Egg White Protein Unfolding by Salt

ISEF Category: Biochemistry

Subcategory: General Biochemistry  ·  Difficulty: Intermediate  ·  Setup: Home Setup  ·  Time: 1 to 2 Months

The Hook

Egg white turns cloudy because proteins lose their shape and stick together. Salt changes how easily that happens. You can track that cloudiness with a smartphone and turn it into a real stability curve. Then you can estimate how much unfolding is favored at each salt level.

What Is It?

Albumin is a protein in egg white. Proteins are long chains that fold into shapes that help them stay dissolved and do their jobs. When salt changes the water around a protein, the balance between the folded and unfolded forms can shift.

A two-state model treats the protein like a switch with two main choices, folded or unfolded. That gives you a simple way to fit your data and estimate ΔG of unfolding, which is the energy difference between those states. Turbidity means cloudiness. As more protein clumps together, the sample scatters more light and looks less clear. An isotherm is just a snapshot at one temperature while you vary salt.

Why This Is a Good Topic

You can run this with egg whites, salt, a phone, and simple containers, but the analysis still feels real. The topic connects to food science, protein stability, and how salt changes texture and appearance in cooking and processing. You also learn how to make a measurement, turn it into numbers, fit a model, and check whether the model actually matches the data.

Research Questions

• How does sodium chloride concentration change the turbidity of egg-white albumin at a fixed temperature?
• What is the effect of different salts, such as sodium chloride, potassium chloride, and calcium chloride, on the estimated ΔG of unfolding?
• Does the fitted midpoint concentration shift when the sample starts at a different protein concentration?
• To what extent does temperature change the shape of the turbidity isotherm and the model fit?
• Which smartphone lighting setup gives the most repeatable turbidity measurements?
• How does pH adjustment alter the apparent stability of egg-white albumin under the same salt range?

Basic Materials

• Fresh egg whites or pasteurized liquid egg whites.
• Table salt and at least one other food-grade salt.
• Distilled water.
• Clear cups or test tubes of the same size.
• Digital kitchen scale with 0.1 g accuracy.
• Measuring spoons or graduated cylinders.
• Smartphone camera.
• White LED desk lamp or light box.
• Plain white background.
• Stirring rods or disposable spoons.
• Labels and permanent marker.
• Coffee filters or fine mesh strainer.

Advanced Materials

• Purified ovalbumin or egg-white protein standard.
• Temperature-controlled water bath.
• UV-Vis spectrophotometer or microplate reader.
• Cuvettes or clear 96-well plates.
• Analytical balance.
• pH meter.
• Magnetic stir plate and stir bars.
• Laboratory-grade salts and buffers.
• Micropipettes and tips.
• Data logger or thermocouple probe.

Software & Tools

• ImageJ: Measures image brightness or turbidity from standardized phone photos.
• Python: Fits the two-state model and plots uncertainty bands.
• Google Sheets: Organizes replicates, calculates averages, and tracks outliers.
• R: Runs curve fitting and compares model variants with confidence intervals.

Experiment Steps

1. Define the salt range, temperature, and protein source you will compare.
2. Build a photo setup that keeps lighting, distance, and background fixed across every run.
3. Choose one signal metric, then decide how you will convert each image into a turbidity value.
4. Plan the two-state model fit, including controls, replicates, and the parameter you will estimate for ΔG.
5. Set rules for rejecting bad runs, comparing salts, and checking whether the model still fits after you remove outliers.

Common Pitfalls

• Letting the phone auto-expose each image, which makes apparent turbidity change even when the sample does not.
• Mixing samples unevenly, which creates local clumps and makes the cloudiness curve jump around.
• Comparing batches of egg whites from different cartons without noting protein variability, which shifts the apparent transition.
• Fitting the model to too few salt points, which hides the midpoint and makes ΔG unstable.
• Changing temperature or lighting between trials, which breaks the isotherm and blurs the salt effect.

What Makes This Competitive

A strong version of this project does more than show that salt changes cloudiness. It maps enough concentration points to capture the full transition, reports uncertainty for ΔG, and checks whether a two-state model really fits better than a simpler line. You can raise it further by comparing several salts or testing whether the same model still works across different egg-white sources. Careful controls and clean image calibration will matter more than fancy gear.

Project Variations

• Compare sodium chloride, potassium chloride, and calcium chloride to see whether ionic charge changes protein stability.
• Repeat the turbidity curve at two pH levels to test whether acidity changes the salt effect.
• Swap whole egg white for purified ovalbumin to see whether the mixture behaves differently from a single protein.

Learn More

• PubMed: Search review articles on protein denaturation, ovalbumin, and salt effects.
• NCBI Bookshelf: Find free biochemistry chapters on protein structure and folding.
• RCSB Protein Data Bank: Look up ovalbumin structure and protein context.
• OpenStax Biology 2e: Read the free textbook sections on proteins and structure.
• MIT OpenCourseWare: Search for biochemistry and physical chemistry lecture notes on protein folding and thermodynamics.