Contents
Functional, Medical and Electronic Coatings

Edible Films and Coatings for Fruit and Vegetable Preservation: Measure How an Edible Coating Wets Fresh and Fresh-Cut Fruits Before Shelf Life Trials

An edible coating only protects produce if it spreads into an even film. Measure the coating's surface tension, its contact angle on the peel and the peel's surface free energy, so you take only well wetting formulations into shelf life trials.

Who this is for: Food scientists, postharvest researchers and coating developers working on edible coatings and edible films for fresh produce.

Where it fits: Formulation screening and the characterization of edible coatings before shelf life trials, and checks when the produce, cultivar or recipe changes.

What it does not do: It does not measure shelf life, weight loss, firmness, microbial load or food safety approval.

Method
Pendant drop surface tension, sessile drop contact angle on the peel and peel surface free energy
Standard
Fully compliant with ISO 19403-2 for surface free energy
Setup
About 2 minutes
Book a 15 minute demo Request a quote
Abhimanyu Photo
Written by
Abhimanyu Bhandankar
Holds an MBA from Schulich School of Business and a BE in IT. He joined Droplet Lab in July 2019 and now leads sales and marketing.
CEO at Droplet Lab
Read More
Droplet-Lab logo
Technical Review by
Droplet Lab Team
Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.
Read More
Abhimanyu Photo
Written By

Abhimanyu Bhandankar

CEO at Droplet Lab

Holds an MBA from Schulich School of Business and a BE in IT. He joined Droplet Lab in July 2019 and now leads sales and marketing.

Droplet-Lab logo
Reviewed By

Droplet Lab Team

Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.

Featured Studies & Publications

Research Paper Contact angle measurement with a smartphone
Research Paper Surface tension measurement with a smartphone using a pendant drop
Why it matters

Why edible coating wetting matters

About 14%

of food produced is lost after harvest and before retail, and fruits and vegetables are among the most affected because they are so perishable.

FAO, The State of Food and Agriculture 2019

18.7 vs 61.5

dyne/cm: the critical surface tension of Fuji apple skin, against a chitosan coating solution too high in surface tension to wet it until Tween 80 was added.

Choi et al., Journal of Food Science 67(7), 2002

4 to 8 days

shelf life of strawberries at 10 °C without and with a modified chitosan edible coating, with weight loss down from 2.02% to 1.37%.

Khan et al., Food Science and Biotechnology 28(4), 2019

Sources: FAO, The State of Food and Agriculture 2019: Moving forward on food loss and waste reduction; Choi W.Y. et al., Wettability of chitosan coating solution on Fuji apple skin, Journal of Food Science, 2002; Khan I. et al., Development of antimicrobial edible coating based on modified chitosan for the improvement of strawberries shelf life, Food Science and Biotechnology, 2019. Figures come from these sources, not from Droplet Lab measurements.

Quick reference

What this edible coating check does and what it does not

A quick reference for food science teams checking fit before reading further.

Evidence Box

Problem this solves

Edible coatings that bead, patch or peel on waxy or cut produce, so shelf life trials fail for reasons a wetting test would have shown.

Standards

Fully compliant with ISO 19403-2 for surface free energy of the peel from contact angles.

Peer reviewed method

The Dropometer drop shape method was validated against a KRUSS DSA100E in two peer reviewed papers, in Review of Scientific Instruments and Colloids and Surfaces A.

Customer case study

A non profit research institute in Nepal measured surface tension, contact angle and surface free energy on tomato skin to choose its edible coating.

Published research

South Dakota State University researchers measured water contact angle with a Dropometer on residue based films that extended raspberry shelf life.

Honest limit

Good wetting is necessary for a working coating but does not prove shelf life. Confirm with storage trials.

Who this is for

What edible coating question are you trying to answer?

Pick the card closest to your role. Each one points to the part of this page that answers it.

Food science researcher

You are developing edible coatings for fresh produce from chitosan, alginate, whey protein or cellulose. Surface tension and contact angle on the real peel rank formulations in an afternoon, so storage trials start with the strongest candidates.

