Pigments & Colours in Food

Food quality is often determined by a variety of sensory attributes, including colour, flavor, texture, and nutritive value. Colour plays a significant role in food acceptability, affecting consumer choice and perception of freshness and ripeness.

1. Pigments in Plants

Natural pigments in plants contribute to the colours of fruits, vegetables, and other plant-based foods. These pigments are primarily located in the cells and include chlorophyll, carotenoids, anthocyanins, betanin, and flavonoids. These pigments not only contribute to the aesthetic appeal of food but also have important roles in nutrition.

Colour

• Definition: Colour refers to the perception of light by the human eye within the visible electromagnetic spectrum (380–730 nm). Colour influences food acceptability in combination with flavor and texture.
• Role: Colour plays an important role in food perception, particularly in relation to ripeness, freshness, and product quality. It also affects the perceived taste and value of the food.

Types of Colourants:

• Colourant: A general term used to describe substances that impart colour to food. These can be natural (plant-based) or synthetic.
  • Dye: A synthetic substance that imparts colour but is typically not used in food, as dyes used in textiles do not meet food safety standards.
  • Lake: A food-safe synthetic colourant that is insoluble in water, typically absorbed on an inert carrier (e.g., alumina) to be added to processed foods. These are often referred to as certified colors.

Plant Pigments

Plant pigments are categorized into two main types:

1. Water-Insoluble Pigments: These are typically found in plastids (such as chloroplasts) and include chlorophyll and carotenoids.
2. Water-Soluble Pigments: These are dissolved in the cell sap and include anthocyanins, flavones, and betanins.

Water-Insoluble Pigments

1. Chlorophyll: The green pigment in leaves and stems, responsible for photosynthesis. There are two main types:

• • Chlorophyll-a: A blue-green pigment.
  • Chlorophyll-b: A yellow-green pigment.
  • Chlorophyll is insoluble in water and contributes to the green color in vegetables like spinach, capsicum, and beans.
  • Structure: Chlorophyll consists of a porphyrin ring that chelates a magnesium atom, with a phytol tail (a 20-carbon alcohol).
  • Deterioration of Chlorophyll: Chlorophyll breaks down when exposed to heat and acids. The cooking process can cause vegetables to lose their green color. Copper compounds (e.g., CuCl2) can help prevent degradation during cooking by forming stable complexes with chlorophyll.

2. Carotenoids: These are lipid-soluble pigments responsible for the yellow, orange, and red colors of fruits and vegetables. Carotenoids include:

• • β-Carotene: A precursor to vitamin A, found in carrots, mangoes, and pumpkins.
  • Lycopene: Found in tomatoes and watermelon, responsible for their red color.
  • Xanthophylls: Yellow pigments found in green leafy vegetables, corn, and peppers.
  • Carotenoids are not masked by chlorophyll in ripe fruits, which gives them their characteristic color.

Water-Soluble Pigments

1. Anthocyanins: These pigments are responsible for red, purple, and blue colors in fruits like grapes, cherries, and blueberries.
   • Structure: Derived from flavylium cation, with various types like pelargonidin, cyanidin, and delphinidin.
   • Effect of pH: Anthocyanins change color with pH. In acidic environments, they appear red, and in alkaline environments, they can turn blue or purple.
   • Effect of Metal: Cooking in aluminum pans can cause anthocyanins to form chelates with metal ions, altering their color.
2. Anthoxanthins: These are colorless or pale yellow pigments found in plants like bananas, apples, and pears.
   • These pigments are more sensitive to changes in pH and metal presence. For example, they turn yellow in alkaline conditions.
3. Betanins: A group of pigments found in beets, cactus fruits, and amaranthus. Betanins can be of two types:
   • Betacyanin: Red-colored.
   • Betaxanthin: Yellow-colored.
   • Betanins are stable under heat and can be used as food colorants.
4. Flavonoids: A large group of water-soluble plant pigments that can be divided into different categories:
   • Flavones: Found in celery, parsley, and herbs, often associated with antioxidant benefits.
   • Flavonones: Found in citrus fruits, important for cardiovascular health.
   • Flavonols: Present in onions, tea, and apples, with quercetin being an example that has antihistamine properties.
   • Flavanols: Found in tea, grapes, and cocoa, beneficial for cholesterol management and overall health.

Flavour Compounds

• Flavour in fruits and vegetables is influenced by the presence of various compounds like sugars (glucose, fructose), organic acids (citric, malic acid), and sulfur compounds.
• Sulfur-containing compounds: Found in garlic, onions, cabbage, and broccoli, contributing to their characteristic taste and smell. These compounds can also have health benefits, including antimicrobial and antioxidant properties.
• Tannins: A group of polyphenolic compounds that contribute to the astringency of fruits and vegetables like apples, pomegranates, and tea. Tannins bind to proteins and can cause a dry mouthfeel.

Sensory Attributes in Food

The sensory qualities of food such as appearance, texture, flavor, and smell are crucial in determining food quality. These attributes are influenced by various internal and external factors:

• Appearance: The external characteristics, such as colour, glossiness, and the presence of abnormalities (e.g., lumps, spoilage), are key factors in food acceptability.
• Colour: Colour can indicate ripeness, doneness, and freshness. For example, the color of a fruit like a banana or tomato can signal its ripeness. The color of roasted meat, baked goods, or beverages also indicates their doneness and quality.

Flavour; Flavour is a complex sensory experience comprising both odour (smell) and taste (perception of sweet, salty, sour, bitter, or umami flavors).

• Odour: The sense of smell is vital for flavor perception, and the volatile compounds in food influence aroma. For example, mangoes have over 280 different volatile compounds that contribute to their distinctive aroma.
• Taste: Taste buds detect five basic tastes: sweet, salty, sour, bitter, and umami. These contribute to the overall flavour experience.