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Determination of total ash content in food products

INTRODUCTION

Total ash refers to the inorganic residue remaining after the total incineration of organic matter present in food.

Because of its non-variable nature, the ash content can be used for assessing the quality of food products with respect to the presence of inorganic substances in it.

PRINCIPLE

Ash refers to the inorganic residue remaining after the total incineration of organic matter.

The ash content is determined by the loss of weight, which occurs from the complete oxidation of the sample at a high temperature of 500 to 600°C through combustion and volatilization of organic materials.

REQUIREMENTS

Apparatus

  • Flat-Bottom Dish – of stainless steel, porcelain, silica, or platinum.
  • Muffle Furnace maintained at 550±10°C.
  • Desiccator

PROCEDURE

  • Weigh accurately about 3 g of the material in the dish, previously dried in an air oven and weighed.
  • Heat the dish gently on a flame at first and then strongly in a muffle furnace at 550±10°C till grey ash results.
  • Cool the dish in a desiccator and weigh. Heat the dish again at 550±10°C for 30 minutes.
  • Cool the dish in a desiccator and weigh.
  • Repeat this process of heating for 30 minutes, cooling, and weighing until the difference between two successive weighings is less than 1 mg.
  • Record the lowest weight.

CALCULATION

Where,
W1 = weight, in g, of the empty crucible,
W2 = weight, in g, of the crucible with ash, and
W = weight, in g, of the test sample.

RESULTS AND INFERENCE

The difference between the results of two concurrent determinations carried out simultaneously or in rapid succession by the same analyst (repeatability) shall not exceed 0.05% by mass.

PRECAUTIONS

  • The temperature of ashing is varied from product to product.
  • The use of a higher temperature for ashing than the required temperature results low value of ash due to the loss of some inorganic matter like inorganic phosphate, sodium, etc.

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