Measure on the produce you will coat; peel wax varies with cultivar and ripeness.

Postharvest or quality manager

You apply a coating on a packing line and need it to cover each fruit evenly. A contact angle check on incoming lots shows when a new cultivar or wash step changes how the coating wets.

Washing and drying change the peel; fix both before measuring.

Coating product developer

You formulate coatings for food, from produce coatings to other coatings in the food industry. Surface free energy of each target peel tells you how much surfactant a coating needs for each crop.

Check approved use rules for each additive in your market.
Fit check

Is this the right test for your edible coating?

It shows whether a coating will wet the peel. It does not show how long the produce lasts.

Good fit if

You compare edible coating formulations before shelf life trials.
You adjust surfactant, plasticiser or polymer levels.
You move a coating to a new fruit, vegetable or cultivar.
You need peel surface free energy with polar and dispersive parts.
You report wettability in papers on edible film and coating development for fresh fruits and vegetables.

Less relevant if

You need weight loss, firmness, colour or decay results.
You need gas or water vapour permeability of the coating film.
You need microbial counts or food safety approval.
Your produce surface is too small or curved to cut a flat peel section.
Summary

How to check edible coating wetting on produce

The answer in under a minute.

Measure the surface tension of each coating solution, its contact angle on the peel, and the peel's surface free energy. A coating whose surface tension is far above the peel's will bead and patch; adding surfactant or changing the polymer and plasticiser levels brings the contact angle down. Take only formulations that wet evenly into shelf life trials.

The Dropometer surface tension and contact angle kit runs all three checks; our contact angle measurement guide and wettability glossary entry explain the method. A research institute in Nepal used it to choose an edible coating for tomatoes, and South Dakota State University researchers used it on corncob residue packaging films for raspberries. Our food and beverages guide covers the wider context.

Expert Quote

Expert perspective on contact angle

A contact angle is a thermodynamic property: fix the liquid and the solid and the same angle appears whether the drop sits on a plate or climbs a capillary.

Dr. Alidad Amirfazli

Professor, Department of Mechanical Engineering, York University; Co-founder, Scientific Advisor, Droplet Lab

The problem

Why edible coatings fail to cover produce

Fruits and vegetables are among the most perishable foods, which makes food preservation after harvest a constant fight: FAO estimates about 14% of all food is lost between harvest and retail. Edible coatings and edible films, thin layers of chitosan, alginate, starch, cellulose derivatives, whey protein or lipids, slow water loss, respiration and decay and protect the quality of fresh produce. Polysaccharide-based coatings such as chitosan and alginate, protein-based edible coatings such as whey protein, and lipids are the main families, and an active edible coating containing an antimicrobial or antioxidant adds protection. The application of edible coatings only works if the coating forms an even, continuous film on the surface of the food. Many peels are covered in natural wax and have low surface free energy, while most coating solutions are water based with high surface tension. The result is a coating that beads, patches or peels, leaving gaps where water escapes and microbes enter. Choi and colleagues showed a chitosan solution at 61.5 dyne/cm could not wet Fuji apple skin, whose critical surface tension was 18.7 dyne/cm, until a surfactant was added. Fresh-cut fruits and vegetables add another problem: the cut tissue is wet and absorbs the coating. For the preservation of fruits and vegetables, the coating has to work on the real peel. Measuring wetting first saves weeks of storage trials on formulations that never covered the produce.

Coating beads or leaves bare patches on waxy peel.
Coated produce loses weight or decays unevenly.
A formulation that worked on one fruit fails on another.
Coating peels or flakes after drying.
Results change between lots, cultivars or ripeness stages.
Troubleshooting

Why an edible coating does not wet and what to change

Why:

Water based coatings have high surface tension, and waxy peels have low surface energy, so the coating cannot spread. Our surface energy guide explains the balance.

How to detect:

  • A high contact angle on the peel, and coating surface tension far above the peel's surface free energy.

Corrective action:

Add or adjust a food grade surfactant such as Tween 80, then remeasure. Our surface tension measurement guide covers the pendant drop method.

