Methods
The formulations of peel jelly were established under two-level full factorial designs within two blocks and one center point. Regarding response optimizer, the amount of sugar and citric acid was obtained; hence, the peel jellies were produced. The evaluation of antioxidant properties was conducted by using total phenolic content (TPC) assay and 1,1 diphenyl-2-picrylhydrazyl (DPPH) free radical assay.