The Brazilian, who struck in the first half as Arsenal won 2-1 in the second friendly of their US tour, endured a torrid time with injury last season.
A recurring knee problem plagued the striker and affected his playing time and fitness.
'It is a fact (he has changed) and you can see,' said Arteta. 'The way he looks, his rhythm, his sharpness, the way he is moving.
'And you can see in his eyes as well that there is again some spark there because he has now got a point to prove and that is good.
Mikel Arteta said Gabriel Jesus has his 'spark' back after scoring in the win over Man United
'He looks really good. He looks really sharp. He has changed a lot of things over the summer. He has come in top condition again.
'He needs to be in that condition to get the best out of himself. He has realised that. And I'm really happy with what he's shown today again.'
On whether calls for Arsenal to sign a new forward has motivated Jesus, he said: 'I think that motivation has to come within himself, with his self demands and how much better he is able to make the team. He has shown it.
'He transformed the energy and the belief of that team and he has got it there. If he is waiting for something external to motivate him, I think it is going to be for a really short period.
'If it's something internally that is happening, that is going to last long and it is going to be consistent. Hopefully that is the case.'