化率高,单位机械能耗高;温度为T3时,产品脆度高、硬度低,膨化率低。含水量为20%时,产品物理特性相对较好;含水量为22.5%时,单位机械能耗较低。喂料速度为20 g/min时,产品物理特性较好,单位机械能耗较高。加工过程中,西农黑大穗的扭矩、压力均高于对照,单位机械能耗和产品物理特性与对照差异极显著(P0.01)。     

Effects of extrusion variables on the properties of waxy hulless barley extrudates

The objective of this research was to investigate the extrudability of waxy hulless barley flour under various extrusion conditions. Waxy hulless barley flour was processed in a laboratory-scale corotating twin-screw extruder with different levels of feed moisture content (22.3, 26.8, and 30.7%) and die temperature (130, 150, and 170 degrees C) to develop a snack food with high beta-glucan content. The effects of extrusion condition variables (screw configuration, moisture, and temperature) on the system variables (pressure and specific mechanical energy), the extrudate physical properties (sectional expansion index, bulk density), starch gelatinization, pasting properties (cold peak viscosity, trough viscosity, and final viscosity), and beta-glucan contents were determined. Results were evaluated by using response surface methodology. Increased extrusion temperature and feed moisture content resulted in decreases in exit die pressure and specific mechanical energy values. For extrudates extruded under low shear screw configuration (LS), increased barrel temperature decreased sectional expansion index (SEI) values at both low and high moisture contents. The feed moisture seems to have an inverse relationship with SEI over the range studied. Bulk density was higher at higher moisture contents, for both low and high barrel temperatures, for samples extruded under high shear screw configuration (HS) and LS. Cold peak viscosities (CV) were observed in all samples. The CV increased with the increase in extrusion temperature and feed moisture content. Although beta-glucan contents of the LS extrudates were comparable to that of barley flour sample, HS samples had generally lower beta-glucan contents. The extrusion cooking technique seems to be promising for the production of snack foods with high beta-glucan content, especially using LS conditions.     

Reduction of ochratoxin A in extruded barley meal

The objective of this work was to determine the effects of extrusion cooking on the stability of ochratoxin A (OTA) in an artificially contaminated hulled barley meal (0.73-mm grain diameter) using a single screw extruder. The extrusion cooking parameters were temperature (140, 160, and 180 degrees C), initial moisture content of barley meal (24, 27 and 30%), and residence time (30, 40, 50, 60, and 70 s). Both unextruded and extruded samples were analyzed for OTA by high-performance liquid chromatography. Extrusion cooking variables significantly affected the stability of OTA (P < 0.05). Greater OTA reductions were achieved at higher residence time (70 s), medium temperature level (160 degrees C), and either high (30%) or low moisture (24%) content of samples. The amount of OTA destroyed during the extrusion process ranged from 17 to 86% depending on the studied parameters. The decrease in the amount of OTA after extrusion cooking followed first-order kinetics, showing that the fastest treatment in OTA reduction was that at 140 degrees C and 24% of moisture content.     

Extrusion Cooking of Starches for Semi-Products

Extrusion cooking is introduced as a modern high-temperature-short-time process. The cooking time at high temperatures is a matter of seconds, which has a favourable effect in maintaining the properties of the ingredients and active substances, while giving high rates for the destruction of micro-organisms. The end-products have a long shelf-life on account of their low process moisture content. The quality of extruder-cooked products depends on the extrusion system. The self-cleaning co-rotating twin-screw extruder with its narrow residence time spectrum is the optimum system. However, the counter-rotating intermeshing machine has certain advantages for products of low viscosity. Continuous extrusion cooking has economic advantages mainly because it replaces many batch processes and because extrusion is carried out entirely or almost entirely with the final moisture content, thus avoiding the necessity to evaporate huge quantities of water.     

物料含水率对大豆蛋白挤压组织化产品特性的影响

物料含水率是植物蛋白挤压组织化过程中重要的操作参数之一,是区分高、低水分挤压工艺的标志.以低温脱脂豆粕为原料,应用德国Brabender DSE-25型双螺杆挤压实验室工作站,研究了物料含水率(28%～53%)对大豆蛋白挤压组织化产品特性的影响.结果表明:物料含水率对大豆蛋白挤压组织化产品特性有重要影响.随着物料含水率的增加,挤压产品的组织化度、吸水率和弹性增大,色泽趋向亮白,硬度和咀嚼度变小.     

