Determination of antioxidant capacity of diverse fruits by electron spin resonance (ESR) and UV–vis spectrometries

Twenty-one kinds of fruits including strawberry, mulberry, lemon, banana, etc. were measured for antioxidant capacity based on their ability to scavenge 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical. Vitamin C equivalent antioxidant capacity (VCEAC) was used to quantify antioxidant capacity of the studied fruits. The results were expressed as mg of ascorbic acid equivalent per 100   g fruit. Each fruit was divided into two parts: harvest part (fresh fruit analyzed immediately), and liquid nitrogen frozen part (fruit frozen and pulverized in liquid nitrogen). Antioxidant capacities of both fresh and frozen fruits were determined, and VCEAC values were proved to have no significant difference. For the frozen fruits, the antioxidant capacities were measured by electron spin resonance spectroscopy (ESR) and UV–vis spectrometry. VCEAC values obtained with UV–vis and ESR range from 11.48 to 345.75   mg/100   g and 7.01 to 366.26   mg/100   g. Experimental results indicated that VCEAC values obtained by two methods were highly correlated.