Antioxidant vegetable extracts through ABTS assay higher than

Antioxidant activity of various winter squash extracts was determined by two spectrophotometric methods, ABTS•+ and DPPH• radical scavenging test. These are widely used methods to evaluate the antioxidant activity in a short time interval (Rufino et al. 2009). The cold water and hot water extracts of all squash exhibited moderate to high antioxidant activity (ABTS value) (Fig. 2), while hot water extract exhibited low to moderate antioxidant activity (DPPH value) (Fig. 3). In both ABTS and DPPH antioxidant assay, hot water extract of buttercup had the highest antioxidant activity (99.4% and 43.3%). Hot water extracts of all squash were higher ABTS radical antioxidant activity than cold water extracts (p < 0.05). All the extracts showed dose?dependent inhibition of ABTS radical. Even after higher dilution (half and one-fifth) delicata had high ABTS radical antioxidant activity follow by butternut, Italian delicacy and buttercup. However, no significant difference (p ? 0.05) was observed between the cold water and hot water in ABTS assay at the half and one-fifth dilution (Fig. 2). The lowest ABTS radical antioxidant activity was observed in cold water extract of butternut MN. In the case of DPPH assay, cold water extracts of all squash were not significantly different (p ? 0.05). Hot water extracts of four squash cultivars (buttercup, kuri, butternut MN, and Italian delicacy) exhibited low to moderate DPPH radical antioxidant activity. These results were in agreement with Mishra et al. (2017), who reported antioxidant activity of vegetable extracts through ABTS assay higher than DPPH assay. However, values obtained by the ABTS assay were higher than those found by the DPPH assay. This could be due to the fact that the ABTS method was more sensitive to determine the antioxidant activity of samples as it could determine antioxidant activity at lower inhibitor concentrations (Badarinath et al. 2010). Another important difference is that ABTS radical can be dissolved in aqueous and organic media, in which the antioxidant activity can be measured, due to the hydrophilic and lipophilic nature of the compounds in sample. In contrast, DPPH can only be dissolved in organic media, especially in ethanol, this being an important limitation when interpreting the role of hydrophilic antioxidants (Wojdy?o et al. 2007). Therefore, bioactive compounds of squash might be lipophilic antioxidant more than hydrophilic antioxidant. Our results showed that all hot water squash extracts had a positive effect on antioxidant activity. This effect is probably due to the production of redox-active secondary metabolites (Maillard reaction and Amadori rearrangement products) (Dini et al. 2013) or oxidation or degradation of antioxidant compounds (Johnson et al. 2011) among the different compounds present in various squash. In addition, the difference affinity to ABTS radical and DPPH radical in antioxidant activity of each phenolic compounds is affected by their chemical structure depending upon the group attached to a basic aglycone (Zheng et al. 2014) which could influence the variations observed in antioxidant activity between two assay used in this study. Moreover, the antioxidant activity of plant-based foods is not only just associated with total soluble phenolics content but also with other bioactive compounds such as carotenoids, vitamins, and micronutrients (Johnson et al. 2003; Velioglu et al. 1998; Martínez-Valdivieso et al. 2015).