Why:

  • Casariego and colleagues found that more chitosan, glycerol or sorbitol lowered wettability and adhesion on tomato and carrot.

How to detect:

  • Contact angle rises as polymer or plasticiser concentration rises.

Corrective action:

  • Run a small concentration series and pick the level that balances wetting with film strength.

Why:

  • Cultivar, ripeness, natural wax and washing all change the peel's surface energy.

How to detect:

  • Peel surface free energy differs between lots or cultivars.

Corrective action:

Measure each new lot or cultivar, and fix washing and drying. Our contact angle reference values for common surfaces give a sense check.

Why:

  • The cut tissue of fresh-cut fruits is wet and porous, so drops soak in rather than sit.

How to detect:

  • The contact angle falls quickly over the first seconds.

Corrective action:

  • Read at a fixed time, blot the surface the same way each time, and compare with whole peel.

Why:

  • Surfactant above what the peel needs adds cost and can change taste or film strength.

How to detect:

  • Contact angle stops falling as surfactant rises.

Corrective action:

  • Use the lowest level that reaches your wetting gate.

Why:

Drop volume, read time and solution temperature change readings. Our guide to reproducible contact angle measurement covers fair comparisons.

How to detect:

  • The same formulation reads differently from day to day.

Corrective action:

  • Lock the method and measure a reference formulation with each set.

Not sure why your coating will not spread?

Bring your coating and a sample of the produce to a call, and we will measure the wetting on screen.

Book a 15 minute demo
Lab records

What an edible coating wetting record contains

Each check produces a record you can file with the formulation and storage trial. These records can feed into your existing lab notebooks and quality records.

Produce identity

Fruit or vegetable, cultivar, lot, ripeness, and washing and drying steps.

Coating identity

Polymer, plasticiser, surfactant and active ingredient levels, and solution temperature.

Method settings

Drop volume, read time, spots per fruit and probe liquids for the peel.

Readings

Coating surface tension, contact angle on the peel and peel surface free energy.

Decision

Take forward, adjust or drop, linked to the shelf life trial.

Drop images

Automatic edge and baseline detection gives the same reading from the same image, so a reviewer can recheck any result.

Measurements

What to measure in the development of edible coatings and films

Coating

Surface tension of the coating solution

Why it matters: It shows how easily the coating can spread.

How to interpret: Lower surface tension usually wets waxy peels better. Compare with the peel's surface free energy.

When it is not enough: Viscous solutions need longer to settle before reading.

Wetting

Contact angle of the coating on the peel

Why it matters: It shows directly whether the coating spreads or beads.

How to interpret: Lower is better wetting. Thresholds are set per produce from your own correlation with coating cover and shelf life.

When it is not enough: Curved or hairy peels need flat sections.

Peel

Peel surface free energy

Why it matters: It shows how much surfactant a coating needs for each crop.

How to interpret: Waxy peels have low values with a small polar part.

When it is not enough: It varies with lot and ripeness.

Spreading

Spreading coefficient

Why it matters: It combines surface tension and contact angle into one ranking number.

How to interpret: It is zero or negative; values closer to zero mean better spreading.

When it is not enough: It does not show film strength, barrier or other properties of edible films.

Validation

Validated measurement approach for edible coatings

How the Dropometer itself has been validated, and where food researchers have used it.

Peer reviewed method

The Dropometer drop shape method is published in Review of Scientific Instruments and Colloids and Surfaces A. Contact angle was validated against a KRUSS DSA100E, with a published accuracy of 0.35°.

See the validation papers

Customer evidence on tomato coatings

The Natural Products and Green Chemistry team at the Research Institute for Bioscience and Biotechnology, a non profit institute in Nepal, measured surface tension, contact angle and surface free energy on tomato skin for each edible coating formulation, chose the best one and moved its grant project to the next phase.

Read the case study
QC Protocol

How to screen edible coating formulations by wetting

Six steps for one produce and one coating base. Repeat for each new crop or recipe.

1

Prepare the peel

Wash and dry produce from one lot the same way, and cut flat peel sections.

