Hello - can I use orange juice as a liquid?

I’ve not tried it with OJ but I think that’d be just fine. These muffins are not meant to be overly sweet, and the citrus flavor would pair well with a fruity olive oil. I’d steer away from a pulp-y orange juice, though. Please report back if you try this!

I'm assuming you mean for the "flavored liquid," about which the recipe says: "1/2 cup flavored liquid (my adaptations employed fruit syrup, honey, and chocolate sauce. Get creative! Coffee or tea would be interesting, too)". The use of sweet liquids implies that the flavored liquid also is for sweetening, so normally I would worry that using OJ would make it not sweet enough, but considering the author suggests coffee/tea and the recipe already has 1.25 cups of sugar in it, I think you'd be just fine with OJ.