I notice that many recipes for oven fried chicken include soaking the chicken in buttermilk to tenderize it. However I keep kosher and cannot mix dairy and meat. Can you suggest an alternative?

Vinegar also tenderizes chicken. You can make "mock" buttermilk by adding a bit of vinegar to soy milk (there are plenty of pareve brands -- refrigerated soy milk tastes best). I'm not sure, though, if the vinegar in the mock buttermilk would be enough to tenderize the chicken. But, you may be able to skip the soaking step altogether. I've always heard that kosher chicken is already more tender due to the salting involved in the kashering process.

BTW, I keep kosher and I'm allergic to cow's milk. I've gotten pretty good at finding dairy substitutes for both meat dishes/meals and "dairy" recipes.