Storage life and kinetic velocity of preserved onion paste at room and refrigerated temperatures

Onion paste is a convenient value-added product, but its high moisture content makes it susceptible to physicochemical deterioration and microbial spoilage during storage. This study evaluated the effects of preservative formulation, packaging material, and storage temperature on the physicochemical stability and acidity degradation kinetics of onion paste over eight months. Onion paste was prepared using three formulations: SB (10% salt, 1% citric acid, and 1000 ppm sodium benzoate), KMS (10% salt, 1% citric acid, and 1000 ppm potassium metabisulphite), and CA (1% citric acid), together with a commercially available market sample (MS). Treated samples were packed in plastic and glass containers and stored at room temperature (25 ± 5 °C) and refrigerated temperature (7 ± 2 °C), whereas the market sample was evaluated in its original plastic packaging. Changes in pH, titratable acidity (TA), total soluble solids (TSS), moisture content, and ash content were monitored at two-month intervals. Preservative treatment, packaging material, storage temperature, and storage duration significantly affected (P<0.001) most quality attributes. The pH increased progressively, whereas TA generally declined during storage. The KMS formulation showed comparatively high acidity retention and maintained TSS of 29.36–31.60 °Brix, moisture content of 71.88–73.55%, and ash content of 8.35–8.98%. SB-treated paste maintained TSS of 28.06–29.56 °Brix, moisture content of 71.34–71.97%, and ash content of 8.30–8.50%. In contrast, CA-treated paste showed lower TSS (21.16–24.70 °Brix), higher moisture content (74.08–80.30%), and substantially lower ash content (0.30–0.96%), while the market sample exhibited the lowest TSS (9.10–12.02 °Brix) and highest moisture content (84.10–90.03%). Acidity degradation was evaluated using a first-order kinetic model, although model fit varied considerably among treatment and storage combinations. The KMS-treated paste stored in glass under refrigerated conditions showed the strongest first-order fit (R² = 0.9153) and a predicted acidity half-life of 1.58 years. The combination of potassium metabisulphite, glass packaging, and refrigerated storage provided the most predictable acidity stability among the tested conditions. The findings provide a quantitative basis for optimizing onion-paste preservation and storage practices and demonstrate the potential of kinetic modelling for shelf-life assessment, quality control, and reduction of storage-related losses.