4D printing of products based on soy protein isolate via microwave heating for flavor development.

The aim of this study is to establish food 4D printing products with the property of automatic flavor change by the post-printing application of microwave as an external thermal stimulus. The combination of a formulation comprised of soybean protein isolate (SPI), k-carrageenan (CAR) and vanilla flavor (VNL) was used as printing material. The change in flavor profile was observed by the level of external heat stimulus as a 4D effect. The results of e-nose revealed a significant difference (P < 0.05) in sensors 2, 5, 6, 9, 10, 12 and 13 in the sample added with vanilla flavor meanwhile GC-MS detected 25 volatiles compounds. Notably, four new generated flavor compounds (1-Octen-3-ol, Maltol, Ethyl maltol and eugenal) were identified when added with vanilla flavor. Moreover, e-tongue results indicated the taste characteristics of the sample with vanilla flavor presenting more intense bitterness, astringency, umami, richness and saltiness. The rheological property and water distribution (LF-NMR) determined at different concentrations levels of carrageenan showed that SPI gel made with 3% (w/v) carrageenan was the most suitable for 3D printing among all three concentrations considered in this study. Overall, the results can conclude that the addition of carrageenan and post-printing microwave heating at an optimum level of microwave power enhanced the printability and flavor of SPI gel.