Impact of Household Cooking Techniques on African Nightshade and Chinese Cabbage on Phenolic Compounds, Antinutrients, in vitro Antioxidant, and β-Glucosidase Activity

Abstract

Different household cooking techniques (boiling, steaming, stir frying, and microwave) were tested on the changes of targeted phenolic compounds, antioxidant property (ferric reducing-antioxidant power (FRAP) activity), α-glucosidase activity, antinutritive compounds, and sensory properties in commonly consumed traditional leafy vegetables in Southern Africa, the non-heading Chinese cabbage (Brassica rapa L. subsp. chinensis) and African nightshade (Solanum retroflexum Dun). Stir frying increased kaempferol-3-O-hydroxyferuloyl-trihexoside, kaempferol-dihexoside, sinapoyl malate, rutin, and isorhamnetin-O-dihexoside in Chinese cabbage leaves, followed by steaming. Similarly, stir frying increased kaempferol-3-O-rutinoside, chlorogenic acid, caffeoylmalic acid, and quercetin-3-O-xylosyl-rutinoside in nightshade, followed by steaming. Biomarkers, sinapoyl malate (Chinese cabbage) and caffeoylmalic acid (nightshade), separated the stir frying from the other cooking techniques. Steaming and stir-frying techniques significantly increased the FRAP activity; whereas boiling and microwaving reduced the tannin, oxalate, and phytate contents in both leafy vegetables and steroidal saponins in nightshade. Stir-fried nightshade leaf extract showed the most effective inhibition against α-glucosidase activity, with an IC50 of 26.4 μg ml−1, which was higher than acarbose, a synthetic compound (positive control; IC50 69.83 μg ml−1). Sensory panelists preferred the stir-fried Chinese cabbage and nightshade leaves, followed by steamed, microwaved, and boiled vegetables.

Cooking African Pumpkin Leaves (Momordica balsamina L.) by Stir-Frying Improved Bioactivity and Bioaccessibility of Metabolites—Metabolomic and Chemometric Approaches

“…Stir-frying can lead to an increase in 4-caffeoylquinic acid due to the isomerisation and transformation of 5-caffeoylquinic acid (chlorogenic acid) [20]. Managa et al [10] also found 4-caffeoylquinic acid during all cooking methods, with stir-frying having the highest concentration. Due to isomerisation and transmutation of 5-caffeoylquinic acid, high temperatures also caused an increase in 4-O-caffeoylquinic acid levels in artichoke [21].…”

“…Samples of freeze-dried African pumpkin leaves (50 mg) were dissolved in ethanol/water (70:30, v/v), ultrasonicated for 30 min and centrifuged at 1000× g for 20 min at 4 • C. The extraction was repeated, and the supernatants were pooled together before filtering using polytetrafluorethylene filters, as described by Managa et al [10].…”

“…Cooking stops the browning enzyme action, reduces or eliminates the bitterness of vegetables and acid components and makes them palatable [8]. Studies have shown the effect of different cooking methods on phenolic compounds, carotenoids and antioxidant activity in leafy vegetables [7,9,10]. Cooking alters the chemical composition of vegetables, decreasing their bioaccessibility and number of bioactive compounds [11].…”

Critical stages for post-harvest losses and nutrition outcomes in the value chains of bush beans and nightshade in Uganda

“…Boiling and stir-frying improve palatability and reduce antinutrients in nightshade, such as tannin, as opposed to the raw vegetable (Managa et al, 2020;Sivakumar et al, 2020). Cooking also eliminates risks of bacterial or fungal contamination while not reducing the anticancerogenic properties of nightshade (Odongo et al, 2018).…”

“…Moreover, the general contribution of bush beans and nightshade to local diets and health should be investigated further. For example, nightshade, while being rich in vitamins, seems to be most interesting for its bioactive plant compounds, including anticancerogenic and antidiabetic values (Managa et al, 2020;Moyo et al, 2018;Odongo et al, 2018). Locals might not know the exact nutrient components of nightshade, but they are well aware of its general health benefit which often motivates nightshade cultivation.…”