Analysis of molecular mobility in corn and quinoa flours through 1H NMR and its relationship with water distribution, glass transition and enthalpy relaxation

• Published in: Food chemistry 2022-03, Vol.373, p.131422-131422, Article 131422
• Main Authors: Rolandelli, Guido, Farroni, Abel Eduardo, Buera, María del Pilar
• Format: Article
• Language: English
• Subjects: 1H NMR; Enthalpy relaxation; Glass transition temperature; Molecular mobility; Water sorption isotherms
• ISSN: 0308-8146; 1873-7072
• DOI: 10.1016/j.foodchem.2021.131422

•Glass transition temperature (Tg) was obtained by 1H NMR free induction decay.•Higher lipid content of quinoa flour reduced its hygroscopicity and Tg values.•Rigid protons signals after Hahn pulse increased with temperature and water content.•Enthalpy relaxation decreased relaxation times of mobile protons after Hahn pulses.•Molecular rearrangement during relaxation may cause biopolymer chains immobilization. Solids-water interactions of corn and quinoa flours were evaluated through 1H NMR, DSC, and water sorption isotherms. Glass transition temperature (Tg), observed by DSC, was better distinguished through FID signals, and correlated to water content through the Gordon and Taylor model. Enthalpy relaxations, identified by thermal analysis at 50–70 °C were studied through transverse relaxation times (T2) measured after Hahn spin-echo sequence, which revealed a rearrangement of the biopolymers structures that cause immobilization of polymer chains and reduced mobility of water molecules with weak interactions with solids (lower T22). The higher lipid content of quinoa flour was manifested after the CPMG sequence (T2 ≈ 100 ms) and caused reduced hygroscopicity and Tg values compared with corn flour systems. 1H NMR resulted efficient for assigning proton populations and understanding the changes in their distribution with temperature, analyzing glass transition and interpreting the implications of enthalpy relaxations processes in corn and quinoa flours.