Jet-cooked papermaking starches studied using 1H NMR-relaxometry and viscometry

Jenna Raunio,Ekaterina Nikolskaya,Yrjö Hiltunen

doi:10.1515/npprj-2019-0092

Abstract

Abstract Two wet-end starches (potato and barley), one surface sizing starch (barley) and one coating binder starch (barley) were jet-cooked. Samples were collected and stored at 90, 60 and 40 °C. 1H NMR-relaxometry and viscometry were used to monitor the jet-cooked solutions as they cooled to room temperature. Samples stored at different temperatures were also monitored using 1H NMR-relaxometry and viscometry. A sediment formed into the surface sizing and coating binder starches stored at 90 °C. The sediment and supernatant were separated and collected, and measured using 1H NMR-relaxometry. The T 2 {T_{2}} relaxation rates of jet-cooked starches showed significant differences between potato and barley starches, as had also been examined in previous studies. The NMR method was also sensitive to differences in solids content and chemical modification (degree of cationization, degree of oxidation and molecular weight). The cooking temperature, cooking speed and viscosity did not influence T 2 {T_{2}} relaxation rates. The sediment separated from the surface sizing and coating binder starches held at 90 °C had a significantly higher relaxation rate than the supernatant, indicating that the sediment contained a high amount of retrograded starch.

Highlights

In papermaking, it is common knowledge that starch should be well-cooked, i. e. fully gelatinized, to enable it to bind properly with cellulose fibers
Wet-end barley starch behaves in a completely different manner; its R2 value is quite low at a high temperature, but unlike in the case of potato starch, the R2 quickly rises with decreasing temperature until about 50 °C
The NMR-relaxometric method used in this study was sensitive to differences between jet-cooked starches based on their botanical origin, their modification and solids content

Summary

Introduction

It is common knowledge that starch should be well-cooked, i. e. fully gelatinized, to enable it to bind properly with cellulose fibers. E. fully gelatinized, to enable it to bind properly with cellulose fibers. Starch has been widely studied in the context of food and papermaking, and there are many books and review articles explaining the structure of starch and the mechanisms behind gelatinization and retrogradation (BeMiller and Maurer 2005, Lehtinen 2000, Maurer 2007, Wang et al 2015). When one reads articles about food starch studies, it is important to notice that often in them the solids content of the starch is much higher than in papermaking, which has a major influence on the mechanisms of the water-starch system. Food starches are often native starches, whereas papermaking starches are typically chemically modified, which influences their behavior (e. g. viscosity) in many ways (BeMiller and Maurer 2005).

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