Post harvest Management of Horticultural Crops (2+1)

Color development in fruits and vegetables

Colour Development in fruit

The change in colour is either due to synthesis of plant pigments are due to unmasking of already existing colour. Change in colour is due to chlorophyll, which is magnesium organic complex. The loss of green colour is due to degradation of chlorophyll structure. Change in colour development is common except avocado, kiwi fruit and Granny Smith Apple. Chlorophyll degradation leads to development of yellow/orange/red/purple pigments.

The principle agents responsible for the degradation are

• Change in pH,
• Oxidation systems or
• Enzymes chlorophyllases.
Carotenoids are stable pigments and remain there till senescence. They are either synthesized during developmental process or they are masked by the presence of chlorophyll. This kind of change is seen in case of banana. While in tomato, the colour pigment lycopene is developed simultaneously with degradation of chlorophyll. Other pigments found in fruits and vegetables are anthocyanins. They are red-purple or blue water soluble phenolic glucosides that are found in vacuoles like in beet root and epidermal cell of apple and grape. They produce strong colour, which often mask carotenoids and chlorophyll.. In acidic pH levels the anthocyanins are red in colour and in alkaline pH they tend to become blue. This gives rise to a phenomena in roses known as ‘blueing’, where as shift from red to blue coloration occur with aging. This is due to depletion of CHO and release of free amino acids resulting in more alkaline pH in the cell sap.

Changes in texture and taste - on ripening of fruits, breakdown of starch to sugars, which affects taste and texture of the produce.

a. Textural Changes

The texture of the fruit softens with ripening. This is because of the action of enzymes like hydrolases ( poly galacturonase, pectin methyl esterase and cellulases) which breakdown the pectins, cellulose and hemicellulose.
Propectin is insoluble form of pectic substances binds to calcium and sugars in the cell wall. On maturation and ripening, propectin gradually broken-down to lower molecular weight fraction which are more soluble in water. The rate of degradation of pectic substances is directly correlated with rate of softening of the fruit.

b. Change in Taste

The primary change in taste is the development of sweetness in fruits after ripening. During ripening the starch break down into simple sugars like glucose, fructose and sucrose which are responsible for sweetness. This change is also mediated through the action of various enzymes like amylase, invertase, phosphorylase, etc.


Colour changes in vegetables

Seeds are consumed as fresh vegetables, for eg. Sweet corn (baby corn), have high levels of metabolic activity, because they are harvested at immature stage. Eating quality is determined by falvor and texture, not by physiological age. Generally seeds are sweeter and tender at an immature stage. With advancing maturity, the sugars are converted to starch, with a result of loss of sweetness: water content also decreases and amount of fiber material increases.

In edible flower/buds/stems/leaves textures is an often dominant character that determines the both harvest date and quality, as loss of turgor through water loss causes a loss of texture. The natural falvour is often less important than texture, as many of these vegetables are cooked and seasoned with salt and spices.

Bulbs/roots/tuber - in these crops using appropriate storage condition their storage shelf life can be prolonged.

Events of changes during maturation/ripening of Horticultural produce