Food gets "broken down" by oxidation, light damage, heat, cold and bacteria/molds. The food saver bags, put in the fridge, pretty much eliminates those factors. I found a good write up on what vitamins get damaged by which factors from the Bellvue College website.
Food Preparation and Storage Impact on Vitamins
Food preparation and preservation methods that use high temperatures for long periods affect heat-sensitive vitamins. Canning is an excellent way to protect foods from bacteria and fungi, but the time and temperature used are important. A short time at high temperature retains more vitamins. Thiamin, riboflavin and vitamin C are destroyed by heat. Acid helps prevent vitamin degradation.
Most foods are best kept at cooler temperatures to minimize spoilage. Freezing is an excellent preservation method with minimal nutrient loss, if foods are kept at 0o F. Some vitamin C is lost by exposure to air while preparing foods for freezing and pantothenic acid, a B vitamin, is destroyed by freezing. Some plant foods, however, cannot be frozen because tissue damage results from freezing. When thawed, damaged tissues are, shall one say, "slimed".
Riboflavinis destroyed by light, including UV light. Milk stored in clear glass jars in the grocery will lose some of its riboflavin.
Some vitamins, notably vitamin C, are destroyed by exposure to air. Chopping or slicing foods exposes more surfaces to air, increasing nutrient loss. All cut foods and juices should be kept in sealed containers.