Rice contains starch.
Starch consists of a mixture of two glucose homopolysaccharides: amylose and amylopectin.
Starch content of most foods cannot be determined directly as starch is contained within a structurally and chemically complex food matrix. Starch often present in a semi-crystalline form (granular or retrograded starch) that is inaccessible to the chemical reagents used to determine its concentration. It is necessary to isolate starch from the other components present in the food matrix prior to carrying out a starch analysis.
The carbohydrate content of a food can be determined by calculating the percent remaining after all the other components have been measured: %carbohydrates = 100 - %moisture - %protein - %lipid - %mineral
Once the starch has been extracted there are a number of ways to determine its concentration:
i) Specific enzymes are added to starch solution to breakdown the starch to glucose. The glucose concentration is then analyzed using High Performance Liquid Chromography method. The starch concentration is calculated from the glucose concentration.
High Performance Liquid Chromography (HPLC) is the most important chromatographic method for analyzing carbohydrates as it is capable of rapid, specific, sensitive and precise measurements. In addition, in HPLC samples can often be analyzed directly.
ii) Iodine is 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.
Theory of HPLC
HPLC is commonly used, a separation technique whereby compounds in a mixture are separated on a stationary phase. The mobile phase containing the sample and the stationary phase are both liquids. HPLC separation is a function of the... [continues]
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