No easy conversation from doughnuts to volts or amps. I give up. But with enough oxygen you can hear up pretty gud with a single doughnut. Then you could use a Stirling engine to pump heat from the fridge to the environment. Energy in a doughnut 224cal according to Wolfram alpha. That’s 940kJ. 940kJ/1hr260watts which should run a fridge for 1 hr. However energy conversion is probably going to leave you with like 10% at most of usable energy so ~6 minutes run time. America needs a lot of doughnuts!