|James Jr, Charles|
Submitted to: Starch/Starke
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2003
Publication Date: 7/15/2003
Citation: Guraya, H.S., James Jr, C., Champagne, E.T. 2003. Physical basis for separation of rice starch using various density gradient systems and its effect on starch recovery, purity and pasting characteristics. Starch/Starke. 55:450-456. Interpretive Summary: Rice starch is commercially purified for use by food industry. Laboratory purification methods are usually used to develop commercial methods or to select rice varieties for introduction into common use. The methods currently used by scientists to purify starches at the laboratory scale change the quality of the starch which results in erroneous results. Some of these methods use expensive salts (cesium chloride) and cannot be used routinely. We evaluated different salt systems for extraction and purifying starch and found the cheapest one. We also tried to understand the physical basis for purification of starch using these methods and found higher density of the salt results in increased starch purity and recovery. A cheaper method using mixture of sodium Chloride and sucrose can be used by breeders and starch manufacturers for preliminary evaluation of rice varieties for introduction into common use. The isolation of starch without artifacts will result in better understanding of the starch structure. This will lead to improved products and processes at a commercial scale.
Technical Abstract: A 32% waxy and non waxy rice flour slurry containing starch-protein agglomerates was physically disrupted in presence of water by use of high pressure homogenizer called microfluidizer®. Microfluidized rice flour slurry from passes 2 and 4 was collected followed by isolation of starch using three different density gradient solutions/systems (CeCl, NaCl/sucrose and ZnSO4.7H2O). Complete deagglomeration was obtained after passing the rice flour slurry four times through the microfluidizer. The recovery of isolated starch varied from 76.28% to 91.20% for different density gradient systems. The degree of deagglomeration did not seem to affect recovery but affected the purity of the isolated starches. All starches produced from pass 4 rice slurry resulted in starches with residual protein below 0.5%. Higher density of the gradient solution resulted in higher recovery and purity of starch. Isolation method had a significant effect on the pasting properties of the isolated starch. Residual protein in isolated starch had a negative correlation with peak viscosity and setback of pass 2 waxy and non-waxy starches. The salts were retained in purified starch despite rigorous washing (at least 75 times greater than the control) and could affect starch properties. Purified starch recovered using salt based density gradient systems cannot be used for starch structural studies.