Impact of moist cooking methods on colour, anti-nutritive compounds and phenolic metabolites in African nightshade (Solanum retroflexum Dun.)

Millicent G Managa; Semagalene Mpai; Fabienne Remize; Cyrielle Garcia; Dharini Sivakumar

doi:10.1016/j.foodchem.2020.126805

Impact of moist cooking methods on colour, anti-nutritive compounds and phenolic metabolites in African nightshade (Solanum retroflexum Dun.)

Food Chem. 2020 Apr 25:325:126805. doi: 10.1016/j.foodchem.2020.126805. Online ahead of print.

Authors

Millicent G Managa¹, Semagalene Mpai¹, Fabienne Remize², Cyrielle Garcia², Dharini Sivakumar³

Affiliations

¹ Phytochemical Food Network Research Group, Department of Crop Sciences, Tshwane University of Technology, Pretoria West, P.O. 0001, South Africa.
² UMR C-95 QualiSud, Université de La Réunion, Saint-Denis, Reunion Island, France.
³ Phytochemical Food Network Research Group, Department of Crop Sciences, Tshwane University of Technology, Pretoria West, P.O. 0001, South Africa. Electronic address: SivakumarD@tut.ac.za.

PMID: 32387944
DOI: 10.1016/j.foodchem.2020.126805

Abstract

Not much information is available on the changes of phenolic metabolites or anti-nutritive compounds in African nightshade leaves during moist cooking. Blanching methods (boiling, microwave, and steaming) using 5-20% lemon juice was compared with the plain water as a control. Lemon juice at 20% significantly increased the total colour differences (ΔE). Chlorophyll content and the overall acceptance were highest for samples steamed in 5% lemon juice. Steam blanching in plain water reduced the tannin, oxalate and phytate contents but showed higher comparative peak responses for steroidal saponins. Neochlorogenic, chlorogenic, and caffeoylmalic acid, kaempferol O-rhamnosyl hexoside, and rutin were identified blanched leaves. Principle component analysis (PCA) discriminated between blanching treatments while Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) showed clear group distinctions between the blanching treatments. Chlorogenic acid, neochlorogenic acid and cryptochlorogenic acid were the responsible biomarkers for the separation of the steam blanching treatments. Thus, steam blanching preserves the functional compounds in nightshade leaves.

Keywords: Antioxidant activity; Chlorogenic acid; Chlorophyll content; Phytate; Traditional leafy vegetable.