Candied or made into preserves might save the fruit for food. Less so for vitamin C. If the concern is less food for energy and more vitamin C to hold off scurvy I think your best bet is to invest in vitamin C in the form of pills, or bulk powder. I like the unsweetened, non-chewable, 500mg tablets.

If you want a chuckle give the non-chewable tablets to someone used to the heavily sweetened chewable version. Vitamin C is quite sour. Chewing the non-chewable sort sort will give you a pucker all the way down to your toes. Fun to watch. Cheap thrills.