In this study, small black beans (Rhynchosia nulubilis : named as Jinunikong in South Korea) which were produced in the Jungsun province of South Korea were selected to use for various cooking recipes because they have been known to contain higher isoflavones and have excellent antioxidant effects than any other domestic soybeans. Physicochemical and antioxidant characteristics of small black beans were analyzed with uncooked beans and four other cooking methods of pan broiling, boiling, steaming,
and pressure cooking. Contents of β-glucosides (daidzin, glycitin, and genistin) and aglycone (daidzein, glycitein, and genistein) in small black beans were significantly different depending on the cooking methods(p<0.001). In addition, inhibitory effects of MCF-7 cell proliferation and migration were analyzed in uncooked, pan broiled, boiled, steamed, and pressure cooked beans.
The results of the experiment showed overall increases in pH measurements, ranging from 6.45 to 6.68. Particularly, pan broiled beans showed pH 6.68 (p<0.001). The lightness and redness after cooking appeared to be more severe than those of uncooked bean. The amount of total polyphenol in pressure cooked beans was highest, showing a value of 7.16 mg/g (p<0.001). Most contents of isoflavones (β-glucoside, aglycone) in uncooked beans appeared to increase after cooking. In particular, the amount of glycitein was highest in pan broiled beans (9.63 ㎍/g). The total of isoflavones differed among the different cooking methods, ranging from highest to lowest in the following order : pan broiled beans (759.49 ㎍/g), pressure cooked beans (725.12 ㎍/g), boiled beans (591.05 ㎍/g), steamed beans (511.61 ㎍/g), and uncooked beans (180.80 ㎍/g) (p<0.001). The inhibitory effects of MCF-7 cell proliferation were analyzed using WST-1 assay with treatments of uncooked, pan broiled , boiled, steamed, and pressure cooked beans depending on protein concentrations (1.25∼640 ㎍/ml). In all cases, rates of cell proliferation decreased as the concentration increased (p<0.001). In particular, the rate of cell proliferation of pan broiled beans was found to be highest in value (59.53%) at a protein concentration
of 640 ㎍/㎖. Estimated cell proliferation rates were derived using non-linear fitting method. As a result, estimated cell proliferation rate for each 100 mg/ml cooking sample was saturated and ranged from lowest to highest in the following order : pan broiled (62.70%), uncooked (77.16%), pressure cooked (80.43%), boiled (81.99%), and steamed (82.65%) beans. Inhibitory effects of MCF-7 cell migration in Boyden''s chamber assay were analyzed using uncooked, pan broiled, boiled, steamed, and pressure cooked beans under three protein concentrations of 40, 160, and 640 ㎍/ml. In the case of pan broiled beans, as the protein concentration increased (40, 160, and 640 ㎍/ml), rates of cell migration into the lower chambers significantly reduced the p-value to less than 0.001 (59.83%, 32.48%, and 21.37%). Estimated cell migration rates were also calculated using non-linear fitting method, which showed excellent correlations in the manner of exponential decay between experimentally measured cell migration rates and converted samples. Estimated cell migration rate for each 100 mg/ml cooking sample was saturated and ranged from to highest in the following order : pan broiled (21.16%), boiled (22.48%), steamed (22.48%), pressure cooked (29.52%), and uncooked (35.03%) beans.
In summary, when cooking methods for small black beans
were selectively modified, significant differences in nutritional and functional contents in the food were identified. Especially, in the case of pan broiled beans and pressure cooked beans, the amount of isoflavones significantly increased and the inhibitory effects of
MCF-7 cell proliferation and migration also showed, suggesting that optimized cooking methods for increasing nutritional and functional contents in cooked food.