Antioxidant Lab Tests Explained: TAC, SOD and Catalase

Short answer: Tests such as total antioxidant capacity (TAC), superoxide dismutase (SOD) and catalase measure activity in a sample under laboratory conditions. They are useful for comparing samples measured with the same method in the same study. They do not tell you what happens after you eat the food or take the supplement: enzymes are proteins and are digested, and in 2012 the USDA withdrew its antioxidant (ORAC) database because such values had not been shown to matter in the body.

What each test measures

Abbreviation	Name	What it is
TAC / TAS	Total antioxidant capacity (status)	A combined reading of how well a sample neutralizes oxidants in a test reaction
SOD	Superoxide dismutase	An enzyme that converts the superoxide radical into hydrogen peroxide
CAT	Catalase	An enzyme that breaks hydrogen peroxide down into water and oxygen
GPx / GSH-Px	Glutathione peroxidase	An enzyme that uses glutathione to neutralize peroxides
GR	Glutathione reductase	An enzyme that recycles glutathione back to its active form
GST	Glutathione S-transferase	Enzymes that attach glutathione to other molecules so they can be cleared
GSH	Reduced glutathione	A small antioxidant molecule made by cells
MDA	Malondialdehyde	A by-product of fat oxidation, used as a marker of oxidative damage
TOS / OSI	Total oxidant status / oxidative stress index	The oxidant side of the balance, and its ratio to TAS

Two very different kinds of study

Measured in a food or product. The sample is a fruit extract or a supplement powder. The result describes that sample in a test tube.
Measured in people. The sample is blood taken before and after a diet or supplement. The result describes a change in the body, which still needs a control group to show cause and effect.

Most numbers you see in supplement marketing come from the first kind. Your body makes its own SOD, catalase and glutathione. Enzymes you eat are broken down like other proteins, so a high SOD value in a powder does not mean more SOD in your cells.

What fruit studies show

A series of laboratory studies from Van Yüzüncü Yıl University in Turkey measured antioxidant enzyme activity in fruit extracts. They are useful for one thing: showing how much these values change with the fruit's color, variety, growing region and processing.

Fruit	Comparison	Catalase (CAT)	Superoxide dismutase (SOD)
Mulberry	Black vs white	1.38 vs 0.76 U/L	2.39 vs 1.05 U/mL
Plum	Green vs black	0.42 vs 0.19 U/L	0.47 vs 0.20 U/mL
Carob	Single sample group	0.21 U/L	0.44 U/mL
Fresh grapes	Aegean vs Marmara region	6.32 vs 3.82 U/L	11.70 vs 6.6 U/L
Raisins	Aegean vs Marmara region	4.17 vs 3.12 U/L	6.05 vs 5.05 U/L
Quince	İzmir vs Van vs Ankara	3.70 vs 2.56 vs 1.23 U/L	5.06 vs 4.54 vs 2.53 U/L

What these numbers suggest:

Color is not a reliable guide. Black mulberry scored about twice as high as white mulberry, but green plums scored higher than black plums.
Where it grows matters. The same fruit varied by region, likely due to climate, soil and variety.
Processing matters. Raisins scored lower than fresh grapes from the same regions.
Units differ. Some results are reported in U/L and others in U/mL, so values cannot always be compared even within one paper.

A related 2024 study of guava fruit linked glutathione and catalase activity to markers of fat oxidation. Its reported values differ between the abstract and the results table, a reminder to check the full paper before quoting a number.

How to read antioxidant numbers in a supplement study

What was measured? The product in a test tube, or the blood of people who took it?
Same method, same study? Only compare values measured the same way. Claims that a product is “far higher than literature values” usually compare different methods and units.
Was there a comparison group? Before-and-after changes in people need a control group to show cause.
Who funded it, and is it a full paper? Conference abstracts are short and have usually not been through full peer review.
Does it measure something people feel? A change in a lab marker is not the same as a health benefit.

What large trials of antioxidant supplements found

Large reviews of trials with antioxidant vitamins such as beta-carotene, vitamin E and vitamin C have not found that they prevent disease or lower the risk of death in healthy people, and some high-dose supplements carried risks. NCCIH notes that eating fruits and vegetables is linked to better health, but that antioxidant supplements have not shown the same benefits.

Where you will see these numbers on this site

Several product pages on GetGutBrain include a short Research notes section that mentions laboratory antioxidant measurements of supplement mixtures. Read those notes with this page in mind: they describe the mixture in a test tube, not an effect in your body.

Sources and further reading

Sources provide context and limitations; they do not turn a general education page into medical advice.

Quick answers

Does a high antioxidant number mean a food is healthier?

Not by itself. Test-tube values depend on the method and have not been shown to predict effects in the body. Eating a variety of fruits and vegetables is the better-supported approach.

Can I absorb SOD or catalase from food or supplements?

Enzymes are proteins and are largely digested like other proteins. Your body makes its own SOD, catalase and glutathione.

Why did the USDA remove its ORAC database?

In 2012 the USDA withdrew its ORAC values, citing a lack of evidence that these laboratory antioxidant values are relevant in the body and concern that they were being misused in marketing.

Are antioxidant supplements a good idea?

Large trials have not shown that antioxidant supplements prevent disease in healthy people, and high doses of some can be harmful. Talk to a healthcare professional before taking high-dose supplements.