Effect of Freeze-Thaw Treatment on<i> </i>Free Radical Scavenging and Linoleic Acid Reducing Potential of <i>Nelumbo nucifera </i>Rhizome Starch: Response-surface Optimization

Abstract

Background/Objective: Repeated freezing and thawing results in the structural, compositional, and functional modifications in food materials. The present study was designed to optimize the effect of Freeze-thaw treatment (FTT) on free radical scavenging and linoleic acid reduction potentials of Nelumbo nucifera rhizome starch (NNRS). Methodology: A 4-factorial response-surface central composite design (CCD) based on three levels of each of the four input factors including freezing temperature (FT: -40, -20, and 0°C), freezing time (Ft: 24, 48, and 72 h), thawing time (Tt: 2, 4, and 6 h), and number of freeze-thaw cycles (FTC: 2, 4, and 6) was constructed. The NNRS was treated at different combinations of input variables as selected by CCD. The Freeze-thaw-treated N. nucifera rhizome starch (FTT-NNRS) was analyzed for antioxidant potential. Principle Findings: A statistically significant main effect (p=0.0017-0.0029) of FTT was observed on free radical scavenging and linoleic acid reducing potential (LARP) of NNRS. The 2, 2-diphenylpicrylhydrazyl (DPPH) radical scavenging potential was found to be a linear positive function of FT and Ft while hydroxyl radical scavenging potential showed a linear linear negative response towards FT and linear positive response towards FTC. The LARP also showed a linear positive response towards FT and Tt and quadratic positive response towards FT. Conclusion: FTT significantly affected the free radical scavenging potential and LARP of NNRS that may be attributed to the time-dependent variation in the structure of starch and exposure of some antioxidant residues after repeated freezing and thawing treatments.