Effect of Relative Humidity on Coating Efficiency in Nonelectrostatic and Electrostatic Coating

ABSTRACT:  Fifteen food powders were coated on aluminum targets at 0, + 25, and –25 kV using corona electrostatic coating at 20% to 80% relative humidity (RH). The effect of RH on 3 losses, that is, targeting loss, coating loss, and transportation loss, which contribute to coating efficiency, was studied. RH had no effect on targeting loss in either nonelectrostatic or electrostatic coating. In nonelectrostatic coating, increasing RH increased coating loss for powders with particle size ≥ 297 μm, but had no effect on powders ≤ 227 μm. Large powders were free-flowing and clumped with increasing RH, and then rolled off the targets, resulting in high coating loss. RH had no effect on nonelectrostatic transportation loss for all powders, except for very high absolute humidity when capillary forces dominated. Electrostatic charging efficiency and powder resistivity decreased with increasing RH. Electrostatic coating loss for salts increased with increasing RH. At high RH, powder resistivity decreases, increasing the charge decay rate, which decreases electrostatic adhesion. Electrostatic coating loss for powders other than salts, whose resistivities are much higher than salts, was not affected by RH until 80% RH. Electrostatic transportation loss for powders other than proteins was not affected by RH. There was no significant difference between positive and negative electrostatic transfer efficiency and adhesion, except for transfer efficiency of soy protein and pork gelatin, whose high positive tribocharging values cause higher positive electrostatic transfer efficiency. A 20% to 60% RH is recommended for both nonelectrostatic and electrostatic coating.     

Corona Compared with Triboelectric Charging for Electrostatic Powder Coating

ABSTRACT:  The purpose of this research was to compare electrostatic and nonelectrostatic coating and determine the improvement between corona and triboelectric charging systems. Graham crackers were coated with food powder at 0, −50, or −95 kV or by tribocharging with teflon or nylon. Five sizes of sucrose from 13 to 138 μm were coated onto the crackers to determine the effect of particle size on coating efficiency. Three proteins, three carbohydrates, and one salt between 35 and 58 μm were analyzed to determine the effect of composition. Electrostatics improved transfer efficiency (TE) up to 27%, adhesion up to 40%, and reduced dust up to 99% over nonelectrostatic coating. Particle size and composition significantly affected the improvement produced by each charging method. As particle size increased, nonelectrostatic TE and adhesion increased, while dust decreased. Electrostatic TE increased and leveled off and adhesion and dust decreased with increasing particle size. Generally, corona TE, adhesion, and dust reduction was the highest, followed by teflon triboelectric, nylon triboelectric, and nonelectrostatic coating. For proteins, teflon produced higher charge to mass, TE, and adhesion than nylon. Although the corona system was most efficient, the teflon triboelectric system produced comparable results for some powders and may be necessary to produce a thick coating while minimizing back ionization and alleviating Faraday Cage effects.     

Food Powder Characteristics Important to Nonelectrostatic and Electrostatic Coating and Dustiness

ABSTRACT: Corn starch, maltodextrin, powdered sugar, cellulose, soy flour, corn flour, wheat flour, cocoa, nonfat dry milk, and salt were coated at 0, 19, and 25 kV using corona particle charging. Particle size, powder charge, density, and flow characteristics (flow index, cohesiveness, angle of repose, Hausner ratio) were correlated to coating efficiency and dustiness. Nonelectrostatic coating efficiency improved with large particle size, small powder charge, and low cohesiveness. Electrostatic coating at 25 kV improved with small particle size, low flow index, and high particle density. Dustiness decreased with large particle size-particle density interaction, high flow index, and low cohesiveness. Electrostatics improved coating efficiency 68% and decreased dustiness 65% (excluding largest salt).     

