Optimising Terung Asam (Solanum lasiocarpum Dunal.) Sauce for Enhanced Phenolics, Flavonoids, and Antioxidant Capacity with Physicochemical Properties and Storage Stability Analysis

Solanum lasiocarpum Dunal, commonly referred to as ‘terung asam’, is a native plant of Borneo Island that is widely utilised in Sarawak, Malaysia, for its culinary and medicinal applications. While terung asam has been commercialised into products such as sauces, research on optimising its sauce formulations remains limited. This study utilised a D-optimal mixture design, a method from response surface methodology, to optimise terung asam sauce (TAS) formulations using terung asam (TA) purée, virgin coconut oil (VCO), and garlic powder (GP). The focus was on three key responses: total phenolic content (TPC), total flavonoid content (TFC), and antioxidant capacity via 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. The physicochemical properties, including pH, colour, water activity, and storage stability analysis, were evaluated for the optimal TAS formulation. The optimal TAS formulation comprised 98.46%, 0.73%, and 0.81% for TA, VCO, and GP, respectively, with both predicted and actual values aligning and meeting acceptance error criteria. The physicochemical parameters for the optimal TAS formulation were within the optimal ranges, while TPC, TFC, and DPPH showed a slight decline over the storage period of 28 days. In conclusion, optimising TAS formulations offers an innovative approach to developing a healthy food product with high antioxidant properties and extended shelf life.