I'm quite fond of
mojo, and of
molho de piri-piri, but like many others as well. I am quite fondof grapefruit-based marinades for chicken and those with grapefruit-lime mixtures.
Citrus juices are quite acidic as you know. Excessive marinating time can cause the chicken flesh to 'cook' in the marinade as the acids denature the proteins. Three ways to combat this: Don't marinate too long (especially important for b/s chicken breasts; make the ratio of non-acids (like oil) to acids high; use less citrus juice and more citrus zest to keep the citrus flavor up but lessen the acid load.
Here's a thought (with options):
1/3 c grapefruit juice, preferably freshly squeezed ruby red but quality commercial is fine*
zest from 1 lime or 1/2 a grapefruit
1 medium clove garlic, pressed
2 t granulated onion
2 t minced fresh thyme or 1 t dried
freshly ground black and/or green peppercorns (I like both)
1 T Dijon mustard
1/2 t salt
1/2 cup evoo
Whisk all but the oil together in a small bowl till smooth. Whisk in the oil in a slow steady stream.
* any combo of juices can be used here--grapefruit alone or mixed with lime and/or lemon and/or orange. If using sweet orange (rather than sour orange), keep the amount small relative to the other juices as sweet orange can be overwhelming. Don't use sweet orange zest here, balance any sweet orange juice addition with zest from lime, lemon or grapefruit.
That's a basic one. You can, for sweetness, add 1/4 c of minced onion or red bell pepper. A little sage and/or marjoram can be added.
Alternatively, an 1/8 c of minced cilantro, a t of Mexican oregano and a pinch of cumin can be added. (Good with a mix that includes lime.)
Alternatively, with a more lemon-based one, add oregano and marjoram, or add rosemary and oregano and up the garlic a bit.
Alternatively, add a t or two of of a good curry powder or garam masala.
Alternatively, with a lemon-based one, add 1.5 t minced fresh ginger, or add the ginger, plus 2 t of mashed pickled serranos plus a good pinch of allspice.
This marinade is light on the salt as it is assumed you will salt your chicken--pieces, parts or whole--lightly before cooking.