Effect of powder and target properties on wrap around effect during coating

Tapioca starch, NaCl (28, 135, and 378 μm), corn starch, cocoa powder, soy protein isolate, cheese powder, wheat protein, modified starch, nacho cheese, and sugar were coated at 0 kV for nonelectrostatic and at 25 kV for electrostatic coating onto metal, wood, unoiled paper, oiled paper, unoiled plastic, oiled plastic, fresh bread, and dry bread. Powders and targets were allowed to naturally tribocharge, or all charge was removed before coating. Powder particle size, flowability, resistivity, and target resistivity were reported. Electrostatic coating produced the same or better wrap around, or percent side coverage as nonelectrostatic coating for every powder and target. The greatest electrostatic improvement was found when using powders that had the worst nonelectrostatic side coverage: large particle size (>135 μm), low resistivity, and low cohesiveness, especially on targets that had high-surface resistivity (2 × 10(5) Ωm). Tribocharging had a similar effect as electrostatic coating. In both nonelectrostatic and electrostatic coating, percent side coverage increased as powder particle size decreased, cohesiveness increased, or target resistivity decreased. In electrostatic coating, percent side coverage increased as powder resistivity increased; however, in nonelectrostatic coating, as powder resistivity increased, percent side coverage increased on only oiled plastic and dry bread. Practical Application: The evenness of powder coating on food is very important for consumer acceptability, since consumers judge food from its appearance before they have a chance to taste it. If thick food targets, such as cakes, donuts, and marshmallows need to be coated, the side coverage, due to the wrap around effect, is important. Choosing powders with small particle size, high cohesiveness and high-powder resistivity, and using electrostatic coating can produce food targets coated on all sides.     

Modeling nonelectrostatic and electrostatic powder coating

The effect of particle size, density, charge and air velocity on transfer efficiency, evenness and separation of mixtures during powder coating was investigated using modeling and experimentation. Electrostatic and nonelectrostatic coating was tested using 28, 234 and 342 μm NaCl and 195 μm starch powders. Transfer efficiency increased as particle size, density or charge increased or as air velocity decreased. Evenness increased as particle size or density decreased, as velocity increased, or as charge increased to a peak. Electrostatic coating produced higher transfer efficiency and evenness than nonelectrostatic coating. Improvement in transfer efficiency and evenness due to electrostatics increased as NaCl size, density, charge or air velocity decreased. Powder mixtures did not separate by size during coating but did separate by density and charge. Starch was affected more by the collisions and charging than NaCl, which caused the separation.     

THERMAL PROPERTIES and MOISTURE SORPTION ISOTHERMS of SPRAY-DRIED ENCAPSULATED MILKFAT

Stable emulsions containing 40 or 60% anhydrous butter oil and carbohydrate encapsulants (sucrose, modified starch or all-purpose flour) were spray dried to produce free-flowing shelf-stable powders, according to a 2 x 3 factorial design, replicated three times. Differential scanning calorimetry profiles showed well-defined melting ranges that were related to encapsulant used. Butter oil was almost completely encapsulated when fat content was 40% and sucrose was used as the wall material. Moisture sorption isotherms of powders with sucrose showed characteristic breaks caused by sugar crystallization followed by moisture desorption, whereas powders with modified starch or all-purpose flour continuously absorbed moisture with increasing relative humidity. the solvent-extractable fat fraction increased with increasing relative humidity in all cases. Scanning electron microscopy showed that sucrose-containing powder particles partially dissolved and fused together as a result of moisture uptake, whereas powders with modified starch or all-purpose flour maintained particle identity, even at 80% relative humidity.     

Effect of hydrogen ion concentration and electrostatic polarity on food powder coating transfer efficiency and adhesion

ABSTRACT:  Two kinds of soy protein isolate, rice protein, whey protein isolate, albumen, bovine collagen hydrolysate, NaCl, and corn starch were used in this study. Solutions were prepared by mixing the powder and distilled water (1:8 ratio) and either H₂SO₄ or NH₄OH to obtain pH 3, 5, 7, 9, and 11. The solutions were dried to produce powders with different hydrogen ion concentrations and the powders were ground. Powders were coated nonelectrostatically and using negative and positive polarity corona electrostatically. There was no solution pH effect on transfer efficiency or adhesion for most powders. However, transfer efficiency and density of both of the soy protein isolates and corn starch changed with solution pH. Solution pH may have affected the density, which affected the transfer efficiency for these powders. Adhesion and cohesiveness of one of the soy protein isolates and corn starch also changed with solution pH. Solution pH may have affected the cohesiveness, which affected the adhesion for these powders. Negative and positive coronas produced the same results for most powders, with no solution pH effect, except for one of the soy protein isolates, rice protein, and corn starch. These powders accumulated on the electrode wires during negative corona electrostatic coating, reducing transfer efficiency and adhesion. This polarity effect was intermittent, implying it is due to tribocharging.     

