The emerging coating technology in food processing sector.

1. To the New Age
I won’t be impressed with technology until I can download food. 1

2. By :
Bhuva Sachin S.
( GKVK, BANGALORE )
Department of Processing and Food Engineering
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Contents
 Introduction
 Electrostatic Powder Coating
 How it works?
 Factors affecting the coating process
 Advantages
 Applications in food processing
 Case studies
 Conclusion
 References

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Introduction
 Food Coating is an industrial process that consists of applying a
liquid or a powder onto the surface of an edible product to
convey new properties.
 Objectives
 To protect from degradation due to environmental conditions.
 To preserve substances such as flavours, colorants, antimicrobial
agents, antioxidants and other bioactive compounds.
 To increase solubility, dispersibility and wettability.

5. A. Tumble drum coating system
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B. Conveyor belt coating system
 Two coating systems are commonly used to coat foods
Tumble drum system & Conveyor belt system

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 Electrostatic Powder Coating
 Electrostatic coating is process that employs charged particles
more efficiently to the target.
 It was developed in the late 1950’s and used in the automotive
painting industry in the 1960s.
 Powder particles are charged before application in order to
distribute evenly.

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Coating
material(s)
Target(s) Parameter(s)
Salt Popcorn Voltage: 21.3 kV
Salt, sugar, corn-
starch,
maltodextrin,
cellulose, flour
Popcorn Voltage: 25kV
RPM of drum:12.25 rpm
Rh: 16.8 – 30.1 %
Powder: 7% by weight
Size of powders: 12 to 144 micron
Natamycin,
cellulose
Cheese Voltage: 20kV
Result: 15–30 % increase in shelf life
Seasonings Potato chips Voltage: 25 kV
Seasoning Banana chips Voltage: 25 kV
Fluidization pressure: 345 kPa
Sodium
erythorbate,
Glucono-delta-
lactone
Meat Voltage: 30 kV
Air flow of injector: 0.81m3/min
 Studies on application of electrostatic powder coating to food
processing

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Coating
material(s)
Target(s) Parameters
Salt,
maltodextrin,
cellulose, corn-
starch, whey
powder, non-fat
dry milk, soy
flour, sugar,
cocoa
Potato chips,
crackers, pork
rinds, white bread,
aluminium foil
Voltage: 25 kV
Fluidization pressure: 345 kPa
Rh: 63-65%
Salts with
different size (25
to 388 micron)
Potato chips Voltage: 25 kV
Conveyor belt speed: 2.88 cm/s
Salt flow rate: 0.72 g/s
Starch, salt,
cocoa powders,
Cheese powders,
Protein, Sugar
Metal, Wood,
Paper, Plastic,
Bread
Temperature: 25 oC
Rh: 35 %
Voltage: 25 kV

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 How it works?
Whole process is divided into three parts,
a. Corona development
b. Charging Powder Particles
c. Powder Deposition and Layer Formation
A. Corona development
 A sharply non-uniform electric
field is created.
 Free electrons present in air
move along the field lines.

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B. Charging Powder Particles
 Uncharged dielectric particle will distort the external electric
field.
 Charge accumulation on the particle occurs until it creates own
electric field.

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 Charging is most strongly affected by field strength, powder
particle size and shape and the time.
 The process is governed by Pauthenier’s equation.

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C. Powder Deposition and Layer
Formation
 Force pushing the powder particles is only electric force.
 Charge of equal value but opposite polarity inside the target
produced is called “mirror charge”.

14. An electrostatic conveyor belt coating system.
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16. (Automatic spraying with cyclone powder recovery)
Industrial Electrostatic Powder Coating Unit
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Factors affecting the coating process
 Factors influencing coating quality:
Powder
• Particle size
• Density
• Flowability
• Charge
• Resistivity
Target
• Surface properties
• Characteristics
 Electrostatic Transfer Efficiency
Powder deposited on a target
Mass of powder entering system

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1. Particle size
 Either directly (pneumatically fed system) or inversely
proportional (gravity-fed system) to the particle size.
 Smaller particles - electrostatic force dominates - greater
charge-to-mass ratio of the particle.
 Large powders - gravitational force dominates.

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2. Powder density
 Most food powders fall within a small range of densities.
 Powders with lower density have lower mass and inertia
and are more likely to remain in the air as dust.