Extrusion conditions and zea mays endosperm hardness affecting gluten‐free spaghetti quality

The effects of extrusion temperature (80, 90 and 100 °C) and flour moisture content (27%, 31% and 35%) on corn spaghetti quality were evaluated according to a factorial experimental design. Flours obtained from a soft and hard endosperm were processed in a Brabender single screw extruder. Corn spaghettis with good cooking characteristics and resistance to overcooking were obtained by extrusion at 27% flour moisture content for the three temperatures used. They have higher resistance to hydration, long cooking time (around 11 vs. 7 min for poor quality) and low cooking loss (lower than 9% for a 10‐min overcooking). Softer endosperm allowed obtaining better spaghetti quality. Among different physicochemical properties, enzyme susceptibility could be used as an indicator of mechanical energy dissipated by friction. During extrusion cooking, the native structure is partially destroyed, and new crystalline ones, corresponding to the amylose–lipid complex, are formed.     

Effects of extrusion conditions on system parameters and physical properties of a chickpea flour-based snack

Response surface methodology (RSM) was used to study the effects of feed moisture content (16–18%), screw speed (250–320 rpm), and barrel temperature (150–170 °C) on extruder system parameters (product temperature, die pressure, motor torque, specific mechanical energy, SME) and physical properties (expansion, bulk density, hardness) of a chickpea flour-based snack. Second-order polynomials were used to model the extruder responses and product properties as a function of process variables. Product temperature and die pressure were affected by all three process variables, while motor torque and SME were only influenced by screw speed and barrel temperature. All three variables affected product responses significantly. Desirable products, characterized by high expansion ratio and low bulk density and hardness, were obtained at low feed moisture, high screw speed and medium to high barrel temperature. It was demonstrated that chickpeas can be used to produce nutritious snacks with desirable expansion and texture properties.     

挤压处理对苦荞粉理化特性及全苦荞挂面品质的影响

为提高全苦荞挂面的加工适应性、蒸煮和质构品质,对苦荞粉进行挤压预处理后与苦荞生粉混合制作全苦荞挂面,探究了挤压处理对苦荞粉的冷糊黏度及凝胶强度的影响,并结合面带、面条的质构品质及面条蒸煮特性探究挤压处理对全苦荞挂面加工性能及食用品质的影响。结果表明,经过挤压后苦荞粉的吸水性指数和水溶性指数分别增加了102.7%和87.5%以上,冷糊黏度显著增加（p<0.05）,挤压后苦荞粉在冷水中可形成凝胶,凝胶强度随挤压加水量的增加或温度的降低而升高;添加挤压苦荞粉促进了面带成型,面带的表面黏附力随苦荞粉冷糊黏度的增加而显著增加（p<0.05）,随挤压苦荞粉凝胶强度的增加,面带的抗拉伸力及面条的硬度和咀嚼性显著增加（p<0.05）,蒸煮损失率及断条率显著下降（p<0.05）。     

Effects of extrusion conditions on secondary extrusion variables and physical properties of fish, rice-based snacks

A formulation containing rice flour, fish powder, menhaden oil and vitamin E was extruded at a feed rate of 10 kg/h using a co-rotating twin-screw extruder. Primary extrusion (independent) variables were temperature (125-145 °C), screw speed (150-300 rpm) and feed moisture (19-23 g/100 g db). Response surface methodology (RSM) was used to study the effects of extrusion conditions on secondary extrusion variables (product temperature, pressure at the die, motor torque, specific mechanical energy input and mean residence time) and physical properties of the extrudates. Second-order polynomial models were computed and used to generate contour plots. Increasing feed moisture and screw speed decreased pressure at the die. Increased screw speed increased product temperature at the die but increased feed moisture lowered it. Increased barrel temperature, feed moisture and screw speed decreased motor torque. Increased screw speed increased specific mechanical energy, while increased feed moisture reduced it. Longer mean residence times were observed at lower screw speeds. Product density increased as feed moisture increased, but decreased with screw speed. Increased feed moisture decreased radial expansion.     

