Thursday, May 07, 2009

What’s That Smell?




What’s That Smell?
Porcini or "beliy grib"

Russian biophysicists and economists found out, which components form smell of porcini (Boletus edulis) and oyster mushrooms (Pleurotus ostreatus). Scientists advise how to cook these mushrooms to preserve their delicious aroma.

Scientists know about 150 volatile chemical compounds, which are responsible for mushroom odour. Quantitative and qualitative composition of these compounds strongly depends on mushroom species, conditions of their growth, and even what part of a mushroom emits odour. Porcini are among tastiest and smelliest mushrooms in Russia, and oyster mushrooms are very popular in our country.

Researchers collected porcini in forests of Smolensk and Tver Regions, and as for oyster mushrooms, they were grown in an agroindustrial firm. Since mushroom lovers mostly care about smell of already coked mushrooms, they were boiled, and porcini were also pickled without any spices to keep natural aroma intact.

Volatile substances from porcini consisted from over 100 chemical compounds, moreover, amount of some compounds was extremely faint: several nanograms in 100 grams of mushrooms. Aroma of oyster mushrooms is not so rich, it contains only 50 volatile substances.

”Oyster
Oyster mushrooms
Heat treatment (boiling, roasting, preserving or drying) has a great effect of composition of volatile substances, that is why cooked mushrooms smell differently than raw ones. Porcini, no matter boiled or pickled, contain substances with strong smell of raw, boiled and roasted mushrooms, as well as mushroom soup. Oyster mushrooms have the same, but less intensive smell. Sometimes mushroom mix smells not like its individual components, and the reason is that some volatile substances can change odour significantly, being the minor part of the smell. Alkyl pyrazines, for instance, smell like roasted mushrooms and add hints of mushrooms aroma to various substances, which smell in a different way.

Raw mushrooms owe their smell mainly to alcohols, compound esters and ketones with eight carbon atoms. Raw porcini contain significant amount of alcohols, pickled ones have less, and boiled porcini contain traces of alcohols, which is possible due to loss of alcohols during heat treatment. Oyster mushrooms also contain eight-carbon alcohols, but much less than porcini. However, key chemicals, which form mushroom smell, are ketones. Mushrooms contain only traces of ketones, but their smell is very strong.

When mushrooms are exposed to heat, sugars and amino acids start chemical interaction, known as Maillard reaction. This reaction results in many compounds, including volatile substances, which smell like cooked mushrooms. Most important component of this smell is called “methional”, which has very intensive smell and changes odour of raw mushrooms despite its low content in them. Since volatile substances in Maillard reaction depend on concentration of free amino acids and monosaccharides, mushroom smell can possibly become even more intensive, when glucose or sucrose are added during cooking.

Moreover, researchers believe that for strong smell of cooked mushrooms, they should be exposed to heat very shortly and without air – this prevents smelly substances from degrading and oxidizing.

Source: Science News

Kizilova Anna

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