Mix soy sauce, orange juice concentrate, orange marmalade, honey, balsamic vinegar, and garlic together in a small saucepan over medium heat; bring to a simmer and whisk until smooth. Remove from heat and let cool to room temperature.

Place the pork tenderloin into a resealable plastic bag and pour in the marinade. Squeeze the air out of the bag, seal, and turn the bag several times to coat the pork tenderloin with marinade. Refrigerate 1 to 2 hours.

Preheat the oven to 350 degrees F (175 degrees C).

Place pork loin and marinade into a baking dish; cover the dish with aluminum foil and roast until an instant-read thermometer inserted into the thickest part of the meat reads at least 155 degrees F (70 degrees C), about 20 minutes. Remove the cover and continue roasting until the pork has browned, 5 to 10 more minutes.

Remove the cover and allow the meat and juices to stand for 10 minutes.

To serve, slice the meat and drizzle with pan juices.

If you prefer a thicker sauce, whisk cornstarch in water until smooth, whisk into the pan drippings, and place over medium heat. Allow to simmer until thickened, 2 to 3 minutes.