Effects of domestic cooking on flavonoids in broccoli and calculation of retention factors

Authors: Wu, Xianli; ZHAO, YANG - US Department Of Agriculture (USDA); Haytowitz, David; CHEN, PEI - US Department Of Agriculture (USDA); Pehrsson, Pamela

Submitted to: Heliyon
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2019
Publication Date: 2/26/2019
Citation: Wu, X., Zhao, Y., Haytowitz, D.B., Chen, P., Pehrsson, P.R. 2019. Effects of domestic cooking on flavonoids in broccoli and calculation of retention factors. Heliyon. 2019 Mar; 5(3): e01310. https://doi.org/10.1016/j.heliyon.2019.e01310.
DOI: https://doi.org/10.1016/j.heliyon.2019.e01310

Interpretive Summary: Flavonoids are a large group of polyphenolic compounds found in fruits and vegetables. The consumption of foods high in flavonoids has been associated with reduced risk of several chronic diseases.The flavonoids content of foods is strongly influenced by domestic cooking, which further impacts the estimation of their dietary intake and potential health benefits. The objectives of this study were to determine how common domestic cooking methods alter complex flavonoids in broccoli; to compare the effects of different cooking methods; and to calculate the retention factors. Raw broccoli was cooked by three common cooking methods (boiling, steaming and microwaving). Flavonoids were chemically analyzed. Eight complex flavonoids were identified and quantified in raw and cooked broccoli samples. Boiling resulted in significant loss of all flavonoids, while steaming and microwaving caused minor loses or even increases of the flavonoids. Apparent retention factors (AR) and true retention factors (TR) were calculated on individual flavonoids. In addition, two different ways to calculate total retention factors, “Retention Factor by Glucoside” and “Retention Factor by Aglycone”, both based on TR, were calculated. In conclusion, domestic cooking significantly altered the flavonoid contents in broccoli, with cooking method and chemical nature being key influential factors. Microwaving appeared to be the best cooking method to preserve complex flavonoids in broccoli.

Technical Abstract: The flavonoids content of foods is strongly influenced by domestic cooking, which further impacts the estimation of their dietary intake and potential health benefits. The objectives of this study were to determine how common domestic cooking methods alter complex flavonoids in broccoli; to compare the effects of different cooking methods; and to calculate the retention factors. Raw broccoli was cooked by three common cooking methods (boiling, steaming and microwaving). Flavonoids were analyzed by HPLC-MS. Seven major kaempferol (Km) tri- or tetra-glycosides and one quercetin (Qn) tri-glycoside were identified and quantified in raw and cooked broccoli samples. Boiling resulted in significant loss of all flavonoids, while steaming and microwaving caused minor loses or even increases of the flavonoids. Apparent retention factors (AR) and true retention factors (TR) were calculated on individual flavonoids. TR varied widely from 30.4% to 174.1%, depending on the cooking method and chemical structure. In addition, two different ways to calculate total retention factors, “Retention Factor by Glucoside” and “Retention Factor by Aglycone”, both based on TR, were calculated. “The Retention Factors by Aglycone” for Km and Qn glycosides, as well as the total flavonoids in broccoli, were 44.6%, 53.2% and 45.1% for boiling; 88.2%, 90.3% and 88.3%% for steaming; and 129.8%, 108.5% and 128.4% for microwaving, respectively. In conclusion, domestic cooking significantly altered the flavonoid contents in broccoli, with cooking method and chemical nature being key influential factors. Microwaving appeared to be the best cooking method to preserve complex flavonoids in broccoli.