Food Colorants and Chlorophyll

Food Colorants

• Color is crucial for food appreciation and quality assessment
• Food industry prioritizes maintaining original raw material colors in processed foods
• Some foods' colors change due to processing (e.g., browning of cake, curing of meat)
• Consumer concern exists regarding the use of synthetic food colorants

Chlorophylls

• Chlorophyll is a green pigment found in leafy vegetables, green apple skin, and unripe fruits
• Chlorophyll plays a vital role in photosynthesis within plant cells, specifically within chloroplasts
• Chlorophylls a and b are porphyrins similar to hemoglobin, but contain magnesium instead of iron
• Chlorophyll is lost naturally during leaf senescence due to chlorophyllase
• When green vegetables are heated, the magnesium in chlorophyll is lost, leading to the formation of pheophytins (a and b). This results in a brownish color
• The acidity of plant cell vacuoles promotes pheophytin formation during cooking
• Keeping the cooking water alkaline (with sodium bicarbonate) is somewhat effective, but also decreases vitamin C and impacts texture and flavor
• In canning peas, chlorophyll loss is common, so artificial colours (like tartrazine and Green S) are added.
• Growing concern regarding tartrazine safety has led to evaluating alternative and safer chlorophyll derivatives as food colors (e.g., sodium copper chlorophyllin)
• Sodium copper chlorophyllin is blue-green and survives the canning process, while copper content is too low to be a health risk.

Carotenoids

• Carotenoids are responsible for the yellow and orange colors in fruits and vegetables
• They are found in chloroplasts
• Classified as terpenoids
• Two main groups: carotenes (hydrocarbons, simplest being lycopene), and xanthophylls (contain oxygen)
• Xanthophylls are created by hydroxylation of carotenes
• Xanthophylls are the dominant pigment in yellow tissues, while carotenes give an orange color
• Examples of carotenoids include crocetin (found in saffron) and bixin (found in annatto, a component of cheddar cheese)
• Carotenoids are relatively stable to heat, but isomerization to cis forms can occur with heating
• Epidemiological studies suggest that consumption of fruits and vegetables rich in carotenoids (e.g., a- and β-carotene, lutein, lycopene) may reduce the risk of certain cancers (e.g., lung and prostate cancer).

Anthocyanins

• Anthocyanins produce pink, red, mauve, violet, and blue colours in flowers, fruits, and vegetables
• They are flavonoids, located in vacuoles within plant cells
• Naturally found as glycosides (with sugars attached)
• Aglycones (sugar-free counterparts) are anthocyanidins (e.g., cyanidin, pelargonidin, delphinidin)
• Anthocyanins complex with metal cations, possibly altering color in canned fruit due to interactions with the metal of the can or container.
• Reactions with sulfur dioxide, a popular preservative in wines/fruit juices, can lead to irreversible fading or bleaching of anthocyanin colours
• Anthocyanin colours are pH-dependent, changing from red to pink to purple/blue, depending on the acidity/alkalinity of the environment.

Betalains

• Beetroot pigments, exhibiting reddish-purple colours.
• Two main groups: betacyanins (purplish red, similar to anthocyanins), and betaxanthines (yellow, less common)
• Beetroot extract is sometimes used as a food colourant, but its heat instability makes it unsuitable for colouring cakes.

Melanins

• Melanins are undesirable brown pigments in damaged plant tissues leading to undesirable browning
• Browning arises when plant tissues are damaged/exposed to air, triggering an enzymatic browning process involving phenolase (or polyphenol oxidase) which oxidizes polyphenolic compounds.
• Prevention of browning can be achieved with blanching/reducing air exposure through immersion
• Chlorogenic acid is a frequently encountered substrate for phenolase in apples, pears, and potatoes.
• In animal tissues, tyrosine is the only substrate for polyphenol oxidase.
• Adding chelating agents, using organic acids (like citric/malic acid), and using sulfur dioxide are ways to inhibit phenolase activity and prevent undesirable browning.

Tea

• Tea leaves have high polyphenol content (over 30%)
• Caffeine (3-4% of dry weight) is a key component
• Tea processing (withering, fermentation, firing) affects its colour, flavour, and astringency

Turmeric

• Dried turmeric roots are used as a food coloring and dyeing agent
• Curcumin is the essential component, giving the yellow hue and acting as a pigment found in curry powder.

Cochineal

• Cochineal is a reddish pigment obtained from insects
• Is used as a food colorant in textiles, leather, and has a heart stimulant effect
• Carminic acid is the primary component

Artificial Food Colorants

• Chemically synthesized food colorants offer various advantages: brighter, more stable, cheaper, wider range of shades.
• Concerns exist about safety, therefore stringent regulations exist regarding their permitted use.
• 0.01-0.1% of population may be intolerant to tartrazine, a common synthetic colorant
• The high costs of safety testing for new synthetic colorants make their introduction difficult.
• Synthetic colorants are usually classified as certified color additives (FD&C dyes and lakes), where FD&C dyes are water-soluble, and FD&C lakes are water-insoluble.
• Pigments from plants and animals are exempt from certification.

Explore the fascinating world of food colorants and chlorophyll in this quiz. Learn about the significance of color in food appreciation, the effects of processing on food appearance, and the critical role of chlorophyll in photosynthesis. Test your knowledge on how cooking affects these pigments and consumer concerns regarding synthetic additives.