Mallinder's men went into Sunday's game without six regulars, including fly-half Charlie Hodgson and prop Andrew Sheridan, and lost scrum-half Bryan Redpath before half-time with a suspected dislocated shoulder.
"When you are playing a top European side, you have to be as close to full strength as you can," said Mallinder. "Losing Charlie last week was probably the turning point of our campaign. We were excellent in the first 30 minutes against Leinster.
"But we can take a lot of positives from today's performance. Our set-piece was outstanding and we played some good rugby. We went out in a very positive frame of mind but I was very impressed with Biarritz's defence."
The Sharks had their quarter-final hopes rubbed out with the 15-0 home defeat to the French side.
Meanwhile, Biarritz who will face another do-or-die clash with Leinster in the south of France next Saturday to determine the winners of pool three. Leinster, were 32-6 winners over the Frenchmen in Dublin, could still go through if they lose.