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3. Powder flowability
 Is a significant factor in predicting how evenly and efficiently
the powder coats a target.
 Depends on the chemical composition, particle size and shape.
 Based on flowability:
a) free-flowing, b) cohesive, and c) non-flowing
 During coating, free-flowing powders usually produce the
most even coating and greatest transfer efficiency.

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4. Powder charge and resistivity
 Charge on a particle influences particle velocity, transfer
efficiency, adhesion and coating thickness.
 Powder resistivity is how quickly a powder particle picks up
charge in the air, or loses the charge once on a target.
Resistivity
Below 1010 Ωm Between 1013 and 1010
Ωm
Above 1013 Ω m
Conductors - pick up &
loss charge quickly
Have a short charge decay
time
Insulators - have slow
charge decay time
Very poor adhesion poor adhesion good adhesion
Always not suitable
coating materials
Suitable for coating Good for coating
e.g. salts e.g. most food powders e.g. cocoa powder

22.  Differences in particle size density and
particle surface charge cause separation
during coating.
 During electrostatic coating, particles
with the same size produces less
separation.
 Small powders have greater charge-to-
mass ratios and land closer to the
nozzle.
 Large powders develop lower charge-
to-mass ratios and so deposit further
away from the nozzle.
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 Separation of Food Powder Mixtures During
Electrostatic Coating

23.  Surface properties: roughness, resistivity, and oil content.
 Roughness influences the adhesion - adhesion increases
because of more contact area for smooth surface.
 Lower resistivity produces better attraction..
 Adhesion is dependent on the oil content.
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 Target Surface Characteristics

24.  Powders will coat the sides of a thick target.
 Can be measured by the percent side coverage.
 In electrostatic coating, increases as powder particle size
decreases, cohesiveness of the powder increases, and powder
resistivity increases.
 Targets with higher water activity, lower resistivity, and
shorter charge decay time produce better percent side
coverage
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 Wraparound Effect During Electrostatic Food Powder
Coating

25.  Appearance and functionality are affected by the evenness.
 For coloured targets, coating evenness can be determined
using a colour parameter
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a) Unevenly coated
b) Evenly coated
 Evenness and Consumer Acceptance

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Advantages
Three-dimensional coating
More even and uniform and reproducible coating
Minimal waste of food powder
Better appearance and taste
Create more variety
Increase shelf life
Increase nutritional value

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Seasoning of salads
To increase shelf life
To enhance the colour
To reduce browning
To increase the nutritional value
To enhance the flavour

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CONCLUSION
 In dry coating techniques, electrostatic coating emerges as a
novel technique which can be used in the food industry in
combination with e.g. conveyer belt, and tumbler drum.
 Coating procedures can be improved through higher transfer
efficiency, better adhesion, low energy usage, less waste
production, and air borne dust (values ranging from 40% to
84% have been reported by different sources depending on the
particle size), which make this method cost effective.
 Studying parameters which affects coating can help food
processors to design the optimal coating systems needed to
provide better coating quality for different foods.
 This technique show significant potential for food
applications.

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References
 AMEFIA, A. E., JAREER M. ABU-ALI AND BARRINGER S. A., 2006, Improved
functionality of food additives with electrostatic coating, Innovative Food Science and
Emerging Technologies, 7: 176-181.
 BARRINGER, S. A. AND SUMONSIRI, N., 2015, Electrostatic coating technologies
for food processing, Annual Review of Food Science and Technology, 6: 7.1-7.13.
 BIEHL, H. L. AND BARRINGER, S. A., 2004, Comparison of the effect of powder
properties on coating transfer efficiency and dustiness in two non-electrostatic and
electrostatic systems, Innovative Food Science and Emerging Technologies, 5: 191-198.
 GUSKOV, S., Electrostatic phenomena in powder coating, Powder Systems Group,
Nordson Corporation.
 KHAN, M. K. I., MAARTEN, A.I. S., SCHROEN, K. AND REMKO M. B., 2012,
Electrostatic powder coating of foods – State of the art and opportunities, Journal of
Food Engineering, 111: 1-5.
 RAO, S. N., AND BARRINGER, S. A., 2006, Calcification of diced tomatoes by liquid
dipping versus electrostatic powder coating, Journal of Food Processing and
Preservation, 30: 71-78.