Search in a big NSMutableArray of NSDictionary

I need to search in a big NSMutableArray of NSDictionary with about 50.000 record. I try with:

for (NSDictionary *aProduct in self.arrProduct) {
    if ([[aProduct objectForKey:@"Name"]rangeOfString:@"search string" options:NSCaseInsensitiveSearch].location != NSNotFound) {
        //got it
    }
}

but with 50.000 object, this function had performance very bad. I do not want to use Sqlite to search. Any idea?

tks,