I have not studied what you refer to—concentration ratios, in essence, or what share of an industry's total revenue is captured by the largest suppliers in it. Professor Brander may have some insight on this.
In the food processing sector, I think there's greater diversity of firm size. Some of the food processors are very large—companies such as Cargill or PepsiCo. Some of them are much smaller. Some are producers of niche products. I doubt the concentration ratio is as high in food processing as it is in food retailing, but I haven't conducted research on that, myself.