04
Wet-Lab Research / Independent Research
Plasma Antioxidant Capacity Study
Presented at the IYRC Winter Conference, 2025.
A ten-participant study using iodometric titration to examine plasma reducing capacity following vitamin C supplementation.
- Experimental Biology
- IYRC
- Human Research
Origin of the Question
Vitamin C is widely associated with antioxidant activity, but measuring its short-term physiological effects usually requires techniques such as HPLC or spectrophotometry. I wanted to test whether a low-cost iodometric assay could still detect measurable changes in plasma reducing capacity after a realistic dietary intervention: 200 mL of fresh orange juice.
Experimental Design
I used a within-subject design with 10 participants, allowing each person to serve as their own control. Participants fasted for approximately 10 hours, avoided Vitamin C-rich foods beforehand, consumed the same 200 mL orange-juice batch, and provided blood samples at baseline and exactly one hour after ingestion.
Methodology
Plasma reducing capacity was measured using 0.001 M iodine with starch endpoint detection, with every sample analyzed in triplicate. I reduced the iodine concentration tenfold from an earlier protocol to increase endpoint volumes and improve measurement resolution, while retaining the same redox stoichiometry.
Results
All 10 participants showed increased reducing capacity one hour after orange-juice intake. Mean iodine consumption rose from 0.0594 to 0.1782 mL, an approximately 200% increase. Paired analysis showed a strong within-subject effect (p < 0.001), while technical variation remained low across triplicate measurements.
Limitations
The assay measures total plasma reducing activity, not Vitamin C specifically, because several endogenous compounds can also reduce iodine. The study was also limited by its small sample size, single post-ingestion time point, and absence of a placebo control, so the findings are best interpreted as a pilot within-subject result rather than a population-level conclusion.
IYRC
The study was selected for presentation at the IYRC Winter Conference, with 45 of 300 applicants accepted (~15%). I later revised the manuscript to strengthen its treatment of research ethics, assay limitations, quality control, and interpretation, particularly distinguishing total plasma reducing capacity from direct Vitamin C concentration.