Effects of probiotic incorporation on the 3D printing properties, rheology, and structural integrity of an optimized sweetened condensed milk matrix

Sweetened condensed milk (SCM) has significant potential for extrusion-based 3D printing applications. Building upon our previously optimized 3D-printable SCM formulation containing 1.2% xanthan gum (XG) and 0.02% jelly carrageenan (JC), we investigated the effects of incorporating microencapsulated probiotics, Lactobacillus helveticus , on the physicochemical and printing properties of the matrix. The resulting activated condensed milk (ACM) system showed substantially enhanced viscoelastic properties: storage modulus (G′) and loss modulus (G″) increased nearly threefold compared to the non-probiotic SCM, while complex viscosity rose markedly across the frequency range, yet shear-thinning behavior was maintained. Probiotic incorporation altered protein secondary structure (decreased α-helix, increased β-sheet) and induced complex synergistic-antagonistic interactions within the hydrocolloid network, as revealed by disulfide bond, electrostatic, and hydrogen bonding analyses. Despite these structural modifications, the ACM system (especially the 1.2% XG + 0.02% JC formulation) demonstrated excellent shape fidelity, enhanced mechanical strength, and appropriate water activity (slightly increased but within acceptable limits) for 3D extrusion, without compromising total sugar content or color quality. These findings elucidated the interactions between live probiotics and dense dairy matrices, offering a viable technical pathway for the development of personalized, probiotic-enriched 3D-printed foods.