Abstract
Abstract The gelatinization of cationic starch during a heating-holding-cooling cycle in a batch cook was monitored by measuring 1H NMR spin-spin relaxation rates R2 on-line. The effect of storage time and temperature (8, 20 and 60 °C) on cationic starch retrogradation was also studied. Clear differences were measured between the gelatinization and retrogradation behavior of potato starch and cereal starches (wheat and barley). The potato starch gelatinized completely when cooked at 95 °C at normal pressure, whereas cereal starches gelatinized only partially. Partial gelatinization lead to rapid retrogradation upon cooling. For fully gelatinized starch, the beginning of retrogradation was slower and began at a lower temperature. NaCl and Na2SO4 did not have a significant impact on the gelatinization of wheat starch but did affect retrogradation. The results show that NMR-relaxometry is suitable for following starch gelatinization on-line from a batch cook and that it can be used to determine whether gelatinization is complete. This technique can thus be a useful tool in paper mills for the on-line quality control of starch solutions.
Highlights
Cationic starch is an essential additive in papermaking for improving the retention, strength, dewatering and formation of the product (BeMiller 2005, Stenius 2007)
The results show that NMR-relaxometry is suitable for following starch gelatinization on-line from a batch cook and that it can be used to determine whether gelatinization is complete
The gelatinization, i. e., cooking, can occur in a jet-cooker at elevated pressure at 120–160 °C, which is the most common method used in paper mills, or in a batch cooker at normal pressure at 90–95 °C (Lehtinen 2000), which is the method used in this study
Summary
Cationic starch is an essential additive in papermaking for improving the retention, strength, dewatering and formation of the product (BeMiller 2005, Stenius 2007). To make high-quality paper, starch must be properly gelatinized before it can be added to the paper machine, because only can it properly bond with cellulose fibers (Neimo 1999). Gelatinization begins with water diffusing into the amorphous part of the starch granules, which causes the granules to swell (Ritota et al 2008). After this effect, the crystalline portions of the granules begin to disintegrate as the double and single helices of amylopectin and amylose begin to unwind and hydrogen bonds begin to break (Wang et al 2015). In addition to a high temperature, shear forces are needed to disintegrate the remaining granules completely (Hermansson and Svegmark 1996)
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