Combine apple juice concentrate, mustard and seasoning in a large resealable plastic bag or shallow pan. Add pork tenderloins and turn to coat evenly. Marinate in refrigerator 8 to 12 hours.
Remove meat from marinade; discard marinade. Place meat in a greased baking pan. Bake uncovered at 350°F for 40 minutes or until pork reaches an internal temperature of 150°F. Let stand for 10 minutes before slicing.
Grilling Variation: Remove pork from marinade; discard marinade. Place pork on grill and cook, turning occasionally for 30 to 40 minutes until pork reaches a temperature of 155°F. Let pork stand for 10 minutes before slicing.