EFFECT OF BLANCHING ON ANTIOXIDANT ACTIVITY, TOTAL FLAVONOIDS AND PHENOLICS OF TWO UNDERUTILISED TRADITIONAL GREEN LEAFY VEGETABLES IN NIGERIA: PIPER UMBELLATUM AND SOLANUM MACROCARPON

Abstract

The effect of blanching on the antioxidant activity, total flavonoid, and phenolic composition in the edible portions of Piper umbellatum and Solanum macrocarpon leaves was investigated. Edible portions of each vegetable were divided into two 450g groups: one portion was blanched for 5 minutes, while the other was unblanched. Antioxidant activity was measured using the DPPH assay, total flavonoids and total phenols were determined using aluminum chloride and Folin–Ciocalteu colorimetric methods, respectively. Blanching led to a marginal increase in the total phenolic content of S. macrocarpon leaves (0.06% (p>0.05)), from 159.3 ± 0.30 to 159.4 ± 0.29 GAE/100g. In contrast, total phenolic content in P. umbellatum was significantly reduced by 93.5% (p<0.00), from 158.5 ± 0.25 to 10.20 ± 0.33 GAE/100g. Total flavonoid content also decreased in both vegetables: a 26.4% loss (p<0.00) in S. macrocarpon (258.3 ± 6.24 to 190.0 ± 7.07 mg/100g) and a 4% loss in P. umbellatum (163.3 ± 6.24 to 156.70 ± 6.24 mg/100g).  DPPH radical-scavenging activity modestly but significantly increased (p<0.05) in blanched samples: 1.6% for S. macrocarpon (61.4 ± 0.34 to 62.5 ± 0.09% inhibition) and 6.3% for P. umbellatum (59.5 ± 0.17 to 63.23 ± 0.25% inhibition). Blanching did not affect the phenolic content of S. macrocarpon but caused significant loss in P. umbellatum; it decreased the flavonoid content of the two vegetables but increased their antioxidant activity. Other factors responsible for the mixed trend observed need further investigation.