my @required = qw ( apple banana orange pear );

my @collections = (
  'foo pear bar apple',
  'apple foo pear orange banana',
  'pineapple appearance',
);

foreach my $collection ( @collections ) {
  foreach my $item ( @required ) {
    $collection .= " $item" unless $collection =~ /\b$item\b/;
  }
}

print "$_\n" for @collections;