2

Characterise the peel

Measure water and diiodomethane contact angles and calculate peel surface free energy; our surface free energy calculator shows the arithmetic.

3

Measure each coating

Measure the surface tension of each formulation by pendant drop at a fixed temperature.

4

Measure wetting on the peel

Place drops of each formulation on the peel and read the contact angle at a fixed time.

5

Rank formulations

Rank by contact angle and spreading coefficient, and take the best into shelf life trials.

We completed our gage R&R study on the unit and it performed very well.

Brandon Barbee

Corporate Quality Engineer, Zeus Industries, Polymer Manufacturing

Download the edible coating wetting SOP

A two page SOP you can adapt for your produce and coatings, with the method lock, peel preparation, gates, a troubleshooting table and a record sheet.

Contact angle measurement with the Dropometer

Contact angle measurement with the Dropometer

Example output

Example edible coating screen on tomato skin

Example data only. Your values and gates will differ and must come from your own produce and trials.

How to read this screen

Example gate: contact angle on the peel at or below 60° and spreading coefficient closer to zero than minus 25 mN/m. The chitosan solution without surfactant beads on the waxy skin. Adding Tween 80 brings it inside the gate. More glycerol makes wetting worse again, so the plasticiser level is reduced before the shelf life trial.

Example edible coating screen

Formulation Surface tension (mN/m) Contact angle on peel (°) Spreading coefficient (mN/m) Result
1.5% chitosan, no surfactant 62.0 92
  • 64.2
 Drop
1.5% chitosan, 0.1% Tween 80 36.0 48
  • 11.9
 Take forward
Plus extra glycerol 40.0 62
  • 21.2
 Adjust
Alginate with Tween 80 33.0 40
  • 7.7
 Take forward
Whey protein, no surfactant 52.0 80
  • 43.0
 Adjust

Example data, not customer data. Tomato skin sections, washed and air dried; coating solutions at 22 °C; contact angle read at 10 s; spreading coefficient from surface tension and contact angle.

Signal order

The order to check signals when a coating will not cover

Check these in order. Each one rules out a cause before you look at the next.

1

Peel preparation

Rules out washing, drying and lot differences.

2

Peel surface free energy

Shows how hard the peel is to wet.

3

Coating surface tension

Shows whether the coating can spread on that peel.

4

Contact angle on the peel

Confirms wetting directly.

5

Shelf life trial

Confirms the effect of edible coatings on the quality of fruits and vegetables; our farming and agriscience guide covers the crop side.

FAQ

Common questions about edible coatings and wetting

Questions food science and postharvest teams ask about edible films and coatings.

An edible coating is applied as a liquid directly onto the food, by dipping, spraying or brushing, and dries in place. An edible film is cast and dried first, then used as edible packaging to wrap or separate food, alongside other packaging materials such as a biodegradable film for food packaging. The polymers used to produce edible films are often the same. Wetting matters most when the edible film or coating is applied as a liquid that must spread over the food.

In any application of edible coating by dipping or spraying, a coating that does not wet the peel forms beads and gaps, so water loss and decay continue where the film is missing. Hershko and Nussinovitch noted that lower surface tension and contact angle of coating solutions lead to better wettability. Measuring wetting first avoids storage trials on coatings that never covered the produce.

They lower the coating's surface tension so it can spread on waxy peel. Choi and colleagues found Tween 80 lowered the surface tension of a chitosan coating and its contact angle on Fuji apple skin. Casariego and colleagues found 1.5% chitosan with 0.1% Tween 80 gave the best wetting on tomato and carrot.

It is the work of adhesion minus the work of cohesion of the coating on the peel, calculated from surface tension and contact angle. It is zero or negative, and values closer to zero mean the coating spreads better. It gives one number to rank formulations on the same produce.

They can, when they cover the produce well. In a study of the effect of edible coating on strawberries, Khan and colleagues found a modified chitosan coating extended shelf life at 10 °C from 4 to 8 days, with lower weight loss and decay. Advances in edible coatings for extending the shelf life of food still depend on produce and storage, so confirm each formulation with your own trials.

