Added synthetic colours are relatively easy to detect: a lab can screen for them by chromatography. Added sugar is harder, because fruit already contains sugar. Labs look at the sugar profile and, for some sugars, at isotope ratios to tell fruit sugar from added sugar.
The first step is a clear spec. State whether the product may contain added sugar, colour or acid, then test against that.
Why it happens
Colour and sweetness drive the price of fruit pulps, powders and concentrates. If the fruit is pale or under-ripe, there is a temptation to add colour or sugar. In some products, such as sweetened mango pulp, added sugar is legitimate and declared. The problem is when it is undeclared or exceeds the agreed level. See sweetened and unsweetened mango pulp.
Testing for added colour
- Synthetic colours: screened by chromatography methods such as HPLC. Ask the lab for a panel covering the yellow, orange and red colours relevant to your product.
- Natural colour check: mango and similar fruits get their colour from carotenoids. Unusually bright colour with low carotenoid content can raise questions.
- Visual signs: colour that bleeds sharply into water, or looks unnaturally even, is worth testing.
Testing for added sugar
These methods have limits. Beet sugar, for example, is harder to detect by carbon isotopes alone. Ask a specialist lab which method suits your product.
- Brix: shows total soluble solids, not where the sugar came from. A Brix above the normal range for the fruit and season is a warning sign.
- Sugar profile: fruits have typical ratios of glucose, fructose and sucrose. Large shifts can suggest added sugar or syrup.
- Isotope ratio analysis: sugar from cane or corn has a different carbon isotope signature from most fruit sugar. Specialist labs use this to detect added sugar in juices and pulps.
- Reference data: results mean more when compared with authentic samples of the same variety and season.
Building it into your contract
Write the claim in the spec, such as "no added sugar" or "no synthetic colour". Name the test method and the lab. Agree what happens if a lot fails. The general approach is in how to write a good specification. Keep retained samples so a result can be checked again. Test the first lots of a new supplier closely, and repeat when the fruit season or source region changes, since natural colour and sugar levels shift with both.
Where we come in
We draw samples from your lots at the factory and send them to NABL-accredited labs with the right panels, and to specialist labs where isotope testing is needed. We write the claims and test methods into your spec before production starts. Begin with a free sourcing review.