The quality of grapes is an important issue for nutritional value and content of antioxidants, which are essential for human health. Yemen is Famous for growing different types of grapes in large quantities. This study aims to validate the analysis methods of determination of total antioxidants (TAC), polyphenols (TPC), flavonoids (TFC), and vitamin C (Vit. C) contents, in terms of linearity, repeatability, accuracy, and limits of detection (LOD) and quantification (LOQ), for measuring TAC, TPC, TFC, and Vit. C in grape samples, with good linearity (R2) are 0.9968, 0.9967, 0.9971, and 0.9966, exhibited high repeatability(% RSD) are ranged (1.452 – 4.836%), (0.720 – 3.240%), (0.766 - 6.001%), and (0.539-2.976%), also high sensitivity (LOD = 0.279, 0.243, 0.288, and 76.376 ppm), LOQ = (0.928, 0.809, 0.961, and 245.588 ppm), and the high accuracy (%R) (80.80-95.00%), (91.44-104.35%), (92.37-101.87), and (88.89-104.65%), respectively. The analysis results of fourteen Yemeni grape samples indicated that the highest value of TAC for a Black grape sample was 6755.3 mg AAE/kg, while the lowest value for the Asmi grape sample was 1621.7 mg AAE/kg. For the TPC, the highest value was 4718.3 mg GAE/kg for the Black grape whereas the lowest content was 1382.3 mg GAE/kg for the Asmi grape. TFC ranged from 341.8 for the Black grape to 32.0 mg QE /kg for the Asmi grape—lastly, Vit. C ranged from 2418.1mg AAE/kg Black grape to 766.5 mg AAE/kg for Asmi grape. This study indicated that Yemeni grape varieties exhibit high TAC, TPC, TFC, and Vit. C contents, which can be used as a natural source of antioxidants.