An edible coating for fresh-cut produce meets cut surfaces that are wet, porous and active, so it soaks in and the contact angle falls quickly. Read at a fixed early time, prepare cut surfaces the same way, and expect different targets from whole peel. Coatings containing calcium or antioxidants are common for fresh-cut fruits.

The use of edible coating ingredients is regulated, and rules differ by market and use. In the EU, glazing agents such as carnauba wax (E 903) and shellac (E 904) are permitted for the surface treatment of listed fruits under Regulation (EU) No 1147/2012. In the US, some chitosan sources have FDA GRAS notices for specific uses only. Check the rules for your ingredient, produce and market; we do not give regulatory advice.

One that measures pendant drop surface tension and sessile drop contact angle, and calculates surface free energy with two liquids. The Dropometer does all three, and it measures the edible coating and the produce on one kit. Our pages on biodegradable packaging film water resistance and spray coverage on leaves cover related wetting checks.

Business impact

What changes when you measure edible coating wetting

Typical changes in how teams work. Benchmarks are given only where a published source exists.

Before and with edible coating wetting checks

Metric Before Dropometer With Dropometer Indicative Benchmark
Formulation screening Shelf life trials on every candidate Wetting screen first, trials on the best No published benchmark; track on your own projects
Surfactant level Trial and error Set from surface tension and contact angle Chitosan at 61.5 dyne/cm did not wet apple skin until Tween 80 was added (Choi et al., 2002)
Moving to a new crop Repeat full trials Measure peel surface free energy first Tomato 28.71 and carrot 26.48 mN/m, both low energy (Casariego et al., 2008)
Shelf life outcome Unknown until the trial ends Unchanged; still needs trials Strawberries 4 to 8 days with a chitosan coating (Khan et al., 2019)

See the check on your own produce

Bring a coating and a sample of the produce. We will show the measurement on a call.

Book a 15 minute demo

Estimate saved formulation work

Enter your own numbers. The result is an estimate, not a Droplet Lab claim.

Edible coating formulation estimate

Estimate saved formulation and shelf life trial work.

Each Dropometer unit is US$5,000; the default models one unit.
Ingredients, produce and storage trial cost for one formulation.
Coating preparation, wetting checks and analysis.
No published benchmark. Use your own estimate and start low if unsure.

Result

~0
Formulations saved per month
~0
Monthly savings
~0
Payback period
~0
First year net benefit

Monthly savings = materials saved + technician time saved from reduced iterations.

Limits

What wetting cannot tell you about an edible coating

Honest limits, so you know when to reach for another test.

It does not measure shelf life, food quality, weight loss or decay.
Curved, hairy or very small produce needs flat peel sections.
Cut surfaces absorb drops; read at a fixed early time.
Peel values change with cultivar, ripeness and washing.
Viscous coatings need time to settle before reading.
It does not show whether an ingredient is approved for food use.

Surface tension, contact angle and peel surface free energy show whether a coating will spread on the produce. Shelf life, weight loss, gas exchange, taste and food safety need their own tests.

Book a 15 minute demo Request a quote
Related

Standards, evidence and related food surface workflows

These pages cover the standard, the customer evidence and related wetting checks for food, crops and films in food packaging.

Standard

ISO 19403-2

Surface free energy from contact angle measurements.

View use case

Case study

Research institute in Nepal

Edible coating formulations for tomatoes, chosen by the numbers.

View use case

Published paper

Soyhull residue films for raspberries

Biodegradable films that improved raspberry shelf life.

View use case

Published paper

Corncob residue films for raspberries

Biodegradable packaging films for post harvest preservation.

View use case

Instrument

Dropometer

Surface tension, contact angle and surface free energy in one kit.

View use case

Related use case

Functional, medical and electronic coatings

All functional coating use cases in one place.

View use case

Related use case

Soil amendment surface energy

Wetting checks for soils and soil amendments.

View use case

Related use case

Improve leaf coverage

Droplet size, retention and wetting on leaves.

View use case

Guide

Food and beverages guide

Surface science for food and drink.

