Dosage-dependent effects of Semen Ziziphi Spinosae on post-acidification inhibition, protein structure and functional properties of goat milk fermented by Lactiplantibacillus plantarum

BACKGROUND: This study aimed to prepare fermented goat milk yogurt (GMY) with graded Semen Ziziphi Spinosae (SZS) supplementation (0.0-2.5 g kg-1), and to explore the regulatory effects and underlying molecular mechanisms of SZS on gel properties, physicochemical quality and protein conformation of GMY co-fermented by Lactiplantibacillus plantarum L3 and commercial starter (YO-MIX 883 containing Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus). Physicochemical and antioxidant properties were assayed. Spectroscopic measurements coupled with particle-size and zeta-potential analyses characterized protein-conformational and colloidal-structure variations.

RESULTS: All GMY exhibited post-acidification during storage. The amount of 0.5-1.0 g kg-1 SZS raised titratable acidity, while 1.5-2.5 g kg-1 restrained acid accumulation. SZS dose-dependently increased hardness and consistency and reduced cohesiveness and adhesiveness; 2.0-2.5 g kg-1 groups showed the densest gel. SZS decreased particle size and raised absolute zeta potential to stabilize casein micelles, reduced L* and elevated total color difference (ΔE), turning samples creamy yellow. It remarkably improved DPPH and ABTS scavenging capacity, with the 2.5 g kg-1 group hitting 93.30 g 100 g-1. Fourier-transform infrared (FTIR), Raman and intrinsic fluorescence spectroscopy verified protein secondary structure rearrangement and reconstructed intermolecular forces. It was found 2.0 g kg-1 was the optimal dosage; overdose disrupted colloidal and protein conformational stability. SZS optimized casein polysaccharide networks through hydrogen, hydrophobic and electrostatic interactions.

CONCLUSION: Appropriate SZS supplementation achieved optimal quality regulation of GMY with substantially enhanced storage stability, gel texture and antioxidant activity. This study uncovered the molecular mechanism by which natural plant bioactive compounds improve fermented milk quality via regulating protein conformation and non-covalent interactions, providing theoretical support for the targeted formulation design of functional fermented dairy products. © 2026 Society of Chemical Industry.