Effect of Storage Conditions on Phytochemical Quality and Free Radical Scavenging Potential of Nelumbo nucifera Rhizome

The current investigation optimized the impact of storage conditions on the phytochemical quality and free radical scavenging potential of Nelumbo nucifera rhizome using a response surface methodology. A bifactorial central composite design (CCD) was constructed at five levels of each of the storage temperatures (S_T: −80, −20, 0, 5, and 10°C) and storage time (S_t: 1, 2, 3, 4, and 5 weeks) consisting of 29 experimental runs with four factorial and four axial points in triplicate and five center points. The rhizome samples were stored at various combinations of S_T and S_t as selected by CCD. The fresh and stored samples were processed to analyze their phytochemical composition and free radical scavenging potential. The stored rhizome samples showed comparatively lower values (p < 0.05) of phytochemical constituents and free radical scavenging potential than the fresh ones. The response surface optimization showed that the samples’ phytochemical content and free radical scavenging potential changed as a linear positive function of S_T and a linear negative function of S_t. A linear positive effect of S_T and a linear negative effect of S_t were observed on the total phenolic content, total flavonoid content, and tannin content, as well as 2, 2-diphenyl-1-picrylhydrazyl, hydroxyl, azino-bis-tetrazolium sulfate cation, and superoxide radical scavenging capacities of N. nucifera rhizome. The optimum levels of S_T and S_t for optimal response of the studied parameters were found to be 8.48°C and 2.0313 weeks, respectively. The study suggests avoiding long-term storage of plant-based foods at very low temperatures to preserve their phytochemical and antioxidant quality.