Electrostatic interaction below pI: In a fruit yogurt at pH 3.8–4.2 (below whey protein pI ~5.1), whey proteins carry a net positive charge. HM pectin (pKa ~3.5) is negatively charged and forms soluble electrostatic complexes with whey proteins. These pectin–protein complexes stabilize the casein matrix by coating denatured whey protein aggregates, preventing their flocculation and phase separation.
Mechanism during thermal processing: Pasteurization (72°C/15s of yogurt pre-mix) partially denatures whey protein, exposing hydrophobic patches. Pectin binds these hydrophobic zones electrostatically + hydrophobically, creating a steric barrier against aggregation during the subsequent fermentation and cooling steps.
✦ Stirred yogurt stabilizer formula: HM Pectin (DE 60–65%) 0.20–0.30% + WPC 80 3.5% + Pectin added pre-pasteurization at 60°C to ensure uniform hydration before heat treatment, pH target post-fermentation 4.0–4.2
28-day stability: At ≥0.25% HM pectin, syneresis measured by centrifugation (700 × g, 10 min) stays <4% across 28 days. Above 0.40%, texture becomes gummy and overruns consumer expectation. Optimize with response surface methodology between 0.20–0.40% range.
