Development and validation of spectrophotometric methods for quantitative determination of total phenolic and total flavonoid content of lyophilizate of the leaf of sweet potato leaf

Sweet potato ( Ipomoea batatas L.) is one of the plants commonly used as traditional medicine, such as anti-inflammatory, anti-diabetes, anti-mutagenic and to increase platelet count. The benefits of sweet potato leaves have been reported as a result of the presence of antioxidant compounds and bioactive compounds, mainly phenolic and flavonoid compounds. In this study, we validated the spectrophotometry method of total phenolic and flavonoid compound of lyophilizate of the leaves of sweet potato juices. The results showed that the coefficient correlation (r) values were 0.97389 for gallic acid standard and 0.99869 for quercetin standard; the recovery rates ranged from 105.08% to 109.92% for phenolic, and from 87.48% to 94.36% for flavonoids respectively; precision with relative standard deviation values ranged from 0.7% to 0.4% for phenolic, and from 0.9% to 0.5% for flavonoids respectively; and the detection limit (LOD) and the quantitation limit (LOQ) for phenolic were 0.0425 μg/mL and 0.128 μg/mL respectively while for flavonoids were 0.17 μg/mL and 0.5 μg/mL respectively. The method was successfully applied in the determination of phenolic and flavonoid contents of lyophilizate of sweet potato leaf juices with the average total phenolic content of 9.83mg GAE/g lyophilizate, while the average total flavonoid level was 5.11mg QE/g lyophilizate.