Effects of cooking on the bioactivity of lotus roots and white onions

Bioactive compounds and antioxidant potentials were determined in fresh lotus roots and subjected to boiling for different periods of time (10, 20, 40, and 60 min). The obtained results were compared with the same indices in fresh and boiled white onions. It was found that fresh vegetables contained higher quantities of bioactive compounds than those boiled for 10 min, and these indices were significantly higher in fresh white onions than in fresh lotus roots (P < 0.05). Polyphenols (mg GAE/g) were 3.65 0.2 ^a and 10.48 0.5 ^b; flavanols (g CE/g)44.13 2.8 ^a and 91.94 4.3 ^b; flavonoids (mg CE/g)0.54 0.02 ^a and 1.04 0.03 ^b; anthocyanins (mg CE/kg)20.61 1.2 ^a and 28.34 1.3 ^b; and tannins (mgCE/g)0.58 0.02 ^a and 1.69 0.03 ^b of lotus roots and white onions, respectively. The highest antioxidant potential was registered in fresh lotus roots and fresh white onions (10.1 0.70 ^a and 15.0 0.8 ^b; 8.1 0.4 ^a and 23.05 1.1 ^b; 18.7 0.9 ^a and 26.9 1.3 ^b M TE/g for FRAP, DPPH, and CUPRAC, respectively (P < 0.05) and 26.9 1.5 ^a and 24.14 1.1 ^a M TE/g for ABTS (P > 0.05). The influence on tumor cell lines Calu-6 (% of cell viability) of fresh lotus roots (75.61 2.03) and boiling boiled for 10 min (76.54 3.14) was significantly higher (P < 0.05) than for fresh white onions (94.18 3.67) and 10 min (97.02 4.16) white onion. By comparison, the tumor cell lines SNU-601 (% of cell viability) showed similar data for both fresh and boiled vegetables in the range of 86.45 4.07 to 87.28 2.42. In conclusion, the boiling led to a decrease of bioactivity; however, lotus demonstrated higher thermostability than white onions. Three-dimensional fluorescence can be used as an additional index for evaluation of properties. Fresh and boiled (for 10 min) lotus roots and white onions could be considered as a functional food with high antioxidative and antiproliferative activities.