Dynamics of secondary metabolite content, vitamin C and antioxidant activity of Sonneratia caseolaris (L.) Engl. mangrove fruit during the ripening process

Sonneratia caseolaris (L.) Engl. is a mangrove species with considerable potential as a natural source of bioactive compounds, particularly antioxidants and vitamin C. This study investigated differences in secondary metabolite content, vitamin C levels, proximate composition and antioxidant activity between unripe and ripe S. caseolaris fruits. This research was conducted at Mangunharjo Beach, Semarang, Central Java, Indonesia, using three different sampling points for replicates. Samples were categorised based on morphological maturity and analysed using spectrophotometric methods, high-performance liquid chromatography (HPLC), Kjeldahl analysis, gravimetric, by the difference methods and the DPPH radical scavenging assay. Data analysis was performed using a paired t-test at a 95 % confidence level and descriptive analysis. The evaluated parameters included phenols, tannins, alkaloids, vitamin C, carbohydrates, proteins, fats, ash, moisture content and antioxidant activity. The results indicated a decline in phenolic, tannin and alkaloid contents in ripe fruits, decreasing from 10.09 to 8.87 % w/w, 1.97 to 1.38 % w/w and 0.05 to 0.04 % w/w, respectively, while vitamin C content increased from 60.62 to 74.33 mg/kg. The IC₅₀ values ​​obtained from the DPPH assay were lower in unripe fruit (1.22 ppm) than in ripe fruit (2.67 ppm), although the difference was not statistically significant. Lower values ​​indicate stronger antioxidant activity. These changes reflect a metabolic shift during fruit ripeness, in which enzymatic oxidation leads to the reduction of phenolic compounds. Overall, the findings highlight the potential of S. caseolaris as a sustainable functional food resource aligned with sustainable development goals 2 and 3.