Hi,
As long as there are no patches of fur missing and he is otherwise acting fine, you are likely dealing with normal shedding. In certain breeds of dogs, the shedding can be very substantial. I had a Chow and I could have filled pillow cases with his hair during the shedding sheason.

The change in your coat's texture could be due to your dog growing up. A smooth and very soft coat sounds like a healthy coat to me and Science Diet is a good food so I woudn't change that. If you're concerned about the shedding, you can look into certain supplements that help reduce it. They are available over the counter.

Have fun,
drphilvegasvet