How to calculate Total Ash Content in a food sample?

When we incinerate a food material, it is left to ashes. The ashes mainly contain the minerals that were present in the food sample. Also, we know that minerals are inorganic in nature because they are not composed of Carbon or hydrogen atoms, instead, they are made of pure substances.

For example, Potassium, Calcium, magnesium carbonate, etc. are the minerals that are present in the wood ash.

burning wood producing ashes

Contents

Definition of Ash-

Ash is the inorganic residue remaining after the total incineration of the sample. The incineration occurs due to the presence of oxygen i.e. Oxidation of sample at high temperature of around 500°C-600°C. This is called Combustion. Also, during this combustion process, the organic compounds are much volatile and thus they are removed and only INORGANIC substances are left.

In this short post, we’ll see how to find the ash content of a food sample. Here, for example, let’s take sample as Potato fried food, also called Aloo Bhujia

Indian Fried Food namkeen Aloo Sev

Step by step procedure-

• Firstly grind the given sample.
• Pass through 1mm sieve.
• Use filtrate as a sample source

1. Weigh around 5g of the sample in a crucible. Make sure the crucible which we are taking is previously dried in a hot air oven and weighed separately the empty weight.

2. Firstly heat the crucible gently on a flame and then heat strongly in a Muffle Furnace at 550°C ±10°C till the grey ash comes.

a muffle furnace- Wikimedia commons

3. Now cool the dish in a desiccator and weigh it finally.

A desiccator

.

4. Repeat the whole 2 & 3, i.e., again heat it in the muffle furnace for 30minutes and then cool in a desiccator and then take the weight. This repetition will continue until the difference between the two successive readings is less than 1mg.

5. Finally, note the lowest weight of the repeated values obtained.

Hypothetical observations-

Empty weight of the crucible (W1)= 32.5089g

Sample + Empty weight of the crucible (before putting in muffle furnace)= 32.5089g

Sample + Empty weight of the crucible (after putting in muffle furnace) (W2)= 32.7089g

Calculations-

So, the final ash content in the sample is 4%.

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