How would that affect the natural enzymes in food items?
None at all.
The gamma radiation simply kills any living thing in a second, from virus up to bacteria and insects.
This was proposed back in the 50’s and 60’s but because people heard ‘radiation’ kills, it was rejected.
It could be done on a mass scale, like truckloads or railcar loads at a time, with no slowdown in the process of delivery. Just drive thru a tunnel and zap the entire load all at once, perfectly safe after that...............