Effect of Indirect-Contact blanching treatment on phytochemicals, antioxidant activities, and enzyme inactivation of calamansi waste

Calamansi waste is rich in phenolic compounds, including sinapic acid, ferulic acid, hesperidin, neohesperidin, tangeretin, naringin, and nobiletin, but sensitive to enzymatic degradation. Blanching is used as a pre-treatment technique to preserve and enhance phytochemical recovery of calamansi waste by inactivating quality-deteriorating enzymes like polyphenol oxidase (PPO) and peroxidase (POD). This study evaluates the efficacy of indirect-contact blanching (IB) as an alternative to conventional hot water blanching (HWB). Various IB temperature-time combinations (75, 85, and 95 ℃ for 1, 3, and 5 min) were followed to assess their effectiveness in inactivating enzymes and preserving phytochemicals in calamansi waste. The IB method involves vacuum-packaging the sample in a heat-resistant pouch before blanching it in hot water. The results demonstrated that IB at elevated temperatures (85–95 ℃) and longer blanching period (3–5 min) effectively inhibited enzyme activities while preserving phytochemicals (total phenolic and flavonoid content) and maintaining antioxidant potentials (2,2-diphenyl-1-picrylhydrazil (DPPH) radical scavenging activity, ferric reducing antioxidant power (FRAP), oxygen radical absorbance capacity). Among all treatments, IB at 95 ℃ for 3 min was the most effective temperature-time combination with 57.63% PPO and 53.91% POD inactivation and improved antioxidant activities (13.09% in DPPH and 17.57% in FRAP). Higher phenolic recovery was observed in the IB-treated sample compared to the unblanched and HWB-treated samples. The improved phytochemical yield and enhanced antioxidant activities in the IB-treated sample suggest that IB is a viable pre-treatment to prevent the leaching of phytochemicals and improve enzyme inactivation to achieve higher phytochemicals recovery from calamansi waste.