Determination of total carbohydrates by anthrone method. Carbohydrates are the important components of storage and structural materials in the plants. Recently, Morse4 and Morris5 have described the use of anthrone for the quantitative estimation of carbohydrates. This method is both quicker and. The precise method of carbohydrate isolation depends on the carbohydrate type, solution as this would cause an underestimation of the carbohydrate content. The Anthrone method is an example of a colorimetric method of determining.
|Published (Last):||15 August 2005|
|PDF File Size:||3.22 Mb|
|ePub File Size:||17.98 Mb|
|Price:||Free* [*Free Regsitration Required]|
Sample Carbohyrrate The amount of preparation needed to prepare a sample for carbohydrate analysis depends on the nature of the food being analyzed. Cellulose is a long linear homopolysaccahride of glucose, typically having up to 10, glucose subunits. This can be achieved by adding chemicals that form an insoluble complex with one of the components, but not with the other, e. The fructose concentration is then determined by estimxtion the fructose into glucose, using another specific enzyme, and repeating the above procedure.
The absorbance at nm is proportional to the carbohydrate concentration initially in the sample. The two methods most commonly used to determine carbohydrate concentration are: It is usually associated with cellulose carboyhdrate hemicelluloses in plant cell-walls.
Prior to analysis, the alcohol can be removed from the solutions by evaporation under vacuum so that an aqueous solution of sugars remains.
Monosaccharides qnthrone measured using the various methods described previously. The food sample to be analyzed is therefore dried, ground to a fine powder and then the lipids are removed by solvent extraction.
A clear aqueous solution of the carbohydrates to be analyzed is placed in a test-tube, then phenol and sulfuric acid are added.
A number of chemical methods used to determine monosaccharides and jethod are based on the fact that many of these substances are reducing agents that can react with other components to yield precipitates or colored complexes which dstimation be quantified.
Once the starch has been extracted there are a number of ways to determine its concentration:. Proteins are usually broken down and solubilized using enzymes, strong acid or strong alkali solutions. On the other hand, many foods contain carbohydrates that are physically associated or chemically bound to other components, e. Titration Methods The Lane- Eynon method is an example of a tritration method of determining the concentration of reducing sugars in a sample.
Estimation of Proteins by Lowry method Colorimetric Analysis: Once all the copper sulfate in solution has reacted, any further addition of reducing sugars causes the indicator to change from blue to white.
Standards of Identity – foods must have compositions which conform to government regulations Nutritional Labeling – to inform consumers of the nutritional content of foods Detection of Adulteration – each food type has a carbohydrate “fingerprint” Food Quality – physicochemical properties of foods such as sweetness, appearance, stability and texture depend on the type and concentration of carbohydrates present.
A gelatinized sample of dry, defatted food is enzymatically digested with a- amylase, amyloglucosidase and protease to break down the starch and protein components. The basis of many fiber analysis techniques is therefore to develop a procedure that mimics the processes that occur in the human digestive system.
Hence, the starch can be separated from the sugars by filtering or centrifuging the solution. In its natural form starch exists as water-insoluble granules 3 – 60 m mbut in many processed foods the starch is no longer in this form because of the processing treatments involved e.
Polysaccharides can be classified according to their molecular characteristics e. The sulfuric acid causes all non-reducing sugars to be converted to reducing sugars, so that this method determines the total sugars present. The basic principle of this method is to isolate the fraction of interest by selective precipitation and then to determine its mass by weighing. The carbohydrates are then separated on the basis of their size: Carbohydrates can also be separated by electrophoresis after they have been derivitized to make catbohydrate electrically charged, e.
Crude fiber measures cellulose and lignin carbohydratr the sample, but does not determine hemicelluloses, pectins and hydrocolloids, because they are digested by the alkali and acid and are therefore not collected.
Some polysaccharides contain all the same kind of monosaccharide homopolysaccharideswhereas others contain a mixture of different kinds of monosaccharide heteropolysaccharides. The Phenol – Sulfuric Acid method is an example of a colorimetric method that is widely used to determine the total concentration of carbohydrates present in foods.
Non-polar molecules can be removed by passing a solution through a column with a non-polar stationary phase.
The monosaccharides and oligosaccharides are soluble catbohydrate the ethanol solution, while the starch is insoluble. This method uses a series of steps to determine the concentration of both glucose and fructose in a sample.
The insoluble component is collected from the filter, dried and weighed.
Specific enzymes are added to the starch solution to breakdown the starch to glucose. Iodine can be added to the starch solution to form an insoluble starch-iodine complex that can be determined gravimetrically by collecting, drying and weighing the precipitate formed or titrimetrically by determining the amount of iodine required to precipitate the starch.
Determination of Carbohydrate by Anthrone Method
By carrying out measurements at a number of different specific wavelengths it is possible to simultaneously determine the concentration of carbohydrates, proteins, moisture and lipids. Some polysaccharides can be digested by human beings and therefore form an important source of energy e. The overall angle of rotation depends on the temperature and wavelength of light used and so these parameters are usually standardized to 20 o C and The carbohydrate content of a food can be determined by calculating the percent remaining after all the other components have been measured: This method is therefore useful only when one knows the type of carbohydrates present, but not their relative concentrations.
The concentration of precipitate present can be determined gravimetrically by filtration, drying and weighingor titrimetrically by redissolving the precipitate and titrating with a suitable indicator.
A wide variety of polysaccharides occur in foods. Lignin is a non-carbohydrate polymer that consists of about 40 aromatic subunits which are estimatlon linked. By definition hemicelluloses are soluble in dilute alkali solutions, but insoluble in water.
7. ANALYSIS OF CARBOHYDRATES
In addition, GC requires caarbohydrate the samples anthroen volatile, which usually requires that they be derivitizedwhereas in HPLC samples can often be analyzed directly. For example, foods are usually dried under vacuum to prevent thermal degradationground to a fine powder to enhance solvent extraction and then defatted by solvent extraction. Starch is the most common digestible polysaccharide found in foods, and is therefore a major source of energy in our diets.