TL;DR: An overall increase of TEAC, FRAP, and TRAP values was observed in all cooked vegetables, probably because of matrix softening and increased extractability of compounds, which could be partially converted into more antioxidant chemical species.
Abstract: The objective of the present study was to evaluate the effect of three common cooking practices (i.e., boiling, steaming, and frying) on phytochemical contents (i.e., polyphenols, carotenoids, glucosinolates, and ascorbic acid), total antioxidant capacities (TAC), as measured by three different analytical assays [Trolox equivalent antioxidant capacity (TEAC), total radical-trapping antioxidant parameter (TRAP), ferric reducing antioxidant power (FRAP)] and physicochemical parameters of three vegetables (carrots, courgettes, and broccoli). Water-cooking treatments better preserved the antioxidant compounds, particularly carotenoids, in all vegetables analyzed and ascorbic acid in carrots and courgettes. Steamed vegetables maintained a better texture quality than boiled ones, whereas boiled vegetables showed limited discoloration. Fried vegetables showed the lowest degree of softening, even though antioxidant compounds were less retained. An overall increase of TEAC, FRAP, and TRAP values was observed in all cooked vegetables, probably because of matrix softening and increased extractability of compounds, which could be partially converted into more antioxidant chemical species. Our findings defy the notion that processed vegetables offer lower nutritional quality and also suggest that for each vegetable a cooking method would be preferred to preserve the nutritional and physicochemical qualities.
TL;DR: Steam processing exhibited several advantages in retaining the integrity of the legume appearance and texture of the cooked product, shortening process time, and greater retention of antioxidant components and activities.
TL;DR: It can be concluded that steaming will ensure better preservation/extraction yield of phenols and glucosinolates than do other cooking methods: steamed tissues are not in direct contact with the cooking material so leaching of soluble compounds into water is minimised and, at the same time, thermal degradation is limited.
TL;DR: In this article, the authors quantify soluble and hydrolyzable polyphenols, ascorbic acid, and antioxidant capacity of fresh conventional and organic retail vegetables (potato, carrot, onion, broccoli, and white cabbage) while evaluating the effect of boiling, microwaving, and steaming on these parameters.
TL;DR: The effects of boiling and steaming processes on the phenolic components and antioxidant activities of whole yellow and black soybeans were investigated and quantitatively determined by HPLC.
Abstract: The effects of boiling and steaming processes on the phenolic components and antioxidant activities of whole yellow (with yellow seed coat and yellow cotyledon) and black (with black seed coat and green cotyledon) soybeans were investigated. As compared to the raw soybeans, all processing methods caused significant (p < 0.05) decreases in total phenolic content (TPC), total flavonoid content (TFC), condensed tannin content (CTC), monomeric anthocyanin content (MAC), DPPH free radical scavenging activity (DPPH), ferric reducing antioxidant power (FRAP), and oxygen radical absorbing capacity (ORAC) in black soybeans. Pressure steaming caused significant (p < 0.05) increases in TPC, CTC, DPPH, FRAP, and ORAC in yellow soybeans. The steaming resulted in a greater retention of TPC, DPPH, FRAP, and ORAC values in both yellow and black soybeans as compared to the boiling treatments. To further investigate the effect of processing on phenolic compounds and elucidate the contribution of these compounds to changes of antioxidant activities, phenolic acids, isoflavones, and anthocyanins were quantitatively determined by HPLC. The pressure steaming treatments caused significant (p < 0.05) increases in gallic acid and 2,3,4-trihydroxybenzoic acid, whereas all treatments caused significant (p < 0.05) decreases in two predominant phenolic acids (chlorogenic acid and trans-cinnamic acid), and total phenolic acids for both yellow and black soybeans. All thermal processing caused significant (p < 0.05) increases in aglucones and beta-glucosides of isoflavones, but caused significant (p < 0.05) decreases in malonylglucosides of isoflavones for both yellow and black soybeans. All thermal processing caused significant (p < 0.05) decreases of cyanidin-3-glucoside and peonidin-3-glucoside in black soybeans. Significant correlations existed between selected phenolic compositions, isoflavone and anthocyanin contents, and antioxidant properties of cooked soybeans.