Use of centrifugation-filtration for determination of syneresis in freeze-thaw starch gels

Several methods for measuring the freeze-thaw stability of starch gels can lead to inaccurate and imprecise estimates of syneresis due to partial reabsorption of separated water by spongy starch gels. This study evaluates a method that combines centrifugation with simultaneous separation of released water through a separator and filter paper. The evaluation procedure used low- and high-amylose rice flour gels treated to 5 freeze-thaw cycles. The traditional centrifugation method was unable to detect significant increases in syneresis (p < .05) of medium-amylose gel after 4 freeze-thaw cycles due to formation of a water reabsorbing spongy structure in 4-5 cycles. For high-amylose flour gel, which forms a spongy structure after the first freeze-thaw cycle, the traditional method did not detect significant change in syneresis values in any of the freeze-thaw cycles. In contrast, the centrifugation-filtration method, which actively separated released water and prevented its reabsorption, detected significant increases (p < .05) in syneresis with each cycle for medium-amylose flour gels. When using this method with high-amylose flour gel, we detected high syneresis values after the first cycle which stayed similar through 2-5 cycles indicating a progressive reduction in freeze-thaw stability of the samples which is consistent with the fact that high-amylose rice flour gels have less freeze-thaw stability than do gels made from medium-amylose flour. In conclusion, this study demonstrated that the centrifugation-filtration method measures syneresis with increased accuracy and precision. The authors recommend adoption of this method for determination of freeze-thaw stability in starch gels. (C) 2007 Elsevier Ltd. All rights reserved.