practical 6 determination of ash

PRACTICAL 6 Determination of Ash. Introduction : Ash is defined as the inorganic residue remaining after a process ,burning. Burning will remove the water and organic matter in the presence of oxidizing agents. Complete burning will indicates the ash content by measuring the information of white ash. Ash content is a measure of the total amount of minerals within a food. Minerals distinguish from all the other components within a food in some measurable way are the only method of analytical techniques applied and give the minerals content information .Nowadays, commonly used methods are based on the fact that minerals are not destroyed by heating, and they have a low volatility compared to other food component. Dry ashing , wet ashing and low temperature plasma dry ashing are the three main types of analytical procedure used to determine the ash content of foods. Different condition will need different method for analysis. Therefore, the method chosen must consider on the reason for carrying out the analysis, the types of food analysed and the equipment available. Theoretically, we should know that ash content of fresh foods rarely exceed 5%, although some processed foods can have ash contents as high as 12% such as dried beef. Ashing method is a dry ashing. It was a high temperature muffle furnace capable of maintaining temperatures of between 500 and 600’ C. Normally, in these high temperature, water and volatile materials will vaporize whereas the organic substances will convert to CO2, H2O and N2 when they are burned in the presence of the oxygen in air. Although most minerals have fairly low volatility at these high temperatures, some are volatile and may be partially lost such as iron, lead and mercury. It is more advisable to use alternative methods that using lower temperature when analysis of determining concentration of the substances. This advice will prevent the problems cause by high temperature. There are many advantages of dry ashing. They are safe, few reagent are required, many samples can be analysed. The purpose of this study is to understand the importance of minerals content in food, analysis and nutrient requirement.

Total Ash Method.

Objective : To determine the total ash content of food sample using dry ashing method.

Principle : Dry ashing refers to incinerations of food samples at high temperature ( 500 to 600 ‘ C ) using muffle furnace. Water and volatile compound are vaporized, while organic substances are burned in the presence of oxygen in air to CO2 and oxides of N2 . Most minerals are converted to oxides, sulfates, phosphates , chlorides and silicates.

Apparatus : Porcelain dish, analytical balanced , Bunsen burner , oven, muffle furnace and tongs.

Procedure : 1. The shallow porcelain dish was dry in oven at 105’ C for 3 hour. The porcelain dish was cool it in a dessicator and weight soon after it has attained room temperatures. 2. 5 g of the homogenised food sample was weight accurately into a porcelain dish. The 3. 4. 5. 6.

sample with high moisture, must dry in an oven at 130’C for one day. The dried sample was char gently over at Bunsen burner until it has ceased smoking. The dish was place in muffle furnace and heat at 500’C for 3 hours. The sample was ash until a whitish or greyish ash is obtained. The dish was remove, cool in desiccator and weigh soon after attaining room

temperature. 7. The dish was replace in muffle furnace and continued heating until a constant weight was obtained. 8. The total ash content of the food sample was calculated .

Result :

Table 6.1 : Determination of Total Ash Data

Sample

Oat

Trial

1 2 3 Mean

Wt of sample

Wt of

Wt of

(g)

crucible (g)

crucible +

5.0009 5.0130 5.0046 5.0061

41.9780 39.4248 35.9231 39.1086

ash (g) 42.0345 39.4813 35.9650 39.1602

% Total ash

1.31% 1.13% 0.84% 1.03%

Calculation : g ash per 100 g the total sample = weight of ash (g) ÷ weight of sample (g) × 100 Trial 1 = (42.0345-41.9780) ÷ 5.0009 = 0.0113 = 0.0113 × 100 = 1.13 % Trial 2 = ( 39.4813 – 39.4248 ) ÷ 5.0130 = 0.0113 = 0.0113 × 100 = 1.31% Trial 3 = ( 35.9650 – 35.9231 ) ÷ 5.0046 = 0.0084 = 0.0084 × 100 = 0.84 %

Acid- Insoluble Ash Method. Introduction :

Acid- Insoluble ash method is designed to measure the amount of ash insoluble to diluted hydrochloric acid.

Principle : The total ash of sample is heated with hydrochloric acid, filtered and weighed . The acid insoluble ash is a measure of the sandy matter or mineral contaminants in foods.

Apparatus : Porcelain dish, watch glass, filter paper , analytical balanced and Bunsen burner.

Chemical : Hydrochloric acid.

