The problem with taking a powdered carbohydrate like maltodextrin before your workout is that is will be rapidly absorbed. It's going to spike insulin levels and blood sugar levels and make you hypoglycaemic half way through your workout.
You always want to stick with low GI slow digesting carbohydrates before your workout to give you stable blood sugar levels and sustained energy throughout your workout. Before each of my workouts, I like to mix whey protein isolation from n2bm.com in a bowl of oatmeal with some flax seeds. It'll give you sustained energy throughout your workout and a great pump. I eat that 60-90 minutes before my workout.
On the other hand, the goal of the post workout meal is replenish depleted amino acid levels and replenish MUSCLE glycogen.
That is when you want to use a fast acting sugar-free carbohydrate source like maltodextrin, waxy maize, vitargo, white rice, white potato etc.
After each of my workouts i have 60g of whey isolate (I use isolation from n2bm.com) + 60-100g of waxy maize carbohydrate powder.