Application of LF-NMR to characterize the roles of different emulsifiers in 3D printed emulsions

Abstract

This study established a 3D printed food emulsions stabilized by whey protein isolate (WPI), hydroxypropylated starch (HS) and carrageenan. Low field nuclear magnetic resonance (LF-NMR) was applied to reveal role of WPI, HS and carrageenan on the mobility of hydrogen protons in these emulsions. T 2 distribution of 2% WPI and HS suspensions showed different hydrogen populations. And a new peak T 21 representing single layer water protons appeared at higher concentration. While T 21 was not found in all carrageenan dispersions. Rising of WPI, HS and carrageenan concentration all led to decline in T cur and T 2W values. For emulsions, increasing WPI concentration from 2% to 6% led to decrease in T 2W and T cur . Decreasing WPI/HS ratio prolonged the decay process as both T 2W and T cur values grew. Four proton signals showed in T 2 profile of most emulsions. The T 25 free water signal was closely correlated with WPI, HS, and carrageenan concentration. Decrease in T 24 peak time were observed when increasing WPI content. Influence of carrageenan on proton mobility of the emulsions were complicated and concentration-dependent, affecting relaxation peak T 21 , T 22 , T 24 , and T 25 . Apparent viscosity and rheological parameters G’ and G” indicated the emulsions exhibiting shear-thinning behavior with gel-like structure. Microstructure study revealed that addition of HS and carrageenan resulted in decline in emulsion droplet size. The printability of these WPI-stabilized emulsions was greatly affected by carrageenan content. Overall, this study proved the feasibility of using LF-NMR as a fast and effective approach for characterizing the effect of different emulsifiers in 3D printed emulsions when various types of emulsifiers existed. • LF-NMR can be used to rapidly characterize the roles of different emulsifiers in emulsions. • Relaxation behavior of emulsions were influenced by the type and concentration of emulsifiers used. • Microstructure, rheological properties, and 3D printability of emulsions were evaluated.