电导率法淀粉糊化温度测定及其影响因素的研究

改进通电加热淀粉悬浮液过程中电导率的测定装置,有效地防止淀粉悬浮液的沉淀及水分散失,提高测量精度,使之可用于淀粉糊化温度的测定,并将结果与差示扫描热量仪fDSCl测量结果进行了比较.并进一步研究淀粉浓度、NaCl浓度和电压对淀粉悬浮液的电导率、加热速率及所测得糊化温度的影响.结果表明:通电加热淀粉悬浮液时,随NaCl浓度的增加,所测得的糊化温度逐渐增大.随淀粉浓度的升高,所测得的糊化温度逐渐降低.随着电压的增大,淀粉悬浮液的电导率和加热速率也随之增大.改进后的装置可准确测定淀粉的糊化温度.与DSC结果相近.     

蛋清、蛋黄溶液的通电加热特性研究

研究了温度、蛋清、蛋黄浓度和电压对蛋清溶液和蛋黄溶液的电导率的影响;研究了蛋清、蛋黄浓度和电压对蛋清溶液、蛋黄溶液加热速率的影响。结果表明,蛋清溶液、蛋黄溶液的电导率随温度、蛋清和蛋黄浓度和电压的增高而增大,且电导率与温度呈线性关系;加热速率随蛋清和蛋黄浓度和电压的增高而加快,且温度与时间呈指数关系。     

蛋清、蛋黄溶液的通电加热特性研究

研究了温度、蛋清、蛋黄浓度和电压对蛋清溶液和蛋黄溶液的电导率的影响;研究了蛋清、蛋黄浓度和电压对蛋清溶液、蛋黄溶液加热速率的影响。结果表明,蛋清溶液、蛋黄溶液的电导率随温度、蛋清和蛋黄浓度和电压的增高而增大,且电导率与温度呈线性关系;加热速率随蛋清和蛋黄浓度和电压的增高而加快,且温度与时间呈指数关系。      

豆浆的通电加热

研究了温度和固形物含量对豆浆电导率的影响，以及固形物含量和施加电压对豆浆通电加热速率的影响。实验证明：豆浆电导率随温度和固形物含量的增高而增大，且电导率与温度为线性关系；加热速率随施加电压和固形物含量增大而加快，豆浆的温度与时间为指数关系。     

基于通电加热技术的猪皮胨凝胶工艺

利用猪皮为主要原料,采用通电加热的方法研制出皮胨凝胶。文中主要研究了:(1)以不同食盐添加量、不同电压条件下对皮胨汤汁加热速率和电导率的影响;通电加热制成的皮胨凝胶与传统工艺制作而成的皮胨凝胶在物理特性及成胨微观结构方面的比较;并在实验的基础上进行了猪皮胨凝胶通电加热技术的深层次数据挖掘。结果表明:随着食盐浓度的升高及电压强度的增强,皮胨汤汁加热速率越快,即皮胨凝结速度越快;(2)通电加热技术制作的皮胨凝胶其弹性、韧性、滑爽程度优于传统工艺制作而成的皮胨凝胶,且其保水性和强度都得到了提高。     

脚板薯淀粉的发酵法制备及其淀粉糊流变特性研究

采用发酵法制备脚板薯淀粉,分析了其淀粉颗粒粒度、淀粉糊透明度及凝沉性等理化性质,并对淀粉质量浓度、糊化pH、温度、不同介质及其浓度对淀粉糊流变特性的影响进行了分析。结果表明:脚板薯淀粉得率为15.2%,纯度为97.6%;淀粉平均粒度为18291.5nm,淀粉糊透光率为27.92%,其凝沉时间短;淀粉糊黏度随着淀粉浓度的增加而增加,随着糊化温度的增加而减小;在酸性条件下,淀粉糊黏度随着糊化pH增加而减小,pH到达8时,黏度达最大值,后随碱性的增强淀粉糊黏度下降。加入食盐、氯化钙和蔗糖均可提高淀粉糊的黏度,且在相同的剪切速率下,淀粉糊黏度随着蔗糖添加量的增大而增大。      

稻米淀粉期化进程研究

对不同初始粒径的稻米淀粉的糊化进程进行了研究。结果表明,淀粉的糊化具有上升,平缓和回落三个除段,在糊化温度以下（60℃）,淀粉颗粒仅存在吸水膨胀,糊化度曲线平坦,糊化温度以上,随加热温度和的升高,淀粉的糊化速度和糊化程度迅速增高,明显开成糊化过程的三阶段,较小的初始粒径会加快糊化进程,增大回落程度,但对糊化程度影响不大,加热温度对糊化特性的影响较淀粉的初始粒径大。     

