Food color is a science signal that affects what people expect to taste, how fresh a food seems, and whether it looks safe to eat. The color we see comes from the wavelengths of light a food reflects to our eyes after other wavelengths are absorbed by pigments or dyes. Natural pigments in plants, animals, and microbes create many familiar colors, from orange carrots to red strawberries.
Food makers also use approved color additives to replace color lost during processing or to make products look consistent.
Key Facts
- Visible light has wavelengths of about 400 to 700 nm, and the reflected wavelengths determine the color we see.
- Chlorophyll absorbs mostly red and blue light and reflects green light, making many leaves and vegetables look green.
- Anthocyanins can change color with pH: red in acidic conditions, purple near neutral, and blue or green in basic conditions.
- Carotenoids such as beta-carotene and lycopene produce yellow, orange, and red colors and are more stable to pH than anthocyanins.
- Absorbance can be modeled by Beer-Lambert law: A = epsilon l c, where absorbance increases with pigment concentration.
- Heat, oxygen, light, and pH can break down pigments or change their structure, which changes food color during cooking and storage.
Vocabulary
- Pigment
- A pigment is a natural colored molecule that absorbs some wavelengths of visible light and reflects or transmits others.
- Food dye
- A food dye is a color additive used to give food a specific color or replace color lost during processing.
- Anthocyanin
- Anthocyanin is a water-soluble plant pigment that gives many berries, grapes, and red cabbage their red, purple, or blue colors.
- Carotenoid
- A carotenoid is a fat-soluble pigment that gives many foods yellow, orange, or red color, such as carrots, pumpkins, and tomatoes.
- Absorbance
- Absorbance is a measure of how much light a substance takes in instead of letting it pass through or reflect.
Common Mistakes to Avoid
- Thinking food has color because it creates light is wrong because most foods reflect and absorb outside light rather than glow on their own.
- Assuming natural colors are always more stable is wrong because many natural pigments, such as anthocyanins and chlorophyll, can change quickly with pH, heat, oxygen, or light.
- Using color as the only test for food safety is wrong because harmful microbes or chemical changes can be present before a visible color change appears.
- Forgetting that pH can change pigment structure is wrong because foods like red cabbage or berry sauces may shift color when mixed with acids or bases.
Practice Questions
- 1 A drink contains a red dye with absorbance A = 0.60 in a 1.0 cm cuvette. If the concentration is doubled and Beer-Lambert law applies, what absorbance is expected?
- 2 A pigment solution absorbs strongest at 450 nm, which is blue light. If it absorbs blue strongly, what general color will it tend to appear: blue, yellow-orange, green, or violet?
- 3 Red cabbage juice turns reddish in lemon juice and bluish-green in baking soda solution. Explain what this color change shows about anthocyanins and pH.