Ash refers to the inorganic residue remaining after either ignition or complete oxidation of organic matter in a foodstuff. A basic knowledge of the characteristics of various ashing procedures and types of equipment is essential to ensure reliable results. Two major types of ashing are used: dry ashing, primarily for proximate composition and for some types of specific mineral analyses; wet ashing (oxidation), as a preparation for the analysis of certain minerals. Microwave systems now are available for both dry and wet ashing, to speed the processes. Most dry samples (i.e., whole grain, cereals, dried vegetables) need no preparation, while fresh vegetables need to be dried prior to ashing. High-fat products such as meats may need to be dried and fat extracted before ashing. The ash content of foods can be expressed on either a wet weight (as is) or on a dry weight basis. For general and food-specific information on measuring ash content, see references (1–11).
KeywordsMuffle Furnace Volatile Element Microwave System Microwave Furnace Ferrous Perchlorate
- 2.AOAC International (2007) Official methods of analysis, 18th edn., 2005; Current through revision 2, 2007 (On-line). AOAC International, Gaithersburg, MD. This contains the official methods for many specific food ingredients. It may be difficult for the beginning student to followGoogle Scholar
- 6.Neggers YH, Lane RH (1995) Minerals, ch. 8. In: Jeon IJ, Ikins WG (eds) Analyzing food for nutrition labeling and hazardous contaminants. Marcel Dekker, New York. This chapter compares wet and dry ashing and summarizes in tables the following: losses of specific elements during dry ashing; acids used in wet oxidation related to applications; AOAC methods for specific elements related to food applicationsGoogle Scholar
- 7.Pomeranz Y, Meloan C (1994) Food analysis: theory and practice, 3rd edn. Chapman & Hall, New York. Chapter 35 on ash and minerals gives an excellent narrative on ashing methods and is easy reading for a student in food chemistry. A good reference list of specific mineral losses is given at the end of the chapter. No stepwise procedures are givenGoogle Scholar
- 8.Smith GF (1953) The wet ashing of organic matter employing hot concentrated perchloric acid. The liquid fire reaction. Anal Chim Acta 8:397–421. The treatise gives an in-depth review of wet ashing with perchloric acid. Tables on reaction times with foodstuffs and color reactions are informative. It is easy for the food scientist to understandCrossRefGoogle Scholar
- 9.Wehr HM, Frank JF (eds) (2004) Standard methods for the examination of dairy products, 17th edn. American Public Health Association, Washington, DC. This text gives detailed analytical procedures for ashing dairy productsGoogle Scholar
- 10.Wooster HA (1956) Nutritional data, 3rd edn. H.J. Heinz, Pittsburgh, PAGoogle Scholar