Drupal 7 : Restrict searchable content type

gistfile1.php

<?php

/**
 * Implements of hook_query_node_access_alter().
 */
function MYMODULE_query_node_access_alter(QueryAlterableInterface $query) {

  $search = FALSE;
  $node = FALSE;
  foreach ($query->getTables() as $alias => $table) {
    if ($table['table'] == 'search_index') {
      $search = $alias;
    }
    elseif ($table['table'] == 'node') {
      $node = $alias;
    }
  }

  if ($node && $search) {
    // Searchable node types
    $allowed_type = array(
      'content_type_1',
      'content_type_2',
    );  
    $query->condition($node . '.type', $allowed_type, 'IN');
  }
}