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Please see attached photos. We are a small food processing plant, and recently it came to my attention some of the carrots we have been purchasing have been having a problem where the heads are turning a dark green/brown coloration. The skin on them also turn dark after processing. There is no slimy or any textural difference to the rest of the carrots, and to the touch they are still completely firm with no give or sign of rot. These are fresh from the distributor, and properly stored in coolers, we source and use fresh vegetables so these do not sit in the coolers for prolonged periods at all.

Just to give more information, our procedure is 1) automatic friction peeler, 2) fresh water rinse, 3) chlorine wash at 200PPM concentration (verified) with contact time of ≈15 seconds, 4) two additional fresh water rinse cycles, 5) carrot chopper.

You can see in the upper photo, after chopping the outer layer of the skin is already starting to turn dark for unidentified reason. Again, our process is rapid and our processing room is air conditioned. There is no slime or decay, but this batch of carrots has been discoloring unusually like this.

My questions are: what is the cause? Is there a food safety impact or is this a quality / aesthetic issue? What are some methods to combat this from happening?

Thank you!

  • You could try skipping specific steps in the process, to see if something from the friction peeler or chlorine wash or carrot chopper are introducing something (oil? some other chemical?) that is causing the reaction. – thrig Feb 26 '16 at 15:51
  • @thrig While it is possible, it is very unlikely an unforeseen contaminant is being introduced to the material; all such risks should be addressed through an assessment in the HACCP/HARPC plan. It is still possible an approved material can cause a chemical reaction the food safety team was not sufficiently knowledgeable to be aware of, but specifically in the case of my question the discoloration was present even prior to any processing (raw material storage segregation is enforced for multiple reasons, e.g., allergen management, identity preservation, GMP's, etc). – Arctiic Feb 25 at 17:46
  • Further, it is also possible the two instances (before and after) are entirely unrelated, as Nette's answer -- the only answer -- assumes. It does sound like a reasonable explanation (the best I can get without ordering a lab analysis, anyway), despite the processing steps' inclusion of a friction peeler (the intended usage being to remove the outer "skin" layer). At the risk of sounding redundant here, I'm pointing this out because working in food safety makes one less willing to dismiss possibilities for no better reason than just improbability. – Arctiic Feb 25 at 18:04
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I ran a school tuckshop and also a college cafeteria for some years and I have seen this many times with new staff members.

The problem with discolouration is any damage to the skin. If preparing carrots in advance or in larger quantities ( sliced, grated, etc ) the skin needs to be thoroughly removed before storage. If any trace of skin is left they will get a brown discolouration.

The heads are a different matter. Carrots are root vegetables and, like potatoes, if any moisture is around the plant will make signs of growth. It's not harmful, they can be cut off a bit further down and any new fine roots which begin to grow can come off with peeling. When cutting down to tops you might see the green colouring further down in the centre. This isn't harmful, in fact nutritionally adds some chlorophyll and folate among others to the diet, but can taste bitter.

Hope this is helpful, good luck

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