脚板薯淀粉的发酵法制备及其淀粉糊流变特性研究

采用发酵法制备脚板薯淀粉,分析了其淀粉颗粒粒度、淀粉糊透明度及凝沉性等理化性质,并对淀粉质量浓度、糊化pH、温度、不同介质及其浓度对淀粉糊流变特性的影响进行了分析。结果表明:脚板薯淀粉得率为15.2%,纯度为97.6%;淀粉平均粒度为18291.5nm,淀粉糊透光率为27.92%,其凝沉时间短;淀粉糊黏度随着淀粉浓度的增加而增加,随着糊化温度的增加而减小;在酸性条件下,淀粉糊黏度随着糊化pH增加而减小,pH到达8时,黏度达最大值,后随碱性的增强淀粉糊黏度下降。加入食盐、氯化钙和蔗糖均可提高淀粉糊的黏度,且在相同的剪切速率下,淀粉糊黏度随着蔗糖添加量的增大而增大。     

紫甘薯全粉流变学特性的研究

以紫甘薯全粉为原料,研究其在不同加工条件如剪切速度、加热、pH值、盐浓度、蔗糖浓度等影响下的流变学特性.结果表明:紫甘薯全粉溶液的黏度随加热时间的延长和溶液浓度的增加而增大;随温度的升高与剪切速率的增加而减小;pH值、盐浓度等对其黏度也有很大影响.     

小米粉RVA糊化特性的研究

采用快速粘度分析仪（Rapid Viscosity Analyser,RVA）测定了在不同浓度、pH及添加蔗糖、食盐、明矾、硬脂酸等条件下小米糊RVA粘度曲线的变化情况,研究了小米淀粉粘度性质及其影响因素。结果显示,浓度对小米糊粘度性质影响显著,随浓度的增高,糊化温度降低,粘度曲线中峰值粘度及最终粘度升高;pH值对小米糊粘度性质影响较大,过高或过低的pH都会导致峰值粘度降低;随蔗糖添加量的增加,糊化温度略有增高;随着氯化钠浓度的增加糊化温度升高,氯化钠可提高小米糊粘度;明矾对小米糊的峰值粘度影响较大,而对糊化温度影响不大;添加硬脂酸的小米糊的最终粘度显著提高,而峰值粘度变化较小。通过研究为进一步了解小米淀粉的粘度特性及产品开发提供理论依据。     

Electrical conductivity and physical properties of surimi-potato starch under ohmic heating

ABSTRACT:  Electrical conductivities of Alaska pollock surimi mixed with native and pregelled potato starch at different concentrations (0%, 3%, and 9%) were measured at different moisture contents (75% and 81%) using a multifrequency ohmic heating system. Surimi-starch paste was tested up to 80 °C at frequencies from 55 Hz to 20 KHz and at alternating currents of 4.3 and 15.5 V/cm voltage gradient. Electrical conductivity increased when moisture content, applied frequency, and applied voltage increased, but decreased when starch concentration increased. Electrical conductivity was correlated linearly with temperature ( R ²≈ 0.99). Electrical conductivity pattern (magnitude) changed when temperature increased, which was clearly seen after 55 °C in the native potato starch system, especially at high concentration. This confirms that starch gelatinization that occurred during heating affects the electrical conductivity. Whiteness and texture properties decreased with an increase of starch concentration and a decrease of moisture content.     

DIFFUSION OF BEET DYE DURING ELECTRICAL AND CONVENTIONAL HEATING AT STEADY‐STATE TEMPERATURE1

Ohmic heating has been shown to alter mass transfer properties of fruit and vegetable tissue. Diffusion of beet dye from beetroot tissue into a fluid was studied during conventional and ohmic heating as a function of steady‐state temperature. The volume of beet dye diffusing into solution during ohmic heating was enhanced with respect to conventional heating at 42C and 58C, but not at 72C. This can be explained by examining the differences in electrical conductivity of beet tissue at these temperatures during conventional and ohmic heating. At 42 and 58C, the electrical conductivity of beet tissue heated ohmically is higher than the electrical conductivity of beet tissue heated conventionally. At 72C, the electrical conductivities of beet tissue during conventional and ohmic heating are equal. The extent of diffusion in the ohmic case is also positively correlated with applied voltage. These results suggest that food processes involving mass transfer can be enhanced by choosing conditions in which the electrical conductivity of a sample under ohmic conditions is maximized.     

EFFECT of SALT and CITRIC ACID ON ELECTRICAL CONDUCTIVITIES and OHMIC HEATING of VISCOUS LIQUIDS

Four hydrocolloid solutions (starch, 4.3%; carrageenan, 1.7%; xanthan, 2%; pectin, 2.5%) were prepared in water with varying amounts of NaCl (0.25, 0.5, 0.75 and 1%). Hydrocolloid concentrations were adjusted to result in an apparent viscosity of 0.2 Pa.s at 20C and 300 s^-1. A voltage of 150 V was applied in a static ohmic heating cell to study the effect of hydrocolloid and salt on electrical conductivity (EC) and temperature profile at their pH. the pH levels were modified by citric acid addition and the combined effect of hydrocolloid, salt and citric acid was investigated. At low salt concentration, carrageenan and xanthan had shortest heating times and highest ECs. This was followed by pectin. Starch was the least effective, having slowest heating rates and lowest ECs. At 1% concentration, the salt effect overcame that of hydrocolloid giving similar temperature profiles and ECs. the effect of citric acid addition was present but negligible.     

