Vegetable pungency

Certain vegetables are also examples of foods with volatile components which stimulate both aroma and pungency. These are all sulphur compounds, present as precursors in the whole vegetable and are converted into the active constituents only by action of enzymes released when the structure is destroyed by cooking or grinding. 

The vegetable radish (Raphanus sativus L.) shows mild pungency attributed to 4-methylthio-3-butenyl isothiocyanate. Other vegetables of the Brassica and Allium species, too, are reported to contain small amounts of these isothiocyanates, but they are possibly diluted and altered during cooking, and so have not been reported as exhibiting sensory pungency in foods. 

Pungency is defined as the gustatory sensory response to specific chemical stimuli found in certain spices and vegetables. 

The essential oil, which is present in the fresh bulb in a concentration of 0.1 to 0.3%, contains diallyl sulphide, diallyl trisulphide and allyl methyl disulphide (derivatives of allicin) as main components. Apart from further allyl polysulphides, the steam distilled oil contains limonene as non-sulphurous component [111]. The high pungency of garlic oil makes it necessary to dilute it, commonly in vegetable oil. One gram of oil is equivalent to 900 g of fresh garlic or 200 g of dehydrated garlic powder [112]. 

The isothiocyanates contain the -N C S group and are found in several pungent vegetables, particularly, (a) allyl isothiocyanate, produced by the enzymatic action of myrosin on the glycoside sinigrin in black mustard seed (b) benzyl isothiocyanate found in garden cress and (c) phenyl ethyl isothiocyanate, responsible for the sharp pungency of horseradish. 

The underground bulb of the onion plant is the sixth leading vegetable crop of the world. It is distinguished by its pungency when raw and the appetizing flavor it imparts when cooked with various other foods. The odor is due to an oil, which readily forms a vapor and escapes into the air when onions are peeled or cut It affects nerves in the nose connected with the eyes, and makes tears flow. 

---