Final answer:
Carbon dioxide (C) is the barrier to oxygen in vacuum packaging and pre-rigor pork sausage manufacturing. It helps preserve food by lowering intracellular pH and preventing spoilage.
Step-by-step explanation:
The barrier to oxygen in vacuum packaging and pre-rigor pork sausage manufacturing is carbon dioxide (C). Carbon dioxide acts as an antimicrobial agent by forming carbonic acid when it becomes a supercritical fluid, which lowers the intracellular pH and has a preserving effect on food products. It is non-toxic and effective at preventing spoilage and maintaining food quality, and it's particularly useful in the preservation of meats.