Brown mustard seed is spherical, medium in size and has a nutty, sweeter and mellow burning flavour. The whole mustard seed has no flavour, but can provide a pungent taste after chewing (Hirasa and Takemasa, 1998). The heat experienced in yellow mustard is on the tongue, whereas in brown and black mustard the heat is also felt in the nose and eyes. The severity of pungent aroma varies with different mustards. The white or yellow type has a less pungent aroma than brown mustard seeds, which have a very pungent aroma. Black mustard seeds have the highest pungency.
In ground mustard, aroma does not persist. However, flavour and pungency are experienced when enzymatic action is triggered in the presence of water, which releases mustard's flavour or pungency. It is due to a variety of isothiocyanate compounds that exist in mustard tissue as glycosides. The major pungent compound of black and brown mustard is allyl isothiocyanate. The release of sensation, especially in brown and black mustard, is delayed and begins at the back of the mouth, with a shooting sensation to the sinuses, owing to the activation of an enzyme, myrosinase. The enzyme myrosinase, in the presence of water, breaks down the glycoside (sinalbin) in yellow mustard or sinigrin in black or brown mustard to para-hydroxybenzyl isothiocyanate, which is responsible for the characteristic pungent aroma. The odours last until the enzyme activities ceases.
Yellow mustard flavour and pungency, like brown or black mustard, can be fully experienced only by triggering the enzyme myrosinase action, which releases them. The most effective enzymatic trigger is in the presence of water at room temperature, although other low-acid liquids such as milk and beer also work. Acidic liquids such as wine, vinegar and lemon juice are poor triggers of mustard's overall flavours, but are good subsequent preservatives of the flavour and they extend the penetrating odour. When water, vinegar, milk, wine or beer is added to mustard, mixed and left to stand for a few minutes, different degrees of flavour sensations are produced. With water a very sharp and hot taste is produced, while with vinegar milder flavour is induced. With milk a milder spicier and pungent flavour is created. With beer a very hot flavour is brought out (Uhl, 2000).
Mustard flour has preservative and antioxidant properties in addition to providing flavour and colour. In salad dressings, the most important property of the spice is its emulsifying function, binding water and oil phases as well providing viscosity. Mustard's fixed oil, which amounts to 30-35% by weight, is extracted by the cold pressed method. The oil is used for cooking in India and other Asian countries, including China and Japan
Mustard oil is extracted from the black mustard seeds, which have been macerated in warm water by steam or water distillation. Crude oil is dark brown in colour and contains a large proportion of free fatty acids. The refined oil is bland and light brown in colour. The characteristic odour of mustard oil is due to sulphur-containing essential oils produced by the hydrolysis of glucosides contained in the seeds. The quality of the mustard oil depends on the contents of the fatty acids and their percentage therein. Mustard oil is hazardous because of its high content of allyl isothiocyanate.
Essential oil is obtained by steam distillation of pressed cakes obtained after extraction of mustard oil (brown seed), after it has been hydrolysed by the enzyme myrosinase to release the allyl isothiocyanate from the glucoside. The essential oil of yellow mustard is obtained by solvent extraction of the press cake because it contains little or no volatile oil. Again, the press cake must first be hydrolysed to release the end products caused by the action of enzymes. Hydrolysis in either case is brought about by maceration of the press cake with warm water.
Oleoresin of mustard seed is usually obtained from a blend of the three different types of mustard to provide a balanced flavour. It is usually a yellow to light brown oily type of liquid with a volatile oil content of 5 ml per 100 g. Two kilograms is equivalent to 45.45 kg of the mustard spice.
Of the spices, condiments and herbs studied with respect to their effect on yeast fermentation in wines, etc., mustard flour was easily the most effective. It was found stronger than the two chemical preservative tried, viz. benzoic acid and sulphur dioxide (Pruthi, 1992). Mustard and its constituent allyl isocyanate have bacteriostatic and bactericidal properties (Charalambous, 1994).
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