Effect of Sodium Chloride Particle Size and Shape on Nonelectrostatic and Electrostatic Coating of Popcorn

ABSTRACT: Sodium chloride of different shapes (hollow pyramid, crushed flake, cube, and porous cube) and sizes (50-200 mesh) were applied by nonelectrostatic and electrostatic powder coating to popcorn coated with 1.2 to 3.3% soybean oil. Electrostatic coating was more efficient than nonelectrostatic in all cases. The smaller the particles, the higher the coating efficiency for both electrostatic and nonelectrostatic coating. Crushed flake and hollow pyramid were more efficient than cube and porous cube shapes. Coating efficiency improved as the oil content increased for nonelectrostatic but not electrostatic coating. Use of electrostatic coating can reduce waste and provide a more efficient coating method by decreasing seasoning or oil needed to reach the target level.     

Flow Properties Of Encapsulated Milkfat Powders as Affected by Flow Agent

Food powders containing softer cores of fatty or flavor components present handling problems, as such powders are generally of very low density and mostly non free-flowing. Three classes of flow conditioners [silica, silicate and stearate], at three levels of concentration, were evaluated to determine effects on bulk and flow properties of sucrose, lactose and modified corn starch as well as butter oil powders encapsulated with the same materials. Silica and silicate were generally effective in improving bulk properties but only silica was effective in improving flow-ability of unencapsulated powders as well as lactose-encapsulated butteroil powder. Washing with isopropanol was effective in improving flow only with the lactose-encapsulated butteroil powder. Butteroil encapsulated in lactose had flow characteristics similar to lactose.     

超微粉碎后粒径对大麦全粉品质特性的影响

本研究主要以大麦为主要原料,探究不同粒径对超微粉碎大麦粉品质特性的影响.研究结果表明,随着粒径的降低,大麦全粉水分、淀粉含量、溶解性、亮度值及白度值显著增加(P<0.05),而膨润力、吸油性、持水性、峰值黏度和回生值则显著降低(P<0.05).微观结构结果表明,随着粒径的降低,大麦全粉粉体的颗粒形状由圆形或椭圆形转为不...     

Sensory Preference, Coating Evenness, Dustiness, and Transfer Efficiency of Electrostatically Coated Potato Chips

Barbeque, sour cream and onion, salt and vinegar, nacho cheese, and salsa seasonings were applied to potato chips at 0 and 25 kV. Sensory evaluation determined that electrostatically coated chips had better coating uniformity and were significantly preferred to nonelectrostatically coated samples. Electrostatic coating was also more even as measured by colorimetry. Particle size and evenness of coating did not significantly affect perceived flavor intensity. Electrostatic coating significantly increased transfer efficiency and decreased dust over nonelectrostatic coating. Particle size and flowability can be used to predict transfer efficiency and dustiness. Chargeability was also important for electrostatic transfer efficiency. Particle size was the most important factor overall.     

Flow Properties of Spray-Dried Encapsulated Butteroil

The interdependence of physical properties of spray-dried butteroil encapsulated in sucrose, lactose or all-purpose flour were evaluated and compared to those of common powders such as spray-dried nonfat dry milk, whole milk powder, and sodium chloride. Powders were evaluated in terms of flow (mass flow rate and angle of repose), bulk (density) and mechanical properties (compressibility and stress relaxation). The powders were classified into three groups by mechanical sieving based on size as: “small particles” (>210 μm), “particles” (+210–420 μm) and “encapsulated particles” (+210–500 μm). The flow and mechanical behavior of encapsulated powders were different (P < 0.05) from the other powders. Encapsulated powders were less flowable (P < 0.05) but the addition of 2% anti-caking/flow agent enhanced flow characteristics.     

