This document discusses methods for determining the ash and mineral content of foods. Ash content refers to the total amount of minerals, which is determined by heating to remove organic matter. Mineral content refers to specific inorganic components. There are three main types of ashing: dry ashing uses high heat to burn organic matter; wet ashing uses acids to digest organic matter; and plasma ashing uses ionized gases. The chosen method depends on the analysis and equipment. Sample preparation is also important to obtain representative and contaminant-free results.

1. Analysis of
Ash & Minerals

2. Dry Matter
1. Organic compounds:
– Carbohydrates
– Lipids
– Proteins
– Nucleic acids
– Vitamins
– Organic acids
2. Inorganic Compounds:
- Minerals

3. • “Ash content” - total amount of minerals
present within a food.
• “Mineral content” - amount of specific
inorganic components present within a food,
such as Ca, Na, K and Cl.

4. Determination of Ash Content
• Ash - inorganic residue remaining after water and
organic matter removed by heating in the presence
of oxidizing agents.
• Principle: Minerals are not destroyed by heating,
and they have low volatility compared to other
food components.

5. • Main types Ashing: dry ashing, wet ashing,
plasma ashing
• Method chosen depends on the reason for
carrying out analysis, type of food analyzed
and equipment available

6. Sample Preparation
• Representative sample.
Typically, samples of 1-10g are used.
Solid foods are finely ground and carefully mixed
(representative sample).

7. • Before ash analysis, samples high in moisture are
dried to prevent spattering.
• High fat samples are defatted by solvent extraction
(facilitates release of moisture and prevents
spattering).
• Avoid contamination of samples by minerals in
grinders, glassware or crucibles etc.

8. Dry Ashing
• Use a high temperature muffle furnace (To between 500
and 600oC).
• Water and other volatile materials are vaporized and
organic substances are burned in the presence of O2 in
air to CO2, H2O and N2.
• Most minerals are converted to oxides, sulfates,
phosphates, chlorides or silicates.

9. • Some minerals are volatile and may be
partially lost, e.g., iron, lead and mercury.
• For such minerals - use an alternative ashing
method that uses lower temperatures.

10. • 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:

11. • The following data was obtained on a sample of hamburger:
sample wt, 2.034 g ; wt after drying, 1.0781 g; and wt of ash,
0.0233 g.
What is the percentage ash on a) a wet weight basis and b)
dry-weight basis?
Wet Basis Ash % = (0.0233 / 2.034) *100
= 1.15 %
Dry Basis Ash % = (0.0233 / 1.0781) * 100
= 2.16 %

12. • Different types of crucible - quartz, Pyrex,
porcelain, steel and platinum.
• Selection depends on sample being analyzed and
furnace temperature used.
• Most widely used - porcelain (relatively
inexpensive, resistant to high temperatures
(< 1200oC) and easy to clean).

13. Platinum
Pyrex
Porcelain
Quartz

14. • Advantages: Safe, few reagents are required, many
samples can be analyzed simultaneously, not labor
intensive, and ash can be analyzed for specific
mineral content.
• Disadvantages: Long time required (12-24 hours),
muffle furnaces are quite costly to run due to
electrical costs, loss of volatile minerals at high
temperatures, e.g., Cu, Fe, Pb, Hg, Ni, Zn.

15. Wet Ashing
• Primarily used in preparation of samples for specific
minerals analysis.
• It breaks down and removes organic matrix
surrounding minerals and left them in an aqueous
solution.
• A dried ground food sample weighed into a flask
containing strong acids and oxidizing agents (e.g., nitric,
perchloric and/or sulfuric acids) heated.

17. • Heating is continued until organic matter is
completely digested, leaving only mineral oxides in
solution.
• Temperature and time - depends on type of acids
and oxidizing agents used.
• Typically, a digestion takes from 10 minutes to a
few hours at about 350oC.
• Resulting solution can be analyzed for specific
minerals.

18. • Advantages: Little loss of volatile minerals
occurs because of the lower temperatures used,
more rapid than dry ashing.
• Disadvantages: Labor intensive, requires a
special fume-cupboard if perchloric acid is used
because of its hazardous nature, low sample
throughput.