"Food can easily become freezer burned when you freeze it in a baggie, but when you vacuum seal it, it helps get all the air out of the surrounding plastic, which helps prevent it from getting freezer burned. "
Turning off the auto-defrost will greatly help eliminate freezer burn. With a Defroster, the Freezer temperature is raised above freezing so ice does not build up. This causes the surface of your food to thaw and refreeze multiple times which promotes freezer burn.
"Meats and vegetables stored in a manual-defrost freezer will last longer than those stored in automatic-defrost freezers. This is because the temperature of a manual defrost freezer remains closer to −18 °C (0 °F) while the temperature of automatic defrost freezers fluctuates, and because automatic-defrost freezers have drier air, thus the rate of sublimation increases."