Antiplasticization and phase behavior in phase-separated modified starch-sucrose blends: A positron lifetime and solid-state NMR study

Francesca Martini; David J Hughes; Gabriela Badolato Bönisch; Thomas Zwick; Christian Schäfer; Marco Geppi; M Ashraf Alam; Job Ubbink

doi:10.1016/j.carbpol.2020.116931

Antiplasticization and phase behavior in phase-separated modified starch-sucrose blends: A positron lifetime and solid-state NMR study

Carbohydr Polym. 2020 Dec 15:250:116931. doi: 10.1016/j.carbpol.2020.116931. Epub 2020 Aug 20.

Authors

Francesca Martini¹, David J Hughes², Gabriela Badolato Bönisch³, Thomas Zwick³, Christian Schäfer³, Marco Geppi¹, M Ashraf Alam², Job Ubbink⁴

Affiliations

¹ Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Moruzzi 13, 56124, Pisa, Italy.
² H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol, BS8 1TL, United Kingdom.
³ DSM Nutritional Products Ltd, Research Center Formulation & Application, P.O. Box 2676, 4002, Basel, Switzerland.
⁴ Department of Food Science and Nutrition, University of Minnesota, 1334 Eckles Ave, St. Paul, MN, 55108, USA. Electronic address: jubbink@umn.edu.

PMID: 33049844
DOI: 10.1016/j.carbpol.2020.116931

Abstract

Interactions, organization and dynamics within phase-separated ternary blends of hydrophobically modified starch (HMS), sucrose and water are investigated using solid-state NMR and positron annihilation lifetime spectroscopy (PALS). Antiplasticization of HMS by sucrose is demonstrated by PALS and ¹H NMR T₁ measurements. Selective solid-state ¹³C NMR experiments show that a large fraction of sucrose is in molecular contact with HMS even at high sucrose contents, indicating that the HMS-sucrose phase separation is only partial. Sucrose is observed to migrate away from the HMS-rich domains at temperatures that are above the lower T_g, but still below the upper T_g. ¹H spin diffusion experiments indicate that phase separation occurs on a nanometric scale, in line with recent theory (Van der Sman, Food Hydrocolloids87, 360-370 (2019)). We infer that the nanoscale structure of the HMS-rich phase allows for intimate molecular contact between the HMS-rich and the sucrose-rich phases and explains the unusual dynamic behavior.

Keywords: (1)H relaxation times; (13)C CP-MAS; Amorphous phase separation; Antiplasticization; Free volume; OSA-starch; Plasticization; Positron annihilation; Sucrose.