function is_post_type($type){
    global $wp_query;
    if($type == get_post_type($wp_query->post->ID)) return true;
    return false;
}
function query_oliverio( $query ) {
	if ( is_admin() || ! $query->is_main_query() )
		return;
	if ( $query->is_main_query() && $query->is_category( 'gastronomia' ) ) {
		$query->set('posts_per_page', 5);
	}
}
add_action( 'pre_get_posts', 'oliverio', 1 );