Abstract
Green leafy vegetables (GLVs), are widely consumed in sub-Saharan Africa in a sauce, and offer significant nutritional and health potential thanks to their high content of micronutrients and bioactive compounds with anti-inflammatory and antioxidant properties. In this region, stunting is still highly prevalent and frequently associated with chronic intestinal inflammation and oxidative stress, affecting nutrient absorption and immunity. In this thesis, 4 African GLVs were identified on the basis of a literature review of their properties: amaranth (Amaranthus spp.); jute mallow (Corchorus olitorius); cassava (Manihot esculenta) and rosella (Hibiscus sabdariffa). Spinach (Spinacia oleracea) was chosen as reference for their anti-inflammatory and antioxidant properties. The specific objective of the work described in this thesis was to assess the antioxidant capacity of GLV and their potential role in modulating intestinal inflammation, with as final goal to contribute to the prevention of intestinal inflammation and oxidative stress.First, mineral, fiber, oxalate, condensed tannin, total polyphenol (TPC), total flavonoid (TFC), lutein and β-carotene content of the five GLVs were determined and the main phenolic compounds identified. The antioxidant capacity (AC) of polar and non-polar GLV extracts were measured by five complementary methods (DPPH, FRAP, ABTS, ORAC and nitric oxide (NO) scavenging) and correlated with GLV carotenoid, TPC and TFC contents. The modulation of inflammation in vitro by GLVs was assessed using a human macrophage cell model (THP-1) and a triculture model of an inflamed intestine (Caco-2 TC7 (enterocytes); HT-29/MTX (goblet cells) and THP-1). Effects were quantified using markers of inflammation (pro-inflammatory cytokines (TNF-α, IL-6, IL-8) and intestinal permeability). Furthermore, modulation of inflammation by GLVs model sauces was assessed after in vitro digestion (IVD) using the triculture model. In addition, bioaccessibility of GLV minerals, TPC and carotenoids was determined.Characterization of the five GLVs revealed the presence of numerous bioactive compounds capable of complex interactions within the food matrix, but quantities varied and depended on the GLV species. Spinach and cassava were the richest in carotenoids, and cassava and rosella in TPC and TFC. The AC of the latter two was higher than the reference (spinach). Polar extracts had AC 2 to 18 times higher than that of non-polar extracts, and AC more strongly correlated with TPC/TFC (R>0.8) than with carotenoids. Bioaccessibility varied widely among the GLVs: 33-66% for PT, 1-6% for β-carotene, 4-14% for lutein, 17-88% for Zn and maximum 20% for Fe.In the LPS-induced inflamed THP-1 model, cassava and rosella extracts induced a concentration-dependent decrease in TNF-α and IL-6 production, as well as a marked effect at 50 µg/mL on IL-8 production. In contrast, in the LPS/INF- inflamed cell triculture model, only cassava extracts decreased the production of TNF-α and IL-8 by THP-1, and only rosella extracts reduced IL-8 production by intestinal cells. No effect was observed on IL-6, regardless of GLV, extract type or cell type. Most digested GLV sauces had no effect on IL-8 and IL-6 production, whatever the GLV, but TNF-α production by THP-1 was reduced. Only rosella sauces decreased IL-8 production by intestinal cells.Despite the mixed responses obtained, this study shows a probable effect of African GLVs on oxidation and intestinal inflammation, in particular cassava and rosella, which is likely correlated with their high content of bioactive compounds. Their effect at intestinal level needs to be confirmed by further in vivo experiments on animal models and humans.