What is Crude Fiber?
Crude fiber is the residue of plant materials remaining after solvent extraction followed by digestion with dilute acid and alkali. The amount of indigestible cellulose, hemicellulose, and lignin in plant-based foods is measured in the diet as “crude fiber.” It is a component of the proximate analysis of food, a technique for determination of crude fiber to analyze the nutritional value of food.
The crude fiber content of a food sample is determined by subjecting the sample to a series of chemical treatments to remove all soluble and easily digestible components, such as sugars, starches, and proteins. Crude fiber is considered as the residual byproduct.
Principle
The main objective of crude fiber analysis is to determine the presence of indigestible ingredients including cellulose, hemicellulose, and lignin in in a food sample. These substances are mostly present in the cell walls of plant-based foods and are not degraded by digestive enzymes in the gastrointestinal tract.
The method for determining crude fiber in foods involves a series of chemical treatments to remove all soluble and easily digestible components from the sample. Proteins, starches, and sugars are normally eliminated while leaving the fiber component behind by acid and alkali treatments.
The remaining fiber components is then wash, dry, and weigh the residual fiber component. The weight of the crude fiber is calculated as a percentage of the initial weight of the food sample. Since it eliminates certain types of lignin and pectin, which might be partly digested, the crude fiber content of a food sample is regarded as an approximate of the total dietary fiber content but is not an accurate measurement.
Apparatus Required for Determination of Crude fiber
- Balance machine
- Muffle furnace
- Hot plate
- Hot air oven
- Measuring cylinder
- Conical flask
- Funnel
- Volumetric flask
- Beaker
- Crucible
- Cotton cloth
Chemical preparation for Determination of Crude Fiber in Food Sample
0.128M Sulfuric Acid
- Fill the volumetric flask with 400ml (approx.) distilled water.
- Transfer 3.5ml of sulfuric acid (98%) to the same flask.
- Wash the pipette to ensure that no acid is left on the surface.
- Rotate the flask to mix the solution and add water to make the final volume of 500ml.
0.313M Sodium Hydroxide
- Take 6.25g of NaOH pellets.
- Fill the volumetric flask with 400ml distilled water.
- Transfer the weighted NaOH to the same flask.
- Shake the flask to dissolve NaOH pellets in water and after that, add water to make the final volume of 500ml.
Procedure of determining crude fiber in Food sample
Step-1
Boiling in Acid
- Measure 200ml of 0.128M sulfuric acid and pour the acid solution into a 500ml conical flask.
- Take a homogenized portion of sample (about 2gm) to weight.
- Transfer the sample into conical flask to mix with Acid solution.
- Place the flask on a hot plate and bring to boil the sample for 30min.
- Shake the conical flask periodically to ensure the proper boiling of sample.
- After 30 min of boiling, take a discard conical flask of 100ml.
- Set a funnel with cotton cloth with the discard flask.
- Filter the boiled sample to drain the acid solution.
- Wash the conical flask with hot water to remove the acid residue completely.
- Also, wash the filtrate with hot water to remove the acid solution.
- Again, place another funnel to the cleaned conical flask and measure 200ml of 0.313M NaOH solution.
- Pour the NaOH solution into the conical flask washing the filtrate.
- Shake or rotate the flask to mix and place on hot plate.
Step-2
Boiling in Base
- Boil the sample with another 30min.
- Shake the conical flask periodically to ensure the proper boiling of sample.
- After 30min of boiling, again filter the sample to drain NaOH solution.
- Wash with hot water to remove NaOH residue completely.
- Collect the filtrate in a clean and dried crucible till no filtrate is left.
Step-3
Drying Fiber
- Place the crucible filled with fiber on hot plate to evaporate the excess water.
- Now, place the crucible in the Hot Air Oven at 230°C for 2 hrs.
- After 2 hrs., take out the crucible from the hot air oven and cool in desiccator.
- After 20min, take weight of crucible containing fiber and note the weight.
- Cover the crucible with its lid.
Step-4
Incineration of fiber
- Place the crucible inside the muffle furnace and burn the fiber at 550°C for 2 hrs.
- After 4 hrs., takeout the crucible from muffle furnace and cool in desiccator.
- Take weight of the crucible containing ash and note the weight.
Step-5
Calculation
Crude fiber % = 
´100
Where,
- Ws is weight of sample
- W1 is weight of crucible with fiber
- W2 is weight of crucible with Ash
Application of determination of crude fiber
The application of crude fiber analysis is primarily in the evaluation of the nutritional quality of animal feed and some plant-based foods.
- Animals Feed: Crude fiber analysis is used to determine the quantity of indigestible structural carbohydrates in animal feed. This information is essential because it aids farmers and producers of animal feed in evaluating the nutrient content of the feed and determine the appropriate amount to feed their livestock.
- Food Industry: In the food industry, crude fiber analysis is also used to assess the fiber content of certain plant-based foods such whole grains, vegetables, and fruits. This information is important for food manufacturers who want to produce high-fiber foods that provide health benefits to consumers.
- Research: The effects of dietary fiber on health outcomes, such as improving digestion, reducing cholesterol levels, and preventing chronic illnesses like heart disease and diabetes, are also studied in research using crude fiber analysis.
Health Benefits of Crude Fiber
Crude fiber, which is primarily composed of cellulose, hemicellulose, and lignin, provides numerous health benefits when included in a well-balanced diet. Here are some of the key health benefits of crude fiber:
- Improved Digestion: Crude fiber acts as a natural laxative, promoting regular bowel movements and preventing constipation. Additionally, it helps to balance out the good bacteria in the stomach, which promotes healthy digestion and reduces the risk of illnesses of the digestive system including inflammatory bowel disease (IBD).
- Reduced Cholesterol level: A high-fiber diet has been showed to reduce cholesterol levels, especially LDL cholesterol (the “bad” cholesterol), which is linked to the development of arterial plaque. This can help to reduce the risk of heart disease and stroke.
- Weight Managements: Crude fiber-rich foods have a tendency to have few calories and may help in promoting satiety and fullness sensations. For those attempting to control their weight or reduce weight, this can be very useful.
- Blood Sugar Regulation: Crude fiber can help to regulate blood sugar levels by slowing down the absorption of glucose in the bloodstream. People with diabetes or those who are at risk for getting the disease may benefit from this.
- Reduced Risk of Chronic Diseases: Consuming sufficient amounts of fiber from food has been associated with a lower risk of chronic conditions like heart disease, stroke, type 2 diabetes, and several cancers.
Foods high in crude fiber include whole grains, fruits, vegetables, legumes, nuts, and whole grains. It’s important to understand that a food’s crude fiber content is different from its total fiber content. Other types of fiber, such as some forms of lignin and pectin, are not included in crude fiber analysis and can also provide health benefits.
Overall, crude fiber analysis is an effective tool to determine the nutritional value of animal feed and some plant-based foods, but it’s essential to interpret the results in the context of other nutritional factors and take into account using different methods to more accurately determine the total fiber content of foods.
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