Procedure : 1. The ash obtained was boil above with 25 ml dilute HCl ( HCl : H2O = 1:2:5 ) for 5 minutes. 2. The dish need to cover if necessary with watch glass to prevent spattering. 3. The insoluble matter was collect by filtering through an ashless filter paper and thoroughly wash with hot water until washing are acid-free. 4. The filter paper was ignite in the original dish. 5. The dish was cool and weigh. 6. The acid-insoluble content obtained was calculate.

Result : Table 6.2 : Determination of Acid-Insoluble Ash Data

Sample

Trial

1 2 3

Oat Mean

Wt of sample

Wt of

Wt of

% Acid-

(g)

crucible (g)

crucible +

Insoluble

acid-

Ash

0.0419 0.0565 0.0565 0.0516

35.9231 39.4248 41.9780 39.1086

Calculation : a) g acid-insoluble ash / 100 g the total sample: = weight of acid-insoluble ash (g) ÷ weight of sample × 100 b) g acid-insoluble ash / 100 g the total ash : = weight of acid-insoluble ash (g) ÷ weight of ash (g) × 100 c) acid soluble ash (%) = % total ash - % acid-insoluble ash

Trial 1 a) = ( 35.9231- 35.8905 ) ÷ 0.0419 × 100 = -77.80% b) = 0.0124 / 0.0113 × 100 = 288.50% c) = 1.13% -77.80 % = 76.67%

Trial 2 a) = (39.4124 - 39.4248 ) ÷ 0.0565 × 100 = -21.95% b) = 0.0326 / 0.0113 × 100 = 288.50%

insoluble (g) 35.8905 39.4124 41.9657 39.0895

77.80% 21.95% 21.77% 40.51%

c) = 1.13% -21.95% = 20.82%

Trial 3 a) = (41.9657 – 41.9780 ) ÷ 0.0565 × 100 = -21.77% b) = 0.0123 / 0.0084 × 100 = 146.43% c) = 21.77% - 146.43% = 124.66%

Discussion : Generally, ash content is a measure of the total amount of minerals present within a food. The higher the ash content, the higher the minerals content in the food. Ash is the inorganic residue remaining after the water and organic matter have been removed by heating in the presence of oxidizing agents, which provides mineral content, a measure of the total amount

specific inorganic components within a food. The ash content of each food will be different due to the different mineral content in each food and the origin of the food .For instance, the sample of my group is oat. Analytical technique for the mineral content are based on the minerals that can be distinguished from all the other components within the food sample. According to the theory for dry ashing, different food has different ash content. For this experiment , the calculation shows that there is different between the theoretical ash with experimental ash content. We believe that the difference due to several reasons. We believe some of the mineral may have eliminated during the experiment due to the volatile property and the temperature of the analytical equipment. They are volatility of minerals, ability of mineral to react with specific chemical reagent to give measurable changes and unique electromagnetic spectra of minerals. For instance, some of the food varies with minerals content due to the minerals eliminated while the food in high temperature. The temperature causes the minerals to gone and reduce. Generally , from sight of theory, determination of the ash and mineral content in the food using analytical technique are importance. The data provided are importance for nutritional labelling. The concentration and type of minerals present able to be stipulated on the label of a food. Some minerals are essential to a healthy diet such as calcium, potassium, and sodium whereas others can be toxic such as lead, mercury, cadmium and aluminium. For this experiment, we get result for mean total ash is a 1.03 % from our sample oat .The total mean acid – insoluble ash is a 40.51 % . For this experiment, we already do the best to do it the experiment but we think there some mistake that we do. For the next , we will be carefully handle this experiment more better than this.

Conclusion :

References : 1. 2. 3. 4.

http://people.umass.edu/~mcclemen/581Ash&Minerals.html http://www.farine-mc.com/2009/09/flour-ash-content.html http://www.scribd.com/doc/25575913/Determination-of-Ash Book : Fennema, Oven.R ., 1996. Food chemistry, 3rd Ed, Marcel Dekker, Inc, New York.

Question :

1. How do you know that the ash is free from carbon ?

We can assess the presence or absence of carbon in ash from the colour of the ash:If ash is greyish to blackish in colour then carbon is present in the ash. If ash is bluish grey to brown in colour then the ash is free of carbon.

2. Why is the sample need to be heated over a Bunsen burner before heating in a muffle furnace ?

3. Why the acid-insoluble ash determination is important in the quality control of certain food?.