A 72-year-old man undergoes a subtotal colectomy for a cecal perforation due to a sigmoid colon obstruction. He has had a prolonged recovery and has been on total parenteral nutrition (TPN) for 2 weeks postoperatively. After regaining bowel function, he experienced significant diarrhea. Examination of his abdominal wound demonstrates minimal granulation tissue. He complains that he has lost his taste for food. He also has increased hair loss and a new perioral pustular rash. Which of the following deficiencies does he most likely have?