Ohmic Tempering of Frozen Potato Puree

Frozen potato puree samples were tempered using an ohmic heating technique. Three salt concentrations (0.50, 0.75, and 1.00 %) and three frequency levels (10, 20, and 30 kHz) were used as experimental variables, and the effects of salt concentration and frequency on ohmic tempering were investigated. Temperature, electrical current, and voltage were measured during the ohmic tempering. Electrical conductivities were evaluated based on the sample geometry and the ohmic heating principle. Increasing the salt concentration and/or frequency increased the electrical conductivity and heating rate, and hence contributed to decreasing the tempering time for the frozen potato puree samples. The tempering time was lowest with the highest salt concentration employed, and longest for the lowest salt concentration and frequency. Temperature differences within the sample during ohmic heating were found to be lowest when employing 0.50 % salt concentration and 10 kHz frequency.     

Ohmic Heating: Concept and Applications—A Review

Ohmic heating, also known as Joule heating, electrical resistance heating, and direct electrical resistance heating, is a process of heating the food by passing electric current. In ohmic heating the energy is dissipated directly into the food. Electrical conductivity is a key parameter in the design of an effective ohmic heater. A large number of potential applications exist for ohmic heating, including blanching, evaporation, dehydration, fermentation, sterilization, pasteurization, and heating of foods. Beyond heating, applied electric field under ohmic heating causes electroporation of cell membranes, which increase extraction rates, and reduce gelatinization temperature and enthalpy. Ohmic heating results in faster heating of food along with maintenance of color and nutritional value of food. Water absorption index, water solubility index, thermal properties, and pasting properties are altered with the application of ohmic heating. Ohmic heating results in pre-gelatinized starches, which reduce energy requirement during processing. But its higher initial cost, lack of its applications in foods containing fats and oils, and less awareness limit its use.     

Thermal characteristics of ohmically heated rice starch and rice flours

ABSTRACT:  Thermal properties of conventionally and ohmically heated rice starch and rice flours at various frequencies and voltages were studied. There was an increase in gelatinization temperature for conventionally heated rice starches since they were pregelatinized and became more rigid due to starch–chain interactions. In addition, there was a decrease in enthalpy (energy needed) for conventionally and ohmically heated starches during gelatinization; thus, the samples required less energy for gelatinization during DSC analysis. Ohmically heated commercial starch showed the greatest decrease in enthalpy probably because of the greatest extent of pregelatinization through ohmic heating. Brown rice flour showed the greatest gelatinization temperature resulting from the delay of starch granule swelling by lipid and protein. Enthalpy of ohmically heated starches at 20 V/cm was the lowest, which was most likely due to the lower voltage resulting in a more complete pregelatinization from a longer heating time required to reach 100 °C. Ohmic treatment at 70 V/cm decreased onset gelatinization temperature of white flour; therefore, it produced rice flour that swelled faster, whereas the conventionally heated sample showed a better thermal resistance.     

CONDUCTIVITIES AND OHMIC HEATING OF MEAT EMULSION BATTERS

The conductive nature of meat emulsions and their ohmic heating rates were investigated by examining model and commercial meat batters. Results indicate that salt or other electrolytic ingredients were essential for ohmic heating, and for a given batter, an increase in salt content increased electrical conductivity and increased ohmic heating rate (P<0.001). Conversely, an increase in fat content caused a reduction in conductivity (P<0.001) leading to an increase in ohmic heating time (P<0.001). Results of a study examining the impact of nonelectrolytic dry ingredients, such as spices, potato starches and soya protein isolates on the conductivity and ohmic heating rates of emulsion batters was inconclusive and further work is needed before definite conclusions can be made in this regard. Overall results suggest ohmic heating could be used for cooking meat batters but would not be as effective for cooking meats to which no salt or other electrolytes have been added.     

Ohmic heating behaviour and electrical conductivity of two-phase food systems

Ohmic heating behaviour and electrical conductivity (EC) of two-phase food systems were studied. Food systems were comprised of a liquid phase using 4% w/w starch solution with 0.5% w/w salt, and a solid phase containing carrot puree and cubes of different sizes (6 and 13 mm) in different concentrations (30 and 50% w/w). A set of experiments was carried out for a wide range of particle concentrations from 0 to 60% w/w. With respect to the particle location, experiments were conducted using 30% w/w cubes (6 mm) placed in parallel, in series and in well-mixed conditions with the liquid phase. Ohmic heating was applied to the food systems using a static cell (20-mm-long Teflon cylinder with 35 mm diameter and 25 mm wall thickness) at a constant voltage gradient of 12.5 V/cm. Electrical conductivity values were calculated as a function of particle size, concentration, location and temperature. It was observed that the heating time increased along with particle size and concentration. Overall values of EC ranged from 0.2 to 1.8 S/m, increasing with the process temperature as it ranged from 20–80 °C, and decreasing as particle size or concentration increased. With respect to the particle location within the ohmic cell, the thermal behaviour was different when the two phases were in parallel, in series or in mixed condition. However, there was no significant difference between overall values of EC when liquid and solid phases were separated as compared with the mixed condition.