A mini-review published in Frontiers in Nutrition argues that glutathione does more in cut fruits and vegetables than soak up free radicals, and that postharvest research has been treating it as a simple chemical additive. The authors, based at Shaoguan University in China, propose it functions instead as what they call a homeostatic orchestrator.

Glutathione, usually written GSH, is a non-protein tripeptide thiol found throughout the plant kingdom. The browning everyone is trying to stop is enzymatic, driven mainly by polyphenol oxidase and peroxidase attacking phenolic compounds once a knife breaks open the cells. One important caveat lands early: because the literature on GSH in fresh-cut produce is thin, several of the mechanisms here are inferred from model plant systems such as Arabidopsis thaliana rather than measured in the crops themselves.

What the treatments did

The review collects studies where GSH was applied directly by dipping, spraying or vacuum infiltration. A 1% weight/volume application on fresh-cut lotus root slices significantly delayed surface discoloration in cold storage while preserving higher internal ascorbic acid, and a 1% dip on fresh-cut wax apple reduced browning incidence and slowed the decline in tissue lightness under refrigeration.

Combinations did better than either component alone. Treating fresh-cut lotus rhizome with 40-kHz ultrasonication for 2 minutes alongside a lower 0.5% GSH concentration inhibited cut-surface browning far more effectively than GSH or ultrasound on its own.

Beyond scavenging

The more interesting argument is mechanistic. The authors describe GSH potentially intervening downstream too: kinetic studies have reported it acting as a mixed-type or non-competitive inhibitor of plant polyphenol oxidases, and it can react with enzyme-generated o-quinones to form colorless conjugates such as 2-S-glutathionyl chlorogenic acid, which may not serve as substrates for further oxidation.

Limitations

This is a mini-review, not new experimental work, and the authors are explicit that direct evidence across diverse fresh-cut horticultural products is still required. They also flag a messy detail in the enzyme data: in purified apple polyphenol oxidase work, the observed inhibition by GSH was largely attributable to a drop in reaction pH under the conditions tested, not to the peptide itself.

Bottom line

The proposal is that GSH metabolism is a target worth engineering rather than an additive worth buying. Whether that holds outside Arabidopsis and a handful of crops is unsettled.