Sulphites in Dried Mango: SO₂ Treatment, Colour and Preservative-Free Options

What does sulphur dioxide do in dried mango?

Cut mango browns quickly. An enzyme in the fruit oxidises its phenolic compounds as soon as the flesh meets air, and during drying and storage slower chemical browning continues. Sulphites interrupt both: they block the enzyme and slow the reactions that darken the fruit afterwards. The result is dried mango that stays bright yellow-orange through drying and for longer on the shelf.

Sulphites are usually applied as a solution before drying (for example sodium metabisulphite). Part of the sulphur dioxide is lost during drying, and further losses occur during storage, so what matters for the buyer is the residual level in the finished product, measured as total SO₂ in mg/kg. A widely used method is the optimised Monier-Williams procedure (EN 1988-1 in Europe, AOAC 990.28 in the US); laboratories also use other validated methods. Agree the method, because results from different methods are not always comparable.

Sulphited or unsulphited: what is the difference?

Sulphited dried mango keeps a bright colour for longer but declares sulphite as a preservative; unsulphited mango is darker and keeps darkening in storage. Unsulphited means no sulphite treatment, not necessarily preservative-free. Any other preservatives and any sulphites present at the applicable declaration threshold still need to be assessed for the label.

In our catalog, sulphite is an option rather than a fixed part of the recipe, and where it is used it is declared and controlled for the destination market.

Why is unsulphited dried mango darker, and how dark is acceptable?

Without sulphite, browning is limited by everything else in the process: the variety and maturity of the fruit, how quickly it is cut and dried, the drying temperature, and the oxygen, light and heat the product meets after packing. A citric acid dip, gentler drying and low-oxygen packaging all slow the darkening; none of them stops it completely.

“Acceptable colour” therefore has to be agreed, not assumed:

• keep a reference sample from the approved lot and state the colour tolerance around it;
• if your quality team measures colour instrumentally, put the method and the range in the specification;
• decide how colour is judged at the end of shelf life, not only at dispatch, because unsulphited mango changes in the warehouse.

Can preservative-free dried mango stay soft?

Yes, but softness and stability pull in different directions. A softer product holds more water; more water raises water activity; higher water activity raises the risk of yeast and mould growth during storage. Without a preservative, that balance is held by process control alone.

Three levers keep an unpreserved soft dried mango both soft and stable:

1. Water activity, not only moisture. Two lots with the same moisture can differ in water activity. Our published target for soft dried mango is water activity at or below the value in the table further down, confirmed by laboratory analysis.
2. Sugar infusion. Dissolved sugar binds water, so a lightly sweetened recipe can stay softer at a safe water activity. See added sugar versus no added sugar.
3. Barrier packaging and storage. A good moisture and oxygen barrier stops the product drying out or picking up humidity. Our moisture and shelf-life guide covers pack choices.

Before relying on “preservative-free” in a shelf-life promise, validate it: moisture, water activity and yeast and mould counts at the start and end of the intended shelf life, in the final pack.

When must sulphites appear on the label?

European Union. Regulation (EU) No 1169/2011 lists “sulphur dioxide and sulphites at concentrations of more than 10 mg/kg or 10 mg/litre in terms of the total SO₂” among the substances that must be declared and emphasised in the ingredient list. The concentration is calculated for the product as sold, ready for consumption. The obligation depends on what is present in the food, so sulphites carried over from a sulphited ingredient in a mix count too. Where sulphite is used as an additive, it is also declared by function and name, for example “preservative: sodium metabisulphite”. Maximum permitted levels are set per food category in Regulation (EC) No 1333/2008; confirm the limit that applies to your product before fixing the specification.

United States. Under 21 CFR 101.100, a sulfiting agent present at 10 parts per million (10 mg/kg) or more in the finished food must be declared, even if it was added only as a processing aid.

Other markets. Many follow the 10 mg/kg threshold of the Codex labelling standard, but format and wording differ. Tell us the destination so the label text and the lot testing match.

What to put in the RFQ and on the COA

A sulphite requirement can be checked lot by lot only when the RFQ sets the policy, the limit and the method, and every COA reports against them:

• Sulphite policy: unsulphited, or sulphited with a maximum residual total SO₂ in mg/kg at dispatch.
• Method and laboratory: the SO₂ method, and whether the result must come from an accredited laboratory.
• COA line: “Sulphur dioxide (total SO₂) — result, unit, method, specification limit” for every lot.
• Claims: if the pack will say “unsulphured” or “no preservatives”, ask for a measured SO₂ result on each lot, not only a statement that none was added.
• Colour: the reference sample, the tolerance, and how colour is judged at the end of shelf life.
• Label: the destination market and who prepares the final label text.

The same approach applies to other soft dried fruits in our range. Our supplier qualification guide explains how to read a COA against the specification, and the export documents guide lists what travels with each shipment.