Factors dominating adhesion of NaCl onto potato chips

ABSTRACT:  In this study, the adhesion factors examined were time between frying and coating, surface oil content, chip temperature, oil composition, NaCl size, NaCl shape, and electrostatic coating. Three different surface oil content potato chips, high, low, and no, were produced. Oils used were soybean, olive, corn, peanut, and coconut. After frying, chips were coated immediately, after 1 d, and after 1 mo. NaCl crystals of 5 different particle sizes (24.7, 123, 259, 291, and 388 μm) were coated both electrostatically and nonelectrostatically. Adhesion of cubic, dendritic, and flake crystals was examined. Chips were coated at different temperatures. Chips with high surface oil had the highest adhesion of salt, making surface oil content the most important factor. Decreasing chip temperature decreased surface oil and adhesion. Increasing time between frying and coating reduced adhesion for low surface oil chips, but did not affect high and no surface oil chips. Changing oil composition did not affect adhesion. Increasing salt size decreased adhesion. Salt size had a greater effect on chips with lower surface oil content. When there were significant differences, cubic crystals gave the best adhesion followed by flake crystals then dendritic crystals. For high and low surface oil chips, electrostatic coating did not change adhesion of small size crystals but decreased adhesion of large salts. For no surface oil content chips, electrostatic coating improved adhesion for small salt sizes but did not affect adhesion of large crystals.     

Bioavailability of Elemental Iron Powders in Bread Assessed with an In vitro Digestion/Caco-2 Cell Culture Model

ABSTRACT: Iron fortification of staple foods is arguably the most widely used strategy for increasing the iron intake of populations. Although FeSO₄ is a bioavailable form of iron, elemental iron powders are often used to fortify products with a long shelf-life, such as wheat flours, to avoid problems associated with the reactive nature of FeSO₄. Therefore, the objectives of this study were to compare the bioavailabilities of elemental iron powders manufactured with different production methods in wheat flour breads and to determine the effects of added ascorbic acid and baking, using an in vitro digestion/Caco-2 cell culture model. Two types of wheat flour (low-extraction and high-extraction) were fortified with 10 different commercial elemental iron powders and baked into breads. Iron bioavailabilities from the resulting breads, with and without added ascorbic acid, were evaluated using FeSO₄ as the control. Depending on the type of wheat flour, bioavailabilities of several powders were comparable to FeSO₄, but there was no consistent trend as to which production method produced the most bioavailable powder. In general, ascorbic acid enhanced, whereas the baking process reduced iron bioavailability from bread. Our results suggest that some elemental iron powders are potential alternatives to FeSO₄. Human studies are warranted before any of these powders are selected for national fortification programs.     

Preparation of low-fat uptake frying batter composite by dry particle coating of microparticulated soybean hull

This study examined the influence of soybean hull-coated frying batter composite on fat uptake during deep fat frying. Soybean hull was microparticulated by impact mill at impact mill speed (IMS) of 6000, 10,000 and 14,000 rpm, and air-classified into coarse and fine fractions at Air Classifying Wheel Speed (ACWS) of 4000, 8000 and 12,000 rpm, respectively. Each soybean hull was dry-coated into wheat flour by dry particle coating system. As the difference in particle size between wheat flour and soybean hull got larger, the coating process became more effective, which indicates the size difference between wheat flour and soybean hull was important for coating effectiveness. When the ratios of wheat flour to soybean hull were 99:1 and 95:5, there were about 3.3 (g/100 g) and 24.4 (g/100 g) of fat content reduction, respectively. Inner crust structures showed slight reduction in cell size and improved cellular integrity with shrinkage in the cell membrane, with increase in soybean hull content. This means soybean hull can form a protective layer and can be applied to the food industry as a frying batter composite to reduce fat uptake.     

