Impact of pH on pea protein–hydroxypropyl starch hydrogel based on interpenetrating network and its application in 3D-printing

Improving the mechanical and 3D printing performance of pea protein (PeaP) hydrogels contributes to the development of innovative plant-based gel products. Herein, we proposed a strategy for constructing PeaP–hydroxypropyl starch (HPS) interpenetrating network hydrogels, in which the structure, strength, and 3D printing properties of the hydrogels were regulated by changing pH. Results showed that pH significantly affected the gelation process of PeaP/HPS hydrogels. The hydrogels formed a lamellar structure at pH 3, a granule aggregation network structure at pH 5, porous structures at pH 7 and 9, and a honeycomb structure at pH 11. The strength of hydrogels formed at different pH values had the following order: pH 3 ＞pH 11 ＞ pH 7 ＞pH 9 ＞pH 5. The storage modulus (G') of the hydrogel at pH 3 was up to 4149 Pa, but only 695 Pa at pH 5. Moreover, hydrogel at pH 3 had the best self-recovery of 55%. 3D printed objects from gel inks at pH 3 exhibited high structural integrity and fidelity at 60 °C. Gelling force analysis indicated hydrogen bonds were the dominant interaction within all hydrogels. Overall, this study suggested that PeaP/HPS hydrogel formed at pH 3 possessed the most excellent mechanical properties and 3D printing capabilities, which may provide insights into the development of novel PeaP-based gel food ingredients and promote the application of PeaP in the food industry.