View use case

How this page was created

Editorial and technical transparency notes for this page.

Transparency Details 4 checklist items
01

Drafting assistance

Drafted with Claude Opus 5.5 (Anthropic) using web search for sources, then edited by the Droplet Lab team.

02

Technical review

Reviewed and edited for technical accuracy by the Droplet Lab Team.

03

Verification steps

Standard identifiers, units, thresholds and key procedural claims are checked against cited sources before publication.

04

Updates

Reviewed every 12 months or when the underlying method changes.

Report a correction

Spotted an issue in this summary? Send a correction request and our team will review it.

Correction Request

We work hard to keep this page accurate and up to date. If you spot an error (wrong revision/year, missing requirement, incorrect interpretation, or broken link), tell us and we'll review it.

Contact us to report a correction
Sources

References

1.
FAO. The State of Food and Agriculture 2019: Moving forward on food loss and waste reduction. Rome, 2019. https://www.fao.org/3/ca6030en/ca6030en.pdf
2.
Choi, W.Y., Park, H.J., Ahn, D.J., Lee, J., Lee, C.Y. Wettability of chitosan coating solution on Fuji apple skin. Journal of Food Science 67(7):2668 to 2672, 2002. https://doi.org/10.1111/j.1365-2621.2002.tb08796.x
3.
Casariego, A. et al. Chitosan coating surface properties as affected by plasticizer, surfactant and polymer concentrations in relation to the surface properties of tomato and carrot. Food Hydrocolloids 22(8):1452 to 1459, 2008. https://doi.org/10.1016/j.foodhyd.2007.09.010
4.
Ribeiro, C., Vicente, A.A., Teixeira, J.A., Miranda, C. Optimization of edible coating composition to retard strawberry fruit senescence. Postharvest Biology and Technology, 2007. https://doi.org/10.1016/j.postharvbio.2006.11.015
5.
Khan, I., Tango, C.N., Chelliah, R., Oh, D.H. Development of antimicrobial edible coating based on modified chitosan for the improvement of strawberries shelf life. Food Science and Biotechnology 28(4):1257 to 1264, 2019. https://doi.org/10.1007/s10068-018-00554-9
6.
Hershko, V., Nussinovitch, A. Relationships between hydrocolloid coating and mushroom structure. Journal of Agricultural and Food Chemistry 46(8):2988 to 2997, 1998. https://doi.org/10.1021/jf971026l
7.
Commission Regulation (EU) No 1147/2012 amending Annex II to Regulation (EC) No 1333/2008 as regards the use of beeswax, carnauba wax, shellac and microcrystalline wax on certain fruits. https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:32012R1147
8.
Paudel, S., Janaswamy, S. Corncob derived biodegradable packaging films: a sustainable solution for raspberry post harvest preservation. Food Chemistry 454, 2024. See our analysis of this paper. https://dropletlab.com/validation/citations/analysis/corncob-derived-biodegradable-packaging-films-a-sustainable-solution-for-raspberry-post-harvest-preservation/
9.
Regmi, S., Janaswamy, S. Biodegradable films from soyhull cellulosic residue with UV protection and antioxidant properties improve the shelf life of post harvested raspberries. Food Chemistry 460:140672, 2024. See our analysis of this paper. https://dropletlab.com/validation/citations/analysis/biodegradable-films-from-soyhull-cellulosic-residue-with-uv-protection-and-antioxidant-properties-improve-the-shelf-life-of-post-harvested-raspberries/
10.
Chen, X. et al. Contact angle measurement with a smartphone. Review of Scientific Instruments 89(3):035117, 2018. https://pubs.aip.org/aip/rsi/article-abstract/89/3/035117/368179/Contact-angle-measurement-with-a-smartphone
11.
Surface tension measurement with a smartphone using a pendant drop. Colloids and Surfaces A: Physicochemical and Engineering Aspects. https://www.sciencedirect.com/science/article/abs/pii/S0927775717307744
12.
Droplet Lab validation papers
13.
Customer publications that cite the Dropometer
14.
Research institute in Nepal case study
15.
Food and beverages guide