当前金刚石工具制作中的几个热点技术

在金刚石工具制作中，为达到胎体对金刚石的化学键接（包镶），采用了各种使金刚石表面金属化的技术。从试验观察来看，国内的金刚石表面预金属化技术还达不到这一目的。高温钎焊即使可实现化学键接，但目前因其难以实现工作层中金属石的新老奖学金替，还不适用于制作孕镶工具。激光焊是把孕镶刀头与钢基体联结起来的最佳技术。对于焊接设备中的核心部伯-激光发生器的性能，最为重要和需关注的应是光斑功率密度（要达到10^6W/cm^2)以及工作气体的耗量和运动部件的寿命。粉末制粒是实现容积式计量的基础，但只有制粒产品有好的圆度和粒径一致性时才能取得预想的效果。     

Changes in the physical properties of honey powder during storage

Honey powders produced by spray drying with the addition of Arabic gum and sodium caseinate were characterised in terms of the influence of storage time on the following physical properties: particle size, moisture content, water activity, bulk density, flowability and hygroscopicity. The storage affected those properties; after 12 weeks of storage, particle size decreased (except Arabic gum powder treated as a control sample), moisture content and water activity increased, hygroscopicity decreased. Changes in bulk density, particle size and moisture content caused the rise of Hausner ratio value; however, the powders were still characterised by a very good flow properties and low cohesiveness. The colour of reconstituted powders was also affected by storage; in most of samples, the darkening, reduction in redness and yellowness were observed. Colour parameters were the most stable in powders obtained with the addition of 2% w/w of sodium caseinate.     

Physicochemical and Nutritional Aspects of Cowpea Flour

Cowpea (Vigna ungiiculata) flour was prepared by soaking.the beans in 25°C tap water for 18 hr, drying in an air draft, milling to a coarse powder, removing the seed coat by an air jet, autoclaving the powder at 121°C for 10 min, redrying in an air draft and grinding to a fine flour. Ths flour was creamy-white, free-flowing, nonhy-groscopic and dispersed readily in water. The conversion of cowpeas to flour resulted in 10% loss of thiamin and riboflavin and 30% loss of niacin. Also the flour contained less K, P, and Mg but more Ca and Na than the raw cowpeas.     

A systematic study of the residence time of flour in a vibrating apparatus used for thermal processing

The dry heat treatment of flour is well established for the production of cake flour for high ratio cakes. This study investigates a new tubular apparatus in which flour is conveyed by vibrations through a helical pipe. Residence time distributions (RTDs) of flour were characterised for various processing conditions and the development of the residence time in extended operation was analysed.A method was developed to accurately determine the RTDs, which could be approximated by normal distributions. The width of the distributions is a critical factor for the accuracy of a thermal process and was identified for different processing conditions. The distributions were narrow, with variations of ± 1% at most.In some cases, the residence time increased over 3.5 h of machine run-time by 7.7%–13.9%. To explain this phenomenon, several hypotheses have been tested. The machine performance was constant with time and no influence of ambient temperature or humidity could be found. It was furthermore shown that changes in the bulk material passing through the apparatus were not the cause of the increase. However, electrostatic charging of the material was observed.Two things led to a reduction in residence time: i) cleaning the pipe with a cleaning pig and water and ii) time, during which the machine is not running. It was suggested that a thin layer of particles inside the pipe in combination with electrostatics effects could be the reason for the residence time increase. Frequent cleaning can therefore allow relatively uniform behaviour and control of residence time.Industrial relevanceThis work investigates the potential application of a novel, vibrating device for the dry heat treatment of flour as a replacement for chlorination in the production of cake flour. Since chlorination was banned in the EU in the year 2000, there is an industrial interest for alternative treatments and equipment to produce flour for high ratio cakes.     

复合米粉挤压膨化制品配方的研究

以大米为基料,面粉、糯米粉、玉米淀粉、马铃薯淀粉为辅料,采用挤压膨化工艺制作膨化制品,研究了大米粉进料颗粒度、各辅料添加量对膨化制品L值、b值、吸水性、水溶性、容重、硬度等品质指标的影响,筛选出了大米粉最佳进料颗粒度为60目。在此基础上设计正交试验,优选出最佳配方为以大米粉为基准(计为100),辅料配比为面粉25%、糯米粉20%、玉米淀粉15%、马铃薯淀粉15%;利用该配方制得产品的L值为59.69、b值为12.96、水溶性指数为30.95%、吸水性指数为5.08g/g、容重为126.72g/L、硬度为617.3g,产品感官品质优良。