Color Flashcards
Identify the qualities and characteristics of food colors
- Characterized by three qualities
1) Hue – actual color name (is it red, yellow, orange green, etc)
2) Saturation or chroma – clarity and purity of the color
3) Intensity – range of lightness to darkness of color (more intense the color, the darker the color) - Surface appearance characteristics
- Shiny
- Glossy
- Cloudy – more opaque
- Translucent – can see through it; transparent
- Shiny and glossy refer to the way that light is reflected
- Cloudy and translucent refer to the transmission of light through the food
Classify pigments by source and solubility
- Plant sources
- Water-soluble – can be lost in cooking water
- — Anthocyanin
- — Betalains
- Lipid-soluble
- — Carotenoids
- — Chlorophylls
- Animal source
- — Myoglobin – water soluble (is what gives color to read meats)
Describe the structure of myoglobin and how it contributes color to red meat
- Beef, lamb, pork, dark meat poultry
- Red meat contains mostly slow-twitch muscle fibers (rely on aerobic metabolism which require oxygen - these muscle fibers contain more myoglobin which can carry more oxygen)
Myglobin (Mb)
- Can bind oxygen
- Gives red meat its color
- Globular protein - water soluble
- Fibrous vs. globular proteins - globular is more soluble
- Composed of globin protein and heme (iron porphyrin ring)
Center of Myoglobin is heme, and the globular part is the globin
Heme part – center of heme molecule/portion is iron.
Iron has 6 binding sites – 4 are part of the ring, the 5th is how it’s bound to the globin ,the 6th is open to bind to oxygen
List the factors that affect color change in red meat
- Packaging material
- Number of bacteria – can turn meat green
- Animal species and age – older animals tend to have darker meat; veal vs. beef is different color
- Amount of Mb – beef and lamb have higher amounts of myoglobin
- Muscle source – I.e. slow twitch and fast twitch
- Oxidation and reduction of iron
Explain the color changes in red meat that occur with: slaughter, exposure to oxygen, aging, cooking, nitrate-curing and contamination
- Living animal – oxygenated Mb in equilibrium with un-oxygenated Mb
- Equal amount of oxygenated and un-oxygenated
- Upon slaughter – unoxygenated Mb with iron in reduced state (Fe+2)
- Purplish-red color
- Ferrous iron
- Upon exposure to air – oxygenation forms of oxymyoglobin
- Bright red color
- Iron is still in its reduced state, however it is oxygenated (bound to oxygen)
- Aging – oxidation forms metmyoglobin with iron in its oxidized state (Fe+3)
- Brownish color
Explain the color changes in red meat that occur with: cooking
- < 140°F: no color change (red)
- Rare
- Oxymyglobin – oxygenated (exposed to oxygen) but not oxidized
- 140°F-170°F: Mb loses ability to bind oxygen, iron loses an electron, hemichrome formed (pink > brown)
- Rare to medium
- Higher temp – Mb loses ability to bind to oxygen
- Hemichrome – tan color (covers up the myoglobin pigment)
- > 170°F: metmyoglobin formed (brown)
- Well done – brown all the way through
Explain the color changes in red meat that occur with: nitrate-curing
(Bacon, sausage ham, etc. )
- Mb reacts with nitric oxide to produce nitrosylmyoglobin (bright pink-red)
- With heat: nitrosylmyoglobin denatured (pink)
- Example: raw ham and cooked ham = same color
- Exposure to light and oxygen: iron oxidized (brown)
- Going to take longer for nitrate cured meat to turn brown than a meat without it > prolongs shelf life and makes it resistant to oxidation
Explain the color changes in red meat that occur with: contamination
- Cholemyoglobin and sulfmyoglobin
- – When meat is exposed to bacteria, it create these two myoglobin compounds
- Result of: bacterial action on contaminated meat
- Oxidation yields: yellow or green color > don’t turn green or yellow until they’re oxidized
Recognize factors that affect stability, colors associated with, and food sources of plant pigments: Anthocyanins/anthocyanidins
- Heat stable, water soluble
- Red-purple
- Water soluble and heat stable – but not pH stable
- Anthocyanins – complexed with sugars
- Anthocyanidins – pigment on its own
- Red in strong acid – color will turn more reddish
- Colorless at pH 4
- Blue at neutral pH
- Eggplant, radish, red cabbage, red potato, berries
Recognize factors that affect stability, colors associated with, and food sources of plant pigments: Anthoxanthins
- Colorless or white
- Heat stable, water soluble
- Can become yellow at pH > 7
- — i.e. in presence of baking soda – can turn more yellow
- Cauliflower, onions, white potato, jicama
Recognize factors that affect stability, colors associated with, and food sources of plant pigments: Betalains
- red-purple/yellow
- heat stable, water soluble
- out of the three, these are the most pH stable
- beets, rainbow chard
Carotenoids - lipid soluble pigments
- Heat and pH-stable
- Heat enhances the bioavailability of bioavailability of the carotenoids
- Carotenes
- Beta-carotene: yellow-orange
- Lycopene: Red-orange
- Carrots, oranges, peaches, tomatoes, red/orange/yellow peppers, winter squash, sweet potato
- Xanthophylls
- Lutein, xeaxanthin: yellow
- Pineapple, corn (Also in dark leafy greens, but don’t see yellow because chlorophyll blocks the color)
Explain the changes in plant pigments with exposure to heat, acid, and enzymes
- Porphyrin ring complexed to magnesium
- Magnesium in the middle of a porphyrin ring
- Green vegetables
- Exposure to acid or heat
- Chlorophyll (bright green) > pheophytin (dull olive green)
- — i.e. pickled green beans or heated/roasted green beans
- — With heat > prolonged exposure to heat will produce > more about timing than amount of heat (as seen in blanching green beans)
- Magnesium replaced by hydrogen
- Chlorophyllase enzyme
- Chlorophyll > chlorophyllide
- — Chlorophyllide – more water soluble > causes color to leak out into water
- With acid/heat: chlorophyllide > pheophorbide (gray-brown)
- — Enzyme action AND exposure to acid
Colorants
- Natural – obtained from natural source
- Synthetic (artificial) – chemically produced
- All are considered food additives
FD&C Colorants
- FDA certified as safe – for use in Foods, Drugs, and Cosmetics
- All water-soluble
