EFFECT OF BLANCHING ON ANTIOXIDANT POTENTIAL AND NUTRIENT/ANTINUTRIENT CONTENT OF TWO VARIETIES OF LAGOS SPINACH (Celosia argentea)

Abstract

Green leafy vegetables, fruits, legumes and cereals are excellent sources of nutrients and antioxidant components. In Nigeria, most of the vegetables undergo processes like blanching or cooking rather than eaten raw. Lagos spinach (Celosia argentea)is one of the underutilized green leafy vegetables. The red and white varieties of this vegetable are commonly consumed in some rural areas in Nigeria and West Africa. This research was carried out to determine the effect of blanching on phytochemical screening, phenolic composition, anti-nutrients content, minerals composition, proximate analysis, minerals bioavailability and antioxidant properties of the vegetables. Also the effect of the aqueous-ethanolic extracts of the vegetables on iron (II) sulphate and sodium nitroprusside induced lipid peroxidation on albino rat’s brain and liver homogenate were assessed using standard procedures. Saponin, steroid and tannin were the major phytochemicals present in the aqueous-ethanolic extracts of the vegetables with alkaloids only present in the white variety. HPLC-DAD qualitative estimation of phenolic compounds revealed the presence of some flavonoids, hydroxycinnamic acids and phenolic acid in the two varieties of the vegetables. Blanching significantly (p<0.05) caused a reduction in most of the phenolic compositions. Similarly, blanching significantly (p<0.05) decreased the Total Phenolic Content (TPC), Total Flavonoid content (TFC) and reducing power of the two varieties of the vegetable while it increased the DPPH scavenging activity, ABTS scavenging activity, Nitric Oxide (NO) and hydroxyl radical scavenging ability of the two varieties of the vegetable with blanched red variety showing higher scavenging ability than the blanched white variety. The vegetable extracts significantly (p<0.05) reduced the accumulation of lipid peroxides in a dose dependent manner. The raw and blanched of the two varieties of the vegetable extracts showed ability to reduce the lipid peroxidation with blanched extracts of the two varieties demonstrating higher ability to decrease lipid peroxidation compared to raw extracts of the vegetable. Proximate composition revealed that blanching caused a significant (p<0.05) decrease in the crude protein and ash content of the vegetable samples while the carbohydrate content was significantly (p<0.05) increased. The result of mineral composition investigation revealed that potassium is the most abundant mineral in the vegetables while the composition of heavy metals like lead and cobalt were minute and below the quantity that can cause problem in man. Blanching brought about a significant decrease in the composition of the minerals in the studied vegetables. However, the decrease was not below the Recommended Dietary Allowance (RDA). Blanching significantly reduced the composition of anti-nutrients. The predicted calcium and zinc bioavailability for the vegetables showed that [Phytate]/[Calcium], [Oxalate]/[Calcium], [Phytate/Zinc] and [Calcium][Phytate]/[Zinc] were below the critical level of 0.5, 2.5, 15 and 200 respectively which are known to impair calcium and zinc bioavailability. The two varieties of the vegetable are nutritious due to the appreciable amount of high crude protein, fibre, carbohydrate and minerals composition. The result of this investigation revealed that the studied vegetable could be explored as functional food in the provision of essential nutrients and the management of free radical mediated diseases. The results further revealed that blanching might be a useful tool for improving the beneficial properties of vegetables.