Blanching is a unit operation prior to freezing, canning, or drying in which fruits or vegetables are heated for the purpose of
1)Inactivating enzymes
2)Modifying texture
3)Preserving color, flavor, and nutritional value
4)Removing trapped air
Hot water and steam are the most commonly used heating media.
Blanching removes trapped air (e.g., in broccoli florets) and metabolic gases within vegetable cells and replaces them with water, forming a semi continuous water phase that favors a more uniform crystal growth during freezing
Gas removal is the main benefit of blanching before canning because it allows easier can fill, reduces strain on can during heating, and reduces can corrosion.
Blanching : Types
Water blanching
Steam blanching
Microwave blanching
Gas blanching
Blanching : Flavour
Blanching indirectly and directly affects the flavor of many products by inactivation of enzymes responsible for off-flavor development.
The most notable is lipoxygenase (LOX) in several vegetables.
Sometimes blanching increases flavor retention, and sometimes it removes undesirable bitter flavors from the product.
Blanching : Texture
Although blanching of vegetables is most often done in hot water or steam, blanching of fruits is often done in calcium brines to firm the fruit through the formation of calcium pectates.
Colloidal thickeners, such as pectin, carboxy methyl cellulose and alginates, also can be used to aid fruit firmness following blanching.
Blanching : Colour
Blanching can have both direct and indirect effects on color.
The former is exemplified by the destruction of pigments, such as chlorophyll, by heat.
Sodium carbonate or calcium oxide are often added to blancher water to protect chlorophyll and to retain the colour of vegetables.
Blanching : Nutritional value
Generally, blanching produces a decrease in the nutritional value of foods.
In addition, vitamins are degraded by heat.
Vitamin C (ascorbic acid) is, by far, the most commonly assayed nutrient in blanching probably because its high solubility and heat susceptibility make it a conservative indicator of nutrient retention.
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