Mallic acid?

i am working on a cider. Old Orchard frozen apple juice concentrate has apple juice, mallic acid, and vitamin c.

I there any issue with using this for a cider?
I've made a cider before with apple juice containing the vitamin c before, just never the mallic acid.

No, that's fine. It's a naturally acid that gives apple juice that flavor- apples are naturally high in malic. The only caution I have is to either keep some sulfite in the must/cider, or be on the lookout for MLF (malolactic fermentation).

Sometimes, winemakers deliberately introduce MLF cultures into wine, as it converts the harsher more tart malic acid into the less harsh lactic acid in the finished wine. With fruits high in malic acid, sometimes that happens naturally at the end of primary fermentation if you don't prevent it.