Ash Content Determination

Abstract

Ash refers to the inorganic residue remaining after either ignition or complete oxidation of organic matter in a food sample. The inorganic residue consists mainly of the minerals present in the food sample. Determining the ash content is part of the proximate analysis for nutritional evaluation. Also, ashing is the first step in the preparation of a sample for specific elemental analysis. Two major types of ashing proce- dures are commonly used, dry ashing and wet ashing. Dry ashing is heating food at elevated temperatures (500–600 °C) in a muffle furnace. Water and volatiles will evaporate, and organic matter will burn in the presence of oxygen and convert to CO2 and oxides of N2 . In contrast, wet ashing is based on oxidizing organic matter using acids and oxidizing agents or their combination. Minerals are thus solubilized with- out oxidation. Food with high-moisture content, such as vegetables, is often dried prior to ashing. Food with high-fat content, such as meat, may need to be dried and their fat extracted prior to ashing. The ash content can be expressed on a wet basis or a dry basis.