itzacraze;1584587; said:
i dont believe ash is an ingredient!!
re http://www-unix.oit.umass.edu/~mcclemen/581Ash&Minerals.html 4. Analysis of Ash and Minerals
4.1 Introduction
- Nutritional labeling. The concentration and type of minerals present must often be stipulated on the label of a food.
- Quality. The quality of many foods depends on the concentration and type of minerals they contain, including their taste, appearance, texture and stability.
- Microbiological stability. High mineral contents are sometimes used to retard the growth of certain microorganisms.
- Nutrition. Some minerals are essential to a healthy diet (e.g., calcium, phosphorous, potassium and sodium) whereas others can be toxic (e.g., lead, mercury, cadmium and aluminum).
- Processing. It is often important to know the mineral content of foods during processing because this affects the physicochemical properties of foods.
4.2. Determination of Ash Content
can be distinguished from all the other components (the “matrix” within a food in some measurable way. The most widely used methods are based on the fact that minerals are not destroyed by heating, and that they have a low volatility compared to other food components. The three main types of analytical procedure used to determine the ash content of foods are based on this principle: dry ashing, wet ashing and low temperature plasma dry ashing. The method chosen for a particular analysis depends on the reason for carrying out the analysis, the type of food analyzed and the equipment available. Ashing may also be used as the first step in preparing samples for analysis of specific minerals, by atomic spectroscopy or the various traditional methods described below. Ash contents of fresh foods rarely exceed 5%, although some processed foods can have ash contents as high as 12%, e.g., dried beef. 4.2.1. Sample Preparation
As with all food analysis procedures it is crucial to carefully select a sample whose composition represents that of the food being analyzed and to ensure that its composition does not change significantly prior to analysis. Typically, samples of 1-10g are used in the analysis of ash content. Solid foods are finely ground and then carefully mixed to facilitate the choice of a representative sample. Before carrying out an ash analysis, samples that are high in moisture are often dried to prevent spattering during ashing. High fat samples are usually defatted by solvent extraction, as this facilitates the release of the moisture and prevents spattering. Other possible problems include contamination of samples by minerals in grinders, glassware or crucibles which come into contact with the sample during the analysis. For the same reason, it is recommended to use deionized water when preparing samples.
4.2.2. Dry Ashing
Dry ashing procedures use a high temperature muffle furnace capable of maintaining temperatures of between 500 and 600 oC. Water and other volatile materials are vaporized and organic substances are burned in the presence of the oxygen in air to CO2, H2O and N2. Most minerals are converted to oxides, sulfates, phosphates, chlorides or silicates. Although most minerals have fairly low volatility at these high temperatures, some are volatile and may be partially lost, e.g., iron, lead and mercury. If an analysis is being carried out to determine the concentration of one of these substances then it is advisable to use an alternative ashing method that uses lower temperatures.
The food sample is weighed before and after ashing to determine the concentration of ash present. The ash content can be expressed on either a dry or wet basis:
where MASH refers to the mass of the ashed sample, and MDRY and MASH refer to the original masses of the dried and wet samples.
