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

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. T2 distribution of 2% WPI and HS suspensions showed different hydrogen populations. And a new peak T21 representing single layer water protons appeared at higher concentration. While T21 was not found in all carrageenan dispersions. Rising of WPI, HS and carrageenan concentration all led to decline in Tcur and T2W values. For emulsions, increasing WPI concentration from 2% to 6% led to decrease in T2W and Tcur. Decreasing WPI/HS ratio prolonged the decay process as both T2W and Tcur values grew. Four proton signals showed in T2 profile of most emulsions. The T25 free water signal was closely correlated with WPI, HS, and carrageenan concentration. Decrease in T24 peak time was observed when increasing WPI content. Influence of carrageenan on proton mobility of the emulsions were complicated and concentration-dependent, affecting relaxation peak T21, T22, T24, and T25. 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.