Effect of hydrogen ion concentration and electrostatic polarity on food powder coating transfer efficiency and adhesion (original) (raw)
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Positive vs. negative electrostatic coating using food powders
Journal of Electrostatics, 2005
Previous studies on electrostatic coating of food powders using negative corona have showed benefits such as an increase in coating deposition and a more even coating. However, no work has been done on the advantages of positive corona. Thus, this study was aimed to determine whether positive or negative corona produced better coating for different food powders. Twenty-three powders were coated onto five aluminum strips using an electrostatic powder applicator. Transfer efficiency (TE), adhesion and dustiness were measured and correlated to particle size, flowability and tribocharging value. The polarity of the tribocharging value for each powder determined whether positive or negative corona produced higher TE. For most proteins, positive corona produced higher TE than negative corona since proteins tribocharge positive. Most carbohydrates tribocharge negative; thus negative corona produced higher TE than positive corona. Salts had relatively small tribocharge values; thus there was no difference between TE of positive and negative corona. No significant difference was observed between positive and negative corona for adhesion and dustiness, though electrostatic coating produced higher TE and adhesion and less dust than nonelectrostatic coating.
Electrostatic powder coating of foods – State of the art and opportunities
Journal of Food Engineering, 2012
ABSTRACT Edible coatings and incorporation of active ingredients can improve food quality (appearance, taste, flavours, and increased shelf life). In this paper, specific emphasis is given to electrostatic application of powder coatings that is known for high transfer efficiency and even coating. This application technique has the potential to reduce excessive use of coating material (up to 68%) and minimise dust release (up to 84%) to the environment. Different parameters (e.g. powder particle size) are discussed that influence powder coating quality and efficiency for both non-electrostatic and electrostatic powder application. Typical food processing systems are reviewed that can be combined with electrostatic powder coating. Finally, an overview of electrostatically coated food products and a short outlook of electrostatic powder coating of foods are given.
Improved functionality of food additives with electrostatic coating
Innovative Food Science & Emerging Technologies, 2006
French fries were coated with smoke extract or glucose and mozzarella cheese slices with sodium erythorbate or cellulose with natamyacin at 0 kV and −25 kV. For the first three samples, transfer efficiency was higher for electrostatically coated products. When the same amount of powder on each sample was compared, electrostatically coated samples showed a greater color development and less mold growth than nonelectrostatically coated samples. This improvement in color and shelf life could be explained by improvement in coating evenness due to the charging of the powder. Cellulose with natamyacin did not show an improvement in transfer efficiency, mold suppression or charge to mass ratio with electrostatic coating. This powder did not charge well because it was cohesive and of the wrong polarity. The smaller the size of the powder, the greater the charge to mass ratio and final color development.
Applied Sciences
Spray drying is used in the food industry to convert liquids into dry powders. The effect of the addition of salt ions before spray drying to improve the heat- and cold-induced gel properties of soy protein isolate (SPI) was investigated. Certain concentrations of Na+ (0.005–0.01 M), Mg2+ (0.005 M), and Ca2+ (0.005 M) significantly increased the hardness, springiness, cohesiveness, chewiness, gumminess, resilience, and water holding capacity of the heat- and cold-induced gels. This effect arises predominantly due to the functional groups buried in the protein matrix that are partially exposed to improve the interactions between the protein molecules. The main interactions that promoted gel formation and maintained the three-dimensional structure of the heat- and cold-induced gels were hydrophobic and disulfide interactions. Analysis using scanning electron microscopy showed that the heat- and cold-induced gels were uniform, had smooth surfaces, and had smaller pores with added Na+ (...
Food Powder Characteristics Important to Nonelectrostatic and Electrostatic Coating and Dustiness
Journal of Food Science, 2002
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).
Journal of Electrostatics, 2007
Ten powders, differing in protein, carbohydrate and salt contents and ranging from 19 to 165 mm were coated by nonelectrostatic and electrostatic coating. Nonelectrostatic transfer efficiency (TE) increased to a maximum before leveling off with increasing particle size. Electrostatic TE either decreased or increased then decreased with increasing particle size. Powders became more free flowing as particle size increased. Since TE increases as powders become more free flowing, TE increased with particle size for both nonelectrostatic and electrostatic coating. For electrostatic coating, the effect of charge decreases with increasing particle size. Thus, the conflicting effects of ability to pick up charge and flowability caused an increase then decrease in the TE for powders coated electrostatically, and can also explain the exceptions. The average improvement in TE by electrostatic coating was 20%, with the improvement increasing as particle size decreased.
