Flavour constituents

FOOD SCIENCE AND PROCESSING 3 (2+1)
Lesson 27 : Processing and Preservation of Fruits - I

Flavour constituents

Volatile flavour compounds are esters, aldehydes, acids, alcohols, ketones and ethers. Some fruits contain essential oils which are also important flavour contributors.

Polyphenols: Polyphenols or tannins comprised catechins, the leucoanthocyanins and hydroxyl acids. Skin and seeds contain high amount of tannin. When a fruit is pressed, such as apples in the preparation of cider or grapes in making juice or wine, the tannins flow out in the juice.

Effects of polyphenols on fruit quality

  • The cause of the undesirable astringency in some fruits and desirable astringency in ciders and wines is due to polyphenols. Astringency is the feeling of puckering that occurs in the mouth when certain compounds, notably flavanols are present.
  • The formation of troublesome haze and precipitates in apple juice, beer and wine has been attributed to the interaction of proteins and phenolic polymers.
  • Development of brown discolouration occurs in cut fruits due to oxidation of phenolic substances (chlorogenic acids, catechins) by the polyphenolase enzymes.
  • The formation to dark-coloured complexes with iron due to sequestering action of the dihydric and trihydric phenolics, which result in undesirable appearance of canned foods.
  • The development of pink to pinkish brown colour in fruits like pear, guava, apple, banana, litchi has been attributed to leuocoanthocyanins.

When bananas ripen, the excessive quantities of flavanols found in the unripe fruit are reduced. A warm and clear environment during ripening of peaches results in a lower content of polyphenols than is developed when cloudy weather prevails. The lower polyphenolic content imparts a reduced astringency.

Bitterness in fruits

Bitterness in citrus fruits can be attributed to compounds of two classes, the limonoids (triterpenes) and the flavanone glycosides (flavonoids).
The Precursor of Limonin is naturally present and stable in intact citrus tissue but when the fruit is squeezed to yield juice, the active compound of the precursor in combination with the acidic pH results in the formation of limonin.

The principal flavonoid bitter tasting component of citrus fruit is the flavanone glycoside, naringin. It is the major flavonoid of grape fruit.

Certain citrus products when heated can develop a bitter off flavour. The compound thought to be resoponsible is limonin which is intensely bitter tasting triterpenes dilactone which can also be naturally occurring in citrus products.
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Last modified: Tuesday, 13 December 2011, 8:47 AM