Effect of Acid and Sugar on the Rheology and Flow Properties of Corn Starch Paste
10/08/08 Brandy Ogg
Ms. Winston MPH, RD, CDE FCS 373
Lab # 2
Introduction
The purpose of this lab is to determine the effects acid and sugar in various amounts have on a cornstarch paste. The importance of this experiment is to examine what causes starch to thicken or thin which is relevant to obtaining the desired viscosity for recipes that involve starch cookery without complication. Factors to be considered in the thickening power of cornstarch include the concentration of starch, extent of gelatinization thus temperature and duration of heat, and the addition of sugar or salt (1).
Background
Gelatinization, a physical change, occurs when starch is heated in water. Due to the solubility of the amylose in the starch granule it migrates out causing hydrogen bonds to break between the amylose and amylopectin as water enters the granule. The amylopectin within the starch granule forms a bond to the hydrogen from the influx of water and swelling occurs. As a result, less free water is available and the mixture is thickened. With continued heating, past the point of gelatinization, viscosity is lost and the granules become compressed resulting in a paste (2).
Method and Materials
Each method was prepared by a separate group and results were recorded for collective use. Method A served as the control which included one tablespoon (16 g) of cornstarch heated in an aluminum pot with the gradual addition of one cup of water (236 ml). The mixture was stirred prominently to prevent lumping while the boiling temperature was reached. The mixture was removed from the heat after boiling and allowed to cool at room temperature until 60 degrees C (140 degrees F) was measured using a thermometer. A line spread test was performed to measure the spread of ¼ cup of the warm mixture. A metallic cylinder held the paste until it was released onto the line spread mat. After 30 seconds of flowing, four readings were recorded to average the spread. This
Ms. Winston MPH, RD, CDE FCS 373
Lab # 2
Introduction
The purpose of this lab is to determine the effects acid and sugar in various amounts have on a cornstarch paste. The importance of this experiment is to examine what causes starch to thicken or thin which is relevant to obtaining the desired viscosity for recipes that involve starch cookery without complication. Factors to be considered in the thickening power of cornstarch include the concentration of starch, extent of gelatinization thus temperature and duration of heat, and the addition of sugar or salt (1).
Background
Gelatinization, a physical change, occurs when starch is heated in water. Due to the solubility of the amylose in the starch granule it migrates out causing hydrogen bonds to break between the amylose and amylopectin as water enters the granule. The amylopectin within the starch granule forms a bond to the hydrogen from the influx of water and swelling occurs. As a result, less free water is available and the mixture is thickened. With continued heating, past the point of gelatinization, viscosity is lost and the granules become compressed resulting in a paste (2).
Method and Materials
Each method was prepared by a separate group and results were recorded for collective use. Method A served as the control which included one tablespoon (16 g) of cornstarch heated in an aluminum pot with the gradual addition of one cup of water (236 ml). The mixture was stirred prominently to prevent lumping while the boiling temperature was reached. The mixture was removed from the heat after boiling and allowed to cool at room temperature until 60 degrees C (140 degrees F) was measured using a thermometer. A line spread test was performed to measure the spread of ¼ cup of the warm mixture. A metallic cylinder held the paste until it was released onto the line spread mat. After 30 seconds of flowing, four readings were recorded to average the spread. This
Bibliography: 1.McWilliams M. Food Fundamentals. (8th ed.) New Jersey: Pearson Prentice Hall 2006. 2.McWilliams M. Foods: experimental perspectives. (6th ed.) New Jersey: Pearson Prentice Hall 2008.