my $text="The respondent uses the following products XXX, YYYYYYYYY, ZZZZZZZ around the house and they are considering using QQQQQQQ too. They are particularly impressed with ZZZZZZZ.";
my %replace=( "XXX"       => "AAA",
              "YYYYYYYYY" => "BBBBBB",
              "ZZZZZZZ"   => "CCCCCC",
              "QQQQQQQ"   => "DDDDDDDD");

my $search=join '|',keys %replace;
$text=~s/($search)/$replace{$1}/g;
print $text;