Ash content in food

Ash or mineral content is the portion of the food or any organic material that remains after it is burned at very high temperatures.

The ash constituents include potassium, sodium, calcium and magnesium, which are present in larger amounts as well as smaller quantities of aluminum, iron, copper, manganese or zinc, arsenic, iodine, fluorine and other elements present in traces.

Ash content represents the total mineral content in foods. Although minerals represent a small proportion of dry matter, often less than 7% of the total, they play an important role from a physicochemical, technological and nutritional point of view.

Determining the ash content may be important for several reasons. It is part of proximate analysis for nutritional evaluation. Ashing is the first step in preparing a food sample for determination of specific elemental analysis.

When powdered foods, are heated to a temperature of about 500°C for at least four hours, the water and other volatile constituents are evolved as vapors and the organic constituents are burnt off in the presence of oxygen of the air, to carbon dioxide and oxides of nitrogen and also eliminated together with hydrogen as water.

The ash content of most fresh foods rarely is greater than 5%. Pure oils and fats generally contain little or no ash; products such as cured bacon may contain 6% ash and dried beef may be as high as 11.6% based on weight basis.

Ash content is a widely accepted index of refinement of foods, such as wheat flour or sugar. Since the mineral content of the bran is about 20 times that of the endosperm, the ash test is reliable indicator of the efficiency of which the separation of bran and germ from the rest of the wheat kernel.
Ash content in food

What is ash content?

What is ash content?
When either organic compounds are decomposed or released at high temperature (500C -600C), the remaining residue is the ash.

This residue consists of oxides and salts containing anions such as phosphates, chlorides, sulfates, and other halides and cations such as sodium, potassium, calcium, magnesium, iron, and manganese.

During the ashing process organic salts decompose, losing the carbon-containing moiety. The metal from such salts forms and oxide or reacts with other anions of the matrix. Some metals (e.g., cadmium and lead) may be volatized during ashing; therefore, if the ash is to be examined for trace elements, care should be exercised to prevent losses during ashing.

For most foods, ashing at 485C or less for 12hrwill give acceptable results for trace elements analysis. Losses of minerals due to carbon release can be appreciable from carbon-containing samples.

This mechanical loss of cash can be avoided by starting the incineration in the muffle furnace at a low temperature (room temperature) and allowing the temperature to rise slowly.

Air currents may be a problem if the door of the furnace is opened suddenly. Generally, samples should not be placed ion areas of the furnace closer than 1 in. from the rear wall and 1.5 in form the front.
What is ash content?