Designing Spoonable Milk Kefir Gels: From Fermentation Optimization to Clean‑Label Gel Structuring with Psyllium

Kefir is a fermented dairy product whose structural properties can be tailored to enhance its nutritional and sensory profile. This study aimed to develop spoonable kefir gels by optimizing fermentation conditions and incorporating psyllium and calcium chloride as structuring agents. In a first step, a full factorial design was used to compare whole and skimmed milk during kefir fermentation, evaluating the effects of inoculum level, temperature, and fermentation time on acidification kinetics through pH and total acidity measurements. Skimmed milk exhibited faster acidification under equivalent conditions, supporting its suitability for reduced-fat formulations. In the second phase, kefir obtained under optimized conditions was gelled with varying concentrations of psyllium and calcium chloride. Rheological characterization was carried out through small-amplitude oscillatory shear and steady-shear flow tests to assess gel strength, viscoelastic balance, and resistance to deformation. The results showed that both psyllium and calcium chloride significantly enhanced the gel network, with interactive effects evident in viscoelastic moduli and flow consistency. Response surface methodology allowed the identification of optimal formulation zones and revealed compositional domains in which low-fat kefir gels with desirable textural and processing attributes could be achieved. These findings support the development of synbiotic, functional dairy gels.