挤压工艺对保鲜方便米饭品质的影响

以双螺杆挤压机加工保鲜方便米饭,研究了进料糊化度、进料水分含量、进料粒度、螺杆转速对方便米饭品质的影响。通过分析感官评定与质构参数的相关性,确定以硬度和咀嚼性为指标评价挤压保鲜方便米饭的挤压工艺。采用单因素试验和正交试验,优化了挤压工艺条件:进料粒度0.425 mm,进料糊化度50%,进料水分质量分数25%,挤压机螺杆转速90 r/min。在此条件下制备的方便米饭硬度为113.56 g,咀嚼性为63.81。米饭颗粒饱满,色泽晶莹,咀嚼性适中,口感好。     

Reaction kinetics in food extrusion: methods and results

Extrusion cooking is a highly efficient food processing technology. During the extrusion process, there are many desirable and undesirable reactions which will determine final product quality. While being heated and sheared simultaneously, food raw materials experience a non-isothermal process and their residence time in the extruder is distributed. All these factors contribute to the difficulties in determining the kinetic parameters for those reactions. Therefore, this paper attempts to review the reaction kinetics in food extrusion. First of all, the kinetic models for the reactions are outlined. After elucidating how to determine reaction time in an extruder, the methodological approaches for determining the reaction order, rate constant, and activation energy of a reaction under isothermal or non-isothermal conditions with or without residence time distribution (RTD) are presented. Then, different models relating the rate constant to its various impact factors, with especially focusing on shear stress, are reviewed. Subsequently, how shear stress is estimated in an extruder, is illustrated. In the last part of this paper, the reported data of rate constant, reaction order, and activation energy for the reactions occurring during food extrusion are summarized, with detailed impacts of temperature, moisture content, shear stress, and determination method on these kinetic parameters. Finally, future research needs are suggested.     

藜麦全粉对面条品质的影响

以小麦粉为原料,将藜麦全粉以不同比例添加到面粉中制备面条,对面粉的粉质特性、糊化特性、面团拉伸特性及面条的品质特性进行研究。结果表明:随着藜麦全粉添加量的增加,混合粉的糊化温度、峰值黏度、最小黏度、最终黏度、崩解值、回生值降低,面团的吸水率、弱化度增加,面团的拉伸能量、延伸度下降,藜麦面条的蒸煮损失率变大、断条率增加,硬度和咀嚼性增加、弹性减小。用藜麦粉代替面粉会降低面团的加工性能和面条品质。     

Effects of selected process parameters in extrusion of yam flour (Dioscorea rotundata) on physicochemical properties of the extrudates

Raw yam (Dioscorea rotundata) flour was cooked and extruded in a Brabender single-screw laboratory scale extruder. Response surface methodology using an incomplete factorial design was applied with various combinations of barrel temperature [100, 125, 150 degrees C], feed moisture content [18, 22, 26%] and screw speed [100, 150, 200 rpm]. Initial viscosity at 30 degrees C, water solubility index, expansion and hardness were determined. The highest values of initial viscosity were at the highest barrel temperatures and the highest moisture contents. At high feed moisture content and high barrel temperatures the yam extrudate flour showed the greatest values of water solubility index. The physical properties of the extruded product showed that at high temperature the lower the moisture content the greater the expansion index. Hardness was influenced directly by moisture content and inversely by extrusion temperature. The extrusion of yam flour led to the production of snacks and pre-gelatinized flours of diverse properties. Also extruded yam flour can be successfully used in the preparation of 'futu' (pre-cooked compact dough), a yam-based food, popular in Western Africa.     

