ANALYTICAL cHEMISTRY - V

Experiment 4

Principle

Fiber content:

• Dietary fiber is mainly needed to keep the digestive system healthy. It also contributes to other processes such as stabilizing glucose and cholesterol levels. Disorders that can arise from a low fiber diet include: constipation, irritable bowel syndrome, heart disease, some low digestion concerns, etc.

• High fiber containing foods are-

Fruits: Bananas, Oranges, Apples, Mangoes, Strawberries, Raspberries

Vegetables: Carrots, Beets, Broccoli, etc.

Grains: Breads, grains, and nuts, as well.

• Definition of fiber - Dietary fiber is most frequently defined as polysaccharides and lignin that are not digested by human enzymes. Most Starch is readily digestive by human glucosidases.

• However, some starch escapes digestion in the small intestine and the starch that is not digested is called resistant starch. Since resistant starch is a plant polysaccharide it technically fits the definition of dietary fiber. Also another common definition of dietary fiber is lignin plus plant non starch polysaccharides. By this definition, resistant starch is not a component of dietary fiber.

Sequential removal of carbohydrates, proteins and fats from the wheat flour and refined wheat flour:

• Treatment with petroleum ether results in the removal of the fat content present in the wheat flour as the fats are soluble in the non-polar solvents like petroleum ether, carbontetrachloride (CCl₄), toluene, etc.

• On refluxing with 1.25% H₂SO₄ solution, the fat present within the cell walls gets dislodged. The starches are hydrolyzed to soluble saccharides. The soluble minerals are washed out and some of the proteins are hydrolyzed to soluble forms.

• Treatment with 1.25% NaOH solution results in the hydrolysis of remaining proteins. This treatment removes tannins and fats. The fats form soaps and are washed out during hot water washings. The un-reacted alkali and the sodium soaps must be completely washed off otherwise, after washing, free alkali gets converted to its oxide leaving black residue even after ignition in the muffle furnace.

Apparatus required

Round bottom flask (250 mL), Water/air condenser, Funnel, Whattmann filter paper No. 1, Beaker, etc.

Chemicals required

Wheat flour, Refined wheat flour, Petroleum ether, 1.25 % H₂SO₄ solution (200 ml), 1.25 % NaOH solution (200ml), etc.

Preparation of reagents

1. 1.25 % H₂SO₄ solution: Take 3.125 ml of concentrated H₂SO₄ and make up the volume to 250 ml in a 250 ml volumetric flask.

2. 1.25 % NaOH solution: Take 3.125 g of NaOH and make up the volume to 250 ml in a 250 ml volumetric flask.

Procedure

• Weigh 3 g of flour and add it to a round bottom flask containing 200 ml of petroleum ether. Heat under reflux conditions for one hour to allow all the fats to solubilize. Filter the contents after cooling to room temperature.

• Now, dissolve the residue in 200 ml of 1.25% H₂SO₄ solution and heat the contents for half an hour in a round bottom flask under reflux conditions. Allow the contents to come to room temperature. Filter it and wash with hot water till it becomes neutral.

• Dissolve the residue in 1.25 % 200 ml NaOH solution and heat the contents in round bottom flask under reflux conditions for half an hour. Allow the contents to come to room temperature and filter it. Wash with hot water till it becomes neutral. Let the residue dry and weigh it in a pre weighed filter paper (Whattmann filter paper No.1).

Calculation

Weight of filter paper = ____________ g.

Weight of filter paper + fiber = ____________ g.

Weigh of fiber = _____________ g.

Fiber content in 3 g flour = ____________ g.

Fiber content in 100 g flour = ____________ g.

About the sample :

Name and brand = _______________.

% Error calculations:

Reported value of fiber = ______________ g. (dietary fiber per 100 g)

% Error = _________________ .

Result

Fiber content per 100 g = _____________ g.

Reported value = _______________ g.

% Error = _____________ .

Reference Material

1. G H Jeffery, J Bassett, J Mendham and R C Denney, Vogel's Textbook of Quantitative Chemical Analysis, 5th Edition

2. S. Suzanne Nielsen, Food analysis, 4th Edition

Questions