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.