挤出处理对玉米面团物性的影响

利用单螺杆挤出机对玉米粉进行改性处理,以玉米面团弹性值为考察指标,在单因素试验基础上采用响应面法研究挤出温度、物料加水量、物料粒度对改性玉米粉面团物性的影响。结果表明:挤出温度150℃、物料含水量43%、物料粒度0.246mm条件下挤出处理后,玉米面团硬度3037.697,黏度-2.162,弹性0.136,内聚性0.259,胶黏性769.195,耐咀性98.484,恢复性0.075,此时面团物性最好,可用于弹性面团食品的加工。     

Extrusion of Hulled Barley Affecting β-Glucan and Properties of Extrudates

Grits from eight different hulled barley cultivars were subjected to extrusion cooking on a twin screw extruder, and the effect of extrusion variables (temperature and moisture) on β-glucan and physicochemical properties was evaluated. The highest bulk density was observed for extrudates extruded at 150 °C and 20% moisture (low temperature high moisture, LTHM) while the highest expansion was observed for the extrudates extruded at 150 °C and 15% moisture (low temperature low moisture). Extrusion reduced the lightness (L*) of the extrudates and the highest decrease observed for LTHM extrudates. Increasing the feed moisture decreased water solubility index (WSI) significantly while increasing the extrusion temperature significantly increased WSI. The high temperature high moisture (HTHM) extrudates exhibited the highest water absorption capacity. The total β-glucan content was not affected by extrusion cooking, but a significant increase in soluble β-glucan was observed with the highest in high temperature low moisture extrudates. The ratio of soluble to insoluble β-glucan varied from 0.7 to 1.5 in the control barley, but after extrusion cooking, the ratio was changed from 1.2 to 3.1. The β-glucan extractability increased by up to 8% after extrusion with extrudates from HTHM showing the highest extractability. The extent of starch gelatinization varied from 80% to 100% upon extrusion, and the highest was observed in HTHM extrudates. A significant decrease in the peak and final viscosity of the extrudates at all the extrusion conditions was observed.     

EFFECT of EXTRUSION VARIABLES ON EXTRUDATE CHARACTERISTICS of FISH MUSCLE-RICE FLOUR BLEND IN A SINGLE-SCREW EXTRUDER

Effects of extrusion variables on extrudate characteristics of fish muscle-rice flour blend containing intermediate moisture (30–50%) were studied in an indigenously developed single screw cooking extruder. Data analysis of the statistically designed response surface experiments showed that expansion ratio and bulk density of extrudates were most influenced by the barrel temperature followed by fish content of the feed. In contrast fish and moisture contents of the feed significantly influenced hardness. A set of optimum process conditions was arrived at 160C barrel temperature, 12% fish content and 27% moisture content. Under these conditions experimental expansion ratio and bulk density matched well with the values predicted from the response model, but hardness deviated significantly. Experimental properties of the extrudates were not, however, affected by the fish variety.     

莲子淀粉重组米制备工艺优化

以不同比例莲子淀粉与碎米粉进行混合后挤压制备重组米,通过对混合粉的糊化特性和重组米的感官品质、质构特性及蒸煮损失率的分析,确定了莲子淀粉重组米的配比。以物料含水量、模头温度、螺杆转速为影响因素,采用响应面试验优化了莲子淀粉重组米挤压的最佳工艺条件。结果表明:随着莲子淀粉添加量的增加,混合粉的峰值黏度、谷值黏度、崩解值、最终黏度及回生值等均逐渐增加;感官评分先增大后减小,在莲子淀粉添加量为30%时较高;质构特性中硬度逐渐增大,弹性、咀嚼性、黏聚性先增大后减小,在莲子淀粉添加量为30%时最大;蒸煮损失率逐渐增大。综合分析,重组米品质在莲子淀粉添加量为30%时达到最佳。重组米的最佳挤压条件为:物料含水量40%、螺杆转速210 r/min、模头温度95 ℃时,重组米评分为69.13分。     

大豆蛋白挤压组织化力学特征和感官评价

以大豆蛋白为原料,开发一种即食性的大豆蛋白组织化挤压产品。采用正交试验设计,通过感官评价得到最适的挤压参数为水分含量15%,转速120r/min,挤压温度160℃,在此条件下得到的挤压产品硬度4.0N,脆度22.1mm,膨胀率329%。扫描电镜观察结果显示产品具有均匀结构,此外,利用扫描量热仪示差测量该产品,产品具有良好的热稳定性。