How to increase performance in multiple Json.Convert deserialization inside a loop?

Question

I have created a loop, and inside this loop, I am using JsonConvert.DeserializeObject multiple times. I wonder if there is any way to improve performance.

foreach (var mainItem in jsonItems)
{
   var jsonItems = JsonConvert.DeserializeObject<List<MainGridViewClass>>(mainItem.JsonString);
   foreach (var item in jsonItems)
   {
      // actions
   }
}