Drying Technology, 2013
To examine the effect of protein adsorption on the fat-water interface on the surface composition of spray-dried particles, whey, hydrolyzed whey, and soy protein isolate emulsions were prepared at three different protein to fat ratios of 1:1, 1:5, and 1:10 and spray dried. Non-hydrolyzed whey protein isolate (WPI) and the more hydrolyzed whey protein solutions at 20.2% degree of hydrolysis (DH) had significantly lower surface tension values with fat than without fat. The correlation between the reduction of surface tension value of an emulsion and the increase in protein surface composition of powder particles was observed for WPI and HWP406 but was not observed for the other protein isolate types. It was clear that the spray-dried emulsions had fat as the dominant component on the surface of the powder particles and that the amount of protein on the surface became severely depressed at higher fat addition levels. In terms of its powder morphology, the unique powder structures such as the indentations and folds usually found on the surface of protein containing powders were not evident because they were compromised by the presence of high surface fat. The powder with higher surface fat had more crumpled particle structures and dimpled surfaces.
Physical Properties of Whey Protein Coating Solutions and Films Containing Antioxidants
Journal of Food Science, 2007
Antioxidants (ascorbyl palmitate and α-tocopherol) were incorporated into 10% (w/w) whey protein isolate (WPI) coating solution containing 6.67% (w/w) glycerol (WPI:glycerol = 6:4). Before incorporation, the antioxidants were mixed using either powder blending (Process 1) or ethanol solvent-mixing (Process 2). After the antioxidant mixtures were incorporated into heat-denatured WPI solution, viscosity and turbidity of the WPI solutions were determined. The WPI solutions were dried on a flat surface to produce WPI films. The WPI films were examined to determine transparency and oxygen-barrier properties (permeability, diffusivity, and solubility). WPI solution containing antioxidants produced by Process 1 and Process 2 did not show any difference in viscosity and turbidity, but viscosity was greater for the WPI solution with rather than without antioxidants. WPI films produced by Process 2 were more transparent than the films produced by Process 1. Oxygen permeability of Process 1 film was lower than Process 2 film. However, both the diffusivity and solubility of oxygen were statistically the same in Process 1 and Process 2 films. Both control WPI films and antioxidant-containing WPI films had very low oxygen solubility, comparable to polyethylene terephthalate films. Permeability of antioxidant-incorporated films was not enhanced compared to control WPI films.
International Journal of Food Science & Technology, 2008
Response surface methodology (RSM) was used to investigate pH and corn oil (CO) addition on gelatin film properties. Test films were evaluated for thickness (T), tensile strength (TS), puncture strength (PT), percentage elongation at break point (E), water vapour permeability (WVP) and oxygen permeability (OP). T, TS and PT increased linearly (P < 0.01) with increasing CO content, but were not significantly affected by pH. pH had both linear and quadratic effects on E values (P < 0.01), while CO content had a lesser effect. WVP decreased as the pH of the film-forming solutions was adjusted away from pH 7.0 or CO addition level increased above 27.25%. OP was affected in both a quadratic and linear manner by pH adjustment and CO addition, respectively. Optimal film-forming conditions were pH (10.54) and CO level (55.18%, w/w), as predicted by response surface methodology. Scanning electron microscopy (SEM) was performed to investigate the microstructures of gelatin films, and confocal scanning laser microscopy (CSLM) was used to investigate fat distributions and protein phase in gelatin films.
Assessment of physical characteristics and dissolution behavior of protein based powders
Procedia Food Science, 2011
Proteins are main constituents of a broad range of food products in powder form, from dairy to dough-based foods. Water is the main responsible of physical properties modifications in powders and many scientific studies have been focusing on characterizing the role of water content and water activity in carbohydrates powders. This work deals with the assessment of physical properties and dissolution behavior of milk proteins powders and their interactions with carbohydrates (lactose). In the first part, micellar caseins, native and denatured-lactoglobulin and Na-caseinate powders were selected and equilibrated at different water activities. In the second part, binary mixtures of proteins with lactose were prepared in different proportions (25:75 and 75:25). Sorption isotherms were built at 25°C and water adsorption kinetics was found to be faster in proteins than in carbohydrates. Thermal analysis (DSC) showed that micellar caseins and Na-caseinate exhibit a clear glass transition, while the measurement was not easy for BLG powders. In binary systems, proteins delayed lactose crystallization, up to a different extent depending on the kind of protein. Dissolution behavior was measured by conductimetry; the protein structure (native vs denatured) and its initial water activity played an important role, especially influencing powder's wettability. The presence of lactose strongly accelerated the dissolution process, in a more important way for BLG. Scientific findings could lead to improved powder engineering, in order to optimize dissolution behavior and storage stability of protein-based foods.