Effect of Heat on Antioxidant Activity of Some Tropical Leafy Vegetables

Abstract

The present study examined the effect of different cooking times on total phenolics, total flavonoids, ascorbic acid content and antioxidant properties of seven tropical leafy vegetables: Pterocarpus mildbraedii, Gongronema latifolium, Ocimum gratissimum, Solanecio biafrae, Piper guineense, Celosia argentea and Solanum melongena. The thermal treatments employed were both long simmer (20 minutes at 80 o C) and short simmer (5 minutes at 80 o C). The result show that both short and long simmer results to a significant decrease (P< 0.05) in the ascorbic acid content in all the vegetables. There was a significant increase in the total phenol, total flavonoid, DPPH radical scavenging ability, reducing property, Fe 2+ chelating ability and hydroxyl radical scavenging ability. In like manner, short simmer treatment enhances the total antioxidant activities of all the vegetables. These results suggest that although thermal treatments enhances the nutritional value of vegetables by increasing the bio -accessible phenolic content and total antioxidant activity, long simmer treatment results in the disruption of the phytochemicals constituents present. The study therefore concludes that short time simmer treatment may result to optimum yield of antioxidant activities in leafy vegetables.

Determination of experimental domain factors of polyphenols, phenolic acids and flavonoids of lemon (Citrus limon) peel using two-level factorial design

“…The total polyphenols, phenolic acids and flavonoids content extracted from the lemon peel was significantly increased as the drying temperature increased from 40 to 60 °C. The trend in our study is similar to previously published results Solanum lycopersicum ( Gümüşay et al, 2015 , Azeez et al, 2019 ), leafy vegetables ( Nwozo et al, 2015 ) and red rice ( Hu et al, 2017 ) which observed the phenolics content was increased as the drying temperature increased. The accumulation of high phenolics during high drying temperature is related to the increment of the release phenolics bound from the cell wall as a result of ester breaks down between phenolic and cell wall due to the heat treatment ( Azeez et al, 2019 ).…”

“…Besides that, heat can break the supramolecular structure of the plant biomass which release more phenolics. As a result, phenolic solubility, diffusion rate and mass transfer are increased while solvent viscosity and surface tension are decreased ( Bunea et al, 2008 , Nwozo et al, 2015 , Mokrani and Madani, 2016 ). The effect of extraction temperature on phenolic content also have been reported by several previous studies on different types of plant sample ( Thoo et al, 2010 , Deng et al, 2017 , Zhou et al, 2018 ).…”

Total Phenolic Contents and Antioxidant Variations in Raw and Cooked Dried Fruit of Xylopia aethiopica

“…Zambrano-Moreno et al [16] reported significant increase in the total phenolic contents of eggplant after boiling. Equally short aquathermal treatment of five minutes at 80°C had been shown to have no detrimental effect on the total phenolic content of Pterocarpus mildbraedii and Celosia argentea, total flavonoid content and reducing power activity of Piper guineense but rather enhance the antioxidant value of the vegetables by increasing the bio-accessible phenolics and flavonoids [17]. The increase in the values of the TPC may be interconnected to increase in the liberation of phenolic compounds from the cellular matrix during the boiling process.…”

Effects of Gongronema latifolium Benth and Celosia argentea Linn supplemented diet on the hepatic and cardiac functions of high-fat diet-induced hyperlipidemic rats

“…The blanched Gongronema latifolium significantly lowered ( p = 0.05) the activities of ALT and AST than the unblanched Gongronema latifolium. According to Nwozo et al (2015), the increase in the antioxidant activity of some vegetables will not be far-fetched from the significant increase in the antioxidant phytochemicals (polyphenolics) that accompanied cooking. This agrees with other reports on the effect of cooking on the antioxidant properties of maize, tomatoes and some tropical green leafy vegetables (Adefegha and Oboh, 2011).…”